Blood Flow Monitoring
The present invention relates to a method of utilizing photoplethysmography obtained from a central site and a non-central site to detect a low blood flow or low blood volume condition. Also disclosed are apparatuses and systems designed to acquire and process physiological information based on photoplethysmograpy signal information from dual sites.
This application is a continuation of U.S. patent application Ser. No. 11/535,295 filed Sep. 26, 2006, which is a continuation of U.S. patent application Ser. No. 10/751,308, Filed Jan. 2, 2004, which is a continuation in part of Ser. No. 10/749,741 filed Dec. 30, 2003, now U.S. Pat. No. 7,024,235, which is a continuation in part of Ser. No. 10/176,310, filed Jun. 20, 2002, now U.S. Pat. No. 6,909,912 and International Application No. PCT/US03/19294, filed Jun. 19, 2003, and claims benefits under 35 U.S.C. §§120 for all above-noted applications. These patent applications are hereby incorporated by reference into this application in their entireties.
FIELD OF THE INVENTIONThe present invention relates to the field of non-invasive measurement of signals indicating arterial blood oxygen saturation by means of pulse oximetry, and of photoplethysmographic signals indicating flow characteristics, and in particular, configurations of a pulse oximeter probe that sample across the cheek or the lip of a living subject or across the nasal ala or nasal septum. Such probes optionally include provision of a supply of oxygen or oxygen-enriched gas to a patient whose blood oxygen saturation is being measured, and/or a sampler of exhaled breath for capnography.
BACKGROUND OF THE INVENTIONDiseases, acute injuries, and other conditions can adversely affect blood flow to and in the limbs. In a general sense, agents and factors that may affect and lower circulation to the limbs, also known as peripheral circulation, include certain drugs, especially vasoconstrictors, poor perfusion per se due to shock, such as results from low blood volume, or septic or cardiogenic shock, certain traumas, external pressure (as from burns), hypothermia, and other mechanical abnormalities or injuries. In particular, decreased peripheral circulation may be caused by a number of disorders within the body including, but not limited to, atherosclerosis, Raynaud's disease, Buerger's disease, chronic obstructive pulmonary diseases (COPD), and embolic occlusive disease.
Poor blood flow reduces the amount of oxygen that is carried in the blood stream to cells. Emergency rooms, intensive care units, burn units, operating rooms, and ambulances treat a variety of critically ill patients in need of continuous monitoring of real time hemoglobin saturation and/or blood pressure readings. If oxygen levels in the blood become very low at peripheral sites, a variety of problems may occur which include inadequate resuscitation, cell death or necrosis that can lead to non-healing lesions, gangrene and amputation of limbs. Also, in progressive diabetes and other conditions that may result in atherosclerosis that affect peripheral circulation and perfusion, non-invasive measurement of circulation and/or resistance status is useful to monitor the progression of the disease and the effectiveness of treatments.
Also, many patients, especially among the elderly, are on chronic oxygen therapy; they are in need of supplemental oxygen on a routine basis. Such patients may have impaired and/or diminished cardiopulmonary capacity. When such patients are ambulatory, their supply of oxygen (usually a tank of compressed oxygen or liquid oxygen) must be transported with them wherever they travel. Oxygen from such supply passes through a regulator and thence, typically, via a tube to the nose where it is inhaled (e.g., via a nasal cannula or the like). Alternatively, the oxygen may be delivered by a cannula directly into the trachea (transtracheal supplemental oxygen). Embodiments of the present invention combine the supply of oxygen or oxygen-rich air with a pulse oximeter that adjusts the release of the supply to better match the actual bodily requirement based on the measured blood oxygen saturation. A pulse oximeter that receives the signal from the pulse oximeter probe is located a distance from the probe itself, and provides a blood oxygen saturation measurement to the user (and/or to a remote monitor), and/or, in certain embodiments acts to adjust the inflow rate or quality of the oxygen or oxygen-rich gas being supplied. This, depending on each particular user and his/her baseline settings, can either extend the life of a given supply of compressed oxygen or oxygen-rich gas, or provide oxygen or oxygen-rich gas on a more accurate, as-needed basis, in the latter case improving the health and/or performance of the user.
As to the latter benefit of this aspect of the present invention, provision of an accurate, as-needed supply of oxygen reduces the risk of and/or alleviates problems of hypoxia that are associated with improper adjustment of supplemental oxygen to patients in need thereof. Hypoxia, low oxygen delivery, or hypoxemia, low oxygen tension in the blood, cause a number of maladies including polycythemia (increased hematocrit) which leads to abnormal clotting. Polycythemia is a compensatory mechanism to chronic hypoxemia that typically builds up over weeks to months. It is typical in persons with chronic lung disease (and also persons living at high altitudes).
A more immediate, primary physiologic compensatory response to oxygen deficit is increased cardiac output. This is normal, such as during increased physical exertion. However, in persons who have impaired cardiocirculatory reserve, increased cardiac output in response to low arterial oxygen level can, under certain circumstances, eventually lead to death. The second immediate physiologic compensatory response to oxygen deficit is the extraction of more oxygen from hemoglobin within the capillaries of the body's organs. This normally happens either during an increase in oxygen demand (i.e., exercise, fever, shivering, etc.), or during normal demand but decreased oxygen delivery (i.e., due to inadequate blood flow, anemia, hypoxia). In such instances, metabolically active cells draw additional oxygen from the red blood cells which ultimately resulting in a decrease in the mixed venous blood's oxygen saturation falling from a typical 65% to 80% level to levels as low as 32% (see Hemodynamic Monitoring—Invasive and Noninvasive Clinical Application, by Gloria Oblouk Darovic, 3rd Ed., 2002, Chapter 12). Chronic hypoxemia can lead to a switch by metabolically active cells to anaerobic metabolism, which, especially in patients with limited cardiopulmonary reserve, can lead to lactic acidosis and eventually death.
Hypoxemia also causes cognitive dysfunction either acutely or chronically which can lead to early dementia and death. Generally, based on the compensatory mechanisms and effects on body tissues, chronic hypoxemia may affect all organs in the body leading to failure of any or all organs.
In general, blood oxygen levels are currently measured by pulse oximetry, which can be divided into transmittance and reflectance types. Transmittance, or transillumination oximetry, involves the process whereby a sensor measures light extinction as light passes through a portion of blood-perfused tissue. Light is transmitted from one side of a portion of blood-perfused tissue, and is recorded by a sensor situated across the portion of tissue. Reflectance oximetry, on the other hand, has both the light source and the sensor on one side of the tissue, and measures reflectance back from the tissue. For both types of oximetry, multiple signals from the light sensor, or detector, are used to estimate the oxygen saturation and pulse rate from changes in absorption of the light detected throughout blood pulse cycles. The technology is based on the differential absorbence of different wavelengths of light by different species of hemoglobin.
Conventional pulse oximetry measurement in certain classes of patients, for instance severely burned patients, can be a significant challenge, yet this monitoring data is vital in operating room and intensive care settings. Most current pulse oximetric approaches depend upon available peripheral sites permitting transillumination oximetry which is sufficient for most surgical conditions and procedures. However, in one example, patients with severe burns often have only a few sites suitable for the effective placement of the transmitting pulse oximeter sensor. These patients often have severe circulatory compromise rendering the current peripheral pulse oximeters less effective.
The technology of pulse oximeters is well known (See “Pulse Oximetry: Principles and Limitations,” J. E. Sinex, Am. J. Emerg. Med., 1999, 17:59-66). Pulse oximetry includes a sensor, or probe, with light source(s) generating at least two different wavelengths of light, and a detector placed across a section of vascularized tissue such as on a finger, toe, or ear lobe. Pulse oximetry relies on the differential absorbance of the electromagnetic spectrum by different species of hemoglobin. In a typical system, two distinct wavelength bands, for instance 650-670 nm and 880-940 nm, are used to detect the relative concentrations of oxygenated hemoglobin (oxyhemoglobin) and non-oxygenated reduced hemoglobin, respectively. The background absorbance of tissues and venous blood absorbs, scatters and otherwise interferes with the absorbance directly attributable to the arterial blood. However, due to the enlargement of the cross-sectional area of the arterial vessels during the surge of blood from ventricular contraction, a relatively larger signal can be attributed to the absorbance of arterial hemoglobin during the systole.
By averaging multiple readings and determining the ratio peaks of specific wavelengths, a software program can estimate the relative absorbance due to the arterial blood flow. First, by calculating the differences in absorption signals over short periods of time during which the systole and diastole are detected, the peak net absorbance by oxygenated hemoglobin is established. The signals typically are in the hundreds per second. The software subtracts the major “noise” components (from non-arterial sources) from the peak signals to arrive at the relative contribution from the arterial pulse. As appropriate, an algorithm system may average readings, remove outliers, and/or increase or decrease the light intensity to obtain a result. The results from one site provide a measurement of arterial oxygen saturation at that site, and also allows calculation of the shape of the pulse at the placement site of the probe, which can be developed into a plethysymograph. Among the various sources of signal interference and modification, it is noted that the shape of red blood cells changes during passage through arterial and venous vessels. This change in shape affects scattering of the light used in pulse oximetry. Algorithms are designed to correct for such scattering.
More sophisticated pulse oximetry systems detect at more than merely two bands, such as the 650-670 nm and 880-940 nm wavelength bands. For instance, the pulse oximetry article from a uni-erlangen web site stated that four LEDs, at 630, 680, 730 and 780 nm, each with 10 nm bandwidths, can determine the four common species of hemoglobin. The article further calculated that the detection of nine wavelengths in the range of 600 to 850 nm would provide greater accuracy in assessing these four forms of hemoglobin, oxyhemoglobin (O2Hb), reduced hemoglobin (HHb), methemoglobin (MetHb), and carboxyhemoglobin (COHb). As used in the present invention, the term “pulse oximeter” or “oximeter” is meant to include all designs and types of pulse oximeters, including current and later developed models that transmit and detect at more than two wavelengths associated with absorption differences of these hemoglobin species.
At present, peripheral vascular resistance can only be measured invasively, or non-invasively by skilled technicians using Doppler flow devices. The use of Doppler and Doppler waveform analysis is now a standard investigation technique for obtaining measurements in blood flow resistance patients with possible circulatory disorders. For example, Dougherty and Lowry (J. Med. Eng. Technol., 1992: 16:123-128) combined a reflectance oximeter and a laser Doppler flowmeter to continuously measure both blood oxygen saturation and perfusion.
A number of patents have been issued directed to monitors, sensors and probes for use in pulse oximetry procedures. For instance, U.S. Pat. No. 6,334,065, issued on Dec. 25, 2001 to Al-Ali, et al., discloses a stereo pulse oximeter that provides for simultaneous, non-invasive oxygen status and photoplethysmograph measurements at both single and multiple sites. The invention is directed to the detection of neonatal heart abnormalities, particularly related to defects of heart-associated vessels, and specifically directed to Persistent Pulmonary Hypertension in Neonates (PHHN), Patent Ductus Arteriosis (PDA), and Aortic Coarctation. All of these conditions result in a flow of differentially oxygenated blood to different peripheral extremities. For instance, in PHHN and PDA, the blood that flows to the right hand is unaffected by the abnormal shunt that results in less oxygenated blood flowing to other areas. Thus, comparison of oxygen saturation values between a pulse oximeter sensor at the right hand and at, for instance, a foot site, is stated to detect or confirm the diagnosis of such neonatal heart abnormalities. Continuous monitoring with such pulse oximetry also is proposed, to provide feedback on the effectiveness of treatments or surgery to deal with these neonatal cardio/cardiopulmonary conditions. U.S. Pat. No. 6,334,065 does not address the use of two probes for detection, confirmation, or monitoring of perfusion- and resistance-related conditions in the patient. Such conditions would not be expected in a neonatal patient, and are instead more likely found in aging patients and in patients with certain accident conditions unrelated to neonatal heart and heart-associated vessel anomalies.
U.S. Pat. No. 6,263,223 was issued on Jul. 17, 2001 to Shepard et al., and teaches a method for taking reflectance oximeter readings within the nasal cavity and oral cavity and down through the posterior pharynx. Whereas the conventional transillumination pulse oximeter probe detects the light not absorbed or scattered as it crosses a vascularized tissue covered by skin (i.e., the LEDs and photodetector are separated by the tissue), a reflectance oximeter probe detects light by backscattering of light that traverses vascularized tissue not bounded by skin and is reflected back to a detector positioned on the same side of the tissue as the LEDs (e.g., on tissue in the mouth). The method includes inserting a reflectance pulse oximeter sensor into a cavity within a subject's skull and contacting a capillary bed disposed in the cavity with the reflectance pulse oximeter sensor. The method uses standard pulse oximeter sensor probes placed over capillary beds close to a buccal surface, posterior soft palate, hard palate or proximal posterior pharynx, including the tongue, nares or cheek. Reflectance pulse oximetry at these sites determines arterial oxygen saturation. One major problem with this device is that it does not permit cross-site comparisons of oxygen saturation values between several tissue sites. In addition, the pulse oximeter device used in this invention is an elongated tube that is inserted far into the nasal or oral cavity down into the pharynx, which is a highly invasive procedure.
