GB1143141A - A method of producing cardiac defibrillation electric pulses and a cardiac defibrillator for carrying out the method - Google Patents

Abstract

1,143,141. Cardiac defibrillators. R. R. KEMDEN. 6 May, 1966 [17 May, 1965], No. 20153/66. Heading A5R. An alternating current cardiac defibrillator comprises electrodes 84, 86 which are connected intermittently through a step-up transformer 12 to an alternating current source for periods of less than 100 milliseconds by a relay switch 74 controlled by a timing circuit 10, so that pulses having the same wave form as the alternating current source and a duration of less than 100 milliseconds reach the electrodes. The transformer 12 steps up a mains alternating voltage of 110 volts to 480 volts r.m.s. The timing circuit is energised through a transformer 14 and includes a rectifier 24. On operating a switch 38 to close contact 36, a capacitor 34 is connected across the rectified voltage and, as it charges, transistor amplifiers 52, 56 conduct to operate relay 74 for a time determined by the time constant of the capacitor. The capacitor is discharged to reset the timing circuit by operating the switch 38 to close contact 42, thus short-circuiting the capacitor. Alternatively, the timing circuit may 'be operated by a signal derived from the heart, e.g. the R-wave of an electrocardiagram.