Method and vascular support system for determining fluid volume flow rate through an implantable vascular support system

Abstract

The present invention relates to a method for determining a fluid volume flow rate (1) through an implantable vascular support system (2), comprising the steps of: a) determining a fluid temperature parameter in the region of a cannula (4) of the support system (2), b) operating a heating element (5) which can cause a change in the fluid temperature in the cannula (4), and c) determining the fluid volume flow rate (1) using at least the fluid temperature parameter or a change thereof and at least one heating element operating parameter or a change thereof. The present invention also relates to a vascular support system.

Description

[0001] Description

[0002] The present invention relates to a method for determining the fluid volume flow rate through an implantable vascular support system, a processing unit, and an implantable vascular support system. The present invention is particularly useful in (fully) implantable left ventricular assist devices (LVADs).

[0003] There are mainly two design variants of implantable left ventricular assist devices (LVADs). The (percutaneous) minimally invasive left ventricular assist system constitutes the first common design variant. The invasive implantable left ventricular assist system at the apex below the chest opening constitutes the second common design variant. In the first variant mentioned, since the (percutaneous) minimally invasive left ventricular assist system is centered in the aortic valve, blood is directly delivered from the left ventricle to the aorta. In the second variant mentioned, blood is delivered from the left ventricle to the aorta via a bypass tube through the apex.

[0004] The task of the cardiac support system is to deliver blood. In this case, the so-called cardiac minute volume (HZV, usually expressed in liters per minute) is clinically highly relevant. In other words, in this case, the cardiac minute volume relates to the total volume flow rate of blood (from the ventricle), especially from the left ventricle to the aorta. It is correspondingly clear that an attempt is made to collect this parameter as a measured value during the operation of the cardiac support system.

[0005] Depending on the level of support, which describes the ratio of the volume flow rate delivered by the delivery device (e.g., the pump of the support system) to the total volume flow rate of blood from the ventricle to the aorta, a certain volume flow rate reaches the aorta via the physiological path through the aortic valve. Therefore, the cardiac minute volume or the total volume flow rate (Q HZV ) from the ventricle to the aorta is usually the sum of the pump volume flow rate (Q p ) and the aortic valve volume flow rate (Q a ). This can be expressed by the following relationship:

[0006] Q HZV = Q p + Q a

[0007] An established method for determining the cardiac minute volume (Q HZV ) in a clinical setting is to use the dilution method. However, this method entirely relies on a percutaneously inserted catheter and can therefore only provide cardiac minute volume measurement data during cardiac surgery. Since it is difficult to detect the cardiac minute volume (Q HZV ) through the LVAD, Q p can be detected through a suitable component of the LVAD. For a high level of support (i.e., Q p / Q HZV ), Q a is close to zero, such that Q pcan be approximately used as the cardiac volume (Q HZV ).

[0008] An established method for measuring the pump volume flow rate (Q p ) is to correlate the operating parameters of the support system, mainly power consumption, and possibly other physiological parameters (such as blood pressure) may be required to supplement. Since these methods are based on statistical assumptions and the basic pump characteristic diagram of the LVAD used, the correlated Q p is error-prone. To improve the measurement quality of the parameter Q p , it is thus desirable to include a flow sensor.

[0009] The object of the present invention is to propose an improved method for determining the fluid volume flow rate in the region of an implantable vascular support system and to create an improved implantable vascular support system.

[0010] In particular, the object of the present invention is to provide a method for determining the fluid volume flow rate in the region of an implantable vascular support system and to create an implantable vascular support system by means of which the fluid volume flow rate in the blood flow region can be determined in a human or animal body in which the vascular support system is implanted or arranged.

[0011] A method for determining the fluid volume flow rate through an implantable vascular support system is hereby proposed, the method comprising the following steps:

[0012] a) determining the fluid temperature parameter in the cannula region of the support system,

[0013] b) operating a heating element that can cause a change in the fluid temperature in the cannula,

[0014] c) determining the fluid volume flow rate using at least the fluid temperature parameter or its change and at least one heating element operating parameter or its change.

[0015] The vascular support system is preferably a cardiac support system, particularly preferably a ventricular support system. The method is preferably used to determine the fluid volume flow rate through a blood vessel or through a cross-section of a blood vessel. For example, the blood vessel is the aorta, especially in the case of a left heart support system, or the main trunk entering the two pulmonary arteries (pulmonary trunk), especially in the case of a right heart support system, preferably the aorta. The method is preferably used to determine the fluid volume flow rate from the ventricle of the heart, particularly from the (left) ventricle of the heart to the aorta, through a (fully) implantable (left) ventricular (cardiac) support system. The fluid is usually blood. The support system is preferably arranged in the left ventricle of the heart or at the outlet of the left ventricle. The support system is particularly preferably arranged at the aortic valve position.

