Implanted vascular support system with means for determining the fluid volume flow of a fluid flowing through it

Description

[0001] The invention relates to an implantable vascular support system. The invention is particularly applicable to (fully) implanted left ventricular assist devices (LVADs).

[0002] Implantable left ventricular assist devices (LVADs) exist primarily in two designs. The first common design is the (percutaneous) minimally invasive left ventricular assist device. The second common design is the apical left ventricular assist device, which is implanted invasively under the chest opening. In the first design, blood is pumped directly from the left ventricle into the aorta because the (percutaneous) minimally invasive left ventricular assist device is positioned centrally in the aortic valve. In the second design, blood is pumped apically from the left ventricle into the aorta via a bypass tube.

[0003] The function of a cardiac support system is to pump blood. In this context, the so-called cardiac output (CO, usually expressed in liters per minute) is of high clinical relevance. In other words, cardiac output refers to the total volume of blood flow (from one ventricle), particularly from the left ventricle to the aorta. Therefore, it is understandable that this parameter is being measured during the operation of a cardiac support system.

[0004] Depending on the level of assistance, which describes the proportion of the volume flow delivered by a means of support, such as a pump in the assist system, to the total volume flow of blood from the ventricle to the aorta, a certain volume flow passes through the aortic valve into the aorta via the physiological pathway. The cardiac output, or total volume flow (QCO) from the ventricle to the aorta, is therefore typically the sum of the pump volume flow (Qp) and the aortic valve volume flow (Qa). This can be expressed by the following relationship: Q HZV = Q p + Q a

[0005] An established method for determining cardiac output (QCO) in the clinical setting is the use of dilution techniques. However, these all rely on a transcutaneously inserted catheter and can therefore only provide cardiac output measurements during cardiac surgery. Since acquiring cardiac output (QCO) via a left ventricular assist device (LVAD) is difficult to implement, Qp can be measured by suitable LVAD components. For high levels of support (i.e., Qp / QCO), Qa approaches zero, so that approximately Qp can be used as cardiac output (QCO).

[0006] An established method for measuring the pump flow rate (Qp) is the correlation of the operating parameters of the support system, primarily the electrical power consumption, possibly supplemented by other physiological parameters such as blood pressure. Since these methods are based on statistical assumptions and the underlying pump characteristic curve of the LVAD used, the correlated Qp values ​​are subject to error. Therefore, incorporating a flow sensor is desirable to improve the measurement quality of the Qp parameter.

[0007] WO 2014 / 141284 A2 describes a kidney pump. It does not include a cannula for pumping blood from a ventricle of the heart into the aorta.

[0008] WO 2012 / 112378 A2 discloses a blood flow assistance system comprising a blood pump with a cannula and a flow sensor. The flow sensor has a heating element in the form of a thermistor, which is positioned in the center of the flow cross-section in a blood stream.

[0009] From WO 2014 / 165635 A2, an implantable blood pump with a heating element and a temperature sensor for determining blood flow is known.

[0010] The object of the invention is to create an improved implantable vascular support system that enables the determination of blood volume flow.

[0011] In particular, it is an object of the invention to create an implantable vascular support system by means of which a fluid volume flow can be determined in a blood-permeated area in a human or animal body in which the vascular support system is implanted or arranged.

[0012] The invention is defined by the claims. The methods are not part of the claimed invention. The determination of a fluid volume flow rate through an implanted vascular support system is described, comprising the following steps: a) Determining a fluid temperature parameter in the area of ​​a cannula of the support system, b) Operating a heating element that can cause a change in the fluid temperature in the cannula, 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.

[0013] The vascular support system is preferably a cardiac support system, particularly preferably a ventricular support system. The method preferably serves to determine a fluid volume flow through a blood vessel or through a cross-section of the blood vessel. The blood vessel is, for example, the aorta, particularly in the case of a left ventricular support system, or the common trunk (pulmonary trunk) into the two pulmonary arteries, particularly in the case of a right ventricular support system, preferably the aorta. The method preferably serves to determine a fluid volume flow from a ventricle of a heart, particularly from a (left) ventricle of a heart to the aorta through a (fully) implanted, (left) ventricular (heart) support system. The fluid is typically blood. The support system is preferably arranged at the outlet of the left ventricle of the heart.The support system is particularly preferably positioned in the aortic valve position.

