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Systolic time intervals and other cardiovascular changes following leg elevation
Aviation, Space, and Environmental Medicine
|November 1, 1979
Summary
Passive leg elevation in humans enhances ventricular performance via the Frank-Starling mechanism or reflex stimulation. This cardiovascular response, observed noninvasively, shows delayed enhancement of heart contractility.
Area of Science:
- Cardiovascular Physiology
- Human Physiology
Background:
- Passive leg elevation increases venous return to the heart.
- Previous studies noted forearm vasodilation in response to leg elevation.
Purpose of the Study:
- To investigate the cardiovascular responses to passive leg elevation.
- To determine the effects on ventricular performance and arterial pressure.
Main Methods:
- Noninvasive monitoring of cardiovascular responses in 16 human subjects.
- Systolic-time-interval analysis to assess ventricular performance.
- Passive leg elevation for 40 seconds.
Main Results:
- Forearm vasodilation occurred promptly.
- Arterial pressure and heart rate remained unchanged.
- Ventricular performance was enhanced after a 6-second delay, lasting throughout leg elevation.
Conclusions:
- The delayed enhancement of ventricular performance may result from the Frank-Starling mechanism.
- Alternatively, reflex stimulation of atrial receptors could increase sympathetic contractility.
- Cardiovascular responses normalized upon lowering the legs.