Sensitivity was 10 μV/division, low-frequency filter was 32-Hz, high-frequency filter was 8 kHz, sweep speed was 2 ms/division, and duration of pulse was 0.2 ms. Rate of pulse and the machine used 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 on the first interphalangeal joint of digit III (middle finger), 9 cm from the stimulating cathode (−) at midpalm level (S2) along a line pointing to the midline of the distal wrist crease. The reference electrode (R) was positioned 2 cm distally on the second interphalangeal joint of digit III. Ground (G) 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 subdermal electrodes placed just below the skin (near-nerve technique). At the wrist (S1), the active stimulating electrode (cathode) was placed near the nerve, proximally to the distal wrist crease. The anode electrode (+) was placed at a transverse distance of 4–5 cm at the level of the near-nerve electrode. In the palm (S2), the subdermal electrodes (both active and reference electrodes) were inserted well outside the zone of compression in the carpal tunnel, 1.5–2 cm distally to the distal edge of the flexor retinaculum. The stimulus was gradually increased in a range between 60 and 110 V until the response was a maximum using 0.2 ms of duration of the current pulse.

The shortest latency was determined from the stimulus onset to the initial positive peak and the longest latency from the stimulus onset to the last separate component of the averaged sensory nerve action potential (SNAP). The sensory nerve conduction velocity (SNCV) over the digit–palm segment was calculated by the conventional method. To determine the conduction velocity in the proximal segment, the latency from the digit to palm was subtracted from the latency from the digit to wrist. The peak to peak amplitude of the sensory responses was measured from the negative peak to the positive peak of the SNAP. Skin temperature was recorded at the first phalanx of the third finger, at the midpalm and at the wrist; it was kept constant at 36 ± 1 °C by means of an infrared lamp. For antidromic normal values (Table 1) and orthodromic normal values (Table 2), the authors studied 32 hands from 32 healthy control subjects (age range 21–62 years). Antidromic pathological values (Table 3) were obtained from 56 hands of 50 patients (age range 21–62 years) with a clinical diagnosis of carpal tunnel syndrome (CTS). Orthodromic pathological values (Table 4) were determined in a smaller sample composed of 32 hands of 32 healthy control subjects (age range 21–62 years).