Two approaches to measure amplitude changes of the sensory nerve action potential over a length of nerve.

Changes in amplitude of sensory nerve action potentials (SNAPs) over a length of nerve have not been used for diagnostic purposes. We measured such changes for median and ulnar nerves in 25 healthy subjects in two ways. The multiple-stimulation method involved three stimulation sites (palm, wrist, elbow) and one recording site on a finger. The multiple-recording method involved stimulation at the wrist and simultaneous recording from two adjacent sites on a finger. Percentile changes in amplitude could be measured in all subjects for the median nerve, but not for the ulnar nerve due to submaximal stimulation in the palm. For the median nerve, the multiple-recording method resulted in a mean amplitude change of 79% +/- 13%, whereas comparison of wrist to palm stimulation in the multiple-stimulus method resulted in a change of 73% +/- 10%. These values are high enough to encourage study into practical applications of such methods in detecting peripheral nerve disease.