Method for determining a total fluid volume flow in the region of an implantable vascular support system and implantable vascular support system

Abstract

The present invention relates to a method for determining a total fluid volume flow (1) in the area of ​​an implantable vascular support system (2), the method comprising the following steps: a) determining a reference temperature (3) of the fluid, b) determining a motor temperature (4) of an electric motor (5) of the support system (2), c) determining a thermal power loss (6) of the electric motor (5), d) determining the total fluid volume flow (1) using the reference temperature (3), the motor temperature (4) and the thermal power loss (6) of the electric motor (5).

Description

[0001] describe

[0002] The invention relates to a method, a processing unit, and an implantable vascular support system for determining a total fluid volume flow in the region of an implantable vascular support system. The invention is particularly useful for (totally) implantable left heart support systems (LVAD).

[0003] Implantable left heart support systems (LVAD) exist mainly in two design variants. On the one hand, there are (percutaneous) minimally invasive left heart support systems. The second variant is a left heart support system that is invasively implanted below the chest opening. A variant according to the first variant transports blood from the left ventricle directly into the aorta, because the (percutaneous) minimally invasive left heart support system is located in the center of the aortic valve. The second variant transports blood from the left ventricle to the aorta via a bypass tube.

[0004] The task of a heart support system is to transport blood. In this respect, the so-called heart-time volume (HZV, usually expressed in liters per minute) is of high clinical relevance. In other words, in this case, the heart-time volume relates to the total volume flow of blood (from the ventricles, in particular from the left ventricle) to the aorta. It is accordingly clear that attempts are made to acquire this parameter as a measured value during operation of the heart support system.

[0005] Depending on the support level, it describes the ratio of the volume flow delivered by the delivery device, such as the pump of the support system, to the total volume flow of blood from the ventricles to the aorta, which arrives via the physiological path through the aortic valve. Thus, the cardiac-time volume or total volume flow (Q) from the ventricles to the aorta is HZV ) is usually the pump volume flow rate (Q p ) and aortic valve volume flow (Q a )

[0006] For determining cardiac-temporal volume (Q HZV ) is to use dilution methods, however, they all rely on percutaneously inserted catheters and therefore can only provide cardio-temporal volumetric data during cardiac surgery. P ) is the correlation of the operating parameters of the support system, mainly the electrical power consumption, possibly supplemented by further physiological parameters such as blood pressure. It has also been proposed to integrate dedicated ultrasound measurement techniques into the support system.

[0007] The heart-time volume, Q, has not yet been proposed or implemented HZV(Totally) implantable tests are those that rely on the support system itself for the test. In particular, fully implantable means that the device required for the test is completely located in the patient's body and remains there. This makes it possible to measure the heart-time volume even outside of cardiac surgery.

[0008] The object of the present invention is to define an improved method for determining the total fluid volume flow in the area of ​​an implantable vascular support system and to create an improved implantable vascular support system.

[0009] In particular, the object of the present invention is to define a method for determining the total fluid volume flow in the area of ​​an implantable vascular support system, and to create an implantable vascular support system, with the help of which the total fluid volume flow in the blood flow area can be determined in a human or animal body in which the vascular support system is implanted or arranged.

[0010] This object is achieved by the method defined in claim 1 and by the implantable vascular support system defined in claim 9 .

[0011] Advantageous embodiments of the invention are defined in detail in the dependent claims.

[0012] The method for determining the total fluid volume flow in the region of an implantable vascular support system as defined in claim 1 comprises the following steps:

[0013] a) determining a reference temperature of the fluid,

[0014] b) determining a motor temperature of an electric motor of the support system,

[0015] c) determining the heat dissipation losses of the electric motor,

[0016] d) determining the total fluid volume flow rate using the reference temperature, the motor temperature and heat dissipation losses of the electric motor.

