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Preload, adrenergic activity, and aortic compliance in normal and hypertensive patients
M A Madkour1, J Levenson, E L Bravo
1Department of Heart and Hypertension, Cleveland Clinic Foundation, OH 44195-5069.
Insights
Aortic compliance, crucial for blood pressure, is lower in hypertensive individuals and inversely related to systolic blood pressure. Preload reduction via lower body negative pressure affected compliance similarly in both groups.
Area of Science:
- Cardiovascular Physiology
- Hypertension Research
Background:
- Aortic compliance significantly influences systolic blood pressure and left ventricular ejection impedance.
- Factors regulating aortic compliance, particularly preload and adrenergic activity, are not well understood.
Purpose of the Study:
- To investigate the impact of preload and adrenergic activity on aortic compliance in normal and hypertensive individuals.
- To compare aortic compliance between normotensive and untreated hypertensive subjects.
Main Methods:
- Aortic compliance was invasively measured using diastolic decay of aortic pressure and systemic vascular resistance.
- Lower body negative pressure (LBNP) was employed to decrease preload stepwise.
- Adrenergic activity was assessed by measuring plasma norepinephrine levels during maximal LBNP.
Main Results:
- Hypertensive subjects exhibited lower aortic compliance at rest compared to normotensive individuals (0.048 vs. 0.071 units, p < 0.001).
- Aortic compliance showed a significant inverse correlation with systolic blood pressure across both groups (r = -0.88, p < 0.001).
- Resting pulmonary wedge pressure was higher in hypertensives, but plasma norepinephrine levels did not differ between groups.
Conclusions:
- Reduced aortic compliance is a characteristic of hypertension, strongly linked to elevated systolic blood pressure.
- Preload reduction through LBNP similarly impacted cardiac filling pressures and cardiac output in both normotensive and hypertensive individuals.
- Resting adrenergic activity, as measured by norepinephrine, did not appear to be a primary determinant of baseline aortic compliance in this study.
Abstract:
Aortic compliance is a major determinant of systolic blood pressure and of impedance to left ventricular ejection. However, little is known about its regulating factors. To assess the effects of preload and adrenergic activity on aortic compliance, we studied 10 normal subjects and nine untreated hypertensive patients at rest and during lower body negative pressure. Aortic compliance was measured invasively from the diastolic decay of the aortic pressure tracing and systemic vascular resistance. Preload was decreased stepwise by lower body negative pressure (-5 to -40 mm Hg) while adrenergic activity was assessed by the change in plasma norepinephrine at a maximum level of negative pressure suction. At rest, aortic compliance was lower in hypertensive subjects compared with its value in normal individuals (0.048 +/- 0.012 [SD] versus 0.071 +/- 0.009 units, p less than 0.001) but correlated inversely with systolic blood pressure in both groups (r = -0.64 in normotensive individuals, r = -0.83 in hypertensive subjects, r = -0.88 for the whole group, p less than 0.001 for all). Whereas resting pulmonary wedge pressure was higher in hypertensive subjects compared with normal individuals (16 +/- 4 [SD] versus 11 +/- 3 mm Hg, p less than 0.05), resting plasma norepinephrine levels were not different between the two groups (261 +/- 139 versus 251 +/- 103 pg/ml). Neither of these two resting indices correlated with baseline aortic compliance in both normotensive individuals and hypertensive patients. During lower body negative pressure (LBNP), cardiac filling pressure (right atrial pressure and pulmonary wedge pressure) as well as cardiac output decreased in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)