The use of underwater acoustic biotelemetry for monitoring the ECG of a swimming patient

Biotelemetry is a special branch of bio-instrumentation which provides a means of transmitting physiological and biological information from one site to another. There are several cardiological conditions in which it is desirable to monitor critical reflexes and responses from a free-swimming patient and this paper describes the transmission through water of an acoustic signals representing the electrocardiogram (ECG), together with their reception and display. The system has a modular design that can be adapted for the transmission of any parameter, such as heart rate, respiration rate or skin temperature, or any three parameters multiplexed together. The transmission involves the following processes, the amplitude of each ECG pulse is sampled to 8-bit resolution, the least significantly bit is discarded to compress the data, then the sample is transmitted by pulse code modulation (PCM). A microcontroller in both the transmitter and receiver allows the ECG data to be sampled, coded, transmitted, received and finally decoded onto its original analogue form. The system has been tested successfully on a swimming pool where multipath reverberation was a severe problem.