[0016] The support system is preferably implanted such that at least part of it, preferably completely, or with at least 50%, particularly preferably at least 85%, or even at least 95% of its (outer) surface is located in the fluid flow. In addition, the support system is preferably located in the fluid flow along at least 50%, particularly preferably at least 85%, or even at least 95% of its length. One end of the support system in the region of which or on which the electric motor is located is preferably at least partially located in the aorta. In addition, the (inlet) cannula of the support system in the region of which or on which it is located at the opposite end is preferably at least partially located in the ventricle (left ventricle) of the heart. In addition, the support system is preferably centered in the aortic valve such that blood is drawn distally from the ventricle and distributed proximally into the ascending aorta. Preferably, the support system is at least partially, preferably completely, or with at least 20%, preferably at least 40%, particularly preferably at least 50% or even at least 95% of its (outer) surface arranged in a blood vessel, such as an artery, particularly the aorta. The support system is particularly preferably implanted such that it is (completely) located in the (ascending or descending) aorta.

[0017] The fluid volume flow rate to be determined is the flow rate through the support system (itself). In other words, this particularly relates to the fluid volume flow rate flowing only through the support system itself. The fluid volume flow rate to be determined generally is the so-called pump volume flow rate (formula symbol Q p ), which (only) quantifies the flow rate through the support system itself. This method is particularly suitable for determining the pump volume flow rate (Q p ) of a (fully) implantable left ventricular assist device (LVAD), particularly at the aortic valve position and / or through the support system itself.

[0018] This method is particularly based on the (thermal) anemometry (measurement) principle for flow rate measurement. The basic principle in this case is that the flowing medium cools the hot body according to the flow rate. This method advantageously allows for continuous and precise measurement of Q p through a sensor element integrated into the LVAD and based on thermal anemometry. With the solution proposed here, the cardiac volume (at least approximately through Q p ) can also advantageously be provided outside the surgical scenario in an amount comparable to when using a dilution catheter.

[0019] The solution proposed here is particularly characterized by integrating one or more heating elements or one or more heating elements and one or more temperature sensors into the inlet cannula of the support system (VAD). In this method, Q p is advantageously calculated from the measured voltage data of at least one heating element and / or at least one temperature sensor. In particular, three possible operating principles can be used in this case, namely constant current anemometry, constant temperature anemometry, or the impulse response method.

[0020] In step a), the fluid temperature parameter in the region of the cannula of the support system is determined. A (separate) temperature sensor can be used for this purpose, for example. This determination can alternatively or cumulatively be carried out by the heating element itself. For example, the series resistance of the heating element can be used for this purpose. The fluid temperature parameter can be the (fluid) temperature, the temperature sensor current, the temperature sensor output (current) signal, or in particular the (temperature-dependent) resistance value of the heating element.

[0021] In step a), the temperature sensor in the region of the cannula of the support system is operated. This operation particularly includes measuring the fluid temperature and / or changing the fluid temperature. The temperature sensor is preferably arranged on the inner or outer surface of the cannula. In addition, at least two temperature sensors can preferably be provided. In this case, one temperature sensor can be arranged upstream of the heating element and another temperature sensor can be arranged downstream of the heating element.

[0022] The cannula is in particular an inlet cannula, which can also be referred to as a suction tube. The (inlet) cannula is preferably configured such that in the implanted state, it can guide the fluid from the (left) ventricle of the heart to the flow generator of the support system and / or the aorta.

[0023] One or more temperature sensors are particularly preferably arranged at a certain distance from the heating element. This allows the advantage that the temperature sensor is not thermally affected by the heating element, which is particularly advantageous if the temperature sensor is a reference temperature sensor. An NTC thermistor, a PTC thermistor, a resistance element such as platinum, a semiconductor junction or a thermocouple can be used as the temperature sensor.

[0024] The temperature sensor or another temperature sensor can be introduced into the heating element or arranged on the heating element. If at least two temperature sensors are provided, in this case it is preferred that the reference temperature sensor is arranged at a certain distance from the heating element and another temperature sensor is introduced into the heating element or arranged on the heating element. If only one temperature sensor is provided, it may be necessary to switch off or not operate the heating element during the measurement of the reference temperature by the temperature sensor. The flat temperature sensor is preferably positioned between the inner wall of the cannula and the heating element, or the temperature sensor is positioned on the heating element. A particularly preferred embodiment is to position the temperature sensor centrally in the heating region of the heating element. A possible embodiment can also be a three-layer structure, in which the heating coil is positioned as a temperature sensor between the lower and middle polyimide films, and the platinum wire coil is positioned as a temperature sensor between the middle and upper polyimide films.

