Abstract:
Disclosed is an implantable one-piece heart prosthesis having a driving artificial ventricle and a driven artificial ventricle. A main actuator is configured to transmit to the driving artificial ventricle diastolic and systolic flow rates having desired respective values for the driving artificial ventricle. An auxiliary actuator is configured to transmit to the driven artificial ventricle correction systolic and diastolic flow rates that correct the systolic and diastolic flow rates transmitted by the main actuator to the driven artificial ventricle.

Description:
FIELD OF THE INVENTION 
     This invention relates to an implantable one-piece heart prosthesis. 
     BACKGROUND OF THE INVENTION 
     From document U.S. Pat. No. 5,135,539, a heart prosthesis being implantable in the pericardial cavity of a patient is known, said prosthesis being capable of replacing the natural left and right ventricles of said patient after ablation thereof and comprising:
         a stiff body in which artificial left and right ventricles are arranged, each of these artificial ventricles comprising a soft pulsatile membrane:
           which is capable of beating under the action of a hydraulic fluid, and   which is provided within a cavity sealingly partitioned by said membrane into two chambers, one of which is intended for blood flow and the other of which is intended for said hydraulic fluid, the blood chamber of the artificial left ventricle being intended to be connected to the natural left atrium and to the aorta, whereas the blood chamber of the artificial right ventricle is intended to be connected to the natural right atrium and to the pulmonary artery;   
           two hydraulic actuators connected to the hydraulic fluid chambers of said cavities within said stiff body, for alternately injecting therein and expulsing therefrom hydraulic fluid and providing desired values of diastolic and systolic flow rates; and   a soft bag widely and sealingly surrounding at least one portion of said stiff body while enclosing said hydraulic actuators, said soft bag serving both as a hydraulic fluid reservoir for said hydraulic actuators and as a compliance chamber.       

     In this known heart prosthesis, each actuator is associated with a ventricle and, in order to comply with physiology, both actuators can operate independently from each other and particularly in a synchronised way, that is both ventricles can be respectively and simultaneously either in diastole or in systole. In this case, the result is that said soft bag undergoes large displacements, since the whole fluid required for animating right and left pulsatile membranes is alternately injected, and then drawn into said soft bag. If the capacity of each ventricle is of about 75 cm 3 , the volume variations of the bag may reach 150 cm 3 . Such high amplitude beats of the bag, on the one hand, may raise issues of housing said prosthesis within the pericardial cavity and, on the other hand, cause an inflammation of the surrounding tissue, with the risk for a thick fibrous capsule to occur, capable of hindering the beats of the bag and altering the operation of the prosthesis. 
     Besides, such a synchronised operation requires that both actuators are capable of the same performance, which is of a high power cost. 
     In order to overcome these drawbacks, it could be possible, as suggested by document WO-0,191,828, to remove one of said actuators and operate the ventricles in phase opposition, one of said ventricles being in diastole whereas the other is in systole. Thus, the hydraulic fluid is transferred from a ventricle into the other with much reduced beats of the bag. In addition, such a heart prosthesis is advantageous in terms of space and power consumption, since it only comprises one actuator. However, it has the drawback of controlling the intake duration of one of the ventricles based on the ejection of the other, such that the diastole durations are necessarily equal to the systole durations, which does not enable physiology to be complied with. In addition, such a heart prosthesis with one single actuator has the risk, in operation, of either drawing the atria and failing to fill the ventricles, or performing too slow ejection and not maintaining a proper pressure. 
     SUMMARY OF THE INVENTION 
     This invention aims at overcoming these drawbacks by improving the heart prosthesis with two actuators described above. 
     For this purpose, according to the invention, such a heart prosthesis with two actuators is remarkable in that:
         one of said actuators is a main one and is provided between the hydraulic fluid chambers of both artificial ventricles, one of which is driving and the other is driven;   the other of said actuators is a auxiliary one and is provided between the hydraulic fluid chamber of said driven artificial ventricle and said reservoir of hydraulic fluid made up by said soft bag;   the main actuator:
           transmits to said driving artificial ventricle diastolic and systolic flow rates having desired respective values for this driving artificial ventricle, and   transmits to said driven artificial ventricle:   a systolic flow rate opposite to said diastolic flow rate of a desired value for said driving artificial ventricle, and   a diastolic flow rate opposite to said systolic flow rate of a desired value for said driving artificial ventricle; and
               the auxiliary actuator transmits to said driven artificial ventricle correction systolic and diastolic flow rates for correcting said systolic and diastolic flow rates transmitted by said main actuator to said driven artificial ventricle and for communicating respectively to the corrected systolic and diastolic flow rates desired values for said driven artificial ventricle.   
