Abstract: A method of estimating blood flow in the brain, comprising: a) causing currents to flow inside the head by producing electric fields inside the head; b) measuring at least changes in the electric fields and the currents; and c) estimating changes in the blood volume of the head, using the measurements of the electric fields and the currents.

Abstract: A method of finding an indication of a degree of cerebro-vascular bilateral asymmetry in a subject, comprising: a) measuring a first impedance waveform and a second impedance waveform of the subject's head as functions of time, in each case by finding a potential difference between two voltage electrodes associated with passing a given injected current through the head between at least two current electrodes, wherein in each case the voltage electrodes are located asymmetrically on the head, or the current is injected asymmetrically into the head, or both, and wherein the locations of the voltage electrodes and the distribution of current injection in measuring the second impedance waveform are minor images of what they are in measuring the first impedance waveform; and b) finding the indication of the degree of bilateral asymmetry from a difference between characteristics of the first and second impedance waveforms.

Abstract: Disclosed herein are methods and systems for creating a complex model of the human anatomy. The anatomy may be modeled using multiple geometries. Generally, a plurality of line-of-sight models may be combined into a composite model. Multiple clouds of points may be used to create surface models which may then be merged into a common volume. The resulting composite model may include portions that are not within a line of sight of a mean center point of the composite model. The surface models may be modeled using polygons, including for example, triangles. Disclosed herein are also ways in which electrophysiology data and/or other information may be mapped from a measurement point to a point on the composite model.

Abstract: A method and apparatus for detection of changes in impedance a patient that includes generating measured impedances, generating an adaptive baseline trend of the measured impedances corresponding to a first time period, generating a short term trend of the measured impedances corresponding to a second time period less than the first time period, and generating a metric of impedance change between the adaptive baseline trend and one of a most recent measured impedance and the short term trend of the measured impedances.

Abstract: Implantable medical device with an impedance determination unit with constant current/voltage source having current feed terminals connected to electrodes for intracorporal placement which generates measuring current pulses having constant current/voltage, for causing a current through a body via intracorporally placed electrodes, a measuring unit for measuring voltage/current strength of voltage/current fed through body, an impedance value determination unit connected to the current/voltage source and adapted to determine an impedance value for each measuring current pulse, and an impedance measuring control and evaluation unit connected to the impedance determination unit which controls the unit and evaluates a sequence of consecutive impedance values, the impedance determination unit further adapted to determine at least intrathoracic and intracardiac impedance values for same period of time, the intrathoracic values sampled with a lower sampling rate than the intracardiac values.

Abstract: An approach for predicting disordered breathing involves detecting one or more conditions associated with disordered breathing. The detected conditions are compared to disordered breathing prediction criteria. A prediction of disordered breathing is performed based on the comparison of the detected conditions to the prediction criteria. At least one of comparing the detected conditions to the prediction criteria and predicting disordered breathing is performed at least in part implantably.

Abstract: Monitoring the hydration and/or nutrition status of a patient by bioimpedance. A bioimpedance method and device that makes use of a refined model by which the conductivity contributions from intracellular tissues can be taken better into account to enable an improved assessment of the body composition of a patient with increased accuracy. The intracellular volume (ICV) of a patient is determined by determining an intracellular electrical resistance Rmix of the patient and deriving the intracellular volume ICV using Rmix by taking into account that a cell of a kind of tissue contributes differently to the electrical resistance Rmix of the intracellular volume ICV compared with a cell of a second kind of tissue. The application also relates to a device for carrying out the method according to the invention and to a computer program product to be used on such a device.

Abstract: A method of determining an impedance of at least one lung of a patient having an implanted pacemaker that comprises first and second leads and a case, the method comprising: a) using the leads and the case to acquire at least a first and a second impedance measurement responsive to impedance of the patient's chest that are at least partially independent; and b) using the impedance measurements to determine the impedance of at least one of the lungs substantially independently of impedance of the other lung.

Abstract: This device uses electrical impedance and signal processing to measure the small change in volume (“Pulse Volume”) of a limb-segment that occurs with each heartbeat. “Pulsatile Flow” is defined as the pulse volume multiplied by the heart rate and is an index of tissue perfusion. This information can be combined with measured blood oxygen saturation to determine how much oxygen is reaching the tissues. The combination of knowing oxygen saturation and tissue perfusion is far more useful than knowing just one or the other of these parameters.