[0025] It is preferably determined in step a), in particular, the reference temperature of the fluid is measured. The reference temperature is preferably determined by a reference temperature sensor, which is particularly preferably a component of the support system. The reference temperature sensor can be arranged, for example, in and / or on the (inlet) sleeve of the support system. The reference temperature generally represents the background temperature of the fluid, that is to say, the fluid temperature, which is particularly not affected by the heat of the heating element and / or the flow inducer of the support system.

[0026] In step b), the heating element that can cause a change in the fluid temperature in the sleeve is operated. In other words, this particularly means that the heating element is configured and arranged such that it can cause a change in the fluid temperature in the sleeve. For this purpose, the heating element can be directly arranged inside the sleeve or on the inner surface of the sleeve. However, (alternatively) the heating element can be arranged in the wall of the sleeve, on the outer surface of the sleeve, or even at a certain distance from the sleeve, as long as the heating element can increase the fluid temperature of at least a part of the fluid inside the sleeve, for example, by heat conduction. For operation, the heating element is usually controlled by an electric current.

[0027] The heating element preferably forms at least one heating wire or heating filament. Preferably, a heating element that covers at least the inner surface of the sleeve in a segmented area or circumferential part and / or longitudinal part is provided, especially a circular or tubular heating element. In addition, the heating element preferably forms in the form of a (flexible) heating film that at least partially covers the inner surface of the sleeve. At least one heating wire is particularly preferably arranged in or on the film. Preferably, the heating wire extends continuously on at least 50% or even (the entire) inner surface of the sleeve covered by the film (for example, in a meandering pattern and / or in the form of a loop). At least two heating wires can be provided. Preferably, the heating wire or heating filament is realized on the inner wall of the sleeve (on the inner side of the sleeve wall), whereby a defined blood volume can be advantageously studied and heating of, for example, the aortic valve can be excluded when the support system slides. If more than one heating element or heating wire is provided, they can be arranged at opposite positions on the inner surface of the sleeve. In addition, the heating element or heating wire is preferably actuated or energized together.

[0028] It is also advantageous if the heating element itself is used as a temperature sensor. The heating element is preferably configured to both cause a change in the temperature of the fluid in the sleeve and detect, in particular measure, the change in the temperature of the fluid in the sleeve. The heating element itself can be used as a temperature sensor, in particular by a suitable selection of the heating element, especially the heating wire material (which changes in resistance in the case of a temperature change). Thus, a preferred embodiment of the heating element is, for example, a (platinum) wire coil between or on a polyimide film (a heating wire made of a platinum alloy and arranged in a meandering pattern). Preferably, the heating element comprises a heating coil made of a conductive, resistive material (for example, a platinum alloy) by means of a thin-film process. In this case, the heating element can, for example, be used as a temperature sensor because the (series) resistance of the heating element is measured. In order to measure the reference temperature or the fluid background temperature, for example, the (series) resistance of the heating element (for example, determined by means of the heating voltage and / or the heating current) can be measured with the heater switched off or in a phase in which the heating element is not operated in the heating state. If the heating element itself can be used as a temperature sensor, then there is no need to provide a (separate or additional) temperature sensor, and in this case, the heating element can be operated in step a) instead of a (separate) temperature sensor. In this context, it is particularly preferred that (only) one (platinum) heating coil, which can also be used as a temperature sensor, is used as the heating element or is used in the heating element. In the off state, i.e., when the heating element is not operated in the heating state, the (platinum) heating element or heating coil can be used as a reference temperature sensor; during operation, i.e., when the heating element is operated in the heating state, it can be used as a heating element and at the same time as an operating temperature sensor. For this purpose, for example, the (known) temperature dependence of the (series) resistance of the heating element can be used.

[0029] In this case, the heating element is a component that is conventionally provided in addition to the electric motor of the support system and is arranged separately from the electric motor in particular. In this case, the heating element is particularly understood to mean an electrically operable component that preferably converts at least 70%, particularly preferably at least 80%, or even at least 90% of the electrical energy supplied to it into heat. Thus, in this case, the heating element does not particularly represent the electric motor of the flow machine that drives the support system.