[0017] The vascular support system is preferably a heart support system, particularly preferably a ventricular support system. "Total volume flow" particularly refers to the total volume flow through a blood vessel or through a cross-section of a blood vessel. The blood vessel is, for example, the aorta, particularly in the case of a left heart support system, or into the common trunk (pulmonary trunk) of the two pulmonary arteries, particularly in the case of a right heart support system, preferably the aorta. The method is preferably used to determine the total fluid volume flow from a ventricle of the heart, particularly from the (left) ventricle of the heart to the aorta in the area of ​​a (completely) implantable (left) ventricular (heart) support system. The fluid is typically blood. The support system is preferably arranged at the outlet of the left ventricle or left heart chamber of the heart. The support system is particularly preferably arranged in the position of the aortic valve.

[0018] The method is particularly suitable for determining the total heart-time volume (HZV, formula symbol Q) of a patient, in particular with a (fully) implantable left ventricular heart support system (LVAD), at the location of the aortic valve and / or from the support system itself HZV ). The method is based in particular on the (thermal) anemometer (measurement) principle of flow measurement. In this case, the basic principle is that the flowing medium cools the hot body according to the flow rate. The method advantageously allows the cardiac-time volume to be available also outside the surgical setting, with a quality comparable to that when using a dilution catheter. This is particularly advantageous because the cardiac-time volume (Q HZV ) has a specific pump volume flow rate (Q p ) of greater clinical relevance, the pump volume flow is primarily used and only quantifies the flow through the support system itself.

[0019] A particular advantage of the method is that, unlike what is usually the case in anemometer methods, no separate heating element is required to generate the heat flow to be measured. Instead, the heat dissipation losses that occur in any case on the electric motor of the LVAD can be used for the anemometer flow measurement. Preferably, no (separate) heating element (in addition to the electric motor) is used to determine the total fluid volume flow. In other words, the electric motor is the only heating element used in the solution proposed herein. In particular, in the solution proposed herein, the heat dissipation losses that occur on and / or in the electric motor of the support system are used for (thermal) anemometer or calorimetric flow measurement. Furthermore, it is preferred that the support system does not have a (separate) heating element (in addition to the electric motor).

[0020] 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 the (inlet) bushing of the support system. The reference temperature generally represents the background temperature of the fluid, in other words, a temperature of the fluid that is particularly unaffected by heat dissipation losses of the electric motor.

[0021] In step b), the motor temperature of the electric motor of the support system is determined, in particular measured. The electric motor can be a component of a flow machine or a component of a pump of the support system. The support system is preferably arranged on or in the fluid flow, so that a heat flow from the support system, in particular from its electric motor, can be dissipated to the fluid flow. The term "motor temperature" can also be understood to mean an internal temperature or an (external) surface temperature of the support system, in particular in the region of the electric motor, which in particular allows preferably direct conclusions to be drawn about the temperature of the electric motor, in particular about the temperature of the coil packaging of the electric motor.

[0022] The support system is preferably implanted so that at least part of its (external) surface is located in the fluid flow, preferably completely or at least 50%, particularly preferably at least 85% or even at least 95%. In addition, the support system is preferably positioned along at least 50%, particularly preferably at least 85%, or even at least 95% of its length in the fluid flow. One end of the support system is preferably at least partly located in the aorta, wherein the electric motor is located in the region of or on said one end. In addition, the opposite end of the support system is preferably at least partly located in the ventricle (left ventricle) of the heart, wherein the (inlet) cannula of the support system is located in the region of or on said opposite end. In addition, the support system is preferably arranged at least partly, preferably completely or at least 50%, particularly preferably at least 85% or even at least 95% of its (external) surface in a blood vessel, such as an artery, in particular the aorta. The support system is particularly preferably implanted so that it is (completely) located in the (descending) aorta.

[0023] In step c), heat dissipation losses of the electric motor are determined. The heat dissipation losses of the electric motor are preferably determined by a current sensor, which preferably measures the current of the electric motor.

[0024] In step d), the total fluid volume flow is determined using the reference temperature, the motor temperature and the heat dissipation losses of the electric motor. In step d), the total fluid volume flow is determined as a function of the reference temperature, the motor temperature and the heat dissipation losses of the electric motor with the aid of at least one heat transfer specification, at least one heat transfer coefficient, at least one calibration factor and / or at least one blood vessel cross section, in particular an aortic cross section.