               
               

     Thus, with the present invention, the beats of the sealed bag are restricted since, in operation, the hydraulic fluid is transferred from one artificial ventricle to the other. However, with said correction flow rates generated by said auxiliary actuator, the diastole and the systole durations are not necessarily equal. 
     Besides, the auxiliary actuator can have a lesser power than said main actuator, such that the power consumption of the prosthesis in accordance with this invention is lower than the power consumption of the known prosthesis with two actuators. In addition, the auxiliary actuator can also have a smaller size than the one of said main actuator. 
     Preferably, the driving artificial ventricle corresponds to the right artificial ventricle, whereas the driven artificial ventricle corresponds to the left artificial ventricle. In addition, it is advantageous that said main and auxiliary actuators are of the volumetric motor pump type. 
     For the convenience of accommodating the prosthesis inside the pericardial cavity, it is also advantageous that said main actuator and said auxiliary actuator are provided in the vicinity of each other. In this case, in order to benefit from the anatomy, said main and auxiliary actuators are provided in the vicinity of the left artificial ventricle and so they communicate commonly with the hydraulic fluid chamber of this latter ventricle, while said main actuator is connected to the hydraulic fluid chamber of the right artificial ventricle by a duct outside said stiff body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the appended drawing will help better understand how the invention can be implemented. In theses figures, identical references denote similar elements. 
         FIG. 1  schematically shows in cross-section a known heart prosthesis which the present invention aims at improving. 
         FIG. 2  schematically illustrates the condition of the heart prosthesis of  FIG. 1  at the end of a systole. 
         FIG. 3  schematically illustrates the condition of the heart prosthesis of  FIG. 1  at the end of a diastole. 
         FIG. 4  schematic shows, in a view similar to  FIGS. 1 to 3 , the heart prosthesis in accordance with this invention. 
         FIG. 5  is the block diagram of the heart prosthesis of  FIG. 4 . 
         FIG. 6  illustrates the operation of the heart prosthesis of  FIGS. 4 and 5  for normal diastolic and systolic flow rates. 
         FIG. 7  illustrates the operation of the heart prosthesis of  FIGS. 4 and 5  for high diastolic and systolic flow rates. 
         FIG. 8  is a perspective view of a practical embodiment of the prosthesis of the invention, wherein its envelope made of a sealed soft bag is assumed to be transparent. 
         FIG. 9  is a top view of the prosthesis of  FIG. 8 . 
         FIG. 10  is a perspective view of the prosthesis of  FIGS. 8 and 9 , after removal of said sealed soft bag and the enveloping cut-out wall. 
         FIG. 11  is a perspective view showing hydraulic actuators and covers of artificial ventricles of the prosthesis of  FIGS. 8 to 10 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The known prosthesis P, schematically depicted in  FIG. 1 , is intended to replace the natural left and right ventricles of an ill heart (not shown), after ablation thereof. The prosthesis P should be able to be accommodated at least substantially in the portion of the pericardial cavity left free following removal of said natural ventricles. 
     As schematically depicted in  FIG. 1 , the prosthesis P comprises:
         a stiff body  1  in which an artificial left ventricle  2  is arranged, comprising a soft membrane  3  which sealingly partitions said artificial ventricle  2  into a chamber  4  for the blood flow and a chamber  5  for a hydraulic fluid, said blood chamber  4  being intended to be connected, on one side to the natural left atrium LA in communication with the pulmonary veins PV and, on the other side, to the aorta AO;   a hydraulic actuator  7 , for example of the volumetric motor pump type, in communication with the hydraulic fluid chamber  5  of the artificial left ventricle  2 ;   an artificial right ventricle  8 , arranged within said stiff body  1  and comprising a soft membrane  9  which sealingly partitions said artificial ventricle  8  into a chamber  10  for the blood flow and a chamber  11  for a hydraulic fluid, said blood chamber  10  being intended to be connected, on one side, to the natural right atrium RA in communication with the vena caves VC and, on the other side, to the pulmonary artery PA; and   a hydraulic actuator  13 , for example also of the volumetric motor pump type, in communication with the hydraulic fluid chamber  11  of the artificial right ventricle  8 .       

