Abstract:
A fluid pressure generating means ( 10 ) for a heart assist device having blood pumping means. The pressure generating means ( 10 ) includes a housing ( 11 ), defining an interior volume ( 18 ), and having a substantially rigid first housing portion ( 12 ), a substantially rigid second housing portion ( 14 ), a flexible third housing portion ( 16 ) extending between the first ( 12 ) and second ( 14 ) housing portions and an inlet/outlet port ( 15 ) adapted for fluid communication with the blood pumping means. The pressure generating means ( 10 ) also includes a fluid filling the housing and a motor ( 20 ) disposed within the housing ( 11 ) and connected between the first ( 12 ) and second ( 14 ) housing portions. Actuation of the motor ( 20 ) moves the first ( 12 ) and second ( 14 ) housing portions relative to one another to generate fluid pressure changes at the inlet/outlet port ( 15 ). A related heart assist device and method for the treatment of congestive heart failure, myocardial ischemia and like conditions are also disclosed.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a fluid pressure generating means for use with a heart assist device.  
         BACKGROUND OF THE INVENTION  
         [0002]    The applicant&#39;s international PCT patent application no. PCT/AU00/00654 (International publication no. WO 00/76288) entitled “Heart Assist Devices, Systems and Methods” (“the PCT application”) discloses numerous embodiments of a novel heart assist device adapted for implantation into a patient. Broadly speaking, the disclosed heart assist devices include: an aortic compression means adapted, when actuated, to compress an aorta of a patient; a fluid reservoir; and a fluid pressure generating means adapted to pump fluid from the fluid reservoir to the aortic compression means so as to actuate the aortic compression means in counterpulsation with the patient&#39;s heart. The relevant portions of the PCT application are incorporated herein by cross-reference.  
           [0003]    It is a first object of the present invention to provide improved fluid pressure generating means suitable for use with the aortic compression means described in the PCT application. It is a second object to provide a fluid pressure generating means which may be placed more conveniently into the body of a patient.  
         SUMMARY OF THE INVENTION  
         [0004]    Accordingly, in a first aspect, the present invention provides a fluid pressure generating means for a heart assist device having blood pumping means, the pressure generating means including:  
           [0005]    a housing, defining an interior volume, and having a substantially rigid first housing portion, a substantially rigid second housing portion, a flexible third housing portion extending between the first and second housing portions and an inlet/outlet port adapted for fluid communication with the blood pumping means;  
           [0006]    a fluid filling the housing; and  
           [0007]    a motor or other actuator means disposed within the housing and connected between the first and second housing portions,  
           [0008]    wherein actuation of the motor or other actuator means moves the first and second housing portions relative to one another to generate fluid pressure changes at the inlet/outlet port.  
           [0009]    In one preferred form, the third housing portion has an outer edge about its periphery and inner edge about an opening and is joined along the outer and the inner edge to the first and second housing portions respectively.  
           [0010]    In another preferred form, the third housing portion is connected to only one of the first and second housing portions and abuts against the other of the first and second housing portions.  
           [0011]    The blood pumping means is preferably adapted to displace blood in the aorta, more specifically the ascending aorta, and preferably by compressing or deforming the aorta of a patient in counter-pulsation with the patient&#39;s heart. More preferably, the blood pumping means is adapted to displace blood from the ascending aorta of the patient. In an alternative arrangement, the fluid pressure generating means can be used to drive a conventional left ventricular assist device or an extra-ventricular co-pulsation heart compression device. In such an arrangement suitable valves are used to ensure the correct direction of blood flow through a pumping chamber driven by the fluid pressure generating means.  
           [0012]    In a further preferred form, one of the first and second housing portions is moveable and the other of the first and second housing portions is fixed, the moveable housing portion being exposed to the outside of the heart assist device and adapted to interface with the lung of a patient.  
           [0013]    In a yet further preferred form, one of the first and second housing portions is moveable and the other of the first and second housing portions is fixed, the moveable housing portion not being exposed to the outside of the heart assist device and the device including a flexible compliance chamber. The compliance chamber is desirably in contact with the lung of a patient.  
