THE EFFECTS OF SELECTED STIMULUS WAVE-FORMS ON PULSE AND PHASE CHARACTERISTICS AT SENSORY AND MOTOR THRESHOLDS

Background and Purpose. The purposes of this investigation were to det ermine the effect of five commonly used voltage waveforms (four pulsed and one sinusoidal) on excitation of sensory and motor nerves and to characterize variables associated with reaching threshold. Subjects. E ighteen healthy subjects were stimulated during one session via surfac e electrodes placed over the forearm and leg. Methods. Stimulation amp litude was increased at a constant rate, and the threshold of sensory and motor excitation was determined. Measured variables included peak voltage, peak current, phase charge, and total pulse charge. Results. Three-factorial, repeated-measures analysis of variance and Newman-Keu ls tests revealed that phase charge varied the least during excitation induced by the five waveforms. Total pulse charge markedly increased when burst of 10 symmetrical pulses, 25 symmetrical pulses, or amplitu de-modulated waveforms were used. Monobasic and symmetrical biphasic w aveforms required the least amount of total pulse charge. All measurem ents were higher during motor threshold than during sensory threshold, and the measurements were higher in the leg than in the forearm. Conc lusion and Discussion. The authors concluded that all five studied wav eforms were effective at threshold excitation of peripheral sensory an d motor nerves. Of the five waveforms, the symmetrical biphasic wavefo rm, having a low total pulse charge, may be the preferred waveform, an d the 25 symmetrical pulses and amplitude-modulated waveforms may be c onsidered the least preferred due to high total pulse charge.