GB1360066A - Stimulator circuit for a body organ - Google Patents

Abstract

1360066 Body organ stimulator GENERAL ELECTRIC CO 30 June 1971 [10 July 1970] 30699/71 Heading A5R [Also in Division H3] A body organ stimulator comprises first and second circuit points, ground and 70, for connection to a d.c. source 72, first and second terminals, ground and 10, for connection to the body organ load RL, terminal 10 being connected to means for providing stimulation pulses through a series capacitor 67, said means including two series-connected controllable devices 60, 63, a pulse generator connected to apply pulses to device 60 to render it conductive, devices 60, 63 being so interconnected that when device 60 is conductive device 63 is non- conductive, a resistor 66 serving with device 63 to establish, when load RL is connected, a quiescent charge state of capacitor 67 such that when device 60 is rendered conductive by the pulse generator alteration of the charge state of capacitor 67 occurs by current flow in load RL and upon termination of the pulse applied by said generator to device 60, device 63 conducts and the quiescent charge state of capacitor 67 is re-established by current flow through device 63 and resistor 66. In a demand heart pacemaker embodiment signals from the heart are passed to a preamplifier and filter 13, which is refractory for a short period of time following receipt of a heart signal, such a signal giving an output 14 normally applied to a gated threshold trigger 15 giving an output 17. The output 17 gives rise to an output 24 from an interference rejector 23 only if the signals 17 are produced at a predetermined rate. The output 24 causes a transistor 25 to conduct to discharge a timing capacitor 30 and thereby prevent stimulation of the heart. If capacitor 30 is not prematurely discharged it charges to a potential at which transistor 34 conducts causing a signal 62 to be applied to the base of transistor 60 thereby discharging the capacitor 67 through the heart to stimulate the heart and causing transistor 63 to stop conducting. The trigger 15 is rendered inactive during the stimulation by means of a signal applied to transistor 19 causing the output 14 to be shunted to ground. The stimulating pulse duration is about two milliseconds following which transistor 63 becomes conductive to rapidly recharge capacitor 67 through the heart until the base-emitter voltage drop on transistor 63 is too small to keep it conducting whereafter recharging is completed through a high resistance 66, such as 1 megohm. Recharging takes place during the refractory period of the heart and of circuit 13; there is almost no net charge flow through the heart. The stimulating pulse amplitude is adjusted by means of a potentiometer 55. Alternative embodiments of the output circuit comprising capacitor 67 and two series-connected transistors are described, in two of which embodiments, Figs. 2, 4 (not shown), the heart is stimulated as capacitor 67 is charged through the heart, the capacitor being subsequently discharged through the heart during its refractory period.