Plasma colloid osmotic pressure increases in humans during simulated microgravity
Hsieh ST, Ballard RE, Murthy G, Hargens AR, Convertino VAAviat Space environ Med 1998; 69:23-6
Abstract
Background: On exposure to microgravity, astronauts lose up to 12% of their plasma volume which may contribute to post-flight orthostatic intolerance. Hypothesis: Whole-body dehydration during prolonged microgravity, simulated by 6° head-down tilt (HDT), may increase plasma colloid osmotic pressure (COP). Method: Seven healthy male subjects (30 - 55 yr of age) were placed in 6° HDT for 16 d. Plasma COP was measured from blood samples drawn immediately before HDT, on day 14 of HDT, and 1 h following bed rest termination using a 20 µL colloid osmometer. Plasma volume was determined before HDT, on day 16 of HDT, and 1 h following bed rest termination using a modified Evans blue dye technique. Results: Plasma COP on day 14 of bed rest (29.9 ± 0.7 mm Hg) was higher (p = 0.001) than pre-HDT value (23.1 ± 0.8 mm Hg), coinciding with a decrease of plasma volume. At 1 h of upright recovery following HDT, plasma volume stayed below baseline and plasma COP remained elevated (26.6 ± 0.6 mm Hg; p = 0.003) as compared with the pre-HDT value. Conclusion: Our results indicate that reduced plasma volume and significantly elevated plasma COP probably reflect an overall loss of extracellular fluids during simulated microgravity.
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Table of Contents for Volume 69, Number 1 of the ASEM journal.