Hemodynamic effects of midodrine after spaceflight in astronauts without orthostatic hypotension.
BACKGROUND
Orthostatic hypotension and presyncope are common and potentially serious risks for astronauts returning from space. Susceptible subjects fail to generate an adequate adrenergic response to upright posture. The alpha-1 adrenergic agonist, midodrine, may be an effective countermeasure. We tested the hypothesis that midodrine would have no negative hemodynamic effect on healthy astronauts returning from space.


METHODS
Five male astronauts participated in preflight and post-flight tilt testing on a control flight as well as on the test flights, where midodrine (10 mg, orally) was administered after landing approximately 1 h before testing.


RESULTS
None of these astronauts exhibited orthostatic hypotension or presyncope before or after either flight. Midodrine did not cause any untoward reactions in these subjects before or after flight; in fact, a modest beneficial effect was seen on postflight tachycardia (p = 0.036).


CONCLUSIONS
These data show that midodrine protected against post-spaceflight increases in heart rate without having any adverse hemodynamic effects on non-presyncopal, male astronauts. Among these subjects, midodrine was a safe cardiovascular countermeasure.
Platts
Steven H
SH
Universities Space Research Association, Houston, TX, USA.
Ziegler
Michael G
MG
Waters
Wendy W
WW
Meck
Janice V
JV