The effects of selected stimulus waveforms on pulse and phase characteristics at sensory and motor thresholds.

BACKGROUND AND PURPOSE

The purposes of this investigation were to determine 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

Eighteen healthy subjects were stimulated during one session via surface electrodes placed over the forearm and leg.

METHODS

Stimulation amplitude 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-Keuls tests revealed that phase charge varied the least during excitation induced by the five waveforms. Total pulse charge markedly increased when bursts of 10 symmetrical pulses, 25 symmetrical pulses, or amplitude-modulated waveforms were used. Monophasic and symmetrical biphasic waveforms required the least amount of total pulse charge. All measurements were higher during motor threshold than during sensory threshold, and the measurements were higher in the leg than in the forearm.

CONCLUSION AND DISCUSSION

The authors concluded that all five studied waveforms were effective at threshold excitation of peripheral sensory and motor nerves. Of the five waveforms, the symmetrical biphasic waveform, having a low total pulse charge, may be the preferred waveform, and the 25 symmetrical pulses and amplitude-modulated waveforms may be considered the least preferred due to high total pulse charge.