U.S. Pat. No. 4,928,691, issued on May 29, 1990 to Nicolson et al., and currently withdrawn, discloses a non-invasive, electro-optical sensor probe and a method for its use. The sensor is enabled to measure light extinction during transillumination of a portion of blood-perfused tissue and to calculate the oxygen saturation and pulse rate from changes in absorption of the light detected. The sensor probe is placed at a central site such as the tongue, cheek, gum or lip of the patient and provides continuous assessment of arterial oxygen saturation and pulse rate. The sensor is malleable and extremely flexible, and is stated to conform to the structure of the skin and underlying tissue. U.S. Pat. No. 4,928,691 states that measurement at the preferred central sites provide accurate oxygen saturation and pulse readings for “patients with lowered or inconsistent peripheral perfusion.” Critically, the probes according to U.S. Pat. No. 4,928,691 are highly flexible, leading to a high likelihood that upon typical movement of the patient there would be mal-alignment between the light source(s) and sensor, resulting in skewed, non-usable, or unreliable signals and results. Also, there is no teaching or suggestion to compare oxygen saturation values between several tissue sites to identify, characterize, or monitor peripheral perfusion conditions in such patients.
U.S. Pat. No. 5,218,962 was issued on Jun. 15, 1993 to Mannheimer et al., teaches a pulse oximetry system which monitors oxygen saturation and pulse rates by sensing the blood characteristics at two or more peripheral sites. The device includes one or more pulse oximetry probes which passes light through unique regions of tissue and a sensor which detects the amount of light passing through the tissue, and an instrument that independently calculates oxygen saturation level within each region. The difference in values represents how much the oxygen saturation of the first region of tissue differs from the oxygen saturation of the second region of tissue. When the difference between the two values is below a set threshold, the '962 patent attributes this to a sufficiently high probability that the value is true, and displays an oxygen saturation value that is a function of the two independent values. Where there is a difference greater than a set threshold, no oxygen saturation value is displayed. Thus, the '962 patent attributes substantial differences between two sites to be due to error, rather than to an indication of a problem with peripheral perfusion and/or resistance.
U.S. Pat. No. 5,335,659, issued on Aug. 9, 1994 to Pologe, teaches a nasal septum probe for photoplethysmographic measurements that clips onto a patient's nasal septum. Pulse oximetry is one of the stated applications for the apparatus. Structurally, the apparatus disclosed and claimed in the '659 patent has a body, or housing, from which two probe arms extend, these arms being sized to enter the nostrils of a nose. One arm bears at least two light sources, and the other arm bears at least one light detector. The probe apparatus securely grasps the nasal septum in such a way that there is contact on both sides of the nasal septum at the same time with both the light sources and the light detector. In all embodiments, the light sources and the light detector actually protrude from the main body of the respective probe arm, and are positioned to exert pressure upon and indent the tissue of the nasal septum. In some embodiments and all claims, a supply of gas is also provided from a source through a support means and to the nasal septum. However, the '659 patent does not disclose a nasal pulse oximeter probe that does not need to press into the tissue of the nasal septum in order to obtain reliable pulse oximetry data, nor a probe that includes an angle, or bend, to reach a desired highly vascular plexus on the septum.
U.S. Pat. No. 6,144,867, issued on Nov. 7, 2000 to Walker, teaches a flexible pulse oximeter sensor assembly capable of doubling over to surround a body part, such as an ear lobe, and comprised of a flexible base having a hole passing through it, a post preferably having a sharp tip, and a grommet. In use the sensor assembly wraps around a body part, and the post, or pin, passes through the body part to secure the probe to the body part. The grommet frames the hole and engages and holds the post. The patent discloses that body parts other than the ear lobe that may be pierced by the post (and, presumably, therefore suitable as a site for use of the sensor) include the webbing between the fingers and toes, the tongue, the nose, eyebrows, cheek/lip, breast nipples, and the foreskin.
WIPO Application No. WO0021435A1, to Barnett et al., was published Apr. 20, 2000. This publication teaches a non-invasive spectrophotometric examination and monitoring of blood metabolites in multiple tissue regions on an ongoing and instantaneous basis. The method includes attaching multiple sensors to a patient and coupling each sensor to a control and processing station enabled to analyze signals conveyed thereto. The control and processing station visually displays the data from multiple sites for direct mutual comparison of oxygen saturation values from multiple sites. A key aspect of the invention is the use of a “near” and a “far” (or “deep”) detector at each detection site. Based on the positioning of the light-generating devices and the near and far sensors, the far sensor receives absorption signals from deeper inside the brain tissue. In a basic configuration, the “near” sensor, or detector, principally receives light from the source whose mean path length is primarily confined to the layers of skin, tissue, and skull, while the “far” detector which receives light sprectra that have followed a longer mean path length and traversed a substantial amount of brain tissue in addition to the bone and tissue traversed by the “near” detector. Other configurations indicate receptors receive signals from sources across the entire brain cross-section. This is stated to provide information about, by calculation differences, the condition of the deeper tissue, in particular the brain. The method is directed to compare oxygen saturation values for cerebral tissue, such as comparing the two hemispheres during surgery. The WO0021435A1 invention distinguishes itself from standard pulse oximetry of arteries close to the surface of the body, and focuses primarily on analysis of deeper tissues and organs. The application does not teach a method to measure “surface” peripheral or central tissue sites for development of information regarding perfusion status.
WIPO Application No. WO0154575A1, to Chen et al., was published on Aug. 2, 2001. This publication teaches a non-invasive apparatus and method for monitoring the blood pressure of a subject. A monitor is used for continuous, non-invasive blood pressure monitoring. The method includes using sensors to detect a first blood pressure pulse signal at a first location on patient and detecting a second blood pressure pulse signal at a second location on the patient; measuring a time difference between corresponding points on the first and second blood pressure pulse signals; and, computing an estimated blood pressure from the time difference. The first and second sensors are placed at locations such as a finger, toe, wrist, earlobe, ankle, nose, lip, or any other part of the body where blood vessels are close to the surface of the skin of a patient where a blood pressure pulse wave can be readily detected by the sensors, and/or where a pressure pulse wave from the patient's heart takes a different amount of time to propagate to the first location than to the second location.
In one regard, a superior monitor system would be able to provide real-time continuous measurements of signals that would be analyzed to provide arterial oxygen saturation, blood pressure, and pulse rate. A superior monitor system would utilize at least two pulse oximeter probes, one of which is placed at a highly perfused central tissue, such as the lip, tongue, nares, cheek, and a second probe placed at a typically less perfused areas such as a finger or toe. Also, in some situations, a peripheral probe may be placed at sites in or distal from areas that may be or are affected by disease- or accident-related diminished blood perfusion to tissues.
An additional aspect of a superior oximeter system provides both an inflow means of oxygen or oxygen-rich gas to a patient in need thereof, and an integral or adjoining pulse oximeter probe. This aspect is in conjunction with the above-described two pulse oximeter probe system, or in a system that only has one oximeter probe. In either case, one pulse oximeter probe, positioned at the nose or mouth, detects the levels of oxygenation saturation of blood in the patient, and detection of low or lowering oxygenation saturation levels results in one or more of: setting off a local or remote alarm or message; increasing the flow of oxygen or oxygen-rich gas to said patient. Likewise, detection of higher or increasing oxygenation levels results in one or more of: setting off a local or remote alarm or message; decreasing the flow of oxygen or oxygen-rich gas to said patient. Preferably, the pulse oximeter probe at the nose or mouth is integral with the delivery means of the oxygen or oxygen-rich gas. Preferably, the control of oxygenation levels is by signaling to (manually or automatically) adjust a valving mechanism that controls output flow from a source of auxiliary of oxygen or oxygen-rich gas. By such feedback mechanism the quantity of oxygen or oxygen-rich gas is conserved, and the needs of such patient are more closely attuned to the fluctuations in oxygen demand during activities at varying levels of exertion during a period of time.
As to references that pertain to the combining of a pulse oximeter with a system to control the inflow of oxygen or other oxygen-rich gas to a patient in need thereof, the following U.S. patents, and references contained therein, are considered to reflect the state of the current art: U.S. Pat. Nos. 4,889,116; 5,315,990; 5,365,922; 5,388,575; 6,371,114; and 6,512,938. None of these references are specifically directed to a combined, preferably integral combined pulse oximeter sensor/nasal cannula, which, when combined with an oximeter, or with an oximeter that controls the inflow of such oxygen or other oxygen-rich gas to the patient, provide the advantages disclosed and claimed herein.
All patents, patent applications and publications (scientific, lay or otherwise) discussed or cited herein are incorporated by reference to the same extent as if each individual patent, patent application or publication was specifically and individually set forth in its entirety.
SUMMARY OF THE INVENTIONOne aspect of the present invention relates to a novel non-invasive vascular perfusion/resistance monitor system having at least two pulse oximeter probes positioned at locations on the body of a patient, the signals from which may be capable of indicating a problem with peripheral perfusion and/or resistance. In practice each probe emits at least two different light frequencies, such as by light-generating diodes (LEDs), and such emitted light is detected by at least one light detector, such as a photodiode detector. A general-purpose computer or a special purpose computer is employed to perform complex mathematical computations based, typically, on the signal intensity and timing from the at least two pulse oximeter probes, and on signals from the light detectors of each of the probes. Proper analysis by software programming in such general-purpose computer or special purpose computer outputs results to a display, printer, etc. that suggests or indicates (depending on relative differences in the signals at different locations, and upon other conditions) whether a condition of diminished or abnormal vascular perfusion/resistance may exist in a selected body area. The system also monitors changes in such conditions during treatment interventions.
In a preferred embodiment, software programming provides for a signal to a user of the device to alert the user when signals from a central or a non-central probe are of such low pulse amplitude that either the probe needs repositioning or that the patient is experiencing extremely low pulse at the probe site (and is therefore in need of acute intervention). The software program also converts the signals from the light detectors to calculate various oxygen saturation values and various blood pressure values (either simultaneously or separately). These values are used for evaluating the vascular perfusion/resistance and/or blood pressure of a patient based on the locations of the two or more probes.
Each probe is designed for monitoring blood oxygen saturation and/or blood pressure at different vascular bed sites on a patient. Critically, one of the at least two sites on a patient is at what is designated a “central source” site (“CSS”). The inventors have discovered that flow directed through the carotid artery and detected at CSS sites, such as the lip, tongue, nasal nares, and facial cheek, are typically strong and unaffected by perfusion-lowering conditions. In patients who do not have perfusion-lowering conditions, a second or third probe site at “non-central” site (NCS), such as an extremity (i.e., fingers, toes, etc.), provides oxygen saturation and pulse values fairly comparable to values from the CSS. However, when a patient has a perfusion-lowering condition, the probe site at an affected extremity provides noticeably different oxygen saturation and pulse values compared to the CSS values. The difference in saturation values between the CSS and one or more sites is then used to assess peripheral vascular resistance, perfusion and/or peripheral vascular disease.
As used in this disclosure, when a particular wavelength or band of wavelength is stated at which an LED or other light-generating source emits light, it is understood that such light-generating source may and probably does emit light across a broader range. However, what is meant by such statement is that such light-generating source is designed to emit at a frequency curve which has a peak at or near such stated wavelength or band. It is further understood that any known means of limiting non-desired light energy, such as by selective filtration, may be used in conjunction with such light-generating sources to improve the accuracy and/or precision of the emissions of such light-generating sources.
As used in this disclosure, a “pad” is meant to indicate a housing, or an enclosure, over a light-generating or a light-sensing device on the probe, which provides a barrier to fluids, and permits transmission of light of the relevant wavelengths to the present invention. A typical pad has a composition of clear plastic.
As used in this disclosure, a “conductor” is meant to indicate any physical pathway or any system that communicates a signal or electricity from a first to a second location. Signals and electricity can be conducted by conventional means, such as by sending electrical impulses along a continuous copper wire, by more sophisticated means, such as by converting the signals into radio waves and transmitting these waves such that a receiver receives the signals and thereafter sends them to the controller, or by any other way now known or later developed.
As used in this disclosure, whether or not so stated in a particular sentence, the term “oxygen” may be taken to mean “oxygen or any oxygen-rich air or other gas mixture that contains oxygen” which is used for provision of oxygen to a patient or to a person in need thereof. The context of a particular usage in this disclosure indicates whether this broader definition is to be used, or whether a particular example is referring instead to the use of pure oxygen exclusively.
