Method for measuring the function of a patient's beating heart - Patent Application 20070122997

Abstract

A system and method for determining the heart's intrinsic cardiac output while maintaining operation of the intracardiac blood pump is provided. The system and method include determining the current drawn by the pump motor, the blood pressure in the ascending aorta, and the change in blood temperature based on thermodilution. An intracardiac blood pump placed in the aorta includes at least one sensor for determining motor current and blood pressure, and a thermistor for determining the change in blood temperature after a precise volume of fluid bolus is introduced into the vasculature. A processor receives the current, pressure, and temperature measurements and calculates the pump output flow and total cardiac output, from which the intrinsic cardiac output is calculated. The intrinsic cardiac output and other clinically relevant variables derived from the measurements inform decisions regarding ongoing therapeutic care, including increasing or decreasing the cardiac assist provided by the intracardiac pump.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 474,278, filed March 21, 2017, and entitled "THERMISTOR IMBEDDED THERAPEUTIC CATHETER," the entire contents of which are incorporated herein by reference. [Background technology]

[0002] background Cardiac output is a measure of the volume of blood the heart pumps through the circulatory system per minute. However, in patients receiving mechanical hemodynamic support, cardiac output is composed of two components: native cardiac output and mechanical cardiac output. Native cardiac output refers to blood flow due to the functioning of the native heart, and mechanical cardiac output refers to the assistance in blood flow provided by an intracardiac mechanical device, such as a cardiac pump (e.g., the Impella 2.5 pump by Abiomed, Inc.). In patients hemodynamically supported by a mechanical circulatory support device, native cardiac output is used to assess patient treatment and progress.

[0003] Measuring intrinsic cardiac output in patients requiring hemodynamic support presents technical and clinical challenges using currently available techniques and approaches, including Doppler ultrasound, continuous wave Doppler, transesophageal Doppler, echocardiography, pulse pressure, calibrated pulse pressure, impedance cardiography, cardiac computed tomography, scintigraphy, magnetic resonance imaging, and thermodilution.

[0004] Currently available technologies have several notable problems. First, each of the available technologies can only measure total cardiac output and fails to account for continuous and differential flow through an operating pump in cardiac output measurements obtained from a mechanically supported patient. Therefore, to directly measure intrinsic cardiac output with these technologies, mechanical support must be temporarily discontinued or minimized to prevent intracardiac devices from interfering with the measurement. A temporary interruption in support exposes the patient to unnecessary risk if the native heart is unable to provide sufficient cardiac output during the interruption. These problems limit the usefulness of these technologies in treating patients supported by mechanical circulatory devices. These technologies are limited in their ability to instantly measure intrinsic and total cardiac output in a repeatable and reproducible manner.

[0005] Other challenges also exist. For example, pulse pressure and echocardiography are clinically known to be less accurate in estimating cardiac output compared with thermodilution. Doppler echocardiography is prone to interference from pump flow. Cardiac computed tomography and scintigraphy expose patients to radiation, and using these modalities, repeated measurements at different flows to determine whether pump weaning is feasible is impractical. In addition, magnetic resonance imaging is incompatible with mechanical support devices; and thermodilution on the right side of the heart requires an additional central vascular route, which may increase the risk of vascular complications and infection. Placement of a Swan-Ganz catheter is sometimes difficult, can induce arrhythmias in patients with acute myocardial infarction, and requires x-rays to confirm the catheter's position if it moves. Summary of the Invention

[0006] overview The disclosed methods and systems overcome the above-mentioned drawbacks associated with currently used methods and provide more accurate and useful information about cardiac function while a patient is receiving mechanical hemodynamic support. Furthermore, this physiological information can provide clinicians with more insight into how a patient will respond when mechanical circulatory support is removed, thereby enabling clinicians to better predict a patient's response. This information is currently unavailable in the clinic.

[0007] Described herein are methods and systems for measuring one or more of total cardiac output, mechanical cardiac output, and intrinsic cardiac output. Exemplary systems and methods use a thermistor embedded within an intravascular blood pump, for example, within a catheter sheath associated with the blood pump. Measurements of intrinsic cardiac output may be made while the intravascular blood pump continues to provide mechanical support to the heart. Intrinsic cardiac output and other variables derived from measurements of intrinsic cardiac output may be displayed to a physician or pump operator to provide real-time information regarding the state and condition of the heart.

[0008] In one aspect, a system for measuring the function of a beating heart is provided. The system includes a sensor system including at least one thermistor for use in an intracardiac pump, configured to measure a patient's cardiac output (one or more of total cardiac output, intrinsic cardiac output, and mechanical cardiac output) and optionally other physiological parameters while the patient is receiving hemodynamic support. An example of a suitable intracardiac blood pump includes a tubular cannula having a proximal opening and a distal opening, a cylindrical surface disposed between the proximal opening and the distal opening and configured to be positioned within the aorta, an electrically driven motor and a rotor disposed within the cannula, and electrical wires configured to supply current to the motor. A catheter may be provided having a proximal end region and a distal end region connected to the cannula. A repositioning sheath may also be disposed around the catheter. A thermistor is disposed within the distal end region of the blood pump or within the catheter. The thermistor is configured to detect the temperature of blood flowing within the aorta of the heart. The system also provides a fluid source configured to provide a bolus, such as through a cold fluid source, which may be of a suitable fluid at a predetermined temperature different from (e.g., lower than) physiological blood temperature and thus capable of altering the temperature of blood in the vasculature flowing into or out of the beating heart.

[0009] Multiple sensors and a processor are used. The processor receives and processes one or more signals from the sensors. In addition to the blood temperature sensor, other sensors may be deployed to measure other parameters. For example, a sensor may be used to detect motor current, and another sensor detects blood pressure within the heart. In one embodiment, the processor is configured to receive a first signal from the motor current sensor indicative of changes in motor current during operation. The processor also receives a second signal from the blood pressure sensor indicative of pressure in the ascending aorta or near the aortic arch, and a third signal from the thermistor indicative of the temperature of blood flowing in the ascending aorta or from the heart to the ascending aorta. The processor then calculates a pump output flow rate based on the first and second signals; calculates a total cardiac output based on the third signal; and calculates the intrinsic cardiac output of the beating heart based on the pump output flow rate and the total cardiac output by subtracting the pump output flow rate from the total cardiac output. A third signal is then used to determine clinically relevant variables, including global end-diastolic volume (GEDV), intrathoracic blood volume (ITBV), intrathoracic thermal volume (ITTV), pulmonary thermal volume (PTV), extravascular lung water (EVLW), cardiac index, global ventricular ejection fraction, and stroke volume.

