Takahashi E, Phillipson E A
Department of Medicine, University of Toronto, Ontario, Canada.
J Appl Physiol (1985). 1991 Apr;70(4):1586-92. doi: 10.1152/jappl.1991.70.4.1586.
Plasma pH has been postulated to change slowly in blood leaving the pulmonary capillaries because of the uncatalyzed dehydration of CO2. If so, there could be a difference between in vivo and in vitro arterial pH, the magnitude of which would be dependent on the venoarterial pH difference (v-aDpH). We tested this hypothesis in anesthetized dogs by changing v-aDpH by airway CO2 loading and by comparing arterial pH measured in vivo by a rapidly responding intravascular pH electrode with that measured in vitro by a conventional glass electrode. Using a multiple regression analysis, we found a small but significant contribution of venous pH to in vivo arterial pH, with a regression coefficient of 0.0718 (P less than 0.0001), suggesting a postcapillary increase of in vivo arterial pH. When carbonic anhydrase was inhibited by the administration of acetazolamide, the effect of venous pH on arterial pH was abolished, and a unique relationship between in vivo and in vitro arterial pH was established (regression coefficient 1.02; P greater than 0.05, comparison with unity). These results could be accounted for in a computer simulation of gas exchange among alveolus, plasma, and erythrocyte. We conclude that there exists a small but measurable postcapillary increase in arterial pH.
由于二氧化碳的非催化脱水作用，有人推测离开肺毛细血管的血液中血浆pH值变化缓慢。如果是这样，体内和体外动脉pH值可能会存在差异，其大小将取决于静脉-动脉pH差值（v-aDpH）。我们通过气道二氧化碳负荷改变v-aDpH，并将快速响应的血管内pH电极在体内测量的动脉pH值与传统玻璃电极在体外测量的动脉pH值进行比较，在麻醉犬身上检验了这一假设。通过多元回归分析，我们发现静脉pH值对体内动脉pH值有微小但显著的影响，回归系数为0.0718（P小于0.0001），这表明毛细血管后体内动脉pH值升高。当通过给予乙酰唑胺抑制碳酸酐酶时，静脉pH值对动脉pH值的影响消失，并且建立了体内和体外动脉pH值之间的独特关系（回归系数1.02；P大于0.05，与1比较）。这些结果可以在肺泡、血浆和红细胞之间气体交换的计算机模拟中得到解释。我们得出结论，动脉pH值在毛细血管后存在微小但可测量的升高。
