The machine used was a Nicolet Viking IV or Dantec Keypoint 4 electromyograph. Sensitivity, low-frequency filter, high-frequency filter, sweep speed, duration of pulse, and rate of pulse were not specified.

This study was performed in the supine position.

Following the orthodromic method [1], signals were recorded proximally at the elbow (R), just above the crease of the antecubital fossa and medial to the biceps tendon (Fig. 1). The authors used a pair of 1 cm diameter stainless steel disk electrodes. The reference electrode was proximal. Following the antidromic method [1], sensory nerve action potentials (SNAPs) were recorded to digit II (index finger) using saline-soaked Velcro ring electrodes (Fig. 2). The active recording (A) electrode was placed on the metacarpal joint; the reference (R) was placed distally, around the distal interphalangeal joint. The ground (G) electrode position was not specified (the figure shows the ground electrode placed over the forearm and on the palm, for the orthodromic and antidromic technique, respectively).

Following the orthodromic method, the median nerve was stimulated on the palm (S1), and at the wrist (S2), using the supramaximal nerve stimulation. Following the antidromic method, the median nerve was stimulated at the midpalm, 6 cm proximal to the digit II (S1); at the wrist, 14 cm proximal to the digit II (S2); and at the elbow (S3). Supramaximal responses were obtained.

Onset latency (ms) was measured from the stimulus onset to the onset of the negative peak of the mixed and sensory response. The negative peak amplitude (μV) was determined from the onset to the peak of the negative peak of the mixed and sensory responses. All mixed nerve and sensory responses were averaged five times to clear onset latencies. For the orthodromic method, distances between the stimulating cathode to the active recording electrode at the elbow were measured, and based on the latency differences of the median nerve at the midpalm and wrist stimulation, wrist–palm mixed nerve conduction velocity (W-Pmix CV), wrist–elbow mixed nerve conduction velocity (W-Emix CV), and elbow–palm mixed nerve conduction velocity (E-Pmix CV) were calculated. For the antidromic method, distances from the stimulating cathode to the active electrode placed over the metacarpal joint of the digit II were measured, and based on the latency differences of the median nerve at the palm, wrist, and elbow stimulation, the median sensory wrist–palm conduction velocity (W-Psen), wrist–elbow conduction velocity (W-Esen), and elbow–palm conduction velocity (E-Psen) were calculated. Surface temperature of the hand was measured and maintained at or above 32 °C. Orthodromic and antidromic sensory nerve conduction techniques were performed on 50 control subjects (Tables 1 and 2) and on 30 patients (mean age 48.3 years) affected by carpal tunnel syndrome (CTS) (Tables 3 and 4).