[0025] According to an advantageous embodiment, it is proposed that a reference temperature is measured, in particular spatially and / or temporally, before the fluid is heated by the electric motor. The reference temperature sensor is preferably arranged at a distance from the electric motor, in particular upstream of the electric motor, preferably on the (inlet) bushing of the support system. The reference temperature sensor is particularly preferably arranged in the region of and / or on the end of the (inlet) bushing opposite the electric motor.

[0026] According to an advantageous embodiment, it is proposed to measure the motor temperature of the electric motor on a surface along which the fluid flows. The surface is typically an (external) surface of a support system in contact with the fluid. For example, the motor temperature can be measured with a motor temperature sensor on an (external) surface of a support system arranged in the region of the (inner) electric motor. Alternatively, the motor temperature of the electric motor can be measured inside the motor. For this purpose, the motor temperature sensor can be arranged inside the electric motor.

[0027] According to an advantageous embodiment, it is proposed that in step d) the flow rate of the fluid is determined, in particular calculated, from calibration data, a reference temperature, the motor temperature and the heat dissipation losses of the electric motor. The calibration data preferably include a characteristic length (e.g., a tube diameter that may be approximated in the region of the aortic valve), the kinematic viscosity of the fluid, the temperature conductivity of the fluid, the thermal conductivity of the fluid and / or the (top) surface of the support system wetted with the fluid.

[0028] According to an advantageous embodiment, it is proposed that in step d) the determined cross-sectional geometry of the aorta in the region of the implantable vascular support system is further taken into account. Preferably the (flow) cross section of the aorta in the region of the support system is taken into account. This value can be determined by the physician, for example, by ultrasound or computed tomography. It can be particularly advantageously determined, in particular for calculating the total fluid volume flow or the heart-time volume, based on the flow velocity of the fluid, the (flow) cross section of the aorta and a (velocity-dependent) calibration factor. The (velocity-dependent) calibration factor can be determined, for example, by calibration in the implant environment, using a dilution catheter as a reference standard.

[0029] According to an advantageous embodiment, it is proposed to further determine the fluid volume flow through the support system. In other words, this relates in particular to the fluid volume flow that flows only through the support system itself. This fluid volume flow is usually the so-called pump volume flow (Q p ), which only quantifies flow through the support system itself. If, in addition to total volume flow or cardiac-time volume (Q HZV ), if the value is known, then it can be obtained from Q p With Q HZV The ratio (i.e. Q P / Q HZV ) The so-called support level is calculated. To determine the pump volume flow, the established method for measuring the pump volume flow discussed at the beginning in connection with the prior art can be used.

[0030] For example, the total fluid volume flow determined in step d) is preferably provided as a control parameter of the support system in step e. The 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 the electric motor and thus also in particular the (blood) delivery rate of the support system.

[0031] According to another aspect, a processing unit is proposed, which is configured to perform the method proposed herein and comprises a memory in which calibration data are stored. As an alternative to the calibration data or in addition to the calibration data, at least one (speed-dependent) calibration factor and / or a thermal model of the electric motor may also be stored in the memory. In addition, the processing unit may comprise a microprocessor that can access the memory. The processing unit preferably receives data from a reference temperature sensor, a motor temperature sensor and / or a current sensor.

[0032] According to another aspect, an implantable vascular support system is provided, comprising:

[0033] a reference temperature sensor for determining a reference temperature of the fluid,

[0034] - electric motor,

[0035] a motor temperature sensor for determining the motor temperature of the electric motor,

[0036] A current sensor for determining at least the current through the electric motor or the heat dissipation losses of the electric motor.

[0037] The support system is preferably a left ventricular heart support system (LVAD) or a percutaneous minimally invasive left heart support system. In addition, the support system is preferably fully implantable. In other words, this means in particular that the devices required for the detection, in particular the reference temperature sensor, the motor temperature sensor and the current sensor are completely located in the patient's body and remain in the body. The support system is particularly preferably configured and / or suitable for being at least partially arranged in a ventricle of the heart, preferably in the left ventricle, and / or in the aorta, in particular at the location of the aortic valve.

