Decreases in maximal oxygen uptake following long-duration spaceflight: Role of convective and diffusive O2transport mechanisms.
We have previously predicted that the decrease in maximal oxygen uptake (V̇o2max) that accompanies time in microgravity reflects decrements in both convective and diffusive O2transport to the mitochondria of the contracting myocytes. The aim of this investigation was therefore to quantify the relative changes in convective O2transport (Q̇o2) and O2diffusing capacity (Do2) following long-duration spaceflight. In nine astronauts, resting hemoglobin concentration ([Hb]), V̇o2max, maximal cardiac output (Q̇Tmax), and differences in arterial and venous O2contents ([Formula: see text]-[Formula: see text]) were obtained retrospectively for International Space Station Increments 19-33 (April 2009-November 2012). Q̇o2and Do2were calculated from these variables via integration of Fick's Principle of Mass Conservation and Fick's Law of Diffusion. V̇o2maxsignificantly decreased from pre- to postflight (-53.9 ± 45.5%,P= 0.008). The significant decrease in Q̇Tmax(-7.8 ± 9.1%,P= 0.05), despite an unchanged [Hb], resulted in a significantly decreased Q̇o2(-11.4 ± 10.5%,P= 0.02). Do2significantly decreased from pre- to postflight by -27.5 ± 24.5% (P= 0.04), as did the peak [Formula: see text]-[Formula: see text] (-9.2 ± 7.5%,P= 0.007). With the use of linear regression analysis, changes in V̇o2maxwere significantly correlated with changes in Do2(R2= 0.47;P= 0.04). These data suggest that spaceflight decreases both convective and diffusive O2transport. These results have practical implications for future long-duration space missions and highlight the need to resolve the specific mechanisms underlying these spaceflight-induced changes along the O2transport pathway.NEW & NOTEWORTHYLong-duration spaceflight elicited a significant decrease in maximal oxygen uptake. Given the adverse physiological adaptations to microgravity along the O2transport pathway that have been reported, an integrative approach to the determinants of postflight maximal oxygen uptake is needed. We demonstrate that both convective and diffusive oxygen transport are decreased following ~6 mo International Space Station missions.
Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma; cade@ksu.edu.|Department of Kinesiology, Kansas State University, Manhattan, Kansas.
C J
CJ
Ade
Department of Internal Medicine, University of Utah, Salt Lake City, Utah.
R M
RM
Broxterman
Department of Health and Kinesiology, Lamar University, Beaumont, Texas; and.
A D
AD
Moore
Department of Kinesiology, Kansas State University, Manhattan, Kansas.
T J
TJ
Barstow
D018480:Astronauts; D001692:Biological Transport / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology; D004058:Diffusion; D005260:Female; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D012189:Retrospective Studies; D013026:Space Flight / Q000379:methods; D014893:Weightlessness
D006454:Hemoglobins; D010100:Oxygen
exercise; maximal oxygen uptake; microgravity; spaceflight