Discrimination between cardiac para- and sympathetic damage in diabetics

To analyze the autonomic mechanism on heart rate (HR) variations, pharmacological studies were performed on 8 healthy subjects and 6 diabetic patients. Three HR variations--in supine resting position, during deep breathing in supine position (respiratory HR variations), and on standing (orthostatic tachycardia; delta HR)--were examined. The results in healthy subjects and diabetics were similar. After administration of parasympathetic blockade with atropine, respiratory HR variations were almost abolished. However, no significant difference in delta HR was found. With the addition of beta-adrenergic blockade with propranolol, delta HR was remarkably reduced. Propranolol alone did not affect the respiratory HR variations, but after propranolol administration delta HR was significantly reduced compared with that of the control. The present studies show that respiratory HR variations are predominantly mediated by parasympathicus, whereas orthostatic tachycardia is mediated by both sympathicus and parasympathicus, particularly by sumpathicus. This result suggests the possibility of discriminating the impairment of the 2 cardiac autonomic nervous systems by these simple and non-invasive tests.