CARDIAC SUPPORT SYSTEM FLOW MEASUREMENT USING PRESSURE SENSORS

Abstract

The invention relates to an implantable vascular support system (10), comprising: —a fluid channel (13) passing through the support system (10) and through which fluid can flow; —a first pressure sensor (18a, b) arranged and configured to determine at least a static pressure or a total pressure in the region of the support system (10); —a second pressure sensor (17) arranged and configured to determine at least a static pressure or a total pressure in the region of the fluid channel (13).

Claims

1. A cardiac support system comprising: a fluid channel passing through the support system configured to permit fluid to flow therethrough; a first pressure sensor configured to determine at least one of a static pressure or a total pressure in a region of the support system; and a second pressure sensor configured to determine at least one of a static pressure or a total pressure in a region of the fluid channel.

2. The support system of claim 1, wherein the first pressure sensor is disposed in an outer side of the support system.

3. The support system of claim 1, wherein the first pressure sensor is disposed in or on an interior surface of the fluid channel.

4. The support system of claim 1, wherein the second pressure sensor is disposed in or on an interior surface of the fluid channel.

5. The support system of claim 1, wherein the first pressure sensor is disposed in a first channel cross-section of the fluid channel through which fluid can flow, wherein the second pressure sensor is disposed in a second channel cross-section of the fluid channel through which fluid can flow, and wherein an area of the second channel cross-section is different from an area of the first channel cross-section.

6. The support system of claim 1, wherein at least one of the first pressure sensor or the second pressure sensor is a MEMS pressure sensor.

7. A method for determining at least one of a flow velocity or a fluid flow volume of fluid flowing through a cardiac support system, the method comprising: determining at least one of a first static pressure or a first total pressure in a region of the support system with a first pressure sensor; determining at least one of a second static pressure or a second total pressure in a region of a fluid channel passing through the support system with a second pressure sensor; and determining at least one of a flow velocity or a fluid flow volume using at least one of the first static pressure, the first total pressure, the second static pressure, or the second total pressure.

8. The method of claim 7, wherein determining at least one of a first static pressure or a first total pressure comprises determining the first static pressure.

9. The method of claim 7, wherein determining at least one of a second static pressure or a second total pressure comprises determining the second total pressure.

10. The method claim 7, further comprising changing a flow cross-section of the fluid after determining at least one of a first static pressure or a first total pressure and before determining at least one of a second static pressure or a second total pressure.

11. A method for determining at least one of a flow velocity or a fluid flow volume of fluid flowing through a cardiac support system, the method comprising: using two pressure sensors of a cardiac support system to determine at least one of a flow velocity or a volume flow of fluid flowing through the support system.

Description

[0039] The solution presented here as well as its technical environment are explained in more detail below with reference to the figures. It is important to note that the invention is not intended to be limited by the design examples shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and to combine them with other components and/or insights from other figures and/or the present description. The figures show schematically:

[0040] FIG. 1a: a percutaneous, minimally invasive left ventricular assist device,

[0041] FIG. 1b: a left ventricular assist device invasively implanted under an opening in the rib cage,

[0042] FIG. 2: an implanted vascular support system,

[0043] FIG. 3: the support system according to FIG. 2 in a detail view,

[0044] FIG. 4: an illustration of a fluid channel through which fluid can flow, and

[0045] FIG. 5: a sequence of a method presented here in a routine operating sequence.

[0046] The vascular support system is preferably a ventricular and/or cardiac support system or a cardiac support system. Two particularly advantageous forms of cardiac support systems are systems which are placed in the aorta, such as the one depicted in FIG. 1a, and systems which are placed apically, such as the one depicted in FIG. 1b.

[0047] The support system 10 is described in the following using a left ventricular assist device (LVAD) as an example. Implanted left ventricular assist devices (LVAD) exist primarily in two design variants, as shown in FIGS. 1b and 1b. FIG. 1a shows a (percutaneous) minimally invasive left ventricular assist device 10, whereas FIG. 1b shows a left ventricular assist device 10 invasively implanted under an opening in the rib cage. The variant of FIG. 1a conveys blood directly from the left ventricle 21 through the atrium 24 into the aorta 22, because the (percutaneous) minimally invasive left ventricular assist device 10 is positioned centrally in the aortic valve. The variant of FIG. 1b conveys the blood from the left ventricle 21 into the aorta 22 via a bypass tube 33.

