Sensory and Motor Nerve Conduction in the Median Nerve in Normal Subjects

Abstract

The normal nerve conduction in sensory and motor fibres of the median nerve has been studied in 20 females and 28 males, 16-62 years of age. There was no significant sex difference in conduction velocity. The intraindividual variation in repeated measurements was 0.9-1.8 m/sec. The conduction velocity decreased with age in all segments, and the interindividual variation was 3.4 to 4.5 mjsec (S,,*). Sensory fibres conducted faster than motor fibres of the same segment, but the difference became gradually eliminated with age. The sensory conduction velocity in the proximal segment (wrist-elbow) decreased more rapidly with age than in the distal segment (digit-wrist). Fast and more slowly conducting fibres were almost equally affected by age, resulting in an increase in the temporal dispersion of the sensory action potential. The amplitude of the sensory potential (log,,, pV) was a function of the temporal dicipersion and of the distance of the near nerve electrode from the nerve. With these corrections the amplitude was independent of age, i.e. there was no evidence of a reduction in the number of fibres. The sensory threshold to electrical stimuli increased with age and-independent of age-with the slowing of the sensory conduction velocity between wrist and elbow.During the past 20 years the determination of sensory and motor conduction velocity has obtained a prominent position in the study of the peripheral nerve function. When measuring the conduction velocity with a standard technique and procedure, age is probably the most important source of variation in normal subjects. Motor and sensory fibres, however, do not seem to be affected in parallel. Thus data presented by La Fratta and Canestrari (17) indicate that the conduction in mixed nerves becomes relatively more slowed by age than in motor fibres. This is consistent with findings by Buchthal and Rosenfalck (3), who examined purely sensory and motor fibres. They showed that sensory nerve conduction was faster than motor in young per-sons, while in old persons (70-88 years) this relationship was in fact reversed. Other electrophysiological parameters change with age, e.g. a significant decrease in the amplitude of the sensory nerve action potential has been demonstrated (3, 15). The present study, however, shows that this was solely due to an increase in the temporal dispersion of the action potential.This study was designed to derive clinically applicable limits of the normal inter-and intraindividual variation of sensory and motor conduction parameters, considering the effect of age and the interaction between the recorded parameters. The relative slowing of conduction in sengory and motor fibres and in distal and proximal segments was analysed. MATERIAL AND METHODSThe material comprised 20 females and 28 males, 16 to 62 years of age. The age distribution was the same in the two sexes. Clinical sym'ptoms or signs of peripheral nerve dysfunction were absent and there was no evidence of diseases known to predispose to peripheral neuropathy. Four persons were...

Reply to “Conduction studies on the sural nerve”

“…Regarding using small amplitudes in a clinical setting, it is important to recognize that sensory potentials are log-normal distributed, recorded with needle ( Nielsen, 1973 ) as well as with surface electrodes ( Andersen, 1985 ) and as such correlated with age and height, which provided more exact reference values.…”