Calibration method and apparatus, and its application to blood flow estimation in intravascular blood pumps.

Abstract

The present invention provides a method and apparatus for estimating blood flow in an intravascular blood pump. [Solution] A method and apparatus for estimating blood flow in an intravascular blood pump includes the step of extracting reference data from a set of reference data acquired in a test environment. The set of reference data includes both the reference motor current (I) of the motor driving the blood pump and the amount of blood flow passing through the blood pump for at least one motor speed under different pump loads, including a first pump load. After the blood pump is installed in the patient's body, a motor current deviation value (ΔI) is calculated from the reference motor current and the patient-specific motor current under the first pump load. Finally, the amount of patient-specific blood flow (FL) passing through the blood pump is estimated using the motor current deviation value ΔI.

Description

Technical Field

[0001] The present invention relates to a calibration method and apparatus and its application to estimating blood flow in an intravascular blood pump. The present invention further relates to a computer program product programmed to execute the above method.

Background Art

[0002] An intravascular blood pump is used to assist the function of a patient's heart as either a left ventricular assist device (LVAD) or a right ventricular assist device (RVAD). The intravascular blood pump according to the present invention typically includes a catheter that is percutaneously inserted into the patient's heart, for example, through the aorta into the left ventricle or through the vena cava into the right ventricle, and a pumping device attached to the catheter. The catheter may have an elongated body with a proximal portion and a distal portion, be extendable along its longitudinal axis, and the pumping device is attached to the catheter at the distal portion remote from an operator such as a surgeon. The pumping device typically includes a pump section having a blood flow inlet and a blood flow outlet. Typically, an impeller or a rotor is rotatably supported around a rotating shaft that conveys blood within the pump housing to create blood flow from the blood flow inlet (e.g., in the left ventricle) to the blood flow outlet (e.g., in the aorta). The blood pump may be driven by a motor included in the pumping device adjacent to the pump section or alternatively by a motor outside the patient's body. In the latter case, the motor is connected to the impeller or rotor by a flexible drive shaft, i.e., a drive cable that extends through the catheter, and is referred to herein as a cable-driven blood pump.

[0003] Estimating the blood flow through the blood pump and providing data to medical staff is important, from which the medical staff can draw specific conclusions regarding the operation of the system and / or the patient's condition. In particular, it is important for the medical staff to confirm that the blood pump is always delivering the blood flow necessary to adequately assist or replace the heart function.

[0004] Typically, a blood pump operates at a selected motor speed, i.e., the impeller or rotor is driven at a predetermined number of revolutions per minute. The motor speed, i.e., revolutions per minute, can be changed as needed. At a given motor speed, the blood flow through the blood pump depends on the pressure difference that the blood pump must overcome. Hereafter, the pressure difference will also be referred to as the "pump load." Therefore, while maximum blood flow occurs when there is no pressure difference, when the pressure difference is high, for example, when the ventricles begin to fill with blood during diastole and the blood pump is pumping blood from the low-pressure ventricles into the high-pressure aorta, blood flow may be zero or even occur, with blood flowing back through the pump. If the total pump flow over a single cardiac cycle is less than the desired blood flow, the motor speed is increased accordingly until the desired blood flow is reached. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] U.S. Patent No. 7,010,954B2 [Overview of the project] [Problems that the invention aims to solve]

[0006] To estimate blood flow, US7,010,954B2 proposes providing the blood pump with a reference table or graph showing blood flow versus pump load at specific motor speeds. Such reference tables or graphs are provided for each motor speed. In this way, when using a first pressure sensor located in the aorta and a second pressure sensor located in the left ventricle, the current blood flow passing through the blood pump can be determined from the measured blood pressure difference by referring to the reference table or graph for the specific motor speed at which the blood pump is driven.

[0007] It has been found that the pump load, that is, the pressure difference that the blood pump must overcome, affects not only the blood flow but also, to some extent, the motor current required to maintain a given motor speed at a set point in order to keep the impeller or rotor rotations per minute constant, independently of the pump load.

