Tilt test in essential hypertension. Differential responses in heart rate and vascular resistance.

Changes in hemodynamic parameters following 50-degree head-up tilt were studied in a population of 56 men, including 35 subjects with sustained essential hypertension and 21 age-matched normotensive controls. The increase in heart rate following tilt was similar in groups and exhibited the same reduction in response with age. The increase in vascular resistance following tilt was strongly and positively correlated with both age and baseline vascular resistance. The latter finding was observed mainly in hypertensive subjects. The study provided evidence that differentiated responses of heart rate and vascular resistance may be observed following orthostasis. In both normal and hypertensive subjects, the age dependence of heart rate response possibly reflected differences in baroreceptor reflex control of parasympathetic and sympathetic activity. In hypertensive subjects, the vascular response was amplified with age and baseline vascular resistance, suggesting a role for structural changes of the vessels in the increased vascular response.