Abstract: Embodiments of the present invention are directed to a physiological monitoring device which is configured to record signals that reflect blood flow and/or blood pressure, and which may also record ECG signals. In one embodiment, a portable monitoring device comprises a plurality of impedance electrodes configured to be coupled to a patient's body and to generate an AC current with an electrical field to detect local electrical impedance of a portion of the patient's body encompassed by the electrical field, the local electrical impedance being a surrogate measure of local blood flow of the portion of the patient's body. At least a portion of the portable monitoring device is configured to be insertable subcutaneously into the patient's body.

Abstract: The system and method may measure and monitor physiological changes in a body. In some embodiments, the system and method may measure the impedance at a site in the body. In some embodiments, the system and method identify, quantify, and localize leaks from a site following surgery. In an embodiment, the system includes a flexible conduit with one or more sensors. A flexible conduit shape may be selected to facilitate monitoring of physiological changes in a body and/or detection of leaks at a desired site. In an embodiment, contrast solution may be ingested by, injected in, and/or delivered to a patient. If a leak is present at a site, salt contrast solution may leak from a site and be detected by sensors in a flexible conduit.

Abstract: Implantable systems, and methods for use therewith, are provided for monitoring for an impending myocardial infarction. A signal indicative of changes in arterial blood volume is obtained. Such a signal can be a photoplethysmography signal or an impedance plethysmography signal. For each of a plurality of periods of time, a metric indicative of the areas under the curve of the signal or number of inflections in the signal is determined. An impending myocardial infarction is monitored for based on changes in the metric indicative of the area under the curve of the signal or number of inflections in the signal, and an alert and/or therapy is triggered in response to an impending myocardial infarction being predicted.

Abstract: An ICG/ECG electrode includes a first electrode and a second electrode, wherein at least one of the first or second electrode senses both an ICG signal and an ECG voltage signal. A physiologic parameter monitoring apparatus includes a set of electrodes, including an electrode for sensing both an ICG voltage signal and an ECG voltage signal corresponding to a patient. The apparatus further includes an ICG monitor for processing the ICG voltage signal sensed by the electrode and an ECG monitor for processing the ECG voltage signal sensed by the same electrode.

Abstract: Methods and systems for monitoring an organ of interest within a patient use one or more sensors to obtain one or more signals indicative of one or more of blood being provided to the organ of interest, blood being received from the organ of interest, and blood present in the organ of interest. Changes in an amount of blood being provided to the organ of interest, an amount of blood being received from the organ of interest, and/or an amount of blood present in the organ of interest are monitored based on changes in the obtained signal(s). Such methods and systems can be used to detect dysfunction of the organ of interest or tumor growth in the organ of interest, but are not limited thereto.

Abstract: Provided herein are methods and apparatus for stroke volume determination by bioimpedance from a patient's upper arm, or brachium, or a patient's thorax, utilizing pulsations of the arteries contained therein. The apparatus includes two or more spaced apart alternating current flow electrodes positioned on the patient's arm or thorax and two or more spaced apart voltage sensing electrodes positioned on the patient's arm or thorax and in-between alternating current flow electrodes. The system and method utilizes the mean value of the second time-derivative of the cardiogenically induced impedance variation of the patient using the measured voltage from the voltage sensors in calculating the stroke volume of the patient.

Abstract: Systems and methods are provided for graphically configuring leads for a medical device. According to one aspect, the system generally comprises a medical device and a processing device, such as a programmer or computer, adapted to be in communication with the medical device. The medical device has at least one lead with at least one electrode in a configuration that can be changed using the processing device. The processing device provides a graphical display of the configuration, including a representative image of a proposed electrical signal to be applied by the medical device between the at least one electrode of the medical device and at least one other electrode before the medical device applies the electrical signal between the at least one electrode and the at least one other electrode. In one embodiment, the graphical display graphically represents the lead(s), the electrode(s), a pulse polarity, and a vector.

Abstract: A system, method and device for monitoring the condition of an internal organ, such as a brain, by providing an internal electrode. The internal electrode is operatively connected to at least one surface, external, electrode, and a system handler. A signal is generated between the electrodes such that the electrical properties, including conductivity and impedance among others, can be measured at and across the electrodes. The electrode arrangement allows for continuous monitoring of an internal organ and, where desired, mapping of the electrical properties thereof. The system obtains pressure readings, nodal conductivity and/or electrode impedance to monitor, map and report the condition of the internal organ. A correlation procedure is provided for generating a graphical representation of the condition of an internal organ from the gathered data.

