Abstract: The invention provides a controller and method for deriving a measure of arterial compliance based on an acquired arterial volume variation signal and an acquired pulse arrival time signal. An oscillometric blood pressure measurement device is used to acquire the arterial volume variation signal. Arterial volume and variation in pulse arrival time are both measured as an applied pressure to an artery are varied by the oscillometric blood pressure measurement device. The arterial volume signal is transformed into a corresponding signal representative of variation in peak-to-peak amplitude of the arterial volume.

Abstract: In some embodiments, a wound monitoring and/or therapy apparatus includes a wound dressing configured to be positioned in contact with a wound, the wound dressing comprising one or more sensors configured to obtain measurement data of at least one of the wound or periwound. The apparatus can also include a controller configured to maintain a device clock indicative of a non-real time clock, receive measurement data obtained by the one or more sensors, and transmit measurement data to a remote computing device according to a security protocol, the security protocol comprising including the device clock associated with the measurement data in the transmission.

Abstract: A physiological signal monitoring system comprising a pendant and a patch. The pendant includes a data store, a processor, and a cellular modem. The patch includes a cradle and electrodes mechanically and electrically connected with a flexible printed circuit board (PCB). When removably coupled with the cradle of the patch, the pendant receives from the electrodes electrical signals from a patient's heart and either stores the signals to the data store or transmits the signals. A single channel patch configuration includes two electrodes positioned at least 8.0 centimeters (CM) apart. A two channel patch configuration employs three electrodes similarly spaced. Removable auxiliary components may connect to the pendant's device interfaces, each configured to receive physiological input such as electromyogram (EMG), electroencephalogram (EEG), body temperature, heart rate, pedometer, blood pressure, pulse oximetry, respiratory rate, posture/body orientation, and sleep monitoring.

Abstract: In some embodiments, a wound monitoring and/or therapy apparatus includes a wound dressing configured to be positioned in contact with a wound, the wound dressing comprising one or more sensors configured to obtain measurement data of at least one of the wound or periwound. The apparatus can also include a controller configured to maintain a device clock indicative of a non-real time clock, receive measurement data obtained by the one or more sensors, and transmit measurement data to a remote computing device according to a security protocol, the security protocol comprising including the device clock associated with the measurement data in the transmission.

Abstract: A system for monitoring a patient includes an inflatable cuff configured to at least partially occlude an artery of the patient, and a sensor configured to determine a first parameter associated with the at least partially occluded artery and to generate an output signal indicative of the first parameter. The system also includes a processor configured to receive the output signal and information indicative of an occlusion efficiency of the cuff. The processor is configured to determine a hemodynamic parameter of the patient based on the output signal and the information.

Abstract: Methods are disclosed for measuring the size of body parts treated by a compression therapy device. Either the volume or circumference of the body part may be measure. The methods my include evacuating an inflatable compression sleeve to a known pressure, inserting the body part into the compression sleeve, inflating the sleeve to a pre-set condition, and then measuring one or more inflation related parameters. The pre-set conditions may include a predetermined pressure, volume, or size of the inflatable cells comprising the sleeve. The inflation related parameters may include the time to fill the cell to a pre-set pressure, the pressure attained after a pre-set time of inflation, or the measure volume of a cell after a pre-set amount of air is introduced into it. The methods may also include deflating the cells from the known inflation state to a second inflation state and measuring similar parameters.

Abstract: Embodiments described herein relate to apparatus and techniques for aligning and coupling a sensor device to a wearable patch. A shoe apparatus is coupled to the wearable patch. The sensor device is coupled to the shoe apparatus via one or more connectors of the shoe apparatus. As the sensor device is inserted into the shoe apparatus, features of the shoe apparatus enable alignment of the sensor device with the shoe apparatus and the one or more connectors.

Abstract: Devices, systems, and methods for monitoring patient hemodynamic status, systemic vascular resistance, reversal of cardiac and respiratory rates, and patient respiratory volume or effort are disclosed. A peripheral venous pressure is measured and used to detect levels, changes, or problems relating to patient blood volume. The peripheral venous pressure measurement is transformed from the time domain to the frequency domain for analysis. A heart rate frequency is identified, and harmonics of the heart rate frequency are detected and evaluated to determine, among other things, hypovolemia or hypervolemia, systemic vascular resistance, and of cardiac and respiratory rates, and patient respiratory volume or effort.

