Objectives: To study the changes in autonomic nervous function during the 4-year follow-up period in diabetic patients and to investigate factors predicting autonomic nervous dysfunction.
Design: A 4-year follow-up study.
Setting: At baseline the study subjects without known cardiovascular disease were recruited from a large group of diabetic and nondiabetic subjects selected randomly from a baseline population.
Subjects: Middle-aged control subjects (n = 44), patients with insulin-dependent diabetes mellitus (n = 32) and patients with non-insulin-dependent diabetes mellitus (n = 32) were studied at baseline and after the 4-year follow-up.
Interventions: Autonomic nervous function tests and exercise test at baseline and after the 4-year follow-up.
Results: At the baseline, heart rate variation during deep breathing was significantly lower in patients with insulin-dependent diabetes (13.0 +/- 1.2 beats min-1; P < 0.05) and in patients with non-insulin-dependent diabetes (12.9 +/- 1.5 beats min-1; P < 0.05) than in control subjects (16.6 +/- 1.1 beats min-1). At baseline, autonomic nervous function score was significantly higher indicating disturbed autonomic nervous function in patients with insulin-dependent diabetes (1.74 +/- 0.19; P < 0.01) than in control subjects (1.24 +/- 0.14), but the difference was not significant between control subjects and patients with non-insulin-dependent diabetes (1.47 +/- 0.12). During the follow-up, autonomic nervous function score increased in patients with non-insulin-dependent diabetes to 2.00 +/- 0.21 (P < 0.001, as compared to baseline), but did not change in patients with insulin-dependent diabetes (1.77 +/- 0.18) or control subjects (1.22 +/- 0.12). In both diabetic groups, the deterioration of autonomic nervous function score during the 4-year follow-up was associated with poor glycaemic control at baseline. Clinical manifestation of coronary heart disease was found in three (7%) control subjects, 12 (37%; P < 0.001) patients with insulin-dependent diabetes and 11 (34%; P < 0.01) patients with non-insulin-dependent diabetes mellitus at follow-up examination. Autonomic nervous function was more abnormal in those insulin-dependent diabetic patients with coronary heart disease than those without.
Conclusions: During the 4-year follow-up the impairment in autonomic nervous function occurred mainly in patients with noninsulin-dependent diabetes. Poor glycaemic control appears to be an important determinant of the progression of autonomic nervous dysfunction in diabetes.