[0038] The current sensor is used to determine the current through the electric motor and / or the heat dissipation losses of the electric motor. The current sensor preferably measures the current through the electric motor and calculates the dissipation losses of the electric motor. If the current sensor supplies only the current as output variable, in particular, it is provided that the current is converted into the dissipation losses of the electric motor in the processing unit of the support system.

[0039] The support system also preferably comprises a cannula, in particular an inlet cannula, and a flow machine, such as a pump. An electric motor is usually a component of the flow machine. The electric motor then drives the flow machine for conveying fluid. The (inlet) cannula is preferably configured so that in the implanted state, it can guide the fluid from the (left) ventricle of the heart to the flow machine. The fluid can be guided to the flow machine through the cannula. The cannula is preferably designed to guide the fluid in the form of blood from the (left) ventricle of the heart into the aorta.

[0040] The support system is preferably elongated and / or tubular.The inlet sleeve and the flow generator are preferably arranged in the region of opposite ends of the support system.

[0041] The reference temperature sensor can be arranged on the cannula or near a region of the cannula at a distance from the flow generator. In particular, the reference temperature sensor can be arranged on the cannula or near a region of the cannula facing away from the electric motor. The reference temperature sensor is particularly preferably arranged at the distal end of the cannula, i.e., where blood flows from the ventricle into the cannula.

[0042] The support system may have a tubular elongated structure having a casing section in which the casing is formed, and having a motor housing section connected to the casing section and in which the electric motor is arranged in the motor housing.

[0043] It is advantageous if the reference temperature sensor is arranged in the region of the cannula section at a distance from the motor housing section.The electric motor is preferably arranged in a motor housing around which the blood can flow in the aorta.

[0044] The support system may further comprise a processing unit configured to determine a total fluid volume flow in a support system area using the reference temperature, the motor temperature and heat dissipation losses of the electric motor.The support system is preferably configured to perform the method presented herein.

[0045] The details, features and advantageous embodiments discussed in conjunction with the method may also be present in the processing unit and / or the support system presented here, and vice versa. In this regard, reference is made entirely to the explanations thereof regarding the detailed characterization of the features.

[0046] The solution presented here and its technical environment are explained in more detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the exemplary embodiments shown. In particular, unless otherwise explicitly stated, some 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 schematically shows:

[0047] Figure 1a It is a percutaneous minimally invasive left heart support system.

[0048] Figure 1b It is a left heart support system that is invasively implanted below the chest opening.

[0049] Figure 2 It is an implantable vascular support system.

[0050] Figure 3 It is the placement of the implantable vascular support system.

[0051] Figure 4is the component architecture that supports the system,

[0052] Figure 5 is a diagram of heat flow.

[0053] Figure 6 is a graphical representation of the temperature curve, and

[0054] Figure 7 is a further illustration of the temperature curve.

[0055] Implantable left ventricular assist systems (LVADs) exist primarily in two design variations, such as Figure 1a and Figure 1b as shown in . Figure 1a A (percutaneous) minimally invasive left heart support system 16 is shown, and Figure 1b A left heart support system 17 is shown invasively implanted below a chest opening. Figure 1a The variant delivers blood from the left ventricle 18 directly into the aorta 9, because the (percutaneous) minimally invasive left heart support system 16 is positioned in the middle of the aortic valve 19. Figure 1b A variant of this method delivers blood from the left ventricle 18 to the aorta 9 via a bypass tube 20 .

[0056] Depending on the support level, it describes the ratio of the volume flow delivered by the delivery device, for example the pump of the support system, to the total volume flow of blood from the ventricle 18 to the aorta 9, which volume flow reaches the aorta 9 via the physiological path through the aortic valve 19. Thus, the cardiac-time volume or the total volume flow (Q) from the ventricle 18 to the aorta 9 is HZV ) is usually the pump volume flow rate (Q p ) and aortic valve volume flow (Q a )

[0057] Figure 2 The implantable vascular support system 2 is schematically shown at the aortic valve position. For further explanation, reference is also made to Figure 3 A schematic arrangement of a support system 2 is shown, wherein reference numerals are used uniformly in all the figures.