While some researchers have attempted to gauge accuracy by comparing the results from two different pulse oximeter probe sites (see U.S. Pat. No. 5,218,962), and other researchers generally recognized that “central” sites are generally more reliable and responsive than “peripheral” sites (see U.S. Pat. Nos. 6,263,223, and 4,928,691), the present invention recognizes the reasons for the inconsistently different results between CSS and non-CSS sites. Specifically, patients having compromised peripheral circulation and/or resistance will tend to have lower peripheral values than patients without such compromised conditions. By such recognition, detection and monitoring impaired peripheral circulation is possible through the present disclosure. The monitoring system of the present invention, in certain embodiments, additionally provides an indication of vascular resistance through continuous monitoring of the transit time difference of the blood oxygen saturation values and the blood pressure values between the two sites.
It is an object of the present invention to provide a monitoring system which includes two pulse oximeter sensors, or probes, connected to a monitor system as a non-invasive means for continuously measuring blood oxygen saturation values and/or blood pressure and/or pulse values, wherein the system detects and monitors changes in vascular perfusion and resistance in a patient. The overall system particularly assesses differences in peripheral blood flow which may be impaired in certain illnesses and accident conditions.
Another object of the present invention is to provide probes functionally constructed to provide more reliable signal reception and transmission for patients, such as those in ICU, surgery, post-operative care, and patients with respiratory, circulatory problems, or under anesthetics. In particular, pulse oximeter probes are configured to be placed, respectively, across the lip or cheek, in the nostrils of the nose, and on the tongue.
Thus, one object of the invention is to provide a novel configuration of an oximeter probe that is well-suited for placement across the lip of the mouth of a patient, or the cheek of a patient, in which one side of the probe is situated outside the oral cavity and a second side is positioned inside the mouth cavity, and the tissue between the two sides is assessed by transillumination pulse oximetry. Another object of the invention is to combine the probe for placement across the lip or cheek of the present invention with sampling devices for capnography sampling, either with or without a structure or assembly for the supply of oxygen, as from a cannula. Another object of the invention is to combine with the probe for placement across the lip or cheek a disposable cover to slip over the probe.
Still another object of the present invention is to utilize the photoplethysmographic data obtained from the probes of the present invention for diagnosis and monitoring of clinical conditions.
Another object of the invention is to provide a novel configuration of an oximeter probe that is well-suited for placement at the nasal cavity of a patient, in which one side of the probe is situated to the left side of the nasal septum, and a second side is positioned to the right side of the nasal septum, and the tissue between the two sides is assessed by transillumination pulse oximetry. This design, in a preferred embodiment, also functions to provide oxygen to the patient through channels provided in the structure of the probe. The embodiments of the nasal probe of the present invention advance the art by obtaining reliable and repeatable pulse oximetry and plethysmography data from the interior nasal septum with the extensions going into the nose being designed and spaced so as to not press into the tissue of the septum. Further, the extensions of the probe, where the light-generating and the light-detecting components are positioned, do not simultaneously contact the respective areas of mucosal tissue of the nasal septum. This provides a more comfortable probe than the prior art that, advantageously, does not impair blood flow in the vascular tissue being evaluated, and does not harm that tissue as may occur from a probe that exerts simultaneous pressure from both sides.
Another object of the invention is to combine the nasal probe of the present invention with sampling devices for capnography sampling, either with or without a structure or assembly for the supply of oxygen, as from a cannula. Another object of the invention is to provide a novel configuration of an oximeter probe that is well-suited for placement on both sides of either the right or the left nasal alar (i.e., the alar nari). One side of the probe is situated to the outside of the nasal nari, and a second side is positioned to the inside of the nasal nari, and the tissue between the two sides is assessed by transillumination pulse oximetry.
Another object of the invention is to provide a novel configuration of an oximeter probe that is well-suited for placement on the tongue of a patient, in which one part of the probe is situated along one surface of the tongue, and an opposing part is positioned in such a manner as to capture a section of the tongue such that a transilluminable cross-section of tongue tissue is held between the two probe parts, and the tongue tissue between the two probe parts is assessed by transillumination pulse oximetry.
It is another object of the present invention to provide pulse oximeter probes dimensioned and configured to be expandable, spring-loaded, and flat surfaced for utilizing measurements on extremities and earlobes; buccal mucosal-buccal surface or dorsal ventral portion of the tongue; and properly sized configurations for the nasal alars (i.e., alar nares) and cheek and/or tongue for critically ill, burned, or traumatized patients. A related object is to provide a configuration for an oximeter probe that utilizes two opposed, substantially flat probe surfaces that tend toward each other, such as by spring tensioning.
It is a further object of the present invention to provide a monitoring system that measures vascular resistance and/or perfusion continuously to improve volume resuscitation and/or drug therapy.
It is still a further object of the present invention to provide a monitoring system that can be used as a multi-probe pulse oximeter to monitor blood oxygen saturation differences, pulse transit time differences, or blood pressure, or any combination thereof.
It is still another further object of the present invention to provide specifically constructed probes used to transmit and receive the light to vascular bed sites that are not normally available for use due to burns, trauma, and surgery on the extremity.
It is still another further object of the present invention to provide a monitoring system that is easily fabricated from low cost material and is adaptable for use in an operating room, intensive care unit, emergency room or other areas to treat patients in need of hemodynamic monitoring.
Still another object of the present invention is to provide a pulse oximeter probe and a supply of oxygen or oxygen-rich air, in combination, and functioning in concert with each other and with oximetry circuitry, such that the level and trend in blood oxygen saturation are determined by the pulse oximeter and changes in blood oxygen saturation direct a change (i.e., an increase or a decrease) in the release of oxygen or oxygen-rich air to the patient whose blood oxygen saturation is being measured. In one type of control of the flow of oxygen or oxygen-rich air, an electronic regulator is controlled by signals from a processor that receives data from the pulse oximeter.
Thus, one particular object of the present invention is to integrate a novel nasal pulse oximeter probe of the present invention with a nasal cannula. Another particular object of the present invention is to integrate a pulse oximeter probe with either a self-container breath apparatus (SCBA) or with the regulator of a self-contained underwater breathing apparatus (SCUBA). Blood oxygen measurements obtained by the so integrated pulse oximeter probe then are used to regulate the percentage oxygen in the supply of gas to the user, and/or to regulate the flow rate to the user upon inhalation. In the case of a SCBA apparatus that is combined with a pulse oximeter probe and oximeter, where that mask is worn in environments with toxic or noxious atmospheres, a critical role of the sensor is to indicate to the user when they are becoming hypoxemic, i.e. when there are potentially dangerous gases leaking into the mask. In the case of a SCUBA apparatus that is combined with a pulse oximeter probe and oximeter, for any dive the oximeter can provide information related to the formation of an air embolus. For deep dives, where specialty mixed gases are used and oxygen concentration in such mixtures are actually reduced from its concentration in air, the oximeter data on blood oxygen saturation provides a warning of current or pending hypoxemia. When further combined with a control to adjust the relative concentration of oxygen to other gases, this device serves to increase the relative oxygen concentration delivered to the diver when the oximeter data trend so indicates the need.
Still another object of the present invention is to provide a pulse oximeter probe and a supply of oxygen or oxygen-rich air, in combination, and functioning in concert with each other and with oximetry circuitry, such that the level and trend in blood oxygen saturation are determined by the pulse oximeter and changes in blood oxygen saturation that indicate a sufficient downtrend in the blood oxygenation status results in a local or remote alarm to alert the patient and/or others to the problem.
Still another object of the present invention is to utilize the photoplethysmographic data obtained from the probes of the present invention for diagnosis and monitoring of clinical conditions.
The foregoing has outlined some of the more pertinent objectives of the present invention. These objectives should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner of modifying the invention as will be described.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the present, as claimed. These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.
FIG. 3A,B depicts a side view and a top view of a pulse oximeter probe for positioning on the tongue of a patient.
The present invention discloses pulse oximeter probes for use with pulse oximeter systems in general. The present invention also discloses a novel non-invasive vascular perfusion and/or resistance status monitor apparatus and methods of using the same.
The probe may be used once and disposed, or may be repeatedly used on different patients. Preferably, the probe frame is constructed of metals, plastics, and other materials subjectable to repeated cleaning with standard antiseptic solutions, or sterilizable by other means. A cable, 7, houses conductors (not shown), such as but not limited to insulated electrical wires, that connect operative components further in the probe, 10, with an oximeter monitor (not shown). A boot, 8, connects the cable, 7, to the proximal arm, 1, of the hook-shaped frame of the probe 10. Preferably the cable, 7, is flexible. The boot, 8, primarily serves to connect the cable, 7, with the frame, and secondarily to provide a handle with which the patient or attendant grip the probe. In other designs of the lip/cheek probe, a boot is not required where a direct connection is made between the cable and the frame of the probe.
In the embodiment depicted in
Each probe 10 is sized appropriately to be placed with the open end, 4, inside a patient's mouth, so that the distance, 6, between the LED pad, 12, and the photodetector pad, 14, conforms to the thickness of the lip or cheek vascular bed of the patient. It is noted that
The embodiment depicted in
Individual conductors provide electrical signals that power the LEDs 17. Other conductors carry signals from the photodetector, 15. Optionally, other sensors, such as for temperature, may be added to the probe, 10, and have individual conductors for them also passing in the cable, 4, to the frame of the probe, 10. The probe, 10, is used to generate data used to calculate oxygen saturation, pulse shape, blood pressure measurement (by measurement of pulse transit time to a second site), and any combination of these.
The bridging section, 2, flexes to permit conformance to a range of tissue thicknesses greater than the nominal unflexed spans, as depicted by distances 5 and 6. The probe in
For instance, in one embodiment of this configuration, the body of the probe, 10, is made of nylon plastic. The flexibility of the bridging section, 2, the proximal arm, 1, and the distal arm, 3, is such that less than 5 grams of force deflects the open end, 4, in one direction or the other (toward or away from the opposing section) by about 1/16 inch. The force required increases logarithmically, such that to move the open end, 4, outwardly 0.25 inch required between about 1,250 to 1,550 grams of force, and the force required to move the open end, 4, inwardly (toward the opposing section) required between about 2,200 to 2,700 grams of force. After such forces the nylon material demonstrated memory, returning to within 1/16 inch of the original position, thus demonstrating a resilient quality to the structure of the probe.
In addition, the material of each of the LED pad, 12, and the photodetector pad, 14, deflects upon application of pressure from adjacent tissue by up to about 0.050 inch. Thus, the overall flexibility is sufficient to accommodate a wide range of sizes of cheek and lip sections, which the axis of light transmission from the LEDs is reliably aligned to the photodiode or other light sensor. While not being bound to a particular theory, it is believed that maintaining appropriately narrow alignment of these elements improves the reliability, precision and accuracy of the signals from the probe.
More flexible probes are alternate embodiments of the present invention. For instance, the structural material and thickness is adjustable such that only between about 150 to 1,250 grams of force moves the open end, 4, outwardly 0.25 inch, and between about 200 to 2,200 grams of force the force moves the open end, 4, inwardly (toward the opposing section).
Less flexible probes also are alternate embodiments of the present invention. For instance, the structural material and thickness is adjustable such that between about 1,550 to 3,500 grams of force moves the open end, 4, outwardly 0.25 inch, and between about 2,700 to 5,000 grams of force the force moves the open end, 4, inwardly (toward the opposing section). Alternately, in a more rigid probe, the structural material and thickness is adjustable such that between about 3,500 to 5,500 grams of force moves the open end, 4, outwardly 0.25 inch, and between about 5,000 to 8,000 grams of force the force moves the open end, 4, inwardly (toward the opposing section). Such probes are made of metals or polymer composite materials. The resiliency is expected to vary inversely, roughly, with the flexibility of probes of such alternative embodiments.
Although in
In specific embodiments depicted herein, two general approaches are used to protect the components of the pulse oximeter probe, 50, from moisture and contamination. Other approaches, as known in the art of medical device construction, also may be used. First, a clear plastic covering, shown as 61 in
Also, typically these pieces of heat-shrink wrap plastic, 61, are sized and positioned to extend onto the approximate bottom half of two extensions, 54 and 56, by about 1/16 inch, to form an integral seal against moisture (this overlap is shown at arrow X in
The above-described first protective approach is sufficient to prevent moisture and contamination of the components within the distal halves of the two extensions, 54 and 56. A second approach, which is an optional and not required for the operation of the pulse oximeter probe, 50, provides additional protection to this and other parts of the pulse oximeter probe, 50. This is shown in
In certain embodiments, the two extensions, 54 and 56, are spaced apart from one another so that, upon insertion into the nostrils of a patient, the inner sides, 65 of the extensions, 54 and 56, fit snugly against the tissue of each side of the septum, to avoid interference from ambient lighting.
Moreover, in certain embodiments, the relationship between the inner sides, 65, and the adjacent tissue of the interior septum is described as A non-contiguous fit as to the interior septum wall, such that, even considering irregularities of the nasal interior septum surface and patient movement, the inner sides, 65, do not make contact with the nasal interior septum mucosal tissue for most, or for all, depending on the patient, of the length of the respective extension's insertion into the nasal passage.
