IMPLANTABLE VASCULAR SUPPORT SYSTEM

Abstract

The invention relates to an implantable, vascular support system (10) having a cannula (13) and an ultrasound measuring device (18), wherein the cannula (13) and the ultrasound measuring device (18) are disposed in the region of mutually opposite ends of the support system (10).

Claims

1.-12. (canceled)

13. An implantable cardiac support system, the system comprising: a cannula; an ultrasound measuring device; and at least one processor configured to: receive signals received from the ultrasound measuring device; and determine a total volume flow of blood in a region of the support system based on the signals received from the ultrasound measuring device.

14. The support system of claim 13, wherein the ultrasound measuring device is disposed on an opposite end from the cannula on the cardiac support system.

15. The support system of claim 13, wherein the ultrasound measuring device is disposed and oriented to perform an ultrasound measurement in a vicinity of the support system.

16. The support system of claim 13, wherein the ultrasound measuring device comprises at least two ultrasound transducers.

17. The support system of claim 16, wherein the ultrasound measuring device comprises at least three ultrasound transducers.

18. The support system of claim 16, wherein at least two of the at least two ultrasound transducers are oriented orthogonally to one another.

19. The support system of claim 13, wherein the ultrasound measuring device comprises a plurality of ultrasound transducers arranged to form an ultrasound array or an ultrasound matrix.

20. The support system of claim 19, wherein the at least one processor is configured to assess a direction of flow of the blood.

21. The support system of claim 13, further comprising a flow machine disposed between the cannula and the ultrasound measuring device.

22. The support system of claim 13, wherein the support system is configured to be implanted in an aortic valve.

23. The support system of claim 13, wherein the support system is elongated between a first end and a second end.

24. The support system of claim 13, wherein the cannula is disposed adjacent to a distal end of the support system comprising an inlet opening, and wherein the ultrasound measuring device is disposed adjacent to a proximal end of the support system.

25. A method for determining a total fluid volume flow of blood in a region of a cardiac support system, the method comprising: performing a first ultrasound measurement with an ultrasound measurement device in a first orientation in a region of an end of the support system, performing a second ultrasound measurement with the ultrasound measurement device in a second orientation different from the first orientation in the region of the end of the support system, determining the total fluid volume flow using the first and second ultrasound measurements.

26. The method of claim 25, further comprising monitoring the support system using the first and second ultrasound measurements.

27. The method of claim 25, wherein the ultrasound measurement device is positioned opposite to a cannula of the support system in the first orientation.

28. The method of claim 25, wherein the ultrasound measurement device is positioned opposite to a cannula in the second orientation.

Description

[0042] The figures show schematically:

[0043] FIG. 1: an implantable vascular support system,

[0044] FIG. 2: a support system, implanted in a heart,

[0045] FIG. 3: an illustration of a flow line image,

[0046] FIG. 4: an illustration of a velocity vector,

[0047] FIG. 5: an illustration of a directional characteristic of an ultrasound transducer,

[0048] FIG. 6: a further implantable vascular support system,

[0049] FIG. 7: an illustration of a directional characteristic of a plurality of ultrasound transducers,

[0050] FIG. 8: a sequence of a here presented method.

[0051] FIG. 1 schematically shows an implantable vascular support system 10. As an example, the support system 10 here is a left ventricular assist device (LVAD) in particular a (percutaneous) minimally invasive left ventricular assist device. The support system is advantageously configured to convey blood directly out of the left ventricle of a heart (through the atrium) into the aorta. For this purpose, the (percutaneous) minimally invasive left ventricular assist device is typically positionable or positioned centrally in the aortic valve.

[0052] The support system 10 comprises a cannula 13 and an ultrasound measuring device 18. The cannula 13 and the ultrasound measuring device 18 are provided in the region of oppositely disposed ends of the support system 10.

[0053] In other words, FIG. 1 in particular shows an LVAD for the aortic valve position with a corresponding support structure, in this case in the simple variant for positioning the flow machine (pump) in the aorta.

[0054] As an example, the support system (LVAD) 10 here comprises a tip 11, which projects into the ventricle 21 (not shown here, see FIG. 2) and can optionally contain sensors. Adjacent to this there are typically openings 12, through which blood can be taken from the ventricle 21 by the system, conveyed through the (inlet) cannula 13 to the flow machine (pump) 17 and discharged into the aorta 22, for example, via openings 14.