[0030] In step c), the fluid volume flow rate is determined using at least the fluid temperature parameter or its variation and at least one heating element operating parameter or its variation. In step c), it is preferred to use at least one temperature sensor operating parameter or its variation and at least one heating element operating parameter or its variation to determine the fluid volume flow rate. In other words, this particularly means using both the temperature sensor operating parameter or its variation and the heating element operating parameter or its variation to determine the fluid volume flow rate. The heating element operating parameter can be understood, for example, as the heating element temperature, the heating element current, or the heating element output (current) signal. The temperature sensor operating parameter can be understood as representing the temperature measured thereby, the temperature sensor current, or the temperature sensor output (current) signal. Here, the variation can particularly be understood as representing a pulse, which can advantageously be transmitted by the heating element and detected by the temperature sensor.

[0031] According to a (first) advantageous embodiment, it is proposed that the heating element operates at a defined electrical power. In this case, the temperature of the heating element can be measured. This (first) embodiment particularly relates to so-called constant current anemometry. In constant current anemometry, the heating element operates at a defined electrical power and the resulting temperature is measured.

[0032] According to a (second) advantageous embodiment, it is proposed to keep the heating element at a constant temperature. In this case, the electrical power of the heating element can be measured. This (second) embodiment particularly relates to so-called constant temperature anemometry. In constant temperature anemometry, the heating element is kept at a constant temperature and the electrical power required therefor is measured.

[0033] According to a (third) advantageous embodiment, it is proposed that the heating element operates in a pulsed manner. In this case, in step c), the variation in the fluid temperature can be detected by means of a temperature sensor, particularly located downstream of the heating element. This (third) embodiment particularly relates to the so-called pulse response method. In the pulse response method, the heating element operates in a pulsed manner and the time is measured until a heat pulse is measured at the downstream temperature sensor. To improve the measurement resolution, the pulse operation can be performed, for example, by means of a binary random number sequence, and the time delay can be determined by an autocorrelator. In addition, it is preferred to additionally consider the maximum amplitude of the response pulse in the calculation.

[0034] Preferably, in step d) for example, the fluid volume flow rate determined in step c) is provided as a control parameter for the support system. The processing unit of the support system can provide this control parameter as an output variable, particularly to the control unit of the support system, which preferably adjusts the power of the electric motor and thus particularly also adjusts the (blood) delivery rate of the support system.

[0035] On the other hand, a processing unit is proposed, which is configured to execute the method proposed herein. The processing unit may have a memory in which calibration data may be stored. As an alternative or supplement to the calibration data, at least one (speed-related) calibration coefficient and / or a thermal model of the heating element may also be stored in the memory. Additionally, the processing unit may include a microprocessor that can access the memory. The processing unit preferably receives data from at least one heating element and / or at least one temperature sensor. The processing unit may also include electronic components for controlling and reading the heating element and the temperature sensor.

[0036] According to another aspect, an implantable vascular support system is proposed, which includes:

[0037] - a temperature measuring device in the region of the cannula of the support system,

[0038] - a heating element that can cause a change in the fluid temperature in the cannula.

[0039] The support system is preferably a left ventricular assist device (LVAD) or a percutaneous, minimally invasive left heart support system. Additionally, the support system is preferably fully implantable. In other words, this particularly means that the devices required for detection, in particular the reference temperature sensor, the motor temperature sensor, and the current sensor, are entirely located within the patient's body and remain there. The support system is particularly preferably configured and / or adapted to be at least partially arranged in the ventricle, preferably in the left ventricle of the heart, and / or arranged in the aorta, particularly at the aortic valve position.

[0040] The temperature measuring device preferably includes a temperature sensor. The temperature measuring device may also preferably include another temperature sensor. However, it is not necessary to separately provide the temperature measuring device from the heating element. Instead, the temperature measuring device may also be formed in the heating element and / or formed by the heating element itself. For this purpose, (implicit) temperature measurement based on the series resistance of the heating element is particularly preferred.

[0041] Furthermore, the support system preferably includes a flow generator, such as a pump. The support system preferably has an electric motor. The electric motor is typically a component of the flow generator. The support system is preferably elongated and / or tubular. Preferably, the (inlet) cannula and the flow generator are arranged in the regions of opposite ends of the support system.

[0042] According to an advantageous embodiment, the support system further includes a processing unit configured to execute the method proposed herein.

[0043] The details, features, and advantageous embodiments discussed in connection with the method may also correspondingly appear in the processing unit and / or support system proposed here, and vice versa. In this regard, full reference is made here to the explanations regarding the detailed characterization of the features.