[0014] The support system is preferably implanted such that at least partially, 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. Furthermore, the support system is preferably located along at least 50%, particularly preferably at least 85%, or even at least 95% of its length in the fluid flow. Preferably, one end of the support system, in the region where the electric motor is located, is located at least partially in the aorta. Furthermore, preferably, the opposite end of the support system, in the region where an (inlet) cannula of the support system is located, is located at least partially in a (the left) ventricle of the heart.Preferably, the support system is positioned centrally within the aortic valve, so that blood is drawn distally from the ventricle and delivered proximally into the ascending aorta. Preferably, the support system is at least partially, more preferably completely, or with at least 20%, more preferably at least 40%, most preferably at least 50%, or even at least 95% of its (outer) surface area located within a blood vessel, such as an artery, particularly the aorta. Most preferably, the support system is implanted such that it is (completely) located within the (ascending or descending) aorta.

[0015] The fluid flow rate to be determined is the flow that passes through the support system itself. In other words, this refers specifically to a fluid flow rate that passes only through the support system. The fluid flow rate to be determined is generally the so-called pump flow rate (symbol Qp), which quantifies (only) the flow through the support system itself. This method is particularly suitable for determining the pump flow rate (Qp) of a (fully) implanted (left) ventricular assist device (LVAD), especially in the aortic valve position and / or through the support system itself.

[0016] The method is based primarily on (thermal) anemometric (measurement) principles for flow measurement. The fundamental principle is that a flowing medium cools a hot body depending on the flow velocity. Advantageously, the method enables continuous, accurate measurement of Qp by a sensor element integrated into an LVAD and based on thermal anemometry. With the solution presented here, cardiac output (at least approximately via Qp) can advantageously be provided outside the operating room setting with comparable accuracy to that obtained using a dilution catheter.

[0017] The solution proposed here is characterized in particular by the integration of one or more heating elements, or one or more heating elements and one or more temperature sensors, into an inlet cannula of a venous assisted retrieval device (VAD). Advantageously, the method calculates Qp from the measured voltage data of at least one heating element and / or at least one temperature sensor. Three possible operating principles can be applied in this process: constant current anemometry, constant temperature anemometry, or a pulse response method.

[0018] In step a), a fluid temperature parameter is determined in the area of ​​a cannula of the support system. A (separate) temperature sensor can be used for this purpose. Alternatively or cumulatively, the determination can be carried out by the heating element itself. For this, for example, an electrical series resistance of the heating element can be used. The fluid temperature parameter can be a (fluid) temperature, a temperature sensor current, a temperature sensor output (current) signal, or a (temperature-dependent) electrical resistance value, particularly of the heating element.

[0019] In step a), a temperature sensor is preferably operated in the region of a cannula of the support system. This operation particularly includes measuring a fluid temperature and / or a change in the fluid temperature. Preferably, the temperature sensor is arranged on an inner or outer surface of the cannula. More preferably, at least two temperature sensors may be provided. One temperature sensor may be arranged upstream and another downstream of the heating element.

[0020] The cannula is specifically an inlet cannula, which can also be referred to as an intake tube. The (inlet) cannula is preferably designed so that, in its implanted state, it can guide fluid from a (left) ventricle of the heart to a flow machine of the support system and / or to the aorta.

[0021] Preferably, the temperature sensor(s) are arranged at a distance from the heating element. This offers the advantage that the temperature sensor is not thermally affected by the heating element, which is particularly advantageous when the temperature sensor serves as a reference temperature sensor. Suitable temperature sensors include thermistors (PTC), resistive elements such as platinum, semiconductor junctions, or thermocouples.

[0022] The temperature sensor, or a further temperature sensor, can be integrated into or arranged on the heating element. If at least two temperature sensors are provided, it is preferred that a reference temperature sensor is arranged at a distance from the heating element and a further temperature sensor is integrated into or arranged on the heating element. If only one temperature sensor is provided, it may be necessary that the heating element be switched off or not operated in a heating state during a measurement of a reference temperature by the temperature sensor. A preferred approach is to place a flat temperature sensor between the inner wall of the cannula and the heating element, or to attach a temperature sensor to the heating element. A particularly preferred implementation is to place the temperature sensor centrally within the heating area of ​​the heating element.Another possible implementation would be a three-layer structure, in which a heating meander is placed between a lower and a middle polyimide film and a platinum wire meander is placed between the middle and an upper polyimide film as a temperature sensor.

[0023] Preferably, in step a), a reference temperature of the fluid is determined, in particular 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, for example, be arranged in and / or on an (inlet) cannula of the support system. The reference temperature typically represents a background temperature of the fluid, in other words, a fluid temperature that is not thermally influenced by the heating element and / or a turbomachine of the support system.