[0055] An example anchoring structure 15, which is connected to the flow machine 17 via a fastening element 16, can secure the system in aortic position or aortic valve position, for example, and/or help prevent shifting of the support system.

[0056] As an example, the support system 10 comprises a flow machine (pump) 17, which is disposed between the cannula 13 and the ultrasound measuring device 18. The flow machine 17 is preferably driven by an electric motor. The flow machine 17 furthermore preferably comprises an impeller (not shown here), which is located in the region of the openings 14 or extends in the region of the openings 14 in the direction of the cannula 13 and/or projects into the cannula 13. The ultrasound measuring device 18 is located at the proximal end of the system (in the region of the aorta). The ultrasound measuring device 18 is typically configured as an ultrasound sensor, as an example here in the form of a total CO flow sensor.

[0057] The support system 10 can be connected or is connected to an implanted or extracorporeal control device (not shown here) by a supply cable 19. The measuring technology with which the sensor signal of the ultrasound measuring device 18 can be evaluated and/or further processed can be implemented in the control device.

[0058] As an example, the ultrasound measuring device 18 here is disposed and oriented such that it can carry out an ultrasound measurement in the vicinity of the support system 10. For this purpose, the ultrasound measuring device 18 is disposed on an outer surface of the support system 1, for example, in particular in the region of the flow machine 17.

[0059] The ultrasound measuring device 18 comprises at least two or at least three ultrasound transducers (not shown here), for example. Preferably, at least two of the ultrasound transducers are oriented orthogonally to one another.

[0060] FIG. 2 schematically shows a support system 10 implanted in a heart 20. According to the illustration of FIG. 2, the support system 10 (LVAD) is implanted in aortic valve position. For this purpose, the support system 10 intersects a plane in which the aortic valves 23 are located. The support system 10 helps to convey blood from the (here left) ventricle 21 of the heart into the aorta 22. FIG. 2 thus shows the system 10, placed in aortic valve position of a heart 20 which consists of the ventricle 21 and the aorta 22 with the aortic valves 23.

[0061] The cardiac output 24, which is also referred to here as the total fluid volume flow, flows in the region of the aorta 22 and is the sum of the blood conveyed by the pump or the flow machine of the support system out of the openings 14 and a possible bypass volume flow past the support system 10 through the aortic valves 23. The spiral curve 25 indicates the swirling blood flow produced by the support system 10. Due to a very rapidly rotating impeller of the flow machine, for example, which is disposed in an impeller cage comprising the openings 14, and the mass inertia of the blood, the flow typically still has a high rotational component even after exiting the impeller cage or the openings 14, as shown in the flow line image in FIG. 3.

[0062] FIG. 3 schematically shows an illustration of a flow line image. As discussed above, FIG. 3 illustrates that the flow still has a high rotational component even after exiting the impeller cage 14. The flow lines show a plurality of spiral curves 25 in the total fluid volume flow 24.

[0063] FIG. 4 schematically shows an illustration of a velocity vector. Accordingly, as shown in FIG. 4, (due to the swirl) the velocity vector of the flow V.sub.G is composed of a flow velocity V.sub.L pointing axially in the direction of the aorta and a tangentially circular rotational velocity V.sub.T. Only the component V.sub.L should be used to determine the volume flow, since typically only this velocity component contributes to the volume flow along the aorta.

[0064] FIG. 5 schematically shows an illustration of a directional characteristic of an ultrasound transducer. Since ultrasound transducers do not have a perfect directional characteristic, but instead have a lobe-shaped sensitivity, in some cases with pronounced side lobes as can be seen in FIG. 5, the ultrasound Doppler spectrum of an ultrasound transducer oriented in the direction of V.sub.L also contains components of V.sub.T (not shown here, see FIG. 4).

[0065] FIG. 6 schematically shows a further implantable vascular support system 10. The reference signs are used consistently, so that reference can be made in full to the statements regarding the preceding figures, in particular FIG. 1.

