Does the conduction velocity distribution change along the nerve?

Nerve conduction velocity distribution (CVD) is a very useful tool to examine the state and function of nerves. Only one record of compound action potential (CAP) may be sufficient to determine the CVD if the shape functions of the single fiber action potentials (SFAP) of fibers are known. Otherwise, CAP recordings from different locations are necessary to determine CVD. In this case, we confront the problem of whether the shape of the CVD changes along the nerve, because many methods that attempt to determine the CVD are based on the assumption that the CVD is invariant along the nerve. There is not a complete solution to this problem, but there are many suggestions allied with the recording conditions to minimise this effect. The other effect that may influence both shapes of CAP and CVD along the nerve is the volume conductor effect. If a suitable model could isolate and eliminate the volume conductor effect, then the spatial variation of CVD may be attributed to the natural conditions of the nerve. In this study, we followed a procedure to eliminate volume conductor effect and then applied our previously published model to examine the spatial variations in CVD. The results show that CVDs estimated at discrete points along the nerve trunk have significantly different patterns. Consequently, it may be concluded that CVD is not uniform along an isolated nerve trunk contrary to the assumptions of the most CVD estimation methods.