[0010] In one aspect, a system for measuring the function of a beating heart is provided, comprising an intracardiac blood pump having a tubular cannula with proximal and distal openings and a cylindrical surface disposed between the proximal and distal openings. The tubular cannula is configured to be placed within the aorta. The intracardiac blood pump also includes an electrically driven motor, a rotor disposed within the blood pump (e.g., within the cannula), and an electrical wire configured to supply electrical current to the motor. In some embodiments, the rotor is fitted within the motor. Optionally, the pump may be powered by an external motor having a drive cable extending through a catheter and to a drive unit located outside the patient's body.

[0011] The system may also include a catheter and a repositioning sheath. A thermistor is included, along with a fluid source configured to provide a bolus of fluid into the blood flow entering or leaving the heart. One or more additional sensors, including sensors for measuring changes in motor current and blood pressure, and a processor are used. The catheter has a proximal end region and a distal end region, the distal end region being connected to the cannula. The repositioning sheath is disposed around the catheter, and a thermistor is disposed within the distal end region of the catheter and configured therein to detect the temperature of blood flowing within the aorta of the heart. The bolus of fluid changes the temperature of blood in the vasculature flowing into or out of the beating heart. A first sensor detects changes in motor current during operation, and a second sensor detects blood pressure in the ascending aorta. The processor is configured to receive a first signal indicative of the change in motor current from the first sensor, a second signal indicative of blood pressure in the ascending aorta from the second sensor, and a third signal indicative of the temperature of blood flowing within the ascending aorta of the heart from the thermistor. The processor is further configured to calculate a pump output flow rate based on the first signal and the second signal, calculate a total cardiac output based on the third signal, and calculate an intrinsic cardiac output of the beating heart based on the pump output flow rate and the total cardiac output.

[0012] In some embodiments, the third signal indicates a change in temperature of blood flowing into the heart caused by the bolus of fluid. In some embodiments, the third signal indicates a change in temperature of blood flowing near or through the proximal opening of the cannula. In some embodiments, the processor is configured to determine total cardiac output by detecting changes in the third signal as a function of time. In some embodiments, the intrinsic cardiac output is calculated by subtracting the pump output flow rate from the total cardiac output. In some embodiments, the thermistor is disposed in a proximal end region of the catheter. In some embodiments, the system further comprises a second thermistor disposed on the catheter, the second thermistor configured to detect blood temperature near the catheter.

[0013] In some embodiments, the processor is further configured to calculate at least one of total end-diastolic volume, intrathoracic blood volume, intrathoracic heat volume, pulmonary heat volume, cardiac index, stroke volume, extravascular lung water, cardiac output, and total ventricular ejection fraction from the first signal, the second signal, and the third signal. In some embodiments, the processor is further configured to display the intrinsic cardiac output on a screen. In some embodiments, the processor is further configured to record and store the intrinsic cardiac output and to display a history of the intrinsic cardiac output as a function of time.

[0014] In another aspect, a method for determining the heart's intrinsic cardiac output during a ventilation-assisted procedure is provided. The method includes positioning a repositioning sheath and an intravascular blood pump in a patient's aorta with a catheter, and driving the intravascular blood pump with a motor current to cause a motor within the pump to pump blood from the left ventricle and into the patient's ascending aorta. The method also includes detecting changes in temperature of blood being pumped from the left ventricle into the ascending aorta; detecting changes in motor current during pumping; detecting pressure within the ascending aorta; calculating, by a processor, a total cardiac output based on the detected changes in temperature; calculating, by the processor, a pump output flow rate based on the detected changes in motor current and the detected pressure; and subtracting, by the processor, the pump output flow rate from the total cardiac output to determine the intrinsic cardiac output. [The present invention 1001] a tubular cannula having a proximal opening and a distal opening, a cylindrical surface disposed between the proximal opening and the distal opening and configured to be positioned within the aorta; an intracardiac blood pump; an electrically driven motor and rotor disposed within said cannula, and electrical wiring configured to supply electrical current to said motor; a catheter having a proximal end region and a distal end region connected to said cannula; a repositioning sheath disposed around the catheter; a thermistor disposed within the distal end region of the catheter and configured to sense the temperature of blood flowing within the aorta of the heart; a bolus of fluid, with an initial temperature different from the physiological blood temperature; A first sensor that detects changes in motor current during operation; a second sensor configured to detect pressure in the ascending aorta; and receiving a first signal from the first sensor indicative of a change in the motor current, a second signal from the second sensor indicative of a pressure in the ascending aorta, and a third signal from the thermistor indicative of a temperature of blood flowing through the ascending aorta of the heart; calculating a pump output flow rate based on the first signal and the second signal; calculating a total cardiac output based on the third signal; and Calculating the native cardiac output of the beating heart based on the pump output flow rate and the total cardiac output. Processor configured to 1. A system for measuring the function of a beating heart, comprising: [The present invention 1002] The system of the present invention 1001, wherein the third signal indicates a change in temperature of blood flowing into the heart, the change being caused by a bolus of fluid. [The present invention 1003] The system of invention 1001 or 1002, wherein said third signal is indicative of a change in temperature of blood flowing near or through said proximal opening of said cannula. [The present invention 1004] The system of any one of claims 1001 to 1003, wherein the processor is configured to determine the total cardiac output by detecting changes in the third signal as a function of time. [The present invention 1005] The system of the present invention 1004, wherein the intrinsic cardiac output is calculated by subtracting the pump output flow rate from the total cardiac output. [The present invention 1006] The system of any one of claims 1001 to 1005, wherein the thermistor is disposed within the proximal end region of the catheter. [The present invention 1007] Any of the systems of inventions 1001 to 1006, wherein the system further comprises a second thermistor disposed on the catheter, the second thermistor configured to detect blood temperature near the catheter. [The present invention 1008] Any of the systems of the present inventions 1001 to 1007, wherein the processor is further configured to calculate at least one of total end-diastolic volume, intrathoracic blood volume, intrathoracic heat capacity, pulmonary heat capacity, cardiac index, stroke volume, extravascular lung water, cardiac output, and total ventricular ejection fraction from the first signal, the second signal, and the third signal. [The present invention 1009] The system of any one of claims 1001 to 1008, wherein the processor is further configured to display the intrinsic cardiac output on a screen. [The present invention 1010] The system of any of claims 1001 to 1009, wherein the processor is further configured to record and store the intrinsic cardiac output and to display a history of the intrinsic cardiac output as a function of time. [The present invention 1011] A method for determining the intrinsic cardiac output of the heart during a ventilatory assistance procedure, comprising the steps of: positioning an intravascular blood pump within the patient's aorta via the catheter and repositioning sheath, and driving the intravascular blood pump with a motor current to cause a motor within the pump to pump blood from the left ventricle and into the patient's ascending aorta; detecting a change in temperature of blood being pumped from the left ventricle into the ascending aorta; detecting a change in motor current during pumping; detecting pressure in the ascending aorta; calculating, by a processor, total cardiac output based on said detected temperature change; calculating, by the processor, a pump output flow rate based on the detected change in the motor current and the detected pressure; and Subtracting, by the processor, the pump output flow from the total cardiac output to determine the intrinsic cardiac output. [Brief explanation of the drawings]