[0066] The support system 10 comprises a cannula 13 and an ultrasound measuring device 18. The cannula 13 and the ultrasound measuring device 18 are provided in the region of oppositely disposed ends of the support system 10.

[0067] For the basic functioning of an ultrasound measurement carried out by means of the ultrasound measuring device 18, the following can be implemented:

[0068] To determine the flow velocity, a frequency shift Δf proportional to the object velocity is measured with the aid of an ultrasound transducer, in particular an ultrasound transducer. Formally, the frequency shift can be written as follows using the Doppler effect:

[00001]$\begin{array}{cc}\Delta f=f_s-f_s\frac{1-\frac{{\stackrel{\_}{\mathrm{ve}}}_{\mathrm{SO}}}{c}}{1-\frac{{\stackrel{\_}{\mathrm{ve}}}_{\mathrm{OB}}}{c}}& \left(1\right)\end{array}$

[0069] Whereby f.sub.S is the transmit frequency, v is the object velocity, c is the propagation velocity and e.sub.S0 or e.sub.0B is the unit vector from the transmitter to the object or object to the observer. For the transducer arrangement, the following applies

{right arrow over (e)}.sub.S0=−{right arrow over (e)}.sub.OB

and Formula (1) can be written as

[00002]$\begin{array}{cc}\Delta f=\frac{2f_{s}v\cos \left(\theta \right)}{c-v\cos \left(\theta \right)}& \left(2\right)\end{array}$

[0070] Whereby θ is the angle between the velocity vector v and the unit vector e.sub.B0. For a propagation velocity of approx. 1500 m/s and flow velocities up to approx. 8 m/s, Formula (2) can be further simplified to:

[00003]$\begin{array}{cc}\Delta f=\frac{2f_{s}v\cos \left(\theta \right)}{c}& \left(3\right)\end{array}$

[0071] At transmit frequencies between 2-8 MHz, frequency shifts of a several hundred and a few kHz can be expected.

[0072] With regard to the integration of the ultrasound measuring device 18 in and/or on the support system 10, the following in particular must be taken into account:

[0073] Due to the geometry of the usually present flow machine (such as a pump) of the support system 10 and/or the possibly present input leads (in particular electrical input leads to the ultrasound measuring device 18), the ultrasound transducer or ultrasound transmitter cannot be oriented freely and the field of view is typically not parallel to the longitudinal flow direction and therefore also “sees” the tangential flow component.

[0074] In order to be able to determine the total fluid volume flow 24 (not shown here, see FIG. 2) or the cardiac output as accurately as possible from the Doppler shift, an arrangement which comprises at least two ultrasound transmitters or ultrasound transducers is preferable. The two ultrasound transmitters or ultrasound transducers are in particular rigid and/or orthogonal to one another.

[0075] According to a particularly advantageous configuration, the arrangement is set up such that the first sonde or the first ultrasound transducer is oriented at most in the direction of the longitudinal flow (e.g. (no more than) 45° to the longitudinal flow) and the second sonde or the second ultrasound transducer is oriented orthogonally to the first.

[0076] If, for example, the vector of the first sonde is

[00004]${\stackrel{.fwdarw.}{e}}_{\mathrm{SO}1}=\left(\begin{array}{c}1\\ 1\\ 0\end{array}\right)\frac{1}{\sqrt{2}}$

then

[00005]${\stackrel{.fwdarw.}{e}}_{\mathrm{SO}2}=\left(\begin{array}{c}-1\\ 1\\ 0\end{array}\right)\frac{1}{\sqrt{2}}$

must advantageously be selected.

[0077] For the object velocity v, which can generally be written as a vector (v.sub.x, v.sub.y, v.sub.z), it thus follows for the first ultrasound transducer

[00006]$\Delta f_1=2f_s\frac{1}{\sqrt{2}}\left(v_x+v_y\right)$

[0078] and for the second ultrasound transducer

[00007]$\Delta f_2=2f_s\frac{1}{\sqrt{2}}\left(-v_x+v_y\right).$

[0079] In this case, simple subtraction can lead to

[00008]$\Delta f_d=4f_s\frac{1}{\sqrt{2}}{v}_x$

[0080] which leads to the elimination of the (tangential) velocity component v.sub.y (v.sub.x here is the longitudinal component of the flow). For other angles, v.sub.y can in particular be calculated according to the projections.

