Usefulness of cardiovascular tests of autonomic function in asymptomatic diabetic patients.

A group of five cardiovascular tests of autonomic neural function was studied in 115 asymptomatic insulin-dependent diabetic patients and nine patients with symptoms of diabetic autonomic neuropathy. In the asymptomatic group, 34 patients had one or more abnormal test. R-R variation during deep breathing was most frequently abnormal, but reliance on this test alone to examine parasympathetic function would have missed 12 of the 34 abnormal patients. The two abnormal responses to isometric exercise in this group were probably false-positive results caused by poor patient effort. In the symptomatic patients, R-R variation during deep breathing was abnormal in all nine, the blood pressure response to standing was abnormal in seven, and the response to isometric exercise was abnormal in three. The blood pressure response to isometric exercise is uncomfortable, requires special equipment, and should probably be confined to the assessment of symptomatic patients in a specialist setting.