[0058] The support system 2 is exemplified here as a left ventricular heart support system (LVAD).

[0059] The support system has a tubular elongated structure with a casing section in which the inlet casing 21 is formed as a casing and comprising a motor housing section connected to the casing section and in which the electric motor 5 is located in the motor housing 23 .

[0060] The support system 2 protrudes distally from the aorta 9 through the aortic valve 19 into the ventricle 18. Here, as an example, the support system 2 has an inlet cannula 21 protruding into the ventricle 18. The fluid volume flow 10 is conveyed (e.g. pumped) from the ventricle 18 into the aorta 9 through the inlet cannula 21 using an electric motor 5 of the support system 2, which drives a flow generator in the form of a pump in the support system 2. Therefore, the fluid volume flow 10 is also referred to as the pump volume flow (Q p ), which only quantifies the flow through the support system 2 itself.

[0061] In addition, Figure 2 and Figure 3 As can be seen in FIG. 1 , some aortic valve volume flow 24 reaches the aorta 9 via a physiological path through the aortic valve 19. Thus, the cardiac-time volume or total fluid volume flow 1 (Q) of the cross-sectional geometry 8 of the aorta 9 from the ventricle 18 to the aorta 9 in the region of the support system 2 is HZV ) is the fluid volume flow rate 10(Q p ) and aortic valve volume flow 24 (Q a This is described by the following equation (1).

[0062] Q HZV =Q p +Q a (1)

[0063] The support system 2 comprises a reference temperature sensor 13 for determining a reference temperature 3 of a fluid, in this case blood as an example. The support system 2 further comprises an electric motor 5 and a motor temperature sensor 14 for determining a motor temperature 4 of the electric motor 5. In addition, the support system 2 has a current sensor (not shown here) for determining heat dissipation losses (not shown here) of the electric motor 5.

[0064] By way of example, the motor temperature sensor 14 is integrated in the motor housing 23, where the heat dissipation losses of the electric motor 5 are dissipated to the surrounding fluid. The motor temperature sensor 14 is configured and arranged so that it can measure the motor temperature 4. For this purpose, the motor temperature sensor 14 can be configured and arranged so that it measures the surface temperature of the motor housing 23 or the temperature of the stator (not shown here) of the electric motor 5. In this case, the temperature of the stator can be approximated by the internal temperature in the motor housing 23 between the motor housing 23 and the coil encapsulation (not shown here). Alternatively, the temperature in the coil encapsulation can also be measured directly.

[0065] The reference temperature sensor 13 detects a reference temperature 3, here by way of example the background blood temperature. For this purpose, the reference temperature sensor 13 is positioned in the heat-unaffected blood flow upstream of the electric motor 5 representing the heat source; here by way of example, in the region upstream of the electric motor 5. For this purpose, the reference temperature sensor 13, such as Figure 2 As shown in , it is arranged in an area where the cannula section is at a distance from the motor housing section at the distal end of the inlet cannula 21 , ie, where blood flows from the ventricle into the inlet cannula 21 .

[0066] Figure 4 The component architecture of the support system 2 is shown schematically. The support system 2 comprises a reference temperature sensor 13 for determining a reference temperature 3 of a fluid, in this case blood, as an example. The support system 2 also comprises an electric motor 5 and a motor temperature sensor 14 for determining a motor temperature 4 of the electric motor 5. In addition, the support system 2 has a current sensor 15 for determining heat dissipation losses 6 of the electric motor 5. For this purpose, as an example, the current sensor 15 determines the current (not shown here) through the motor 5 and converts it into heat dissipation losses 6. According to Figure 4 , the support system 2 further comprises a processing unit 11 which is configured to determine a total fluid volume flow (not shown here) in a region of the support system 2 using the reference temperature 3, the motor temperature 4 and the heat dissipation losses 6 of the electric motor 5. In addition, the support system 2 has an electronically readable memory 12 with calibration data 25.