[0008] Therefore, it is possible to create a reference table or graph showing the correlation between blood flow and motor current for each motor speed. Accordingly, according to the present invention, motor current is monitored rather than ventricular and aortic pressure.

[0009] Data used in reference tables or graphs, such as motor current and blood flow, can be recorded within the test bench assembly by operating the pump in a liquid under a given motor speed and a predetermined pump load while recording the flow generated by the pump. The pump load can be increased over time while recording the motor current and blood flow, for example, from zero load (no pressure difference between the blood flow inlet and outlet, i.e., maximum blood flow) to maximum load (no pump function, i.e., no flow). Such reference tables or graphs can be created for several different motor speeds. As described above, the motor current changes slightly as the pump load and flow change. Since the motor current, blood flow, pump load, and motor speed are measured and recorded in the test bench while performing the above procedure, the blood flow under a given motor speed and pump load can be determined based on the motor current.

[0010] Depending on the design of the blood pump and some losses, the motor current may increase or decrease as the flow increases or the pump load decreases. For example, in a particular blood pump, if the pump load increases, the motor current will increase, or in other words, an increase in motor current indicates a decrease in blood flow. In contrast, in other blood pumps, if the pump load increases, the motor current may decrease, or in other words, an increase in motor current may indicate an increase in blood flow through the pump.

[0011] When a blood pump is implanted in a patient's body, almost always unexpected losses occur. Several parameters, such as motor parameters and pump parameters, can affect the relationship between motor current and blood flow. The viscosity of the blood passing through the pump and / or the purge fluid administered into the patient's blood via the catheter can also have an effect. Furthermore, frictional losses, particularly the friction of the flexible drive shaft within the catheter of a cable-driven blood pump, can have an effect, and such friction can fluctuate depending on the curvature of the catheter as it passes through the patient's vascular system. Therefore, once a blood pump is implanted in a patient's body, it is impossible to reliably determine blood flow based on motor current measured at a given motor speed. [Means for solving the problem]

[0012] Therefore, a particular object of the present invention is to provide a method and apparatus for estimating blood flow in an intravascular blood pump to assist medical staff in monitoring blood flow when operating an intravascular blood pump in a patient's body. A further object of the present invention is to provide each computer program product programmed to operate the corresponding apparatus by performing this method.

[0013] The above-mentioned objectives are resolved by the features of the independent claim. Preferred embodiments of the present invention are described in the dependent claims.

[0014] Therefore, a method used for estimating blood flow in an intravascular blood pump, -(a) Extracting reference data obtained in a test environment, which includes both the reference motor current of the motor driving the blood pump and the amount of blood flow through the blood pump for at least one motor speed under different pump loads, including a first pump load; -(b) After the pump has been placed in the patient's body, the step of measuring the patient-specific motor current for at least one motor speed under the first pump load, -(c) Subsequently, the steps of calculating the motor current deviation value from the reference motor current under the first pump load and the patient-specific motor current for at least one motor speed under the first pump load, -(d) Finally, we propose a method that includes the step of applying a motor current deviation value to estimate the patient-specific blood flow rate passing through the blood pump.

[0015] "Motor speed," "speed level," or "motor speed level" refers to the rotational speed of the motor, which is correlated with the rotational speed of the pump's rotor or impeller and can be specified, for example, in revolutions per minute.

[0016] "Pump load" is defined as the pressure difference of the liquid that must be overcome when pumping the liquid through the pump. In other words, "pump load" can be understood as the pressure difference between the blood inlet and blood outlet of the pump. Therefore, as mentioned above, when the pump is operating at a given motor speed, the flow is maximum under zero pump load and zero under maximum pump load.

[0017] "Liquid flow," "blood flow," "flow," and "blood volume" refer to the volume of liquid or blood transported per unit time, for example, via a pumping device. Therefore, flow can be measured in liters per minute.

[0018] "Reference data," such as reference motor current, refers to data obtained within the test environment. Therefore, in order to estimate the blood flow passing through the pump installed in the patient's body, reference data is extracted, for example, as a reference table or graph previously obtained within the test environment.

