Abstract: Systems are methods described for calculating, in real-time, various oxygenation parameters including total oxygen transport, mixed venous blood oxygen tension and mixed venous blood oxyhemoglobin saturation in a patient. The system preferably uses a computer, an arterial pressure line and a blood chemistry monitor to assist a physician in accurately determining when to give a patient a blood transfusion or otherwise alter the clinical management of that patient.

Abstract: A thermodilution catheter having a heating filament which is fabricated so as to be thin and flexible enough to avoid contact with the patient's blood. The heating filament is either inserted in a preformed catheter lumen, incorporated into a wall of the catheter body itself, or wrapped around the catheter body wall and surrounded by an external sheath. Generally, the covering of the heating filament is minimally thin so as to allow the heat from the heating filament to be transferred to the surrounding blood and to minimally increase the overall cross-sectional area. Since the heating filament does not directly touch the patient's blood, the outer surface may be made smooth so as to prevent inducement of blood clots. In addition, the heating filament may be maintained at a safe temperature by forming the heating element of a flexible material having a high temperature coefficient of resistance, low thermal capacitance and high thermal conductivity.

Abstract: An electronic stethoscope having two listening heads, functionally equivalent to one another, each containing a microphone. The signal of one microphone is subtracted from the signal of the other microphone, and the resulting difference signal is amplified, using either analog or digital signal processing techniques. The amplified difference signal is transduced to sound by headphones. Sounds which originate in the plane equidistant from both microphones (the “midplane”) are eliminated altogether, a fact which may be exploited to dissect a composite sound into two component sounds. Other sounds are attenuated in a predictable pattern, producing a focusing effect which increases as the microphones are brought closer together. The stethoscope incorporates features which minimize electromagnetic interference, enhance low-frequency throughput, reject amplified Johnson noise, and conserve battery power.

Abstract: The invention estimates a cardiac performance value such as cardiac output (CO) and cardiac ejection fraction (EF) by sensing a downstream indicator concentration signal y(t) that corresponds to an indicator (preferably heat) signal x(t) injected upstream in a patient's blood channel. The signal x(t) is preferably generated as a series of alternating transitions between a high state and a low state, such as a PRBS signal. The signal y(t) is then divided into at least one sub-signal that is synchronous with x(t). A decay parameter &tgr; that minimizes a cost function that includes a time-domain channel relaxation model is then calculated. The cardiac performance value is then calculated based on this value for &tgr;. For each transition of the injected indicator signal, a corresponding segment of the indicator concentration signal is preferably isolated, and a segment relaxation parameter is then calculated.

Abstract: A cardiac stimulating apparatus and method is described that non-intrusively determines an amount indicative of hemodynamic pulse pressure from an accelerometer signal. The amount indicative of pulse pressure is determined over several cardiac cycles and is used to optimize cardiac performance by evaluating the amount indicative of pulse pressure over varying timing intervals. The timing intervals are measured between at least one of intrinsic and paced stimulations of pre-selected chambers of the heart and a maximum pulse pressure indicates the optimum timing interval under manipulation. The cardiac stimulating apparatus and method may be used in any of several pacing modes including A-V pacing, V-V pacing, or A-A pacing.

Abstract: A thermodilution catheter having a heating filament which is fabricated so as to be thin and flexible enough to avoid contact with the patient's blood. The heating filament is either inserted in a preformed catheter lumen, incorporated into a wall of the catheter body itself, or wrapped around the catheter body wall and surrounded by an external sheath. Generally, the covering of the heating filament is minimally thin so as to allow the heat from the heating filament to be transferred to the surrounding blood and to minimally increase the overall cross-sectional area. Since the heating filament does not directly touch the patient's blood, the outer surface may be made smooth so as to prevent inducement of blood clots. In addition, the heating filament may be maintained at a safe temperature by forming the heating element of a flexible material having a high temperature coefficient of resistance, low thermal capacitance and high thermal conductivity.