[0067] The measurement data of the reference temperature sensor 13, the motor temperature sensor 14 and the current sensor 15 are transmitted to the processing unit 11. The processing unit 11 processes the measurement data to form the blood flow velocity or the (total) blood volume flow using the calibration data 25 from the memory 12. The processing unit 11 also includes an output 26 to a communication unit (not shown here), an output 27 to a power supply (not shown here) and an output 28 to a motor controller (not shown here).

[0068] Figure 5 Schematically, a diagram of an exemplary heat flow (horizontal arrows) to a fluid flow (vertical arrows) or a total fluid volume flow 1 through an electric motor 5 is shown. In this case, as an example, the electric motor 5 comprises a movably mounted rotor (not shown here) and a stationary coil package 22, which is offset by an external air gap and connected to a stator 29. Figure 5 The heat conduction transition from the coil encapsulation 22 of the electric motor 5 to the blood flow via the stator 29 is therefore schematically shown in another way. The loss mechanisms in the electric motor 5 are mainly related to Joule current heat losses Pv (see equation (2) below).

[0069] P V =RTW I 2 (2)

[0070] Here, R TW Indicates the operating temperature T W The winding resistance of the lower coil package 22. In the case of copper, the winding resistance R TW is the winding temperature T W This is described by the following equation (3):

[0071] R TW =R 25 ·(1+ αC u(T W -25)) (3)

[0072] Among them, R 25 Winding resistance at 25°C, T w is the winding operating temperature, constant α cu =0.0039K -1 .

[0073] In addition, iron losses such as magnetization losses also occur according to the following equation (4):

[0074] P V，magn =π / 30·M Magn ·n (4)

[0075] The eddy current losses in the stator back iron material are given by the following equation (5):

[0076] P V,Eddy =const·n 2 (5)

[0077] n is the number of revolutions of the motor, M Magn is the magnetic friction torque. In addition, bearing losses from the motor bearings are generated, which can usually be ignored.

[0078] The thermal resistance between the heat source and the heat sink is measured in Kelvin / Watt (K / W). Figure 5 As shown in , the determining heat transfer mechanism between the coil package and the blood flow is heat conduction through the layers of the motor to the outside. To determine the temperature, the heat capacity of the individual components traversed by the heat flow and the corresponding heat transfer resistance are required. Since it can be adequately assumed that the electric motor is in stationary operation and is therefore in thermal equilibrium, the heat capacity can be neglected. All necessary parameters can be determined in advance and can be stored in the processing unit.

[0079] Figure 6 A diagram of the temperature profile along the material layer sequence from the coil encapsulation 22 via the stator 29 and the motor housing 23 to the total fluid volume flow 1 is schematically shown. Figure 6Show the basis Figure 5 The highest temperature exists in the coil package 22 where the heat source and current flow. The winding temperature 31 of the coil package 22 (formula symbol T W ) is therefore Figure 6 For simplicity, it is assumed here that the heat distribution is constant over the entire thickness of the coil package 22. Due to the finite thermal conductivity of the stator material and the housing material, a linear temperature gradient is generated through the stator 29 and the motor housing 23, or in the non-simplified case of a cylindrical motor housing 23, a logarithmic temperature gradient is generated.

[0080] When considering the simplified principle, the winding temperature 31 (formula symbol T W )for:

[0081] T W =T A +(R th1 +R th2 )·P v (6)

[0082] T W =T A +(R th1 +R th2 )·R TW I 2 (7)

[0083] T W =T A +(R th1 +R th2 )·R 25 ·(1+α Cu (T W -25℃ (8)

[0084]

[0085] Here, the current 30 (formula symbol I) and the surface temperature 32 (formula symbol T A ) is the only variable parameter. th1 The thermal resistance between the coil package 22 and the stator 29 is described. th2 describes the thermal resistance between the stator 29 and the fluid flow. The current 30 (formula symbol I) can be determined by measurement with the current sensor 15, for example in the control device of the current sensor, and is therefore precisely known. The surface temperature 32 (formula symbol T A ) represents the temperature on the surface 7 of the electric motor 5 along which the fluid flows. In other words, the surface 7 is in the blood flow.

