Pacemaker with high resistance batteries - uses low resistance load which is compensated by switches controlled by comparator

摘要

Pacemakers have low resistance circuits in order to match the low resistance load formed by the heart. However modern pacemakers use lythium batteries which have a high internal resistance and should therefore operate with a high load resistance in order to avoid instability. The problem is solved by feeding the battery voltage to one input of a comparator and the voltage across a reservoir capacitor to the other. The output of the comparator controls a circuit which maintains a constant voltage level at the capacitor. A comparator (10) with high input resistance samples the battery voltage (Ur) and the voltage (Uc) of the capacitor (4) whose discharge through the heart (1) produces the stimulating pulse. The output of the comparator controls switches (8,9) which will tend to counteract the fluctuations of the voltage levels of the capacitor.