A bi-phase enabled serial acquisition system for remote processing of digitized ECG

This paper presents an approach for acquiring digitized ECG samples in a personal computer using an offline communication technique. For this, two standalone embedded modules are placed at the two ends of the communication link. The transmit end module collects ECG samples from the source and stores them in a RAM. Finally it converts each data byte into a bi-phase encoded bit stream for transmission using a standard telephone set through post office telephone line. The receive-end module, coupled with the telephone receiver decodes the ECG data, and then delivers them to a desktop computer through the serial port. An application software in the computer is used to store these samples for visual inspection. The detailed architecture and test results are discussed with synthetic ECG data available from PTB diagnostic ECG database (ptb-db) under Physionet.

ECG signal acquisition from remote patients for diagnosis and clinical decision making has been one of thrust areas of engineering and scientific research from long time. Several communication media have been used for transmission of patients’ ECG. In such Tele-ECG applications, portability, and programmability of the associated components are most desirable features. From clinical point of view, reliability of ECG data is given utmost importance.In this paper, a technique of remote ECG acquisition in a desktop computer is described which may be useful for providing the healthcare service in rural districts of India. At first, the patient’s ECG is to be acquired in a rural clinic by a portable hardware unit, which is based on a standalone embedded system. The acquisition module consists of a low-offset instrumentation amplifier as the prime signal condition unit, followed by digitization of the signal for storage in an on-board RAM. Then a bi-phase encoding scheme is utilized for offline communication of the stored data through a telephone line using the microcontroller unit (MCU) of the transmit module. The MCU also performs data framing and data packaging for transmission. At the receive end, another portable hardware, based on an embedded system decodes the data from the serial bit-stream received. Each decoded byte is delivered to a desktop computer through serial port for storage and analysis. An application software is used which calibrates the data bytes to original millivolt level samples and these are stored in a two column text file against the corresponding sampling instants. A plot of the ECG is also generated on the front panel of the application software for visual analysis by a physician. The system is tested with satisfactory results using synthetic ECG data from PTB diagnostic ECG database available under Physionet for a short distance of communication.Figure optionsDownload as PowerPoint slideHighlights
► Objective is to develop an offline remote ECG acquisition system using PSTN line.
► ECG samples are acquired by a standalone embedded system before bi-phase encoding.
► Decoding of ECG data at receive end is done by another embedded system.
► Data bytes are serially sent to PC for storage in file, graphical plot generation.
► A GUI is developed to perform operations on the PC using menus and icons.