Design of an inexpensive take-home recorder for cardiac monitoring.

Circuitry utilizing integrated circuits has been designed as peripheral equipment to a cassette recorder for inexpensive take-home cardiac monitoring. The circuitry is for frequency modulation for recording and demodulation upon playback of three synchronous multiplexed analog signals: the ECG signal, a reference signal which after demodulation is subtracted from the ECG signal to compensate for variable tape speed, and an episode signal actuated by the patient during ECG recording to indicate a particularly noticeable episode. The original goals were to keep the total component cost under $100.00, to produce clinically acceptable ECG tracings, and to design the components such that they could be used with most common battery powered cassette recording systems. The components, excluding the cassette recorder, can be purchased for less than $60.00. An expensive item is the cassette recorder which has considerable variations in price ($40.00 - $100.00). The circuitry described in this thesis has been designed to work with the Concord Model F-26 cassette recorder and other cassette recorders of similar quality. The quality (signal to noise ratio) of the ECG reproduction, although acceptable, could probably have been improved were in not for the degradation of the phase lock loop FM demodulator with an input of multiplexed signal, which reduced the lock range; and therefore required a reduction of the gain of the ECG amplifier. The design goal of the project was achieved since the recorder and components can be purchased for less than $100.00 (in single quantities) and the system provided acceptable ECG's for clinical use. The knowledge and experience gained for this thesis project has been of considerable value. Hopefully this work will lead to further experiments, improvements, and other applications of physiological monitoring with an inexpensive cassette recording system.