Sensitivity was 10 μV/division, sweep speed was 1 ms/division, and the machine used was a Medelec MS3R electromyograph. Low-frequency filter, high-frequency filter, duration of pulse, and rate of pulse were not specified.

This study was performed in the supine position.

Following the orthodromic method [1], sensory nerve action potentials (SNAPs) were recorded to digit III and at the wrist (Figs. 1 and 2). For digit III recordings (digital nerve sensory action potentials), a couple of tinned copper fuse wires were applied to the proximal phalanx of digit III, with the active (A) recording electrode placed near the base of digit III. For the wrist recordings (wrist nerve sensory action potentials), two tinned copper fuse wire electrodes were placed on the median nerve at the wrist, with the active (A) recording electrode placed proximal to the wrist crease. The distal recording and the proximal stimulating electrodes were placed at least 3.5 cm apart, and the distance between the recording electrodes was constant at 1.5 cm. For digit III recordings, ground (G) electrode position was between stimulating and recording electrodes placed to digit III. For the wrist recordings, 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 III (recording to the proximal phalanx of digit III) and stimulated to digit III (recording proximally at the distal wrist crease) using the proximal stimulating and distal recording electrodes which were already in place for the digital nerve sensory action potential recordings. To overcome the problem of a stimulus artifact, a specially designed stimulator with a high degree of isolation from the recording apparatus was developed. The stimulator was battery powered, with a 300-V maximum output.

Peak to peak amplitude (μV) was measured from negative to positive peak. For digital potentials, sensory nerve conduction velocity (SNCV) was calculated to the onset and to the peak latency, and it was measured in meter per second (m/s). For wrist potentials, sensory nerve conduction velocity (m/s) was calculated to the peak latency only, since the onset of the lower amplitude potential was sometimes difficult to define. Careful preparation of the skin was important in reducing the stimulus artifact. The hand was immersed in hot water until the skin temperature over the distal phalanx of the finger to be examined was at or above 35 °C, and the temperature was maintained at this level by radiant heat from a DC lamp. For normal values (Table 1), the authors studied a total of 94 control subjects – age range 20–80 years (75 subjects with digital skin temperature of 35–36 °C, mean age 32.4 years; 19 subjects with a digital skin temperature of 30–32 °C, mean age 34.8 years). Pathological values (Table 2) were obtained from 16 patients with symptoms of carpal tunnel syndrome (CTS), 15 women and 1 man (age range 35–70 years, mean age 55.9 years), and 18 diabetic patients divided into two groups: Group 1, 11 diabetic patients with a temperature at the tip of digit III of 35 °C (age range 30–75 years, mean age 52.4 years), and Group 2, 7 diabetic patients with a temperature at the tip of digit III of 30 °C (age range 37–77 years, mean age 55.0 years).