Abstract: Cardiac stroke volume and output are estimated using an arterial pressure signal, which may be obtained either invasively, using a catheter-mounted pressure sensor, or non-invasively, with an external plethysmographic sensor mounted with a finger cuff. Both pulsatile and non-pulsatile (continuous) components of the sensed pressure signal are analyzed. Stroke volume is estimated as a function of the ratio between the area under the entire pressure curve and a linear combination of various components of impedance. Depending on the embodiment, first and/or second time derivatives of the pressure signal are used to determine the impedance components. The estimated stroke volume is preferably corrected based on the amount of deviation from a reference pressure of the mean pressure, which itself is determined from the sensed pressure signal. The invention is thus able to estimate stroke volume and cardiac output from the pressure signal alone, with no need for calibration using other highly invasive techniques.

Abstract: A method for the measurement of cardiac output in a patient in which the arterial blood pressure waveform of a patient from a blood pressure monitoring device over a period of time is subjected to various transformations and corrections, including a Fourier analysis in order to obtain the modulus of the first harmonic. The nominal stroke volume is then determined from the first harmonic and data relating to the arterial blood pressure and heart rate. The nominal cardiac output is then obtained from the nominal stroke volume.

Abstract: A system for sensing a characteristic of fluid flowing to or from the body of a human or animal comprising a conduit having a first end adapted to be outside the body, a second end adapted to be received within the body, and a flow passage through which fluid can flow between the first and second ends and a probe including a sensor for sensing a characteristic of the fluid. The probe is mounted on the conduit with the sensor in the flow passage. The sensor is isolated from the fluid flowing in the flow passage.

Abstract: A device for individual in-vivo determination of the compliance function C(p)=dV/dp of the vascular system downstream of a ventricle and/or systemic blood flow of a living being from the blood pressure p(t) and a reference cardiac output COref.

Abstract: A heart stimulator has a circuit for determining cardiac output and for producing a control signal corresponding to the determined cardiac output, and a controller for controlling cardiac stimulation dependent on the control signal. The circuit for determining cardiac output includes a pressure sensor which measures pressure in the right ventricle and which generates an electrical pressure signal corresponding to the measured pressure, and an integrator supplied with the pressure signal which integrates the pressure signal between a start time and stop time to produce an integration result corresponding to the cardiac output, which is used to form the control signal. The pressure signal is bandpass filtered during a systolic phase to identify opening of a valve at the right ventricle as the start time, and to identify closing of the valve as the stop time.

Abstract: Apparatus and methods for non-invasively determining cardiac output using partial re-breathing techniques are disclosed in which the apparatus is constructed with an instantaneously adjustable deadspace for accommodating differences in breathing capacities of various patients. The apparatus is constructed of inexpensive elements, including a single two-way valve which renders the apparatus very simple to use and inexpensive so that the unit may be readily disposable. The method of the invention provides a novel means of estimating cardiac output based on alveolar CO2 values rather than end-tidal CO2 values as previously practiced. A program for calculating cardiac output is also disclosed.

Abstract: Apparatus and methods for non-invasively determining cardiac output using partial re-breathing techniques are disclosed in which the apparatus is constructed with an instantaneously adjustable deadspace for accommodating differences in breathing capacities of various patients. The apparatus is constructed of inexpensive elements, including a single two-way valve which renders the apparatus very simple to use and inexpensive so that the unit may be readily disposable. The method of the invention provides a novel means of estimating cardiac output based on alveolar CO2 values rather than end-tidal CO2 values as previously practiced. A program for calculating cardiac output is also disclosed.

Abstract: A system and method for measuring total circulating blood volume and cardiac output employing an analyte diffusion approach. The analyte sensor as well as the analyte-containing fluid infusion procedure may be carried out with instruments which are inserted in the bloodstream at peripheral locations of the body spaced from the heart. A controller is provided to automatically carry out these measurements as well as to provide threshold comparisons for alerting the practitioner to excursion in the parameters. The preferred analyte containing fluid is an ammoniacal fluid and the preferred sensed components is ammonia gas.

