Simple and novel method for measuring conduction velocity of A delta fibers in humans

We report a simple new method for measuring the conduction velocity (CV) of A delta fibers in normal subjects. A large positive component of somatosensory evoked potential (SEP) whose peak latency was approximately 250 ms was clearly recorded only when strong electrical stimulation causing a definite painful feeling was applied to the skin. The CV of the peripheral nerve was calculated by measuring the latency difference of this component between the distal-stimulated SEP and proximal-stimulated SEP and the distance between two stimulus sites. The CV was approximately 11.4 m/s, (range 8.8-15.9 m/s), in the range of A delta fibers. The sleep effect on pain-related SEP was also observed in 3 subjects. The amplitude of pain-related SEP decreased with the progress of sleep stage. This simple and novel method is available in most clinics and should be very useful in investigating the physiologic functions of peripheral nerves in patients as well as normal subjects.