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Hypovolemia Induced Orthostatic Hypotension in Presyncopal Astronauts and Normal Subjects Related to Hypoadrenergic ResponsivenessCirculating blood volume is reduced during spaceflight, making astronauts hemodynamically compromised. After landing, astronauts separate into two groups. One group compensates for the hypovolemia with a hyper-sympathetic response during upright tilt testing and can complete a tilt test with few symptoms. The other group is unable to mount a hyper-sympathetic response and experiences orthostatic hypotension and presyncope during upright tilt tests. We tested the hypothesis that hypovolemia alone, in the absence of spaceflight, also would cause subjects to separate into presyncopal and non-presyncopal groups according to their sympathetic responses during tilt. We studied 20 subjects, including 10 veteran astronauts, on three occasions. On Days 1 (normovolemia) and 3 (hypovolemia), plasma volume, tilt tolerance and supine and standing plasma norepinephrine levels were measured. Forty hours prior to Day 3, subjects were given intravenous furosemide, followed by 36 hours of a 10MEq Na diet. Statistical comparisons were made between normovolemia and hypovolemia responses. This protocol reproduced landing day tilt test outcomes with 100% fidelity in the astronauts. Similarly to patterns reported after flight, non-presyncopal subjects had greater norepinephrine responses to tilt during hypovolemia compared to normovolemia (580 plus or minus 79 vs. 298 plus or minus 37 pg/ml, P less than 0.05), but presyncopal subjects had no increase (180 plus or minus 44 vs. 145 plus or minus 32 pg/ml, P=NS). This model can be used to predict astronauts who will become presyncopal on landing day, so that prospective, individualized countermeasures can be developed. Within patient populations, it can be used to study the interaction of volemic state and the sympathetic nervous system.
Document ID
20080026097
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Meck, Janice V. (NASA Johnson Space Center Houston, TX, United States)
Platts, Steven H. (Universities Space Research Association Houston, TX, United States)
Waters, Wendy W. (Wyle Labs., Inc. Houston, TX, United States)
Shi, Shang-Jin (Wyle Labs., Inc. Houston, TX, United States)
Hayashi, Yuho (Texas Univ. Health Science Center Houston, TX, United States)
Perez, Sondra A. (Wyle Labs., Inc. Houston, TX, United States)
Ziegler, Michael G. (California Univ. San Diego, CA, United States)
Date Acquired
August 24, 2013
Publication Date
April 1, 2006
Subject Category
Life Sciences (General)
Meeting Information
Meeting: Experimental Biology 2006
Location: San Francisco, CA
Country: United States
Start Date: April 1, 2006
End Date: April 5, 2006
Funding Number(s)
CONTRACT_GRANT: NAS98-HEDS-02-424
CONTRACT_GRANT: NCRR M01-RR02558
CONTRACT_GRANT: M01RR00827
Distribution Limits
Public
Copyright
Public Use Permitted.

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