More particularly, a non-contiguously-fitting probe (such as 50, and its extensions, 54 and 56) is sized and constructed so that when placed into a nose size for which it designed (i.e., adult size, etc.), there is not a pressing or a continuous contact against the mucosal tissue of the interior nasal septum by both extensions where are positioned the light-generating components (such as LEDs 62 and 64) and the light detecting component(s) (such as photodetector 66). This contrasts with prior art that is disclosed to provide a continuous, even if light, pressure upon both sides of the interior nasal septum mucosal tissue, and/or that clips the probe against the mucosal tissue of the interior septum. Also, as to construction compared with the latter prior art example, the dimensions, materials and assembly of the present invention are such that there is not imparted to the two extensions, 54 and 56, an inward-flexing compressive force that causes attachment (as contrasted with incidental and/or partial contact) of the two extensions, 54 and 56, to the mucosal tissue of the nasal interior septum. Even more particularly, in part to avoid the possibility of irritation of the mucosal tissue of the interior septum walls, further, in certain embodiments, the entire surface of the inner sides, 65, from the inner faces, 67 (of the molded outer shell, 69) to the distal end of each extension, is planar and without any protruding areas, sections or components.
As to an example of the relative sizing between the thickness of the nasal interior septum and the span, 70, between the inner sides, 65, of opposing extensions, 54 and 56,
Further, in certain embodiments of the present invention, the space between inner sides, 65, of opposing extensions 54 and 56, where the light-generating and the light-detecting components are positioned, for adult-sized probes, is between about 0.300 and 0.420 inches. In other embodiments, for such adult-sized probes, the space is between about 0.330 and 0.390 inches. In other embodiments, for such adult-sized probes, the space is between about 0.350 and 0.370 inches. Corresponding size ranges are within the skill of the art to determine for pediatric-sized nasal pulse oximeter probes comprising a non-contiguous fit, based on the measured thickness of the nasal interior septum for such pediatric patients, and the range of spacing given factors of comfort and probable incidence of ambient light interference (recognizing, for instance, that neonates have greater light transmission through their tissues).
In certain embodiments support for the distal ends of the inner sides, 65, generally is through contact with columella. This fleshy tissue extends laterally, to various extents in different individuals, from a plane generally defined by the surface of the more interior mucosal lining of the interior septum. The columella is less sensitive and less subject to damage by direct contact than that more interior mucosal lining of the interior septum. Thus, in embodiments such as that depicted in
Thus, when the extensions 154 and 156 fit snugly against the columella, and are not found uncomfortable over time by the user, this comprises one example of a good fit. Further, such bracing contact with tissue of the columella is not mutually exclusive with the fit described as non-contiguous. That is, in many uses, the same embodiment both contacts the columella with its extensions and, more interiorly, there is not a pressing or a continuous contact against the mucosal tissue of the interior nasal septum by both extensions where are positioned the light-generating components (such as LEDs 62 and 64) and the light detecting component(s) (such as photodetector 66). More broadly speaking, the same embodiment may both 1) provide a beneficial fit against the columella and 2) provide a non-contiguous fit more interiorly.
However, it has been observed that certain larger columellae, in certain patients, deviate outward the extensions of the nasal probe such that the distal ends of the two extensions, respectively bearing the light-generating and the light-detecting components, are positioned an undesirably long distance from each other. To deal with this, in other certain embodiments, each of the inner faces of the extensions comprise a deviation in the shape of the extension to allow for a relatively larger-sized columella. This is advantageous for persons having large columellae, so that their columellae do not force the extensions to spread outwardly to an undesirable distance from the interior nasal septum. In such embodiments, depending on the sizing of the nasal probe (see below) and the size of the patient's nose and columella, there might be no contact with the columella, in which case the support for the weight of the extensions is on the part(s) of the probe main section that is in contact with the upper lip. Where, given the respective sizes of probe and columella, there is contact, with such accommodation for the columella the spreading of the ends of the extensions is less than it would be otherwise.
Further, it is recognized that the flexibility of the nasal probe main section, 52, and the two extensions, 54 and 56, are important in achieving the operational performance of the nasal probes of the present invention. One nasal probe has been constructed with TPE plastic and had a measured flexibility of 60 durometer units. Another nasal probe, also made with TPE plastic, was manufactured and had a measured flexibility of 87 durometer units. In general, with regard to the plastic used for nasal probe main section, 52, and the two extensions, 54 and 56, the preferred range for plastic flexibility is between about 60 and about 90 durometer units.
Per the above, the distance between the probe extensions in relation to the average dimensions of the septa of the target patient group is one factor that provides for a suitable non-contiguous fit to obtain good pulse oximetry data without undesirable patient discomfort and/or tissue damage that results from a direct clipping of the probe extensions (arms) to the mucosal tissue of the nasal septum. Critical to this approach is not designing nor operating the nasal probe to applying pressure to, attach to, or clamp on to, the nasal mucosal tissue where the pulse oximeter readings are being taken. It has been noted that practitioners in the field have expressed the need to, and have practiced, applying pressure to a probe in order to stabilize the probe. While this may be required in finger or other extremity probes, this is contraindicated when considering the delicate mucosal tissue that lines the septum. Thus, in the present invention, the nasal probes, in their sizing, material selection, and overall design, are such that they perform to obtain pulse oximetry data by passing light through the nasal septum, and the probes do this without applying pressure to the nasal septum from both sides at the same time. That is, if any incidental contact is made to the actual nasal mucosal tissue from one extension, where either the light-generating or the light-detecting component is positioned, the other such area (where the light-generating or the light-detecting component is positioned) on the other extension is not then in contact with the opposing side of the nasal septum mucosal tissue.
In summary, the nasal pulse oximeter probes of the present invention are designed, sized and constructed to direct light against sensitive and highly vascularized mucosal tissue of the nasal septum without pressing against such tissue from both sides simultaneously, and to provide for long-term use with minimal irritation or tissue necrosis.
Another aspect of certain embodiments of the present invention is that the light-generating and the light-detecting components do not protrude from the respective planes of the inner faces of their respective extensions. This is consistent with the teaching of the present invention that there is neither a need nor a desire to press into the mucosal tissue of the nasal septum at the site adjacent to these components. In most embodiments, these components are positioned on respective diode pads. These pads are placed within the respective extensions, and as a result, in certain embodiments, are recessed within the respective extensions.
Further as to the specific construction of the embodiment depicted in
As to the specific area of the nasal septum that is preferred for use of a nasal pulse oximeter probe such as the one depicted in
Thus, in general, the two extensions, 54 and 56, are angled so that upon insertion and proper placement into position in the nostrils, the LEDs 62 and 64, located on extension 54, emit light directed through a region that includes the preferred, proximal area of the nasal septum. Most preferably, the LEDs 62 and 64, located on extension 54, directed light exclusively through the highly vascularized region of the septum known alternately as Kiesselbach's plexus and Little's area.
In addition, a stabilizer, 58, embodied in
As for the probe described above in
Cables 61R and 61L preferably form a loop that may lie above the ears of the patient, and join to form a single cable (not shown). This single cable preferably terminates in an electrical plug suited for insertion into a matching socket in the pulse oximeter monitor system (not shown). In another preferred embodiment, the single cable terminates by connecting to an adapter cable, which in turn connects to a socket in the pulse oximeter monitor system (not shown). In a typical application, the signals from the light-sensing photodetector, 66, are ultimately received and processed by a general purpose computer or special purpose computer of the monitor system (not shown). As used herein, the terms “monitor system” and “monitoring system,” may refer to the component that receives data signals from one or more probes, that is, the component that comprises the general or specific-purpose computer that analyzes those data signals (i.e., the processor). This may be a stand-alone unit (i.e., a console or, simply, pulse oximeter), or a module that transmits data to a central system, such as a nurse's station. However, depending on the context, the terms “monitor system” and “monitoring system” also may encompass the entire assemblage of components, including such component and the one or more probes and the conductors (i.e., connecting wiring) that transmit data and control signals.
Also, it has been learned that a nasal probe, such as 50 in
When this method is practiced, due to the natural bend of the rolled cable (or tubing), the resultant cables 61R and 61L, when placed over the ears, tend to gently orient the probe extensions, 52 and 54, axially inward, toward a desired vascularized part of the nasal septum. As such, comfortable nasal probes are produced, and the probes are more easily adjusted to desired positions. Also, it has been observed that probes made this way more generally maintain their desired positions, and this is believed due to there being no undesirable countervailing force (i.e., the rotational force of some cables not assembled per this method) against whatever means are used to keep the probes in place.
Further with regard to embodiments of the nasal probe that provide a non-contiguous fit when inserted into a nose of a patient, use of such probes thusly to obtain photoplethysmographic data unexpectedly provides superior results in comparison to prior art methods that simultaneously press (albeit lightly) both sides of the interior nasal septum, or, more severely, that grasp the nasal septum in such a way that there is contact on both sides of the nasal septum at the same time with both the light sources and the light detector. That is, an improved method for obtaining pulse oximetry and other photoplethysmographic data is described as follows:
-
- a) Through size estimation of the nasal septum to be used for data collection, providing a nasal probe for insertion around the septum such that said probe non-contiguously fits said septum;
- b)Inserting one extension of the nasal probe into each of the two nostrils of a patient, wherein one extension comprises at least two light-generating components that emit light at at least two different wavelength bands, and the other extension comprises at least one light-detecting component that detects light transmitted from said at least two light-generating components; and
- c) Measuring, selectively, pulse oximetry and/or other photoplethysmographic properties of the blood flow in vascularized interior septum tissue positioned between said at least two light-generating components and said at least one light-detecting component;
- d)Wherein said blood flow is not dampened by a simultaneous pressing of said tissue from both sides at the point of measurement of said data.
Among other benefits, the data taken from the less dampened (compared to finger probes) vascularized tissue of the interior nasal septum provides more distinct signals having clearer information about cardiovascular parameters.
Further, it is noted that such method optionally additionally includes locating a desired highly vascularized arterial plexus, such as Kiesselbach's plexus, for the point of measurement, such as by using perfusion index locating means, detection by lower LED power requirement, or other means known in the art.
Further with regard to embodiments of the lip/cheek probes, use of such probes to obtain photoplethysmographic data provides superior results. That is, an improved method for obtaining pulse oximetry and other photoplethysmographic data is described as follows:
-
- a) Through size estimation of the thickness of the lip or cheek to be used for data collection, providing a lip/cheek probe dimensioned for insertion around the lip or cheek so as to not squeeze the tissue, to avoid constriction of blood vessels therein (such constriction measurable by comparative data with probes having different distances between the pads);
- b) Placing the distal arm of said probe into the mouth to a desired position; and
- c) Measuring, selectively, pulse oximetry and/or other photoplethysmographic properties of the blood flow in vascularized tissue positioned between said at least two light-generating components and said at least one light-detecting component.
In particular, it is noted that the probe, after initial placement to a desired position, is adjusted to a more desired position providing a good signal. This is done such as by comparing signals from the different possible positions. Thereafter the cable leading from the probe (which typically is placed over the top of one ear) is taped to the outside cheek to stabilize and maintain this selected position. It has been found that a desired positioning often is with the bridging section, 2, of the probe positioned in or near one corner of the mouth, with the cable leading over one ear. In such positioning the light-generating and the light-detecting components are positioned around an area of the cheek a distance from the corner of the mouth. It is noted that the lip/cheek probe has been found to function consistently, without interference from movement of the mouth, in patients who are under anesthesia or on sedating medications. This is not meant to be limiting, as other uses are considered appropriate, taking into account, as needed, a possible effect of mouth movement and resultant interference of signals during periods of such movement.
In a variation of the nasal probe, such as is exemplified in one embodiment in
The arms, 104 and 106, are tensioned to close against one another by a spring (not shown) which has a fulcrum at or near an axle, 109, that hingedly connects the two arms, 104 and 106, near one end. At or near the other end is an LED pad, 112, on one arm, 104. Within this pad, 112, are two light generating sources, here shown as LEDs 114 and 115. Opposite this housing, 112, on arm 106, is a photodetector pad, 116. Within this pad, 116, is at least one photodetector, 118. Electrical wire conductors (not shown) connect the LEDs, 114 and 115, and the photodetector, 118, to a pulse oximeter monitor system (not shown), via a cable, 120, passing from one end of the arm, 104. The inner surfaces of the arms, 104 and 106, in some variations of this probe are knobby or otherwise textured, especially around the LED pad, 112, and the photodetector pad, 116. This texturing is designed to better maintain a stable position of the probe, 100, on the tongue without use of excessive pressure of the spring.