Abstract: A physiological monitoring system and method for the determination of at least one physiological parameter using a first low energy physiological sensor to produce a first physiological sensor signal and a high energy physiological sensor to produce a second physiological sensor signal. A motion sensor produces a motion reference signal that a mode selector switch uses to select either the first low energy physiological sensor or the second high energy physiological sensor. Alternatively, a motion related embedded component in the second physiological sensor signal is used by the mode selector switch to select in the first low energy sensor or the second high energy sensor.

Abstract: Systems and methods for tracking or viewing a user's physiological parameters before, during, and/or after physical activity. In some versions, a sensor device can be worn on a user's body and is configured to detect multiple physiological parameters and to wirelessly communicate with a mobile computing device. Optionally, the detected physiological parameters can be used to determine a selected set of work-out parameters, which can be concurrently displayed on the mobile computing device during the user's exercise/activity or after the exercise period. In some implementations, each of a plurality of users can wear a respective body-worn sensor device, and all of the sensors devices can wireless communicate with a designated mobile computing device for purposes of collectively (and concurrently) monitoring sets of physiological parameters for all of the users during the same workout, practice, or other activity.

Abstract: A patient worn sensor assembly for detecting, recording, and communicating patient vital signs includes several structural features that can provide increased signal quality, reduction in signal noise, increased patient comfort, increased reliability, and increased adhesion to a patient's skin. The patient worn sensor can track vital sign information such as blood pressure, body temperature, respiratory rate, blood oxygenation, heart rhythm (via ECG), heart rate, blood glucose level, and hydration (bio-impedance) levels. The sensor can also track and record additional information about patients, including patient movement, activity, and sleep patterns.

Abstract: Methods are disclosed for measuring the size of body parts treated by a compression therapy device. Either the volume or circumference of the body part may be measured. The methods may include evacuating an inflatable compression sleeve to a known pressure, inserting the body part into the compression sleeve, inflating the sleeve to a pre-set condition, and then measuring one or more inflation related parameters. The pre-set conditions may include a pre-determined pressure, volume, or size of the inflatable cells comprising the sleeve. The inflation related parameters may include the time to fill the cell to a pre-set pressure, the pressure attained after a pre-set time of inflation, or the measured volume of a cell after a pre-set amount of air is introduced into it. The methods may also include deflating the cells from the known inflation state to a second inflation state and measuring similar parameters.

Abstract: The present invention provides a simple auto electronic tourniquet which does not inflict pain on a person receiving the tourniquet in a preparatory stage before venipuncture and which shortens the time required in preparation for venipuncture. The simple auto electronic tourniquet includes a manchette (wrapping member) wrapped around an upper arm and a controller provided on the manchette for controlling pressures to the upper arm by the wrapping member. The controller includes a diastolic blood pressure detecting circuit and a pressure setting and maintenance circuit. The pressure setting and maintenance circuit setting pressures of the manchette at a time when changes of a biological signal are detected by the diastolic blood pressure detecting circuit as target pressures.

Abstract: A system for monitoring a patient includes an inflatable cuff configured to at least partially occlude an artery of the patient, and a sensor configured to determine a first parameter associated with the at least partially occluded artery and to generate an output signal indicative of the first parameter. The system also includes a processor configured to receive the output signal and information indicative of an occlusion efficiency of the cuff. The processor is configured to determine a hemodynamic parameter of the patient based on the output signal and the information.

Abstract: An ECG data acquisition device is provided, including a main housing, at least two electrodes, an ECG signal acquisition circuitry having a processor and a memory for storing acquired data, a connector for communication, and a movable housing, covering the connector and having at least an electrode mounted thereon, wherein as executing the ECG signal acquisition, the movable housing is in a first state, and as communicating with an external equipment, the movable housing is moved to a second state for exposing the connector and electrically disconnecting the electrode thereon from the ECG signal acquisition circuitry.

