Abstract:
A heart assistance device for the pulsatile delivery of blood. A first and a second pump chamber are provided, and also a pump. Both pump chambers each have a fluid chamber and a blood-carrying chamber. By means of the pump, each fluid chamber can be filled with a fluid or emptied thereof in such a way that an expansion or contraction of the fluid chamber takes place. During the expansion of the fluid chamber of one pump chamber, a compression of the blood-carrying chamber of the same blood chamber takes place. 
     The pump is designed as a roller cell pump or vane pump.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The disclosure refers to a heart assistance device for the pulsatile delivery of blood. 
         [0003]    2. Discussion of the Background Art 
         [0004]    Mechanical circulatory support systems (VAD: ventricular assist devices) find clinical application for about 15 years and are the last option for the preservation of life in cases of manifested cardiac insufficiency. Heart assistance systems take over a part of the pumping work and thereby stabilize circulation until a donor organ is available. Recent studies have shown that, under this therapy, the heart function can improve as far as to allow an explantation of the system without subsequent heart transplantation. 
         [0005]    Artificial heart pumps can be adapted to various requirements and are available without any waiting period. However, there are limitations with respect to the technology used and the compatibility. For example, the blood can be damaged by the pumping. The power supply to the systems, which are presently exclusively electrically operated, via wires through the abdominal wall, bears a high risk of infection for the patient. 
         [0006]    Low degrees of efficiency lead to high energy consumption and to a heating up of the surrounding tissue. Assisted circulation often has to be kept up for months or years. Further, the systems are subjected to high mechanic stresses. Since a short-term replacement of the blood pumps is not possible, they have to feature a high durability and operational reliability. 
         [0007]    With known drives for heart assistance devices the structural size makes implantability impossible to achieve in some cases. Further, a high wear of mechanical parts of the drive, and thus a shortening of the useful life, exist. Moreover, loud driving noises can occur. Other known disadvantages are a low degree of efficiency or a low output that translates as a low volume flow and an insufficient assistance. Known implantable pumps only have one pump chamber which can assist only one ventricle, preferably the left one. Further, implantable single chamber pumps additionally require a compensation for the volume delivered. Presently, this problem is solved with a volume compensation container (vent) that has to be implanted along with the device and causes additional complications. 
         [0008]    It is an object of the present disclosure to provide an improved heart assistance device that in particular is simpler to implant. 
       SUMMARY 
       [0009]    A heart assistance device for the pulsatile delivery of blood comprises a first and a second pump chamber as well as a pump. Each of the two pump chambers comprises a fluid chamber and a blood-carrying chamber, each fluid chamber being adapted to be filled with a fluid or emptied by means of the pump such that the fluid chamber is expanded or contracted. When the fluid chamber of a pump chamber is expanded, the blood-carrying chamber of the same pump chamber is compressed. According to the disclosure, the pump is designed as a roller cell pump or a vane pump. 
         [0010]    In a preferred embodiment of the disclosure the pump operates in a reversing mode. This has the advantage that the necessary energy for the systemic circulation has to be made available only at the relevant times. Comparable hydraulic drives are known from prior art, which, however, use different pumping principles and therefore comprise more and larger moving parts. The result thereof is a higher moment of inertia and a lower degree of efficiency. Another advantage obtained from the use of a roller cell pump or a vane pump in an alternating mode is that fewer pressure surges occur and unnecessary friction losses are avoided. At the moment of a reversal of rotation the blocking bodies no longer have a sealing effect so that a pressure compensation can occur that is energetically favorable. 
         [0011]    Generally, the drive of the disclosure comprises few moving parts, and thus comprises few friction components. The use of a suitable hydraulic liquid allows for a further reduction of the friction losses. 
         [0012]    The above-mentioned avoidance of pressure surges results in reduced stress on all components connected with the hydraulic circuit. Therefore, fewer stress peaks are generated in the relevant components, such as the membranes, for example, whereby less wear is caused. It is another advantage that the roller cell pump or the vane pump has as a characteristic, depending on the configuration, not to build up further pressure once a specific pressure is achieved, whereby inherent safety is guaranteed. Thus, the pump has a mechanical pressure limitation that, in the extreme case, prevents the destruction of the implant. 
         [0013]    It is advantageous to integrate the drive system formed by the alternating pump and the motor into the implant. Due to the high overall efficiency, the pump unit can be designed smaller as compared to other drive systems and therefore requires less volume in a patient&#39;s body. 
         [0014]    The heart assistance device of the disclosure is therefore more compact, less prone to wear and more silent than known drive concepts, and, moreover, it can be operated for a longer period of time. Accordingly, a fully implantable system can be provided that minimizes the risk of infection for a patient. Further, a particularly high level of running smoothness can be achieved. The heart assistance device of the disclosure may be operated, for example, with double-chamber systems, such as the DLR-LVAS, or with systems having one pressure chamber and one compensation container. 
         [0015]    In an alternative embodiment it is possible to operate the pump in one direction, the heart assistance device comprising valves to redirect the fluid flow. 