[0086] Figure 7Another illustration of a temperature curve is schematically shown. Figure 7 The area of ​​the surface 7 at two different flow rates is shown according to Figure 6 In other words, Figure 7 The dependence of the temperature (surface temperature and therefore also the stator temperature and therefore also the coil package temperature) on the flow rate of the fluid flow or blood is shown in printed form.

[0087] like Figure 7 As shown in FIG, a liquid film with a thickness of 33 is formed near the surface 7. Figure 7 As shown in FIG. , the thickness 33 of the liquid film and the surface temperature 32 (the formula symbol T A ) and reference temperature 3 (Formula symbol T B ) A -T B is a function of the flow rate of the fluid, and the reference temperature represents the background temperature of the fluid (blood). Figure 7 , a lower flow velocity of the fluid along the surface 7 results in a higher surface temperature 32 ′ than the surface temperature 32 , which is generated at a relatively higher flow velocity.

[0088] The heat flow through the liquid film is

[0089]

[0090] Among them, α B is the heat transfer coefficient from the top of the housing to the wetted surface A of the blood and surface 7.

[0091] The heat transfer coefficient is defined as

[0092]

[0093] Where Nu is the dimensionless Nusselt number, λ is the thermal conductivity of the fluid (here blood), and L is the reference length, which can be, for example, the diameter of a tube. Furthermore, it applies to the Nusselt number averaged over the entire body surface, since it is a function of the dimensionless Reynolds number Re and the Prandtl number Pr:

[0094] Nu=f(Re,Pr) (12)

[0095] These can be calculated individually from geometry and flow (Re and Pr) or from fluid properties (Pr) and stored in the calibration data memory. The Reynolds number is defined as

[0096]

[0097] where L is the characteristic length (e.g., pipe diameter), v is the kinematic viscosity of the fluid, and u is the flow rate sought. The Prandtl number is a pure material variable and is given by

[0098]

[0099] where a is the thermal conductivity of the fluid. If this definition is inserted into the convective heat flow through a liquid film (Eq. (10)), the known heat flow is obtained The result of this insertion is shown in equation (15) below. From the energy balance, it is known that for the stationary case considered here, the heat flow (in terms of magnitude) corresponds essentially to the heat dissipation loss 6 (formula symbol P V ).

[0100] Here, the surface temperature 32 (formula symbol T A ) can be measured by means of the motor temperature sensor 14, for example directly on the surface 7, or the motor temperature sensor 14 can measure the temperature inside the motor, and the surface temperature 32 (formula symbol T A ) is determined by the logarithmic temperature relationship with the temperature distribution in the motor housing (see Figure 6 and Figure 7 ). Reference temperature 3 (Formula symbol T B ) is determined by the reference temperature sensor 13. The parameters L, v, a, λ and A are usually stored in the system as calibration data.

[0101]

[0102] In this case, if the cross-sectional geometry 8 of the patient's aorta 9 in the region of the support system is known (determinable, for example, by ultrasound, computed tomography or magnetic resonance tomography), the total fluid volume flow 1 can be determined from the flow velocity u determined in this way (formula symbol Q HZV ). The corresponding relationship is specified in the following equation (16):

[0103] Q HZV =k(u)uO (16)

[0104] Here, k(u) is a calibration factor depending on the flow curve, u is the calculated flow velocity, and O is the measured aortic cross section (cf. Cross-sectional geometry 8).

[0105] The solution proposed here allows in particular one of the following advantages:

[0106] Fully implantable, particularly with pump integration and / or automatic determination of Q HZV , rather than just Q p.

[0107] The anemometer measurement method using the waste heat of the VAD motor instead of an additional heating element does not result in additional heat input into the organism.

[0108] This also prevents additional current consumption, thereby extending the battery runtime of the autonomous system.

