The machine used was a TECA TE-4. 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 using surface electrodes at the wrist from the median nerve (R1) by stimulation of digit II (S1) and stimulation of the palmar branches (S2) of the median nerve (Fig. 1). Signals from the ulnar nerve were recorded at the wrist (R1) by stimulation of digit V (Fig. 2). For the median nerve (R1), electrodes were placed between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL) muscles (ideally proximal to the distal wrist crease). From the cathode stimulating points (−), the proximal distance of 14 cm for the digit II–wrist and 8 cm for the palm–wrist was premeasured and marked over the median nerve as appropriate. These points were the sites for fixing the bar-type recording surface active electrode (A), with the reference (R) placed more proximally along the nerve. For the ulnar nerve (R2), electrodes were placed just lateral to the tendon of the flexor carpi ulnaris (FCU) muscle, ideally proximal to the distal wrist crease. From the cathode stimulating points (−), the proximal distance of 14 cm for the digit V–wrist was premeasured and marked over the ulnar nerve as appropriate. These points were the sites for fixing the bar-type recording surface active electrode (A), with the reference (R) placed more proximally along the nerve. The electrodes for the median and ulnar recordings at the wrist were placed at the identical distance (14 cm) from stimulating sites for the median and ulnar nerves at digit level (S1). Ground (G) electrode position was not specified in the report; the figure shows the ground electrode placed on the palm. The median and ulnar nerve recordings were made separately.

Stimulations were applied to the median and ulnar nerves separately. The median nerve was first stimulated at digit II (S1) using ring electrodes; then it was stimulated on the palm (S2) using a handheld bipolar stimulator. For digit II stimulation (S1), the stimulating ring electrode (−) was placed around the proximal interphalangeal point of digit II (index finger); the ring anode (+) was placed 3 cm distally; for palm stimulation (S2), the cathode electrode (−) was placed between the 2nd and 3rd metacarpal interspace at a point where the thenar crease intersected a horizontal line drawn across to the base of the thumb webspace. The ulnar nerve was stimulated at digit V (S1) using ring electrodes. For digit V stimulation (S1), the stimulating ring electrode (−) was placed around the proximal interphalangeal point of digit V (little finger); the ring anode (+) was placed 3 cm distally.

Peak latency (ms) was measured from the stimulus artifact to the peak of the negative deflection of the evoked sensory nerve action potential (SNAP) to the nearest 0.05 ms. Negative peak amplitude (μV) was measured from the baseline to the peak of the negative deflection of the SNAP, to the nearest microvolt. All tests were done in a room temperature of 23 °C. When the hands were clinically warm, nerve conduction studies were performed bilaterally in all control subjects and bilaterally in patients with symptoms on both sides. Interelectrode distances were measured with a flexible steel tape. For normal values (Table 1) the authors studied 22 healthy subjects (11 men and 11 women, average age 39.2 years, age range 25–69 years), and 36 hands from 22 patients (mean age 41.7 years, age range 26–70 years) with a history suggestive of carpal tunnel syndrome (CTS) were also studied (Table 2).