[0024] In step b), a heating element is operated that can cause a change in the fluid temperature within the cannula. In other words, this means, in particular, that the heating element is designed and arranged in such a way that it can induce a change in the fluid temperature within the cannula. For this purpose, the heating element can be located directly inside the cannula or on an inner surface of the cannula. However, it is (alternatively) possible for the heating element to be located in a wall of the cannula, on an outer surface of the cannula, or even at a distance from the cannula, as long as the heating element is capable of increasing the fluid temperature of at least a portion of the fluid inside the cannula, for example, through heat conduction. The heating element is typically operated by an electric current.

[0025] Preferably, the heating element is formed with at least one heating filament or thermofilament. A particularly preferred heating element is round or tubular, lining the inner surface of the cannula at least in a segmental or circumferential section and / or longitudinal section. Furthermore, the heating element is preferably formed as a (flexible) heating film that at least partially lines the inner surface of the cannula. At least one heating filament is particularly preferably arranged in or on the film. Preferably, the heating filament extends (for example, in a meandering pattern and / or in loops) continuously over at least 50% or even the entire inner surface of the cannula lined by the film. At least two heating filaments may be provided. It is preferred if the heating element...The thermofilament is integrated into the cannula wall (on the inner surface of the cannula), which advantageously allows for the examination of a defined blood volume and prevents heating of, for example, the aortic valve should the support system slip. If more than one heating element or heating filament is provided, these can be arranged at opposite positions on the inner surface of the cannula. Preferably, the heating elements or heating filaments are controlled or energized together.

[0026] It is also advantageous if the heating element itself is used as a temperature sensor. Preferably, the heating element is configured to both cause a change in the fluid temperature within the cannula and to detect, and in particular measure, a change in the fluid temperature within the cannula. In particular, by a suitable selection of the heating element, especially the heating filament material (resistance change with temperature change), the heating element itself can be used as a temperature sensor. An advantageous embodiment of the heating element is, for example, a (platinum) wire meander (meander-shaped heating filament made of a platinum alloy) between, for example, polyimide films or attached to a film. Preferably, the heating element has heating meanders produced using a thin-film process from conductive, resistant materials (e.g., platinum alloy).The heating element can be used as a temperature sensor, for example, by measuring its series resistance. To measure the reference temperature or fluid background temperature, the series resistance of the heating element can be measured, for instance, when the heater is switched off or during a phase in which the heating element is not operating in a heating state (e.g., determined by a heating voltage and / or heating current). If the heating element itself can be used as a temperature sensor, no (additional or separate) temperature sensor needs to be provided, and in step a), the heating element can be operated instead of the (separate) temperature sensor. In this context, it is particularly preferred that (only) a (platinum) heating meander, which can also be used as a temperature sensor, is used as the heating element or within the heating element. In the switched-off state, i.e.,If the heating element is not operating in a heating state, the (platinum) heating element or heating meander could be used as a reference temperature sensor; in operation, i.e., when the heating element is operating in a heating state, it could function as both a heating element and an operating temperature sensor. For this purpose, a (known) temperature dependence of a heating element (series) resistor could be used, for example.

[0027] The heating element is a component regularly provided in addition to an electric motor of the support system, and is specifically arranged separately from the electric motor. Here, a heating element is understood to be, in particular, an electrically operated component that preferably converts at least 70%, more preferably at least 80%, or even at least 90% of the electrical energy supplied to it into heat. Consequently, a heating element here specifically does not refer to an electric motor that drives a turbomachine of the support system.

[0028] In step c), the fluid volume flow rate is determined using at least the fluid temperature parameter or its change and at least one heating element operating parameter or its change. Preferably, in step c), the fluid volume flow rate is determined using at least one temperature sensor operating parameter or its change and at least one heating element operating parameter or its change. In other words, this means, in particular, that the fluid volume flow rate is determined using both a temperature sensor operating parameter or its change and a heating element operating parameter or its change. A heating element operating parameter can be, for example, a heating element temperature, a heating element current, or a heating element output (current) signal.A temperature sensor operating parameter can be understood as a measured temperature, a temperature sensor current, or a temperature sensor output (current) signal. A change, in this context, can be understood in particular as a pulse, which is advantageously emitted by the heating element and detected by the temperature sensor.

