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

• Published in: Acta Physiologica Vol. 230; no. 2; pp. e13486 - n/a
• Main Authors: Skattebo, Øyvind, Calbet, Jose A. L., Rud, Bjarne, Capelli, Carlo, Hallén, Jostein
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.10.2020; John Wiley and Sons Inc
• Subjects: arteriovenous oxygen difference; Blood flow; cardiac output; Catheters; exercise; Hypoxemia; Leg; leg blood flow; limiting factors; maximal oxygen uptake; Oxygen; oxygen diffusion; Perfusion; Review; stroke volume; cardiac output; oxygen diffusion; limiting factors; maximal oxygen uptake; exercise; arteriovenous oxygen difference; leg blood flow; stroke volume
• ISSN: 1748-1708; 1748-1716; 1748-1716
• DOI: 10.1111/apha.13486

We analysed the importance of systemic and peripheral arteriovenous O2 difference ( a-v¯O2 difference and a‐vfO2 difference, respectively) and O2 extraction fraction for maximal oxygen uptake ( V˙O2max). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with V˙O2max. Articles (n = 17) publishing individual data (n = 154) on V˙O2max, maximal cardiac output ( Q˙max; indicator‐dilution or the Fick method), a-v¯O2 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. Q˙max and two‐LBF increased linearly by 4.9‐6.0 L · min–1 per 1 L · min–1 increase in V˙O2max (R2 = .73 and R2 = .67, respectively; both P < .001). The a-v¯O2 difference increased from 118‐168 mL · L–1 from a V˙O2max 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 V˙O2max (R2 = .17; P < .001), systemic O2 extraction fraction increased up to ~90% ( V˙O2max: 4.5 L · min–1) with no further change (exponential decay model: R2 = .42). Likewise, leg O2 extraction fraction increased with V˙O2max to approach a maximal value of ~90‐95% (R2 = .83). Muscle O2 diffusing capacity and the equilibration index Y increased linearly with V˙O2max (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 V˙O2max, enhanced O2 extraction fraction (≥90%) contributes to the remarkably high V˙O2max in endurance‐trained individuals.