Sensitivity was 20 μV/division, sweep speed was 1 ms/division, duration of pulse was 0.05 ms, and the machine used was a TECA TE-4. Low-frequency filter, high-frequency filter, and rate of pulse were not specified.

This study was performed in the supine position.

Following the antidromic method [1], signals were recorded using ring electrodes at digit III (Fig. 1). The active recording electrode (A) was placed at the base of digit III (middle finger), 14 cm from the stimulating cathode (−) at the wrist (S1) and 7 cm from the midpalm level (S2) along a line pointing to the midline of the distal wrist crease. The reference electrode (R) was positioned 4 cm distally on the second interphalangeal joint of digit III. Ground (G) electrode was placed on the dorsum of the hand (the figure shows the ground electrode placed on the palm).

Stimulation was applied separately at two points: at the wrist (S1) and in the palm (S2) with a monopolar pin. At the wrist (S1), the cathode (−) was placed over the median nerve (proximally to the distal wrist crease), 14 cm from the recording ring electrode or near the base of digit III. The anode electrode (+) was placed proximally. In the palm (S2), the cathode (−) was placed 7 cm from the recording ring electrode or near the base of digit III, along a line from the recording site (R) and stimulation site (S1) at the wrist. The anode electrode (+) was placed proximally. Supramaximal stimulation was used at the wrist and in the palm with a duration of the pulse of 0.05 ms. In stimulating the nerve, the authors used the monopolar pin as it has the advantage of delivering a supramaximal stimulation with much less current than is required with surface electrodes because the pin electrode bypasses the high impedance of the skin and decreases the chance of stimulation spread to adjacent nerves [2].

Peak latency (ms) was measured from the stimulus onset to the negative peak of the SAP. Negative peak amplitude (μV) was measured from the baseline to the negative peak. Surface measurements were made using a tape measure over the skin. Midpalm skin temperatures, measured with a surface thermistor in all subjects, were more than 31 °C. The authors studied 100 hands (Table 1) from 50 healthy control subjects (28 women, 22 men, age range 20–68 years).