Abstract A demand pacer which provides electrical heart-stimulating 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 so that the capacitor is fed by unipolar pulses. Pulses occuring 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, occuring 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.
A monitoring system for determining if the time interval between any two successive waveforms in a series of repetitive waveforms is greater than a minimum time interval comprising means for detecting each of the successive waveforms in said series of repetitive waveforms, said detecting means including frequency discrimination means for making said detecting means insensitive to pre-selected frequency components in said repetitive waveforms, means responsive to each detection of a waveform by said detecting means for producing a unipolar current pulse, a capacitor, means for applying each unipolar current pulse to said capacitor for charging said capacitor to a fixed value responsive to each detection of a waveform, means for discharging said capacitor following the application thereto of each unipolar current pulse, and means responsive to an instantaneous rise in potential greater than a predetermined value across said capacitor simultaneously with the application thereto of a unipolar current pulse for indicating that the time interval which elapsed after the last detected waveform exceeds said minimum time interval.
Claim 2
Dependent Claim
167 words
A monitoring system for determining if the time interval between any two successive waveforms in a series of repetitive waveforms is greater than a minimum time interval comprising means for detecting each of the successive waveforms in said series of repetitive waveforms, said detecting means including frequency discrimination means for making said detecting means insensitive to pre-selected frequency components in said repetitive waveforms, means responsive to each detection of a waveform by said detecting means for producing a unipolar current pulse, a capacitor, means for applying each unipolar current pulse to said capacitor for charging said capacitor to a fixed value responsive to each detection of a waveform, means for discharging said capacitor following the application thereto of each unipolar current pulse, and means responsive to an instantaneous rise in potential greater than a predetermined value across said capacitor simultaneously with the application thereto of a unipolar current pulse for indicating that the time interval which elapsed after the last detected waveform exceeds said minimum time interval.
Claim 3
Dependent Claim
18 words
A monitoring system in accordance with claim 1 wherein said minimum time interval is greater than one-sixtieth second.
Claim 4
Dependent Claim
44 words
A monitoring system in accordance with claim 2 wherein said current pulse applying means includes means for preventing a rise in potential across said capacitor which exceeds said predetermined value responsive to the width of a detected waveform being less than a minimum width.
Claim 5
Dependent Claim
42 words
A monitoring system in accordance with claim 1 wherein said series of waveforms consists of waveforms in an electrocardiographic signal and said minimum time interval is intermediate the normal time intervals between successive natural heartbeats and a time interval of one-sixtieth second.