Extreme derangements of acid-base balance in exercise: Advantages and limitations of the Stewart analysis

The acid-base analysis method described by Stewart (1981) was applied to the greyhound, an animal that undergoes large changes in intra- and extracellular hydrogen ion concentrations during a race. Increases in plasma [H+] especially during the first 15 min of recovery, induced by increases in lactate concentration in the plasma, were reduced by lowering of PCO2 (hyperventilation) and removal of Cl- from the plasma. [H+] calculated by the Stewart method is similar to that measured directly with a pH electrode when the strong ion difference is within 10 meq/L, of resting values (approximate to 40 meq/L); thus the measured independent variables were sufficient to account for the [H+] using the Stewart analysis. When the strong ion difference became lower than 30 meq/L, increased variability between measured and calculated [H+] occurred. An error analysis demonstrated the importance of minimizing measurement error of all independent variables, including as many strong and weak electrolytes as possible in the analyses, using the most accurate dissociation constants possible, and understanding the dissociation behavior of the weak electrolytes, especially the plasma proteins, when using the Stewart analysis. The Stewart method of analyzing acid-base balance can contribute to improved training methods for obtaining maximum exercise performance.