Abstract: The present disclosure relates to methods, apparatus and sensor for measurement of cardiovascular quantities. In particular, a method for determining one or more cardiovascular quantities is disclosed, the method comprising determining the distension of a vessel enclosed by tissue having a skin surface, wherein determining the distension is based on a first sensor signal indicating capacitance variations between a first electrode and a second electrode; determining the vascular stiffness of the vessel; and determining the blood pressure based on the distension and the vascular stiffness of the vessel.

Abstract: A system and method for monitoring a health condition are disclosed. The system includes a patient management application, a data store and a monitoring device. The monitoring device includes an optical sensor, a Doppler sensor, and a computing device adapted to provide health parameter values including oxygen saturation of the blood, blood flow, blood pressure, heart rate, and cardiac output.

Abstract: A method for generating a sampled plethysmograph data, includes measuring a plethysmograph waveform indicative of a first cardiac cycle and a second cardiac cycle, each cycle including a systolic waveform and a diastolic waveform. The method further includes estimating a first start time and a first duration for the systolic waveform of the first cardiac cycle and computing a plurality of amplitudes at a plurality of time instants for the first duration. The method further includes determining a second start time and a second duration of the systolic waveform of the second cardiac cycle. The method also includes assigning the second cardiac cycle, the second start time, and the second duration to the first cardiac cycle, the first start time, and the first duration respectively. The method further includes iteratively performing the steps of measuring, estimating, computing, determining and assigning for the plurality of cardiac cycles acquired sequentially in time.

Abstract: A blood flow image diagnosis device which diagnoses a blood flow map by separating, on the basis of a plurality of blood flow maps covering a specified time including one or more cardiac beats, a blood flow of a surface layer blood vessel observed in a surface layer in an observation region of a body tissue from a background blood flow of a peripheral background region. The device distinguishably displays a first blood flow map of the surface layer blood vessel and a second blood flow map of the background blood flow. The device calculates and compares information on a blood flow including blood flow value, blood flow waveform, or blood vessel diameter in the first and second blood flow maps, and displays the calculated information.

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: Provided according to embodiments of the invention are methods for monitoring an individual including securing a photoplethysmography (PPG) sensor comprising at least one emitter and at least one detector onto skin overlying an ophthalmic artery region of the individual; and obtaining PPG signals generated by the PPG sensor. Sensors for photoplethysmographic monitoring at the ophthalmic artery region are also provided.

Abstract: A blood flow measuring apparatus includes a sensor unit including a light emitter configured to emit light onto a measurement area and a light receiver configured to receive the light transmitted through the measurement area; at least one more light receiver configured to receive the light transmitted through the measurement area; and a control part configured to measure a blood flow state of the measurement area according to signals outputted by the light receivers. The light emitted by the light emitter is received by the light receivers arranged at different distances from the light emitter and the light receivers output the signals responsive to the received light. The control part measures the blood flow state of the measurement area by performing an arithmetic process to cancel a component of oxygen saturation in the blood, said component being included in the signals outputted by the light receivers.

Abstract: Techniques for estimating a cardiac chamber or vascular pressure based upon impedance are described. A device or system may measure an impedance between at least two electrodes implanted within or proximate to a cardiovascular system. The device or system may estimate a pressure of an element of the cardiovascular system based on a relationship between impedance and volume of the element, and based on a empirical relationship between the volume and the pressure. The device or system may also estimate the dimension of the element based on the impedance-volume relationship, or other characteristics based on the impedance. Because the impedance measurements may be obtained, in some examples, by using electrodes and leads implanted within the cardiovascular system and coupled to an implantable medical device, a practical estimation of a cardiovascular pressure can be obtained on a chronic basis without requiring the use other invasive sensors, such as micronanometer transducers.

Abstract: A system and method for multiple players to play an interactive game is disclosed herein. The system preferably includes monitoring device monitoring the vital signs of a user, a game console and a video monitor. The monitoring device is preferably an article having an optical sensor and accelerometer. The monitoring device preferably provides for the display of the following information about the user: pulse rate; blood oxygenation levels; calories expended by the user of a pre-set time period; target zones of activity; time; distance traveled; and/or dynamic blood pressure. The article is preferably a band worn on a user's wrist, arm or ankle.