[0019] The test environment can simulate human blood vessels or organs, and therefore can accurately simulate the operation of the blood pump within the human body in order to keep deviation values ​​such as motor current deviation values ​​low during the operation of the blood pump within the human body.

[0020] The present invention is particularly suitable for cable-driven intravascular blood pumps. Losses due to cable friction within the catheter increase depending on the number of bends and the sharpness of the bends, which can vary from patient to patient. Therefore, the deviation between the reference motor current measured in a test environment and the corresponding specific motor current that occurs during actual use can vary from patient to patient, especially in cable-driven blood pumps.

[0021] The aforementioned reference data includes the reference motor current of the motor driving the pump and the amount of fluid flow produced by a specific reference motor current at a given motor speed. The reason for acquiring this data for different pump loads is, as mentioned above, that the motor current is adjusted in response to changes in pump load in order to maintain a given motor speed, and furthermore, the fluid flow passing through a steadily driven pump changes in response to changes in pump load. Reference data acquired for a given motor speed, showing the correlation between fluid flow and motor current, is advantageously presented as a reference table or graph. As mentioned above, depending on the design of the blood pump, the motor current may increase or decrease in response to an increase in blood flow rate or a decrease in pump load.

[0022] Such a graph or look-up table may be created for a plurality of motor speeds, for example 2, 3, 4, 5, 6, 7, 8, 9, 10 or more motor speeds. Pairs of motor current values and fluid flow values for other motor speeds may be interpolated based on pairs of motor current values and fluid flow values for the next higher and next lower motor speeds for which reference data is available. In either case, the pairs of motor current values and fluid flow values obtained under different pump loads for each given motor speed include at least a first pair of motor current values and fluid flow values for a particular “first” pump load. This is important in the next step in which, after a blood pump is installed in a patient, patient-specific motor currents are measured for each motor speed under the first pump load. The two motor currents, i.e., the reference motor current and the patient-specific motor current, are comparable to each other because they are obtained at the same motor speed under the same pump load, i.e., the first pump load. Thus, a motor current deviation value can be calculated from the reference motor current and the patient-specific motor current for the motor speed under the particular first pump load, and the same process may be carried out for other pump loads and other motor speeds. These motor current deviation values may then be used in a further process to estimate the patient-specific blood flow rate through the blood pump.

[0023] For example, motor current deviation values can be used to create a set of patient-specific reference data based on the original set of reference data. As described above, the original set of reference data shows the dependence of motor current and fluid flow on different motor speeds in a test environment, for example in the form of a graph or look-up table. The motor current deviation values can be applied to all reference motor current values to estimate the blood flow through a blood pump implanted in a patient.

[0024] When applying the calculated motor current deviation value to the original set of reference data, the calculated motor current deviation value can be used to shift the correspondence diagram in the graph or reference table by simply adding it to the original reference motor current for all fluid flows and all motor speeds, so that the fluid flow in the patient-specific set of reference data represents the actual blood flow passing through the blood pump installed within the patient.

[0025] It may be assumed that the motor current deviation value for one first pump load at one first motor speed is approximately the same for all pump loads at the first motor speed at which the deviation value was calculated. Consequently, one motor current deviation value can be calculated for each motor speed and added, most preferably to all of the reference motor currents in the set of original reference data for that particular motor speed, to determine a complete patient-specific graph or reference table for that motor speed.

[0026] Furthermore, the same (single) motor current deviation value calculated for a particular motor current can also be added to the reference motor currents in the set of original reference data for a motor speed different from the particular motor speed at which the value was calculated, so that only one motor current deviation value needs to be calculated overall.

[0027] However, more preferably, a single motor current deviation value is calculated individually for each motor speed for which the reference data is available in the set of reference data, because the motor current deviation values can vary significantly between different motor speeds in some blood pumps.

