Cephalad redistribution of intravascular and extravascular fl uid occurs as a result of weightlessness during spacefl ight. This provokes cardiovascular, cardiopulmonary, and autonomic nervous system responses. The resulting altered functional state can result in orthostatic hypotension and intolerance upon landing and return to a gravity environment. In-fl ight lower body negative pressure (LBNP) transiently restores normal body fl uid distribution. Early in the U.S. space program, LBNP was

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... ised as a way to test for orthostatic intolerance. With the development of the Skylab Program and longer duration spacefl ight, it was realized that it could provide a method of monitoring orthostatic intolerance in fl ight and predicting the post-landing orthostatic response. LBNP was also investigated not only as an in-fl ight cardiovascular orthostatic stress test, but also as a countermeasure to cardiovascular deconditioning on Soviet space stations, Skylab, and the Shuttle. It is still being used by the Russian program on the International Space Station as an end-offl ight countermeasure.