Grassi B, Poole D C, Richardson R S, Knight D R, Erickson B K, Wagner P D
Department of Medicine, University of California, San Diego, La Jolla 92093-0623, USA.
J Appl Physiol (1985). 1996 Mar;80(3):988-98. doi: 10.1152/jappl.1996.80.3.988.
Muscle O2 uptake (VO2) kinetics in response to an augmented energetic requirement (on-transition) has never been directly determined in humans. We have developed a constant-infusion thermodilution technique that allowed rapid measurements of leg blood flow (Qleg) and, in conjunction with frequent serial measurement of arteriovenous O2 content difference across the leg [(Ca - Cv)O2leg], permitted the determination of the VO2 of the leg (VO2leg) at 3- to 4-s time intervals. VO2leg kinetics during the on-transition was taken as a close approximation of muscle VO2 (VO2mus) kinetics. Alveolar VO2 (VO2A), Qleg, leg O2 delivery [(Q.CaO2leg)], (Ca - Cv)O2leg, and VO2leg kinetics were determined in six trained subjects [age 22.8 +/- 4.4 (SD) yr; maximal O2 uptake 59.1 +/- 5.3 ml.kg-1.min-1] during the transition from unloaded pedaling to a workload (loaded pedaling; LP) (183 +/- 20 W) well below the previously determined ventilatory threshold. For all variables, two distinct phases were recognized. During the first 10-15 s of loaded pedaling (phase I), VO2A, Qleg, and (Q.CaO2)leg increased rapidly, whereas VO2leg increased only slightly and (Ca - Cv)O2leg actually decreased. After phase I, all variables showed a monoexponential increase (phase II), with similar time courses [slightly faster for (Ca - CV)O2leg]. In a consideration of both phases, the half times of the responses among variables were not significantly different: 25.5 +/- 2.6 s for VO2A, 26.6 +/- 7.6 s for Qleg, 26.9 +/- 8.3 s for (Q.CaO2leg, 23.5 +/- 1.3 s for (Ca - Cv)O2leg, and 27.9 +/- 5.7 s for VO2leg. We conclude that during the on-transition the kinetics of VO2A and VO2leg, as measured by these methods, are similar. The analysis of the early phase (first 10-15 s) of the on-transition indicates that bulk delivery of O2 to the working muscles is not limiting VO2leg kinetics. However, the present results cannot discriminate between maldistribution of blood flow/VO2 vs. inertia the intracellular oxidative machinery as the limiting factor.
在人类中，从未直接测定过肌肉对能量需求增加（起始转换）的氧气摄取（VO₂）动力学。我们开发了一种持续输注热稀释技术，该技术能够快速测量腿部血流量（Qleg），并结合对腿部动静脉血氧含量差[（Ca - Cv）O₂leg]的频繁连续测量，从而能够以3至4秒的时间间隔测定腿部的VO₂（VO₂leg）。起始转换期间的VO₂leg动力学被视为肌肉VO₂（VO₂mus）动力学的近似值。在6名训练有素的受试者[年龄22.8±4.4（标准差）岁；最大摄氧量59.1±5.3 ml·kg⁻¹·min⁻¹]从无负荷蹬车转换到远低于先前测定的通气阈值的工作负荷（负荷蹬车；LP）（183±20 W）过程中，测定了肺泡VO₂（VO₂A）、Qleg、腿部氧气输送[（Q·CaO₂leg）]、（Ca - Cv）O₂leg和VO₂leg动力学。对于所有变量，可识别出两个不同阶段。在负荷蹬车的最初10 - 15秒（阶段I），VO₂A、Qleg和（Q·CaO₂）leg迅速增加，而VO₂leg仅略有增加，（Ca - Cv）O₂leg实际上下降。在阶段I之后，所有变量均呈单指数增加（阶段II），时间进程相似[（Ca - CV）O₂leg略快]。综合考虑两个阶段，各变量反应的半衰期无显著差异：VO₂A为25.5±2.6秒，Qleg为26.6±7.6秒，（Q·CaO₂leg为26.9±8.3秒，（Ca - Cv）O₂leg为23.5±1.3秒，VO₂leg为27.9±5.7秒。我们得出结论，在起始转换期间，通过这些方法测量的VO₂A和VO₂leg动力学相似。起始转换早期阶段（最初10 - 15秒）的分析表明，向工作肌肉的大量氧气输送并非VO₂leg动力学的限制因素。然而，目前的结果无法区分血流量/VO₂分布不均与细胞内氧化机制的惰性作为限制因素。