           [0014]    The actuating means desirably includes a nut coupled to one of the first and second housing portions and a threaded shaft coupled to the other of the first and second housing portions, the threaded shaft and the nut being threadedly engaged and the motor being adapted to rotate the nut relative to the threaded shaft. In one arrangement, the nut is connected to the moveable one of the first and second housing portions and the threaded shaft is connected to the fixed one of the first and second housing portions. In another arrangement, the threaded shaft is connected to the moveable one of the first and second housing portions and the nut is connected to the fixed one of the first and second housing portions.  
           [0015]    In an embodiment, the outflow of the fluid from the inlet/outlet port is axial to the housing. In another embodiment, the outflow of the fluid from the inlet/outlet port is radial to the housing. In a further embodiment, the outflow of the fluid from the inlet/outlet port is tangential to the housing.  
           [0016]    A surface of the device is preferably curved to fit snugly with the chest wall and/or mediastinum and/or diaphragm of a patient.  
           [0017]    The blood pumping means is preferably in the form of a fluid operated cuff adapted to surround the patient&#39;s aorta.  
           [0018]    The fluid filling the housing is preferably a liquid. The liquid is preferably an oil or saline. The oil is preferably a silicone oil and desirably has viscosity between 10 and 100 centistokes, most desirably between 10 and 30 centistokes.  
           [0019]    In a second aspect, the present invention provides a heart assist device including:  
           [0020]    a blood pumping means adapted, when actuated, to cause or assist the movement of blood around the patient&#39;s vasculature;  
           [0021]    a fluid reservoir;  
           [0022]    a fluid pressure generating means adapted to pump fluid from the fluid reservoir to a housing containing both the fluid reservoir and the fluid pressure generating means that is so shaped and dimensioned as to be adapted to lie in the plueral cavity, adjacent to the lung, when the blood pumping means is functionally positioned within the patient.  
           [0023]    In a third aspect, the present invention provides a method for the treatment of congestive heart failure, myocardial ischemia and like conditions, the method comprising:  
           [0024]    inserting into the plueral cavity within the chest (preferably the right chest) of a patient, and adjacent to the lung, a housing containing a fluid reservoir and a fluid pressure generating means adapted to pump fluid from the fluid reservoir to blood pumping means functionally placed in the patient so as to cause or assist the movement of blood around the patient&#39;s vasculature.  
           [0025]    Until now most implanted heart assist devices have been placed in the abdominal cavity of a patient. This is disadvantageous as it complicates the surgical procedure and is unduly invasive for the patient. The few proposals for placement of such a device in the chest cavity have proposed the placement of the device against the inside of the chest wall so that the device can be wired to the ribs of the patient. It was apparently felt that this was necessary to support the weight of the device and to prevent it from moving around in the patient. The present inventors have found that the device may be placed against the mediastinum directly adjacent the patient&#39;s heart and attached to surrounding soft tissue. The device will thus lie in the plueral cavity, adjacent to the lung. The device preferably lies in a sagittal plane within the patient&#39;s body. Desirably, the device will not touch the inside surface of the chest wall at all. This placement will reduce pain for the patient and make placement of the device easier for the surgeon implanting the device.  
           [0026]    Preferably, the blood pumping means referred to in the above method is adapted to compress the aorta of a patient in counter-pulsation with the patient&#39;s heart. More preferably, the blood pumping means is adapted to compress the ascending aorta of the patient.  
