Method and apparatus for calibrating and using in estimating blood flow in an intravascular blood pump

Abstract

A method and apparatus for use in estimating blood flow in an intravascular blood pump, including retrieving reference data from a reference data set obtained in a test environment. The reference data set includes, for different pump loads including a first pump load, both a reference motor current (I) of a motor driving the blood pump and a fluid flow through the blood pump for at least one motor speed. After the blood pump is placed in a patient, a patient-specific motor current is measured at the first pump load for the motor speed, and a motor current deviation value (ΔI) is calculated from the reference motor current (I) at the first pump load and the patient-specific motor current. Finally, the motor current deviation value ΔI is used to estimate a patient-specific blood flow through the blood pump.

Description

[0001] Divisional application

[0002] This application is a divisional application of patent application No. 201980007903.3, filed on January 8, 2019, entitled "Method and apparatus for calibrating and using in estimating blood flow in an intravascular blood pump". Technical Field

[0003] This invention relates to a method and apparatus for calibration and use in estimating blood flow in an intravascular blood pump. The invention also relates to a computer program product programmed to perform the method. Background Technology

[0004] Intravascular blood pumps are used to support the function of a patient's heart, serving as either a left ventricular assist device (LVAD) or a right ventricular assist device (RVAD). In the context of this invention, an intravascular blood pump typically includes a catheter and a pumping device attached to the catheter, which 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. The catheter may have an elongated body with proximal and distal portions and may extend along a longitudinal axis, wherein the pumping device is attached to the catheter at a distal portion, away from the operator, such as a surgeon. The pumping device typically includes a pump segment having a blood flow inlet and a blood flow outlet. To induce blood flow from the blood flow inlet (e.g., in the left ventricle) to the blood flow outlet (e.g., in the aorta), an impeller or rotor is typically rotatably supported within a pump housing about a rotational axis for delivering blood. The blood pump can be driven by a motor adjacent to the pump segment included in the pumping device or can be optionally driven by a motor outside the patient's body, in which case the motor is connected to the impeller or rotor via a flexible drive shaft, i.e., a drive cable, extending through a catheter, and is referred to herein as a cable-driven blood pump.

[0005] It is important to estimate the blood flow through the blood pump to provide data to healthcare professionals from which they can draw conclusions about the system's operation and / or the patient's condition. In particular, it is crucial for healthcare professionals to ensure that the blood pump consistently delivers the necessary blood flow to adequately support or replace cardiac function.

[0006] Typically, the blood pump operates at a selected motor speed, i.e., the impeller or rotor is driven at a defined number of revolutions per minute. The motor speed or number of revolutions per minute can be changed as needed. At a given motor speed, the blood flow through the blood pump depends on the pressure differential the pump must overcome. Hereinafter, the pressure differential will also be referred to as the "pump load." Accordingly, maximum blood flow occurs when there is no pressure differential, and the blood flow can be zero, or even backflow through the blood pump can occur if the pressure differential is high, for example when the ventricles are beginning to fill with blood and the blood pump is pumping blood from the low-pressure ventricles into the high-pressure aorta, such as during diastole. When the total pump flow during the cardiac cycle is less than the desired amount of blood flow, the motor speed is accordingly increased until the desired amount of blood flow is reached.

[0007] To estimate blood flow, US 7,010,954 B2 proposes providing a lookup table or graph for a blood pump, in which blood flow is given relative to pump load for a specific motor speed of the blood pump. This lookup table or graph is provided for various motor speeds. In this way, using a first pressure sensor placed in the aorta and a second pressure sensor placed in the left ventricle, one can refer to the lookup table or graph for the specific motor speed at which the blood pump is driven and infer the current blood flow through the pump from the measured blood pressure difference.

[0008] It has been found that pump load, i.e. the pressure difference that the blood pump needs to overcome, not only affects blood flow, but also to some extent affects the motor current required to maintain a given motor speed at the set point, i.e., to keep the number of revolutions per minute of the impeller or rotor constant independently of the pump load.