     Besides, a soft bag  12  widely and sealingly surrounds at least one portion of the stiff body  1  by enclosing the hydraulic actuators  7  and  13 . Such soft bag  12  forms a reservoir  14  for the hydraulic fluid moved by said actuators  7  and  13 . 
     In the pump P, each actuator  7  and  13  is specifically dedicated to one of the artificial ventricles  2  or  8 , respectively, such that both actuators  7  and  13  have the same power. 
     When, as schematically illustrated by  FIGS. 2 and 3 , actuators  7  and  13  are phase controlled, such that systoles of the artificial ventricles  2  and  8  occur simultaneously ( FIG. 2 ) and diastoles of said artificial ventricles  2  and  8  also occur simultaneously ( FIG. 3 ), the volume of the reservoir  14  made up by the soft bag  12  varies widely. Indeed, in the case of simultaneous systoles ( FIG. 2 ), both hydraulic fluid chambers  5  and  11  are filled with this fluid, such that the reservoir  14  contains little hydraulic fluid and volume thereof is reduced. By contrast, when said artificial ventricles  2  and  8  are in a condition where diastoles thereof are simultaneous ( FIG. 3 ), both hydraulic fluid chambers  5  and  11  empty, such as that reservoir  14  is filled with hydraulic fluid and volume thereof is large. 
     The prosthesis Pt, according to this invention and depicted in  FIGS. 4 ,  5  and  8  to  11 , makes it possible to avoid such a high variation of the volume of the reservoir  14 , while requiring a lesser operating power. 
     Such prosthesis Pt is the same as the prosthesis P described above with respect to elements  1  to  5 ,  8  to  12  and  14 . However:
         the actuator  7  is replaced by an actuator  7   t  of lower power; and   the actuator  13  is replaced by an actuator  13   t  of the same power, but arranged in another way. Indeed, the actuator  13   t  is not arranged (as the actuator  13 ) between the hydraulic fluid chamber  11  and the reservoir  14  anymore, but between the hydraulic fluid chambers  5  and  11  of both artificial ventricles  2  and  8 .       

     Thus, said actuator  7   t  is of lesser power and can be less cumbersome than said actuator  13   t.    
     The block diagram of the prosthesis Pt, shown in  FIG. 5  and wherein the artificial ventricles  2  and  8  are depicted as cylinders in which pistons made up of the membranes  3  and  9  move respectively, helps better understand the operation of the prosthesis Pt of  FIG. 4 . It can be seen that the actuator  7   t  is provided in a link  15  connecting the reservoir  14  and the fluid chamber  5  of the artificial ventricle  2  and that the actuator  13   t  is provided in a link  16  connecting both fluid chambers  5  and  11  of the artificial ventricles  2  and  8 . 
     A device  17  controls the operation of actuators  7   t  and  13   t , such that the actuator  13   t  plays a leading role, whereas the actuator  7   t  plays a secondary role in correcting the flow rate. 
     The operation of the prosthesis Pt is explained in further detail thereafter with respect to the time chart of  FIG. 6 . In this time chart, different hydraulic fluid flow rates d are shown (corresponding to blood rates respectively) as a function of time t. There is particularly shown (in full line) a curve  18  corresponding to flow rates of desired values for the main actuator  13   t  during diastoles D 8  and systoles S 8  of the artificial ventricle  8 , as well as (in dash lines) a curve  19  corresponding to flow rates with desired values for the auxiliary actuator  7   t  during diastoles D 2  and systoles S 2  of the artificial ventricle  2 . It will be noticed that, in the example shown, the systoles S 2  and S 8  have lower durations than the diastoles D 2  and D 8 . 
     The device  17  controls the main actuator  13   t  such that it transmits to the artificial ventricle  8  the desired diastolic and systolic flow rates, represented by curve  18 . The artificial ventricle  8  therefore supplies the desired blood volumes. 