           [0027]    In a fourth aspect, the present invention provides a heart assist device including:  
           [0028]    a blood pumping means adapted, when actuated, to cause or assist the movement of blood around the patient&#39;s vasculature;  
           [0029]    a fluid reservoir; and  
           [0030]    a fluid pressure generating means driven by an electric motor and adapted to pump a liquid from the fluid reservoir to the blood pumping means;  
           [0031]    the electric motor having a cogging torque which is sufficiently low that the natural systolic blood pressure of the patient is sufficient to cause liquid in the blood pumping means to be returned to the fluid reservoir in the event that the electric motor stops. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    Preferred embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings in which:  
         [0033]    [0033]FIG. 1 is a schematic longitudinal sectional view of a first embodiment of a fluid pressure generating means according to the invention;  
         [0034]    [0034]FIG. 2 is a schematic longitudinal sectional view of a second embodiment of a fluid pressure generating means according to the invention;  
         [0035]    [0035]FIG. 3 is a schematic longitudinal sectional view of a third embodiment of a fluid pressure generating means according to the invention connected to a heart assist device;  
         [0036]    [0036]FIG. 4 a  is a perspective view of a fourth embodiment of a fluid pressure generating means according to the invention;  
         [0037]    [0037]FIG. 4 b  is an underside perspective view of a housing portion of the fluid pressure generating means shown in FIG. 4 a;    
         [0038]    [0038]FIG. 4 c  is a schematic longitudinal sectional view of the fluid pressure generating means shown in FIG. 4 a ; and  
         [0039]    [0039]FIG. 5 is a schematic longitudinal sectional view of a fifth embodiment of a heart assist device according to the invention;  
         [0040]    [0040]FIG. 6 is a perspective view of the device shown in FIG. 5; and  
         [0041]    [0041]FIG. 7 is a perspective view of the device shown in FIG. 6 after implantation into the pleural cavity, medial to the lung, of a patient. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]    Referring firstly to FIG. 1, there is shown a schematic longitudinal sectional view of a first embodiment of a fluid pressure generating means according to the invention, in the form of pump  10 . The pump  10  includes a housing, indicated generally by the reference numeral  11 , comprising a substantially rigid bell-shaped first housing portion  12 , a substantially rigid flat circular second housing portion  14  and a flexible third housing portion or membrane  16 .  
         [0043]    The first, second and third housing portions  12 ,  14  and  16  together define an external boundary of the housing  11  around an interior volume denoted  18 , which is filled with a silicone oil. The second housing portion  12  itself formed from a cone-shaped portion  12   a  which is sealingly connected, after assembly of the pump  10 , to a cylindrical portion  12   b.    
         [0044]    The cone-shaped portion  12   a  also includes an inlet/outlet port  15 , which is connected in fluid communication with an aortic compression means or blood pumping means (not shown) by a conduit  17 .  
         [0045]    The membrane  16  is substantially annular in configuration and has enlarged inner and outer edges  16   a  and  16   b  which are sealingly received in corresponding circumferential recesses  12   c  and  14   a  provided in the first and second housing portions  12  and  14  respectively.  
         [0046]    The pump  10  also includes an electric motor, indicated generally by the reference numeral  20 , within the interior volume  18  of the housing  11 . The motor includes a rotor  21 , rotor laminations  22 , magnets  24 , stator  25 , stator laminations  26 , end windings  28  and bearings  30 .  
         [0047]    The stator  25  is fixed to the housing portion  12   a  by a number of screws  30  (only one shown). The rotor  21  is fixed to a nut  32 , which is itself threadedly engaged with a threaded shaft  34  through ball bearings (not shown). The shaft  34  is fixed to the housing portion  14  by screw  36 . The stator  25  also includes a number of guide journals  38  (only one shown) through which are guided a corresponding number of shafts  40  that depend from the housing portion  14 .  
         [0048]    Power and control signals are fed to the motor  20  through lines  42  and  44  respectively.  
         [0049]    The operation of the pump  10  will now be described. Energising the motor  20  to rotate in a first direction rotates the nut  32  relative to the threaded shaft  34  which causes the threaded shaft  34  to move in a direction parallel to its longitudinal axis in a first direction indicated by arrow  46 . FIG. 1 shows the shaft  34  at the end of its travel in this direction and after driving the housing portion  14  away from the housing portion  12  to increase the interior volume  18  and cause a suction or negative pressure at the inlet/outlet port  15 . This suction actively deflates the aortic compression means (not shown).  
         [0050]    Energising the motor to rotate in the opposite direction causes the threaded shaft  34  to move parallel to the longitudinal axis in the opposite direction indicated by arrow  48  and draw the portion  14  towards the housing portion  12 . The end limit of travel in this direction is indicated in phantom in FIG. 1 and, with reference to which it should be noted that, the guide shaft  40  abuts the inner surface of the housing portion  12   a  at the limit of its travel at recess  50 . Drawing the flexible portion  14  towards the housing portion  12  reduces the interior volume  18  which causes a positive pressure at the inlet/outlet port  15  and drives fluid from the interior volume  18  to inflate the aortic compression means.  
