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

Abstract

SUMMARY 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 agematched normotensive controls. The increase in heart rate following tilt was similar in both 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. (Hypertension 10: 29-34, 1987) KEY WORDS • essential hypertension • baroreceptor reflex mechanisms • orthostasis W HEN a normal person changes from the recumbent to the erect position, the central blood volume and heart volume are decreased and the cardiac output (CO) is reduced by about 20%.'" 3 Diminished CO accompanying reduced peripheral resistance should result in a sharp fall in arterial pressure unless reflex cardioacceleration and vasoconstriction occur at the same time because of the baroreceptor reflex compensatory mechanisms.3 For that reason, baroreceptor reflex mechanisms may be adequately evaluated using passive tilting on a tilt table from the horizontal to the erect position, 4 " 8 during which muscular pumping action of the legs 9 is minimal or absent.The mechanisms resulting in the changes in heart rate and systemic vascular resistance on standing are complex, involving baroreceptors of the high and the low pressure systems and even ergoreceptors in the skeletal muscles.3 ' ltM5 Furthermore, adequate studies

Morning blood pressure surge is associated with arterial stiffness and sympathetic baroreflex sensitivity in hypertensive seniors

“…Therefore, it seems that hypertensive patients with greater arterial stiffness have a lesser ability to buffer against BP increases in the morning. Based on the finding that the contribution of total peripheral resistance (TPR) to BP change by orthostasis became greater, while the contribution of heart rate (HR) decreased with age in hypertensive subjects (16), the sympathetic baroreflex, which regulates BP via vasoconstriction, may play a more important role in control of morning BP in elderly hypertensive subjects. The morning surge is actually assessed with night time BP and morning BP for 2 h after waking up (12), suggesting that the morning surge includes BP rises upon standing.…”

Limb venous compliance responses to lower body negative pressure in humans with high blood pressure

“…These findings are in agreement with previous investigations reporting that the increase in vascular resistance in response to head-up tilt was amplified in hypertensive subjects compared with NTs, and was positively correlated with age and baseline values. 36 The exaggerated vascular resistance response to head-up tilt in hypertension has not been explained by a greater sympathetic response. 37 Thus, mechanisms other than autonomic neural regulation should be taken into consideration.…”

“…37 Thus, mechanisms other than autonomic neural regulation should be taken into consideration. London et al 36 suggested that vascular wall hypertrophy might amplify the vascular resistance responses to head-up tilt. In addition, hormonal responses to central hypovolemia could induce different vascular resistance responses.…”

The Haemodynamic Instability Score (HIS) for assessment of cardiovascular reactivity in hypertensive and normotensive patients

“…10,[17][18][19][20] When a normal adult stands upright, 500-700 ml of blood are pooled in the legs, reducing cardiac output and arterial pressure. The fall in pressure activates baroreceptors, which then increase sympathetic outflow and inhibit parasympathetic activity, leading to vasoconstriction, increased heart rate and increased myocardial contractility.…”