[0015] These and other objects and advantages will become apparent from the following detailed description considered in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout. [Figure 1] Figure 1A illustrates a standard thermodilution method for measuring the total cardiac output of a beating heart according to one embodiment, and Figure 1B illustrates a curve showing the temperature fluctuation ΔT of blood in an artery. [Figure 2] FIG. 1 illustrates a transpulmonary thermodilution method for measuring the total cardiac output of a beating heart according to one embodiment. [Figure 3] FIG. 1 is a block diagram of a method for determining the intrinsic cardiac output of a beating heart using signals generated by thermodilution with a heart pump placed inside the beating heart, according to one embodiment. [Figure 4] FIG. 1 is a perspective view of a transdermal pump according to one embodiment. [Figure 5] FIG. 1 is a perspective view of a transpulmonary thermodilution (TPTD) assembly including a percutaneous pump and a thermistor inserted into a dual lumen sheath during manufacture, according to one embodiment. [Figure 6] FIG. 6 illustrates placement of the TPTD assembly of FIG. 5 within the ascending aorta of a patient with a beating heart, according to one embodiment. [Figure 7] FIG. 1 illustrates an exemplary controller displaying intrinsic cardiac output and other variables. [Figure 8] FIG. 6 illustrates a method for determining intrinsic cardiac output using the setup of FIG. 5 according to one embodiment. [Figure 9]FIG. 10 shows cardiac output measured by the Impella thermodilution catheter compared to a reference cardiac output measurement. [Figure 10] FIG. 10 shows the percentage error of the Impella thermistor system observed in sequential experiments. [Figure 11] 11A and 11B show results obtained using the Impella thermistor system during low cardiac output. [Figure 12] 12A and 12B show results obtained using the Impella thermistor system during high cardiac output. [Figure 13] FIG. 10 illustrates the thermistor placed within the Impella catheter and its relative position to the component parts of the Impella pump. DETAILED DESCRIPTION OF THE INVENTION

[0016] Detailed Description Below, various concepts related to the method and system of the present invention are described in more detail for measuring total cardiac output, mechanical cardiac output, and intrinsic cardiac output using thermistors embedded in an intravascular blood pump, e.g., in a catheter sheath associated with a mechanical support device. These calculations can be performed simultaneously while the heart is beating to enable determination of the heart's intrinsic cardiac output. It should be understood that the concepts of the present disclosure are not limited to any particular mode of implementation, and thus the various concepts introduced above and discussed in more detail below may be implemented in any number of ways. Examples of implementations and applications are provided for illustrative purposes only and are not limiting.

[0017] The methods and systems described herein utilize thermodilution techniques to enable the measurement of total, mechanical, and intrinsic cardiac output using a thermistor embedded in the catheter sheath of an intravascular blood pump. Measurement of intrinsic cardiac output may be performed while the intravascular blood pump continues to provide maximum mechanical support to the heart. Intrinsic cardiac output and other variables derived from the measurements may be displayed to a physician or pump operator to provide information regarding the state and condition of the heart.

[0018] FIG. 1A illustrates a thermodilution technique used to measure a patient's cardiac output by detecting temperature changes in the patient's blood after application of a heat source. The diagram includes a pulmonary artery 110, an intraluminal device 120, a temperature sensor 130, a fluid reservoir 140, and a fluid bolus 150. In this technique, a clinician gains access to the patient's pulmonary artery 110 using the intraluminal device 120. In a specific embodiment, the intraluminal device 120 is a syringe. The temperature sensor 130 is inserted into the pulmonary artery 110 using a right heart catheter, such as a Swan-Ganz catheter. Such a catheter gains access to the pulmonary artery 110 from a different location than that used by the intraluminal device 120. The temperature sensor 130 is positioned within the vasculature in the direction of blood flow from the access point of the intraluminal device 120. A cold fluid bolus 150 is then introduced into the superior vena cava 110 using the intraluminal device 120. A precise volume of fluid bolus 150 is introduced into pulmonary artery 110 from fluid reservoir 140 contained in a syringe. Fluid bolus 150 should be at a temperature different from physiological blood temperature. In some embodiments, fluid bolus 150 is at a temperature lower than the patient's blood; i.e., the fluid is cold. In some embodiments, fluid bolus 150 has a temperature of approximately 4°C. In some embodiments, fluid bolus 150 is saline. In some embodiments, fluid bolus 150 comprises a physiologically compatible fluid, such as a 5% glucose solution. In traditional thermodilution techniques, where a fluid bolus is injected into the superior or inferior vena cava and a thermistor is in the pulmonary artery, the cold fluid passes only through the right atrium and right ventricle. Furthermore, traditional thermodilution techniques require access to the patient's right heart.

[0019] FIG. 1B shows a plot 200 displaying a thermodilution curve 210 indicating the temperature fluctuation ΔT of blood in a patient's pulmonary artery 110, as detected by the temperature sensor 130. A fluid bolus 150 is introduced at time t_0, and the temperature change peaks and begins to decline and dissipate. This indicates the length of time it takes for the injected cold fluid to flow through the thermistor. Total cardiac output is determined by calculating the area under the curve 210 over a predetermined time 220, such as between time t_1 and time t_2 in FIG. 1B, using well-established algorithms and mathematical techniques. Additional variables may be extracted from the thermodilution curve, including the mean transit time (MTt) 213 and the downslope time (DSt) 211. MTt 213 represents the time it takes for half of the fluid bolus 150 to pass through the thermistor, while DSt 211 is calculated from the exponential downward slope of the thermodilution curve. MTt 213 and DSt 211, in conjunction with thermodilution curves, total cardiac output, and other measurements, can be used to calculate a variety of clinically relevant variables.

[0020] One drawback of using the traditional thermodilution technique shown in FIG. 1A to determine total cardiac output is the need to traverse the right heart to place a thermistor and Swan-Ganz catheter in the pulmonary artery (e.g., in FIG. 1A , accessing the pulmonary artery 110 with an intraluminal device 120 and accessing the pulmonary artery 110 with a temperature sensor 130 using a catheter from a different access site). Having multiple access sites around the heart can increase the risk of vascular complications and infection. Additionally, placing a catheter in the pulmonary artery can be difficult, carries the risk of vascular injury and arrhythmia, and requires x-rays to confirm correct positioning after each catheter movement.

