Constable P D
Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, Illinois 61802, USA.
J Appl Physiol (1985). 2001 Sep;91(3):1364-71. doi: 10.1152/jappl.2001.91.3.1364.
The strong ion approach provides a quantitative physicochemical method for describing the mechanism for an acid-base disturbance. The approach requires species-specific values for the total concentration of plasma nonvolatile buffers (A(tot)) and the effective dissociation constant for plasma nonvolatile buffers (K(a)), but these values have not been determined for human plasma. Accordingly, the purpose of this study was to calculate accurate A(tot) and K(a) values using data obtained from in vitro strong ion titration and CO(2) tonometry. The calculated values for A(tot) (24.1 mmol/l) and K(a) (1.05 x 10(-7)) were significantly (P < 0.05) different from the experimentally determined values for horse plasma and differed from the empirically assumed values for human plasma (A(tot) = 19.0 meq/l and K(a) = 3.0 x 10(-7)). The derivatives of pH with respect to the three independent variables [strong ion difference (SID), PCO(2), and A(tot)] of the strong ion approach were calculated as follows: dpH/dSID(+) = 1 + 10(pK(a)-pH)/(2.303 x [SPCO(2)10(pH-pK'(1)1 + 10(pK(a)-pH + A(tot)10(pK(a)-PH]]; dpH/dPCO(2) = S10(-pK'(1)/[2.303[A(tot)10(pH)(10(pH + 10(pK(a))(-2) - SID(+)10(-pH)]], dpH/dA(tot) = -1/[2.303[SPCO(2)10(pH-pK'(1) + SID(+)10(pK(a)-pH)]], where S is solubility of CO(2) in plasma. The derivatives provide a useful method for calculating the effect of independent changes in SID(+), PCO(2), and A(tot) on plasma pH. The calculated values for A(tot) and K(a) should facilitate application of the strong ion approach to acid-base disturbances in humans.
强离子方法提供了一种定量的物理化学方法来描述酸碱紊乱的机制。该方法需要血浆非挥发性缓冲剂总浓度（A(tot)）的物种特异性值以及血浆非挥发性缓冲剂的有效解离常数（K(a)），但尚未确定人类血浆的这些值。因此，本研究的目的是使用体外强离子滴定和二氧化碳张力测定获得的数据来计算准确的A(tot)和K(a)值。计算得到的A(tot)值（24.1 mmol/l）和K(a)值（1.05×10⁻⁷）与马血浆的实验测定值有显著差异（P < 0.05），且与人类血浆的经验假设值（A(tot) = 19.0 meq/l和K(a) = 3.0×10⁻⁷）不同。强离子方法中pH相对于三个自变量[强离子差（SID）、PCO₂和A(tot)]的导数计算如下：dpH/dSID(+) = [1 + 10^(pK(a)-pH)]²/(2.303×[SPCO₂10^(pH-pK'(1)[1 + 10^(pK(a)-pH)]² + A(tot)10^(pK(a)-PH]]；dpH/dPCO₂ = S10^(-pK'(1)/[2.303[A(tot)10^(pH)(10^(pH + 10^(pK(a))⁻² - SID(+)10^(-pH)]], dpH/dA(tot) = -1/[2.303[SPCO₂10^(pH-pK'(1) + SID(+)10^(pK(a)-pH)]], 其中S是CO₂在血浆中的溶解度。这些导数为计算SID(+)、PCO₂和A(tot)的独立变化对血浆pH的影响提供了一种有用的方法。计算得到的A(tot)和K(a)值应有助于将强离子方法应用于人类的酸碱紊乱。
