| 摘要 |
<p>A demand pacer which provides electrical heartstimulating impulses in the absence of natural heartbeats. In a pacer of this type, if the natural heartbeat detector is erroneously triggered, it is possible for impulses to be inhibited when they are actually needed. Erroneous operation of the detector in the invention is partially prevented by tuning it to the dominant frequencies in the electrical signal which is generated as a result of a localized ventricular depolarization. These frequencies, however, are relatively close to 60 Hz, and thus 60 Hz stray signals might erroneously cut off the generation of impulses. For this reason, a capacitor charging circuit is provided in the detecting circuit. All input signals are processed 50 that the capacitor is fed by unipolar pulses. Pulses occurring at a 120 Hz rate (from the processing of stray 60 Hz signals) occur so rapidly compared to the discharge time constant of the capacitor circuit that the voltage across the capacitor does not change appreciably. Heartbeat signals, on the other hand, occurring at the much slower rate of approximately 72 per minute, allow the capacitor to discharge sufficiently after each charging pulse such that a large pulsating signal is developed across the capacitor. It is each pulsating signal which shuts off the generation of an impulse. In the presence of 60 Hz stray signals, the pacer functions in its continuous mode.</p> |
