GB1298189A - Electromedical apparatus - Google Patents

Abstract

1298189 Cardiac defibrillator MEDTRONIC Inc 19 April 1971 [9 Feb 1970 (2)] 21311/71 Heading A5R A cardiac defibrillator comprises; storage means for storing electrical energy, an electrode for connecting the storage means to the heart of a patient, switching means operable to discharge the storage means through the electrode into the heart, sensing means for connection with the heart for continually sensing the heart function, and a discriminator associated with the sensing means and adapted to discriminate between normal heart function and cardiac fibrillation as sensed by the sensing means, said sensing means and discriminator being arranged for automatically operating said switching means, so causing the energy stored in said storage means to be applied through said electrode directly to the heart in order to defibrillate the malfunctioning heart. The sensing means may take the form of a probe in the right ventricle of the heart which is sensitive to the blood pressure in the right ventrical. By means of a bridge arrangement 40 a signal is obtained from the probe which is a measure of the pressure at the sensing probe. The signal is fed into a discriminator 42 which analyzes the signal and produces an output signal pulse the amplitude of which is above a certain predetermined level if the input signal is from a normal heart, but which is below said predetermined level if the input signal is derived from a malfunctioning heart. The output of the discriminator 42 is fed via a cable 56 into a sawtooth generator 44. If the signal pulses from the discriminator are above said predetermined level (i.e. if they correspond to a healthy heart) the sawtooth generator is triggered by each pulse and the characteristic sawtooth output (58) is obtained (see Fig. 4, not shown). If the signal pulses are below said pre-determined level (i.e. if they correspond to a malfunctioning heart) the sawtooth generator is not triggered by the pulses and its output voltage rises steadily (54). If the sawtooth generator is not triggered its output voltage after about six seconds is sufficient to turn on the transistor in the relay stage 46. This transistor in turn operates the relay 64 which connects a low voltage supply to a converter 48, the output of which (about 2500 volts) is applied to the capacitor 70. A resistor chain, neon tube 74, transistor 72 and silicon controlled rectifier 76 serve to discharge the capacitor through the electrodes 26, 28 when said capacitor is fully charged. If at any time after the initial sensing of a malfunction the heart resumes normal operation the sawtooth generator will be triggered, causing the relay to revert to its open circuit state and stop the charging of the capacitor; thus if the heart re-starts of its own accord no shock will be delivered. After the first shock, if the heart does not restart further shocks will be delivered at time intervals the duration of which is equal to the sum of the time delay caused by the sawtooth generator and the time taken to charge the capacitor.