title: Presyncopal/non-presyncopal outcomes of post spaceflight stand tests are consistent from flight to flight.
abstract: BACKGROUND
  The overall prevalence of orthostatic hypotension after short duration (6-18 d) spaceflight is 20% with existing countermeasures. However, it is not known if the outcomes of stand tests for orthostatic tolerance are consistent within individuals on subsequent flights, or if first time fliers are more (or less) likely to experience orthostatic hypotension and presyncope than are veteran astronauts.
  
  
  METHODS
  There were 50 astronauts who were studied retrospectively. Stand test data, which had been collected before and after spaceflight, were compared from at least two flights for each astronaut. For 25 of these astronauts, their first flight in this database was also their first spaceflight. For the remaining 25, their first flight in this database was their second, third, or fourth flight, as data were available.
  
  
  RESULTS
  No subject became presyncopal during preflight testing. Of the 50 subjects, 45 (90%) had the same outcome on their first and second flights of this study. Of 14 subjects on whom we had data from a third mission, 12 had the same stand test outcome on all 3 flights (86% same outcome across 3 flights). There was no correlation between flight duration and orthostatic tolerance (r = 0.39).
  
  
  CONCLUSIONS
  These data support the idea that astronauts are predisposed to orthostatic tolerance/intolerance after spaceflight and that this predisposition is not altered by subsequent flights. Flight durations within this data set did not alter the likelihood of orthostatic intolerance and rookie fliers were no more likely to experience orthostatic intolerance than were veteran astronauts.
authors.affiliation: Wyle Life Sciences, Human Adaptation and Countermeasures Office, Houston, TX, USA.
authors.forename: David S
authors.initials: DS
authors.lastname: Martin
authors.forename: Janice V
authors.initials: JV
authors.lastname: Meck
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D018480:Astronauts; D019992:Databases as Topic; D005260:Female; D006112:Gravitation; D006439:Hemodynamics; D006801:Humans; D007024:Hypotension, Orthostatic / Q000150:complications / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011187:Posture; D012189:Retrospective Studies; D013026:Space Flight; D013575:Syncope / Q000209:etiology / Q000503:physiopathology*; D000078329:Workforce