[0028] Alternatively, instead of constructing patient-specific sets of reference data, one or more single motor current deviation values ​​can be stored as described above and derived from any patient-specific motor current measured during blood pump use within the patient's body. In this case as well, if one (single) motor current deviation value is applied to all referenced motor speeds, patient-specific blood flow rates for each motor speed can be obtained and provided to the medical staff.

[0029] Most importantly, it is crucial to identify a suitable "first" pump load from which to measure the patient-specific motor current, since it is important to correlate the patient-specific motor current with the corresponding reference motor current under the same "first" pump load.

[0030] Since it is generally possible to identify specific moments in the cardiac cycle with the assistance of pressure sensors and / or EKG, the timing of patient-specific motor currents measured at a given motor speed can be correlated with the corresponding reference motor currents in a set of reference data.

[0031] However, according to a particularly preferred embodiment of the present invention, the patient-specific motor current that determines the motor current deviation value is measured under a pump load that is clearly identifiable by the motor current value, so no additional sensors are required. More specifically, the following points should be considered. At a given motor speed, the maximum blood flow rate passing through the pump occurs at the minimum load, or in other words, when the pressure difference between the blood inlet and blood outlet is zero, i.e., when the heart valves are open. As will be described later, a preferred pump load is shown in which the patient-specific motor current that determines the motor current deviation value is measured with the heart valves open.

[0032] More specifically, in a preferred embodiment, the blood pump is positioned in the patient's vascular system such that the blood inlet is located in the ventricle, e.g., the left ventricle, and the blood outlet is located in the patient's blood vessel, e.g., the aorta, and the ventricle and blood vessel are separated by a natural valve, e.g., the aortic valve. For example, if the valve is open during systole, the blood inlet and outlet are not separated by pressure, and therefore the pressure difference between them is zero. At this point, when the pressure difference between the blood inlet and outlet is zero, the blood flow through the pump is at its maximum level at the selected motor speed, and the motor current at that motor speed level reaches either the maximum or minimum. Therefore, the maximum blood flow rate for a given motor speed occurs with either the minimum or maximum motor current, depending on the design of the blood pump. Thus, depending on the design of the blood pump, either the maximum motor current or the minimum motor current can be interpreted as indicating an open heart valve state, which, as described above, indicates a suitable pump load for measuring the patient-specific motor current to determine the motor current deviation value.

[0033] From the set of reference data, it is clear whether the open state of the heart valves (i.e., maximum blood flow from the blood pump) can be identified by the maximum or minimum motor current value, i.e., according to the slope of the flow curve in the reference table or graph. In other words: if the slope of the flow curve is negative, the minimum motor current indicates the open state of the heart valves, such as the aortic valve, and maximum blood flow; if the slope of the flow curve is positive, the maximum motor current indicates the open state of the heart valves, such as the aortic valve, and maximum blood flow.

[0034] Therefore, the "first pump load" at which the patient-specific motor current is measured is preferably the pump load when the heart valve, for example, the aortic valve, is open.

[0035] Therefore, the step of measuring the patient-specific motor current for at least one motor speed under the first pump load preferably includes the step of measuring the maximum or minimum patient-specific motor current for a particular motor speed.

[0036] The efficiency of the pump may be further affected by parameter changes due to various largely unknown reasons while the pump is inside the patient's body. Therefore, it is preferable to repeat the above method in the sense of recalculating the actual motor current deviation value after some time has passed, in addition to the previously calculated patient-specific motor current deviation value. In other words, if the motor current deviation value changes over time compared to the previously calculated motor current deviation value, the previously calculated motor current deviation value should be replaced with the actual motor current deviation value.

[0037] For example, the actual patient-specific motor current can be measured for at least one motor speed, and the deviation from the previously measured patient-specific motor current, which was stored as the updated reference motor current, can be calculated. Thus, the previously measured patient-specific motor current or the previously updated reference motor current can be updated (further) to more closely approximate the actual patient-specific motor current.