Abstract: Provided herein are methods and apparatus for stroke volume determination by bioimpedance from a patient's upper arm, or brachium, or a patient's thorax, utilizing pulsations of the arteries contained therein. The apparatus includes two or more spaced apart alternating current flow electrodes positioned on the patient's arm or thorax and two or more spaced apart voltage sensing electrodes positioned on the patient's arm or thorax and in-between alternating current flow electrodes. The system and method utilizes voltage sensed by the voltage sensing electrodes to calculate a cardiogenically induced impedance variation value of the patient, and to determine a stroke volume of the patient by multiplying the cardiogenically induced impedance variation value by a volume conductor VC and by a left ventricular ejection time TLVE.

Abstract: A measurement system for examining a section of tissue on a patient in which electric current and/or voltages are applied to a patient in at least one location and are measured on the section of tissue to be examined by at least one electrode of a contact surface of the measurement system. As a result, conclusions can be drawn about the interior of the section of tissue to be examined. The electrode is at least partially surrounded by a conductor element for contacting with a potential which deviates from that of the conductor element.

Abstract: A phase line tilt calculating unit (actual measurement) receives phase characteristics Pa(f) and Pb(f) outputted from frequency conversion units, and calculates phase difference characteristics of actual measurement based on a phase difference on each frequency component between the phase characteristics. A phase line tilt calculating unit (model) calculates phase difference characteristics between a transfer function Ga(f) and a transfer function Gb(f) calculated by a transfer function calculating unit, and outputs the calculated phase difference characteristics to a search unit. The search unit fits a variable k and determines a variable kopt (optimum solution) in which a tilt g(k) and a tilt gexp substantially match each other. The variable kopt is an index indicating a degree of arterial sclerosis of a subject.

Abstract: Methods, systems and devices are provided for monitoring respiratory disorders based on monitored factors of a photoplethysmography (PPG) signal that is representative of peripheral blood volume. The monitored factors can be respiratory effort as well as respiratory rate and/or blood oxygen saturation level. The systems and devices may or may not be implanted in a patient.

Abstract: A post-operative, arterial patency monitoring system for monitoring patency of an artery of a limb including: a first probe positioned adjacent a first tissue area of a limb for producing first output signals dependent upon a first arterial blood supply to the first tissue area; a second probe positioned adjacent a second different tissue area of the limb for producing second, different output signals dependent upon a second arterial blood supply to the second tissue area; and means for processing the first output signals to produce a first arterial blood supply metric for the first arterial blood supply and a second, different, arterial blood supply metric for the first arterial blood supply; means for processing the second output signals to produce the first arterial blood supply metric for the second arterial blood supply and the second arterial blood supply metric for the second arterial blood supply; means for using a predetermined function that takes as its arguments at least the first and second arteri

Abstract: Impedance analysis can be used to measure calf muscle pump (CMP) function in a patient. This may be done by applying electrical signals via a first set of electrodes, and measuring the impedance via a second set of electrodes. The change in impedance as the patient undergoes calf extension or exercise may be measured, and the change in impedance may then be used to assess CMP function. The change in impedance may be used to determine an indicator indicative of the volume of blood ejected by the CMP.

Abstract: An volume of a patient can be mapped with a system operable to identify a plurality of locations and save a plurality of locations of a mapping instrument. The mapping instrument can include one or more electrodes that can sense a voltage that can be correlated to a three dimensional location of the electrode at the time of the sensing or measurement. Therefore, a map of a volume can be determined based upon the sensing of the plurality of points without the use of other imaging devices. An implantable medical device can then be navigated relative to the mapping data.

Abstract: A system for measuring physiological aspects has a non-invasive monitor configured to generate monitor signals relating to fluid characteristics in the body. A computational device is operatively connected to the monitor and is configured to process the monitor signals to generate characterising data relating to at least one of regional fluid volumes, intra/extracellular fluid volume ratios and blood flow. A data output device is connected to the computational device and is configured to output the characterising data. A method and a computer program product for measuring physiological characteristics are also provided.