[0081] Both transmitters or ultrasound transducers having the viewing window in the x-y plane can in particular be realized by using an additional anchoring stent. To be able to look at a specific depth plane, it is furthermore advantageous to use the pulsed-wave Doppler method.

[0082] An advantageous expansion to three orthogonally positioned sondes or ultrasound transducers can advantageously contribute to being able to omit an otherwise potentially additionally inserted stent for fixing. This may minimally increase the computational effort.

[0083] An advantageous approach to being able to solve the previously described problem, according to which ultrasound transducers disposed at the end of the support system 10 opposite to the cannula 13 cannot be oriented as desired, in particular the field of view of which typically cannot be oriented (exactly) parallel to the longitudinal flow direction, is the integration of at least two ultrasound transducers disposed orthogonally to one another on the surface of the support system 1. Ideally, one transducer with a main sensitivity direction S.sub.L would be oriented parallel to V.sub.L (not shown here, see FIG. 4) and another transducer would look radially outward (S.sub.T). However, such an (ideal) installation situation is (as described above) not usually practicable due to the design, for example due to the geometry of the typically present flow machine (such as a pump) of the support system 10 and/or the possibly present input leads (in particular electrical input leads to the ultrasound measuring device 18).

[0084] A particularly advantageous (practical) approach with an exemplary orthogonal orientation of two ultrasound transducers to one another is illustrated in FIG. 6. FIG. 6 illustrates (with two unlabeled arrows) an advantageous orientation of the main sensitivity directions (unit vectors e.sub.so1 and e.sub.so2) of the two ultrasound transducers to the main flow components S.sub.L and S.sub.T. This is intended to clarify that e.sub.so1 and e.sub.s02 do not necessarily have to be parallel to S.sub.L and S.sub.T; rather the orthogonality condition(s) and a known angle to S.sub.L are sufficient to advantageously enable the most accurate ultrasound acquisition of the flow.

[0085] Assuming an ideally focusing ultrasound transducer, the element would in particular provide no measurement signal at all in radial direction, because the transducer is oriented at a right angle to the flow V.sub.L and also at a right angle to the flow V.sub.T. However, the same side lobe effects act on the transducer S.sub.T as on the transducer S.sub.L. The influence of the rotating flow component V.sub.T can advantageously be compensated in a possible downstream signal processing.

[0086] Another advantage of the transducer in S.sub.T direction can be seen in this transducer (in the implanted state in aortic valve position) being able to look in the direction of the aortic wall.

[0087] The aortic wall can be identifiable as a strong reflection in the received signal. Based on the approximately known speed of sound in blood, the distance between the sensor (and thus the support system) and the aortic wall can be inferred from the signal transit time between an emitted pulse and received aortic wall echo.

[0088] By integrating a plurality of (for example three) radially outward looking ultrasound transducers, the exact position of the support system in the aorta and/or the aortic cross-section can advantageously be determined with sufficient accuracy. Monitoring the position of the support system in the implanted state advantageously contributes to being able to check and/or ensure whether and/or that the transducer S.sub.L is (substantially) parallel to V.sub.L even after a longer implantation time and/or during upper body movements of the patient, or being able to determine the angle cos(θ) in Formulas 1-3. A determination of the aortic cross-section by means of the ultrasound transducer can advantageously contribute to being able to infer the volume flow in liters per minute as accurately as possible from the flow velocity determined via a Doppler ultrasound measurement.

[0089] The approach described above in particular also has the advantage of being cost-effective. In particular, only at least two ultrasound transducers are needed and, if necessary, also only two electrical supply cables between the transducers and a (possibly extracorporeal or not also implanted) control electronics. However, this approach in particular does not allow the actual velocity vector field to be calculated and displayed. The calculations are also based in particular on the (normally justified) assumptions of a flow field that corresponds substantially to the flow field shown in FIG. 3.

[0090] FIG. 7 schematically shows an illustration of a directional characteristic of a plurality of ultrasound transducers. As an example, FIG. 7 shows different directional characteristics that can be set with a plurality of ultrasound transducers arranged to form an ultrasound array.