[0029] The heating element is operated with a defined electrical power. The temperature of the heating element is then measured. This (first) configuration applies in particular to so-called constant-current anemometry. In constant-current anemometry, the heating element is operated with a defined electrical power and the resulting temperature is measured.

[0030] According to a (second) advantageous embodiment, it is proposed that the heating element be kept at a constant temperature. The electrical power of the heating element can then be measured. This (second) embodiment relates in particular to so-called constant-temperature anemometry. In constant-temperature anemometry, the heating element is kept at a constant temperature and the electrical power required to maintain this temperature is measured.

[0031] According to a (third) advantageous embodiment, it is proposed that the heating element be operated in pulsed mode. In this embodiment, a change in fluid temperature can be detected in step c) by means of a temperature sensor, which is located, in particular, downstream of the heating element. This (third) embodiment relates in particular to a so-called pulse response method. In the pulse response method, the heating element is operated in pulsed mode, and the time until the thermal pulse is detected at a temperature sensor located downstream is measured. To improve the measurement resolution, the pulsed operation can be achieved, for example, by a binary random number sequence, and the time delay can be determined by an autocorrelator. Furthermore, it is preferred that the maximum amplitude of the response pulse be additionally taken into account in the calculation.

[0032] Preferably, the fluid volume flow determined in step c) is provided, for example, in step d) as a control parameter for the support system. A processing unit of the support system can provide this control parameter as an output variable, in particular to a control unit of the support system, which preferably regulates the power of an electric motor and thus, in particular, also the (blood) delivery rate of the support system.

[0033] In addition, a processing unit is proposed for carrying out a method proposed herein. The processing unit may include a memory in which calibration data can be stored. Alternatively or additionally to the calibration data, the memory may also contain at least one (speed-dependent) calibration factor and / or a thermal model of the heating element. Furthermore, 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 an electronic assembly for controlling and reading data from the heating element and the temperature sensor.

[0034] Another aspect is the proposal for an implantable vascular support system, encompassing: a temperature measuring device in the area of ​​a cannula of the support system, a heating element that can cause a change in the fluid temperature of the cannula.

[0035] The support system is preferably a left ventricular assist device (LVAD) or a percutaneous, minimally invasive left ventricular assist device. It is further preferably fully implantable. In other words, this means, in particular, that the means required for data acquisition, especially the reference temperature sensor, the motor temperature sensor, and the current sensor, are located entirely within the patient's body and remain there. The support system is particularly preferably designed or suitable for placement at least partially within a ventricle, preferably the left ventricle of a heart and / or an aorta, particularly in the aortic valve position.

[0036] The temperature measuring device preferably comprises a temperature sensor. More preferably, the temperature measuring device can also include a further temperature sensor. However, it is not essential that the temperature measuring device be provided separately from the heating element. Rather, the temperature measuring device can also be formed within the heating element and / or by the heating element itself. Particularly preferred is an (implicit) temperature measurement via a series resistor in the heating element.

[0037] Preferably, the support system includes a turbomachine, such as a pump. Preferably, the support system also includes an electric motor. The electric motor is typically an integral part of the turbomachine. The support system is preferably elongated and / or tube-like. A (feed) cannula and a turbomachine are preferably arranged at opposite ends of the support system.

[0038] The support system also includes a processing unit set up to carry out a procedure proposed here.

[0039] The details, features, and advantageous configurations discussed in connection with the process may also occur in the processing unit and / or support system presented here, and vice versa. In this respect, full reference is made to the explanations provided therein for a more detailed characterization of the features.

[0040] The solution presented here and its technical context are explained in more detail below with reference to the figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the situations explained in the figures and combine them with other components and / or findings from other figures and / or the present description. The figures schematically show: Fig. 1a a percutaneous, minimally invasive left ventricular assist device (LVAD), Fig. 1 a left ventricular assist device implanted invasively under the chest opening, Fig. 2 an implanted vascular assist device capable of performing a constant current and constant temperature procedure, Fig. 3 a component architecture of an assist device according to Fig. 2 , Fig. 4 an illustration of a control loop of a support system according to Fig. 2 Fig. 5 shows another implanted vascular support system capable of performing a constant current and constant temperature procedure; Fig. 6 shows another implanted vascular support system capable of performing a pulse response procedure; Fig. 7 shows another implanted vascular support system capable of performing a pulse response procedure; and Fig. 8 shows time-dependent measurement profiles for the support system according to Fig. 6 oder Fig. 7 .