[0038] Preferably, each subsequent iteration occurs at a predetermined time interval. The advantage of this is that, when the blood pump operates for a longer period, the motor current can be adjusted so that a specific amount of blood flow is maintained even if certain characteristics of the blood, patient, purge fluid, or system change. For example, such time intervals may be specified in seconds, minutes, hours, or days. Each time interval may be set by the medical staff.

[0039] Additionally or alternatively, the following iterations may occur due to changes in at least one influencing feature, such as motor current, temperature, or viscosity changes of the blood and / or purge fluid, or physical properties of the blood pump, such as the motor temperature of the blood pump. The calculation of the motor current deviation value may be repeated whenever a significant change in one or more of these features is observed.

[0040] Regarding the extraction of reference data in a test environment, this is preferably performed using a specific type of blood pump and fluid, the fluid not necessarily having to be blood. In either case, the fluid is preferably selected to have flow behavior equivalent to that of blood flow. Similarly, it is preferable that the temperature of the fluid matches that of the patient's blood. These measures help improve the accuracy of the reference data and its comparability with the measured patient-specific data.

[0041] According to one particular embodiment, the liquid used in the test environment contains water and glycerol in a mixture ratio that results in a viscosity equal to that of blood at human body temperature. This offers the advantage of being able to directly manufacture the test solution.

[0042] It is even more preferable that the blood pump set up in the test environment simulates the curve of a catheter within the human vascular system. In other words, it is preferable that the catheter guiding the blood pump is set up to match the curvature of the test bench, corresponding to the placement of a blood pump within the human vascular system.

[0043] The advantage of this method is that it provides steps of the method that can be similarly implemented as structural features in each device used for blood flow estimation. Such devices have structural features that implement the corresponding steps of the method described above. Thus, the features referred to in this method and device can be used interchangeably so that the device performs the proposed method and the proposed method operates the device. Furthermore, a computer program product can implement this method and operate the device when executed, for example, on a computer. [Brief explanation of the drawing]

[0044] Further advantages are shown in the attached drawings. [Figure 1] This diagram shows the intravascular blood pump located in the left ventricle of the heart. [Figure 2] This figure shows a graph illustrating the relationship between motor current and fluid flow in a test environment passing through one exemplary pump for nine different sets of motor speeds. [Figure 3] Figure 2 additionally shows two exemplary motor current deviation values ​​ΔI at the maximum blood flow passing through the pump for two different motor speeds. [Figure 4] This figure shows the change over time of the motor current I over multiple cardiac cycles at different left ventricular pump speeds N. [Figure 5] This is a flowchart illustrating a method used to estimate blood flow through intravascular blood pumps. [Modes for carrying out the invention] [Examples]

[0045] Figure 1 shows a human heart 10 into which an intravascular blood pump is inserted through the aorta 11, crossing the aortic valve 20. The intravascular blood pump includes a catheter 12 and a pumping device 13 attached to the distal end of the catheter 12. The pumping device includes a pump section 14 and a cannula 15 having an inlet opening 16 and an outlet opening 17, and further having a pigtail-shaped soft, flexible tip 19 that keeps the pumping device 13 away from the heart wall to prevent the inlet opening 16 from being sucked into the heart wall. An impeller or rotor rotates within the pump section 14 to transport blood from the inlet opening 16 through the outlet opening 17. The pumping device 13 may further include a drive unit in a single housing together with the pump section 14 to drive the impeller or rotor. However, in the embodiment shown in Figure 1, the pumping device is driven by a flexible cable 18 that is routed through the catheter 12. Instead of the pump shown in Figure 1, other intravascular blood pumps with a significantly larger diameter after expansion compared to the pump section 14 shown in Figure 1, such as expandable blood pumps, may be used.

[0046] Clearly, losses such as surface friction occur within the catheter 12 during the operation of the drive cable 18. The amount of loss also depends on the number of bends and the bending radius, and may vary from patient to patient, or even in the same patient if the blood pump is repositioned or moved within the patient's vascular system over time. Therefore, the energy required to drive the impeller at a given rotational speed within the pump unit 14 may vary depending on the individual circumstances.

