Constable P D
College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
J Appl Physiol (1985). 1997 Jul;83(1):297-311. doi: 10.1152/jappl.1997.83.1.297.
The Henderson-Hasselbalch equation and Stewart's strong ion model are currently used to describe mammalian acid-base equilibria. Anomalies exist when the Henderson-Hasselbalch equation is applied to plasma, whereas the strong ion model does not provide a practical method for determining the total plasma concentration of nonvolatile weak acids ([Atot]) and the effective dissociation constant for plasma weak acids (Ka). A simplified strong ion model, which was developed from the assumption that plasma ions act as strong ions, volatile buffer ions (HCO-3), or nonvolatile buffer ions, indicates that plasma pH is determined by five independent variables: PCO2, strong ion difference, concentration of individual nonvolatile plasma buffers (albumin, globulin, and phosphate), ionic strength, and temperature. The simplified strong ion model conveys on a fundamental level the mechanism for change in acid-base status, explains many of the anomalies when the Henderson-Hasselbalch equation is applied to plasma, is conceptually and algebraically simpler than Stewart's strong ion model, and provides a practical in vitro method for determining [Atot] and Ka of plasma. Application of the simplified strong ion model to CO2-tonometered horse plasma produced values for [Atot] (15.0 +/- 3.1 meq/l) and Ka (2.22 +/- 0.32 x 10(-7) eq/l) that were significantly different from the values commonly assumed for human plasma ([Atot] = 20.0 meq/l, Ka = 3.0 x 10(-7) eq/l). Moreover, application of the experimentally determined values for [Atot] and Ka to published data for the horse (known PCO2, strong ion difference, and plasma protein concentration) predicted plasma pH more accurately than the values for [Atot] and Ka commonly assumed for human plasma. Species-specific values for [Atot] and Ka should be experimentally determined when the simplified strong ion model (or strong ion model) is used to describe acid-base equilibria.
亨德森 - 哈塞尔巴尔赫方程和斯图尔特的强离子模型目前用于描述哺乳动物的酸碱平衡。当将亨德森 - 哈塞尔巴尔赫方程应用于血浆时存在异常情况，而强离子模型并未提供一种实用方法来确定非挥发性弱酸的总血浆浓度（[Atot]）以及血浆弱酸的有效解离常数（Ka）。一种简化的强离子模型是基于血浆离子可作为强离子、挥发性缓冲离子（HCO₃⁻）或非挥发性缓冲离子的假设而开发的，该模型表明血浆pH由五个独立变量决定：二氧化碳分压（PCO₂）、强离子差、单个非挥发性血浆缓冲物质（白蛋白、球蛋白和磷酸盐）的浓度、离子强度和温度。简化的强离子模型从根本层面传达了酸碱状态变化的机制，解释了将亨德森 - 哈塞尔巴尔赫方程应用于血浆时出现的许多异常情况，在概念和代数上比斯图尔特的强离子模型更简单，并且提供了一种用于确定血浆[Atot]和Ka的实用体外方法。将简化的强离子模型应用于经二氧化碳平衡仪处理的马血浆时，得到的[Atot]值（15.0±3.1 毫当量/升）和Ka值（2.22±0.32×10⁻⁷ 当量/升）与通常假定的人血浆值（[Atot]=20.0 毫当量/升，Ka = 3.0×10⁻⁷ 当量/升）有显著差异。此外，将实验测定的[Atot]和Ka值应用于已发表的数据（已知的马的PCO₂、强离子差和血浆蛋白浓度）时，预测马血浆pH的准确性高于通常假定的人血浆[Atot]和Ka值。当使用简化的强离子模型（或强离子模型）描述酸碱平衡时，应通过实验确定特定物种的[Atot]和Ka值。
