Sensory threshold measurements for electrical stimulation of the digits

Repeated impedance measurements of electrical stimulation to the finger using the stimulator of an electromyograph were evaluated in seven normal subjects to determine whether reliable threshold values to perception of pain could be obtained. Stimuli were delivered through ring or disc electrodes separated by 3 cm and interfaced to the skin of the digit with EKG paste. Stimulation through these electrodes produced only relative values of threshold, expressed as a potentiometer dial setting. Such values proved to be meaningful only when repeated during a single session. A possible reason for the apparent unreliability of repeated measurements over time is discussed. When a constant current source was substituted, reliable and consistent threshold measurements were obtained. It is suggested that the clinician wishing to make accurate, repeatable and quantified measurements of patient thresholds to electrical stimulation of the finger employ a nonloading source, namely, a constant current or constant voltage stimulator.