Local and long distance transmission and storage of electrocardiograms and other low frequency signals.

WE HAVE previously reported the successful transmission of electrocardiograms over telephone facilities using frequency modulation. Before seriously considering the possibility of transmitting electrocardiograms as a service it was necessary to determine whether or not acceptable transmissions could be uniformly obtained over message channels as they exist in the long distance telephone service. Since the telephone plant is designed and maintained primarily for the intelligible transmission of speech, it did not necessarily follow that electrocardiographic signals could be transmitted without distortion over all message channels. Such a study, which provided critical tests of the method used, was, of course, far beyond the scope and facilities of the Cardiovascular Service alone.*