Diabetic autonomic neuropathy in children: immediate heart-rate response to standing.

The immediate heart-rate response to standing was used to investigate possible autonomic neuropathy in a group of 38 insulin-dependent diabetic patients in the paediatric age group. The controls and most of the diabetics showed the characteristic response to standing of a rapid increase in heart-rate and a fall to the resting rate within 15 seconds. Some diabetics showed a flat response or a prolonged gradual increase of heart-rate on standing. The usual method of describing the change in heart rate that occurs in response to standing is to compare the R-R intervals at the 30th and 15th beats (30:15 ratio). This is considered less appropriate in children because of the wider variability in heart rate due to sinus arrhythmia. An alternative ratio, the "maximum R-R/minimum R-R ratio" is proposed. This ratio is calculated by dividing the length of the maximum R-R interval (which occurred after the minimum R-R interval during the 30 second recording) by the length of the minimum R-R interval. Compared to 38 index-selected age and sex matched controls, the diabetics showed a significantly lower mean "maximum R-R/minimum R-R ratio (P = 0.033). Six of the diabetics had results lower than the lowest control result. This test gives a prevalence rate of changes suggestive of diabetic autonomic neuropathy of approximately 15% in this age group.