     However, because of the existing link  16  between the hydraulic fluid chambers  5  and  11  of the artificial ventricles  2  and  8 , the main actuator  13   t  imposes to the artificial ventricle  2  systolic and diastolic flow rates represented by curve  20  in chain dotted lines, such that the systolic and diastolic flow rates of said artificial ventricle  2  are respectively the opposites of diastolic and systolic flow rates of the artificial ventricle  8  (curve  18 ). In such operation, the artificial ventricle  8  is therefore a driving one whereas the artificial ventricle  2  is a driven one. 
     Also, in order that the artificial ventricle  2  can receive the desired flow rates represented by curve  19 , the device  17  controls the auxiliary actuator  7   t  such that it transmits to said artificial ventricle  2 , correction systolic and diastolic flow rates (represented by curve  21  in  FIG. 6 ) capable of correcting said systolic and diastolic flow rates (curve  20 ) imposed by the main actuator  13   t.    
       FIG. 6  shows diastolic and systolic flow rate forms corresponding to average normal blood flow rates, for example in the order of 5 liters per minute. In the case where the blood flow rate is high, for example in the order of 8 liters by minute, the flow rate forms would rather be as depicted in  FIG. 7 . In this case, the curves  18  and  19  would look like identical sinusoids in phase opposition, such that therefore, no correction would be required from the auxiliary actuator  7   t  (which is depicted in  FIG. 7  because curve  21  merges with axis of the sinusoids  18  and  19 ). 
     In the practical embodiment depicted in  FIGS. 8 and 9 , the prosthesis Pt is in the form of an anatomical shape volume (corresponding to that of the pericardial cavity) comprising a plate  31  on which a connecting port  32  for the natural left atrium LA, a connecting port  33  for the natural right atrium RA, a connecting port  34  for the aorta AO and a connecting port  35  for the pulmonary artery PA, are bored. In addition, on these figures, the base  36  of an electrical connection with the outside of said prosthesis Pt is depicted. 
     The heart prosthesis is sealingly enclosed within the soft bag  12  (assumed to be clear in  FIG. 8 ) surrounding said prosthesis, in a wide fashion, and filled with hydraulic fluid actuated by the actuators  7   t  and  13   t , immersed in this fluid. The soft bag  12  provides the reservoir  14  acting as a tarpaulin for this hydraulic fluid. 
     The body  1  and the actuators  7   t  and  13   t  are wrapped in a stiff cut-out wall  37 , serving as a strainer and enabling hydraulic fluid flow inside the bag  12 . The cut-out wall  37  prevents said soft bag from being suctioned by actuators  7   t  and  13   t.    
     On  FIG. 10 , an embodiment of the body  1  and actuators  7   t  and  13   t  as a whole located inside the cut-out wrapping wall  37  and soft bag  12  is depicted in perspective. In this figure, it can be seen that the auxiliary and main actuators  7   t  and  13   t  have been provided close to each other, in the vicinity of the artificial left ventricle  2 . In addition, as shown more clearly in  FIG. 11 , the outside walls  2 E and  8 E of the hydraulic fluid chambers  5  and  11  of the artificial ventricles  2  and  8  (see also  FIG. 4 ) are formed by removable covers  38  and  39  intended to seal said ventricles, respectively. 
     The auxiliary actuator  7   t  communicates with the chamber  5  of the artificial left ventricle  2  through a port  40  going through the cover  38  and acting as the link  15  of  FIG. 5 . The main actuator  13   t  communicates, on the one hand, with the chamber  5  of the artificial ventricle  2  through the same port  40  and, on the other hand, with the chamber  11  of the artificial ventricle  8  through an outside duct  41  opening to a port  42  in the cover  39 . The duct  41  and the ports  40  and  42  correspond to the link  16  of  FIG. 5 . 
     As depicted in  FIG. 11 , the actuators  7   t  and  13   t , the covers  38  and  39  and the duct  41  can be integral with one another to form a construction unit. 
     In  FIG. 10 , electronic driving elements are further depicted, such as a sensor  43  for the pressure inside the soft bag  12 , a sensor  44  for the pressure in the left artificial ventricle  2  and a sensor  45  for the pressure in the right artificial ventricle  8 .