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NIRS-Derived Tissue Oxygen Saturation and Hydrogen Ion Concentration Following Bed RestLong-term bed rest (BR), a model of spaceflight, results in a decrease in aerobic capacity and altered submaximal exercise responses. The strongest BR-induced effects on exercise appear to be centrally-mediated, but longer BR durations may result in peripheral adaptations (e.g., decreased mitochondrial and capillary density) which are likely to influence exercise responses. PURPOSE: To measure tissue oxygen saturation (SO2) and hydrogen ion concentration ([H+]) in the vastus lateralis (VL) using near infrared spectroscopy (NIRS) during cycle ergometry before and after . 30 d of BR. METHODS: Eight subjects performed a graded exercise test on a cycle ergometer to volitional fatigue 7 d before (pre-BR) and at the end or 1 day after BR (post-BR). NIRS spectra were collected from a sensor adhered to the skin overlying the VL. Oxygen consumption (VO2) was measured by open circuit spirometry. Blood volume (BV) was measured before and after BR using the carbon monoxide rebreathing technique. Changes in pre- and post-BR SO2 and [H+] data were compared using mixed model analyses. BV and peak exercise data were compared using paired t-tests. RESULTS: BV (pre-BR: 4.3+/-0.3, post-BR: 3.7+/-0.2 L, mean+/-SE, p=.01) and peak VO2 (pre-BR: 1.98+/-0.24, post-BR: 1.48 +/-0.21 L/min, p<.01) were reduced after BR. As expected, SO2 decreased with exercise before and after BR. However, SO2 was lower post compared with pre-BR throughout exercise, including at peak exercise (pre-BR: 50+/-3, post-BR: 43+/-4%, p=.01). After BR, [H+] was higher at the start of exercise and did not increase at the same rate as pre-BR. Peak [H+] was not different from pre to post-BR (pre-BR: 36+/-2; post-BR: 38+/-2 nmol/L). CONCLUSIONS: Lower SO2 during exercise suggests that oxygen extraction in the VL is higher after BR, perhaps due to lower circulating blood volume. The higher [H+] after BR suggests a greater reliance upon glycolysis during submaximal exercise, although [H+] at peak exercise was unchanged. Taken together, these data suggest that longer duration BR induces a number of changes that result in peripheral adaptations which contribute to cardiovascular and muscular deconditioning as measured by NIRS-derived SO2 and [H+] in the VL and may contribute to lower post-BR exercise tolerance. Supported by the National Space Biomedical Research Institute through NASA NCC 9-58
Document ID
20100036854
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Lee, S. M. C. (Wyle Integrated Science and Engineering Group Houston, TX, United States)
Everett, M. E. (Houston Univ. Houston, TX, United States)
Crowell, J. B. (MEI Technologies, Inc. Houston, TX, United States)
Westby, C. M. (Universities Space Research Association Houston, TX, United States)
Soller, B. R. (Reflectance Medical, Inc. Westboro, MA, United States)
Date Acquired
August 25, 2013
Publication Date
January 29, 2010
Subject Category
Aerospace Medicine
Report/Patent Number
JSC-CN-22052
Meeting Information
Meeting: 82nd Annual Scientific Meeting of the Aerospace Medical Association
Location: Anchorage, AK
Country: United States
Start Date: May 8, 2011
End Date: May 12, 2011
Funding Number(s)
CONTRACT_GRANT: NCC9-58
Distribution Limits
Public
Copyright
Public Use Permitted.

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