Sensitivity was 40 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.

Following the orthodromic method [1], signals were recorded on the course of the median nerve (Fig. 1) above the wrist (R1), at the elbow (R2), and in the axilla (R3). For recording at the wrist (R1), 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. For recording at the elbow (R2), the active (A) electrode was placed proximally to the wrist in the antecubital fossa; the reference (R) electrode was placed proximally to the active electrode. For recording in the axilla (R3), electrodes were placed medially on the course of the median nerve, with the active (A) electrode placed proximally to the elbow and the reference (R) electrode placed proximally to the active electrode. The authors also performed orthodromic method to the elbow (R1) and axilla (R2) recording sites stimulating the median nerve at the wrist (Fig. 2). Distances between the recording and stimulating electrodes were not fixed. Bipolar silver electrodes applied to the skin were used for recording. In cases in which the nerve action potentials were extremely small, the author used needle electrodes for recording. In these cases, the needles were inserted through the skin and placed in the vicinity of the median nerve with an interelectrode distance of 3–4 cm. With needle electrodes, the amplitude of the sensory nerve action potential (SNAP) was always greater than that obtained with surface electrodes, but the latency from stimulus to response remained the same. The 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 (S) using surface silver electrodes. The active stimulating electrode (cathode, −) was placed near the metacarpophalangeal joint (at the base of the digit); the anode (+) was positioned distally in the region of the terminal interphalangeal joint. The author used supramaximal electric stimulus as reported by Dawson [2]. SNAPs recorded at the elbow (R2) and in the axilla (R3) were extremely small; however, when the median nerve was stimulated at the wrist, a large potential could be orthodromically recorded at the elbow and in the axilla.

Onset latency (ms) was measured from onset of the stimulus artifact to the junction of the negative inflection potential and the baseline; this was converted to sensory nerve conduction velocity (SNCV) and measured in meter per second (m/s), reflecting the conduction in the largest afferent sensory fibers. Temperature was maintained between 26 and 30 °C. The temperature of the extremities ranged between 33 and 36 °C, surface measurements (34–37 °C, intramuscular measurements). If the extremities were cooler than this, they were warmed with a heating pad during the procedure. Mayer [1] recorded SNAPs at the wrist, at the elbow, and in the axilla in 64 healthy (Table 1) subjects (age range 10–35 years, 30 cases; age range 36–50 years, 16 cases; age range 51–80 years, 18 cases), in 41 patients (Table 2) with diabetes mellitus without clinical evidence of peripheral neuropathy (age range 10–35 years, 14 cases; age range 36–50 years, 19 cases; age range 51–80 years, 8 cases), and in 64 patients (Table 3) with diabetes mellitus with clinical evidence of peripheral neuropathy (age range 10–35 years, 9 cases; age range 36–50 years, 22 cases; age range 51–80 years, 33 cases).