[0009] Accordingly, it is possible to devise a lookup table or graph for each motor speed, in which blood flow is correlated with motor current. Therefore, according to the invention, motor current is monitored, rather than ventricular and aortic pressures.

[0010] Data used in lookup tables or graphs, such as motor current and blood flow rate, can be recorded in the test bench assembly by running the pump in the fluid at a given motor speed and a defined pump load while simultaneously recording the flow rate generated by the pump. The pump load can be increased over time, for example, from zero load (no pressure difference between the blood flow inlet and outlet, i.e., maximum flow rate) to maximum load (no pump function, i.e., no flow rate), while motor current and blood flow rate are recorded. It is possible to formulate such lookup tables or graphs for a variety of different motor speeds. As mentioned, the motor current changes slightly with changes in pump load and flow rate. When motor current, blood flow rate, pump load, and motor speed are measured and recorded in the test bench during the procedure explained above, it is possible to determine the flow rate at a given motor speed and pump load based on the motor current.

[0011] Depending on the blood pump design and various losses, the motor current can increase or decrease with increasing flow rate, or conversely, with decreasing pump load. For example, in some blood pumps, the motor current increases with increasing pump load, or in other words, the increased motor current indicates a decrease in blood flow. Conversely, in other blood pumps, the motor current can decrease with increasing pump load, or in other words, the increased motor current can indicate an increase in blood flow through the pump.

[0012] Once a blood pump is implanted in a patient's body, virtually no unknown losses occur. Various parameters, such as motor and pump parameters, can affect the relationship between motor current and blood flow. Furthermore, the viscosity of the blood passing through the pump and / or the cleansing fluid administered to the patient's blood via catheter can also have an impact. Additionally, frictional losses can have an effect, particularly the friction of the flexible drive shaft within the catheter of a cable-driven blood pump, where such friction can be high or low 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 the flow rate based on the motor current measured at a given motor speed. Summary of the Invention

[0013] Therefore, a particular object of the present invention is to provide a method and apparatus for estimating blood flow in an intravascular blood pump, which assists medical personnel in monitoring blood flow when operating an intravascular blood pump in a patient's body. Another object of the present invention is to provide computer program products, respectively programmed to implement the method and operate the corresponding apparatus.

[0014] These objectives are addressed by the features of the independent claims. Preferred embodiments of the invention are specified in the dependent claims.

[0015] Accordingly, a method for estimating blood flow in an intravascular blood pump is proposed, comprising the following steps:

[0016] -(a) Retrieve baseline data obtained in the test environment, including both the baseline motor current of the motor driving the blood pump and the fluid flow rate through the blood pump at different pump loads including the first pump load for at least one motor speed.

[0017] -(b) After the pump is placed in the patient, measure the patient-specific motor current at a first pump load for the at least one motor speed.

[0018] -(c) Then, calculate the motor current deviation value from the reference motor current at the first pump load and the patient-specific motor current at the first pump load for the at least one motor speed, and

[0019] -(d) Finally, the motor current deviation value is used to estimate the patient-specific blood flow through the blood pump.

[0020] "Motor speed", "speed level" or "motor speed level" refers to the rotational speed of a motor, which is related to the rotational speed of the pump's rotor or impeller, and can be specified as, for example, revolutions per minute.

[0021] "Pump load" is defined as the pressure difference in the fluid that must be overcome when fluid is pumped through the pump. In other words, "pump load" can be understood as the pressure difference between the pump's blood flow inlet and blood flow outlet. Therefore, as mentioned above, when the pump is running at a given motor speed, the flow rate is at zero and the pump load is at its maximum, and the flow rate is at its maximum and the pump load is zero.

[0022] "Fluid flow rate," "blood flow rate," "flow rate," and "blood volume" refer to the volume of fluid or blood delivered per unit of time, for example, through a pumping device. Accordingly, flow rate can be measured in liters per minute.

