Orthostatic intolerance and vasovagal syncope after spaceflight

Abstract

Postflight orthostatic intolerance is commonly observed in astronauts after their return to Earth. It is defined as the development of symptomatic intolerance to upright posture after flight, with concomitant tachycardia and progressive hypotension. With sustained upright posture, progression to frank vasovagal syncope is possible, though rare. This phenomenon is a consequence of several physiologic and autonomic adaptations that occur during spaceflight, including loss of plasma volume, muscle mass, cardiac atrophy, loss of vasoconstrictor function, vestibular dysfunction, and alterations in autonomic function. A variety of in-flight and postflight countermeasures have been developed to counteract these neurophysiologic consequences of spaceflight.