Abstract: Provided herein are methods and apparatus for stroke volume determination by bioimpedance from a patient's upper arm, or brachium, or a patient's thorax, utilizing pulsations of the arteries contained therein. The apparatus includes two or more spaced apart alternating current flow electrodes positioned on the patient's arm or thorax and two or more spaced apart voltage sensing electrodes positioned on the patient's arm or thorax and in-between alternating current flow electrodes. The system and method utilizes voltage sensed by the voltage sensing electrodes to calculate a cardiogenically induced impedance variation value of the patient, and to determine a stroke volume of the patient by multiplying the cardiogenicaly induced impedance variation value by a volume conductor VC and by a left ventricular ejection time TLVE.

Abstract: A system and method for determining smooth muscle motor activity in body organs. The system comprises electrodes for recording an analog signal in the subject's body, an analog to digital converter that converts the analog signal to a digital signal and a processor. Processing the digital signal includes obtaining power spectra of the digital signal, and identifying one or more frequency peaks in the power spectra. A peak in the power spectrum is identified within a frequency range in which an organ generates slow waves. The energy of the identified frequency peak is measured and an energy above a characteristic threshold is indicative of smooth muscle motor muscle motor activity in the respective organ.

Abstract: A method of measuring blood flow including several steps. In an initial step a first ultrasound beam is oriented in a direction substantially perpendicular to the direction of the blood flow to be measured. Next, the Doppler spectrum obtained from the backscattered echoes of said first ultrasound beam is measured. Subsequently, the ultrasound beam is reoriented so that the Doppler spectrum of the backscattered echoes of the ultrasound beam is substantially symmetrical around the zero frequency. The Doppler frequency of the backscattered echoes of a second ultrasound beam oriented at a fixed angle to the first ultrasound beam is then measured. Finally, the rate of blood flow is calculated based on the angle between the ultrasound beams and the measured Doppler frequency of the backscattered echoes of the second ultrasound beam.

Abstract: A method of estimating cerebral blood flow by analyzing IPG and PPG signals of the head, the method comprising: a) finding a maximum slope or most negative slope or the IPG signal, within at least a portion of the cardiac cycle; b) finding a maximum slope or most negative slope of the PPG signal, within at least a portion of the cardiac cycle; c) finding a ratio of the maximum or most negative slope of the IPG signal to the maximum or most negative slope of the PPG signal; and d) calculating a cerebral blood flow indicator from the ratio.

Abstract: The invention relates to a method and device for determining the flow in a blood vessel, comprising the determining the relation between the shear rate and the impedance of flowing blood, measuring the impedance in the blood in a cross-section of the blood vessel, determining the shear rate from this relation and the measured impedance, determining the size of the cross-section of the blood vessel, selecting a theoretical relative flow distribution over the blood vessel cross-section, determining the average flow speed on the basis of the average shear rate and the relative flow distribution, and determining the flow volume from the determined average flow speed and the cross-section.

Abstract: A system for measuring/monitoring the vital signs of a patient especially blood pressure, comprising a plurality of electrodes arranged at least in the waistband of an undergarment, and means for deriving measurements from the electrodes using pulse-transit times.

Abstract: In a system and method for peripheral impedance plethysmography, an electrode for application to the patient's limb includes two outer current electrodes and two inner voltage electrodes. A distance between the two inner electrodes is automatically input into an analyzing device, either as a pre-stored value or as determined automatically from the electrode. Peripheral blood flow is calculated in accordance with that distance.

Abstract: Systems and methods for measuring intracranial pressure and brain compliance are provided. In one aspect, for example, a method for noninvasive measurement of brain compliance in a subject may include calculating a phase shift between an intracranial pulsatile perfusion flow measured from the subject and an extracranial pulsatile perfusion flow measured from the subject, and determining brain compliance of the subject from the phase shift between the intracranial pulsatile perfusion flow and an extracranial pulsatile perfusion flow. Though various methods of calculating phase shift are contemplated, in one aspect such a calculation may include calculating an intracranial frequency waveform corresponding to the intracranial pulsatile perfusion flow, calculating an extracranial frequency waveform corresponding to the extracranial pulsatile perfusion flow, and calculating a phase difference between the intracranial frequency waveform and the extracranial frequency waveform.

