Magnetic Tape-Recording Electrophysiologic Monitor

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THE clinical use of an instrument that records the electrocardiogram continuously for long intervals1 indicated the desirability of constructing a multichannel monitoring device that displays several physiologic phenomena simultaneously and records them on magnetic tape. The design and construction of a recording and monitoring device for the study of physiologic functions involved the following engineering problems: (1) picking up and amplifying information that is available only at low levels; (2) recording and reproducing low frequencies and slowly varying functions; (3) blanking and electronic switching to permit observation of several functions simultaneously; (4) displaying functions on the screen of a large cathode ray tube; (5) circuitry that creates a minimum of artifacts and rejects externally induced artifacts (such as power-line interference and contact potentials); (6) maximum ease of operation and dependability of the instrument.

This report describes and discusses the multichannel monitoring devices that we have developed and have used for three years.

Figure 1 is a block diagram and Figure 2 is a photograph of the first instrument that was developed. The magnetic tape recorder has four recording heads, four reproducing heads and one erase head. The tape speed is 1⅞ inches per second, permitting more than eight hours of continuous recording. The tape-transport mechanism is mounted as a drawer.

Low-Level Amplification

The electrocardiographic amplifiers were specially designed to operate with minimal voltages and currents on the elements, thus permitting low operating temperatures and consequent minimal deterioration of tubes and other components. Stability is obtained by means of regulated power. . .



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