Patent GB-1381812-A (GB)
Title: Implantable artificial heart
IPC: A61M60/835
Filed: 1972-01-17
Abstract: 1381812 Implantable artificial heart COMMISSARIAT A L'ENERGIE ATOMIQUE 17 Jan 1972 [22 Jan 1971] 2158/72 Heading A5R [Also in Division F1] An implantable artificial heart comprises a motor formed by a heat engine following a Stirling cycle; a pump formed by right-hand and left-hand piston-and-cylinder devices 18, 16 and 17, 15, with the pistons 18, 17 linked by a common rod 19 which is controlled by the motor; ducts 23, 22 filled with liquid and connecting the right-hand pump chamber 16 and left-hand pump chamber 15 respectively to chambers corresponding to the right-hand ventricle and auricle, (VD) and (OD), Fig. 1 (not shown) and to the left-hand ventricle and auricle (VG) and (OG), respectively; a casing 29 containing the motor and the pump; and the motor comprising a working cylinder 5 and a secondary coaxial cylinder 7, both containing gas, a piston 6 common to both cylinders 5 and 7, a heat source 1 at the head of the working cylinder 5, (the piston 6 acting as the heat sink), a regenerator 9 in the working cylinder 5 having a structure which is permeable to longitudinal gas flow, and movable between positions contacting the heat source 1 and contacting the piston 6, means 13, 14 and 26-28 for releasably locking the piston 6 at the inner and outer ends respectively of its stroke in the cylinder 5, means 10 for releasably locking the regenerator 9 to the piston 6, and means 11, 12 for moving the regenerator 9 from the piston 6 to the heat source 1. A buffer volume 24 with a flexible diaphragm contains liquid maintained at a reference pressure near to atmospheric and communicates with the spaces outside pistons 17, 18 and with the two auricular chambers (OD), (OG), Fig. 1 (not shown). The means for releasably locking the piston 6 at the inner end of its stroke are magnetic armatures 13 fixed to the piston 6, which cooperate with magnets 14 mounted on a support of the casing 29. The means for releasably locking the piston 6 at the outer end of its stroke are a catch 26 carried by the piston 6, cooperating with a fixed ratchet stop 27, and releasable by an escapement 28 carried by the common rod 19 of the pump. The means for releasably locking the regenerator 9 to the piston 6 is the constitution of the piston 6 as a permanent magnet which attracts a magnetic pallet 10 fixed to the regenerator 9. The means for moving the regenerator 9 away from the piston 6 is a plunger 11 attached to the pallet 10 and movable to compress gas contained in an axial bore extending through the piston 6, the bore being closed by a fixed plunger 12. Similar spring action is achieved by compression of the gas in the secondary cylinder 7, and an associated volume 8, by the piston 6. The cylinders 15, 16 of the pump are coaxial with each other and with the working cylinder 5. The common rod 19 is cylindrical and is slidable along the working cylinder 5: An annular flange 19' of the rod 19, when in abutment with the support for the magnet 14, defines one limit of the travel of the rod 19 and pistons 17, 18. The heat source 1 is a radioelement such as Pu 238 enclosed in a sheath, in a thermal capacitance 2 having a high latent heat of fusion, and in thermal insulation 3. The operating cycle is: (i) at the end of the systole (contraction) phase, as shown, the regenerator 9 contacts the heat source 1; the pallet 10 is drawn to the magnetic piston 6, so that the regenerator 9 traverses the cylinder 5. The gas flows through the regenerator 9 and is thus heated at constant volume. (ii) The increase in gas pressure thus caused is sufficient to overcome the attraction between the armature 13 and the magnet 14, and the piston 6 and regenerator 9 together are moved outwards. The gases in the axial bore of the piston 6 and in the secondary cylinder 7 are thus compressed. The expansion is isothermal at the temperature of the heat source 1. The movement of the piston 6 allows the outward movement of the rod 19, pistons 17, 18 and thus the expansion of the cylinders 15, 16 of the pump, thus initiating the diastole (expansion) phase. Movement of the piston 6 ceases when the catch 26 engages the stop 27. (iii) The gas in the axial bore of the piston 6 is then sufficiently compressed to overcome the magnetic attraction between the piston 6 and the pallet 10, and the regenerator 9, now at the temperature of the heat sink (the piston 6), again traverses the cylinder 5, cooling the gas therein at constant volume. The pump pistons 15, 16 having moved outwardly sufficiently for the escapement 28 to release the catch 26 from the stop 27, the drop in pressure in cylinder 5, aided by the increased pressure in the secondary cylinder 7, causes the piston 6 to move inwardly, and with it the rod 19 and the pump pistons 17, 18. The pump cylinders 15, 16 thus contract, initiating the systole phase. The compression is isothermal.