[0021] FIG. 2 illustrates a transpulmonary thermodilution technique for measuring the total cardiac output of a beating heart 301 according to one embodiment. The diagram includes the heart 301, including the right atrium 302, right ventricle 304, left atrium 306, and left ventricle 308, the aorta 309, and the aortic arch 310. The diagram also includes aspects of the pulmonary circulation, including peripheral veins 312 and peripheral arteries 314. Blood flows from the left atrium 306 to the left ventricle 308, into the aorta 309, and across the aortic arch 310 to the entire body. The blood returns to the heart 301 through the right atrium 302 and right ventricle 304. In transpulmonary thermodilution, a cold fluid bolus is injected into the peripheral vein 312 at point 316. The blood passes through the pulmonary circulation, and the temperature of the blood is measured by a thermistor (not shown) placed in the aorta 309 at point 318. Injecting the cold fluid bolus into a peripheral vein eliminates the need to place an additional right heart catheter into the heart to inject the fluid. Using a peripheral vein for fluid bolus injection poses less risk to the patient than placing an additional catheter, such as a Swan-Ganz catheter, into the heart. In some embodiments, the fluid bolus is injected into the inferior vena cava. In some embodiments, a thermistor is placed near the aortic valve.

[0022] The total cardiac output is calculated from the measured temperature change. The temperature measured by the thermistor at point 318 is recorded over time as a thermodilution response curve. The total cardiac output may be calculated from the recorded temperature measurements based on the area under the curve showing the change in measured temperature over time, as depicted in FIG. 1B. The total cardiac output is equal to the sum of the intrinsic cardiac output and the output of the cardiac assist device. Determining the intrinsic cardiac output using thermodilution allows for real-time determination of the intrinsic cardiac output while the pump is running. The intrinsic cardiac output can be used to assist medical professionals in making decisions regarding the use of cardiac assist devices.

[0023] Additionally, by measuring the mean transit time (MTt) and downslope time (DSt), which are the area under the curve of ΔT versus time (see, e.g., Figure 1B), additional clinically relevant variables can be calculated. Temperature variations over time, measured by the thermistor and recorded as a thermodilution curve, can also be used to calculate global end-diastolic volume (GEDV), intrathoracic blood volume (ITBV), intrathoracic thermal volume (ITTV), pulmonary thermal volume (PTV), extravascular lung water (EVLW), cardiac index, global ventricular ejection fraction, and stroke volume. These variables may provide the physician or operator with additional information about cardiac function and the degree of pulmonary congestion that can guide therapeutic decisions.

[0024] PTV can be calculated by multiplying total cardiac output by DSt. PTV represents the distribution of cold fluid volume in the pulmonary circulation. ITTV is calculated by multiplying total cardiac output by MTt. ITTV represents the distribution of cold fluid volume. GEDV represents the volume of blood contained in all four chambers of the heart and is an index of cardiac preload and is calculated by subtracting PTV from ITTV. It can alternatively be expressed as GEDV = total cardiac output × (MTt - DSt). GEDV can be used to clinically evaluate a patient's response to volume loading, allowing clinicians to more accurately assess cardiac preload. ITBV represents the volume of blood in the heart and in the pulmonary circulation and can be used to provide clinicians with information about the cardiac volume status and cardiac function. ITBV can be calculated by multiplying GEDV by 1.25, or alternatively, by multiplying 1.25 × CO (total cardiac output) × (MTt - DSt). EVLW is calculated from ITBV and ITTV. EVLW is a volumetric measure of fluid volume in the pleural cavity. EVLW is calculated by subtracting ITBV from ITTV. EVLW can be used to measure pulmonary congestion, which often accompanies left ventricular failure after acute myocardial infarction. Cardiac index is a global measure of cardiac function calculated by the formula CI = CO / BSA, where CI is cardiac index, CO is cardiac output, and BSA is body surface area. Calculating cardiac index using either total or intrinsic cardiac output can provide clinically relevant information. Stroke volume is an index of left ventricular function using the formula SV = CO / HR, where SV is stroke volume, CO is cardiac output, and HR is heart rate. Cardiac power is a measure of cardiac function in watts calculated using the equation CPO = mAoP * CO / 451, where CPO is cardiac power, mAoP is mean aortic pressure, CO is cardiac output, and 451 is a constant used to convert mmHG x L / min to watts. Equation: Based on TIFF0007737973000001.tif9128, additional variables can also be calculated from thermodilution measurements, where Q is the flow rate; T b is the initial temperature in the femoral artery; T iis the temperature of the injected fluid; K is a constant corresponding to the specific heat of the blood and fluid, taking into account the densities of the selected fluid and blood (if saline is used, K is equal to 1.1021); V i is the injected volume, V d is the dead space volume in the catheter through which the fluid is injected; AUC is the area under the thermodilution curve in °C·s. All of the above cardiac variables can be readily calculated using measurements obtained with the thermistor and transcutaneous pump.

[0025] 3 shows a block diagram 405 illustrating a transpulmonary thermodilution system that can be used to determine the intrinsic cardiac output of a beating heart. The system uses signals measured by a cardiac assist device and an implantable temperature sensor. The system includes a pump 400 contained within a sheath 452 and a thermistor 424, a first sensor 425, a second sensor 423, a first signal (SIG 1) 427, a second signal (SIG 2) 435, a third signal (SIG 3) 429, a processor 431, and an output variable (CO NAT) 433. Pump 400 and thermistor 424 are delivered through sheath 452 to a position within the heart and aorta. Pump 400 includes a first sensor 425 that outputs a first signal 427 to processor 431 and a second sensor 423 that outputs a second signal 435 to processor 431. First sensor 425 may be a motor current sensor and may output first signal 427 to processor 431, which is a signal of the current drawn by the pump motor. Second sensor 423 may be a pressure sensor that outputs second signal 435 to processor 431, which is a signal of the pressure within the aorta. Thermistor 424 is located within sheath 452 near the proximal end of pump 400 and measures temperature changes in the blood surrounding the pump and thermistor and outputs a third signal 429 to processor 431 indicative of the temperature change in the blood at the location of the thermistor. In embodiments, a bolus of cold saline is introduced into the vasculature, although other fluids may also be used. A temperature change, measured by the thermistor 424, occurs as the saline bolus flows through the vasculature, changing the temperature of the blood flowing into or out of the heart. The first signal 427 and the second signal 435 are collected in a processor 431 and used to calculate a pump output flow rate 437. A third signal 429, derived from the thermistor 424, is collected in a processor 431 and used to calculate a total cardiac output 439 while the heart is beating or not. For example, the intrinsic cardiac output (CO ) is calculated. NAT The pump output flow 437 is subtracted from the total cardiac output 439 to determine the intrinsic cardiac output 433, which represents the state of the heart while it is beating, such as the total cardiac output 439 (ie, the total cardiac output 439).