Abstract: A low power processing system for processing bursted amplitude modulated signals performing impedance-related measurements across a load including injecting current pulses of constant amplitude across the load using at least a first electrode and a second electrode, the current pulses including bursts of a plurality of pulses at a pulse frequency at which the current pulses are repeated, the bursts transmitted at a burst frequency; detecting voltages across at least a third electrode and a fourth electrode; high pass filtering the voltages to produce filtered voltages; amplifying the filtered voltages to produce amplified voltage signals; bandpass filtering the amplified voltage signals with a bandpass filter with a center frequency equal to approximately the pulse frequency to generate first filtered signals; rectifying the first filtered signals to produce rectified signals; integrating the rectified signals to produce integrated signals; sampling-and-holding the integrated signals after each burst to captu

Abstract: A method is disclosed for diagnosing, monitoring and treating cardiovascular pathologies. Among the hemodynamic parameters of interest are peripheral resistance, compliance, and cardiac (left ventricular) output. Peripheral resistance determined according to the present invention has been found to be a reliable indicator, not only of hypertension, but also of the cause of the hypertension. The determined peripheral resistance can be compared against a predetermined threshold value. This comparison helps to foster a diagnosis of a hypertensive condition.

Abstract: A method is disclosed for diagnosing, monitoring and treating cardiovascular pathologies. Among the hemodynamic parameters of interest are peripheral resistance, compliance, and cardiac (left ventricular) output. Peripheral resistance determined according to the present invention has been found to be a reliable indicator, not only of hypertension, but also of the cause of the hypertension. The determined peripheral resistance can be compared against a predetermined threshold value. This comparison helps to foster a diagnosis of a hypertensive condition.

Abstract: A method of non-invasively estimating the intrapulmonary shunt in a patient. The method includes non-invasively measuring respiratory flow, respiratory carbon dioxide content, and arterial blood oxygen content. A re-breathing process is employed to facilitate an estimate of the patient's pulmonary capillary blood flow. Any inaccuracies of the arterial blood oxygen content are corrected to provide a substantially accurate arterial blood oxygen content measurement. The respiratory flow, carbon dioxide content and arterial blood oxygen content measurements, and the pulmonary capillary blood flow estimate are employed to estimate an intrapulmonary shunt of the patient. The invention also includes a method of determining the total cardiac output of the patient which considers the estimated intrapulmonary shunt.

Abstract: A compliant controller implements a biological model of a primate muscle so as to provide simultaneous position and force control with nonlinear damping for an actuator. The compliant controller uses one or more position sensors but does not require the use of a force sensor to provide force control. The compliant controller implements a force determining algorithm that is a function of an initial actuator position, a subsequently sensed actuator position, a desired actuator position and a position calculated from a nonlinear damping function. The algorithm updates or resets the initial actuator position or the calculated position depending upon the amount of actuator movement sensed. The compliant controller in accordance with the force determining algorithm and resetting of the various position values allows a desired position to be quickly attained while allowing the controller to compliantly respond to the presence or removal of an unknown or unexpected disturbing force.

Abstract: Apparatus and method for noninvasively determining cardiac performance parameters including 1) lengths of systolic time intervals, (2) contractility index, (3) pulse amplitude ratios while performing the Valsalva maneuver, (4) cardiac output index, and (5) a pulse wave velocity index. A catheter having at least one balloon is inserted into the esophagus and pressurized and positioned adjacent the aortic arch to sense aortic pressure. The effects of aortic pressure on the balloon are utilized to determine at least one of the cardiac performance parameters. The catheter may include a second balloon which is spaced from the aortic balloon a distance such that when the second balloon is in a position adjacent the left atrium to sense left atrial pressure the aortic balloon is in a position adjacent the aortic arch to sense aortic pressure, this distance being related to the distance between the left atrium and aortic arch in most adult persons.