[0044] The solution proposed here and its technical environment will be explained in more detail below with reference to the accompanying drawings. It should be noted that the present invention should not be limited by the exemplary embodiments shown. In particular, unless otherwise explicitly stated, partial aspects of the facts explained in the drawings can also be extracted and combined with other components and / or insights from other drawings and / or this specification. The following is schematically shown:

[0045] Figure 1a Percutaneous minimally invasive left heart support system,

[0046] Figure 1b Invasively implanted left heart support system below the chest opening,

[0047] Figure 2 Implantable vascular support system that can perform constant current and constant temperature methods,

[0048] Figure 3 According to Figure 2 Component architecture of the support system,

[0049] Figure 4 According to Figure 2 Illustration of the control circuit of the support system,

[0050] Figure 5 Another implantable vascular support system that can perform constant current and constant temperature methods,

[0051] Figure 6 Another implantable vascular support system that can perform pulse response methods,

[0052] Figure 7 Another implantable vascular support system that can perform pulse response methods, and

[0053] Figure 8 According to Figure 6 or Figure 7 Measured value time curve of the support system.

[0054] There are mainly two design variants of the implantable left heart support system (LVAD), as shown in Figure 1a and 1b as shown. Figure 1a shows the (percutaneous) minimally invasive left heart support system 7, while Figure 1b shows the apical left heart support system 8 invasively implanted below the chest opening. According to Figure 1a the variant directly delivers blood from the left ventricle 9 into the aorta 10 because the (percutaneous) minimally invasive left heart support system 7 is centered in the aortic valve 11. According to Figure 1b the variant delivers blood from the left ventricle 9 via a bypass tube 12 through the apex to the aorta 10.

[0055] Figure 2 Schematically shows an implantable vascular support system 2 in the aortic valve position that can perform constant current and constant temperature methods.

[0056] The support system 2 is, for example, a left ventricular assist device (LVAD), a tubular elongated structure with a cannula portion, in which a (proximal) cannula 4 is formed, and has a flow generating portion that is connected to the cannula portion and in which a flow generator 32 is provided. The support system 2 projects distally from the aorta 10 through the aortic valve 11 into the ventricle 9. The (proximal) cannula 4 of the support system 2 projects into the ventricle 9. A fluid volume flow rate 1 is conveyed, for example, from the ventricle 9 through the cannula 4 using the flow generator 32 of the support system 2 (for example, a pump that can have an electric motor), for example pumped into the aorta 10. Thus, the fluid volume flow rate 1 is also referred to as the pump volume flow rate (Q p ), which only quantifies the flow through the support system 2 itself.

[0057] In addition, it can be seen that a certain aortic valve volume flow rate 26 reaches the aorta 10 via the physiological path through the aortic valve 11. Thus, the cardiac volume or total fluid volume flow rate 27 (Q Figure 2 in the region of the support system 2 from the ventricle 9 to the aorta 10 through the cross-sectional geometry 33 of the aorta 10 is the sum of the fluid volume flow rate 1 (Q HZV ) and the aortic valve volume flow rate 26 (Q p ). a )

[0058] A temperature sensor 3 is arranged in the region of the cannula 4. For this purpose, the temperature sensor 3 is located, for example, at the distal end of the cannula 4 (in the ventricle 9, from where fluid such as blood flows). The support system 2 also includes a heating element 5 that can change the fluid temperature in the cannula 4, for example, by Joule heating or ohmic resistance heating when the heating element 5 is energized.

[0059] According to Figure 2 the temperature sensor 3 is a reference temperature sensor that detects a reference temperature 21, which is, for example, the background blood temperature in this case. For this purpose, the (reference) temperature sensor 3 is located in the thermally unaffected blood flow upstream of the heating element 5, which represents the heat source, here, for example, in the region before or upstream of the heating element 5. Instead of a separate (reference) temperature sensor 3, the value of another (second) temperature sensor is arranged, for example, at the height of the heating element 5, or if the system is not operating and thus this other temperature sensor is not affected by the heating element 5, it can also be used downstream (see Figure 5 , 6 : reference numeral 24; Figure 7: Reference numeral 3). Since the blood temperature of a resting patient changes only slowly, this value can also represent a good estimate of the background temperature. In addition, depending on the design of the heating element 5, the resistance of the heating element 5 itself can also be used as the temperature sensor 3.

