cardiac volume were compared between the 2 flights. Data show Midodrine prevented severe
falls in stroke volume, cardiac output, systolic pressure, and severe increases in heart rate
without increasing blood flow resistance, thus preventing orthostatic hypotension. The
significance of this finding is that Midodrine appeared to protect a previously susceptible crew
member from post-spaceflight OH. It appeared to do this primarily by maintaining venous blood
return without causing increase in blood pressure. These results suggest a single, 10-mg oral
dose of Midodrine shortly after landing may protect crew members from post-spaceflight
orthostatic hypotension without causing a rise in blood pressure. A follow-up study with 5 male
crew members who had not been susceptible to OH following their previous spaceflights shows
there were no statistically significant differences between BP or cardiac output. No subject
experienced reduced blood pressure or fainting symptoms during any test. These results,
combined with bed rest studies, suggest that Midodrine may help prevent post-flight fainting
and the drug appeared to be well tolerated in test subjects and could potentially be made
available to crew members before reentry, allowing for the maximal benefit at landing (Platts
2004, 2006).
PUBLICATION(S)
Platts SH, Ziegler MG, Waters WW, Meck JV. Hemodynamic effects of Midodrine after
spaceflight in astronauts without orthostatic hypotension. Aviation, Space, and Environmental
Medicine. 2006;77(4):429-433.
Platts SH, Ziegler MG, Waters WW, Meck JV. Midodrine prescribed to improve recurrent post-
spaceflight orthostatic hypotension. Aviation, Space, and Environmental Medicine.
2004;75(6):554-556.
Waters WW, Ziegler MG, Meck JV. Postspaceflight orthostatic hypotension occurs mostly in
women and is predicted by low vascular resistance. Journal of Applied Physiology. February
2002; 92(2):586-594. doi: 10.1152/japplphysiol.00544.2001.
This investigation is complete; however additional results are pending publication.