[0023] "Benchmark data," such as benchmark motor current, refers to data obtained in the testing environment. Accordingly, in order to estimate blood flow through a pump placed inside a patient's body, benchmark data is retrieved, for example, as a lookup table or graph, from data previously obtained in the testing environment.

[0024] The test environment can simulate human blood vessels or organs, and therefore, essentially simulate the behavior of a blood pump in the human body when it is running to keep deviation values ​​low, such as motor current deviation values.

[0025] This invention is particularly suitable for cable-driven intravascular blood pumps. The losses caused by friction within the cable in the catheter increase substantially with the number of bends and tight bend radii, and can vary from patient to patient. Therefore, the deviation between the reference motor current measured in the testing environment and the corresponding specific motor current occurring in actual use can vary from patient to patient, especially in cable-driven blood pumps.

[0026] The reference data includes a reference motor current for the motor driving the pump and the amount of fluid flow generated at that particular reference motor current at a given motor speed. This data is obtained for different pump loads; to maintain a given motor speed, the motor current is adjusted as the pump load changes, and, moreover, because the fluid flow through a continuously driven pump varies with changing pump loads, as explained above. The reference data obtained for a given motor speed and associated with the fluid flow relative to the motor current is advantageously presented as a lookup table or graph. As stated above, depending on the blood pump design, the motor current may increase or decrease with decreasing pump load, or with increasing blood flow, respectively.

[0027] Such charts or lookup tables can be generated for more than one motor speed, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, or more motor speeds. The motor current and fluid flow rate pairings for other motor speeds can be interpolated based on the motor current and fluid flow rate pairings for the next higher and next lower motor speeds that have been obtained for their reference data. In any case, the motor current and fluid flow rate pairings obtained for each given motor speed at different pump loads include at least a first motor current and fluid flow rate pairing for a specific "first" pump load. This is important for the next step after the blood pump is placed in the patient, where the patient-specific motor current at the first pump load is measured for the respective motor speeds. The two motor currents, namely the reference motor current and the patient-specific motor current, are comparable to each other because they are obtained at the same pump load for the same motor speed, i.e., the first pump load. Therefore, the motor current deviation value can be calculated from the reference motor current at the specific first pump load for the motor speed and the patient-specific motor current, and the same process can be performed for other pump loads and, consequently, for other motor speeds. These motor current deviation values ​​can then be used in further processes to estimate the patient-specific blood flow through the blood pump.

[0028] For example, motor current deviation values ​​can be used to create a patient-specific baseline dataset based on an initial baseline dataset. As mentioned, the initial baseline dataset shows the dependence between motor current and fluid flow rate for different motor speeds in the test environment, for example, in the form of a graph or lookup table. Motor current deviation values ​​can be applied to all baseline motor current values ​​to estimate the blood flow rate through the blood pump implanted in the patient.

[0029] When the calculated motor current deviation value is applied to the initial reference data set, the graph or the corresponding graph in the lookup table can be shifted for all fluid flow rates and all motor speeds by simply adding the calculated motor current deviation value to the initial reference motor current, so that the fluid flow rate in the patient-specific reference data set indicates the actual blood flow rate through the blood pump placed in the patient.

[0030] It can be assumed that the motor current deviation value at a first motor speed for a first pump load is approximately the same for all pump loads at the first motor speed for which the motor current deviation value has been calculated. Therefore, a motor current deviation value can be calculated per motor speed and added to more than one reference motor current in the initial reference data set for that particular motor speed, most preferably to all reference motor currents in the initial reference data set for that particular motor speed, thereby establishing a complete patient-specific chart or lookup table for that motor speed.

[0031] Furthermore, the same (single) motor current deviation value calculated for a specific motor current can also be added to the reference motor current in the initial reference data set for motor speeds other than the specific motor speed for which the motor current deviation value has been calculated, so that overall only a single motor current deviation value needs to be calculated.

