Relationship between impaired parasympathetic and sympathetic cardiovascular control in diabetes mellitus

We have investigated the relationship between vagal and sympathetic lesions in 62 diabetic patients and compared the results with those from 37 healthy subjects. Vagal function was assessed by heart rate changes with forced breathing. Sympathetic control was measured by the heart rate and blood pressure changes after standing and the concomitant plasma catecholamine response. The integrity of the postganglionic sympathetic neuron was evaluated separately by testing sudomotor function. Impaired sympathetic control was found only in 15 diabetic patients with severely impaired or absent vagal heart rate control. In 12 patients the chief abnormalities consisted of a delayed and diminished heart rate increase, an excessive fall in systolic blood pressure (greater than 20 mmHg) in combination with an abnormally small noradrenaline increment (less than 120 ng/l) and a lesion of the postganglionic sympathetic neuron. Three patients with severely impaired parasympathetic heart rate control in combination with an intact postganglionic sympathetic neuron demonstrated a large noradrenaline increase on standing (greater than 700 ng/l). Measurement of vagal heart rate control and testing of sudomotor function makes it possible to classify a spectrum of abnormal cardiovascular responses to standing in diabetic patients.