[0026] In some embodiments, pump 400 is any suitable lung assist device. In some embodiments, pump 400 is an intracardiac blood pump. Pump 400 includes a motor that pulls blood through pump 400 to provide support for the pumping function of the heart. Pump 400 is connected to an external controller or processor 431 by a catheter. Pump 400 is delivered to a desired location within the heart, such as across the aortic valve, through sheath 452. In some embodiments, first signal 427 includes both a pressure measurement at second sensor 423 on pump 400 and a motor current from first sensor 425. In some embodiments, processor 431 includes a lookup table used to determine pump output flow 437 based on the motor current reported by first signal 427 and the pressure reported by second signal 435.

[0027] Because the fluid bolus injected into the vasculature is cooler than the temperature of the blood, the fluid bolus changes the temperature of the blood. The thermistor 424 may detect the change in blood temperature as the bolus reaches and passes through the thermistor 424. Total cardiac output can be calculated as described with respect to FIG. 1B.

[0028] FIG. 4 shows a perspective view of a percutaneous pump 500 configured to measure blood temperature during use within the heart. The percutaneous pump 500 includes a cannula 520, a pump housing 521, a catheter 534, a distal end 540, a proximal end 541, a distal projection 528, an inflow aperture 538, an outflow aperture 536, and a sensor 523. The catheter 534 is coupled to the pump housing 521 at the proximal end 541 of the percutaneous pump 500. In some embodiments, the percutaneous pump 500 includes a motor. In such cases, the catheter 534 may house electrical wires connecting the pump motor to one or more electrical controllers or sensors. In certain embodiments, the percutaneous pump 500 is driven by a pump having a motor located outside the patient's body (and connected to the pump by a flexible drive shaft). The catheter 534 may also house other components, such as a purge fluid conduit, a guidewire conduit, or other conduits. The pump housing 521 includes one or more outflow apertures 536 configured to expel or drain blood drawn into the cannula 520 out of the percutaneous pump 500. In some embodiments, the percutaneous pump 500 includes one or more sensors disposed on the cannula 520, the pump housing 521, or the catheter 534. For example, one or more pressure sensors 523 may be disposed on the percutaneous pump 500 to sense changes in pressure within the heart. The pressure sensors 523 send signals to a processor (not shown) indicative of pressure measurements within the heart. The pressure measurements may be used by the processor, along with motor current measurements derived from the motor current information, to understand the output of the cardiac assist device or the cardiac assistance being provided to the heart by the percutaneous pump 500.

[0029] 5 shows a perspective view of a transpulmonary thermodilution (TPTD) assembly 603 including a percutaneous pump 600 (e.g., percutaneous pump 500 of FIG. 4 or any suitable percutaneous pump) inserted within a sheath 652 and a first thermistor 624. The percutaneous pump 600 includes a cannula 620, a pump housing 621, a catheter 634, a distal end 640, a proximal end 641, a distal projection 628, an inflow aperture 638, an outflow aperture 636, and a sensor 623. The first thermistor 624 includes a temperature-sensitive head 630. A second thermistor 634 is disposed on the cannula 620. The percutaneous pump 600 and first thermistor 624 are delivered to the patient's heart using the repositionable sheath 652. The sheath 652 includes a first lumen 642 sized to deliver the percutaneous pump 600 and a second lumen 644 sized to deliver the first thermistor 624. In some embodiments, the percutaneous pump 600 may be preloaded into the sheath 652 during manufacturing. As shown, the sheath 652 may be a dual lumen sheath for delivering the percutaneous pump 600 and the first thermistor 624 to the heart. Dual lumen sheaths are described in more detail in co-pending U.S. patent application Ser. No. 14 / 827,741, entitled "Dual Lumen Sheath for Arterial Access," which is incorporated herein by reference.

[0030] The first thermistor 624 is delivered to the heart through a sheath 652 so as to be positioned adjacent to the proximal end 641 of the percutaneous pump 600. In this position, the first thermistor 624 has access to the vasculature through the same sheath as the percutaneous pump 600 so that it can be placed without requiring additional access to the vasculature. Positioning the temperature-sensitive head 630 of the first thermistor 624 near the percutaneous pump 600 enables the first thermistor 624 to detect changes in the temperature of the blood flowing through the aorta and exiting the percutaneous pump 600 at the outflow aperture 636. While the first thermistor 624 is depicted in a position adjacent to the proximal end 641 of the percutaneous pump 600, it will be apparent to those skilled in the art that the first thermistor 624 may be positioned elsewhere in the vasculature, including within the aortic arch or femoral artery.

[0031] As shown, in some embodiments, a second thermistor 643 may be added to the percutaneous pump 600 to derive temperature changes at two locations within the heart and aorta. In some embodiments, the presence of the second thermistor 643 allows for more accurate readings and more precise cardiac output measurements compared to pumps having a single, first thermistor 624. For example, while the first thermistor 624 is depicted within the sheath 652, it may alternatively be embedded within the sheath 652 or within the catheter 634 of the percutaneous pump 600. Similarly, the first thermistor 624 may be disposed within the sheath and the second thermistor 643 may be disposed on the catheter. For example, the second thermistor 643 may be disposed proximate to the outflow aperture 636 to accurately detect the fluid temperature of the blood exiting through the outlet aperture 636. In some embodiments, the sheath 652 is a single-lumen sheath. In some embodiments, the first thermistor 624 is placed in the femoral artery rather than in the ascending aorta. Those skilled in the art will recognize that the percutaneous pump 600 may be designed to include a single thermistor or multiple thermistors.

[0032] In some embodiments, the first thermistor 624 is embedded within the sheath 652 or within the catheter 634 of the percutaneous pump 600, rather than being delivered through the second lumen 644. A thermistor embedded within the sheath 652 or catheter 634 as part of the assembly, rather than being loaded through the second lumen 644, may require less setup and, as a result, the assembly may be easier and less time-consuming to place.

[0033] In some embodiments, the temperature-sensitive head 630 of the thermistor 624 may be formed from a semiconductor material, such as sintered metal oxide, encapsulated in epoxy or glass. The thermistor 624 includes a catheter 645 that connects the thermistor 624 through a sheath 652 to a processor (not shown) located outside the patient's body. The processor records the blood temperature sensed by the temperature-sensitive head 630 of the thermistor 624. A physician or operator may inject a bolus of saline or other fluid into the patient's vasculature to change the blood temperature. The thermistor 624 measures the temperature of the blood as it flows through the heart / aorta, and this measurement may be used to determine total cardiac output using the thermistor 624. A thermistor 624 located on or near the transcutaneous pump 600 may be used to determine total cardiac output while the transcutaneous pump 600 delivers continuous mechanical support to the heart.

