Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men

Abstract

We analysed the importance of systemic and peripheral arteriovenous O2 difference ((Formula presented.) difference and a-vfO2 difference, respectively) and O2 extraction fraction for maximal oxygen uptake ((Formula presented.)). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with (Formula presented.). Articles (n = 17) publishing individual data (n = 154) on (Formula presented.), maximal cardiac output ((Formula presented.); indicator-dilution or the Fick method), (Formula presented.) difference (catheters or the Fick equation) and systemic O2 extraction fraction were identified. For the peripheral responses, group-mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a-vfO2 difference and O2 extraction fraction (arterial and femoral venous catheters) were obtained. (Formula presented.) and two-LBF increased linearly by 4.9-6.0 L · min–1 per 1 L · min–1 increase in (Formula presented.) (R2 =.73 and R2 =.67, respectively; both P <.001). The (Formula presented.) difference increased from 118-168 mL · L–1 from a (Formula presented.) of 2-4.5 L · min–1 followed by a reduction (second-order polynomial: R2 =.27). After accounting for a hypoxemia-induced decrease in arterial O2 content with increasing (Formula presented.) (R2 =.17; P <.001), systemic O2 extraction fraction increased up to ~90% ((Formula presented.) : 4.5 L · min–1) with no further change (exponential decay model: R2 =.42). Likewise, leg O2 extraction fraction increased with (Formula presented.) to approach a maximal value of ~90-95% (R2 =.83). Muscle O2 diffusing capacity and the equilibration index Y increased linearly with (Formula presented.) (R2 =.77 and R2 =.31, respectively; both P <.01), reflecting decreasing O2 diffusional limitations and accentuating O2 delivery limitations. In conclusion, although O2 delivery is the main limiting factor to (Formula presented.), enhanced O2 extraction fraction (≥90%) contributes to the remarkably high (Formula presented.) in endurance-trained individuals.