The use of the H reflex in serial evaluation of nerve conduction velocity.

Conduction velocity (CV) in the H pathway, expressed by a mixed (sensorimotor) index (HCV), showed a very reduced intra-individual variability when compared to conventional conduction parameters in normal subjects. HCV, tested serially over increasing intervals of time, was about 4 times more stable than motor CV in deep peroneal nerve and about 6 times more stable than the sensory CV in sural nerve. The HCV was so accurate in showing marginal conduction changes that it clearly revealed, in normal persons, a circadian rhythm of conduction velocity, well correlated with circadian variations of body temperature, which totally escaped conventional conduction parameters. owing to its reduced variability, this conduction parameter represents, within the limits in which it can be reliably used in clinical application, a first choice tool for longitudinal conduction studies.