         [0016]    As an alternative thereto, the heart assistance function can comprise two roller cell or vane pumps, each connected with a fluid chamber and alternately delivering in opposed directions. Here, the quantity of fluid delivered into the fluid chambers is adjustable via the rotational speed of the roller cell or vane pump. 
         [0017]    Depending on the arrangement, it may be advantageous to additionally connect an external compensation chamber to the hydraulic system of the pump. Thereby, an additional safety factor is provided, since pressure surges that the hydraulic pump does not absorb and that can damage the structure of the system have to be attenuated. Here, the connection can be made near the hydraulic pump or at the respective hydraulic chambers. 
         [0018]    It is particularly preferred that the heart assistance device comprises a housing, the two pump chambers and the pump itself being arranged in the housing and the pump being arranged between the pump chambers. This allows for a particularly flat structure. The pump chamber can comprise a flexible blood chamber and a fluid chamber with a rigid or flexible housing. 
         [0019]    As an alternative, the two pump chambers can be arranged inside the housing, while the pump is arranged outside the housing and is connected with the pump chambers via rigid or flexible lines. Thereby, a flexible arrangement can be achieved. 
         [0020]    In a further alternative embodiment each pump chamber has its own housing, wherein these housings are not interconnected and the pump chambers are connected with each other in particular exclusively via the pump and rigid or flexible lines between the pump and the pump chambers. Thus, the drive forms a flexible connection between the components. 
         [0021]    In another alternative embodiment each pump chamber has its own housing, both housings being connected through a joint. The same may be, for instance, a ball joint, a hinge or another suitable joint. Also in this case, the pump is arranged outside the housing and is connected with the pump chambers through rigid or flexible lines. 
         [0022]    In another alternative embodiment the two pump chambers are not connected directly, but in particular exclusively through the pump and or rigid or flexible lines between the pump and the pump chambers. Here, both pump chambers are enclosed by a common flexible membrane, with the pump being arranged either inside or outside the membrane. This allows for a flexible arrangement of the pump chambers. 
         [0023]    In all embodiments described above, the pump chambers can comprise a flexible blood chamber and a fluid chamber with a rigid or flexible housing. 
         [0024]    It is particularly preferred that the pump chambers are of a seamless design and comprise a reinforcement in the form of a stiffening element arranged at one or a plurality of pump chamber locations that are subjected to high mechanical stresses. It is further preferred to realize the pump chambers in a manner optimized in terms of flow. Due to the measures mentioned, the risk of deposits is minimized. Further, enhanced compression can be achieved, whereby minimal shearing of the blood is guaranteed, since no kinks are formed as they are known from prior art systems. The blood chamber comprises a flexible membrane, with the stiffening being either flexible or rigid. 
         [0025]    It is particularly preferred for the stiffening element to present flow guiding elements on the outside for guiding the fluid flow. 
         [0026]    The disclosure further refers to a method for operating a heart assistance device comprising two roller cell or vane pumps, each connected with a fluid chamber and alternately delivering in opposed directions. In the event of a failure of one of the pumps, the remaining pump switches to a reversing operation mode and thus takes over the entire pumping effort. Thereby, an increased resilience can be achieved. 
         [0027]    The disclosure further refers to the use of a roller cell pump or a vane pump as a drive for a heart assistance device with two blood chambers. 
         [0028]    The following is a detailed description of preferred embodiment of the disclosure with reference to the Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    In the Figures: 
           [0030]      FIGS. 1-5  are schematic illustrations of different possible arrangements of the pump in the heart assistance device of the disclosure, 
           [0031]      FIG. 6  is a schematic illustration of a blood chamber with an integrated stiffening element, 
           [0032]      FIG. 7  is a schematic illustration of a roller cell pump. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]    Referring to  FIG. 1 , the heart assistance device comprises a first  14  and a second pump chamber  16 , as well as a pump  18 . The pump has connections to the left and the right pump chamber and is arranged between the pump chambers. The entire device comprises a common housing. That means that both pump chambers  14 ,  16 , as well as the pump  18  are arranged in this housing. 
         [0034]    Referring to  FIG. 2 , it is possible as an alternative to arrange the two pump chambers  14 ,  16  in the housing and to arrange the pump  18  outside the housing and to connect the pump with the pump chambers  14 ,  16  via rigid or flexible lines  22   a ,  22   b.  Thus, the drive can be arranged between the pump chambers  14 ,  16  in a flexible manner. 
         [0035]    In the embodiment illustrated in  FIG. 3  each pump chamber  14 ,  16  comprises a housing of its own, wherein these housings are not interconnected and the pump chambers  14 ,  16  are exclusively connected with each other via the pump  18  and rigid or flexible lines  22   a,    22   b  between the pump  18  and the pump chambers  14 ,  16 . 
         [0036]    In the embodiment illustrated in  FIG. 4  each pump chamber  14 ,  16  also has a housing of its own, with the housings being connected by means of a joint  24 . Again the pump  18  is arranged outside the housing and is connected with the pump chambers  14 ,  16  via lines  22   a,    22   b.    
         [0037]    The embodiment illustrated in  FIG. 5  comprises a common flexible membrane  26  surrounding the two pump chambers  14 ,  16 . The pump  18  can be arranged inside or outside the membrane  26 . The pump  18  is connected with the pump chambers  14 ,  16  by means of flexible or rigid lines  22   a,    22   b.    
