Conduction of neural impulses in diabetic neuropathy

Objective: To measure the conduction velocity, absolute refractory period and duration of the action potential for individual afferents of the median nerve in diabetic patients and to examine correlations between measures and with temperature and compare this to data from normal subjects. Methods: The technique of percutaneous microneurography was used to record from individual afferents and intradermal electrical stimuli were applied to generate action potentials in distal axons. Results: Like normal afferents, afferents in diabetic subjects demonstrated temperature sensitivity. Durations of the action potential and refractory periods correlated with temperature (r=−0.59 and r=−0.51). Conduction velocities and durations of the action potential did not differ between diabetic (means of 34 m/s and 0.42 ms) and normal (means of 34 m/s and 0.45 ms) subjects. However, refractory periods were significantly shorter in diabetic (mean 1.3 ms) than in normal (mean 1.8 ms) nerves and the normal correlation between conduction velocity and refractory period was disrupted. Conclusions: The results reveal disturbances of the axonal recovery process in diabetic patients, possibly due to membrane potential fluctuations after the generation of an action potential. Uncovering specific excitability changes in diabetic nerve facilitates the design of pharmacological interventions for restoring nerve function.