Abstract: A method of analyzing a signal representing a physical parameter to obtain information from said signal and to extrapolate information contained in said signal and/or to ignore an interfering component in part of said signal, said signal representing either only a first portion of a skew distribution, or a first portion of a skew distribution and a second portion containing an interfering component, in which the area of a skew distribution, preferably a lognormal distribution is measured. The method is particularly applicable to the measurement of cardiac output. Apparatus for carrying out the method is also disclosed.

Abstract: A technique for determining blood flow in a living body by changing the thermal energy level by a predetermined amount at a site in a blood flow path and detecting temperatures at locations upstream and downstream of the site. The temperature difference at such locations is determined and the blood flow is calculated as a function of the change in energy level and of the temperature differences measured prior to and following the change in energy level.

Abstract: Method and apparatus for continuous, non-invasive determination of cardiac output which processes a sequence of non-invasive cardiography signals which are quantitatively dependent upon cardiac output within a computer system and associated neural network capable of generating a single output signal for the combined input signals, wherein the neural network applies weighting factors determined during a training phase to force the output signal to match the known value of cardiac output determined by invasive means and reports the single output signal as the determined value of cardiac output.

Abstract: The present invention is a method and system for continuously monitoring cardiac output. In a preferred embodiment, the method and system of the present invention comprises a pneumotachograph, differential pressure transducer, and a signal amplifier/conditioner interconnected to a programmed digital computer. A patient, preferably, inserts the pneumotachograph in his mouth or, alternatively, the pneumotachograph is connected to a patient's tracheal cannula. As the patient exhales and inhales the differential pressure transducer measures the drop in pressure as air flows through the pneumotachograph thereby producing a weak electrical signal non-linearly proportional to flow. Next, the weak signal is directed through the amplifier/signal conditioner which increases the amplitude and removes some of the noise contained in the transducer output.

Abstract: A technique for determining blood flow in a living body by changing the thermal energy level by a predetermined amount at a site in a blood flow path and detecting temperatures at locations upstream and downstream of the site. The temperature difference at such locations is determined and the blood flow is calculated as a function of the change in energy level and of the temperature differences measured prior to and following the change in energy level.

Abstract: A method is disclosed for diagnosing, monitoring and treating cardiovascular pathologies. Among the hemodynamic parameters of interest are peripheral resistance, compliance, and cardiac (left ventricular) output. Peripheral resistance determined according to the present invention has been found to be a reliable indicator, not only of hypertension, but also of the cause of the hypertension. The determined peripheral resistance can be compared against a predetermined threshold value. This comparison helps to foster a diagnosis of a hypertensive condition.

Abstract: The invention includes a dilution sensor for determining a blood property in a peripheral artery distal to the heart and lungs, wherein the dilution sensor may be exposed to the blood flow by passing through a pressure arterial catheter.

Abstract: Procedure and device for determining cardiac output volume which involves applying an electrical potential to create a current flow through tissue of the patient's heart, placing a first measuring electrode on skin of the patient near the heart and inserting a second measuring electrode into the patient's body at a position on an opposite side of the heart from the first measuring electrode so that a straight-line heart-traversing projection extends through the heart between the first and the second measuring electrodes. In one embodiment the second measuring electrode is in a blood vessel and in another embodiment there are a plurality of second measuring electrodes with the best one being determined by Electrocardiogram equipment.

Abstract: A system is provided for use in measuring the cardiac output of a living being. The system includes at least one sensor for measuring the lung carbon dioxide elimination rate of the living being and a processor for predicting the cardiac ouput level of the living being as a function of the current value of the lung carbon dioxide elimination rate based upon the predictive increase in cardiac output as the lung carbon dioxide elimination rate of the living being increases. Structure is provided for determining the cardiac ouput of an intubated living being and a non-intubated living being.

Abstract: A method for the measurement of cardiac output in a patient in which the arterial blood pressure waveform of a patient from a blood pressure monitoring device over a period of time is subjected to various transformations and corrections, including autocorrelation, whereby the pulsatility and heart rate of the patient are obtained. The nominal stroke volume is then calculated from the pulsatility and the nominal caridac output obtained by multiplying the stroke volume by the heart rate.