The photodetector 118, which typically is a light-sensing photodiode, detects changes in the light emitted by the LEDs 114 and 115 as that light is differentially absorbed between and during pulses across the capillaries of the tongue tissue between the two arms, 104 and 106. In one embodiment, LED 114 emits light around 650-670 nm, and LED 115 emits light around 880-940 nm. The electrical impulses are timed to be offset from one another. The photodetector, 118, detects the light passing through the tongue which is situated between the first housing, 112, and the second housing, 116 of arms 104 and 106 when the probe 100 is in use. As discussed above, loss of signal through vascularized tissue such as the tongue is due both to background tissue absorption and the absorption by the blood in the arteries, which expands during a pulse. The signals from photodetector 118 pass through conductors (not shown) housed in cable 120 to the processor of the monitor system (not shown). Cable 120 preferably terminates in an electrical plug suited for insertion into a matching socket in the pulse oximeter monitor system (not shown). In another preferred embodiment, cable 120 terminates by connecting to an adapter cable, which in turn connects to a socket in the pulse oximeter monitor system (not shown). In a typical application, the signals from the light-sensing photodetector, 118, are ultimately received and processed by a general purpose computer or special purpose computer of the monitor system (not shown).
There are numerous means for hingedly joining the first arm and the second arm other than by an axle passing through the extensions of each arm (e.g., by axle 109). Other means include hinges of various materials and designs as known in the art, co-fabrication of the arms with a thinner section of flexible plastic between the two arms at one end, and pins, screws, and other fasteners as are known to those skilled in the art.
Similarly, means for tensioning the first arm and the second arm, so as to properly maintain tension on a section of the tongue of a patient, can be effectuated by means other than the spring described above. Separate elastic bands may be attached or may surround the arms, such as by attaching to protrusions spaced appropriately along the arms. Also, the natural flexibility and resilience of a co-fabricated structure comprising both arms connected by a section of resilient plastic can provide both the means for hinging and the means for tensioning. Such fabrications may be deemed suitable for disposable units.
It is noted that for this and other probes disclosed herein, a single source generating at least two different light frequencies may be utilized instead of LEDs. Alternately, more than two LEDs may be used, such as to generate light at more than two frequency bands, for instance to increase accuracy and/or detect other forms of hemoglobin. Also, light receiving sensors, or photodetectors, other than photodiodes may be used, and more than one such sensor may be used in a single probe.
The pulse oximeter probes, such as 10, 50, and 100 as depicted and as used with the monitoring systems in the present invention, take measurements by transillumination as opposed to reflectance. This is the preferred configuration. However, for any of these probes, both the light-generating devices, and the photodetector devices, can be configured adjacent to one another, on one arm or extension, to measure reflectance of the tissue on the interior of the mouth (e.g., the cheek), the lip, the nasal septum, or the tongue.
By “substantially flattened” is meant that the height of the structure of a side is small relative to the greater of the length or width of that side. Preferably the ratio of the height to the greater of the length or width of a “substantially flattened” side is between about 0.2:1 and 0.001:1, more preferably this ratio is between about 0.02:1 and 0.005:1, and yet more preferably this ratio is between about 0.01:1 and 0.005:1. For greater applicability to typical physical requirements in use, each side also is substantially longer than wide. By “substantially longer than wide” is meant that the width of the structure of a side is small relative to the length of that side. Preferably the ratio of the width to the length of a side described as “substantially longer than wide” is between about 0.7:1 and 0.02:1, more preferably this ratio is between about 0.025:1 and 0.05:1, and yet more preferably this ratio is between about 0.025:1 and 0.1:1. At a minimum, with regard to nasal pulse oximeter probes of the present invention, the key functional attributes of extensions that are substantially flattened and/or substantially wide, as used herein, is that the width of such extensions is sufficient to house the components (i.e., circuit boards bearing LEDs and photodetectors, or the LEDs and photodetectors themselves), and the length of such extension is sufficiently long to provide the LEDs and photodetectors on opposite sides of a desired region of vascularized tissue. The same functional logic applies to other sensors disclosed and claimed herein.
Also, it is noted that in place of the spring, 18, any hinging means as known in the art can be used. Such hinging means may include a raised section along or separate from the sides, such that a fixed space is created at the point of the hinging means. This would obviate the need for a bend in the sides at the spring, 18, as shown in
Also, the above substantially flattened sides with hinging means may be produced without light-emitting and light-detecting structures, and sleeves, such as described below, bearing such structures, would then be slipped over the sides to yield an operable oximeter probe. For instance, as shown in
In operation, the devices depicted in
Thus, another aspect of the present invention is a disposable sleeve that fits over any of the pulse oximeter probes disclosed and claimed herein, and over conventional probes. A sleeve is constructed of a flexible material, and is relatively thin, in the general range of 0.005 to 0.050 inches thick, more preferably in the range of 0.010 to 0.025 inches thick, and most preferably in the range of 0.010 to 0.015 inches thick. The sleeve is manufactured to slide over the major structural features of the probe to provide a barrier to reduce the chance of contamination from one patient to a second patient using the same probe. An example of such sleeve is shown in
In some sleeve embodiments, a stretchable aspect of one or more parts, or of the entire sleeve, stretches over a protuberance or other prominence at one or more parts of the major structural features over which the sleeve is sliding, and improves the fit of the sleeve. This also better assures that the sleeve does not slide off the probe during normal uses. Alternate means to secure the sleeve onto the probe such as are known to those of skill in the art may be used. The sleeves themselves can be disposable; however, the sleeves also can be made of easily sterilizable materials and be sterilized between uses.
The probes and the sleeve covers of the present invention are supplied as clean or as sterile, depending on the needs of the end user and the budgetary constraints of the end user. Clean but not sterile probes and sleeves will be less expensive, and may be suitable for many applications. Where there is an elevated risk of major harm from an infection, for instance in immunocompromised patients undergoing transplants with immunosuppressive drugs or undergoing chemotherapy, sterile probes would be more appropriate than merely clean probes. Many configurations of the probes are cleanable using alcohol and/or detergent/disinfectant solutions, and other configurations are disposable.
All of the above disclosed probes operate in a typical manner of a pulse oximeter, as described herein and in articles and patents cited and incorporated by reference. Each LED emits its specific frequency hundreds of times per second, and the absorption (or transmittance) readings by a sensor, such as a photodiode, are transmitted to a computer. There a software system performs averaging (optionally deleting outliers), and by differences in wavelengths' absorption or transmittance at the pulse peaks, determines arterial oxygen saturation. In a standard two-LED system, this is done by an algorithm that calculates the ratio of the peak absorbence at 650-670 nm divided by the base absorbence at this wavelength range, and compares this ratio to the peak absorbence at 880-940 nm to the base absorbence at the 880-940 nm range. The base absorbence reflects the non-pulse background absorbence by tissues other than the artery at maximum width during the pulse. This calculation provides an estimate of arterial oxygen saturation. A graph of the pulse surge, or shape, over time, also can be obtained.
All of the above-disclosed probes are expected to have significant use in the intensive care units, operating rooms, post-surgery recovery rooms, and in ambulance related situations where a patient in need of monitoring has few suitable monitoring sites. The size and shape of each probe will depend on whether the patient is an adult or child.
When two or more probes are used together, data from multiple probes is processed to provide continuous and simultaneous cross-site comparisons of the arterial blood oxygen saturation status at and comparisons between two or more tissue sites (and, as desired, blood pressure estimates based on transit time differences and/or other related parameters). The monitoring system receiving these signals includes at least one program containing computer software (not shown) comprising instructions which causes the computer processor to receive and calculate various oxygen saturation values. Optionally, the monitoring system may receive signals from separate probes or sensors to assess blood pressure values, which optionally may be compared (either simultaneously or separately) with blood pressure estimates based on signals received from each of the probes determining arterial blood oxygen saturation and vascular perfusion/resistance of a patient. Depending upon the software used, and the addition of separate blood pressure probes or sensors, the monitor may be used as a dual pulse oximeter, a saturation difference monitor, a transit time monitor, a periodic blood pressure monitor, or a noninvasive continuous blood pressure monitor. Specific examples are provided below that demonstrate a non-exclusive range of applications for the monitoring system which compares signals from a central source site (CSS) with signals from at least one advantageously positioned peripheral site (PS), as those terms are defined herein.
The method shown in
Further, a variation of the method of
The apparatuses, methods and systems of the present invention can be applied to both humans and animals, i.e., to living vertebrate organisms. Its application in human medicine (adult & pediatrics) would significantly improve the estimation of vascular perfusion or resistance by pulse oximetry; however, veterinary medicine also would greatly benefit from its use. This superior monitoring system would utilize at least two pulse oximeter probes, one of which is designed for use with a highly perfused central tissue, such as a lip, tongue, nares, cheek; and the other probe is designed for use to less perfused areas such as peripheral tissues, or any combination thereof.
The following specific examples are meant to be demonstrative, but not limiting, of the possible applications of the present invention.
EXAMPLE 1Data from a small number of volunteer subjects was obtained. This data provided preliminary support for the hypothesis that differences in CSS and PS estimates of arterial blood oxygen saturation levels can provide diagnostic information about the status of peripheral blood circulation. These data are summarized below.
All sets of data were taken three times, except that data for subjects 1 and 9 were only taken two times (duplicate data sets). Subjects 1-3 had no history of chronic obstructive pulmonary disease or other conditions that would be expected to cause lowered peripheral circulation. Except for one reading of 93% for subject 1, all estimates of arterial oxygen saturation were 95% or higher, and the PS (a finger, using a standard commercial probe) readings were within two percentage points of either CSS sites (lip and cheek). For the data set in which subject l′s cheek probe reading was 93%, the lip reading was 98% and the finger reading was 96%. Overall, the data of subjects 1-3 suggest that in a healthy subject the CSS and PS readings taken at or near the same time will be relatively close, within about 5 percentage points or less, and all of the readings will be high.
Subject 4 had average readings at the PS finger site of 89%, and at the CSS cheek site, 88.7%, so these sites has essentially identical estimates. No signal was recorded at the lip CSS. Although there was no difference between the CSS cheek and the PS readings, the oxygen estimate was low and indicated a generalized problem.
Subject 5 had a PS average of 85%; the lip CSS average was 88.3%, and the cheek CSS average was 91.3%. The absolute levels are low, and the difference between CSS and PS values ranges from about 3 for the lip to about 6 for the cheek. This appears to suggest a peripheral circulation problem, and the low absolute levels indicate a generalized problem with oxygenation. This subject was known to have COPD.
Subjects 6-8 were known to have COPD. The average values for finger, lip and cheek were 85, 90, and 89, respectively for Subject 6. The 4-5% less percent saturation for the peripheral site supports the present hypothesis. Subject 7′s finger data varied between 77-80% during the readings, and is considered unreliable. One of subject 8′s data points for the finger was 79%, whereas the other two were 85%. This suggests that the 79% reading is erroneous. Disregarding this data point, Subject 8 had 85%, 87.3%, and 85.6% averages for the finger, lip and cheek sites, respectively. Here, all readings are fairly close, and the absolute values are alarmingly low. The data from this subject do not support the hypothesis; however the circulation for this subject may not be impaired peripherally. Further investigation can resolve this and other points.
Regarding the latter, subject 11's data was anomalous in that the finger site averaged 93.3%, whereas the lip and cheek sites averaged 90.7% and 86.7%, respectively. The reason for this is unknown; the data could be spurious or could indicate unusual circulation in a small percentage of the population. Individual differences in circulatory systems (based in part on genetics, and in part on non-genetically based embryological development, and on physical conditioning) may form the basis for such anomalies in a percentage of the population. Highly variable and incomplete data for Subjects 9 and 10 were considered to render the value of their data questionable, and those data were not analyzed.
Thus, this preliminary data provided some indication of differences between CSS and PS and differences between normal and circulation-compromised subjects. The data also supported the need to investigate broader populations with known circulatory conditions to develop more predictive guidelines for the probe data differences. Even with the limited data of this example, it is apparent that the comparison of CSS and PS sites can provide a useful assessment of the state of the circulatory system even where there is no major difference, and there is not a disease state presenting itself. That is, such results of roughly equivalent CSS and PS data at a high oxygen saturation level would support a conclusion that the peripheral circulation is not impaired.
EXAMPLE 2An elderly patient with relatively advanced diabetes comes in for monitoring of the status of perfusion in the right leg, which is diagnosed with severe atherosclerosis and related impaired vascular perfusion. A monitor of the present invention is utilized, with one CSS probe measuring signals across the nasal septum, and a PS probe on the large toe of the right foot. A new medication is started, and ongoing weekly data from the monitor tracks the changes in perfusion in the right leg by comparing oxygen saturation values of the CSS probe with the values of the PS probe. Such data indicates the degree of effectiveness of the new medication.
