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Tolerance to head-up tilt and suspension with elevated legs
P Madsen1, L B Svendsen, L G Jørgensen
1The Copenhagen Muscle Research Center, Department of Anesthesia, Denmark.
Aviation, Space, and Environmental Medicine
|August 26, 1998
Summary
Normal individuals often experience near-fainting during head-up tilt tests. Elevating the legs prevents these orthostatic intolerance symptoms by securing venous return, crucial for safe transportation.
Area of Science:
- Physiology
- Cardiovascular Research
Background:
- Orthostatic hypotension can cause disabling syncope, with potential fatal outcomes during vertical transport.
- Normal orthostatic tolerance is not well-defined, necessitating studies on physiological responses to postural changes.
Observation:
- Head-up tilt to 50 degrees induced presyncope and hypotension in 87% of healthy volunteers within an hour.
- Leg elevation during suspension prevented presyncope in 89% of subjects, highlighting its role in maintaining venous return.
Findings:
- Presyncope during head-up tilt correlated with reduced central blood volume, indicated by increased thoracic electrical impedance and decreased oxygen saturation.
- Leg elevation effectively counteracted orthostatic stress by promoting venous return, preventing near-fainting.
Implications:
- The high incidence of presyncope in healthy individuals suggests caution when evaluating patients with syncope.
- Securing venous return through leg elevation is vital during patient transport, especially in critical situations like helicopter rescues.