Abstract: Disclosed is an bioelectrical impedance measuring apparatus which is simplified in structure and which is easy to use. A measuring apparatus comprising a personal data input unit which is used in inputting personal data and a plurality of electrodes which are used in measuring bioelectrical impedance is improved according to the present invention in that it comprises: a memory in which the personal data are stored via said personal data input unit; and a control device which carries out a required control by using at least one selected electrode to store the personal data in said memory or to retrieve the personal data from said memory.

Abstract: A method of estimating cerebral blood flow includes obtaining a measure of time-varying blood volume in the head, using an impedance plethysmography (102 and 104), obtaining a measure of time-varying blood volume in the scalp, and using the time-varying blood volume in the head and scalp to estimate cerebral blood flow.

Abstract: A method and system for determining contact assessment includes the steps of positioning a catheter at a tissue treatment site, where the catheter has a proximal end portion and a distal end portion, the proximal end portion defining at least one fluid inlet port and at least one fluid outlet port, an expandable membrane defining a cooling chamber a coolant injection lumen in fluid communication with the at least one fluid inlet port and the cooling chamber, a coolant return lumen in fluid communication with the at least one fluid outlet port and the cooling chamber, the coolant injection tube, the cooling chamber, and the primary coolant return lumen defining a fluid pathway and a temperature sensor located near the coolant return lumen; measuring an internal temperature of the chamber, and modifying the position of the catheter in response to the measured temperature. The method and system can also use a measured impedance to determine contact assessment.

Abstract: In an venous distensibility evaluation index measuring apparatus, a pressure adjusting section generates a pressure to supply it to a venous occluding section; in response thereto the venous occluding section starts to press a vein in the upper arm; upon this operation, an electrode section causes a current to flow, while detecting a voltage at that time; an impedance conversion section converts this detected voltage in combination with the supplied current into an impedance; an impedance transition gradient calculating unit determines a gradient of a rate of change in impedance to the elapsed time; a venous distensibility evaluation index determining unit determines a venous age corresponding to said gradient of the rate of change in impedance to the elapsed time as well as a venous sclerosis level corresponding to the venous age based on the relation data stored previously in a storage section; and finally a display section indicates the venous age and the venous sclerosis level.

Abstract: A method and system for measuring the electrical impedance of sections of a living body. The measurement is carried out utilizing a plurality of electrodes each of which is disposed on a section of the living body, where the electrodes are capable of applying an electrical current through at least one probed section, and measure the electrical voltage over the probed section. The voltages over the probed sections are measured and the impedances (Z(t)) and their changes (?Z(t)), and the resistances R(t) and their changes (?R(t)), are calculated, by considering the electrical current distortion components resulting from the electrical currents flowing in the other sections which are not probed, utilizing an electrical model based on the distribution of the electrical currents through the body sections.

Abstract: A method and apparatus for determining an initial flow rate in a conduit is disclosed. A known change is made to the flow to be measured, resulting changes (or values corresponding to these changes), or relative changes in the flow to be measured are monitored and the initial flow in the conduit is calculated from the value of the known change and monitored changes. Devices to practice the method include catheters having one or two sensors and one or two sites for introducing the volume change.

Abstract: The present invention provides a noninvasive and portable medical monitoring system for monitoring the change in time of the electrical impedance of a portion of a living body, such as the lungs or the brain with an inbuilt data acquisition system and a PC motherboard. The present invention also provides a computer implementable method for monitoring and measurement of cardiac output and blood flow index using impedance plythesmographic techniques.

Abstract: Provided herein are methods and apparatus for stroke volume determination by bioimpedance from a patient's upper arm, or brachium, utilizing pulsations of the brachial artery contained therein. The apparatus includes two or more spaced apart alternating current flow electrodes positioned on the patient's arm proximate the brachial artery and two or more spaced apart voltage sensing electrodes positioned on the patient's arm proximate the brachial artery. The voltage sensing electrodes are positioned between the alternating current flow electrodes on the arm. An alternating current source is electrically connected to the alternating current flow electrodes and a voltmeter electrically is connected to the voltage sensing electrodes. A data input device is provided along with a processing unit in communication with the data input device, the alternating current source, alternating current flow electrodes, the voltmeter, and voltage sensing electrodes.