[0034] In one example, a bolus of cold saline is introduced into the patient's vasculature, for example, in the femoral vein. The temperature of the blood flowing past the thermistor 624 is then monitored, and temperature changes over time are measured and used to extract variables, including total cardiac output and other variables indicative of cardiac function. These clinically relevant variables may be provided to the physician and operator without shutting down the percutaneous pump support, thereby providing a real-time assessment of intrinsic cardiac output during operation of mechanical circulatory support. In this manner, hemodynamic support can be maintained while important information about cardiac output is obtained. Additionally, the response to pump flow can be assessed instantaneously without moving the patient. Variables calculated from the thermistor and other center measurements may be presented to the physician or operator to enable decisions regarding the patient's care and the amount of cardiac support required. Intrinsic cardiac output may be determined based on variables extracted from the thermistor 624 temperature measurements and information derived from other sensors, including the motor current sensor and pressure sensor on the percutaneous pump.

[0035] The temperature change over time measured by the thermistor 624, as well as measurements from other sensors on the transcutaneous pump 600, are received as input signals by the processor. The processor includes software and / or firmware containing programming that enables the processor to receive and record the input signals and convert them into variables that can be used to calculate intrinsic cardiac output and / or other related variables. Intrinsic cardiac output is calculated using the formula: CO N = CO TOT - CD Flow where CO N is the heart's own cardiac output; CO TOT is the total cardiac output derived from thermistor temperature measurements; CD flowis the flow rate of the cardiac device or percutaneous pump, calculated from the motor current and pressure drawn by the pump motor. A physician or operator may determine that the patient should be weaned from the cardiac assist device or that increased support is required based on the calculated intrinsic cardiac output and other variables that may be calculated by the processor. Using a thermistor to provide these variables to physicians and clinicians increases patient safety during the weaning process.

[0036] Figure 6 shows the placement of the TPTD assembly 603 of Figure 5 within the ascending aorta 710 of a beating heart 701. The heart 701 includes a right atrium 702, a right ventricle 704, and a left ventricle 708, as well as aspects of the pulmonary circulation, including an aortic arch 709, an aorta 710, and an aortic valve 719. The aorta 710 is connected to a femoral artery 712. A percutaneous pump 700 is positioned within the heart 701. The percutaneous pump 700 includes a sheath 752, a cannula 720, a pump housing 721, a catheter 734, a pressure sensor 723, and a distal projection 728. The percutaneous pump 700 extends across the aortic valve 719 so that a distal portion of the cannula 720 of the percutaneous pump 700 is within the left ventricle 708 and a proximal portion of the cannula 720 of the percutaneous pump 700 is within the aorta 710. A thermistor 724 is located at the proximal end of the percutaneous pump 700 within the aorta 710 and may be implanted within the sheath 752 or catheter 734. The pump 700 is coupled to a processor 731, including a display screen 707, located outside the patient's body. The pump housing 721 may house a motor (not shown) and an impeller (not shown). The percutaneous pump 700 may be powered by an implantable motor disposed within the pump housing 721. The impeller and motor draw blood from the left ventricle 708 into a cannula 720, pass it across an aortic valve 719, and eject the blood into the aorta 710. The percutaneous pump 700 also includes a pressure sensor 723 proximate to the pump housing. The percutaneous pump 700 may be positioned over a guidewire or sheath, such as sheath 752. The sheath 752 may be a dual-lumen sheath as illustrated in FIG. 5, or a single-lumen sheath. A catheter 734 extends from the percutaneous pump 700, through the patient's vasculature, and out an incision 716 in the femoral artery 712. In some embodiments, the catheter 734 houses a drive shaft, a purge line, a saline line, or other lines or lumens that extend from outside the patient's body to the percutaneous pump 700.

[0037] By placing a thermistor 724 near the pump housing 721 at the proximal end of the transcutaneous pump 700, changes in temperature of blood moving through the heart can be measured. A signal from the thermistor 724 may be sent to a processor 731 to calculate total cardiac output, including both native cardiac output and that assisted by the transcutaneous pump 700. By using flow estimates derived from measurements of the motor current supplied to the transcutaneous pump 700 and pressure measurements from the pressure sensor 723, native cardiac output and other variables indicative of cardiac function may be rapidly determined and provided to a physician or device operator.

[0038] During use, a physician or device operator may monitor the function of the percutaneous pump 700 on a display screen 707 coupled to the processor 731. The display screen 707 may provide an estimate of the flow rate through the percutaneous pump 700 based on the current drawn from the motor. To provide the physician and operator with additional information regarding the pump and cardiac function, a thermistor 724 is positioned near the pump housing 721, downstream from the saline bolus injection site. This placement of the thermistor relative to the percutaneous pump and saline bolus injection provides consistent and reliable temperature change measurements and thermodilution curves. The thermistor 724 may be implanted within the catheter 734, the sheath 752, or the pump 700. The thermistor 724 is positioned within the aorta 710 to detect the temperature of blood flowing through the percutaneous pump 700. The placement of the thermistor 724 allows for the measurement of total cardiac output or other important hemodynamic parameters during operation of the percutaneous pump 700 using transpulmonary thermodilution. Concurrent with measuring total cardiac output by the thermistor 724, the cardiac assist provided by the percutaneous pump 700 may be measured using the motor current drawn by the pump motor and the pressure measured within the heart to calculate the flow rate through the percutaneous pump 700. This information is useful to a physician or operator in making decisions about the continued care of the patient. The additional information about cardiac function provided by the thermistor 724 used with the percutaneous pump 700 can be helpful in determining whether to wean the patient from the cardiac assist device or to increase the support provided by the device.

[0039] The thermistor 724 has a temperature-sensitive tip that can be used as a sensor to measure the temperature of the surrounding blood. In some embodiments, the thermistor 724 is sized to approximately 38-42 gauge. In some embodiments, the thermistor 724 is threaded into the percutaneous pump 700's catheter 734 after the pump is placed within the heart 701. In some embodiments, the temperature-sensitive tip is placed proximate to the pump housing 721. In some embodiments, the temperature-sensitive tip is placed approximately 3 cm, 4 cm, 5 cm, 6 cm, or any other suitable distance from the pump housing 721. In some embodiments, multiple temperature-sensitive thermistors are placed to determine temperature changes at two locations within the heart and aorta. Placing the thermistor 724 proximate to the pump housing 721 within the ascending aorta 710 allows for measurement of total cardiac output. In some embodiments, the thermistor 724 measures the temperature of the surrounding blood and reports the temperature to an extracorporeal processor 731, which records the temperature as a function of time. In some embodiments, the processor 731 calculates and records intrinsic cardiac output at intervals to track intrinsic cardiac function.

[0040] Measurements from the thermistor 724 and the transcutaneous pump 700 may be displayed to physicians and clinicians in real time on the display 707. Additionally, historical data may be recorded for individual patients so that time-dependent measurements can be compared and displayed longitudinally. This information may enable physicians and clinicians to make decisions regarding adjustments to cardiac assist device support or weaning the patient from the cardiac assist device. The interface or display 707 may also indicate whether the patient is improving or declining over time, as indicated by an increase or decrease in intrinsic cardiac output. This information may be provided to physicians and clinicians without disconnecting the heart from the cardiac assist device.