         [0038]      FIG. 6  shows a schematic illustration of a seamless, flow-optimized pump chamber comprising a stiffening element  28  at the location most subjected to stress. This stiffening element  28  may have flow guiding elements, not illustrated, on its outer side for guiding the fluid flow. 
         [0039]      FIGS. 1-5  illustrate a bi-ventricular heart assistance system comprising two main chambers or blood chambers  14 ,  16  that are preferably formed from a pressure-resistant material. For the left half of the heart, supply and discharge lines for the transportation of blood are connected to the left ventricle (inlet of the pump) and to the aorta (outlet of the pump). In analogy with the left half of the heart, the connections for the right half of the heart are made to the right ventricle and the pulmonary artery. In heart assistance, the natural heart remains in the body, while the assistance system assumes a part of the pumping work and thereby relieves the natural heart. 
         [0040]    A membrane or a flexible pumping bag divides each blood chambers  14 ,  16  into a blood-carrying chamber  14   b,    16   b  and a fluid or hydraulic chamber  14   a,    16   a.  When pressure is built up in this fluid chamber, the pressurized blood chamber is simultaneously compressed. The blood volume is reduced in favor of the hydraulic volume and the volume in the blood chamber is emptied into circulation after the flaps at the outlet have been opened. The flaps are each arranged at a supply and a discharge at the blood-carrying chambers such that a unidirectional blood flow is guaranteed. 
         [0041]    By the above described arrangement of the chambers  14 ,  16  and the hydraulic pump  18  it is possible to fill one blood chamber as the other blood chamber is compressed. Due to the incompressibility of the hydraulic fluid, the second blood chamber can also be filled by suction, whereby a constant blood deliver rate is guaranteed. When the first blood chamber  14   b  is emptied, the direction of rotation of the hydraulic pump  18  is reversed and the second blood chamber  16   b,  now filled, is emptied, while the first blood-carrying chamber  14   b  is refilled. 
         [0042]    A roller cell pump as illustrated in  FIG. 7  may be used to convey the fluid. This pump comprises a cylindrical rotor  32  comprising a number of radial milled slots or recesses  34  arranged at regular intervals along its circumference. The depth and the shape of the milled slots  34  are chosen such that a cylindrical blocking body  36 , whose diameter is at most equal to the width of the milled slot  34 , can sink completely into this milled slot  34  such that the round surface of the blocking body  36  is flush with the circumference of the rotor  32 . Preferably, the blocking bodies  36  are roller cylinders. All milled slots  34  are respectively provided with a blocking body  36 . 
         [0043]    The rotor  32  is housed in a round pump chamber  38  (stator), with the stator  38  and the rotor  32  being arranged eccentrically. The stator  38  has two lateral openings  40 ,  42  that serve as an inlet or outlet opening for the hydraulic fluid, depending on the direction of rotation of the rotor  32 . 
         [0044]    The blocking bodies  36  are movable within the limits of the eccentricity determined by the rotor position and are pressed against the wall of the stator  38  by centrifugal forces. The eccentricity and the positions of the inlet and outlet openings  40 ,  42  are designed such that two adjacent blocking bodies  36  sealingly block a partial volume in the area of maximum eccentricity between the inlet and outlet openings. Due to the rotation of the rotor arrangement, a volume is thus displaced from the inlet opening to the outlet opening. 
         [0045]    The roller cell pump may be designed such that the direction of the volume flow can be reversed by changing the direction of rotation. The axis of the rotor  32  simultaneously forms the shaft of a non-illustrated compact electric motor providing for the rotational movement of the rotor  32 . 
         [0046]    Preferably, the hydraulic fluid used is a liquid other than the blood of a patient, which liquid is biocompatible or even hemocompatible. Biocompatibility can be achieved with various silicone oils. If, for example, a saline solution is used, it is even possible to achieve hemocompatibility. 
         [0047]    Due to the fact that the entire pump unit is situated in the hydraulic fluid and is constantly washed in the same, good heat dissipation from the electric motor can be achieved. Further, the heat buffered in the hydraulic fluid can be transferred to the blood in the pump chambers  14 ,  16 . Since this process is continuous, there is no risk of heat being trapped, whereby the risk for the patient can be reduced. The service life of the pump is extended because of the uniform temperature prevailing. 
         [0048]    As mentioned above, the arrangement can be driven by a single drive that constantly reverses its direction of rotation. As an alternative, a second hydraulic pump can be used, whereby a dedicated hydraulic pump is provided for each pumping direction. A reversal of directions that is detrimental to the drive shaft is excluded in this case, since each hydraulic pump only changes the rotational speed, but not the direction of rotation. 
         [0049]    Preferably, the roller cell rotor (pump rotor) is arranged between two bearings  44 ,  46 , where an electric drive is used that preferably is configured as a brushless electric motor. 
         [0050]    As an alternative to the roller cell technology, a vane pump could also be used as the pump, wherein the blocking bodies are designed as flat plates instead of cylindrical rollers. The basic function of the pump remains unchanged.