Mechanisms of post-flight orthostatic intolerance

J Gravit Physiol. 1994 May;1(1):P122-4.


Post-flight orthostatic intolerance is a dramatic physiological consequence of human adaptation to microgravity made inappropriate by a sudden return to 1-G. The immediate mechanism is almost always a failure to maintain adequate tissue perfusion, specifically perfusion of the central nervous system, but vestibular dysfunction may occasionally be the primary cause. Orthostatic intolerance is present in a wide range of clinical disorders of the nervous and cardiovascular systems. The intolerance that is produced by spaceflight and 1-G analogs (bed rest, head-down tilt at a moderate angle, water immersion) is different from its clinical counterparts by being only transiently present in subjects who otherwise have normal cardiovascular and regulatory systems. However, the same set of basic pathophysiological elements should be considered in the analysis of any form of orthostatic intolerance.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptation, Physiological / physiology*
  • Adrenergic alpha-Agonists / pharmacology
  • Baroreflex / physiology
  • Blood Pressure / drug effects
  • Cardiac Output / physiology
  • Heart Rate / physiology
  • Hemodynamics / physiology*
  • Humans
  • Hypotension, Orthostatic / etiology
  • Hypotension, Orthostatic / physiopathology*
  • Phenylephrine / pharmacology
  • Posture / physiology
  • Space Flight*
  • Supine Position
  • Vasoconstrictor Agents / pharmacology
  • Weightlessness / adverse effects*


  • Adrenergic alpha-Agonists
  • Vasoconstrictor Agents
  • Phenylephrine