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 he modynamic response to a change in posture in essential hypertension, I nvasive hemodynamic measurements were performed in the supine and sitt ing position in 110 men, aged 16 to 64 years, in whom cardiovascular c omplications were virtually excluded. The change of systolic and diast olic 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, wa s not significantly (P >.10) related to age. Heart rate (+9 beats/min) and systemic vascular resistance (+4.6 mm Hg/L/min) increased (P < .0 01) on sitting; cardiac output (-1.7 L/min), stroke volume (-31 mL), a nd pulmonary capillary wedge pressure (-2.1 mm Hg) fell (P <.001). Whe reas the postural changes of heart rate (P <.01), cardiac output (P <. 001), stroke volume (P <.001), and wedge pressure (P =.06) were less p ronounced 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 di ffered 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 p atients suggest less thoracic blood volume displacement to the lower p arts of the body, possibly resulting from a lesser peripheral venous d istensibility. The increase of heart rate in response to the upright p osture is less pronounced at older age, whereas the reflex control of the peripheral vasculature is preserved and blood pressure maintained.