[0041] 7 shows an exemplary controller screen 807 displaying total cardiac output and other cardiac variables. The exemplary controller screen 807 displays a placement signal 846, a motor current signal 827, a total cardiac output 829, an intrinsic cardiac output 830, a continuous intrinsic cardiac output 833, an intrinsic cardiac trend 841, an extravascular lung water measurement 866, a total end-diastolic volume measurement 868, a flow status indicator 854, a purge system indicator 852, a system power indicator 850, an alarm button 856, a flow control button 858, a display button 860, a purge system button 862, and a menu button 864.

[0042] The placement signal 846 displays a blood pressure measurement. The placement signal 846 displays blood pressure over time, and the displayed measurement may be derived from a sensor on the intravascular pump (such as intravascular pump 500 of FIG. 4, intravascular pump 600 of FIG. 5, or intravascular pump 700 of FIG. 6) while the pump is running. The placement signal 846 may be used by a physician to determine the placement of the pump within the heart by monitoring the measured pressure to determine when the pump is in proper placement within the heart. The motor current signal 827 displays a measurement over time of the current drawn by the pump motor in mA. The motor current signal 827 may display a measurement measured by a sensor on the pump motor within the pump or within the processor or controller itself. The placement signal 846 and the motor current signal 827 may be used along with the pressure measurement to calculate the flow rate of the intravascular pump by accessing a lookup table based on the motor current and the intracardiac pressure. The flow rate provides a measure of the mechanical assist provided to the heart by the intravascular pump, or the pump output flow rate.

[0043] Total cardiac output 829 displays a measure of the total cardiac output resulting from the heart's natural beating and mechanical assistance, as measured by intracardiac thermodilution. Total cardiac output is measured by a thermistor that detects changes in blood temperature within the heart in response to a bolus of saline injected into the vasculature. Based on the detected changes in blood temperature over time, total cardiac output is calculated. Total cardiac output is displayed in L / min. Spontaneous cardiac output 830 can be calculated by subtracting the pump output flow rate from total cardiac output 829. Total intrinsic cardiac output, displayed in L / min, provides the operator with information about the output provided by the heart itself. This can be useful in making therapeutic decisions, especially regarding weaning the patient from cardiac assist devices such as an intravascular pump. Continuous intrinsic cardiac output 833 displays the calculated intrinsic cardiac output for multiple intervals to provide the operator with historical data. Intrinsic cardiac trend 841 additionally provides the operator with a quick overview of cardiac function based on historical data of continuous cardiac output 833. For example, on the controller screen 807, the most recent intrinsic cardiac output (CO ) reported in the list of continuous intrinsic cardiac output 833 can be displayed. NAT3 ) is the previous recorded intrinsic cardiac output (CO NAT2 and CO NAT1 ), indicating that the cardiac intrinsic output is now increasing. Therefore, intrinsic cardiac trend 841 displays a status of "improving." In some embodiments, controller screen 807 includes entries for greater or lesser values ​​in the display of continuous intrinsic cardiac output 833. In some embodiments, additional recorded entries are accessed on additional screens of the controller screen. Presenting the operator with a history of intrinsic cardiac output allows the operator to understand trends in the patient's cardiac function and health. This information can be useful in determining whether to increase or decrease cardiac support.

[0044] Additional cardiac measurements may be reported on the control screen 807 to provide the operator with additional clinically relevant information. For example, extravascular lung water measurement 866 and total end-diastolic volume measurement 868 are displayed on the control screen 807. EVLW and GEDV can be calculated from intrinsic cardiac output, as discussed with respect to FIG. 2 . Other hemodynamic measurements may also be calculated from the placement signal 846, motor current signal 827, and total cardiac output 829 and displayed on one or more screens of the control screen 807. The control screen 807 also includes a flow status indicator 854 that displays the current flow rate of the intravascular pump, as well as the maximum and minimum flow rates reached during the current operating session. A purge system indicator 852 displays the current status of the purge flow system, including the current flow rate of the purge fluid. A system power indicator 850 displays the charge status of the internal backup battery and whether the battery is charging and / or plugged in. The control screen 807 includes a series of buttons that allow the operator to access additional screens for controlling the pump and purge system, such as a purge system button 862 and a flow control button 858. An alarm button 856 may allow the operator to set or turn off an alarm, or may emit a sound or light if a measurement goes above or below a preset limit. A display button 860 allows the operator to access additional display screens, and a menu button 864 allows the operator to access a menu.

[0045] Control screen 807 may include additional or different information displays, buttons, and status indicators. Control screen 807 is provided as a non-limiting example of a control screen that may be used in connection with the systems of FIGS. 5 and 6.

[0046] FIG. 8 shows a method 900 for determining intrinsic cardiac output using the setup of FIG. 5 according to one exemplary embodiment. In step 902, an intravascular blood pump, such as intravascular blood pump 500 of FIG. 4, intravascular blood pump 600 of FIG. 5, intravascular blood pump 700 of FIG. 6, or any other suitable intravascular blood pump, is placed in the aorta (e.g., as shown in FIG. 6). The intravascular blood pump may be delivered with the use of a guidewire and / or a repositionable catheter. The placement of the intravascular blood pump may be monitored by the use of fluoroscopy, by monitoring the pressure around the pump within the heart, or by any other suitable means. The intravascular blood pump is placed in the aorta so that the inflow aperture is located in the left ventricle and the outflow aperture is located in the aorta. In some embodiments, the intravascular blood pump is placed across the aortic valve.

[0047] In step 904, the intravascular blood pump is driven by a motor current to pump blood from the left ventricle into the ascending aorta. The intravascular blood pump draws blood into the pump through an inflow aperture located in the left ventricle and ejects the blood through an outflow aperture into the ascending aorta to support the heart's native function. The ejected blood is carried into the blood flowing through the aorta.

[0048] A precise volume bolus of saline is injected into the vasculature at a location upstream from the location of the intravascular pump (e.g., in the femoral vein) in step 906. The saline bolus is cooler than the blood in the vasculature and causes a change in the temperature of the blood flowing through the vasculature into the left ventricle and into the aorta.

[0049] In step 908, a change in temperature of the blood being pumped from the left ventricle into the ascending aorta is detected. The change in blood temperature is detected by a sensor or thermistor located at the proximal end of the intravascular pump. As the saline bolus passes through the vasculature and through the heart, the thermistor detects the temperature of the blood flowing through it. As blood is pumped from the left ventricle into the ascending aorta with the aid of the intrinsic heart function and the pump, the thermistor detects the change in temperature and sends an analog signal indicative of the change to the processor.

[0050] At step 910, a change in motor current supplied to the pump while it is running is detected. The motor current may be detected by a sensor located in the pump motor or external to the pump. At step 912, the pressure in the ascending aorta is detected while the pump is running. The blood pressure in the aorta is detected by a pressure sensor on the pump. The detected motor current and the detected pressure are also output to the processor.