         [0051]    The motor  20  is actuated cyclicly in this manner in counterpulsation with the patient&#39;s heart in response to signals received from an ECG monitor or systemic arterial pressure, as disclosed in the PCT application.  
         [0052]    Referring now to FIG. 2, there is shown a schematic longitudinal sectional view of a second embodiment of a fluid pressure generating means according to the invention, in the form of pump  60 . The pump  60  is similar to the pump  10  shown in FIG. 1 and like features are indicated with like reference numerals. Differences between the pumps  10  and  60  are described in detail below.  
         [0053]    Firstly, the housing portion  12   a  of the pump  60  includes an opening  62  sealed by a second flexible membrane  64  which forms a compliance chamber  65 . The chamber  65  is in fluid communication with the interior volume  18 . Secondly, the inlet/outlet port  15  is provided in a further housing portion  66  which is sealed with respect to the side of the second housing portions  14  and third housing portion  16  that is remote the motor  20 . The housing portion  66  creates, in conjunction with the housing portions  14  and  16 , a second interior volume  68  in fluid communication with the aortic compression means or blood pumping means (not shown) via conduit  17 .  
         [0054]    The operation of the pump  60  is similar to that as described with reference to the pump  10  with the exception that the movement of the housing portion  14  causes volume changes in the second interior volume  68  which in turn inflates and deflates the aortic compression means. The movement of the housing portion  14  also causes fluid movement in the part of the interior volume  18  within the first, second and third housing portions  12 ,  14  and  16  and these changes cause an identical volume change in the interior of the compliance chamber  65 , which is shown having a decreased volume in response to the compression means being inflated. The chamber  65  will have an increased volume in response to the compression means being deflated, as is shown in phantom.  
         [0055]    As the interior volumes  18  and  68  are maintained sealed from one another by the second and third housing portions  14  and  16 , the pump  60  can be configured to use different fluids in each of the interior volumes  18  and  60 , as desired. For example, a saline solution can be used in the interior volume  68  and a lubricating oil can be used in the interior volume  18  which contains the motor  20 .  
         [0056]    [0056]FIG. 3 is a schematic cross sectional side view of a third embodiment of a fluid pressure generating means according to the invention, in the form of pump  80 . The pump  80  is shown connected to an aortic compression means or blood pumping means in the form of cuff  82 . The pump  80  is similar to the pump  60  described in relation to FIG. 2 and like reference numerals will be used to indicate like features. Differences between the pumps  60  and  80  are described in detail below.  
         [0057]    Firstly, the pump  80  has a first external substantially rigid cylindrical housing portion  84 , a pair of second internal substantially rigid housing portions  86   a  and  86   b  and a third substantially flexible housing portion  88 . The latter seals an end of the first housing portion  84 . The pump  80  also includes a second flexible housing portion  90  which seals the other end of the second housing portion  84  and forms a compliance chamber  92 . Secondly, the second housing portion  86  and the third flexible housing portion  88  abut, but are not connected, to each other.  
         [0058]    The operation of the pump  80  is similar to that described with reference to pump  60  in that the motor  20  is energised to reciprocally drive the threaded shaft  34  and thus the second housing portion  86   a  in directions  46  and  48  parallel to the longitudinal axis of the threaded shaft  34 .  
         [0059]    [0059]FIG. 3 shows the pump  80  in a position after movement of the second housing portion  86   a  in the direction  46  and driving fluid from the second interior volume  68  into the cuff  82  to inflate same. In this position, the second membrane of  64  is drawn into the interior of the second housing portion  84  to maintain the interior volume  18  constant. Driving the threaded shaft  34  in the opposite direction  48  results in the housing portion  86   b  forcing the membrane  64  to the position shown in phantom which is external the second housing portion  84 . This also results in the third housing portion  88  being drawn to the position also shown in phantom to maintain the interior volume  18  constant. As previously described in relation to pump  60 , when the third housing portion  86  is in this position fluid is drawn into the second interior volume  68  from the cuff  82  to deflate same.  
