Threshold tracking provides a rapid indication of ischaemic resistance in motor axons of diabetic subjects.

An early abnormality in the peripheral nerves of patients with diabetes mellitus is that it takes a long period of limb ischaemia to block conduction. As a diagnostic test, however, the procedure is time consuming (30 min of ischaemia). We have now used an electronic feedback system to track threshold changes in human motor axons during and after a short period of ischemia (10 min) induced by a pressure cuff. The strength of stimulus current applied over an appropriate nerve was adjusted to maintain a constant amplitude of muscle action potential. This method reveals an increase in excitability during the first few minutes of ischaemia, and a post-ischaemic depression. Both changes in excitability were consistently much reduced in diabetic subjects compared with normal controls.