[0032] However, more preferably, the single motor current deviation value is calculated separately for each of the motor speeds available in the reference data set, for its reference data, because in some blood pumps the motor current deviation value can vary significantly between different motor speeds.

[0033] Alternatively, instead of creating a patient-specific set of reference data, the one or more individual motor current deviation values ​​can be stored raw and subtracted from any patient-specific motor current measured during the use of the blood pump in the patient. This will similarly result in and provide healthcare professionals with patient-specific blood flow for each individual motor speed, or, if a (single) motor current deviation value is applied to all the mentioned motor speeds, then patient-specific blood flow for all motor speeds.

[0034] A key point is to identify the appropriate “first” pump load where the patient-specific motor current is measured, because it is important to correlate the patient-specific motor current with the corresponding reference motor current at the same “first” pump load.

[0035] With the aid of pressure sensors and / or EKG, it is generally possible to identify specific moments in the cardiac cycle that would allow correlation between the timing of patient-specific motor current measurements at a given motor speed and the corresponding reference motor current in a reference dataset.

[0036] However, according to a particularly preferred embodiment of the invention, the patient-specific motor current used to determine the motor current deviation value is measured at a pump load that is clearly identifiable by the motor current value, thus eliminating the need for any additional sensors. More specifically, the following is considered: at a given motor speed, the maximum blood flow through the pump occurs at the minimum load, or in other words, at the zero pressure difference between the blood flow inlet and outlet, i.e., when the heart valves are open. As will be explained, the heart valve opening status is indicated by the preferred pump load at which the patient-specific motor current is measured to determine the motor current deviation value.

[0037] More specifically, in a preferred embodiment, the blood pump is placed in the patient's vascular system such that the blood flow inlet is placed in a ventricle, such as the left ventricle, and the blood flow outlet is placed in a blood vessel, such as the aorta, separated by a natural valve, such as the aortic valve. Once the valve opens, for example during cardiac contraction, the blood flow inlet and outlet are no longer separated in terms of pressure, and therefore, the pressure difference between them is zero. At this point of zero pressure difference between the blood flow inlet and outlet, the blood flow through the pump will be at its maximum level for a selected motor speed, and the motor current will be at its maximum or minimum for that motor speed level. Accordingly, the maximum blood flow for a given motor speed will occur at either the minimum or maximum motor current, depending on the design of the blood pump. Thus, depending on the design of the blood pump, the maximum or minimum motor current can be used as an indicator of the opening state of the heart valve, which, as mentioned above, marks the preferred pump load at which the patient-specific motor current is measured to determine the motor current deviation value.

[0038] From the baseline dataset, it is clear whether the opening state of the heart valves (i.e., the maximum blood flow of the pump) can be identified by the maximum or minimum motor current value, depending on the angle of the flow curve in the lookup table or graph. In other words: if the angle of the flow curve is negative, then the minimum motor current refers to the opening phase of the heart valve, such as the aortic valve, and indicates the maximum blood flow; while if the angle of the flow curve is positive, then the maximum motor current refers to the opening phase of the heart valve, such as the aortic valve, and indicates the maximum blood flow.

[0039] Therefore, the “first pump load” at which the patient-specific motor current is measured is preferably the pump load when the heart valves, such as the aortic valve, are open.

[0040] Accordingly, the step of measuring the patient-specific motor current at the first pump load for the at least one motor speed preferably includes measuring the maximum or minimum patient-specific motor current for a specific motor speed.

[0041] The pump's efficiency can be further affected by changes in parameters due to various largely unknown reasons while the pump is in the patient's body. Therefore, it is preferable to iterate the method described above in the sense that the motor current deviation value is recalculated relative to a previously calculated patient-specific motor current deviation value after a short period of time. In other words, if the motor current deviation value changes over time, such as when compared to a previously calculated motor current deviation value, then the previously calculated motor current deviation value is replaced by the actual motor current deviation value.

