A TERMINAL FOR THE DIGITAL STORAGE AND TRANSMISSION OF ELECTROPHYSIOLOGICAL SIGNALS

Abstract

The population of Saskatchewan is widely but thinly distributed. This creates difficulties in providing specialized health services, such as the interpretation of electro­physiological signals, to the many small remote communities. It is not economically justifiable to situate specialists, such as cardiologists in small communities where the volume of work to be done is small. Aside from this, physicians with advanced skills don't care to reside in small communities. Efforts to train lay readers have so far been strongly opposed by the medical profession. To improve these interpretive services in remote areas, it is therefore proposed to telemeter the electro­physiological signals to a larger center for diagnosis. This thesis describes the nature of and rationale for the construction of an economical device which would enable the transmission of electrophysiological signals over a single voice grade telephone line. The equipment which was constructed digitized three simultaneous channels of 100 HZ bandwidth each. Provision is made for later expansion to four channels. The digitized samples are recorded on an economical digital cassette tape recorder. Characters are inserted prior to recording for error detection and correction. Use·of this intermediate storage enables the playback of the recorded data over the communications channel at any speed less that 1200 baud. The digitized signals can thus be transmitted directly, over relatively narrow band channels such as the direct distance dial (DDD) telephone network. Analog circuitry was constructed to suitably, condition electrocardiographic signals for transmission by this system. However, the device could be used for other data of similar characteristics. The equipment was successfully tested using a computer to perform the necessary decoding and reconversion of the transmitted data to its original form. The total cost of the parts for this system was approximately $3,000.