Partition of plasma hydrogen ion concentration changes during repeated sprints.

The research article is about a study conducted to understand the impacts of repeated sprints on blood acid-base balance in eight well-trained Arabian horses. The researchers particularly assessed the role of lactic acid in altering blood hydrogen ion concentrations (acidity) during the sprints, and they found that during an exertion like sprinting, respiration effectively offsets the metabolic effects on acidity.

Study Design and Method

• The study involved eight well-conditioned Arabian horses performing nine consecutive sprints. The research is designed to explore changes in blood acidity and lactic acid concentrations during repeated physical strain or sprints.
• Analysis of plasma sampled from the jugular veins of these horses provided data on pH levels, partial pressure of CO2 (PCO2), as well as concentrations of ions like sodium (Na+), potassium (K+), chloride (Cl-), and lactic acid.
• The researchers used Stewart’s physiological model, an approach that provides a comprehensive and intricate understanding of acid-base balance within the body, to interpret their findings.

Key Findings

• Maximum levels for the strong ion difference (SID), PCO2, and hydrogen ions concentration ([H+]) were all reached through the initial sprints. As the horses continued sprinting, the concentration of hydrogen ions started to decrease again.
• The study found that changes in total concentration of weak nonvolatile acids (Atot) and SID were contributing to the increases in hydrogen ion concentration ([H+]), but this effect was counterbalanced by a steady decrease in PCO2.
• Of all factors considered, PCO2 was the most influential determinant of [H+] during the nine repeated sprints. The expected substantial influence of lactic acid on [H+] was tempered by opposing increases in sodium and potassium ion concentrations.

Correlations and Implications

• The study revealed two statistically significant correlations: a positive correlation between decreasing hydrogen ion concentration and PCO2, and a negative correlation between hydrogen ion concentration and lactic acid.
• This strongly suggests that the normal respiratory response during intense physical activity (like sprinting) effectively compensates for the acidity induced by metabolic processes.
• Interestingly, the researchers observed a tight correlation between increasing hydrogen ion concentration and lactic acid levels during the transition from rest to sprint. This implies that during initial stages of exertion, lactic acid does indeed significantly contribute to increases in blood acidity.

Analysis – Physiological vs Empirical

• The results of the physiological (Stewart model) and empirical (statistical regression) analyses largely agreed with each other, but with some differences in emphasis.
• While the empirical regression analysis emphasized the importance of lactic acid during the period of transition from rest to work, the physiological analysis based on the Stewart model highlighted the importance of PCO2.

The research thus indicates that respiration’s role in regulating acidity levels in blood during repeated physical exertion holds greater significance than previously thought, and the established role of lactic acid as the primary effector merits reconsideration.