[0060] If a separate reference temperature sensor is used (e.g. Figure 2 In the case of the temperature sensor 3 shown in the figure, the separate reference temperature sensor should be positioned in the support system 2 in such a way that it is not affected by the thermal output of the heating element 5, for example, at the tip of the support system 2 pointing toward the ventricle 9 and / or the cannula 4, and / or upstream of the heating element 5 (with respect to the blood flow) in a thermally decoupled manner. As a result, the temperature increase can advantageously be determined by supplying thermal energy to the observed fluid volume. Due to the directional flow in the medium, the exemplary minimum distance of the reference temperature sensor from the heating element 5 is determined, in particular (primarily), by the thermal conductivity of the carrier material. For non-metallic carrier materials, a distance of at least 5 mm [millimeters] is advantageous.

[0061] The principle of operation here is based on a good understanding of the heat capacity of a fluid (in this case blood) (formula symbol C; see Figure 4 23 in FIG. 2 ), and based on determining the electrical power dQ required to heat the blood by defining the temperature dT:

[0062]

[0063] Using a well-known heat capacity C (provided in the algorithm), the measured energy supply dQ and the temperature increase dT determined from the two measured (fluid) temperatures, it is thus possible to calculate the fluid volume V or the fluid volume flow rate 1 transferred during the observation period (formula symbol Q). In this case, the background blood temperature required for the difference dT can be calculated with the help of the (reference) temperature sensor 3 or, if the heating element has been inactive for a sufficiently long time, from the value of another temperature sensor (see the above explanation).

[0064] In this case, the heating element 5 is formed, for example, with a heating wire or hot wire. The hot wire is realized on the wall inside the cannula 4, which can also be called the suction tube, as a result of which a limited blood volume can be advantageously studied and heating of, for example, the aortic valve 11 can be excluded when the support system slides.

[0065] About the basis Figure 2 The operating mode of the embodiment of Figure 4 The following explanation.

[0066] Figure 3 Schematically shows the Figure 2Component architecture of the support system. In this case, the support system 2 includes, for example, a control unit 13, a temperature sensor 3, and a heating element 5 formed, for example, as a heating wire or a heating filament. As an example, the control unit 13 is here a component of the processing unit 6 of the support system 2.

[0067] Figure 4 Schematically shows according to Figure 2 A diagram of the control circuit of the support system 2. The reference numerals are used uniformly, such that the explanation of the operating mode regarding the embodiment according to Figures 2 to 4 Refers to Figure 2 And 3 .

[0068] Figure 4 The exemplary control circuit shown in can be implemented in the control unit 13 according to Figure 3 , and the control unit can in turn be a component of the support system 2, in particular a component of the processing unit 6 of the support system 2. The control circuit includes a controller 14 and a heating element 5. The disturbing variables affecting the heating element 5 (control path) are the reference temperature 21, the fluid volume flow rate 1, and the heat capacity 23 (of the fluid, here blood). Here, the control variable is the current 20 and is returned to the controller 14. Here, the current 20 (control variable) and the voltage 19 (manipulating variable) are returned together through the determined actual power 17. The control deviation 18 is obtained by subtracting the actual power 17 from the target power 16. The above disturbing variables of the fluid volume flow rate 1, the reference temperature 21, and the heat capacity 23, as well as the current 20 (control variable) and the voltage 19 (manipulating variable), are also provided to the calculation unit 15. The calculation unit determines the actual power 17 from the voltage 19 and the current 20 and the actual resistance 22 of the heating element 5, and also determines the heating element temperature 25 from the actual resistance 22 (for example, based on the known temperature correlation of the resistance). The calculation unit 15 calculates the fluid volume flow rate 1 from which, where the latter can be provided as an average volume flow rate.

[0069] In an embodiment determined as a constant current anemometry, the heating element 5 is here provided with a constant power, for example, by the controller 14 in the control unit 13, and the resistance 22 for measuring the heating element temperature 25 and the reference temperature 21 is read from the reference temperature sensor 3 (or the heating element resistance 22 when the heater is off, i.e., when the heating element 5 is not operating in the heating state) in order to determine the reference temperature 21). The fluid volume flow rate 1 or Q is calculated in the calculation unit 15 based on the electrical heating element power consumption 17, the heating element temperature 25 determined based on the resistance 22 of the heating element 5, and the reference temperature 21. p .

[0070] In an embodiment for constant temperature and wind speed measurement, the heating element temperature 25 of the heating element 5 is hereby, for example, maintained at a defined temperature by the controller 14 or maintained at a defined temperature increase based on a reference or background temperature 21. Based on the required wire power consumption 17 and the background temperature 21, the fluid volume flow rate 1 or Q is calculated in the calculation unit 15 of the control unit 13 p .