[0042] For example, the actual patient-specific motor current for the at least one motor speed can be measured, and the deviation can be calculated from a previously measured patient-specific motor current, which may have been stored as an updated reference motor current. Accordingly, the previously measured patient-specific motor current or the previously updated reference motor current can be (further) updated toward the actual patient-specific motor current.

[0043] Preferably, the next iteration is triggered by a predefined time interval. This provides the advantage that, even when the blood pump is operated for a longer period of time, the motor current can be calibrated to maintain a specific amount of blood flow, even if specific characteristics of the blood, patient, cleaning fluid, or system have changed. For example, such time intervals can be specified in the range of seconds, minutes, hours, or days. The individual time intervals can be configured by medical personnel.

[0044] Alternatively, the next iteration can be triggered by at least one influencing characteristic, such as a change in motor current, the temperature or viscosity of the blood and / or cleaning fluid, or a change in the physical properties of the blood pump, such as the motor temperature of the blood pump. Whenever a significant change in one or more of these characteristics is observed, the calculation of the motor current deviation value can be iterated.

[0045] The retrieval of benchmark data in the testing environment is preferably achieved using a blood pump and fluid of a certain type, wherein the fluid does not necessarily have to be blood. In any case, the fluid is preferably selected to have a flow behavior equivalent to that of blood. Similarly, it is preferred that the fluid temperature matches the patient's blood temperature. These measures help improve the accuracy of the benchmark data and its comparability with measured patient-specific data.

[0046] According to one specific implementation, the fluid used in the testing environment comprises a mixture of water and glycerol in a proportion that provides a viscosity equal to that of blood at human body temperature. This provides the advantage that the testing fluid can be produced directly.

[0047] Further preferably, the blood pump setup in the test environment simulates the curvature of the catheter in the human vascular system. In other words, preferably, the catheter guiding the blood pump is configured to have a curvature in a test bench based on the placement of the blood pump in the human vascular system.

[0048] Advantageously, the method provides method steps that can be implemented as structural features in separate devices for estimating blood flow. Such devices have structural features that respectively implement the corresponding steps of the method described above. Accordingly, the features of the method and the device can be used interchangeably, enabling the device to perform the proposed method and the proposed method to operate the device. Furthermore, a computer program product can implement the method and operate the device, for example, when executed on a computer. Attached Figure Description

[0049] Further advantages are provided in the context of the accompanying drawings, which illustrate:

[0050] Figure 1 It is an intravascular blood pump placed in the left ventricle of the heart;

[0051] Figure 2 It is a graph illustrating the relationship between motor current and fluid flow rate through an exemplary pump in a test environment for a set of nine different motor speeds.

[0052] Figure 3 yes Figure 2 The graph shows two additional exemplary motor current deviation values ​​ΔI for two motor speeds at the maximum flow rate through the pump.

[0053] Figure 4 The variation of motor current I over time at different rates N of the left ventricular pump is shown over multiple cardiac cycles; and

[0054] Figure 5 It is a flowchart depicting a method used to estimate the blood flow rate through an intravascular blood pump. Detailed Implementation

[0055] Figure 1 A human heart 10 is shown, with an intravascular blood pump inserted into the heart 10 through the aorta 11 and across 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 segment 14 and a cannula 15 having an inlet opening 16 and an outlet opening 17, and also having a soft, flexible distal end 19 in the form of a pigtail, which keeps the pumping device 13 away from the heart wall to prevent suction of the inlet opening 16 against the heart wall. An impeller or rotor rotates within the pump segment 14 to deliver blood from the inlet opening 16 through the outlet opening 17. The pumping device 13 may also include a drive segment for driving the impeller or rotor, housed in a single housing and accompanying the pump segment 14. However, in Figure 1 In the embodiment shown, the pumping device is driven by a flexible cable 18, which is guided within the conduit 12. Instead of... Figure 1 The pump shown in the diagram can be replaced with other intravascular blood pumps, such as expandable blood pumps, whose diameter will be substantially larger after expansion, as shown in the diagram. Figure 1 The pump segment 14 shown in the figure is compared.