Abstract: According to one embodiment, a medical image diagnostic apparatus includes a storage unit, a blood flow information generation unit and a blood flow inhibition index generation unit. The storage unit stores volume data or data of a series of images regarding an organ of an object. The blood flow information generation unit generates, based on the volume data or the data of the series of images, first blood flow information of a first region and second blood flow information of a second region different from the first region. The blood flow inhibition index generation unit generates, based on the first blood flow information and the second blood flow information, a blood flow inhibition index representing a degree of inhibition of a blood flow in a blood vessel regarding the first region or the second region.

Abstract: Contact pressure sensing apparatus for use with exercise equipment sensors are described. An example apparatus includes a sensor to detect a physiological condition of a user of an exercise device through physical contact with the user and a pressure sensor to detect a contact pressure applied by the user to the sensor.

Abstract: Embodiments provide systems and methods for displaying a fluid responsiveness predictor (FRP) based on an analysis a physiological signal detected by a physiological sensor applied to a patient. A method may include detecting the signal of the patient with the physiological sensor, determining an FRP with a FRP determination module, wherein the determining operation comprises analyzing at least one characteristic of the physiological signal over time to determine the FRP, receiving a report request to report the FRP at a requested time through a user interface, generating a reported FRP in relation to the requested time using the FRP determination module, and displaying the reported FRP on a display. The displaying operation may include displaying the FRP using at least one graphic representation.

Abstract: The invention concerns a measurement device to capture at least one vital parameter of a person in a motor vehicle with a steering wheel. The measurement device includes a finger sensor device with an optical sensor device, where the finger sensor device is attached to the steering wheel in the transition zone between a steering wheel spoke and the hub of the steering wheel.

Abstract: A method of delivering therapy to a target site. The method includes (a) obtaining a base image of the target site, (b) injecting a dose of a mix of a therapeutic agent and a contrast agent into a first injection location at the target site via a needle passing through a catheter, (c) collecting sequential fluoroscopic images of a contrast agent dispersion cloud at the first injection location, (d) determining a contrast agent dispersion area from the sequential fluoroscopic images, (e) determining a therapeutic agent dispersion area from the contrast agent dispersion area, (f) marking the therapeutic agent dispersion area on the base image of the target site, and (g) repeating (b) through (f) until the target site is substantially covered with overlapping therapeutic agent dispersion areas corresponding to a plurality of injections at a plurality of injection locations at the target site.

Abstract: Apparatus is provided, including a sensor, adapted to generate a sensor signal indicative of biorhythmic activity of a user of the apparatus, the sensor signal having a first characteristic, indicative of a voluntary action of the user, and a second characteristic, indicative of a benefit-related variable of the user. The apparatus also includes a control unit, adapted to receive the sensor signal, and, responsive to the second characteristics generate an output signal which directs the user to modify a parameter of the voluntary action indicated by the first characteristic.

Abstract: The present invention provides a technique for continuous measurement of blood pressure based on pulse transit time and which does not require any external calibration. This technique, referred to herein as the ‘Composite Method’, is carried out with a body-worn monitor that measures blood pressure and other vital signs, and wirelessly transmits them to a remote monitor. A network of body-worn sensors, typically placed on the patient's right arm and chest, connect to the body-worn monitor and measure time-dependent ECG, PPG, accelerometer, and pressure waveforms. The disposable sensors can include a cuff that features an inflatable bladder coupled to a pressure sensor, three or more electrical sensors (e.g. electrodes), three or more accelerometers, a temperature sensor, and an optical sensor (e.g., a light source and photodiode) attached to the patient's thumb.

Abstract: Embodiments include a system for determining cardiovascular information for a patient. The system may include at least one computer system configured to receive patient-specific data regarding a geometry of the patient's heart, and create a three-dimensional model representing at least a portion of the patient's heart based on the patient-specific data. The at least one computer system may be further configured to create a physics-based model relating to a blood flow characteristic of the patient's heart and determine a fractional flow reserve within the patient's heart based on the three-dimensional model and the physics-based model.