Abstract: A method and apparatus for identifying a central blood volume and monitoring changes in the central blood volume during hemodialysis to assist in predicting an onset of intradialytic morbid events. A method of determining a central blood volume mean transit time in a patient system having the central volume and a tubing portion includes measuring a system mean transit time through the tubing portion and the central volume; calculating a tubing portion mean transit time corresponding to passage of an indicator through the tubing portion; adjusting the measured system mean transit time in response to the calculated tubing portion mean transit time to produce the central volume mean transit time and calculating a central volume by multiplying the central volume mean transit time by the cardiac output. This technology can be used not only in hemodialysis, but in intensive care units or during the surgery with extracorporeal circulation systems.

Abstract: An apparatus, operation and method for the noninvasive diagnosis of cardiovascular disease or disorder through angiosonospectrography. Through implementation of the present invention physiological signals relating to the heart and associated blood vessels are detected, processed and identified, allowing for the early diagnosis of cardiovascular disease or disorder. An apparatus for diagnosing cardiovascular disease or disorder in accordance with the present invention includes a sensor assembly comprising a housing, and electronic module, a shock dampener, a mounting means, a piezoelectric transducer, an acoustic coupling and a back cover. The sensor assembly is connected to a data acquisition module which in turn is connected to a signal processing means, a remote connection means and a monitor. An improved acoustic coupling is disclosed that provides low-loss acoustic transmission coupling between the skin of the patient and the detector.

Abstract: A vascular impedance measurement instrument includes a transducer to obtain a digitized arterial blood pressure waveform. The digitized data is used to determine cardiac output, and to subsequently obtain measurements of impedance parameters using the modified Windkessel model of the arterial system. The instrument is used as an aid in diagnosing, treating and monitoring patients with cardiovascular disease.

Abstract: The cardiac ejection fraction EF is estimated based on the parameters of a model of an indicator (such as thermal) dilution through the heart. A channel model is defined by an upstream indicator injector, such as a heater, positioned preferably in the right atrium/ventricle and a downstream indicator concentration sensor, such as a thermistor. The preferred model is a lagged normal transfer function, which has as one of its output parameters the indicator decay constant .tau. of the blood channel. The heart rate HR is also measured. The ejection fraction EF is then calculated continuously as EF=1-exp(-60/(.tau.*HR)). The cardiac output CO is also estimated in the model, preferably based on an estimate of the zero-frequency gain of the lagged normal transfer function. End diastolic volume EDV is then also calculated continuously as a function of CO, HR and EF.

Abstract: A multi-lumen catheter capable of measuring cardiac output continuously, mixed venous oxygen saturation as well as other hemodynamic parameters. The catheter is also capable of undertaking therapeutic operations such as drug infusion and cardiac pacing. The catheter includes optical fibers for coupling to an external oximeter, an injectate port and thermistor for bolus thermodilution measurements, a heating element for inputting a heat signal and for coupling to an external processor for continuously measuring cardiac output, and a distal lumen for measuring pressure, withdrawing blood, guidewire passage or drug infusion. In a preferred embodiment, the catheter includes a novel lumen configuration permitting an additional infusion lumen for either fast drug infusion or cardiac pacing.

Abstract: An apparatus is in development which measures the blood outflow through the heart valves by means of the bolus thermodilution method and which from then on measures the continuous cardiac output, considering the formula of Gorlin and the measurement of the blood pressure in the compartments of the heart.

Abstract: Apparatus and method are provided for obtaining a measure of blood flow, and more specifically cardiac output, by analyzing blood temperature variations in the arterial tract. In a first embodiment, a lead carrying two closely spaced temperature sensors is positioned so that the sensors are in the atrial tract and produce temperature signals representative of small cyclical temperature variations of the blood outputted from the heart. The two signals have substantially similar patterns for each cardiac cycle, but the signals are separated by a short time (.increment.T) representative of the distance between the two sensors. The patterns are correlated to find .increment.T, from which cardiac output is calculated. In an alternate embodiment, a single blood temperature sensor is employed along with a sensor for determining cardiac contractions, and a measure of cardiac output is obtained by comparing the time difference between a feature of the blood temperature signal with the time of cardiac contraction.