[0047] Figure 2 shows graphs P1-P9 of blood flow FL passing through the pump for nine different motor speeds N1-N9 with respect to motor current I (motor speed N is related to the rotational speed of the impeller). As mentioned above, the higher the pressure difference that the blood pump must overcome, the lower the blood flow FL passing through the pump. As can be seen from Figure 2, the motor current I is not constant for each motor speed N, but changes as the amount of blood flow FL passing through the pump changes. In the specific example shown in Figure 2, the data was actually recorded from an expandable cable-driven blood pump. In this case, the motor current I decreases as the blood flow FL passing through the pump increases. In other blood pumps, especially non-expandable blood pumps, it has been found that the motor current I increases as the blood flow FL increases.

[0048] The individual measurement points in graphs P1-P9 were obtained by measuring both the blood flow FL and motor current I passing through the pump under different pump loads in the test environment. The test environment was designed to closely resemble conditions within the human body as much as possible. For example, the fluid in the test environment was selected to have flow behavior equivalent to that of blood flow. Furthermore, the temperature was equal to that of a patient's blood, e.g., 36-37°C. In addition, the fluid in the test environment contained water and glycerol in a mixture ratio that resulted in a viscosity equivalent to that of blood. The bending and curvature of the catheter were also approximated to follow the average human vascular system.

[0049] However, as suggested herein, since blood flow FL is estimated based on motor current I rather than any pressure signal, graphs P1-P9 for different motor speeds N1-N9 need to be adjusted for each individual patient, because deviations in the patient-specific motor current used by the blood pump in the patient's heart compared to the reference motor current I of the corresponding set of reference data can lead to misinterpretations, as will be further explained with reference to Figure 2.

[0050] As shown in Figure 2, when the blood pump is driven at motor speed P9, the blood flow FL is approximately 5.2 lL / min due to the pressure difference to be overcome (slightly below the maximum blood flow FL of approximately 6.5 lL / min). In this situation, if the patient-specific motor current deviates from the reference motor current I9 by a positive motor current deviation value ΔI9, medical staff may incorrectly conclude from the set of reference data that the blood flow FL is only approximately 1.8 lL / min. Alternatively, in the same situation, if the patient-specific motor current deviates from the reference motor current I9 by a negative motor current deviation value -ΔI9 (not shown in Figure 2), medical staff may not find any corresponding reference motor current, or the flow estimation system may send an error signal.

[0051] Therefore, to avoid such misunderstandings, medical staff can draw conclusions about correct blood flow by generating a reference table or graph that includes patient-specific motor current values ​​for medical staff to refer to. Thus, after the blood pump is installed in the patient's body, the patient-specific motor current can be measured for each operating point of the pump, i.e., for motor speed N9 at a specific pump load (and similarly for all other motor speeds), and the corresponding motor current deviation value ΔI9 can be calculated as the difference between the reference motor current I9 and the patient-specific motor current measured for these specific pump loads.

[0052] However, as described above and further explained with reference to Figure 3, the motor current deviation value ΔI is calculated for only one specific "first" pump load and added to all reference motor currents for a given motor speed N in the set of reference data. This "first" pump load preferably corresponds to the minimum pump load state within the cardiac cycle, i.e., the open state of the heart valves. This is because such a state can be easily detected based solely on the measured motor current I, i.e., when the motor current I is either maximum or minimum. However, for completeness, if the pressure sensor and / or EKG are in place, any other arbitrary pump load may also be used as the specific "first" pump load from which the motor current deviation value ΔI is determined.

[0053] In either case, a new or updated set of reference data can be generated by adding the calculated motor current deviation value ΔI to the corresponding reference motor current. This can be done for all pump loads for which a reference motor current is available in the reference data set in order to obtain a complete patient-specific set of reference data for motor speed N. Furthermore, this procedure can be performed individually for each motor speed N1 to N9.

