Autonomic function in children with type 1 diabetes mellitus.

We investigated autonomic function in 58 children and young adults with Type 1 diabetes mellitus (aged 7-22 years, duration from 3 to 18, 8.6 +/- 3.4 years) and in 74 healthy controls (6-21 years) using power spectral analysis of blood pressure and heart rate in addition to conventional standard autonomic function tests: deep breathing, the Valsalva manoeuvre, and a standing test. None of the diabetic patients were symptomatic. Reproducibility of the tests was assessed by determining the coefficient of variation in 9 controls (7.8-37.7%). Thirteen per cent of the subjects had difficulty in adequately performing the Valsalva manoeuvre. After adjustment for age, sex, body mass index, and respiratory frequency, results of the Valsalva manoeuvre and deep breathing were not different between patients and controls and there was no significant postural reduction in systolic blood pressure (> or = 20 mmHg) in the patients. Heart rate variation in the supine position during natural breathing was low in patients, although power spectral analysis of heart rate variation did not show a significant decrease in the power density in the high and the low frequency in patients compared to healthy controls. Beat-to-beat blood pressure fluctuation was significantly lower in patients and correlated with metabolic control (mean annual haemoglobin A1c), but not with disease duration and was abnormal in 7 diabetic children (12%). In contrast, tests of vagal activity were not impaired in the patients in this age range. We concluded that vagal involvement in Type 1 diabetic patients determined by spectral analysis of R-R intervals in addition to conventional tests is uncommon, but that beat-to-beat blood pressure variation was more likely to be affected.