Hicks James W, Wang Tobias
Departmemt of Ecology and Evolutionary Biology, University of California, Irvine, CA, USA.
Section for Zoophysiology, Department of Bioscience, Aarhus University, Universitetsparken, 8000 Aarhus C, Denmark.
Comp Biochem Physiol A Mol Integr Physiol. 2021 Apr;254:110888. doi: 10.1016/j.cbpa.2020.110888. Epub 2020 Dec 25.
Elevations of metabolic rate, for example during physical activity, elicit immediate and coordinated respiratory and cardiovascular responses that ensure adequate diffusive and convective fluxes of O from the environment (water or air) to the mitochondria where ATP is produced. The same physiological responses also provide for CO to be removed in the opposite direction. There is significant variation in the morphology of the cardiovascular and respiratory structures among vertebrates, and a varying reliance on aerobic versus anaerobic metabolism to power activity. However, gas exchange in all vertebrates can be decribed as diffusive and convective steps in series, and we summarise data on the diffusive step across the respiratory surface of gills and lungs in this graphical review. Based on relatively constant arterial partial pressures of O and CO from rest to near maximal levels of physical activity, we conclude that under normoxic conditions, the diffusive step within the respiratory system exert no or small limitations for either O or CO exchange at or near maximal rate of oxygen consumption (VOmax). However, there are exceptions, such as the exercise-induced arterial hypoxemia (EIAH) in racehorses, and elite human athletes. Our analysis also indicates that exercise-induced arterial hypercapnia (i.e. a rise in arterial PCO) at or near VOmax is not common among vertebrates. Across the vertebrate spectrum, the diffusive and perfusive conductances (D/βQ) of water and air-breathing vertebrates are well-matched to maximal rates of gas exchange, and diffusion is not a limiting factor when aerobic metabolism increases.
代谢率的升高，例如在体育活动期间，会引发即时且协调的呼吸和心血管反应，以确保氧气从环境（水或空气）到产生三磷酸腺苷（ATP）的线粒体有足够的扩散和对流通量。同样的生理反应也能使二氧化碳以相反方向排出。脊椎动物的心血管和呼吸结构形态存在显著差异，对有氧代谢和无氧代谢来为活动提供能量的依赖程度也各不相同。然而，所有脊椎动物的气体交换都可以描述为串联的扩散和对流步骤，在此图表综述中，我们总结了关于鳃和肺呼吸表面扩散步骤的数据。基于从休息到接近最大体育活动水平时相对恒定的动脉血氧分压和二氧化碳分压，我们得出结论，在常氧条件下，呼吸系统内的扩散步骤在氧气消耗最大速率（VO₂max）时或接近该速率时，对氧气或二氧化碳交换没有或仅有很小的限制。然而，也有例外情况，比如赛马和优秀人类运动员中的运动诱发动脉低氧血症（EIAH）。我们的分析还表明，在VO₂max时或接近VO₂max时，运动诱发动脉高碳酸血症（即动脉血二氧化碳分压升高）在脊椎动物中并不常见。在整个脊椎动物范围内，水栖和空气呼吸脊椎动物的扩散和灌注传导率（D/βQ）与最大气体交换速率匹配良好，当有氧代谢增加时，扩散不是限制因素。
