Sensitivity was 20 μV/division, sweep speed was 2 ms/division, duration of pulse was 0.1–0.4 ms, and the machine used was a Tektronix electromyograph. 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 surface electrodes from the median and ulnar nerves separately. For the median nerve (R1), the active recording electrode (A) was placed around the proximal interphalangeal joint of digit II; the reference electrode (R) was placed over the distal interphalangeal joint of digit II (Fig. 1). For the ulnar nerve (R1), the active recording electrode (A) was placed around the proximal interphalangeal joint of digit V; the reference electrode (R) was placed over the distal interphalangeal joint of digit V (Fig. 2). Adjacent digits were kept from inadvertently contacting each other. Ground (G) was placed on the dorsum of the hand, between the recording and stimulating electrodes (the figure shows the ground electrode placed on the palm).

Stimulation with the cathode distal was applied over the median and ulnar nerves at points 7 and 14 cm proximal to the proximal interphalangeal joint of digit II and digit V, respectively. Conduction time for the wrist–digit segment of the nerve was obtained by stimulating at 14 cm (wrist level), while the palm–digit conduction time was obtained by stimulating at 7 cm (midpalmar level). For the median and ulnar nerves, stimulation was applied at the wrist level (S1) and at the midpalmar level (S2). For each nerve, the conduction time for the wrist–palm segment was obtained by subtracting the palm–digit conduction time from the wrist–digit conduction time. The authors used only supramaximal stimulation.

Onset latency (ms) was measured from the stimulus onset to the onset of the negative deflection of the evoked sensory nerve action potential (SNAP); peak latency (ms) was measured from the stimulus onset to the peak of the negative deflection of the SNAP. All latencies for each subject were determined at the same session and at room temperature. The authors studied 30 normal (Table 1) subjects (age range 22–68 years) and 33 patients (Table 2) suspected clinically of having carpal tunnel syndrome (CTS) and normal distal sensory latency (sample data were not given).