[0056] Clearly, the drive cable 18 will suffer losses when operated, such as surface friction within the catheter 12. The amount of loss also depends on the number and radius of the bends, which can vary from patient to patient, or even for the same patient, if the blood pump is repositioned or moved within the patient's vascular system over time. Accordingly, the energy required to drive the impeller within the pump segment 14 at a given rotational speed can vary depending on the individual.

[0057] Figure 2 The diagram P1 to P9 shows the flow rate FL through the pump versus the motor current I for nine different motor speeds N1 to N9, where motor speed N is related to the impeller rotational speed. As mentioned above, the higher the pressure differential the pump must overcome, the lower the flow rate FL through the pump will be. (The last sentence appears to be incomplete and possibly refers to a different topic.) Figure 2 As can be seen, the motor current I is not constant for each motor speed N, but changes as the flow rate FL passing through the pump changes. For example, in... Figure 2In the specific embodiment shown, data is actually recorded from an expandable, cable-driven blood pump. In this case, the motor current I decreases as the flow rate FL through the pump increases. In other blood pumps, particularly non-expandable ones, it has been found that the motor current I increases as the flow rate FL increases.

[0058] The measurement points for individuals in Figures P1 to P9 were obtained by measuring both the blood flow rate FL through the pump and the motor current I at different pump loads in the test environment. The test environment was designed to approximate conditions in the human body as closely as possible. For example, the fluid in the test environment was chosen to have flow behavior equivalent to that of blood. Furthermore, the temperature was equal to the patient's blood temperature, for example, between 36 and 37°C. Additionally, the fluid in the test environment contained a mixture of water and glycerol in proportions to provide a viscosity equal to that of blood. Furthermore, the catheter's tortuosity and curvature were approximated based on the average human vascular system.

[0059] However, because blood flow FL is estimated based on motor current I, as proposed in this paper, rather than on any pressure signal, the charts P1 to P9 for different motor speeds N1 to N9 must be calibrated for each individual patient. This is because patient-specific motor current deviations in the use of the blood pump within the patient's heart, compared to the baseline motor current I in the corresponding baseline dataset, can lead to misinterpretations, as referenced in the figure. Figure 2 Further explanation.

[0060] As in Figure 2 As shown, when the blood pump is driven using motor speed P9 and due to the pressure difference to be overcome, the blood flow rate FL is approximately 5.2 L / min (slightly lower than the maximum blood flow rate FL of approximately 6.5 L / min). When the patient-specific motor current deviates from the reference motor current I9 by a positive motor current deviation value ΔI9 under these conditions, then the medical personnel will incorrectly infer a blood flow rate FL of only approximately 1.8 L / min from the reference data set. Alternatively, when the patient-specific motor current deviates from the reference motor current I9 by a negative rather than positive motor current deviation value -ΔI9 under the same conditions (in... Figure 2 (not shown in the image), then medical personnel will not find any corresponding reference motor current or flow estimation system sending an error signal.

[0061] Therefore, to avoid such misinterpretation, lookup tables or charts with patient-specific motor current values ​​are generated. Medical personnel can refer to these tables or charts and deduce the correct blood flow from them. Accordingly, after the blood pump is placed in the patient, patient-specific motor currents can be measured at the pump's respective operating points, i.e., at specific pump loads, for motor speed N9 (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.

[0062] However, as already explained above and will be referenced Figure 3 To further explain, the motor current deviation value ΔI is calculated only for a specific "first" pump load and added to all reference motor currents for a given motor speed N in the reference dataset. This "first" pump load preferably corresponds to the state of minimum pump load during the cardiac cycle, i.e., the opening state of the heart valves, because such a state can be easily detected individually based on the measured motor current I, i.e., when the motor current I is at its maximum or minimum. However, for completeness, if the pressure sensor and / or EKG are in place, then any other pump load can be considered as the motor current deviation value ΔI within its determined specific "first" pump load.

