Restoration of plasma volume after 16 days of head-down tilt
induced by a single bout of maximal exercise.
Convertino, Victor A., Keith A. Engelke, David A. Ludwig, and Donald
F. Doerr.
Physiology Research Branch, Clinical Sciences Division, Brooks Air
Force Base, TX 78235, Department of Physiology, University of
Florida, Gainesville, FL 32610;, Department of Mathematics &
Statistics, University of North Carolina, Greensboro, NC 27412, NASA
-Kennedy Space Center, FL 32899
APStracts 2:0201R, 1995.
Seven healthy men performed maximal exercise 24 h before the end of 16
days exposure to 6 head-down tilt (HDT) to tested the hypothesis that
such an exercise technique could restore plasma volume (PV) at the
end of a simulated space mission. Exercise consisted of supine
cycling with graded work rates increasing by 16 W/min to volitional
fatigue and required an average of 16 min. The experimental protocol
was a standard cross-over design in which the order of treatment
(exercise or control) was counterbalanced across all 7 subjects.
Plasma volume, fluid intake (ad libitum), urine output, renal
function, and hormones associated with fluid homeostasis were
measured before HDT, 24 h before the end of HDT just prior to
exercise, and at the end of HDT 24 h after exercise. HDT reduced PV
by 16% in both control and exercise conditions. Maximal exercise
completely restored plasma volume within 24 h to 3.9 +/- 3.2 % of
pre-HDT levels despite continued HDT. Compared to control, exercise
induced a 660-ml larger positive fluid balance due to greater fluid
intake and reduced urine volume during the 24 h after exercise. These
results suggest that one bout of maximal leg exercise prior to return
from 16 days of spaceflight may be completely effective in
stimulating thirst and restoring plasma volume to preflight levels.
Received 7 November 1994; accepted in final form 6 July 1995.
APS Manuscript Number R635-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.