[0071] Figure 5 Another implantable vascular support system 2 in which the constant current and constant temperature methods can be carried out is schematically shown. According to Figure 5 the support system 2 and the support system 2 according to Figure 2 have many common features, such that reference is made in this regard to the above explanation regarding Figure 2 . According to Figure 5 the design variant and the design variant according to Figure 2 differ in that another (second) temperature sensor 24 is positioned in thermal coupling with the heating element 5, such that the temperature of the heating element 5 can be determined not based on the resistance 22 of the heating element 5, but rather based on the resistance of the additional temperature sensor 24

[0072] Figure 6 Another implantable vascular support system 2 in which the pulse response method can be carried out is schematically shown. In this variant, another temperature sensor 24, preferably arranged on the wall inside the cannula 4, is spaced apart from the heating element 5 (in the direction of the flow machine 32, downstream of the heating element 5), such that the transit time and the thermal dilution effect can be observed. As in the above design variant, here the optional (see Figure 7 ) reference temperature sensor formed by the temperature sensor 3 is located upstream in order to determine the reference or background temperature 21 of the fluid (here: blood). In this case, it is ensured that the temperature sensor 3 and the additional temperature sensor 24 are thermally decoupled from the heating element 5, and the other temperature sensor 24 is also thermally decoupled therefrom due to its spatial proximity to the flow machine 32. Depending on the carrier material, a distance of 5 - 10 mm is suitable in this case

[0073] The heating element 5 is acted upon by a power pulse 31 and introduces a defined amount of energy E p into the blood volume of the cannula 4, which results in an increase in the blood temperature. Due to the (pump) activity of the flow machine 32, the blood further flows in the direction of the other temperature sensor 24 at a flow rate related to Q p , which observes the maximum temperature T p after a transit time Δt related to Q m . Based on E p or the heating element power consumption 17, using Δt, the reference temperature 21 and T m , the fluid volume flow rate 1 or Q is calculated in the control unit 13p (either by a time Δt or by a time Δt and an amplitude height T m ).

[0074] The observable effect is the passage time, where a high fluid volume flow 1 corresponds to a short passage time from the heating element 5 to the other temperature sensor 24, and an amplitude variation based on the fixed thermal resistance of the heating element 5 to the blood volume and the fixed heat capacity 23 of the blood, where a slow fluid volume flow 1 corresponds to a sharp temperature rise at the other temperature sensor 24, while a fast flow corresponds to a small temperature rise.

[0075] Figure 7 Another implantable vascular support system 2 in which the pulse response method can be carried out is schematically shown. According to Figure 7 the support system 2 has many common features with the support system 2 according to Figure 6 such that reference can be made in this regard to the explanations above regarding Figure 6 . The difference is that only one temperature sensor 3 is provided in Figure 7 . This temperature sensor is preferably on the wall inside the cannula 4 and in this case serves the purpose achieved by the other temperature sensor 24 in the embodiment according to Figure 6 . Thus the embodiment according to Figure 7 is managed without a (separate) reference temperature sensor.

[0076] Figure 8 Schematically shown is the measured value time curve of the support system 2 according to Figure 6 or Figure 7 . The temperature curve measured by means of the temperature sensor arranged downstream of the heating element 5 (reference numeral 24 in Figure 6 and reference numeral 3 in Figure 7 ) is plotted at time 29, where the temperature is measured as a voltage value via an analog / digital converter such that both the voltage 19 and the analog / digital converter output 28 are plotted at time 29. Various measured value curves are plotted, namely a first measured value curve 34, a second measured value curve 35, a third measured value curve 36, a fourth measured value curve 37, a fifth measured value curve 38 and a sixth measured value curve 39, where the measured value curves are arranged according to decreasing fluid volume flow (pump volume flow); thus the measured value curve 39 represents the temperature curve at the temperature sensor in the case of a low fluid volume flow and thus the measured value curve 34 represents the temperature curve at the temperature sensor in the case of a high fluid volume flow. Additionally, as an example only the time difference 30 until the pulse 31 up to the measured value curve 39 is marked. It can clearly be seen that the time difference 30 is inversely proportional to the fluid volume flow, as is also the amplitude (maximum value) of the measured value curves. Additionally, in accordance with Figure 8In the illustration, pulses 31 of other measurement value curves 34, 35, 36, 37, and 38 can also be seen, so there are a total of six pulses 31. For the interpretation of the measurement value curves, refer to the above regarding Figure 6 and 7 for the interpretation, especially the observed effects described there.

[0077] The solution proposed here has one or more of the following advantages in particular:

[0078] · By integrating the sensor into the inlet cannula of the VAD, contact between the tissue and the heating element can be prevented, thereby preventing tissue damage.

