Effect of age on the hemodynamic response to posture in nonelderly hypertensive patients.

The objective of this study was to assess the effects of age on the hemodynamic response to a change in posture in essential hypertension. Invasive hemodynamic measurements were performed in the supine and sitting position in 110 men, aged 16 to 64 years, in whom cardiovascular complications were virtually excluded. The change of systolic and diastolic intraarterial pressure, from 153/83 mm Hg after 30 min of supine rest to 156 (P < .05)/92 (P < .001) mm Hg after sitting for 10 min, was not significantly (P > .10) related to age. Heart rate (+9 beats/min) and systemic vascular resistance (+4.6 mm Hg/L/min) increased (P < .001) on sitting; cardiac output (-1.7 L/min), stroke volume (-31 mL), and pulmonary capillary wedge pressure (-2.1 mm Hg) fell (P < .001). Whereas the postural changes of heart rate (P < .01), cardiac output (P < .001), stroke volume (P < .001), and wedge pressure (P = .06) were less pronounced in older than in younger patients, the increase of systemic vascular resistance was not related to age (P > .10). The slopes of the postural changes of heart rate and of systemic vascular resistance differed significantly (P = .01). The results were not confounded by the level of blood pressure or weight. In conclusion, the smaller postural falls of cardiac output, stroke volume, and wedge pressure in older patients suggest less thoracic blood volume displacement to the lower parts of the body, possibly resulting from a lesser peripheral venous distensibility. The increase of heart rate in response to the upright posture is less pronounced at older age, whereas the reflex control of the peripheral vasculature is preserved and blood pressure maintained.