Claims

1. A method for determining a total fluid volume flow of blood in a region of a cardiac support system, the method comprising: determining a reference temperature of the blood, wherein the reference temperature represents a temperature of the blood that is not affected by heat dissipation losses of an electric motor of a heart support system, determining a motor temperature of an electric motor of the cardiac support system, determining the heat dissipation losses of the electric motor, and The total fluid volume flow is determined using a correlation between the total fluid volume flow and heat dissipation losses of the electric motor, wherein the heat dissipation losses are calculated as a function of the reference temperature and the motor temperature. 2 . The method of claim 1 , further comprising heating the blood by the electric motor, wherein determining the reference temperature comprises measuring the reference temperature before heating the blood by the electric motor. 3 . The method of claim 1 , wherein determining the motor temperature comprises measuring a motor temperature of the electric motor at a surface along which the blood flows. The method of claim 1 , wherein determining the motor temperature comprises measuring a motor temperature of the electric motor within the motor interior.

5. The method of claim 1, further comprising determining a flow rate of the blood based on calibration data, the reference temperature, the motor temperature, and heat dissipation losses of the electric motor.

6. The method of claim 1, wherein determining the total fluid volume flow is based in part on a cross-sectional geometry of the aorta in a region of the cardiac support system.

7. The method of claim 1 further comprising determining a fluid volume flow rate of a portion of the blood flowing through the support system.

8. A computer-readable storage medium having computer-readable instructions stored thereon, wherein when the computer-readable instructions are executed by a processing unit, the processing unit: determining a reference temperature of the blood flowing through the region of the heart support system, wherein the reference temperature represents a blood temperature that is not affected by heat dissipation losses of an electric motor of the heart support system, determining a motor temperature of an electric motor of the cardiac support system, determining heat dissipation losses of the electric motor, and The total fluid volume flow of the blood is determined using a correlation between the total fluid volume flow and heat dissipation losses of an electric motor, wherein the heat dissipation losses are calculated as a function of the reference temperature and the motor temperature.

9. A cardiac support system comprising: a reference temperature sensor configured to determine a reference temperature of the blood, wherein the reference temperature represents a temperature of the blood that is not affected by heat dissipation losses of an electric motor of the heart support system, Electric motor, a motor temperature sensor configured to determine a motor temperature of the electric motor, and A current sensor is configured to determine at least a current through the electric motor or a heat dissipation loss of the electric motor.

10. The support system according to claim 9 further comprises a processing unit configured to determine the total fluid volume flow of blood in the area of ​​the cardiac support system using a correlation between the total fluid volume flow and heat dissipation losses of the electric motor, wherein the heat dissipation losses are calculated using a function of the reference temperature and the motor temperature.

11. The support system according to claim 9, comprising a flow machine and a cannula, wherein the flow machine is configured to transport blood, the cannula is configured to guide blood to the flow machine, and wherein the electric motor is configured to guide blood to the flow machine.

12. The support system of claim 11, wherein the cannula is configured to direct blood from a ventricle of the heart into the aorta.

13. The support system according to claim 11, wherein the reference temperature sensor is arranged on the casing or near an area where the casing is a certain distance away from the flow machine.

14. The support system of claim 11, wherein the reference temperature sensor is disposed on the bushing or near an area of ​​the bushing facing away from the electric motor.

15. The support system of claim 11, further comprising: a tubular elongated structure comprising a casing section, said casing section comprising said casing, and A motor housing includes a motor housing section configured to be connected to the bushing section, wherein the electric motor is arranged in the motor housing. 16 . The support system according to claim 15 , wherein the reference temperature sensor is arranged in an area of ​​the bushing section at a distance from the motor housing section.

17. The support system of claim 9, wherein the electric motor is disposed in a motor housing, wherein the motor housing is configured to allow blood to flow in the aorta around the motor housing.

18. The support system of claim 15, wherein the motor housing is configured to allow blood to flow around the motor housing in the aorta.

19. The support system of claim 15, wherein the motor temperature sensor is configured to measure a surface temperature of the motor housing.

20. The support system of claim 9, wherein the motor temperature sensor is configured to measure a temperature of a stator of the electric motor.

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