Correlation studies of velocity, amplitude, and duration in median nerves

Nerve conduction velocity is the parameter most often attended to when performing nerve conduction studies, but amplitude and duration of the nerve potentials should also provide important information about the status of the nerve examined. This study compared the results of amplitude and duration measurement to nerve conduction velocity to determine whether or not the various parameters correlated. Using standard techniques, median nerve motor and sensory conduction studies were performed on 390 unselected patients. The results were analyzed and correlation statistics calculated between the parameters of velocity, duration, and amplitude. Amplitude and duration of evoked potential correlated relatively poorly with conduction velocity (r2 = 0.26). Sensory and motor fibers were often affected differently in cases with probable carpal tunnel syndrome (CTS). Proximal motor conduction velocity correlated best with distal evoked potential amplitude (r2 = 0.27) in the CTS cases. The use of residual latency appeared to add little helpful diagnostic information. It was concluded that different parameters measure different physiologic processes that are to a considerable degree independent of each other.