Abstract: Embodiments include a system for determining cardiovascular information for a patient. The system may include at least one computer system configured to receive patient-specific data regarding a geometry of the patient's heart, and create a three-dimensional model representing at least a portion of the patient's heart based on the patient-specific data. The at least one computer system may be further configured to create a physics-based model relating to a blood flow characteristic of the patient's heart and determine a fractional flow reserve within the patient's heart based on the three-dimensional model and the physics-based model.

Abstract: Systems and methods are provided for monitoring changes in blood volume using waveforms in the peripheral vasculature. In particular, the systems and methods relate to detecting ventilation-induced variation (VIV) of waveforms in the peripheral vasculature. Advantageously, the systems and methods may relate to analyzing VIV in peripheral venous pressure (PVP). Thus, the VIV of PVP may be measured, wherein decreased VIV is indicative of decreased blood volume In exemplary embodiments, such as involving spontaneous breathing, it may be necessary to account for changes in respiratory signal strength. Thus systems and methods are also provided for assessing coherence between ventilation and VIV for a flow or pressure waveform. Specifically, coherence is evaluated by comparing the waveform to a detected respiratory signal. Finally, systems and method are provided for distinguishing the impact of respiration on the PG signal during hypervolemia as compared to hypovolemia.

Abstract: A method for measuring reactive hyperemia in a subject is disclosed. The method includes performing a first segmental cuff plethysmography to generate a baseline arterial compliance curve and/or a baseline pressure-area (P-A) curve, performing a second segmental cuff plethysmography to generate a hyperemic arterial compliance curve and/or a hyperemic P-A curve, and calculating an area between the baseline and the hyperemic curves. The size of the area can be used as an indication of endothelial dysfunction (ED) and ED-related diseases.

Abstract: Devices, systems, and methods for determining fractional flow reserve. At least one method for determining fractional flow reserve of the present disclosure comprises the steps positioning a device comprising at least two sensors within a luminal organ at or near a stenosis, wherein the at least two sensors are separated a predetermined distance from one another, operating the device to determine flow velocity of a second fluid introduced into me luminal organ to temporarily displace a first fluid present within the luminal organ, and determining fractional flow reserve at or near the stenosis based upon the flow velocity, a mean aortic pressure within the luminal organ, and at least one cross-sectional area at or near the stenosis. Devices and systems useful for performing such exemplary methods are also disclosed herein.

Abstract: An apparatus and a method for determining the volume amount of a physiological volume (EVLW) from the system response to two successive system disturbances, taking into account that an intrinsic physical property of the physiological volume is influenced by the first (or previous, respectively) system disturbance, is described. By introducing a cold bolus to the central venous blood stream, a flowed-by volume, such as extravascular lung water, is cooled down. The driving temperature gradient for heat transfer is reduced when a second cold bolus is introduced. From the difference of the system response to the first bolus injection and the second bolus injection EVLW can be determined.

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: In measurement requiring application of pressure to a tissue of a living body such as blood pressure measurement, noise due to vibration tends to occur. It is difficult to accurately measure a pulse wave and a blood pressure value. It is also difficult to measure blood pressure in life activities or to measure blood pressure at intervals or continuously where a tonometer is always attached. There is consequently a problem of holding a biologic information detecting apparatus. The present invention solves the problems by providing an easy-to-wear biologic information detecting apparatus for stably detecting biologic information. The biologic information detecting apparatus includes a sensor for detecting biologic information in a pair of arms connected via a spindle, and the sensor is tightly attached to a projecting part in a living body, particularly, a tragus of an auricle.

Abstract: A medical diagnostic device performs diagnostics for assessing the ability of the arteries to respond to an increase in blood flow. The medical diagnostic device determines relative changes in arterial volume of the limb segment during a time period after a stimulus relative to the arterial volume of the limb segment during a baseline period using the amplitudes or other portions of the component pulse waves (such as early systolic components) of volume pulse waves during the baseline period and after the stimulus.

