Maximal exercise performance after adaptation to microgravity.
Levine, Benjamin D., Lynda D. Lane, Donald E. Watenpaugh, F. Andrew
Gaffney, Jay C. Buckey, C. Gunnar Blomqvist.
Department of Internal Medicine, Division of Cardiology, University
of Texas Southwestern Medical Center at Dallas, and the Institute for
Exercise and Environmental Medicine, Presbyterian Hospital, Dallas,
TX
APStracts 3:0173A, 1996.
Background: The cardiovascular system appears to adapt well to
microgravity but is compromised upon re-establishment of
gravitational forces leading to orthostatic intolerance and a
reduction in work capacity. However maximal systemic oxygen uptake
and transport, which may be viewed as a measure of the functional
integrity of the cardiovascular system and its regulatory mechanisms,
has not been systematically measured in space or immediately after
return to earth following spaceflight. Methods: We studied 6
astronauts (4m/2F, age 35-50) before, during, and immediately after 9
or 14 days of microgravity on 2 Spacelab Life Sciences Flights (SLS-1
and SLS-2). VO2 peak was measured with an incremental protocol on a
cycle ergometer after prolonged submaximal exercise at 30% and 60% of
VO2peak . We measured: gas fractions by mass spectrometer and
ventilation via turbine flow meter for the calculation of breath-by
-breath oxygen uptake, heart rate (HR) via ECG, and cardiac output
(Qc) via CO2 re-breathing. Results: Peak power and oxygen uptake were
well maintained during spaceflight and not significantly different
compared to two weeks pre-flight. VO2 peak was reduced by 22%
immediately post-flight (p<0.05), entirely due to a decrease in
peak stroke volume and Qc. Peak heart rate, blood pressure, and
systemic a-vO2 difference were unchanged. Conclusion: We conclude
that peak systemic oxygen uptake is well maintained in the absence of
gravity for 9-14 days, but is significantly reduced immediately upon
return to earth, most likely due to reduced intravascular blood
volume, stroke volume, and cardiac output.
Received 20 June 1995; accepted in final form 21 March 1996.
APS Manuscript Number A659-2.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 April 96