Preexercise hypervolemia does not affect arterial hypoxemia in Thoroughbreds performing short-term high-intensity exercise.

The research investigates the effects of pre-exercise induced increase in blood volume (hypervolemia) on oxygen deficiency (arterial hypoxemia) in Thoroughbred horses undertaking high-intensity exercise. Contrary to previous findings on submaximal exercise, the results reveal no significant changes in the arterial hypoxemia in horses performing maximal exercise despite pre-exercise hypervolemia.

Research Methodology

• The study was conducted on two sets of experiments on seven exercise-trained Thoroughbred horses. These experiments, labeled “control” and “hypervolemia studies”, were performed in a random order, 7 days apart.
• In resting horses, hypervolemia was induced with NaCl (18.0 +/- 1.8% increase in plasma volume) administered via a nasogastric tube, 285-290 minutes before exercise.
• Different health measures such as blood-gas and pH measurements, concentrations of plasma protein, hemoglobin, and blood lactate were determined at rest and during incremental exercise leading to maximal exertion.

Findings and Conclusion

• The research found that arterial hypoxemia, desaturation of hemoglobin, hypercapnia (excessive carbon dioxide), acidosis (excessive acid in the body fluids), and hyperthermia (abnormally high body temperature), developed during maximal exercises of both experiments. However, there were no statistically significant differences found between the two treatments.
• The data suggests that a pre-exercise 18% expansion of plasma volume didn’t significantly affect the development and/or severity of arterial hypoxemia in Thoroughbreds performing maximal exercise.
• Even though blood lactate concentration and arterial pH remained unaffected, the pre-exercise induced expansion of blood volume considerably attenuated the exercise-induced expansion of the arterial-to-mixed venous blood oxygen content gradient.

Implications

• Contrary to previous research findings, this study found that pre-exercise hypervolemia doesn’t affect the arterial hypoxemia in horses performing high intensity exercises. This suggests that hydration status may impact horses differently depending on the intensity of their exercise.
• The study’s results suggest further avenues for examination, including looking at the longer term effects of hydration on performance, or expanding the study to include more horses or different breeds for a more general understanding of the relationship between hydration status and exercise performance.