[0091] When the ultrasound measuring device 18 comprises a plurality of ultrasound transducers that are arranged to an ultrasound array or an ultrasound matrix, it can in particular contribute to carrying out a method referred to as 3D/4D vector flow imaging. In this case, the ultrasound measuring device preferably comprises a plurality of ultrasound transducers arranged in a matrix. Depending on the control (phase delay of the ultrasound pulse), the directional characteristic and/or the orientation of the ultrasound measuring device or the ultrasound element (S.sub.T or S.sub.L in the above example) can be changed electronically, as shown in FIG. 7 in the simplified case of a linear array. This in particular makes it possible to operate in a “scanning” manner with the matrix arrangement, i.e. traverse many different angles and to determine the Doppler flow velocity for each angle. This can be used in the signal processing step to determine the three-dimensional flow vector field.

[0092] FIG. 7 shows examples of ultrasound array control. In each case the control is shown to the left of the ultrasound elements as a plot. The line corresponds to the x-axis. A small ultrasound pulse can be seen on it. The time axis accordingly points to the left, i.e. pulses shown further to the left arrive at the ultrasound transducer later than pulses shown further to the right. FIG. 7 shows how the shape of the directional characteristic and/or the orientation of the main beam direction (of the entire ultrasound array) can, for example, be changed. On the left (1): normal characteristic, as it would, for example, also result from a massive element of the same size. In the middle (2): example of a change of the natural focus, i.e. the distance to the ultrasound transducer, in which the highest power concentration takes place and where a pulsed-wave Doppler system would also preferably place its time of observation. On the right (3): example of a linear phase delay from bottom to top so that the beam is panned.

[0093] Based on the technology of the so-called PMUT (piezoelectric micromachined ultrasound transducer) and/or CMUT (capacitive micromachined ultrasound transducer), miniaturized ultrasound arrays, which, because of their dimensions, are suitable for integration into a vascular implantable support system, are possible.

[0094] The advantage of using an ultrasound array and/or an ultrasound matrix, is that the entire cross-sectional anatomy of the aortic wall can be captured. Furthermore, a complete 3D vector field of the flow conditions in the aorta can be recorded by appropriate control of the matrix transducer.

[0095] The use of an array/matrix transducer therefore in particular represents a kind of generalization or an advantageous further development of the approach described above from at least two ultrasound transducers to 256 or more transducers (elements). At the cost of higher system complexity, this can advantageously resolve the orientation requirement and/or eliminate the need for a fixation stent.

[0096] In addition to a highly accurate calculation of the cardiac output, the vector field can also be used as a parameter for a self-monitoring of the support system. Therefore, it is to be expected that a closure of a discharge opening 14 will have significant effects on the vector field. This could possibly be determined algorithmically and used for system monitoring.

[0097] FIG. 8 schematically shows a sequence of a here presented method. The method is used to determine a total fluid volume flow 24 (not shown here, see FIG. 2) in the region of an implanted vascular support system. The shown sequence of the method steps a), b) and c) with Blocks 110, 120 and 130 is only an example and can be the result of a regular operating sequence, for example. Steps a) and b) in particular can also be carried out at least partially in parallel or even simultaneously. In Block 110, a first ultrasound measurement is carried out with a first orientation in the region of an end of the support system opposite to a cannula of the support system. In Block 120, a second ultrasound measurement is carried out with a second orientation different from the first orientation in the region of the end of the support system opposite to the cannula of the support system. In Block 130, the total fluid volume flow is determined using the ultrasound measurements carried out in Steps a) and b).

[0098] The solution presented here in particular enables one or more of the following advantages: [0099] The integration of the sensor in the proximal end of the support system can eliminate the need for additional implantation steps; [0100] The measurement principle with orthogonal measurement directions and/or the three-dimensional vector field measurement can increase the measurement accuracy in the case of a prevailing strong swirl of the flow; [0101] The measurement position in the aorta enables a determination of the total CO in an advantageously simple manner; [0102] Changes in the flow profile (primarily based on the vector field method) can be used to infer changes in the pump and/or the aorta. For example, thromboses at the pump outlet or the retaining structures can have an effect on the flow field, which can be identified via a slow change in the vector field (keyword condition monitoring, predictive maintenance).