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Initial blood pressure fall on stand up and exercise explained by changes in total peripheral resistance
R L Sprangers1, K H Wesseling, A L Imholz
1Department of Cardiology, Academic Medical Center, Amsterdam, The Netherlands.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 1, 1991
Summary
Standing upright causes a rapid drop in blood pressure due to decreased total peripheral resistance. The cardiopulmonary reflex is the main cause, though other factors may contribute to vasodilation.
Area of Science:
- Physiology
- Cardiovascular Research
Background:
- Understanding the immediate hemodynamic adjustments upon standing is crucial for explaining orthostatic intolerance.
- Blood pressure regulation involves complex interactions between cardiac output and peripheral resistance.
Purpose of the Study:
- To investigate the mechanisms responsible for the initial drop in blood pressure when moving from a supine to an upright position.
- To differentiate the roles of cardiopulmonary reflexes, local metabolism, and central command in this response.
Main Methods:
- Beat-to-beat intra-arterial pressure measurements in eight healthy males.
- Calculated stroke volume, cardiac output, and total peripheral resistance using pulse contour analysis.
- Compared responses to standing, passive head-up tilt, and brief cycle exercise.
Main Results:
- Standing caused a transient 25% fall in mean blood pressure, driven by a 36% decrease in total peripheral resistance.
- Passive tilt showed gradual hemodynamic changes, while cycling induced a 17% blood pressure fall and 41% resistance decrease.
- Increased right atrial pressure without esophageal pressure changes during standing and cycling suggested cardiopulmonary reflex activation.
Conclusions:
- The cardiopulmonary reflex is identified as a primary mediator of peripheral vasodilation upon standing.
- Local metabolic vasodilation and central command-mediated cholinergic vasodilation may also contribute to the observed decrease in vascular resistance.