[0079] · The advantage of integration into the inlet cannula is the (flow) geometry, so the volume of blood under study is known, which can simplify or replace the calibration of the sensor depending on the implementation variant. Commercially available catheters require the administration of an ice water bolus for calibration relative to the vascular volume.

[0080] · Continuous Q p measurement allows for the rapid diagnosis of suction, i.e., the suction of the inlet tube on the ventricular wall, thereby weakening the pump function.

[0081] In summary, special attention should be paid to the following preferred features of the present invention:

[0082] A method for determining the fluid volume flow rate 1 through an implantable vascular support system 2 includes the following steps:

[0083] a) determining a fluid temperature parameter in the region of the cannula (4) of the support system (2),

[0084] b) operating a heating element (5) that can cause a change in the fluid temperature in the cannula (4),

[0085] c) determining the fluid volume flow rate (1) using at least the fluid temperature parameter or its change and at least one heating element operating parameter or its change.

[0086] An implantable vascular support system, i.e., a vascular support system that can be arranged in a human or animal body, includes a temperature measuring device in the region of the cannula 4 of the support system 2 and includes a heating element 5 that can cause a change in the fluid temperature in the cannula (4).

Claims

1. A computer processing unit configured to execute a method for determining a blood volume flow rate through a heart support system, the method comprising: Determining a first temperature parameter of blood delivered by a flow driver through a cannula by a first temperature sensor, the first temperature sensor being located at the cannula inlet; Determining a second temperature parameter by a second temperature sensor, the second temperature sensor being thermally coupled to a heating element or disposed between the heating element and the flow driver; Operating a heating element located downstream of the first temperature sensor to change the temperature of the blood in the cannula downstream of the first temperature sensor and upstream of the flow driver; And Determining the blood volume flow rate based on 1) at least one of the first temperature parameter and the second temperature parameter of the blood, and 2) a heating element operating parameter.

2. The computer processing unit according to claim 1, wherein the first temperature sensor is located at least 5 mm upstream of the heating element.

3. The computer processing unit according to claim 1, wherein the first temperature sensor is located at the distal end of the cannula.

4. The computer processing unit according to claim 1, wherein the first temperature sensor is located in an opening of the cannula inlet.

5. A heart support system comprising: A flow driver configured to deliver blood through a cannula; A first sensor disposed in a cannula region upstream of the flow driver and configured to measure a temperature parameter of the blood at the cannula inlet; A heating element located downstream of the first sensor and upstream of the flow driver and configured to change the temperature of the blood in the cannula downstream of the first sensor region; And A second sensor thermally coupled to the heating element or disposed between the heating element and the flow driver.

6. The heart support system according to claim 5, further comprising a computer processing unit configured to determine a blood volume flow rate through the cannula based on 1) the temperature parameter of the blood and 2) a heating element operating parameter.

7. The heart support system according to claim 5, wherein the flow driver is configured to deliver blood through the cannula, towards the flow driver.

8. The heart support system according to claim 5, wherein the cannula is configured to direct blood from a ventricle of the heart to the aorta.

9. The heart support system according to claim 5, wherein the first sensor includes a temperature sensor for measuring a reference temperature, and the temperature sensor is disposed at an end of the cannula facing away from the flow driver.

10. The heart support system according to claim 5, wherein the heating element is disposed on an inner wall of the cannula.

11. The heart support system according to claim 5, wherein the heating element is disposed within the cannula between the first sensor and the flow driver.

12. The heart support system according to claim 5, wherein the heating element is formed as a heating wire.

13. The heart support system according to claim 5, wherein the second sensor is thermally coupled to the heating element.

14. The heart support system according to claim 5, wherein the second sensor is arranged between the heating element and the flow inducer.

15. The heart support system according to claim 5, further comprising: a tubular elongate structure having a cannula portion in which the cannula is formed, and a flow inducer portion connected to the cannula portion and in which the flow inducer is arranged.

16. The heart support system according to claim 7, wherein the second sensor comprises a temperature sensor configured to measure the blood temperature, and wherein the temperature sensor is arranged between the heating element and the flow inducer for measuring the temperature of the blood directed towards the flow inducer.

17. The heart support system according to claim 16, wherein the temperature sensor is arranged on the inner wall of the cannula.

18. The heart support system as claimed in claim 5, wherein the first sensor is located at least 5 mm upstream of the heating element.

19. The heart support system as claimed in claim 5, wherein the first sensor is located at the distal end of the cannula.

20. The heart support system as claimed in claim 5, wherein the first sensor is located in the opening of the cannula inlet.

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