Abstract
A cardiac support system (20) is equipped with a retaining structure (30) for the cardiac support system, said retaining structure (30) being intended to fix the cardiac support system in place. The cardiac support system comprises a device for monitoring the integrity of the retaining structure (30).
Claims
1.-12. (canceled)
13. A cardiac support system comprising: a retaining structure; and a device configured to monitor an integrity of the retaining structure.
14. The cardiac support system of claim 13, wherein the retaining structure comprises a stent structure.
15. The cardiac support system of claim 13, wherein the device comprises at least one actuator-sensor combination.
16. The cardiac support system of claim 13, wherein the device comprises an ultrasonic element.
17. The cardiac support system of claim 13, wherein the device is configured to couple a current into the retaining structure.
18. The cardiac support system of claim 17, wherein the retaining structure comprises constrictions configured to divide the current into partial current flows.
19. The cardiac support system of claim 13, wherein the device comprises one or more electrical conductor tracks positioned on the retaining structure.
20. The cardiac support system of claim 13, wherein the device comprises one or more electrical conductor tracks inserted into the retaining structure.
21. A method for monitoring an integrity of a retaining structure of a cardiac support system, the cardiac support system comprising: the retaining structure; and a device configured to monitor the integrity of the retaining structure.
22. The method of claim 21, wherein the device of the cardiac support system comprises at least one actuator-sensor combination, and wherein the method further comprises: detecting signals of the retaining structure of the cardiac support system with the at least one actuator-sensor combination; and evaluating the signals to infer the integrity of the retaining structure.
23. The method of claim 22, wherein evaluating the signals comprises conducting a vibration analysis by producing vibrations using sound technology.
24. The method of claim 22, wherein evaluating the signals comprises conducting an impedance analysis to determine an impedance with a coupled current.
25. The method of claim 22, wherein evaluating the signals comprises examining an integrity of electrical conductor tracks placed on the retaining structure.
26. The method of claim 22, wherein evaluating the signals comprises examining an integrity of electrical conductor tracks inserted into the retaining structure.
Description
[0016] Further features and advantages of the invention emerge from the following description of design examples in conjunction with the drawings. The individual features can be realized individually or in combination with one another.
[0017] The drawings show:
[0018] FIG. 1 a schematic sectional view of a human heart with an implanted cardiac support system (blood pump);
[0019] FIG. 2 a three-dimensional illustration of a cardiac support system with a retaining structure;
[0020] FIG. 3 a schematic line drawing of a cardiac support system with a retaining structure;
[0021] FIG. 4 a schematic cross-section through a cardiac support system in the region of the retaining structure to illustrate coupled current flows;
[0022] FIG. 5 the electrical equivalent circuit diagram resulting from FIG. 4 and
[0023] FIG. 6 a schematic cross-section through a cardiac support system in the region of the retaining structure to illustrate coupled vibrations.
[0024] FIG. 1 shows a human heart 10, with a tubular cardiac support system 20 inserted in aortic valve position, i.e. between the ventricle (left ventricle) 11 and the aorta 13. The cardiac support system 20 is a blood pump that is implanted in a minimally invasive manner. The cardiac support system 20 extends with its tip into the ventricle 11 and passes through the aortic valves 12, so that the blood from the ventricle 11 is pumped into the aorta 13 (in the direction of the arrow) by means of the cardiac support system 20.