[0048] Depending on the level of support, which describes the proportion of volume flow conveyed by a conveying means, such as a pump of the support system, to the total volume flow of blood from the ventricle 21 to the aorta 22, a specific amount of volume flow reaches the aorta 22 via the physiological path through the aortic valve. The cardiac output or the total volume flow (Q.sub.co) from the ventricle 21 to the aorta 22 is therefore usually the sum of the pump volume flow (Q.sub.p) and the aortic valve volume flow (Q.sub.a).

Q.sub.CO=Q.sub.p−Q.sub.a

[0049] FIG. 2 schematically shows an implanted vascular support system 10. The cardiac support system 10 is implanted in a heart 20. The reference signs are used consistently, so that reference can be made in full to the above statements.

[0050] FIG. 2 shows a heart 20 with a minimally invasive cardiac support system (VAD pump) 10 as an example. The VAD is positioned centrally in the aortic valves 23 between the ventricle 21 and the aorta 22 and conveys a blood volume flow 31 from the ventricle 21 into the aorta 22 to support the cardiac output 32 of the patient.

[0051] FIG. 3 schematically shows the support system 10 according to FIG. 2 in a detail view. The reference signs are used consistently, so that reference can be made in full to the above statements.

[0052] FIG. 3 schematically shows an implantable vascular support system 10 comprising: [0053] a fluid channel 13, which passes through the support system 10 and through which fluid can flow, [0054] a first pressure sensor 18a or 18b, which is disposed and configured to determine at least a static pressure or a total pressure in the region of the support system 10, [0055] a second pressure sensor 17, which is disposed and configured to determine at least a static pressure or a total pressure in the region of the fluid channel 13.

[0056] According to the illustration of FIG. 3, as an example, the support system 10 further comprises a tip 11, which can contain sensors (for example temperature, pressure), an inlet cage with openings 12 for drawing in a liquid (here: blood), an inlet cannula 13 for delivering the blood to a (not shown) pump element in an impeller cage 14 provided with an opening, from which the blood can again exit the inlet cannula 13. Connected to this, as an example, is a drive (electric motor) 15 and an electrical supply cable 16.

[0057] In order to be able to estimate the cardiac output, the blood volume flow 31 through the inlet cannula 13 of the support system 10, which is also referred to as the so-called pump volume flow (symbol Q.sub.p), is to be measured here. For this purpose, it is proposed here that two pressure sensors 17 and 18a/18b be integrated in or on the support system 10.

[0058] In Configuration A, the first pressure sensor 18a is positioned on the outside of the support system or the VAD pump 10, preferably in a region with a negligible flow velocity, e.g. on the outside of the tip 11, on the outside of a constriction 19 or on the outside of the inlet cannula 13. In other words, this means in particular that, in Configuration A, the first pressure sensor 18a is disposed in the region of an outer side of the support system 10.

[0059] In Configuration B, the positioning of the first pressure sensor 18b differs as shown in FIG. 4. Here, the first pressure sensor 18b is seated inside the inlet cannula 13 at a position with a known flow cross-section A.sub.1. In other words, this means in particular that, in Configuration B, the first pressure sensor 18b is disposed in or on a channel interior surface of the fluid channel 13.

[0060] In both Configurations A and B, another (second) pressure sensor 17 is used, which is disposed in or on a channel interior surface of the fluid channel (13). In FIG. 3, as an example, the second pressure sensor 17 is positioned in the inlet cannula 13 and preferably in an annular constriction 19 with the known flow cross-section A.sub.2.

[0061] FIG. 3 according to Configuration B therefore also shows that a first pressure sensor 18b is disposed in or on a channel interior surface of the fluid channel 13 in the region of a first channel cross-section A.sub.1 through which fluid can flow and a second pressure sensor 17 is disposed in or on the channel interior surface of the fluid channel 13 in the region of a second channel cross-section A.sub.2 through which fluid can flow different from the first channel cross-section through which fluid can flow.

[0062] The pressure measured by the pressure sensors 17 and 18a,b now depends on the flow velocity prevailing there. For a known fluid with a known density ρ, for a frictionless flow or a flow that has negligible losses between the pressure sensors, it follows that: [0063] for Configuration A with the known cross-sectional area A.sub.2 at the position of the second pressure sensor 17:

[00004]$Q=A_2.Math.\sqrt{\frac{2.Math.\Delta p}{\rho }}$ [0064] for Configuration B with the known cross-sectional areas A.sub.1 at the position of the first pressure sensor 18a,b and A.sub.2 at the position of the second pressure sensor 17:

[00005]$Q=\frac{A_2.Math.\sqrt{\frac{2.Math.\Delta p}{\rho }}}{\sqrt{1-{\left(\frac{A_2}{A_1}\right)}^2}}$

[0065] For both configurations, the two pressure sensors 17 and 18a,b should preferably be positioned close to one another, because this can minimize any distortions in the result due to occurring pressure losses.

