Vogiatzis Ioannis, Zakynthinos Spyros, Boushel Robert, Athanasopoulos Dimitris, Guenette Jordan A, Wagner Harrieth, Roussos Charis, Wagner Peter D
Medical School of Athens University, Department of Critical Care and Pulmonary Services, Evangelismos Hospital, Athens, Greece.
J Physiol. 2008 May 1;586(9):2381-91. doi: 10.1113/jphysiol.2007.150128. Epub 2008 Mar 13.
Exercise is well known to cause arterial PO2 to fall and the alveolar-arterial PO2 difference(Aa PO2 ) to increase. Until recently, the physiological basis for this was considered to be mostly ventilation/perfusion ((.)VA/(.)Q) inequality and alveolar-capillary diffusion limitation. Recently, arterio-venous shunting through dilated pulmonary blood vessels has been proposed to explain a significant part of the Aa PO2 during exercise. To test this hypothesis we determined venous admixture during 5 min of near-maximal, constant-load, exercise in hypoxia (in inspired O2 fraction, FIO2 , 0.13), normoxia (FIO2 , 0.21) and hyperoxia (FIO2 , 1.0) undertaken in balanced order on the same day in seven fit cyclists ((.)VO2max, 61.3 +/- 2.4 ml kg(-1) min(-1); mean +/- S.E.M.). Venous admixture reflects three causes of hypoxaemia combined: true shunt, diffusion limitation and ((.)VA/(.)Q) inequality. In hypoxia, venous admixture was 22.8 +/- 2.5% of the cardiac output; in normoxia it was 3.5 +/- 0.5%; in hyperoxia it was 0.5 +/- 0.2%. Since only true shunt accounts for venous admixture while breathing 100% O2, the present study suggests that shunt accounts for only a very small portion of the observed venous admixture, Aa PO2 and hypoxaemia during heavy exercise.
众所周知，运动可导致动脉血氧分压（PO2）下降，肺泡-动脉血氧分压差（Aa PO2）增大。直到最近，人们认为其生理基础主要是通气/血流比值（(.)VA/(.)Q）失衡和肺泡-毛细血管扩散受限。最近，有人提出通过扩张的肺血管进行动静脉分流可解释运动期间Aa PO2增大的很大一部分原因。为验证这一假设，我们让7名健康的自行车运动员（(.)VO2max为61.3±2.4 ml·kg-1·min-1；均值±标准误）在同一天按平衡顺序分别在低氧（吸入氧分数，FIO2，0.13）、常氧（FIO2，0.21）和高氧（FIO2，1.0）条件下进行5分钟接近最大强度的恒定负荷运动，并测定运动期间的静脉血掺杂情况。静脉血掺杂反映了导致低氧血症的三种因素的综合作用：真性分流、扩散受限和(.)VA/(.)Q失衡。在低氧条件下，静脉血掺杂占心输出量的22.8±2.5%；在常氧条件下为3.5±0.5%；在高氧条件下为0.5±0.2%。由于仅真性分流可解释呼吸100%氧气时的静脉血掺杂情况，因此本研究表明，在剧烈运动期间，分流仅占所观察到的静脉血掺杂、Aa PO2增大及低氧血症的非常小的一部分。
