A simplified strong ion model for acid-base equilibria: application to horse plasma.

This research paper introduces a simplified strong ion model for acid-base balance, which considers plasma ions as either strong ions, volatile buffer ions, or nonvolatile buffer ions. The model is applied to horse plasma to reveal a more accurate prediction of plasma pH. It suggests that specific values for total plasma concentration of nonvolatile weak acids and effective dissociation constant for plasma weak acids should be experimentally determined for different species.

Background of Acid-Base Equilibria Models

• The article discusses two existing models for explaining acid-base equilibria (commonly experienced in the mammalian body): the Henderson-Hasselbalch equation and Stewart’s strong ion model.
• The authors reveal the limitations of these models when they are applied to plasma – the liquid component of blood. These limitations mainly include unrecognized anomalies and lack of a practical method for determining crucial plasma components.

A New Approach: Simplified Strong Ion Model

• The researchers propose a ‘simplified strong ion model’, a variant of Stewart’s strong ion theory, but with simpler concepts and formulas.
• This model assumes plasma ions in three categories: strong ions, volatile buffer ions (such as bicarbonate HCO-3), or nonvolatile buffer ions (like proteins).
• The plasma pH, according to this model, is determined by five independent variables: carbon dioxide partial pressure (PCO2), strong ion difference (the difference in concentration between strong cations and anions), concentration of nonvolatile plasma buffers (albumin, globulin, and phosphate), ionic strength (a measure of the concentration of all ions present in the solution), and temperature.

Application of the Simplified Strong Ion Model to Horse Plasma

• The new model was applied to horse plasma, using carbon dioxide tonometry (a method to measure gas concentration in the blood).
• The researchers found that the values for total nonvolatile weak acid concentration ([Atot]) and the dissociation constant for weak plasma acids (‘Ka’) in horse plasma are significantly different from those typically assumed for human plasma.
• Using these experimentally derived values for total nonvolatile weak acid concentration and dissociation constant, the model could accurately predict the pH of horse plasma.

Implications of the Research

• This study suggests the necessity of experimentally determining species-specific values for total plasma concentration of nonvolatile weak acids and plasma weak acids’ dissociation constant when applying the simplified strong ion model.
• The paper proposes that understanding acid-base equilibria in various bodies could benefit from species-specific data. As such, it calls for deeper investigation.