A Low-Power Combination Electrocardiogram-Respiration Telemetry Transmitter

An FM-FM-modulated radio-telemetry transmitter for detecting and transmitting an electrocardiogram (ECG) and respiration activity simultaneously on a single carrier frequency in the 88-108 MHz band is described. Respiration is detected by the impedance pneumographic principle by using the same pair of electrodes used for the ECG. The circuit requires less than 350 μA from a ± 7 V mercury battery supply and about 185 μA from a 1.35 V mercury battery. Signals can be transmitted over distances up to 50 ft for about 4 weeks without battery replacement and appreciable changes in calibration.