Exercise-induced conduction velocity increment: a marker of impaired peripheral nerve blood flow in diabetic neuropathy

Summary Severe microvascular disease exists at the stage of clinical diabetic neuropathy. A non-invasive test that will identify those diabetic subjects who will eventually develop neuropathy is essential for early intervention. Sural sensory conduction velocity was recorded (x 3) in 12 non-neuropathic diabetic subjects, 15 diabetic subjects with established neuropathy and 16 age-matched normal control subjects, before and after exercise to 80% age/sex predicted maximum heart rate. Fixed sural electrodes were used. Subcutaneous temperature was recorded by a needle thermocouple placed near the sural nerve. Sural sensory conduction velocity increased significantly after exercise in normal subjects (p<0.01, mean increase 5.07 m/s) and non-neuropathic diabetic subjects (p<0.02, mean increase 3.99 m/s) but not in neuropathic subjects (mean increase 0.99 m/s). Subcutaneous temperature rose significantly in normal subjects (p<0.01, mean increase 2.07°C) and non-neuropathic diabetic subjects (p<0.001, mean increase 2.52 °C) but not in neuropathic subjects (mean increase 0.15 °C). However, sural sensory conduction velocity increased by 1.2 m · s^–1. °C^–1 following direct warming of the limb in six neuropathic subjects which was comparable to that of normal and non-neuropathic subjects (1.49 and 1.48 m · s^–1. °C^–1). The impairment of exercise conduction increment in diabetic neuropathy suggests impaired nerve blood flow in diabetic neuropathy.