[0025] FIG. 2 shows further details of the per se known cardiac support system 20. The stent-like retaining structure 30 with which the cardiac support system 20 can be fixed in aortic valve position (see FIG. 1) is clearly visible. The retaining structure 30 comprises an annular ring or crown element 31, which is mounted via a plurality of retaining arms 32, which are attached to the actual cardiac support system 20 via a connection element 33. There are also two or more legs 34, by means of which the retaining structure and thus the entire cardiac support system is held or fixed in aortic valve position. These legs 34 can be omitted, if necessary, but the legs are generally advantageous because said legs can fix the system in the direction of rotation in a particularly stable manner. The retaining structure 30 is preferably produced by laser cutting the structure from a one-piece tube and then expanding it. Such a retaining structure can alternatively be produced as a wire mesh, for example. FIG. 3 shows a further configuration of a cardiac support system 40 in a schematic view, in which the retaining structure 50, as in the configuration in FIG. 2 (but without legs), comprises an annular ring structure 51, retaining arms 52 and a connection element 53 via which the entire retaining structure 50 is attached to the actual cardiac support system. The basic structure of a cardiac support system is explained in the following with reference to FIG. 3. Corresponding components are also present in the cardiac support system 20, which is shown in FIG. 2. The approximately tubular cardiac support system 40, which is an intravascular blood pump, comprises a tip 41 which may contain various sensors. The tip 41 is adjoined by an inlet cage 42, via which the blood is conducted, for example from the left ventricle into the interior of the cardiac support system 40. This is adjoined by a cannula 43 in which the blood continues to flow. The flow machine or an impeller which conveys the blood is disposed in the region of the impeller cage 44. The flow machine or the impeller is driven by an electric motor located in the region 45. The electric motor 45 is electrically supplied by means of a supply cable 46. Control and data transfer for the cardiac support system 40 takes place via the supply cable 46 as well, whereby the supply cable 46 is connected to an implanted or extracorporeal control and/or supply device (not shown here). The impeller cage 44 is provided with openings, through which the blood is released into or flows out of the aorta. For positioning and fixing purposes, the cardiac support system 40 is, as already discussed, equipped with a retaining structure 50, which is attached to the cardiac support system 40 via a connection element 53, for example in the region of the electric motor 45.
[0026] Conventional medical stents are often made from tubes of a nickel-titanium alloy by laser cutting. Conventional stents can alternatively be made of meshes of wire material, for example. Nickel-titanium alloys are particularly suitable for this wire material as well. Because nickel-titanium alloys have shape memory properties, these alloys are also particularly suitable for producing the retaining structure for the cardiac support system shown here. A desired shape can be “stored” in the material with the aid of a temperature process. The structure is strongly deformed in ice water, for example, and for example completely compressed, so that it can be inserted into the patient's body through a thin catheter. Contact with the warm blood activates the stored shape and the stent or the retaining structure unfolds to the embossed original shape.
[0027] In the cardiac support system of the present invention, the integrity or intactness of the retaining structure is monitored. This solves the problem that the cardiac support system is subjected to mechanical stress with each heartbeat and that this continuous stress can cause deterioration or a defect, e.g. a break, in the retaining structure. This can have serious consequences, because the retaining structure is usually solely responsible for keeping the cardiac support system in position. The retaining structure can be monitored in a variety of ways, preferably by coupling in a small current or by coupling in sound waves.
