Physio-control Manufacturing Corporation

Stephen P LaBrash

John R Stice

Dennis R Seguine

A method and apparatus for monitoring an electrocardiograph waveform, and for returning an electrocardiograph trace to the middle of a display, such as a chart recorder strip. The monitoring circuit includes an amplifier and a switch for switching the frequency response curve of the monitoring circuit. In a first position, the switch causes the monitoring circuit to have a slow frequency response curve, which allows for accurate monitoring of ECG waveforms. In a second position, the switch causes the monitoring circuit to have a fast frequency response curve, which allows the amplifier of the monitoring circuit to quickly be brought out of saturation. The amplifier of the monitoring circuit becomes saturated when a defibrillation or pace pulse has been applied to a patient who is being monitored. The switch is controlled by a pulse waveform control signal that is provided by a microprocessor. By varying the duty cycle of the control signal, the frequency response curve of the monitoring circuit can be shifted. By changing the duty cycle of the pulse waveform in incremental steps, certain problems can be avoided, such as erroneous QRS detect marks that are otherwise produced. The incremental steps in which the duty cycle of the pulse waveform is changed may be predetermined, or they may be adjusted according to feedback from the amplifier.

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Seattle, WA, United States of America

Stephen P LaBrash