Abstract: In measurement requiring application of pressure to a tissue of a living body such as blood pressure measurement, noise due to vibration tends to occur. It is difficult to accurately measure a pulse wave and a blood pressure value. It is also difficult to measure blood pressure in life activities or to measure blood pressure at intervals or continuously where a tonometer is always attached. There is consequently a problem of holding a biologic information detecting apparatus. The present invention solves the problems by providing an easy-to-wear biologic information detecting apparatus for stably detecting biologic information. The biologic information detecting apparatus includes a sensor for detecting biologic information in a pair of arms connected via a spindle, and the sensor is tightly attached to a projecting part in a living body, particularly, a tragus of an auricle.

Abstract: A system for assessing blood circulation in a subject's limb, including detection means for detecting a signal dependent upon the arterial blood volume in a limb of the subject when the subject is in a first posture and also when the subject is in a second posture, different to the first posture; and processing means for calculating a quantitative indicator that is dependent upon the ratio of the signal for the first posture to the signal for the second posture.

Abstract: Devices, systems, and methods for the localization of body lumen junctions and other intraluminal structure are disclosed. Various embodiments permit clinicians to identify and locate lesions and/or anatomical structures within a lumen and accurately place leads and/or devices within a lumen, through determining the intralumen conductance and/or cross-sectional area at a plurality of locations within the body lumen.

Abstract: A compression device includes at least one pressurizable bladder to substantially occlude blood flow into skin capillary beds adjacent to the at least one pressurizable bladder, and a plurality of perfusion sensors. In operation a first-angiosome sensor detects the perfusion parameter of a skin capillary bed in a first angiosome of the limb, and a second-angiosome sensor detects the perfusion parameter of a skin capillary bed in a second angiosome of the limb that is different from the first angiosome. A control circuit maps sensor signals from the first-angiosome sensor to the first angiosome or a first artery of the limb, and maps sensor signals from the second-angiosome sensor to the second angiosome or a second artery of the limb different from the first artery of the limb. For each perfusion sensor, the control circuit determines whether the received sensor signals are indicative of peripheral artery disease.

Abstract: 2-D projection images show the variation over time of the distribution of a contrast medium in an examination subject. Each projection image comprises pixels having pixel values corresponding to one another in the projection images that are determined by identical areas of the examination subject. A computer subdivides an image that is to be displayed from the projection images into parcels in one perfusion region. For each parcel, the computer determines a characteristic value and, based on the characteristic value, a projection color. It assigns the projection color to the parcel. The characteristic value is determined based on the pixel values occurring in the parcel of the projection image or their differences from the pixel values of a corresponding parcel of another projection image. The computer outputs a subarea of the projection image containing the perfusion region. It represents each parcel of the perfusion region in its assigned projection color.

Abstract: In one aspect, a conductance catheter is provided for measuring the volume of a fluid. The conductance catheter comprises a series of electrodes and a circuit to compensate for variations in sensitivity of the electrodes in the catheter. In another aspect, a resistivity sensor is provided for determining the resistivity of a fluid. The sensor comprises a series of electrodes spaced such that the total distance between endmost electrodes does not exceed the diameter of the catheter deploying the sensor.

Abstract: Systems and methods of extracting information relating to diameter and/or diameter changes in small blood vessels such as arterioles. This information may be used to assess a degree of vasoconstriction and/or vasodilatation. In one method, changes in vessel cross-section due to pulse wave arrival is assessed in both arterioles and in larger arteries. A time delay between the changes and/or a change in time delay is optionally associated with arteriole cross-section and/or changes therein.

Abstract: A system for assessing blood circulation in a subject's limb, including detection means for detecting a signal dependent upon the arterial blood volume in a limb of the subject when the subject is in a first posture and also when the subject is in a second posture, different to the first posture; and processing means for calculating a quantitative indicator that is dependent upon the ratio of the signal for the first posture to the signal for the second posture.

Abstract: An apparatus for measuring a blood volume, includes: a first calculator which calculates a first blood volume by using information on a cardiac output of a subject; and a second calculator which calculates a second blood volume by using information on oxygen metabolism of the subject.

Abstract: An implantable medical device for monitoring tissue perfusion that includes a light source emitting a light signal and a light detector receiving emitted light scattered by a volume of body tissue. The light detector emits a signal having an alternating current component corresponding to the pulsatility of blood flow in the body tissue volume. A processor receives the current signal and determines a patient condition in response to the alternating component of the current signal.