EXAMPLE 3A critically burned patient is brought into an emergency room. As vital signs and assessment is taking place, a pulse oximeter probe as shown in
A patient suspected of having Chronic Pulmonary Obstructive Disease is admitted to an emergency room with breathing difficulties. The patient also reports pain in both legs after involved in a minor traffic accident, which is the immediate cause of admission. Minor bruising is apparent on the front of the left leg. Along with other tests and monitoring, a pulse oximeter monitor of the present invention is utilized, with on CSS probe on the nares of the nose, and a PS probe on the large toe of each of both feet. Alarmingly, the CSS probe estimates that the arterial oxygen saturation at the CSS site is below about 85 percent, indicating hypoxia. The pulse oximeter monitor in both PS sites estimates even lower oxygen saturation, by about 5 percent, compared to the CSS site. There is no response to bronchodilator therapy, and the chest x-ray shows moderate fibrosis, and no attenuated vessels or hyperinflation. The initial diagnosis, aided by the pulse oximetry data, is bronchial COPD. Oxygen therapy is provided, and the pulse oximetry data is utilized to monitor increases in blood oxygen saturation both at the CSS and PS sites.
It is noted that the following paragraphs, through and including Example 5, describe embodiments of the present invention which combine, preferably integrally, a pulse oximeter probe with a nasal cannula through which is delivered a supply of oxygen or oxygen-rich air. In some of these embodiments, the combined pulse oximeter sensor/nasal cannula with oximeter is used to monitor and provide information regarding the oxygen saturation status, using data obtained from the sensor through the tissue of the nasal septum, to the user of the device, to caretakers of that user, and/or to a remote station that utilizes the information. For instance, the user can view current and/or historical trend data and manually adjust the flow rate of the oxygen or oxygen-rich air accordingly. Alternately, a user of said combined pulse oximeter sensor/nasal cannula with oximeter, in advance of a period of expected increased exertion, may increase the flow rate of his/her auxiliary oxygen supply. Then, during such exertion, such user refers to the oximeter data output and further adjusts the flow rate as needed to attain or remain within a desired range of blood oxygen saturation as indicated by the data output from the oximeter.
In other embodiments, the combined pulse oximeter sensor/nasal cannula is used in further combination with a central processing unit that sends signals to automatically adjust the flow rate of the oxygen or oxygen-rich air to the use. For instance, and not to be limiting, during more strenuous exertion, arterial blood oxygen saturation of a person needing oxygen supplementation therapy is expected to decline appreciably. In such circumstance, this drop in oxygen saturation is detected by the pulse oximeter probe, the trend data is analyzed by a program in the central processing unit, and a signal is sent to a valving mechanism that results in a greater oxygen flow directed through the user's cannula. A feedback loop, the data from the nasal pulse oximeter going to the central processing unit monitoring system, subsequently decreases the flow when the data indicates arterial blood oxygen saturation has exceeded a designated percentage. By such feedback loop approach, the oxygen delivered via the nasal cannula is better optimized for actual physical exertion and/or changing metabolic requirements.
In other embodiments, which are preferred in certain applications, the use of data from the nasal pulse oximeter to regulate oxygen flow to the nasal cannula is combined with other approaches to conserve oxygen, which include, but are not limited to:
-
- 1. detection of the inhalation phase of the respiration cycle to provide the oxygen (or oxygen-enriched gas) only during inhalation (or a key segment of the inhalation, i.e., the initial ⅔ of the inhalation);
- 2. providing oxygen every other breath; and
- 3. providing greater volume and/or flow rate at key part(s) of inhalation cycle (i.e., increased “shot size”).
In yet other embodiments, which are preferred in certain applications, the data from the nasal pulse oximeter is combined with data collection of other parameters. For instance, in studying sleep disorders, a number of parameters are measured, for instance, pattern or dynamics of respiration (flow rate, inhale/exhale over time cycles), pulse rate, etc. In embodiments of the present invention, the use of the combined nasal pulse oximeter probe is combined with other monitoring sensors at the nose that detect, for instance, but not to be limiting, air flow and air pressure, such as during sleep, to analyze an individual's sleep disorder, such as sleep apnea.
Thus, when blood saturation information from the so-combined pulse oximeter probe is processed over time, and when trends are detected in the oximeter probe data processor that indicate a need for more or for less oxygen to the patient, based on, respectively, lower or higher blood oxygen saturation readings than a desired range, one or more outcomes result. As noted above, one outcome is to automatically adjust the supply of oxygen or oxygen-rich air to provide a needed increase (if readings were trending lower) or a decrease (if readings were trending higher, above a desired range, and conservation of the supply were desired) of that supply. Another outcome is to provide an alarm signal (audible, flashing, etc.) locally, for recognition by the patient or a nearby attendant. Yet another possible outcome is to provide a remote alarm, such as by cellular telephone transmission, to a physician's office, an ambulance service or hospital, etc.
Further, it is noted that there exist in presently used devices other approaches to conserving the supply of oxygen or oxygen-rich air. One commonly used approach, often referred to a the “pulse-dose” system, delivers oxygen to the patient by detecting the patient's inspiratory effort and providing gas flow during the initial portion of inspiration. This method is reported to reduce the amount of oxygen needed by 50 to 85% (compared to continuous flow) and significantly reduces the cost, the supplies needed, and the limitations on mobility caused by a limited oxygen supply.
For example, as the patient initiates a breath, the cannula tip senses the flow, a solenoid valve opens, and a burst of oxygen is rapidly delivered to the patient. The size of the burst or flow varies among different manufacturers. Commonly, the pulsed-dose system takes the place of a flow meter during oxygen therapy and is attached to a 50 PSIG gas source. In most devices the patient or operator can choose the gas flow rate and the mode of operation (either pulse or continuous flow). Typically, a battery-powered fluidic valve is attached to a gaseous or liquid oxygen supply to operate the system.
In addition, other approaches are used to further reduce oxygen usage when using the pulse-demand system. One such approach is to reduce the dose of oxygen delivered to the patient during each pulsation. Another approach, in combination or independently of the last one, is to deliver a burst only on the second or third breath instead of every breath. In addition, the size of the oxygen pulse dose will change with the flow setting with increases in flow delivering larger doses of oxygen and vice versa.
It is noted that potential problems encountered when using the pulse-demand system include: no oxygen flow from the device; and decreased oxygen saturations in the patient. If no oxygen flow is detected, then possible causes include a depletion of the gas supply, an obstruction or disconnection of the connecting tubing, or, critically for a pulse-demand system, an inability of the device to detect the patient's effort to breath. If the device cannot detect the patient's inspiratory effort, the sensitivity will need to be increased or the nasal cannula will need to be repositioned in the nares.
A decrease in the patient's oxygen saturation should always be a cause for alarm and may indicate a change in the patient's medical status, tachypnea, or a failure in the device. In any case, a backup system should be available in order to verify whether the problem is with the device or with the patient.
Thus, although in common use, the limitations of many pulse-dose systems are: relatively high cost of the system; technical problems may be associated with such a complicated device (including disconnections, improper placement of the device, and a possible device failure); lack of accommodation for an increased need during exercise, stress, illness, etc. and variable operation of the device if not properly set up.
Variations on the pulse-dose system include delivering oxygen to the patient at the leading edge of inspiration. This allows oxygen to be supplied exactly when needed. Thus, when the patient inhales, a relatively higher quantity of oxygen is delivered for travel deep into the lungs, increasing the probability of greater utilization and uptake in the red blood cells in the person's bloodstream. Other variations on the pulse-dose system are known in the art.
The present invention is used independently of the pulse-dose system, or, alternatively, in conjunction with such system, to conserve the supply of oxygen or oxygen-rich gas, and to better adjust the supply to the actual demands of the patient/user as that person's physical activities and demands vary over time. In particularly preferred embodiments, the pulse oximeter probe that is in combination with an outlet (e.g., the end of a cannula) of the supply of oxygen or oxygen-rich gas is fashioned to be integral with, or securely fastened to, that outlet. This provides greater surety of signals and proper insertion of the outlet. For instance, when the pulse oximeter probe is integral with the nasal cannula, if the probe and device are accidentally moved from their proper location (e.g., entrance of nose, or mouth), then the oximeter readings (including pulse) will deviate sharply from normal. In such instance an alarm can be quickly sounded and the problem rapidly corrected. Thus, this provides a distinct advantage in comparison to peripheral probes, such as finger or toe probes.
Another aspect of the present invention is adding as an additional sensor a capnography sensor (such as an infrared sensor) to estimate the concentration of carbon dioxide in the exhaled breath. This may be useful to detect more rapidly than pulse oximetry the failure of ventilation means (such as the wrong gas being provided to the patent), or carbon dioxide poisoning. Regarding the latter, the article entitled “Management of carbon monoxide poisoning using oxygen therapy” by T W L Mak, C W Kam, J P S Lai and C M C Tang, in Hong Kong Medicine Journal, Vol. 6, No. 1, March 2000 is instructive.
Also, as to the detection of a failure of ventilation means, when the present invention's combined nasal pulse oximeter sensor/cannula is attached to a pulse oximeter that is programmed to distinguish normal from abnormal pulse ranges, and when the combined nasal pulse oximeter sensor/cannula falls away from the user's nose (e.g., by accident during sleep or sedation, etc.), an alarm can be quickly provided based on the lack of pulse in the proper range. In this way the combined nasal pulse oximeter sensor/cannula more rapidly detects a loss of supplemental oxygen more rapidly than typical capnography detectors as to this reason for loss of ventilation.
Thus, the following examples are to be understood to be usable independently or in combination with the above described other approaches to conserving the supply of oxygen or oxygen-rich gas, and/or with other approaches known in the art but not described above, including those referred to in references cited herein.
EXAMPLE 5As discussed for
Also, as discussed for
Further as to the plastic covers, 161, one is fitted over each of the structures, 163, that contain the LEDs 162 and 164, located on extension 156, and the photodetector 166, located on extension 154. The plastic covers, 161, preferably do not interfere with light transmission. Apart from heat-shrink sealing, other means of attaching the plastic covers, 161, to the extensions 154 and 156, include, but are not limited to, sonic welding, spot gluing, hot gluing, press fitting, and other such methods of attachment, as are employed in the art, that are used to attach components of a medical device for entry into an orifice of a living subject. In general, the combined nasal pulse oximeter probe/cannula devices of the present invention are designed to be disposable, due to problems associated with cleaning between uses. However, it is within the scope of the invention that appropriate plastics, components and construction are employed so as to allow an appropriate level of sterilization of such devices between uses.
As for the nasal pulse oximeter probe depicted in
The first approach described above for the nasal oximeter probe in
Further, using the shrink-wrapping construction described above to cover the distal halves of the extensions 154 and 156, and dimensioning the spacing between the extensions 154 and 156 as indicated above for a non-contiguous fit, the extensions 154 and 156 are found to fit without irritation to the mucosal cells lining each side of the interior septum, as from a rough or uneven surface. For example, without being limiting, when using heat sealing plastic as the covering, 161, the thickness of this material, and any finish on the adjoining edge, will affect the extent of a sensible ridge at the junction of the covering, 161, and the molded outer shell, 169, but nonetheless provide a comfortable fit.
The nasal septum extends in the midline from the tip of the nose anteriorly to the posterior border of the hard palate posteriorly. It is bordered inferiorly by the roof of the mouth (the hard palate) and superiorly by the floor of the cranium. As to a specific area of the nasal septum that is preferred for use of a nasal pulse oximeter probe such as the one depicted in FIGS. 8A,B, at least one highly vascularized, and thus more suitable, area of the nasal septum is located approximately 0.5-1.0 cm. from the posterior border of the nostril and approximately 2.0-2.5 cm. superior to the floor of the nasal cavity in the midline. Being more highly vascularized, such thereby provides more consistent and reliable signals than less vascularized areas that are, relative to this, more proximal (the tip of the nose) or more distal (further posterior towards the back of the nasal cavity). In particular, and more specifically, the highly vascularized area of the septum, known alternately as Kiesselbach's plexus and Little's area, is a preferred target area for detection of blood oxygen saturation levels by a nasal pulse oximeter probe of the present invention.
The pulse oximeter nasal probe of the present invention is designed so that, when properly positioned, it passes its light through such highly vascularized areas. In the particular device shown in FIGS. 8A,B, an angle of inflection, 170, is shown between plastic housing, 152, and the two extensions, 154 and 156. This angle properly is measured as an interior deviation from a straight line extended from the plastic housing, 152. In preferred embodiments, the angle of inflection, 170, is between about 0 and about 33 degrees, in more preferred embodiments, the angle of inflection, 170, is between about 10 and about 27 degrees, and in even more preferred embodiments, the angle of inflection, 170, is between about 10 and about 20 degrees. In
Further, it is noted that in typical use contact by an inner face of one extension with nasal mucosal tissue interior to the columella precludes contact by the inner face of the other extension with the nasal mucosal tissue interior to the columella. Further, in many if not most instances, where there is a snug fit against the columella, there is little or no contact by the more distal, inward sections of the respective extensions against the nasal mucosal tissue interior to the columella. Where a patient has a substantially deviated septum, there may be contact by one extension on one side, but this is believed, in most cases, to preclude contact by the other side once interior of any contact with the columella.