[0028] FIG. 4 shows the elements of the retaining structure 50 in a schematic manner in cross-section. The following explanations can also correspondingly be applied to the retaining system 30 of FIG. 2. FIG. 4 serves to explain the monitoring of the retaining structure, whereby a current is coupled into the retaining structure 50 and an impedance analysis is used to check the integrity of the retaining structure 50. The section shows the retaining structure 50, which is disposed in the region of the electric motor 45 of the cardiac support system. The connection element 53 is disposed directly on the housing of the region 45 in a ring shape. The retaining arms (webs) 52, which support the annular ring element 51, extend away from the connection element 53. A small alternating current is coupled into the retaining structure 50 via two capacitive electrodes 60. The electrodes 60 are located on the surface of the housing in the region 45, whereby correspondingly aligned parallel coupling surfaces are provided in the connection element 53. The current i.sub.0 is coupled in via the electrodes 60. The coupled current i.sub.0 is divided into the currents i.sub.1, i.sub.4 and i.sub.5 based on the conductivity of the connection element 53. It is advantageous here for the connection element 53 to comprise constrictions 54. In this example, the connection element 53 is subdivided into four individual segments by the constrictions 54 and each segment is labeled with the reference sign 53. Due to the constrictions 54, the tangential electrical resistance for the current paths i.sub.4 and i.sub.5 is so large that a significant portion, for example at least 10% of the current, flows through the retaining arms 52 to the outer ring element 51 (i.sub.1). In the ring element 51, the current flow i.sub.1 is divided into the partial current flows i.sub.2 and i.sub.3, which flow around the outside in the direction of the counter electrode 60 on the opposite side of the electric motor housing (region 45). To prevent short circuits resulting from the conductivity of the surrounding blood, it is expedient to apply an electrically insulating coating to the retaining structure 50, for example with parylene C. This coating material has proven to be very advantageous in medical technology due to its good biocompatibility for a final production step. A coupling of the measurement current i.sub.0 capacitively through the surface insulation layer is possible, whereby the layer structure between the coupling electrodes 60, the surface insulation layer and the connection element 53 corresponds to the cross-section through a so-called plate capacitor.
[0029] The electrical equivalent circuit diagram resulting from FIG. 4 is shown in FIG. 5. The total impedance Z.sub.G can be recorded and monitored by an impedance measuring device not shown in more detail here. The integrity of the retaining structure 50 can be inferred from an evaluation of the total impedance Z.sub.G. The total impedance Z.sub.G is determined from the two coupling impedances R.sub.Ko between the coupling electrodes 60 and the connection element 53. Added to this are components R.sub.V of the individual segments of the connection element 53 which are conductively connected to one another via the constrictions 54, components R.sub.S of the four retaining arms 52 (webs) and components R.sub.K of the four crown segments, which form the crown element 51. In the event of damage, for example a break or superficial damage to a connecting arm 52, the respective impedance of the affected component increases. Therefore, by preferably continuously monitoring the total impedance Z.sub.G, the structural integrity of the retaining structure 50 can correspondingly be inferred.
[0030] In a similar configuration of the retaining structure, it is not the retaining structure itself, i.e. for example a wire mesh, that is used as an electrical conductor; instead electrically conductive conductor tracks are placed on or inserted into the retaining structure. In this configuration, too, the integrity of the retaining structure can be inferred by coupling in a current and analyzing the resulting impedance. To produce such a retaining structure, the actual retaining structure can first be grounded in an insulating manner before placing the electrically conductive conductor tracks on it, for example by means of lithographic surface coating. Other options are screen printing or dispensing a conductive material. Finally, an insulating surface is expediently produced. Thus, for example, a single continuous conductor can be routed from a coupling electrode 60 via the connection element 53, a retaining arm 53 and the ring element 51 to the other coupling electrode 60 on the opposite side of the connection element 53. This eliminates the need for the parallel circuit shown in FIG. 5, which limits the value of the impedance swing in the event of a break in a parallel conductor. Such a pure series circuit enables a maximum impedance increase (Z.sub.G.fwdarw.∞), so that a very simple analysis and evaluation can be carried out.
[0031] FIG. 6 illustrates a further configuration for monitoring the integrity of the retaining structure. This figure again schematically shows the retaining structure 50 with the individual segments of the connection element 53, which are respectively separated from one another by constrictions 54. The retaining arms 52 and the outer, circumferential ring element 51 are shown as well. This configuration is based on a sound element 70, for example a piezo actuator, which excites mechanical resonances 71 in the retaining structure 50. The resonances can be measured by means of a receiver (sensor), whereby this receiver is not shown here in more detail and can be integrated in the actuator. The eigenmodes excited in this manner (modal analysis, overelevation of characteristic resonances, frequency-dependent transfer function or similar) or the natural oscillations and any changes that may occur are used to monitor signs of aging, for example, or damage or deformations or changes in position (damping).
