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.

Difference in response of vascular resistance to orthostasis in patients with borderline and sustained essential hypertension.

Changes in hemodynamic parameters following 50-degree head up tilt were studied in a population of 78 males, including 30 patients with sustained essential hypertension, 30 patients with borderline hypertension, and 18 normotensive controls of the same age. The increase in vascular resistance following tilt was significantly higher in hypertensive subjects. In patients with sustained hypertension, baseline vascular resistance was significantly higher than in normotensive controls, and it was strongly correlated with its change following orthostasis. In patients with borderline hypertension, baseline vascular resistance was similar to that of normotensive controls and did not correlate with its change following orthostasis. The latter result suggests an abnormality in the autonomic nervous control in patients with borderline hypertension, possibly mediated by cardiopulmonary mechanoreceptors in the low pressure system.

Cardiac mass and aortic distensibility following calcium blockade in hypertension.

Calcium-entry blockade produced by verapamil was studied in 13 subjects with sustained essential hypertension. Noninvasive echo-Doppler methods were used to evaluate cardiac structure and function, maximum aortic acceleration (used as an indirect index of cardiac performance), and carotid-femoral pulse-wave velocity. Measurements were performed in baseline conditions, following 12 weeks of active treatment, and 4 weeks of placebo. Following verapamil, blood pressure (BP) significantly decreased (p less than 0.001) with a slight reduction in cardiac output (p less than 0.05) and a more substantial decrease in heart rate (p less than 0.002). No significant change occurred in maximum acceleration and in the curve relating percent fractional shortening to end-systolic stress, suggesting that verapamil decreased BP with minor changes in cardiac performance. Cardiac mass decreased by approximately 6.3% whereas pulse-wave velocity did not change, suggesting that the small decrease in cardiac mass could be related to the lack of improvement in the capacitative component of vascular impedance, as judged from the determination of pulse-wave velocity. The study provides evidence that calcium blockade due to verapamil results in a dissociation between the antihypertensive effect and the absence of significant changes in cardiac and arterial structure and function.