         [0060]    [0060]FIGS. 4A to  4 C show a fourth embodiment of a fluid pressure generating means according to the invention, in the form of pump  100 . The pump  100  is similar to the pump  10  shown in FIG. 1 and like components have been referred to with like reference numerals. However, the pump  100  has been designed to be as thin as possible (dimensions: 82 mm long; 60 mm wide; and  45  nun deep) in order to allow positioning in a patient&#39;s chest in contact with the mediastinum adjacent the heart. The pump  100  is placed with the planar housing portion  14  lying in a sagittal plane and as with the edge of the housing  100  clear of the inside surface of the chest wall. This orientation is chosen so as to minimise pain and trauma to the patient and also minimise the length of conduit required between the pump  100  and the aortic compression means (not shown). This positioning also assists the surgeon in placing the device.  
         [0061]    Referring finally to FIGS.  5  to  7 , there is shown a schematic longitudinal sectional view of a fifth embodiment of a fluid pressure generating means according to the invention in the form of pump  120 . The pump  120  is shown connected to an aortic compression means or blood pumping means in the form of cuff  122 . The construction and operation of the pump  120  is similar to die pump  10  shown in FIG. 1 and like features are indicated with like reference numerals. The size of the pump  120  is similar to the pump  100  shown in FIGS. 4A to  4 C, except it is more ovate and has flattened sides (See FIG. 6). The ovate form of the pump  120  and the positioning of the cuff  122  nearer one end allows the device to be placed in the plural cavity, medial to the lung, and lying in a sagittal plane within the patient&#39;s body, as is shown in FIG. 7. The pump  120  does not touch the inside surface of the patient&#39;s chest wall in this position. FIG. 7 also shows an external battery pack  123  which powers the pump  120 .  
         [0062]    The main differences between the pumps  10  and  120  are as follows. Firstly, the flexible third housing portion  16  is sealingly connected about its outer edge  16   b  to the substantially rigid ovate cup-shaped first housing portion  12 . The connection and sealing is achieved by a sealing rim  124  on the third portion  16  being snugly received in an annular recess  126  on the first portion  12 . Secondly, the substantially rigid flat ovate second housing portion  14  is received within a corresponding recess in the third portion  16 , on the interior side of the third portion  16 , and is thus within the interior volume  18 .  
         [0063]    [0063]FIG. 5 shows the pump  120  in a position after movement of the second housing portion  14  in the direction  46 , which draws fluid into the interior volume  18  from the cuff  122  and deflates same. Driving the threaded shaft  34  in the opposite direction  48  forces the second housing portion  14  towards the motor  20  (see the position of the shaft  34  shown in phantom). As previously described, when this occurs, fluid is forced from the interior volume  18  into the cuff  82  to inflate same.  
         [0064]    An advantage of the preferred embodiments of fluid pressure generating means described above is the liquid surrounding the motor is used both as a driving fluid to inflate/deflate the compressions (either directly as per the embodiments of FIGS. 1 and 4 exchanging fluid. The liquid also dampens sound made by the pump mechanism. This simplifies the construction, and minimises the size, of the fluid pressure generating means.  
         [0065]    Whilst the fluid pressure generating means will normally actively drive both the inflation and deflation of the aortic compression means, the motor is preferably designed so that the cogging torque of the motor is sufficiently low that the natural systolic blood pressure of the patient is sufficient to deflate the cuff. If the motor is inactivated for any reason with the cuff in an inflated condition (and thus with the aorta partially occluded), this arrangement means that the natural systolic blood pressure will deflate the cuff by pushing fluid from the cuff into the housing and passively driving the second housing portion away from the motor.  
         [0066]    It will be appreciated by person skilled in the art that numerous variations and/or modifications can be made to the invention as shown in the specific embodiments without departing from the spirit or scope of invention as broadly described. For example, the embodiments of the invention are not restricted for use with the embodiments of the heart assist device shown in the PCT application. The specific embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.