[0041] Implantable left ventricular assist devices (LVADs) exist mainly in two design variants, as described in the Fig. 1a und 1b shown. Fig. 1a shows a (percutaneous) minimally invasive left ventricular assist device 7, while Fig. 1b Figure 8 shows an apical left ventricular assist device (AVAD) invasively implanted below the chest opening. The variant according to Fig. 1a It pumps blood directly from the left ventricle 9 into the aorta 10, since the (percutaneous) minimally invasive left ventricular assist device 7 is positioned centrally in the aortic valve 11. The variant according to Fig. 1b It pumps blood apically from the left ventricle 9 via a bypass tube 12 into the aorta 10.

[0042] Fig. 2 schematically shows an implanted vascular support system 2 in aortic valve position, which can operate using a constant current and constant temperature procedure.

[0043] The support system 2 is, for example, a left ventricular assist device (LVAD). It is a tube-like, elongated structure with a cannula section in which an (inlet) cannula 4 is formed, and with a fluid machine section connected to the cannula section in which a fluid machine 32 is arranged. The support system 2 extends from the aorta 10 through the aortic valves 11 distally into the ventricle 9. The (inlet) cannula 4 of the support system 2 extends into the ventricle 9. A fluid volume flow 1 is conveyed, for example, pumped, through the cannula 4 from the ventricle 9 into the aorta 10 using the fluid machine 32 (e.g., a pump, which may include an electric motor) of the support system 2. Therefore, 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.

[0044] Furthermore, in Fig. 2 to recognize that a certain aortic valve volume flow 26 enters the aorta 10 via the physiological pathway through the aortic valves 11. The cardiac output, or the total fluid volume flow 27 (QCO) passing through the cross-sectional geometry 33 of the aorta 10 in the region of the support system 2 from the ventricle 9 to the aorta 10, is therefore the sum of fluid volume flow 1 (Qp) and aortic valve volume flow 26 (Qa).

[0045] A temperature sensor 3 is arranged in the area of ​​the cannula 4. For this purpose, the temperature sensor 3 is positioned, by way of example, at the distal end of the cannula 4 (in the ventricle 9, where the fluid, e.g., blood, flows in). Furthermore, the support system 2 has a heating element 5 that can cause a change in the fluid temperature in the cannula 4, e.g., by Joule heating or ohmic resistance heating, when the heating element 5 is energized.

[0046] Regarding temperature sensor 3 according to Fig. 2 This is a reference temperature sensor that detects a reference temperature 21, which here is, for example, the background blood temperature. For this purpose, the (reference) temperature sensor 3 is placed in the thermally unaffected blood flow upstream of the heating element 5, which represents a heat source; here, for example, in the area upstream of the heating element 5. Instead of a separate (reference) temperature sensor 3, the value of another (second) temperature sensor, e.g., located at the level of the heating element 5 or downstream of it, can also be used (see Figure 3). Fig. 5 , 6 : Reference numeral 24; Fig. 7 Reference numeral 3) can be used when the system is not in operation and therefore this additional temperature sensor is not affected by the heating element 5. Since the blood temperature changes only slowly in a resting patient, this value can also provide a good estimate of the background temperature. Furthermore, depending on the design of the heating element 5, the electrical resistance of the heating element 5 itself can also be used as a temperature sensor 3.

[0047] If a separate reference temperature sensor is used, as shown in the illustration according to Fig. 2 If the temperature sensor 3 is positioned within the support system 2 in such a way that it is not affected by the heat emitted by the heating element 5, for example, at the tip of the support system 2 or the cannula 4 pointing towards the ventricle 9, and / or thermally decoupled upstream (of the blood flow) from the heating element 5. This advantageously makes it possible to determine the temperature rise by supplying thermal energy to the observed fluid volume. Due to the directed flow in the medium, an exemplary minimum distance between the reference temperature sensor and the heating element 5 is determined in particular (mainly) by the thermal conductivity of the substrate material. Distances of at least 5 mm [millimeters] are advantageous for non-metallic substrate materials.

[0048] The operating principle here is based on the fact that, given a sufficiently known thermal capacity (symbol C; see reference 23 in Fig. 4 ) of the fluid, here blood, to determine the electrical power dQ necessary to heat the blood by a defined temperature dT: C = d Q d T

[0049] Given a sufficiently known heat capacity C (which is stored in the algorithm), a measured energy input dQ, and a temperature difference dT determined from two measured (fluid) temperatures, the fluid volume V processed during the observation period, or the fluid volume flow rate 1 (symbol Q), can be calculated. The background blood temperature required for the difference dT can be calculated either via a (reference) temperature sensor 3 or from the value of another temperature sensor (see above) if the heating element has been inactive for a sufficiently long time.

