Effect of exercise-induced arterial O2 desaturation on (V)over-dot-O2max in women

Purpose: We have recently reported that many healthy habitually active women experience exercise induced arterial hypoxemia (EIAH). We questioned whether EIAH affected (V)over dotO(2max) in this population and whether the effect was similar to chat reported in men. Methods: Twenty-five healthy young women with widely varying fitness levels ((V)over dotO(2max), 56.7 +/- 1.5 ml . kg(-1) min(-1); range: 41-70 mL . kg(-1 .)min(-1)) and normal resting lung function performed two randomized incremental treadmill rests to (V)over dotO(2max) (FIO2: 0.21 or 0.26) during the follicular phase of their menstrual cycle. Arterial blood samples were taken at rest and near me end of each workload during the normoxic test. Results: During room air breathing at (V)over dot O-2max, SaO(2) decreased to 91.8 +/- 0.4% (range 87-95%). With 0.26 FIO2, SaO(2) at (V)over dotO(2max) remained near resting levels and averaged 96.8 +/- 0.1% (range 96-98%). When arterial O-2 desaturation was prevented via increased FIO2, 9(V)over dotO(2max) increased in 22 of the 25 subjects and in proportion to the degree of arterial O-2 desaturation experienced in normoxia (r = 0.88). The improvement in (V)over dotO(2max) when systemic normoxia was maintained averaged 6.3 +/- 0.3% (range 0 to + 15%) and the slope of the relationship was similar to 2% increase in (V)over dotO(2max) for every 1% decrement in the arterial oxygen saturation below resting values. About 75% of the increase in (V)over dotO(2max) resulted from an increase in (V)over dotO(2) at a fixed maximal work rate and exercise duration, and the remainder resulted from an increase in maximal work rate. Conclusions: These data demonstrate that even small amounts of EIAH (i.e., >3% Delta SaO(2) below rest) have a significant detrimental effect on (V)over dotO(2max) in habitually active women with a wide range of (V)over dotO(2max). Tn combination with our previous findings documenting EIAH in females, we propose that inadequate pulmonary structure/function in many habitually active women serves as a primary limiting factor in maximal 0, transport and utilization during maximal exercise.