Effects of aging on the cardiopulmonary receptor reflex in hypertensive patients.

In order to evaluate the effects of aging on cardiopulmonary receptor function in hypertensive patients, hemodynamic responses after unloading were studied in middle aged and older hypertensive patients. Twenty-one hypertensive patients were divided into 2 groups according to age. The younger group consisted of 9 patients less than 65 years old (mean age: 57.2 years) and the older group contained 12 patients more than 65 years old (77.2 years). Following 10 min rest, deactivation of cardiopulmonary receptors was obtained by reducing central venous pressure through the application of graded negative pressures of -10, -20, and -40 mmHg to the lower body. Blood pressure, pulse rate, and forearm blood flow were measured at baseline and at each level of negative pressure. Furthermore, plasma norepinephrine and plasma renin activity levels were measured at baseline and at -40 mmHg. Forearm blood flow was measured by venous occlusive plethysmography using a Silastic strain gauge applied around the forearm. Forearm peripheral vascular resistance was calculated by dividing the mean arterial pressure by the forearm blood flow. Baseline mean blood pressure, pulse rate, and peripheral vascular resistance were similar in both age groups. Following lower body negative pressure (LBNP), mean blood pressure and pulse rate did not change, suggesting the selective deactivation of cardiopulmonary receptors. The increase in peripheral vascular resistance at LBNP of -40 mmHg in the older group (20.0 +/- 6.2) was significantly lower than that in the younger group (15.5 +/- 8.9, p less than 0.05). Furthermore, the increase in peripheral vascular resistance after LBNP was inversely related to age (Y = -0.32X + 38.8, r = -0.43, p less than 0.05). Increases in plasma norepinephrine and plasma renin activity in the older group were not different from those in the younger group. It is concluded that the sensitivity of cardiopulmonary baroreceptor function in hypertensive patients deteriorates with increasing age.