[0050] The heating element 5 is shown here as an example formed with a heating filament or thermofilament. The thermofilament is integrated into the wall of the cannula 4, which can also be referred to as the suction tube, thus advantageously allowing a defined blood volume to be examined and preventing heating of, for example, the aortic valve 11 in the event of slippage of the support system.

[0051] Regarding the operating mode of the execution according to Fig. 2 The following statements regarding Fig. 4 referred.

[0052] Fig. 3 schematically shows a component architecture of a support system according to Fig. 2 The support system 2 comprises, by way of example, a control unit 13, a temperature sensor 3, and a heating element 5, which is designed, by way of example, as a thermo- or heating filament. The control unit 13 is, by way of example, a component of a processing unit 6 of the support system 2.

[0053] Fig. 4 schematically shows an illustration of a control loop of a support system 2 according to Fig. 2 The reference numerals are used uniformly, so that the operating mode of the embodiment according to the Figuren 2 bis 4 here also on the Figuren 2 und 3 Reference is made to this.

[0054] The in Fig. 4 The exemplary control loop shown can be implemented in control unit 13. Fig. 3 The system is implemented, which in turn can be a component of the support system 2, in particular a processing unit 6 of the support system 2. The control loop comprises a controller 14 and the heating element 5. The disturbances influencing the heating element 5 (controlled system) are the reference temperature 21, the fluid volume flow rate 1, and the heat capacity 23 (of the fluid, here blood). The controlled variable is the current 20, which is fed back to the controller 14. The current 20 (controlled variable) and the voltage 19 (manipulated variable) are fed back together via the determined actual power 17. The control deviation 18 results from subtracting the actual power 17 from the setpoint power 16.The aforementioned disturbance variables fluid volume flow rate 1, reference temperature 21, and heat capacity 23, as well as the current 20 (controlled variable) and the voltage 19 (manipulated variable), are also provided to a processing unit 15, which determines the actual power 17 and the actual electrical resistance 22 of the heating element 5 from the voltage 19 and the current 20, and also determines the heating element temperature 25 from the actual electrical resistance 22 (e.g., based on the known temperature dependence of the resistance). The processing unit 15 then calculates the fluid volume flow rate 1, which can be provided as an averaged volume flow rate.

[0055] In the implementation as constant-current anemometry, the heating element 5 is supplied with constant power by the controller 14 in the control unit 13, and both the electrical resistance 22 for measuring the heating element temperature 25 and the reference temperature 21 are read from the reference temperature sensor 3 (or the heating element resistance 22 when the heater is switched off (i.e., the heating element 5 is not operating in a heating state) to determine the reference temperature 21). In the calculation unit 15, the fluid volume flow rate 1 or Qp is calculated based on the electrical heating element power consumption 17, the heating element temperature 25 determined based on the electrical resistance 22 of the heating element 5, and the reference temperature 21.

[0056] In the constant-temperature anemometry configuration, the heating element temperature 25 of the heating element 5 is maintained at a defined temperature or temperature range above the reference or background temperature 21 by the controller 14. Based on the required filament power consumption 17 and the background temperature 21, the fluid volume flow rate 1 or Qp is calculated in the calculation unit 15 of the control unit 13.

[0057] Fig. 5 Figure 2 schematically shows another implanted vascular support system 2 that can operate using a constant current and constant temperature method. The support system 2 according to... Fig. 5 has many similarities with support system 2 according to Fig. 2 , so that in this respect reference is made to the above statements regarding Fig. 2 Reference is made to the following version. Fig. 5 differs in this respect from the one after Fig. 2 , that a further (second) temperature sensor 24 is thermally coupled to the heating element 5, so that the temperature determination of the heating element 5 can take place not via the electrical resistance 22 of the heating element 5, but via the electrical resistance of the further temperature sensor 24.

[0058] Fig. 6 Figure 1 schematically shows another implanted vascular support system 2 that can perform a pulse response procedure. In this variant, an additional temperature sensor 24, preferably arranged within the wall of the cannula 4, is spatially separated from the heating element 5 (in the direction of the flow machine 32, downstream of the heating element 5), so that transit time and thermal dilution effects can be observed. As with the previously described embodiments, an optional (see Figure 2) Fig. 7 The reference temperature sensor, here formed by temperature sensor 3, is placed upstream to determine the reference or background temperature 21 of the fluid (here: blood). Care is taken to ensure that temperature sensor 3 and the additional temperature sensor 24 are thermally decoupled from the heating element 5, and that the additional temperature sensor 24, due to its proximity to the turbomachine 32, is also thermally decoupled from it. Depending on the substrate material, a distance of 5-10 mm is suitable.

