Degree of arterial desaturation in normoxia influences O2max decline in mild hypoxia


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Abstract

Degree of arterial desaturation in normoxia influences O2max decline in mild hypoxia. Med. Sci. Sports Exerc., Vol. 31, No. 5, pp. 658-663, 1999.Purpose:Elite endurance athletes display varying degrees of pulmonary gas exchange limitations during maximal normoxic exercise and many demonstrate reduced arterial O2 saturations (SaO2) at O2max-a condition referred to as exercise induced arterial hypoxemia (EIH). We asked whether mild hypoxia would cause significant declines in SaO2 and O2max in EIH athletes while non-EIH athletes would be unaffected.Methods:Nineteen highly trained males were divided into EIH (N = 8) or Non-EIH (N = 6) groups based on SaO2 at O2max (EIH < 90%, Non-EIH > 92%). Athletes with intermediate SaO2 values (N = 5) were only included in correlational analyses. Two randomized incremental treadmill tests to exhaustion were completed-one in normoxia, one in mild hypoxia (FIO2 = 0.187; ∼1,000m).Results:EIH subjects demonstrated a significant decline in O2max from normoxia to mild hypoxia (71.1 ± 5.3 vs 68.1 ± 5.0 mL·kg−1·min−1, P < 0.01), whereas the non-EIH group did not show a significant ΔO2max (67.2 ± 7.6 vs 66.2 ± 8.4 mL·kg−1·min−1). For all 19 athletes, SaO2 during maximal exercise in normoxia correlated with the change in O2max from normoxia to mild hypoxia (r = −0.54, P < 0.05). However, the change in SaO2 and arterial O2 content from normoxia to mild hypoxia was equal for both EIH and Non-EIH (ΔSaO2 = 5.2% for both groups), bringing into question the mechanism by which changes in SaO2 affect O2max in mild hypoxia.Conclusions:We conclude that athletes who display reduced measures of SaO2 during maximal exercise in normoxia are more susceptible to declines in O2max in mild hypoxia compared with normoxemic athletes.

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