[0054] Furthermore, assuming that the motor current deviation value ΔI9 obtained at motor speed N9 is approximately identical to the motor current deviation values ​​ΔI1...ΔI8 for all other motor speeds N1~N8, the motor current deviation value ΔI9 can be similarly applied to each set of reference data for motor speeds N1~N9.

[0055] Alternatively, instead of creating a new or updated set of reference data, each motor current deviation value ΔI or ΔI1 to ΔI9 can be stored and derived from the motor current measured when the pump is placed in the patient's vascular system, so that the measured motor current can be compared to a previously stored set of reference data.

[0056] Most realistically, as illustrated in Figure 3, single motor current deviations ΔI7 and ΔI9 are measured when the heart valve, such as the aortic valve, is open when the blood pump is pumping blood from the left ventricle into the aorta. This moment is easily detected because it marks the top point of graphs P1-P9 shown in Figure 3, i.e., the point of maximum blood flow FL. Therefore, in the embodiment shown in Figure 3, the motor current deviations ΔI7 and ΔI9 of the corresponding patient-specific motor currents are measured when each patient-specific motor current reaches its maximum value, which indicates the open state, i.e., the state in which the blood flow FL passing through the blood pump is at its maximum, compared with the reference motor currents I7 and I9. As shown in Figure 3, the motor current deviations ΔI7 and ΔI9 are applied to all other reference data relating to the corresponding motor speeds I7 and I9, respectively. New or updated graphs of motor speeds I7 and I9 are identified as P7ΔI7 and P9ΔI9 in Figure 3. The same process may be carried out for the remaining motor speeds P1-P6 and P8.

[0057] Again, as mentioned above, in certain situations, it is also acceptable to calculate a single motor current deviation value ΔI for a single motor speed N and apply that single motor current deviation value to other motor speeds.

[0058] Figure 4 shows the time-dependent change in motor current I over multiple cardiac cycles at different motor speeds N. The curves shown in Figure 4 were acquired after the pump was positioned in the patient's left ventricle. For each motor speed N, three cardiac cycles were monitored and recorded, and as can be seen from the figure, the motor current changes similarly across each cardiac cycle. In particular, the curves show the maximum and minimum motor currents for each cycle. As shown in Figure 3, from the set of reference data and the negative slope of the motor current graph P, it is clear that the minimum motor current corresponds to the minimum pump load and maximum blood flow conditions; therefore, this minimum motor current is used as the patient-specific motor current value when calculating the motor current deviation value ΔI for the corresponding motor speed N. In other blood pumps where the slope of the motor current graph P is positive, the maximum motor current is used as the patient-specific motor current value when calculating the motor current deviation value ΔI.

[0059] Figure 5 shows a method for estimating blood flow. In the first step 100, reference data is obtained from a set of reference data acquired in the test environment. These reference data include both the reference motor current I of the motor driving the blood pump and the amount of fluid flow FL passing through the blood pump for at least one motor speed N (nine motor speeds N1 to N9 shown in graphs P1 to P9 in the example of Figure 3) under different pump loads, including a “first” pump load which is the minimum pump load at the maximum blood flow FL passing through the pump, i.e., with the heart valves open.

[0060] Next, in the second step 101, after the blood pump has been placed in the patient's body, the patient-specific motor current for each motor speed N is measured at the "first" pump load, i.e., preferably the minimum pump load and maximum blood flow. In the example in Figure 3, it is clear from the graphs P1 to P9 showing the reference motor currents I1 to I9 that the minimum motor current corresponds to the point of minimum pump load and maximum blood flow FL, indicating that the measurement target is the minimum patient-specific motor current.

[0061] Subsequently, in step 102, the motor current deviation value ΔI is calculated by subtracting the measured patient-specific motor current from the corresponding reference motor current I of the reference data set, i.e., from the reference motor current obtained for the “first” (minimum) pump load at the specific motor speed N.

[0062] Finally, in step 103, as described above, the motor current deviation value ΔI is applied to all reference motor currents I for at least the particular motor speed N, in order to accurately estimate the blood flow FL that passes through the blood pump when the blood pump is placed in the patient's body.