[0059] The heating element 5 is subjected to a power pulse 31 and introduces a defined amount of energy Ep into the blood volume of the cannula 4, leading to an increase in blood temperature. Due to the (pump) activity of the fluid machine 32, the blood flows further towards the temperature sensor 24 at a flow velocity Qp-dependent, which observes a temperature maximum Tm after a Qp-dependent transit time Δt. Based on Ep or the heating element power consumption 17, the fluid volume flow rate 1 or Qp is calculated in the control unit 13 using Δt, the reference temperature 21, and Tm (transit time Δt or transit time Δt and amplitude Tm).

[0060] The observable effects are both a transit time, where a high fluid volume flow 1 corresponds to a short transit time from the heating element 5 to the further temperature sensor 24, and, due to the fixed thermal resistance from the heating element 5 to the blood volume and the fixed thermal capacity 23 of the blood, an amplitude change, where a slow fluid volume flow 1 corresponds to a strong temperature increase at the further temperature sensor 24 and a high flow to only a small temperature increase.

[0061] Fig. 7 Figure 2 schematically shows another implanted vascular support system 2 that can perform a pulse response procedure. The support system 2 according to... Fig. 7 has many similarities with support system 2 according to Fig. 6 , so that in this respect reference is made to the above statements regarding Fig. 6 Reference is made to... The difference is that in Fig. 7 Only one temperature sensor 3 is provided. This is preferably located inside the cannula 4 and fulfills the purpose that the further temperature sensor 24 fulfills in the embodiment according to Fig. 6 fulfilled. Thus, the embodiment according to Fig. 7 without a (separate) reference temperature sensor.

[0062] Fig. 8 schematically shows time-dependent measurement trends for support system 2 according to Fig. 6 or Fig. 7 . Here, the temperature sensor arranged downstream of the heating element 5 (reference numeral 24 in ) is used. Fig. 6 and reference numeral 3 in Fig. 7 The measured temperature profiles are plotted over time 29, with the temperature being measured as a voltage value via an analog-to-digital converter, so that both the voltage 19 and an analog-to-digital converter output 28 are plotted over time 29. Several measurement profiles are shown, namely a first measurement profile 34, a second measurement profile 35, a third measurement profile 36, a fourth measurement profile 37, a fifth measurement profile 38, and a sixth measurement profile 39, whereby the measurement profiles are ordered according to descending fluid volume flow rate (pump volume flow rate). Measurement profile 39 thus represents the temperature profile at the temperature sensor at low fluid volume flow rate, and measurement profile 34 represents the temperature profile at the temperature sensor at high fluid volume flow rate. Additionally, the time difference 30 until the pulse 31 of measurement profile 39 was measured is marked, but only as an example.It is clearly evident that the time difference 30 is inversely proportional to the fluid volume flow rate, as is the amplitude (the maximum) of the measured value. Furthermore, the following is shown in the representation: Fig. 8 Pulses 31 of the further measurement curves 34, 35, 36, 37 and 38, a total of six pulses 31, can also be identified. For an explanation of the measurement curves, reference is made to the preceding explanations regarding the Fig. 6 und 7 , in particular reference to the effects described and observed therein.

[0063] The solution proposed here offers, in particular, one or more of the following advantages: Integrating the sensor into the VAD's inlet cannula prevents tissue contact with the heating element, thus avoiding tissue damage. This integration into the inlet cannula has the advantage that the (flow-through) geometry, and therefore the blood volume being measured, is known, simplifying or even eliminating sensor calibration depending on the implementation. Commercially available catheters require the administration of an ice water bolus to calibrate to the blood vessel volume. Continuous Qp measurement enables the rapid diagnosis of suction, i.e., the inlet tube being drawn against the ventricular wall, which impairs pump function.

[0064] In summary, the following preferred features of the invention are particularly noteworthy: A method for determining a fluid volume flow rate 1 through an implanted vascular support system 2 comprises the following steps: a) Determining a fluid temperature parameter in the area of ​​a cannula (4) of the support system (2), b) Operating a heating element (5) that can cause a change in the fluid temperature in the cannula (4), 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.