[0066] As an example, the first pressure sensor 18a,b and the second pressure sensor 17 are implemented as MEMS pressure sensors.

[0067] FIG. 4 schematically shows an illustration of a fluid channel through which fluid can flow. An equation for determining the fluid volume flow is derived below using the illustration of FIG. 4.

[0068] Based on Bernoulli's pressure equation for incompressible fluids. The equation is:

[00006]$p_t=p+\frac{\rho }{2}.Math.v^2=\mathrm{const}.\approx \mathrm{const}.$

[0069] Equalizing the (constant) total pressure at two points 1, 2, it follows that:

[00007]$p_1+\frac{\rho }{2}.Math.v_1^2=p_2+\frac{\rho }{2}.Math.v_2^2$

[0070] This results in the pressure difference Δp:

[00008]$\Delta p=p_2-p_1=\frac{\rho }{2}.Math.\left(v_1^2-v_2^2\right)$

[0071] The resulting constant mass flow is:

{dot over (m)}=ρ.Math.v.Math.A=const

[0072] Solving for the flow velocity v, it follows that:

[00009]$v=\frac{\stackrel{.}{m}}{\rho .Math.A}$

[0073] Substituting the flow velocity v in the equation for the pressure difference Δp results in:

[00010]$\Delta p=\frac{\rho }{2}.Math.{\stackrel{.}{m}}^2.Math.\left({\left(\frac{1}{\rho .Math.A_1}\right)}^2-{\left(\frac{1}{\rho .Math.A_2}\right)}^2\right)$

[0074] After a rearrangement, it follows that:

[00011]$\stackrel{.}{m}=\sqrt{\frac{\frac{2.Math.\Delta p}{\rho }}{\left({\left(\frac{1}{\rho .Math.A_1}\right)}^2-{\left(\frac{1}{\rho .Math.A_2}\right)}^2\right)}}$

[0075] After a rearrangement, it follows that:

[00012]$\stackrel{.}{m}=\frac{\rho .Math.A_2}{\sqrt{1-{\left(\frac{A_2}{A_1}\right)}^2}}.Math.\sqrt{\frac{2.Math.\Delta p}{\rho }}$

[0076] A volume flow Q can be determined as a quotient of mass flow to density:

[00013]$Q=\frac{\stackrel{.}{m}}{\rho }$

[0077] After substitution, the equation for determining the fluid volume flow is as follows:

[00014]$\stackrel{.}{m}=\frac{A_2}{\sqrt{1-{\left(\frac{A_2}{A_1}\right)}^2}}.Math.\sqrt{\frac{2.Math.\Delta p}{\rho }}$

[0078] In the above derivation, Configuration A describes the limit case for v.sub.1 tending to zero, which in the above equation A.sub.1 corresponds to tending to infinity.

[0079] FIG. 5 schematically shows a sequence of a here presented method in a routine operating sequence. The method is used to determine at least a flow velocity or a fluid volume flow of a fluid flowing through an implanted vascular support system 10. The shown sequence of the method steps a), b) and c) with Blocks 110, 120 and 130 is only an example. Steps a) and b) in particular can also be carried out at least partially in parallel or even simultaneously. In Block 110, at least a static pressure or a total pressure in the region of the support system is determined by means of a first pressure sensor. In Block 120, at least a static pressure or a total pressure in the region of a fluid channel, which passes through the support system and through which fluid can flow, is determined by means of a second pressure sensor. In Block 130, at least the flow velocity or the fluid volume flow is determined using the pressures determined in Steps a) and b).

[0080] The solution presented here in particular enables one or more of the following advantages: [0081] Continuous, accurate measurement of Q.sub.p using a system-integrated flow sensor. Q.sub.p is thus available as a control parameter of the support system, even outside the surgery scenario, with a quality comparable to that when using a CCO (Continuous Cardiac Output) thermodilution catheter. [0082] When using pressure sensors, in particular MEMS pressure sensors, energy-efficient volume flow measurement is possible. [0083] Compared to ultrasonic transducers, for example, a (MEMS) pressure sensor is very small.