GB1419980A - Electromedical stimulation apparatus - Google Patents

Abstract

1419980 Electromedical stimulating apparatus MEDTRONIC INC 11 Jan 1973 [13 Jan 1972 30 June 1972] 1608/73 Heading A5R [Also in Division H3] Electromedical stimulating apparatus comprises a power source 1, Figure 3, connected to a pulse generator 2, 3, 4 supplying stimulating pulses to terminals 5, 6 and including a timing circuit arranged so that for decreases in power supply voltage from an initial to a predetermined value, the width of pulses provided by the generator increase sufficiently to maintain the total energy of each pulse not less than the total energy of each pulse with said initial voltage value. The stimulator may be a heart pacemaker, or an implantable nerve or muscle stimulator. An asynchronous heart pacer which is implantable has an oscillator 3 Figure 3 in an off state of which all the transistors of the pacer are non-conductive and a previously charged capacitor 29 discharges until its voltage essentially balances the turn on voltage of transistor 22 at which time transistor 22 turns on turning on transistors 39, 31 and thus 42 to discharge a capacitor 45 through the heart. In the "on" state capacitor 29 charges up until its voltage is substantially equal to the voltage at a junction 16 less the base-emitter drop of transistor 22 at which time the oscillator turns off. If the voltage at the junction of resistors 20, 21 is above or below a predetermined level when the oscillator turns on transistors 10, 11, 12 turn on or remain off respectively and the charging path of capacitor. 29 includes transistor 12 if turned on. The pulse width is thus increased in a stepwise manner when the output of battery 7 falls below a predetermined level. The pulse width can be adjusted by adjusting a potentiometer 36 coupled magnetically to extracorporeal adjusting means. When transistors 10, 11, 12 are unable to turn on the voltage at junction 16 increases and therefore capacitor 29 charges to a higher voltage before transistor 22 turns off. Accordingly the discharge time of capacitor 29 is longer and a decrease in pulse rate accompanies the pulse width increase. A demand pacemaker includes a heart beat amplifier 53, Figure 4, which causes a transistor 55 to discharge a capacitor 58 if a heart beat is detected within a predetermined interval. Transistors 60, 62 and 75 in combination with feedback circuit including a capacitor 83 form an astable multivibrator pulse generator which is turned on whenever capacitor 58 charges to a predetermined level. When the pulse generator turns on a transistor 59 discharges capacitor 58 and a transistor 80 discharges a capacitor 89 through the heart. The feedback loop including capacitor 83 maintains the pulse generator on after discharge of capacitor 58 until capacitor 83 has discharged to a level at which transistor 60, and thus transistors 62, 75, 59, turn off. Decreases in the power supply 50 output voltage are felt at a reference junction 86 so that proportionate and substantial increases in stimulating pulse width and interpulse interval results.