[0063] In any case, a new or updated baseline dataset can be created by adding the calculated motor current deviation value ΔI to the corresponding baseline motor current, and this is performed for all pump loads available in the baseline dataset for that baseline motor current, to obtain a complete patient-specific baseline dataset for motor speed N. Furthermore, this process can be performed separately for each of the motor speeds N1 to N9.

[0064] Furthermore, assuming that the motor current deviation value ΔI9 obtained at motor speed N9 is approximately the same as the motor current deviation values ​​ΔI1...ΔI8 for all other motor speeds N1 to N8, the motor current deviation value ΔI9 can be similarly applied to the reference data set for each of the motor speeds N1 to N9.

[0065] Alternatively, instead of creating a new or updated set of reference data, the respective motor current deviation values ​​ΔI or ΔI1 to ΔI9 can be stored and subtracted from the motor current measured, such as when the pump is placed in the patient's vascular system, so that the measured motor current is comparable to the previously stored set of reference data.

[0066] In the most practical way, such as in Figure 3As exemplarily illustrated, for two motor currents I7 and I9 and their corresponding motor current graphs P7 and P9, the single motor current deviation values ​​ΔI7 and ΔI9 are measured in the opening state of the heart valves (e.g., the aortic valve) when the blood pump is pumping blood from the left ventricle into the aorta. This moment is readily detectable because it is marked on... Figure 3 The highest point in the charts P1 to P9 shown is the point of maximum flow FL. Therefore, in Figure 3 In the embodiment shown, compared with reference motor currents I7 and I9, the corresponding patient-specific motor current deviation values ​​ΔI7 and ΔI9 are measured when the respective patient-specific motor current reaches its maximum value, because this marks the state of the on state or the state of the maximum flow rate FL through the blood pump. As in Figure 3 As shown, the motor current deviation values ​​ΔI7 and ΔI9 have been applied to all other reference data related to the corresponding motor speeds I7 and I9. New or updated charts for motor speeds I7 and I9 are available in [the table / reference]. Figure 3 The middle part is labeled as P7 ΔI7 and P9 ΔI9 The same operation can be performed for the remaining motor speeds P1 to P6 and P8.

[0067] Again, as mentioned above, in some cases it may be acceptable to calculate a single motor current deviation value ΔI for a motor speed N and apply that single motor current deviation value to other motor speeds.

[0068] Figure 4 The variation of motor current I over time at different motor speeds N over multiple cardiac cycles is shown. (As in...) Figure 4 The curves shown were obtained after the pump had been placed in the patient's left ventricle. For each motor speed N, three cardiac cycles were monitored and recorded, and as can be seen, the motor current changed in the same characteristic manner within each cardiac cycle. Specifically, the curves show the maximum and minimum motor currents for each cycle. This is because the data is derived from a baseline dataset and from other datasets. Figure 3 The negative tilt of the motor current graph P clearly shows that the minimum motor current corresponds to the state of minimum pump load and maximum flow rate. Therefore, when calculating the motor current deviation value ΔI for the corresponding motor speed N, this minimum motor current is used as the patient-specific motor current value. For other blood pumps with a positive tilt of the motor current graph P, the maximum motor current would be used as the patient-specific motor current value for calculating the motor current deviation value ΔI.

[0069] Figure 5A method for estimating blood flow is illustrated. In the first step 100, baseline data is retrieved from a set of baseline data already obtained in the test environment. This baseline data includes different pump loads, including a "first" pump load, for at least one motor speed N (in... Figure 3 In the embodiment, for the nine motor speeds N1 to N9 (as shown in Figures P1 to P9), the reference motor current I of the motor driving the blood pump and the amount of fluid flow FL through the blood pump, the "first" pump load is preferably the minimum pump load at the maximum flow rate FL through the pump, i.e., in the open state of the heart valve.

