Patent GB-826766-A (GB)
Title: Device for stimulating periodic functions of the body
Inventor: DAVIES JOHN GEOFFREY
IPC: A61N1/365
Filed: 1956-12-06
Abstract: 826,766. Cardiac stimulators. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Dec. 6, 1957 [Dec. 6, 1956], No. 37400/56. Class 81 (2). [Also in Group XL (c)] A cardiac stimulator comprises electrical impulse generating means, which delivers electrical impulses at predetermined time intervals, and has means for regulating the time intervals and means responsive to an externally applied signal for disabling the impulse delivering means for a predetermined period, the disabling means being arranged on receipt of a further externally applied signal during the period to hold the impulse delivering means disabled during a further period of predetermined duration. As shown, a timing circuit includes a gas tube V2 which has, in addition to the main cathode and anode, a priming anode and a trigger electrode connected across a high-tension supply, in the form of either a battery HTB or a direct current supply from the mains. When main switch S1 is closed, a capacitor C3 charges through resistors R6, R7 and a second capacitor C4 charges through resistors R9, R11. When C3 has charged up to the breakdown potential of the trigger gap, the latter fires and the tube V2 conducts so that the second capacitor C4 discharges through a relay D in the anode circuit of the tube V2 thus momentarily operating contacts dl to disconnect the tube V2 from the high-tension supply. On extinction of the tube V2 contacts dl are again made and the cycle is repeated. The cycle period is primarily controlled by the time constant of the first capacitor C3 which is adjusted to the normal rate of heart beats. A neon tube V3 normally discharges when switch S1 is closed but is extinguished at the same time as tube V2 thus serving as a visual indication of the operation of the timing circuit. Capacitors C8, C9, C10 in an impulse producing circuit are selectively connected in parallel across the high tension supply through a potentiometer R13, On operation of the relay D in the timing circuit, the selected capacitor C8, C9 or C10 is disconnected from the high-tension supply and connected momentarily by contacts d2 to patient electrode terminals OP. The capacitors C8, C9, C10 have different values in the range of 1-4 Áfds. A cut-out circuit having input terminals IP connected to an electrocardiagraph or other heart-responsive means, e.g. a transistor, includes a double triode V1 and is operable only when the high-tension supply is from the mains. The cut-out circuit is arranged to disable the impulse producing and timing circuits for a period of 6 secs. if the heart makes a spontaneous beat. Relays A, B are connected in the cathode circuits of each half VIa, VIb respectively of the double triode which is normally at cut off. When an " R-wave " due to a spontaneous heart beat reaches the grid of the triode part VIa, the relay A is energized and contacts a1 connect a capacitor C2 associated with the grid of the part VIb across the high-tension supply so that the relay B is energized to disconnect contacts b1 in the timing circuit. The time constant C2, R4, R5 is such that contacts b1 are held open for 6 secs. If a second " R-wave " is received in this period, the cut-out circuit operates for a further 6 sees. To prevent the cut-out circuit responding to impulses generated by the impulse producing circuit, contacts d3 in the cut-out circuit are disconnected when the relay D is energized. In cases where spontaneous heart beats tend to occur in step with the stimulator pulses, the stimulator pulse is cut out periodically, a selector being arranged to move one step each time the relay D in the timing circuit is energized. In one position of the selector, reached periodically, a circuit is established through another relay which disconnects contacts in the impulse producing circuits, thus disabling them, and simultaneously closes a contact in the cut-out circuit so that if an " R-wave " due to a spontaneous heart beat is received, the cut-out circuit operates as before to disable the timing and impulse producing circuits for 6 secs. The impulse producing circuit may be arranged so that the polarity of the patient electrodes is reversed periodically.