Central circulatory and peripheral O2 extraction changes as interactive facilitators of pulmonary O2 uptake during a repeated high-intensity exercise protocol in humans

It has frequently been demonstrated that prior high-intensity exercise facilitates pulmonary oxygen uptake \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$({\dot{V}\hbox{O}_2})$$\end{document} response at the onset of subsequent identical exercise. To clarify the roles of central O2 delivery and/or peripheral O2 extraction in determining this phenomenon, we investigated the relative contributions of cardiac output (CO) and arteriovenous O2 content difference \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\hbox{a-}{\bar{\rm v}\hbox{DO}_2})$$\end{document} to the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}\hbox{O}_2}$$\end{document} transient during repeated bouts of high-intensity knee extension (KE) exercise. Nine healthy subjects volunteered to participate in this study. The protocol consisted of two consecutive 6-min KE exercise bouts in a supine position (work rate 70–75% of peak power) separated by 6 min of rest. Throughout the protocol, continuous-wave Doppler ultrasound was used to measure beat-by-beat CO (i.e., via simultaneous measurement of stroke volume and the diameter of the arterial aorta). The phase II \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}\hbox{O}_2}$$\end{document} response was significantly faster and the slow component (phase III) was significantly attenuated during the second KE bout compared to the first. This was a result of increased CO during the first 30 s of exercise: CO contributing to 100 and 56% of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}\hbox{O}_2}$$\end{document} speeding at 10 and 30 s, respectively. After this, the contribution of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox{a-}{\bar{\rm v}\hbox{DO}_2}$$\end{document} became increasingly more predominant: being responsible to an estimated 64% of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}\hbox{O}_2}$$\end{document} speeding at 90 s, which rose to 100% by 180 s. This suggests that, while both CO and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox{a-}{\bar{\rm v}\hbox{DO}_2}$$\end{document} clearly interact to determine the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}\hbox{O}_2}$$\end{document} response, the speeding of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}\hbox{O}_2}$$\end{document} kinetics by prior high-intensity KE exercise is predominantly attributable to increases in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox{a-}{\bar{\rm v}\hbox{DO}_2}$$\end{document}.