[0070] Then, in the second step 101, after the blood pump is placed in the patient, the patient-specific motor current for the respective motor speed N is measured at the “first” pump load, i.e., preferably at minimum pump load and maximum flow rate. Figure 3 In one embodiment, a minimum patient-specific motor current is measured, as can be clearly seen from graphs P1 to P9, which show the reference motor currents I1 to I9, at the point where the minimum motor current corresponds to the minimum pump load and the maximum flow rate FL.

[0071] Then, 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 in the reference data set, i.e., from the reference motor current obtained at that particular motor speed N for the “first” (minimum) pump load.

[0072] Finally, in step 103, the motor current deviation value ΔI is applied to at least all the reference motor currents I at that particular motor speed N to enable a correct estimation of the blood flow FL passing through the blood pump when it is placed in the patient, as described above.

[0073] Those skilled in the art will recognize that the method steps may include sub-steps. For example, as mentioned, the application of the motor current deviation value ΔI to the reference motor current I may be such that a new or updated patient-specific lookup table or chart P is created, which the medical personnel or system can refer to; or, the motor current deviation value ΔI may be added to the reference motor current I only when the blood flow FL is estimated by the medical personnel or system. Furthermore, the motor current deviation value ΔI measured and calculated for a specific motor speed N can also be applied to all other motor speeds.

[0074] Furthermore, the second step 101, measuring the patient-specific motor current at a given motor speed N under a "first" pump load, may include a sub-step of monitoring and preferably recording the patient-specific motor current at that motor speed N over one or more complete cardiac cycles. More preferably, the patient-specific motor current is monitored and preferably recorded at more than one motor speed N over one or more complete cardiac cycles, and most preferably at all motor speeds N, with the reference motor current I obtained from a reference dataset.

Claims

1. A method for creating a baseline dataset for subsequent use in a method for estimating blood flow in a motor-driven intravascular blood pump (12, 13), comprising the following steps: - Place the blood pump in the test environment. - Obtain, as reference data, both the reference motor current (I) of the motor driving the blood pump and the fluid flow rate (FL) through the blood pump at different pump loads for at least one motor speed (N), wherein the reference data is obtained by measuring the reference motor current (I) of the motor driving the blood pump and the fluid flow rate (FL) through the blood pump at the different pump loads for the at least one motor speed (N). 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 of claim 1, wherein the test environment simulates a human blood vessel or organ, wherein the catheter guiding the blood pump is configured to have a curvature in the test environment according to the placement of the blood pump in the human blood vessel or organ.

4. The method of claim 1, wherein the test environment simulates human blood vessels or organs, wherein the step of obtaining the baseline data in the test environment includes using a fluid.

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

6. The method of claim 4, wherein the fluid is selected to have a flow behavior equal to that of blood.

7. The method of claim 4, wherein the fluid comprises water and glycerol in a mixing ratio to provide a viscosity equal to that of blood.

8. The method of claim 1, wherein the reference data obtained for a given motor speed (N) and associated as fluid flow rate (FL) with motor current (I) is stored as a lookup table or chart.

9. The method of claim 8, wherein the lookup table or chart is generated for more than one motor speed (N).

10. The method of claim 9, wherein the pairing of motor current (I) and fluid flow rate (FL) values ​​for other motor speeds (N) is interpolated based on the motor current and fluid flow rate values ​​for the next higher and next lower motor speeds that have been obtained from the baseline data.

11. The method of claim 1, wherein the pairing of motor current (I) and fluid flow rate (FL) values ​​obtained for each given motor speed (N) at different pump loads includes a pairing of first motor current and fluid flow rate values ​​for a particular "first" pump load.

12. The method of claim 11, wherein the "first" pump load is the pump load with the highest fluid flow rate (FL).

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

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

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

16. The method of claim 15, wherein the same motor current deviation value is applied to the reference data set for each of the motor speeds.

Images