Sensitivity was 20 μV/division, sweep speed was 1 ms/division. Low frequency filter, high-frequency filter, duration of pulse, rate of pulse, and the machine used were not specified.

This study was performed in the supine position, with the subject lying on a couch and covered with blankets.

Following the orthodromic method, signals were recorded at the wrist and just above the elbow and on the course of the median nerve [1]. For recording at the wrist (R), the active (A) electrode was placed proximally to the distal crease at the wrist; the reference (R) electrode was placed 3 cm proximally to the active electrode (Fig. 1). For recording at the elbow (R), the active (A) electrode was placed proximally to the wrist; the reference (R) electrode was placed proximally to the active electrode (Fig. 2). Distances between recording and stimulating electrodes were not fixed; the authors mapped out the course of the median nerve, before applying the recording electrodes, by stimulation and observation of the motor response. In a few patients, the course of the nerve could not be determined in this way; in such a case, recording electrodes were placed over the expected position of the nerve trunk and adjusted to give the largest response to sensory stimulation. Ground (G) electrode position was not specified in the report; the figure shows the ground electrode placed on the palm.

The median nerve was stimulated distally to digit II (recording at the wrist) and proximally at the wrist (recording just above the elbow). For stimulation to digit II (S), the authors used silver strips (2–4 mm wide) covered by lint moistened in saline and firmly wrapped around the finger for stimulating the sensory fibers of the median nerve. The active stimulating electrode (cathode, −) was placed near the metacarpophalangeal joint (at the base of the digit, proximal to the recording site); the anode (+) was positioned distally in the region of the terminal interphalangeal joint (distal to the recording site). For stimulation at the wrist (S), the same electrodes used for the stimulation to digit II were used, firmly wrapped on the skin at the wrist level. Supramaximal stimulation was mainly used, a few subjects were unable to tolerate the repetitive stimuli required to obtain superimposed records, and in such cases, single sweeps were photographed.

Distal peak latency (ms) was measured from the stimulus artifact to the peak of the negative deflection of the evoked sensory nerve action potential (SNAP). Peak amplitude (μV) was measured from negative to positive peak. All tests were carried out in a warm room with the subject lying on a couch and covered with blankets. Before examining people with cold hands, the arms were immersed in hot water for 5 or 10 min before the session, but no other method of controlling temperature was attempted. The authors [1] studied 28 normal median nerves (Table 1) in 29 patients with suspected carpal tunnel syndrome (CTS) (Table 2), referred by members of the hospital staff for routine electrodiagnosis. Values from stimulation of the wrist and recording at the elbow were not reported.