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Sixteen-Day Bedrest Significantly Increases Plasma Colloid Osmotic PressureUpon exposure to microgravity, astronauts lose up to 10% of their total plasma volume, which may contribute to orthostatic intolerance after space flight. Because plasma colloid osmotic pressure (COP) is a primary factor maintaining plasma volume, our objective was to measure time course changes in COP during microgravity simulated by 6 deg. head-down tilt (HDT). Seven healthy male subjects (30-55 years of age) were placed in HDT for 16 days. For the purpose of another study, three of the seven subjects were chosen to exercise on a cycle ergometer on day 16. Blood samples were drawn immediately before bedrest on day 14 of bedrest, 18-24 hours following exercise while all subjects were still in HDT and 1 hour following bedrest termination. Plasma COP was measured in all 20 microliter EDTA-treated samples using an osmometer fitted with a PM 30 membrane. Data were analyzed with paired and unpaired t-tests. Plasma COP on day 14 of bedrest (29.9 +/- 0.69 mmHg) was significantly higher (p less than 0.005) than the control, pre-bedrest value (23.1 +/- 0.76 mmHg). At one hour of upright recovery after HDT, plasma COP remained significantly elevated (exercise: 26.9 +/- 0.87 mmHg; no exercise: 26.3 +/- 0.85 mmHg). Additionally, exercise had no significant effect on plasma COP 18-24 hours following exercise (exercise: 27.8 +/- 1.09 mmHg; no exercise: 27.1 +/- 0.78 mmHg). Our results demonstrate that plasma COP increases significantly with microgravity simulated by HDT. However, preliminary results indicate exercise during HDT does not significantly affect plasma COP.
Document ID
Document Type
Conference Paper
Hargens, Alan R.
(NASA Ames Research Center Moffett Field, CA United States)
Hsieh, S. T.
(Armstrong Lab. Brooks AFB, TX United States)
Murthy, G.
(Armstrong Lab. Brooks AFB, TX United States)
Ballard, R. E.
(NASA Ames Research Center Moffett Field, CA United States)
Convertino, V. A.
(NASA Ames Research Center Moffett Field, CA United States)
Wade, Charles E.
Date Acquired
August 20, 2013
Publication Date
January 1, 1994
Subject Category
Aerospace Medicine
Meeting Information
Aerospace Medical Association Meeting(Anaheim, CA)
Funding Number(s)
PROJECT: RTOP 199-14-12-04
PROJECT: RTOP 199-14-13-02
Distribution Limits
Work of the US Gov. Public Use Permitted.
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