Non-linear effects of age on nerve conduction in adults.

The effects of age on conduction and amplitude in median and ulnar (motor and sensory), superficial radial, sural and common peroneal (motor) nerves of adults were prospectively investigated. Four routinely recorded parameters, including conduction velocity, amplitude and duration, were considered for each sensory nerve and measurements of conduction velocity, terminal motor latency and amplitude were made for each motor nerve. The resulting 25 sets of data were analysed using both linear and quadratic regression. The three sets of terminal motor latency data showed no age dependence while in six other instances there was a linear relationship with age (three of these being motor amplitude). The remaining 16 sets of data were statistically best represented by quadratic analysis. The shapes of the paraboli were remarkably similar, reaching a maximum (conduction velocity and amplitude) or minimum (duration) value in the fourth decade and thereafter declining or rising respectively at an accelerating rate. With only one exception, quadratic curves of the same parameter were shown to be parallel. Tables of normal data which make accurate adjustments for the aging effect can be constructed from this analysis for use in routine clinical investigation.