Autonomic and electrophysiological studies in patients with signs or symptoms of diabetic neuropathy.

Thirty-five patients with symptoms or signs of diabetic neuropathy were tested for autonomic neuropathy by measuring heart rate and blood pressure changes during an orthostatic tilt test, a single deep breath and the Valsalva manoeuvre and these results were related to electrophysiological measurements made on the common peroneal and sural nerves. The sural sensory action potential (SAP) was more strongly correlated with these tests of autonomic function (particularly with the brake index of the orthostatic tilt test (P less than 0.001) and the fall in systolic blood pressure 1 min after tilt (P less than 0.001], than the common peroneal nerve compound motor action potential, its minimum F wave latency or nerve conduction velocities. Patients with a detectable sural SAP had significantly higher brake indices than those with absent sural SAPs. Significant correlations were also obtained with the common peroneal motor nerve conduction velocity (MNCV) and autonomic tests and patients with MNCV less than and greater than 38 m/sec showed significant differences in many autonomic tests. The sural SAP amplitude, being less susceptible to factors that influence nerve conduction velocity, may be useful in identifying patients with an autonomic neuropathy.