Real-time autonomic responses to insulin-induced hypoglycaemia in volunteers with type I diabetes compared to controls.

Objective: Hypoglycaemia is a severe risk of insulin-treatment in diabetes, and in type 1 diabetes (T1D), the normal counterregulatory autonomic mechanisms are diminished. This study investigated the recovery of both parasympathetic and sympathetic tone from hypoglycaemia to normoglycemia in T1D in comparison to controls. Methods: Six individuals with T1D without complications and six age and sex-matched controls were included in this explorative acute intervention study. Electrocardiogram, skin blood flow (SBF, sympathetic measure), cardiac vagal tone (CVT, parasympathetic measure), and plasma glucose were measured at baseline, at hypoglycaemia, and at 30-, 60-, 120-, and 240-minutes post-hypoglycaemia. Results: Insulin injection induced hypoglycaemia with a reduction of CVT in both controls and individuals with T1D, but no consistent response in SBF. Normoglycemia was reached by 120-minutes, though T1D showed delayed glucose recovery at 30- and 60-minutes with an overshoot at 240-minutes. SBF showed no consistent changes but was lower in T1D at 240-minutes. CVT increased consistently, recovering after 60-minutes in the individuals with T1D and 30-minutes in the controls, with a heightened at 240-minutes in the individuals with T1D. Conclusion: CVT as a measure of cardiac parasympathetic function responds consistently to both hypoglycaemia and during recovery in individuals with T1D and controls, but SBF as a measure of cutaneous sympathetic function does not. There are defective counterregulatory mechanisms in T1D shown by delayed recovery of blood glucose and rebound overactivity of both cardiac parasympathetic tone and sympathetic cutaneous vasoconstriction.