Effects of Age and Hypertension on Autonomic nervous Regulation of Circulatory System

Abstract

Effects of age on autonomic circulatory functions, plasma norepinephrine, plasma renin activity and lymphocyte β receptor were investigated in normotensive and hypertensive subjects. Autonomic functions were tested by Valsalva maneuver, 70° head up tilting, cold pressor and atropine injection (0.02mg/kg iv). Baroreceptor reflex sensitivity index (BRSI) measured with a linear relationship between systolic blood pressure and RR interval in the Valsalva maneuver was significantly decreased with aging. Hypertensives had significantly lower values of BRSI than age-matched normotensives. The magnitude of the change in heart rate in Valsalva maneuver (Tachycardia ratio) was also depressed in hypertensives. The increase in heart rate was also inhibited in normotensive and hypertensive elderly subjects on atropine, cold pressor and tilting tests. The ratio of the increase in heart rate to increase in plasma norepinephrine on tilting was reduced with aging the both groups. In normotensives, aging caused an increase in plasma norepinephrine at rest and a decrease in response of plasma renin activity on tilting. Neither affinity nor capacity of binding sites in lymphocytes for radio-labeled pindolol was affected by age and hypertension. These results suggest that parasympathetic and sympathetic regluation of heart rate are altered with aging and that hypertension has additive effects on these changes. These dysfunctions may be caused at least in part, by the reduced baroreflex sensitivity as well as the decreased sympathetic responsiveness of hearts, apparently due to a postreceptor defect.