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

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