Thus, for the embodiments depicted in
As noted above, in certain embodiments contact with the nasal interior septum mucosal tissue is avoided or minimized by one or more of: sizing of the probe (particularly spacing between opposing inner faces), flexibility of the material used, other design features, and lack of design and/or structure to compress or clip any part of the probe to the tissue of the nasal septum. Thus, in various more preferred embodiments, the inner sides (i.e., 65 or 165), of the two extensions, (i.e., 54 and 56 or 154 and 156), if they ever contact the tissue (mucosal nasal lining) of the interior septum, do so lightly, resting without excessive pressure, so as to avoid the development of necrosis of the mucosal tissue. This applies even when the nasal probe is used over extended periods of time. Also, it is noted that a snugly fitting probe, as described in certain embodiments and within its broader context, comprises probes that contact comfortably the columella, whilst remaining spaced from (i.e., facing, adjacent to), the tissue of the nasal interior septum.
Further, referring to
Also, because Kiesselbach's plexus actually is comprised of a region of highly vascularized tissue, rather than a discrete point, and given anatomical variation among persons, a range of approximately +/−0.25 cm from the above indicated measured point also is acceptable as a target area to obtain unexpected superior results with a nasal pulse oximeter probe. It also is recognized, based on the approximate size of the Kiesselbach's plexus, that placing the probe so it measures saturation within a range as large as approximately +/−0.75 cm from the measured point may also provide these unexpected superior results (by having the light pass through this highly vascularized region). However, given the variations noted above, this is less preferred than the range of approximately +/−0.25 cm. from the measured point. Under certain circumstances, a range of approximately +/−0.50 cm. from the measured point is considered acceptable. Given the basic morphology and sizing of the nares, design and placement of nasal pulse oximeter probes such that they pass light through nasal septum tissue within these larger ranges, but not within the smaller approximately +/−0.25 cm. range, frequently requires probes of the present invention that are designed to have smaller (i.e., thinner, narrower) profiles than the profile depicted in
Also, for any of these ranges to target Kiesselbach's plexus, it is appreciated that the angle of a particular individual's lip in relation to the nose, and the placement of the nasal probe sensor on the upper lip, affect the exact location of the probe's light producing and light sensing components on the plexus. As noted, it has been learned that a nasal pulse oximeter, such as is depicted by 150 (with or without the oxygen cannula element), that has an angle of inflection, 170, of about 15 degrees, has been found to provide superior results in testing. This 15 degree angle to reach Kiesselbach's plexus with the light-generating and the light-detecting components, in order to obtain superior sensing data, takes into account that for many patients, there is an angle of the upper lip, tilting about 15 degrees. This is represented in
However, it is appreciated that the shape and angle of person's upper lip, and orientation to the nasal cavity, do vary. Thus, in certain embodiments, it is desirable to adjust the exact angle of the nasal probe in relation to the upper lip (such as by gently twisting it as it is being secured to the upper lip) to obtain the most preferred area for data. Also, optionally, the pulse oximeter is comprised of circuitry and data output that provides a “perfusion index” to assist in improved placement of the probe so that the light-generating and light-detecting components are placed in or near to the desired Kiesselbach's plexus. As known in the art, the perfusion index is the ratio between the pulsatile and the non-pulsatile components of the light that reaches the light-detecting component. This provides a means to find which position has a greater pulsatile component, and can assist, when needed, in orienting a nasal probe to obtain a superior or the preferred site. It is noted, however, that in trials, the probe having a bend of 15 degrees, as shown in
Also shown in
Means of stabilizing the probe, 150, such as elastic straps (not shown) from any part of the device that span the head of the patient, typically are employed, and depend on the type of application and the comfort requirements of the user. More particularly, in order to stabilize the desired position of the nasal probe of the present invention (whether it is with or without a cannula), several specific approaches are useful. One approach to reversible attachment of the nasal probe to the patient is to apply tape to all or part of the patient's upper lip, where the side of the tape to the patient's upper lip has an adhesive suited for the purpose and desired contact period, and the other, exposed side has one or more sections of either the hook or the loop of hook-and-loop type fabric. The side of the nasal probe to rest on the upper lip (“back side”) is comprised of one or more sections of the hook-and-loop type fabric to complement the sections on the tape's exposed side, and by virtue of alignment and pressing together of the sections on the nasal probe and the upper lip, the nasal probe is positioned on the upper lip. This type of reversible attachment can be modified as needed, particularly when the strength of the adhesion of the hook-and-loop type fabric is lessened just to the strength needed to maintain the probe in position in view of the typical range of forces acting to dislodge it. A variation is to apply tape to the back side of the nasal probe, where the tape has adhesive on the side toward the probe, and hook-and-loop type fabric on the opposite side, facing and attachable to the hook-and-loop type fabric on the tape of the upper lip.
Another approach to reversible attachment of the nasal probe to the patient is to apply double-sided adhesive tape to all or part of the patient's upper lip. Then the back side of the nasal probe is pressed against the adhesive on the upward-facing side of the double-side adhesive tape. A variation is to apply the double-sided adhesive tape first to the back side of the nasal probe, then orient the probe into its position against the upper lip with the extensions in the nares, and then press against the upper lip to obtain adhesion thereto. When using such approaches, it is advantageous to have a stabilizer (such as 58, in
Yet another approach to reversible attachment of the nasal probe to the patient is to apply single-sided adhesive tape over the top of the nasal probe. This is done before or after the nasal probe has been positioned with the extensions in the nares and the back side against the upper lip, and the tape is pressed into the skin of the face adjoining the nasal probe, to secure the probe in place.
As for the probes depicted in FIGS. 1 and 2A-D and described above, timed electrical impulses from a pulse oximeter monitor system pass through two wires or other signal transmission means (not shown) in cables held within conduit passing within 182 to produce the light from LEDs 162 and 164. At least one photodetector, 166, is positioned within extension 154 to face and oppose LEDs 162 and 164 on extension 156. The photodetector 166, which typically is a light-sensing photodiode, detects changes in the light emitted by the LEDs 162 and 164 as that light is differentially absorbed between and during pulses across the capillaries of the septum tissue between the two extensions, 156 and 154. In one embodiment, LED 162 emits light around 650-670 nm, and LED 164 emits light around 880-940 nm. The electrical impulses are timed to be offset from one another, so that the light from each of the two LEDs, 162 and 164, is emitted at different times. The photodetector, 166, detects the light passing through the septum of the nose, which is situated between extensions 156 and 154 when the probe 150 is in use. As discussed above, loss of signal through vascularized tissue such as the nasal septum is due both to background tissue absorption and the absorption by the blood in the arteries, which expands during a pulse. The signals from photodetector 166 pass through conductors (not shown) to the processor of the monitor system (not shown). As examples, not meant to be limiting, a single cable passing from one side of the device, 150, or two cables that may form a loop that may lie above the ears of the patient, or join to form a single cable (not shown), pass signals to the two LEDs, 162 and 164, and from the photodetector 166. In one preferred embodiment, a single cable, formed from the joining of two cables leading from the device, 150, terminates in an electrical plug suited for insertion into a matching socket in the pulse oximeter monitor system (not shown). In another preferred embodiment, the single cable terminates by connecting to an adapter cable, which in turn connects to a socket in the pulse oximeter monitor system (not shown). In a typical application, the signals from the light-sensing photodetector, 166, are ultimately received and processed by a general purpose computer or special purpose computer of the monitor system (not shown).
Per the disclosure preceding this example, this combination nasal pulse oximeter is used either in combination with the needed computer processing to interpret and provide a viewable (or audible in the case of an alarm) data output of arterial blood oxygen saturation for the user or health care worker, or, in alternative embodiments, this function is further combined with the means to regulate and adjust the flow of oxygen or oxygen-rich gas that is being delivered by adjustment of a valve controlling such flow.
EXAMPLE 6The present invention also is adapted for embodiments which utilize, in combination, pulse oximeter detection of arterial blood oxygen saturation, in combination with a supply of oxygen, air, or a gas mixture providing a variably supply of oxygen, where the flow rate and/or amount of oxygen provided in the gas mixture is controlled based at least in part by the changes and levels of arterial blood oxygen saturation, as detected by the pulse oximeter. Applications for such combination devices (pulse oximeter/oxygen supply directed by controller with pulse oximeter data as an input) include, but are not limited to: self-contained breathing apparatuses (SCBA); self-contained underwater breathing apparatuses (SCUBA); high altitude breathing systems, and medical gas delivery systems. The following figures and related disclosure provides only one, non-limiting embodiment to present the basic concepts of the present invention as applied to a SCUBA regulator.
For SCUBA systems using HE/Ox mixtures, additional oxygen can be provided when indicated by the data from the oximeter, and/or by a manual control (such as the diver pressing a button to increase, with a second button to decrease oxygen flow incrementally). The same approaches apply to more complex dive gas mixtures, such as Triox (oxygen enriched air with helium) and Trimix (hypoxic oxygen, helium and nitrogen). By appropriate control mechanisms and algorithms (adjusted to compensate for physiological differences at different depths), a diver using such embodiments of the present invention extends the dive time on a particular quantity of oxygen, and/or has more oxygen when more oxygen is needed, and less oxygen when less oxygen is sufficient. This results in a safer, healthier dive experience.
The above disclosed improvements in the monitoring of blood oxygen saturation and adjustment of gases supplied to a SCUBA diver also apply to users of self-contained breathing apparatuses (SCBA) that are not used for underwater diving. For example, firemen and other emergency workers use SCBA in environments in which they may exert considerable energy and have transient very high oxygen demands. The above-disclosed embodiments, and variations of these known to those of skill in the relevant arts, provide benefits to such users.
As described above, Kiesselbach's Plexus is a vascularized area in the anteroinferior part of the interior nasal septum, and is supplied by sphenopalatine, greater palatine, superior labia and anterior ethmoid arteries. These vessels originate from both the internal and external carotids and are the most frequent cause of epistaxis (nose bleed).
To demonstrate the utility of Kiesselbach's Plexus as a site for pulse oximetry, data was recorded from a more vascularized region of the nasal septum (i.e., Kiesselbach's plexus) using a probe of the present invention in its intended positioning. This data was compared to data from two adjacent sampling sites, one inferior and posterior, and one anterior and superior to Kiesselbach's plexus. Since all three sampling sites are capable of giving a signal for pulse oximetry with a standard pulse oximeter monitor, relative LED power provided a marker of utility. A lower LED power required to obtain a measurement indicates a stronger source signal. Such lower power requirement is apparent when the probe is placed so as to transmit light through the vascularized area identified as Kiesselbach's plexus. Also, as further discussed herein, a stronger signal source in the nasal or cheek/lip areas generally provide improved signals for use in plethysmography.
A nasal probe of the present invention, having a 15 degree inward angle, or inflection along its extensions, was utilized for the comparison. This probe has a side view similar to the probe in
The data indicates that the probe in its intended position, with the back of the probe's main section against the upper lip, provides superior data. This is indicated by virtue of FIG. 18B′s LED Power reading of 66, compared to the LED Power readings of 108 and 102 for
Further, it is noted that in some subjects, a nasal probe of the present invention, when placed in the position as indicated above for
To address problems of “off scale” readouts for nasal probe data collected from some subjects, it has been further learned that various types of “filters” can be implemented to eliminate this problem. Two general approaches to “filtering” are electrical and light approaches. An example of the electrical approach is to place a resistor in series to both of the light producing LEDs. This proportionally decreases the amount of light emitted at both wavelengths. As to the light approach, a filter, such as a white material, a translucent or an opaque cover, can be physically placed over all or part of the light-producing LEDs, over the photodetector, or both, to reduce the light input into the photodetector, such that a readable signal can be generated in such subjects. This reduces the amount of both wavelengths of light received at the photodetector without dramatically altering the ratios of such wavelengths. Without being limited, yet another way to compensate for the more vascularized, higher light output areas of the nose, lip and cheek is simply to use smaller light-detecting photodiodes. If the response curve for the smaller photodiode remains the same compared to its larger counterpart, just it active area reduced, this would keep the light level ratios of the respective wavelengths proportional. For instance, a 0.4 mm size active area may be used instead of a 0.8 mm size active area. Other methods as known to those of ordinary skill in the art can likewise be employed to deal with the higher signal, particularly for probes that are used in pulse monitor equipment with algorithms designed for signals from finger probes. By adjusting the amount of light by any of the above means, and upon consequent adjustment of the output parameters of the oximeter, as many occur in certain units, the sensor output achieves a more acceptable range for monitoring.
In conclusion, the area of Kiesselbach's plexus across the nasal septum is the area in the nose of strongest signal for pulse oximetry as demonstrated by this simple experiment. It is noted that even using a filtered probe and placing it anteriorly of Kiesselbach's plexus a power level 2.5 times lower than what is required by the finger provides a good signal. As discussed above, one approach to locating this desired site is to use the probes having the desired bend, or angle of inflection. Another approach, which may only be needed in a small number of instances, is to use the perfusion index feature on a pulse oximeter device, and position where the index is highest.
