The history of the development of electromyography. Part I: 1925-1945
Edward J. FINE, Peiyun CHU, and Linda A. LOHR
The authors recount the development of the first electromyography equipment during 1925-1945. The first electromyography (EMG) machines were built by their users to substantiate Sherrington’s concept of the motor unit by recording action potentials from muscles and to estimate the velocity of conduction in nerves. Innovative devices overcame the technological limits of string galvanometers used previously to record bioelectrical potentials. In 1920 Forbes and Thacher developed the vacuum tube amplifier to detect millivolt intensity discharges. The duration of the nerve and muscle action potentials, lasting only 3-15 ms, required nearly instantaneous display that could not be recorded by the slower moving mirror galvanometers. Gasser and Erlanger refined the cathode ray tube pioneered by Braun in the 1890s, into an oscilloscope that could display rapidly changing compound nerve discharges. The waves were preserved by photography for analysis. In 1929 Bronk and Adrian developed the concentric bipolar electrode to record potentials from single muscle fibers. Bronk in 1929 added a loud speaker to his EMG apparatus to “hear potentials” that “he could not see.” Matthews’ invention of the differential amplifier minimized electrical interference and allowed recording of microvolt potentials directly from sensory nerves. By 1941, physiologists such as Birdsey Renshaw bought EMG machines custom manufactured to meet their specific research needs by companies such as Grass Instrument Company, instead of making their own equipment from components. We will show examples of recordings made by these machines.
Denny-Brown and Pennybacker employed an EMG machine with differential amplifier and oscilloscope to distinguish fibrillations from fasciculations in 1938. In 1945 EMG was first employed to determine the functional integrity of nerves injured by war wounds. Electromyography became a tool for diagnosis after technical problems of amplification, display and permanent recording were solved.
Tenth Annual Meeting of the International Society for the
History of the Neurosciences (ISHN) and
St. Andrews, Scotland, 2005