Abstract: A method of determining cardiac volume including the steps of positioning a catheter in a blood-filled chamber of a patient's heart. The catheter comprises an elongated body having a distal end, a proximal end, a plurality of spaced electrodes arrayed on the outer surface of the catheter and spaced apart a predetermined distance from each other to define a distal electrode, a proximal electrode and a plurality of pairs of adjacent electrodes between the distal and proximal electrodes to define volume segments within the chamber.

Abstract: Cardiac output of a test individual is determined in a noninvasive method, by processing CO.sub.2 expirogram data obtained from the individual. The method also noninvasively determines pulmonary arterial blood CO.sub.2 concentration for the test individual. An apparatus for carrying out this noninvasive method includes a database of computed numerical CO.sub.2 expirograms, a device for measuring experimental CO.sub.2 expirogram data and means for processing the data sets to determine cardiac output.

Abstract: A system for measuring biological functions of a patient, such as cardiac output, filters noise from a signal provided by a thermistor catheter inserted into the body of the patient. A signal-conditioning cable is disposed between the catheter and an instrument which processes the signal to measure cardiac output. The cable includes circuitry which forms, in combination with a thermistor of the catheter, a low-pass filter for attenuating thermal and high-frequency noise from the signal provided to the instrument. The instrument can more accurately measure cardiac output with the filtered signal than with an unfiltered signal. Although the circuitry which forms the low-pass filter may be combined with the catheter or the instrument, it is preferred to dispose the circuitry in a separate cable to reduce manufacturing costs of the catheter and retrofitting costs of existing instruments.

Abstract: Cardiac output is measured utilizing a catheter in conjunction with the indicator dilution technique. Non-thermal analyte-containing fluid is used as the injectate. This fluid is biocompatible with and metabolizable within the body of the patient. An analyte concentration sensor is mounted upon the catheter and located downstream within the bloodstream from the port from which the analyte-containing fluid is expressed. Because of the matching of rapid concentration sensor response with an analyte-containing fluid which is metabolizable, the measurement of cardiac output may be carried out as often as about one to three minutes in conjunction with an infusion interval substantially less than the measurement frequency interval. The analyte-containing fluids are selected from a group consisting of ammoniacal fluid, heparin, ethanol, a carbon dioxide releasing fluid, glucose, and anesthesia agent.

Abstract: A method of determining cardiac volume including the steps of positioning a catheter output including the steps of positioning a catheter in a blood-filled chamber of a patient's heart. The catheter comprises an elongated body having a distal end, a proximal end and a plurality of spaced apart electrodes arrayed on the outer surface of the catheter. The electrodes are spaced apart a predetermined distance from each other to define a distal electrode, a proximal electrode and a plurality of pairs of adjacent electrodes between the distal and proximal electrodes to define volume segments within the chamber.

Abstract: A vascular impedance measurement instrument includes a transducer to obtain a digitized arterial blood pressure waveform. The digitized data is used to determine cardiac output, and to subsequently obtain measurements of impedance parameters using the modified Windkessel model of the arterial system. The instrument is used as an aid in diagnosing, treating and monitoring patients with cardiovascular disease.

Abstract: A system (method and apparatus) for hemodynamic measurements of the cardiac activity, including the stroke volume and cardiac output on the basis of a blood pressure pulse wave of a patient. Using a function that relates cardiac activity to an anthropometric parameter of the patient (height or arm span), ordinates of the pulse wave, and time intervals of certain characteristic points of the pulse wave, the stroke volume and/or cardiac output are obtained. The pulse wave can be determined by means of an optical sensor clipped to an ear lobe of the patient. The characteristic points and time intervals from the initial point of the pulse wave to the characteristic points are obtained under computer control. The measured values of the time intervals and ordinates are inputted to the computer which computes cardiac output, stroke volume and other cardiac information related thereto.