Abstract: An interface unit for receiving a body part of a subject at which a noninvasive hematocrit measurement is to be obtained includes a narrow monitoring element with a receptacle for receiving at least a portion of the body part and contacts that are configured for establishing electrical communication with contacts of electrodes that are to be positioned over the receptacle before the body part is placed therein. In addition, the monitoring element may include a pressure port that communicates pressure into the receptacle. The interface unit also includes a cover which is configured to partially enclose the body part, to ensure that electrical communication is established between the contacts and the electrodes, and to facilitate the application of pressure to the body part. The electrodes may be in the form of electrically isolated electrode pairs, which may be formed as a strip with minimal material wastage.

Abstract: Disclosed is an animal health care system, comprising: a weight input unit; an impedance measurement unit; an inter-leg distance input unit; and a health assessment data calculation unit. According to the present invention said weight input unit enters weight value of an animal, and said impedance measurement unit includes impedance measurement electrodes each for contacting with a root of each leg of the animal and measures impedance between front and rear legs of the animal. Furthermore, said inter-leg distance input unit enters the distance between the roots of front and rear legs of the animal, and said health assessment data calculation unit calculates health assessment data, based on the weight value of the animal, the impedance between front and rear legs of the animal, and the distance between the roots of front and rear legs of the animal.

Abstract: The invention provides a device that measures a patient's blood pressure without using an inflatable cuff. The device includes an optical module featuring an optical source and a first optical sensor that generates a first set of information; a flexible, thin-film pressure sensor that generates a second set of information; and a processing module, configured to receive and process the first and second sets of information to calculate a time-dependent blood pressure value.

Abstract: A method of analysis of medical signals which uses wavelet transform analysis to decompose cardiac signals. Apparatus for carrying out the method, and cardiac apparatus adapted to employ the method are also described.

Abstract: Methods, apparatuses, media and signals for evaluating a vessel. One method includes receiving at least one measurement of a physical dimension of the vessel, and producing an indication of abnormality in the vessel, in response to the at least one received measurement and at least one population-based parameter for the vessel. Producing may include producing an indication of stenosis of the vessel, in response to the physical dimension measurement and a population-based reference dimension for the vessel. This may include producing a population-based percent stenosis value in response to a ratio of the physical dimension measurement to the population-based reference dimension. Producing may further include identifying a shape characteristic of the vessel, which may include producing a tapering comparison value in response to the tapering of the vessel and a population-based average tapering value. The vessel may include a coronary artery segment, for example.

Abstract: Energy efficient methods and systems for using multi-dimensional activity sensors with implantable cardiac devices are provided. In certain embodiments the output of a passive activity sensor (used for rate responsive pacing) is used to trigger temporary use of a relatively high power multi-dimensional activity sensor. In other embodiments, the output of a relatively low power oxygen saturation sensor is used to trigger temporary use of a relatively high power multi-dimensional activity sensor. This description is not intended to be a complete description of, or limit the scope of, the invention.

Abstract: The sensor has four electrodes arranged on a common base, three of which are made as closed circuits, placed one into another, whereas the fourth electrode is placed inside the smallest circuit. The external and the central electrodes form a pair of current-feeding electrodes, whereas the electrodes disposed between them form a pair of measuring electrodes. The second design option of the sensor has three electrodes, two of which are made as closed circuits placed one into another, whereas the third electrode is placed inside the electrode that is smaller. The external and the central electrodes form a pair of current-feeding electrodes, and the electrode arranged between them together with the external or the central electrode form a pair of measuring electrodes. The design of sensors makes it possible to use them in combination with biological signal sensors of non-rheographic modality, for example, pulse wave, temperature. The sensor may be incorporated in wristwatch or bracelet.

Abstract: A method and system are provided for determining a condition of a selected region of epithelial tissue. At least two current-passing electrodes are located in contact with a first surface of the selected region of the tissue. A plurality of measuring electrodes are located in contact with the first surface of the selected region of tissue as well. Electropotential and impedance are measured at one or more locations. An agent may be introduced into the region of tissue to enhance electrophysiological characteristics. The condition of the tissue is determined based on the electropotential and impedance profile at different depths of the epithelium, tissue, or organ, together with an estimate of the functional changes in the epithelium due to altered ion transport and electrophysiological properties of the tissue.

Abstract: Body function measuring apparatus which provides: (1) an indication of the body function being measured, and (2) a loose probe condition by determining that the difference between the rate of change of a first body function signal, developed by a first sensor in the probe, and the rate of change of a second body function signal, developed by a second sensor in the probe, exceeds a predetermined threshold.