Sensitivity was 20 μV/div (digit–wrist) and 50 μV/div (palm–wrist), low-frequency filter was 2 Hz, high-frequency filter was 10 kHz, duration of pulse was 0.1 ms, and rate of pulse was approximately 1/s. Sweep speed and the machine used 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 (R) from the median nerve by distal stimulation (digit II and digit III) and stimulation on the palm. 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 (−), proximal distance of 14 cm for digit II–wrist and digit III–wrist recordings (Figs. 1 and 2) and a fixed distance of 8 cm for the palm–wrist recording (Fig. 3) were premeasured and marked over the median nerve proximally to the wrist crease as appropriate. These points were the sites for the recording surface disk electrodes embedded in Bakelite (interelectrode distance 3 cm), the active (A) electrode was placed distally, and the reference (R) electrode was placed proximally along the nerve. Digit–wrist and palm–wrist recordings were made separately. For the palm–wrist recording, the active recording (A) electrode was placed proximal to the wrist crease and the reference electrode (R) was placed over the dorsum of the hand. The figure shows the reference electrode (R) placed 3 cm proximally to the active electrode (A) proximal to the wrist crease.

Stimulations were applied to the median nerve distally to digit II and to digit III and to the palm. Stimulations were applied to digit II and to digit III (S) using ring electrodes placed on the proximal (−) interphalangeal joint of digit II (index finger) and of digit III (middle finger) and on the distal (+) interphalangeal joint of the same digits. The authors used anatomical landmarks for the ring electrode placement; no fixed interelectrode distance was used for the distal stimulation to digit II and to digit III. For the palm stimulation (S), the author specified that the fibers of the median nerve supplying sensory receptors in digit II (index finger) and in digit III (middle finger) were stimulated as they crossed the palm at 8 cm from the recording electrode (A) placed at the wrist. The authors did not specify if surface disk electrodes (the same used for wrist recordings) or a handheld bipolar stimulator was used for palm stimulation.

Onset latency (ms) was measured from the onset of the stimulus to the onset of the negative deflection of the evoked sensory nerve action potential (SNAP); peak latency (ms) was measured from the onset of the stimulus to the negative peak of the wave. The negative peak amplitude (μV) was measured from the stimulus artifact to the peak of negative deflection of the sensory nerve action potential (SNAP); peak to peak amplitude was measured from negative to positive deflection of the wave. Durations (ms) were recorded from the onset of the negative deflection to its return to the baseline and from the onset of the negative wave to the positive peak. The orthodromic conduction from finger to palm (6 cm) was calculated by deducting the value obtained in the transcarpal nerve conduction from the 14 cm distance latency from finger to wrist (digit II–wrist and digit III–wrist). Temperatures were monitored at the point of stimulation and at the point of recording. All tests were performed with stable temperatures ranging from 31 to 33 °C (the majority were 32 °C), when necessary the limb was warmed with an infrared lamp. Normal values (Tables 1, 2, and 3) were obtained from 30 median nerves of 30 healthy subjects (age range 22–58 years, mean age 37.8 years). The side to side latency difference was analyzed from 15 subjects who were tested bilaterally.