[0051] In step 914, a first cardiac output is calculated based on the detected temperature change. The temperature change detected by the thermistor is used to calculate total cardiac output, as described with respect to FIGS. 1B and 5. In some embodiments, step 914 may occur immediately after the temperature change detected by the thermistor is transmitted to the processor, such as immediately after step 908. In step 916, a pump flow rate is calculated based on the detected motor current and the detected pressure. The processor accesses a lookup table that provides a flow rate for a given motor current and detected pressure. The flow rate determined from the lookup table is the pump output flow rate of the intravascular pump and indicates the amount of assistance being provided to the heart by the pump. In step 918, the pump flow rate is subtracted from the first cardiac output to determine intrinsic cardiac output. The intrinsic cardiac output indicates the stroke volume and pumping power being provided by the patient's own heart. The intrinsic cardiac output may be used by a physician or pump operator to make therapeutic decisions such as increasing or decreasing the assistance provided by the intravascular pump or weaning the patient from pump assistance. Steps 914, 916, and 918 occur within a processor coupled to the pump.

[0052] The intrinsic cardiac output and other variables calculated from the first cardiac output and pump flow rate may, in some embodiments, be displayed to a physician or pump operator, such as on a display such as that depicted in FIG. 7. Providing these variables to a physician allows the physician to make informed decisions about the patient's care. From these variables, the physician can derive more knowledge and understanding about the patient's cardiac condition, which enhances patient safety, especially when weaning the patient from an intravascular pump.

[0053] Figure 9 shows cardiac output measured by the Impella thermodilution catheter compared to the reference cardiac output measurement. All measurements were performed in triplicate; individual measurements are indicated by circles (o) and the average of each triplicate measurement is indicated by crosses (x). The solid black line indicates the theoretical perfect agreement, while the dashed-dotted line indicates the linear regression of all measurement points. The dashed lines indicate the upper and lower 10% error bounds. As can be seen in Figure 9, the Impella system demonstrated good agreement across the entire range of measured cardiac output.

[0054] Figure 10 shows the percentage error of the Impella thermistor system observed in sequential experiments. Black dots represent the error for each triplicate measurement. The data is presented in experimental order. As can be seen, the calculated error was consistent throughout the sequential experiments.

[0055] Figures 11A and 11B show results obtained using the Impella Thermistor System during low cardiac output. Figure 11A shows the raw data trace of temperature change measured using the Impella Thermistor System during low cardiac output. The open circles indicate the time of injection of 4°C saline. The dotted lines indicate the time limits of the mean transit time. The portion of the curve bounded by asterisks indicates the portion of the curve used to measure downslope time. Figure 11B shows the measured and calculated variables derived from the thermodilution curve shown in Figure 11A.

[0056] Figures 12A and 12B show results obtained using the Impella Thermistor System during high cardiac output. Figure 11A shows the raw data trace of temperature change measured using the Impella Thermistor System during high cardiac output. The open circles indicate the injection of 4°C saline. The dotted lines indicate the time limits for mean transit time. The portion of the curve bounded by asterisks indicates the portion of the curve used to measure downslope time. Figure 12B shows the measured and calculated variables derived from the thermodilution curve shown in Figure 12A.

[0057] FIG. 13 illustrates the thermistor placed within the Impella catheter and its relative position to the component parts of the Impella pump.

[0058] The foregoing is merely illustrative of the principles of the present disclosure, and the methods and systems of the present invention may be practiced in other than the described embodiments, which are presented for purposes of illustration and not limitation. It should be understood that the methods and systems disclosed herein, although illustrated for use in an intravascular blood pump system, may also be applied to other cardiac assist devices.

[0059] Variations and modifications will occur to those skilled in the art after reviewing this disclosure. For example, the placement of the thermistors relative to the blood pump, sheath, and catheter of a blood pump system may be arranged in any suitable manner so that the thermistors are configured to detect changes in blood temperature within a patient's heart. The features of the present disclosure may be implemented in any combination and subcombination (including multiple subsidiary combinations and subcombinations) with one or more other features described herein. The various features described or illustrated above, including components thereof, may be combined or integrated into other systems. Additionally, certain features may be omitted or not implemented.

[0060] Examples of modifications, substitutions, and alternatives are ascertainable by one skilled in the art and could be made without departing from the scope of the information disclosed herein.

Claims

1. A method of operating an intracardiac blood pump system having an intracardiac blood pump, a thermistor, a first sensor, a second sensor, and a processor, comprising: the thermistor detecting a change in temperature of blood being pumped by the intracardiac blood pump from the left ventricle into the ascending aorta, the intracardiac blood pump being driven by a motor current to cause a motor of the intracardiac blood pump to pump blood from the left ventricle into the patient's ascending aorta; detecting a change in motor current with the first sensor during operation of the intracardiac blood pump; detecting pressure in the ascending aorta with the second sensor; the processor calculating a total cardiac output based on the detected change in temperature, the total cardiac output including (a) cardiac assist provided by the intracardiac blood pump and (b) native cardiac output of the beating heart; the processor calculating a pump output flow rate based on the change in motor current detected by the first sensor and the pressure detected by the second sensor, the calculated pump output flow rate being indicative of the cardiac assist provided by the intracardiac blood pump; and while the intracardiac blood pump is operating, the processor calculating the intrinsic cardiac output of the beating heart based on the pump output flow rate and the total cardiac output. A method comprising:

2. The method of claim 1 , wherein the detected change in temperature indicates a change in temperature of blood flowing into the heart.

3. 2. The method of claim 1, wherein the step of calculating the intrinsic cardiac output includes the processor subtracting the pump output flow from the total cardiac output.

4. 2. The method of claim 1, further comprising the processor calculating at least one of total end-diastolic volume, intrathoracic blood volume, intrathoracic heat volume, pulmonary heat volume, cardiac index, stroke volume, extravascular lung water, cardiac output, and total ventricular ejection fraction from the detected change in temperature, the detected change in motor current, and the detected pressure.

5. The method of claim 1 , further comprising the processor displaying the intrinsic cardiac output on a screen of the intracardiac blood pump system.

6. the processor preserving the intrinsic cardiac output; and the processor displaying the history of the intrinsic cardiac output as a function of time on a screen of the intracardiac blood pump system. The method of claim 1 further comprising:

7. 7. The method of claim 6, further comprising the processor determining, based on a history of the intrinsic cardiac output, whether the intrinsic cardiac output is improving over time.

8. 8. The method of claim 7, further comprising the processor displaying on the screen a status indicating whether the intrinsic cardiac output is improving over time.

9. 2. The method of claim 1, wherein the step of calculating the pump output flow rate includes the processor accessing a look-up table that provides a flow rate that is the pump output flow rate for a given motor current and sensed pressure.

Images