Autonomic nervous system control of heart rate in essential hypertension.

In order to evaluate the role of the autonomic nervous system in controlling heart rate (HR) in essential hypertensive patients (EH), we studied 13 untreated EH, WHO I-II, aged 21-68 years, and 10 normotensive subjects (N), aged 20-68 years. The average variation of heart period (VHP) during regular breathing was used as an index of parasympathetic control of HR. Measurements were carried out supine and during tilting, before and after propranolol (0.15 mg/kg intravenously). A sympathetic control index of HR was derived from the ratio HR before/HR after propranolol. A parasympathetic control index of HR was also obtained from the ratio HR before/HR after atropine (0.03 mg/kg intravenously). The VHP was constantly lower in EH than N (P < 0.001) before and after propranolol, supine and standing. The parasympathetic control index of HR was significantly higher in EH (P < 0.001). A significant negative correlation was found between VHP and the parasympathetic control index (r = -0.73) plotting together all values found in EH and N. The sympathetic control index of HR did not differ between EH and N. These results indicate a lower parasympathetic influence on HR in this group of EH compared with N, while sympathetic control was similar in the two groups. This difference in vagal control of HR persists in the presence of increased sympathetic activity (tilting) and after beta-blockade.