Abstract: A thermodilution catheter having a heating filament which is fabricated so as to be thin and flexible enough to avoid contact with the patient's blood. The heating filament is either inserted in a preformed catheter lumen, incorporated into a wall of the catheter body itself, or wrapped around the catheter body wall and surrounded by an external sheath. Generally, the covering of the heating filament is minimally thin so as to allow the heat from the heating filament to be transferred to the surrounding blood and to minimally increase the overall cross-sectional area. Since the heating filament does not directly touch the patient's blood, the outer surface may be made smooth so as to prevent inducement of blood clots. In addition, the heating filament may be maintained at a safe temperature by forming the heating element of a flexible material having a high temperature coefficient of resistance, low thermal capacitance and high thermal conductivity.

Abstract: A method is disclosed for diagnosing, monitoring and treating cardiovascular pathologies. Among the hemodynamic parameters of interest are peripheral resistance, compliance, and cardiac (left ventricular) output. Peripheral resistance determined according to the present invention has been found to be a reliable indicator, not only of hypertension, but also of the cause of the hypertension. The determined peripheral resistance can be compared against a predetermined threshold value. This comparison helps to foster a diagnosis of a hypertensive condition.

Abstract: A device for continuously monitoring the output of a heart in a surgical patient includes a probe head attached at one end to a catheter adapted to be inserted into the patient. The probe head includes a probe and a pair of flexible flat projections extending outwardly from opposite sides of the probe for securing the probe head in the transverse sinus of the patient. At least one transducer is positioned in the probe for detecting a condition of the heart. A hollow needle is adapted for receiving the probe head prior to its installation in the patient, such that the probe head can be installed in the patient immediately after medianstemotomy and division of the patient's pericardium by inserting the needle through the patient's chest wall.

Abstract: A thermodilution catheter having a heating filament which is fabricated so as to be thin and flexible enough to avoid contact with the patient's blood. The heating filament is either inserted in a preformed catheter lumen, incorporated into a wall of the catheter body itself, or wrapped around the catheter body wall and surrounded by an external sheath. Generally, the covering of the heating filament is minimally thin so as to allow the heat from the heating filament to be transferred to the surrounding blood and to minimally increase the overall cross-sectional area. Since the heating filament does not directly touch the patient's blood, the outer surface may be made smooth so as to prevent inducement of blood clots. In addition, the heating filament may be maintained at a safe temperature by forming the heating element of a flexible material having a high temperature coefficient of resistance, low thermal capacitance and high thermal conductivity.

Abstract: The present invention provides an diagnostic apparatus and method for physiologically measuring the biological responses of a selected group of muscles during exercise. Biological responses measured include blood flow, blood pressure, transcutaneous oxygen, and lymphatic clearance rate. The apparatus comprises a pressure plate attached to an axle. A spring mechanism is attached to the pressure plate to bias the plate towards the resting position. The spring may be adjusted so as to increase the resistance to the group of muscles being exercised and induce fatigue.

Abstract: Method, system, and apparatus for evaluating hemodynamic parameters and, in particular, cardiac output. A pulmonary artery catheter is described which incorporates a diffuser of gas biocompatible with the body such as oxygen at an indwelling region such that the gas may be employed to carry out a dilution technique to measure cardiac output. A mixed venous blood gas level then is measured at the pulmonary artery using a gas sensor. The preferred gas sensor employs oximetry to derive values of mixed venous oxygen saturation. An alternate embodiment utilizes an electrode/electrolyte approach as the gas sensor to carry out measurement of dissolved oxygen in mixed venous blood. The system utilizes a microprocessor driven controller to develop multiple evaluations over sequential measurement intervals and to compute a variety of hemodynamic parameters including the noted cardiac output.