MULTIPLE-VARIABLES EXPLAIN THE VARIABILITY IN THE DECREMENT IN (V)OVER-DOT-O-2MAX DURING ACUTE HYPOBARIC HYPOXIA

Purpose: We used multiple regression analyses to determine the relatio nships between the decrement in sea lever (SL, 760 Torr) (V) over dot O-2max during hypobaric hypoxia (HH) and variables that could alter or be related to the decrement in (V) over dot O-2max. Methods: HH condi tions consisted of 682 Torr. 632 Torr, and 566 Ton, and the measured i ndependent variables were SL-(V) over dot O-2max, SL lactate threshold (SL-LT), the change in hemoglobin saturation at (V) over dot O-2max b etween 760 and 566 Torr (Delta SaO(2max)), lean body mass (LBM), and g ender. Male (N = 14) and female (N = 14) subjects of varied fitness, t raining status, and residential altitude (1,640-2,460 m) completed cyc le ergometry tests of (V) over dot O-2max at each HH condition under r andomized and single-blinded conditions. Results: (V) over dot O-2max decreased significantly from 760 Torr after 682 Torr (similar to 915 m ) (3.5 +/- 0.9 to 3.4 +/- 0.8 L.min(-1), P = 0.0003). Across all HH co nditions, the slope of the relative decrement in (V) over dot O-2max ( %(V) over dot O-2max) during HH was -9.2%/100 mm Hg (-8.1%/1000 m) wit h an initial decrease from 100% estimated to occur below 705 Torr (610 m). Step-wise multiple regression revealed that SL-(V) over dot O-2ma x, SL-LT, Delta SaO(2max), LBM, and gender each significantly combined to account for 89.03% of the variance in the decrement in (V) over do t O-2max (760-566 Torr) (P < 0.001). Conclusions: Individuals who have a combination of a large SL-(V) over dot O-2max, a small SL-LT ((V) o ver dot O-2, L.min(-1)), greater reductions in Delta SaO(2max), a larg e LBM, and are male have the greatest decrement in (V) over dot O-2max during HH. The unique variance explanation afforded by SL-LT, LBM, an d gender suggests that issues pertaining to oxygen diffusion within sk eletal muscle may add to the explanation of between subjects variabili ty in the decrement in (V) over dot O-2max during HH.