[0063] Those skilled in the art will understand that the steps of this method may include sub-steps. For example, as described above, the motor current deviation ΔI is applied to the reference motor current I only when a new or updated patient-specific reference table or graph P is created that can be referenced by medical staff or the system, or when the motor current deviation ΔI is added to the reference motor current only when medical staff or the system estimates the blood flow FL. Furthermore, the motor current deviation ΔI measured and calculated for a particular motor speed N may be applied to all other motor speeds as well.

[0064] Furthermore, the second step 101, which measures the patient-specific motor current for each motor speed N under the “first” pump load, may include a substep of monitoring and preferably recording the patient-specific motor current over one or preferably more complete cardiac cycles at the motor speed N. More preferably, the patient-specific motor current is monitored and preferably recorded over one or more complete cardiac cycles at multiple motor speeds N, and most preferably at all motor speeds N for which a reference motor current I is acquired in a set of reference data.

Claims

1. A method for creating a set of reference data to be used later in a method for estimating the fluid flow in an intravascular blood pump driven by motors (12, 13) that later drive the intravascular blood pump, - The step of placing the blood pump in the test environment, - A step of acquiring both the reference motor current (I) of the motor driving the blood pump and the amount of fluid flow (FL) passing through the blood pump as reference data for at least one motor speed (N) under different pump loads, - The reference data is obtained by measuring the reference motor current (I) of the motor driving the blood pump and the amount of fluid flow (FL) passing through the blood pump for the at least one motor speed (N) under the different pump loads, Includes, A method wherein the test environment simulates human blood vessels or organs.

2. The method according to claim 1, wherein the blood pump is a cable-driven blood pump.

3. The method according to claim 1, wherein the test environment simulates a human blood vessel or organ by setting a catheter that guides the blood pump in a curved shape within the test environment, in accordance with the manner in which the blood pump is positioned in a human blood vessel or organ.

4. The method according to claim 1, wherein the test environment simulates human blood vessels or organs, and the step of acquiring the reference data within the test environment includes using a liquid.

5. The method according to claim 4, wherein the temperature of the liquid is made equal to the temperature of the patient's blood.

6. The method according to claim 4, wherein the liquid is selected to have flow behavior equivalent to that of blood flow.

7. The method according to claim 4, wherein the liquid contains water and glycerol in a mixing ratio that gives a viscosity equal to the viscosity of blood.

8. The method according to claim 1, wherein reference data obtained for a given motor speed (N) and correlated as fluid flow (FL) versus motor current (I) is stored as a reference table or graph.

9. The method according to claim 8, wherein the reference table or graph is generated for a plurality of motor speeds (N).

10. The method according to claim 9, wherein pairs of motor current (I) and fluid flow (FL) values ​​for a further motor speed (N) are interpolated based on pairs of motor current and fluid flow values ​​for the next highest and next lowest motor speeds for which reference data has been acquired.

11. The method according to claim 1, wherein each pair of motor current (I) and fluid flow (FL) values ​​obtained under different pump loads for each given motor speed (N) includes, respectively, a first pair of motor current and fluid flow values ​​for a specific first pump load.

12. The method according to claim 11, wherein the first pump load is the pump load that maximizes the liquid flow (FL).

13. The method according to claim 1, comprising the step of creating a new or updated set of reference data by adding a calculated motor current deviation value (ΔI) to a corresponding reference motor current (I).

14. The method according to claim 13, wherein the step of creating the new or updated set of reference data is performed for a given motor speed (N) for all pump loads in which a reference motor current is available in the set of reference data, thereby obtaining a complete patient-specific set of reference data for the given motor speed (N).

15. The method according to claim 14, wherein the step of creating the new or updated set of reference data for all pump loads in which a reference motor current is available in the set of reference data for a given motor speed (N) is performed individually for each of a plurality of motor speeds (N1 to N9).

16. The method according to claim 15, wherein the same motor current deviation value (ΔI9) is applied to the set of reference data for each of the plurality of motor speeds (N1 to N9).

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