ORIGINAL PAPER NORMAL VARIATION OF NERVE CONDUCTION IN THREE PERIPHERAL NERVES

IN recent years applied physiology has begun to play an important part in medical diagnosis. The object of this paper is to provide some base-line normal values for nerve conduction in three peripheral nerves—the ulnar, median, and lateral popliteal nerves—as these nerves are frequently the subject of conduc-tion tests. It has been well described by Weiss (1956) that when a nerve is constricted there is generalized thinning of the axon distal to the point of constriction. Conduction velocity in nerve is proportional to the calibre of the axon (Hodes et ah, 1948), and this proportionality is valid also for nerves after injury (Hursh, 1939). It therefore follows that, as the calibre of the axon decreases, so also does conduction velocity. Now that more modern techniques have been developed and concentric needle electrodes are standard equipment it is felt that a series of normal subjects should be examined, their conduction velocities and latencies recorded, and the artifacts encountered discussed. In previously published series skin electrodes (Hodes et ah, 1948; Norrise/a/., 1953) and coaxial needle electrodes (Thomas et ah, 1959) have been used to pick up the action potential from the activated muscles. MATERIALS AND METHODS Conduction velocity was measured in thirty medical and physiotherapy students on three nerves—the median, ulnar, and lateral popliteal. The equip-ment used was the standard electromyograph at St. Thomas's Hospital, London, designed and developed in the electronic section. A bipolar electrode consisting of two saline-soaked tufts 1 cm. in diameter and 2 cm. apart was supplied from a balanced constant-voltage stimulator delivering a rectangular pulse of 0-1 millisecond duration percutaneously. A concentric needle electrode was used to pick up the action potential from the muscle under study, and this was photographed synchronously from the cathode-ray oscilloscope on the electro-myograph. To decrease skin resistance and current distortion at the source of stimula-tion the skin over the nerve under study was prepared with an abrasive paste consisting of pumice suspended in glycerin. This partially removed the stratum corneum of the epidermis, which layer offers the highest impedance to th