Digital transmission of 12-lead electrocardiograms and duplex speech in the telephone bandwidth

A system was developed which allowed the simultaneous communication of digitized, full duplex speech and electrocardiography (ECG) signals in realtime. A single band-limited channel was used over a standard telephone line providing 3 kHz bandwidth. The full duplex speech was compressed to 2400 bit/s using linear predictive coding, while multiple ECG signals were processed by a novel ECG compression technique. Extensive use of digital signal processing reduced the combined bit rate to less than 9600 bit/s, allowing the use of low-cost commercial modems. The ECG communications system was tested in clinical trials. It enabled a hospital-based clinician to provide diagnostic and treatment advice to a remote location over the standard telephone network.