[0065] An implantable, i.e., arrangable in the human or animal body, vascular support system includes a temperature measuring device in the area of ​​a cannula 4 of the support system 2 and has a heating element 5 that can cause a change in the fluid temperature in the cannula (4).

Claims

1. Implantable vascular support system (2), comprising a tubular, elongate structure a cannula portion in which a cannula (4) is designed for pumping blood from a ventricle of a heart into an aorta, a turbomachine portion connected to the cannula portion, in which a turbomachine (32) is arranged for pumping blood from a ventricle of a heart through the cannula (4) into an aorta, a temperature sensor (3) for measuring a reference temperature (21), which is arranged at one end of the cannula (4) facing away from the turbomachine (32), a heating element (5) which is arranged in the cannula (4) between the temperature sensor (3) and the turbomachine (32) and can cause a change in the fluid temperature in the cannula (4), a control unit (13) in which a control loop, which includes a controller (14), is implemented, and a processing unit (6) containing a calculating unit (15) which determines a volumetric flow Qp of blood through the cannula (4) on the basis of at least one heating element operating parameter or a change thereof, and on the basis of a reference temperature (21) measured by means of the temperature sensor (3).

2. Support system according to claim 1, wherein the calculating unit (15) determines the volumetric flow Qp of blood through the cannula (4) using a heating element operating parameter in the form of a temperature of the heating element (5) or in the form of a temperature rise above the temperature determined by means of the temperature sensor (3) and using a heating element operating parameter in the form of an electrical power consumption of the heating element (5).

3. Support system according to claim 1 or 2, wherein the heating element (5) in the cannula (4) is arranged in a portion of the cannula (4) spaced apart from the temperature sensor (3) and the turbomachine (32), and wherein the heating element (5) can cause a change in the fluid temperature in the cannula (4) when an electric current is passed through the heating element (5) so that it experiences ohmic resistance heating.

4. Support system according to any of claims 1 to 3, wherein the controller (14) supplies the heating element (5) with a constant power and the calculating unit (15) receives a determined temperature (25) of the heating element (5).

5. Support system (2) according to any of claims 1 to 4, wherein the calculating unit (15) receives a temperature (25) of the heating element (5) determined on the basis of the electrical resistance (22) of the heating element (5).

6. Support system according to claim 1, wherein the controller (14) maintains the heating element (5) at a defined temperature or at a defined temperature rise above the temperature determined by means of the temperature sensor (3), and the calculating unit (15) receives the electrical power consumption of the heating element (5) as a heating element operating parameter.

7. Support system according to claim 1 or 6, wherein an additional temperature sensor (24) thermally coupled to the heating element (5) is provided for detecting the temperature of the heating element (5).

8. Support system according to any of claims 1 to 7, wherein the temperature sensor (3) is arranged on an inner wall of the cannula (4).

9. Implantable vascular support system (2), comprising a tubular, elongate structure a cannula portion in which a cannula (4) is designed for pumping blood from a ventricle of a heart into an aorta, a turbomachine portion connected to the cannula portion, in which a turbomachine (32) is arranged for pumping blood from a ventricle of a heart through the cannula (4) into an aorta, a temperature sensor (24, 3) which is spatially separated from the heating element (5) and arranged between a heating element (5) arranged in the cannula (4) and the turbomachine (32), wherein the heating element (5) can cause a change in the fluid temperature in the cannula (4) when an electric current is passed through the heating element (5) so that it experiences ohmic resistance heating, a device for applying a power pulse to the heating element (5), as a result of which a defined amount of energy Ep is introduced into the blood volume of the cannula (4), and a device for measuring the temperature of the blood flowing through the cannula (4) by means of the temperature sensor (24, 3), and a device for calculating the volumetric flow Qp on the basis of a detected runtime Δt for a temperature maximum of the temperature detected by means of the temperature sensor (24, 3) or a device for calculating the volumetric flow Qp on the basis of a detected runtime Δt for a temperature maximum Tm of the temperature detected by means of the temperature sensor (24, 3) and an amplitude level of the temperature maximum Tm.

10. Support system according to claim 9, characterized in that the temperature measuring device has an additional temperature sensor (3) for measuring a reference temperature, which sensor is arranged at one end of the cannula (4) facing away from the turbomachine.

11. Support system according to any of claims 1 to 10, characterized in that the heating element (5) is designed as a heating filament or a thermofilament.

12. Support system according to any of claims 1 to 11, wherein the heating element (5) is arranged on an inner wall of the cannula (4).