Sensitivity was 10 μV/division, low-frequency filter was 20 Hz, high-frequency filter was 5 kHz, sweep speed was 1 ms/division, and the machine used was a Dantec Counterpoint. Duration of pulse and rate of pulse were not specified.

This study was performed in the supine position.

Following the antidromic method [1], signals were recorded from digit II (index finger) using ring electrodes. The active electrode (A) was placed around the base of digit II; the reference (R) was placed 4 cm distally, on the same finger (Fig. 1). Ground (G) electrode was placed on the dorsum of the hand (the authors used 3 cm disk electrode). The figure shows the ground electrode positioned on the palm.

The median nerve was stimulated using the surface electrodes at two points along its course: at the wrist (S1) and on the palm (S2). At the wrist (S1), shocks were applied proximal to the distal wrist crease, at distance of 13 cm from the active ring electrode (A). The anode was proximal. The terminal portion of the median nerve was stimulated on the palm (S2) at a distance of 6.5 cm from the active ring electrode (A), along a line connecting the wrist and the webspace between digit II (index) and digit III (middle finger). If the palmar stimulation resulted in a baseline distortion due to the shock artifact, the anode was repositioned in order to obtain a suitable baseline. The anode was proximal. The palmar sensory study was performed with minimal technical problems, requiring on average an additional 5 minutes to perform. In the paper, the authors performed also a motor conduction study to the abductor pollicis brevis (APB) muscle stimulating the median nerve at the wrist and on the palm (see motor conduction studies).

Negative peak amplitude (mV) was determined from the baseline to the negative peak of the SNAP. Authors calculated the mean palm–wrist SNAP amplitude ratio. Identical sensitivity (2 μV/division) was used for measuring both distal and proximal latency to the carpal tunnel. Hands were maintained at 32–35 °C during testing utilizing a thermistor-controlled Dantec infrared heater with the sensor placed in the midpalm. Normal values (Table 1) were obtained from 30 control hands of 20 healthy adult volunteers (12 men and 8 women, age range 22–50 years, average age 36 years), and pathological values were recorded from 59 consecutive hands of 45 patients (12 men and 33 women, age range 27–79 years, average age 52 years) with carpal tunnel syndrome (CTS).