EXAMPLE 8Several specific profiles of data are provided from patients who underwent various procedures in a teaching hospital and who wore the pulse oximeter probes of the present invention. This data is illustrative of the value of the nasal probes of the present invention. For all figures below, the data designated as “PULSE OX 1” or “P-OX 1” is from a nasal probe measuring data across the interior nasal septum, the data designated as “PULSE OX 2” or “P-OX 2” is from a cheek/lip probe measuring data across the cheek (below the lip), and the data designated as “PULSE OX 3” or “P-OX 3” is from a conventional finger probe.
Also, during testing with certain patients, given increased sensitivity from the nasal probe, it was observed that respiratory rate can be accurately measured from the nasal photoplethysographs since the nasal probe is more sensitive to volume changes. That is, changes in the “envelope” of the plethysmograph DC component indicates the breathing cycle, and this, upon quantification of these cycles, can estimate respiratory rate. One example of this is provided in
Use of the nasal or cheek probes independently or in conjunction with the finger probe can also be used to evaluate the effects on cardiac output, blood pressure and perfusion in spontaneously breathing and mechanically ventilated patients. For instance, when a normal subject breathes spontaneously, there is little or no observable effect on the plethysmograph from a finger probe. However, both the nasal and cheek probes demonstrate a drop in the “envelope” of the plethysmograph. This is explained by an increase in venous return to the right side of the heart and a decrease in blood flow from the left ventricle due to negative pressure relative to atmospheric pressure produced in the thoracic cavity during normal breathing. This fall in the “envelope” of the plethysmograph is exaggerated during spontaneous breathing against resistance, such as pulmonary diseases that narrow the airways and during hypovolemia or low cardiac output. In addition to the fall in the “envelope” of the plethysmograph, there is often a decrease in the maximum amplitude of the plethysmograph, which becomes more pronounced (a greater decrease) with hypovolemia, poor cardiac output or poor perfusion. Comparing the nasal or cheek plethysmographs with the finger plethysmograph may be an additional means to follow these effects over time.
During mechanical ventilation, changes opposite to those observed with spontaneous breathing occur in both the “envelope” of the plethysmograph and the amplitude. Positive pressure ventilation increases intrathoracic pressure, which in turn increases blood flow from the left ventricle and results in a rise above baseline in the “envelope” and an increase in the amplitude of the plethysmograph. Hypovolemia and/or poor cardiac output diminish these salutary effects.
Further, evaluation of the plethysmograph during both spontaneous and mechanical ventilation can be used to determine the optimal level of positive end expiratory pressure (PEEP) for a patient. PEEP is an important parameter for optimizing the oxygenation of a patient. Depending on the volume and cardiac status of a patient, different levels of PEEP can be tolerated. Since a higher PEEP raises the baseline intrathoracic pressure, it impedes venous return to the heart and can cause decreased cardiac output. If a subject is hypovolemic, vasodilated or has poor cardiac output, excessive PEEP may lead to hypotension, lactic acidosis and eventually shock. If inadequate PEEP is given, the patient will be hypoxemic, which can also lead to lactic acidosis and shock. Thus, there is an optimal PEEP for each subject depending on his or her pulmonary, volume and cardiac status. Excessive PEEP narrows the amplitude of the plethysmograph and causes exaggerated excursions in the “envelope” of the plethysmograph.
Evaluation of the “envelope” of the plethysmograph and the effects of ventilation on the amplitude of the plethysmograph can be used to provide a level of PEEP that allows adequate oxygenation without compromising cardiac output. If oxygenation remains poor at a given level of PEEP, volume expansion with fluids and/or drug treatment can improve cardiac output and allow the patient to tolerate the higher level of PEEP. Evaluation of the plethysmograph provides a non-invasive means of determining the effects of positive pressure ventilation and PEEP on the cardiac output of the patient.
It is noted that an appreciation of data obtainable from pulse oximetry probes is found in the scientific article, “The peripheral pulse wave: information overlooked,” W. B. Murray and P. A. Foster, J. Clin. Monitoring 12:365-377, 1996. This reference discusses in detail the bases for changes in the wave form obtainable from pulse oximeter peripheral probes, and the significance of changes in such wave forms during anesthesia. All material in this reference is hereby particularly incorporated by reference into this disclosure. Further, it is noted that this reference focused on the use of the ear, or peripheral locations, and so did not fully appreciate the types and improved quality of data obtainable from a desired vascular site of the interior nasal septum, or from the cheek/lip probe, as described herein. Also, it is appreciated that the probes of the present invention find utility not only in patients who are inactive, such as those undergoing anesthesia during surgery, but also in patients who are awake and, selectively, ambulatory.
Thus, as observable from the above figures, the use of a nasal probe of the present invention, which does not require pressure against the septum wall to operate, advantageously provides photophethysmographic data that is able to detect cardiac, pulmonary, and other abnormalities non-invasively, and better than more remote sites, such as a finger or a toe. While not being bound to a particular theory, this is believed due to the combination of: 1) not applying pressure to the vascularized site (thereby not damping more subtle signals of heartbeat patterns, etc.); 2) accessing an arterial bed supplied by a major vessel, the internal carotid artery; and 3) accessing this arterial bed in a position that is not subject to additional noise and dampening (as is found in extremity sites, such as the finger or toe).
EXAMPLE 9In many instances when pulse oximetry is being used to detect, for instance, arterial blood oxygen saturation, and/or, when plethysmography is being used to detect other cardiovascular parameters, there also is a desire or need to measure carbon dioxide during exhalation, particularly the end tidal carbon dioxide of the patient. It is recognized, for instance, that monitoring the carbon dioxide during the exhalation cycle more quickly detects airway obstruction than pulse oximetry, and, where there is an endotracheal intubation, provides the most reliable indicator of proper intubation. A graph of the concentration of carbon dioxide in exhaled gas plotted over time is referred to as a capnogram. An instrument capable of displaying only end tidal values is called a capnometer, while an instrument capable of graphically displaying end tidal carbon dioxide is called a capnograph. The shape of the capnogram reveals information about the integrity of a breathing system and the physiology of the patient's cardiorespiratory system. As such, capnography is the preferred method of end tidal carbon dioxide monitoring.
Accordingly, another aspect of the present invention is the combination of the nasal pulse oximeter of the present invention with sampling structures that direct exhaled gas for carbon dioxide measurements to provide data for either a capnometer or a capnograph.
For instance, and not to be limiting,
In operation, oxygen from a supply source (not shown), delivered via oxygen supply tube 484, is released at the apertures, 430, in front of the patient's nose and above the patient's mouth (seen better in
As for the combinations described above for the nasal probe, the lip/cheek probe of the present invention also is combined with 1) a carbon dioxide sampling device, 2) a source of oxygen or oxygen-rich gas; or 3) both of these.
For example, and not to be limiting,
Additionally, the three-pronged sampling end, 94, is taped or otherwise secured to the upper lip, as may be appropriate for a particular patient. In use, the carbon dioxide concentration is measured over time and volume, and one or more capnographs is obtainable. Such combined apparatus has use with persons undergoing sleep studies and other research, and in other applications where oxygen need not be supplied.
The lip/cheek probe also may be combined with a cannula device to provide gas, such as oxygen or an oxygen-rich gas mixture, to a patient in need thereof. For instance, and not to be limiting, the tubing assembly designated as 90 in
Thus, the lip/cheek probe of the present invention may be combined to form a single, operational unit with any other style of oxygen supply/carbon dioxide sampler device, that is, an integral multi-functional device. This provides the advantage of obtaining reliable data, such as for arterial oxygen saturation, while only occupying essentially the same space and path of tubing/wiring, as does the oxygen supply/carbon dioxide sampler device alone. The data from the probe can be integrated with the data from the capnography unit to obtain a better picture of the patient's respiratory and circulatory function and condition. Additionally, as for other types of probes described above, an additional feature is added, namely a control means to adjust the flow rate of the gas that is provided, where such control is directed by the blood oxygen saturation data obtained from the probe.
Although depicted above as separate units combined after production, the combinations described above alternatively are integral units designed and sized such that the lip/cheek probe therein functions as described in this disclosure. Also, protective sleeves, as described for the lip/cheek probe alone, are envisioned to be shaped and manufactured in accordance with the teachings herein, and used for these multi-function devices.
Preferably, the probes and sleeves are easily fabricated from low cost materials and are adaptable for use in an operating room, intensive care unit, emergency department, post-surgery recovery areas and other areas to treat patients in need of hemodynamic monitoring. The monitoring system is particularly applicable for use with patients in whom hypotension or poor perfusion are problematic. In addition, the monitoring system is particularly well suited for use with multi-trauma and thermally injured patients who either have severe peripheral vasoconstriction or have severely damaged or destroyed peripheral vascular beds. Through combining at least two pulse oximeters capable of measuring desired parameters at at least two locations into a single monitor system, the present invention provides a more accurate assessment of perfusion and resistance in patients, than any of the presently available single probe pulse oximeters.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims.
Claims
1. A method of determining hypovolemia in a subject, said method comprising obtaining a first photoplethysmographic (PPG) signal from a central source site of said subject; wherein a change between said second PPG signal relative to said first PPG signal indicates a low blood volume condition in the subject.
- obtaining a second PPG signal from a non-central site of said subject; and
- monitoring for a difference between said first PPG signal relative to said second PPG signal;
2. The method of claim 1, wherein said central source site is a nasal alar, nasal septum, cheek or lip of said subject.
3. The method of claim 1, wherein said central source site is a nasal alar of said subject.
4. The method of claim 1, wherein said central source site is a nasal septum of said subject.
5. The method of claim 1, wherein said non-central site is an extremity of said subject.
6. The method of claim 1, wherein said non-central site is a finger or toe of said subject.
7. The method of claim 1, wherein a decrease of said second PPG signal relative to said first PPG signal indicates a low blood flow/low blood volume condition in the subject.
8. A method of determining hypovolemia in a subject, said method comprising wherein a decrease of said second PPG signal relative to said first PPG signal indicates a low blood flow/low blood volume condition in the subject.
- monitoring for a difference between a first PPG signal obtained from a central source site of said subject and a second PPG signal obtained from a non-central site of said subject;
9. The method of claim 8, wherein said central source site is a nasal alar, nasal septum, cheek or lip of said subject.
10. The method of claim 8, wherein said central source site is a nasal alar of said subject.
12. The method of claim 8, wherein said central source site is a nasal septum of said subject.
13. The method of claim 8, wherein said non-central source site is an extremity of said subject.
14. The method of claim 8, wherein said non-central source site is a finger or toe of said subject.
15. An apparatus for analyzing photoplethysmography signals from at least two sites on a living vertebrate, to determine the presence or absence of, or to monitor changes in, impaired peripheral perfusion or volume status comprising: means for determining a change in blood volume at at least one non-central site based on the extent to which said at least one non-central site has a lower photoplethysmography signal than said central source site or the photoplethysmograpy signal from one non-central site decreases relative to the signal at the central site over time.
- a. means for receiving pulse oximeter probe signals from at least two sites on a living vertebrate, wherein at least one said site is a central source site and at least one said site is a non-central site; and
16. The apparatus of claim 15, further comprising a means for presenting results to a user of said apparatus.
17. A monitor system for analyzing photoplethysmography signals from at least two sites on a living vertebrate, to monitor changes in blood flow, comprising:
- a. output circuitry to deliver timed signals to energize light generating components of at least two pulse oximeter probes;
- b. input circuitry to receive signals from said at least two pulse oximeter probes positioned said at least two sites on a living vertebrate, wherein at least one said site is a central source site and at least one said site is a non-central site;
- c. a computer loaded with software to 1. provide timed signals to energize said light generating components; 2. average sufficient signals from each pulse oximeter probe site to obtain a statistically reliable average; 3. calculate a time-set estimate of a photoplethysmography signal based on said statistically reliable average; 4. repeat steps 2 and 3 to obtain sequential time-set estimates of a photoplethysmography signal from each site; 5. compare a sequential time-set estimate of the photoplethysmography signal from the central source site with a sequential time-set estimate, taken at a similar time, of the photoplethysmography signal from the at least one non-central site; and 6. determine a change in blood volume to said at least one non-central site based on the extent to which said non-central site has a lower photoplethsymography signal than said central source site.
18. A monitor system of claim 17, further comprising a read-out device to provide results to a user of said system.
19. The monitor system of claim 17, further comprising software in said computer for estimating blood pressure through analysis of pulse time delay between said at least two sites.
20. A method of observing respiration in a patient, said method comprising monitoring changes in the envelope of a PPG signal from a central source site of said patient.
Type: Application
Filed: Jul 27, 2011
Publication Date: Mar 29, 2012
Inventor: RICHARD J. MELKER (GAINESVILLE, FL)
Application Number: 13/191,594
International Classification: A61B 5/1455 (20060101);
