Determinants of oxygen delivery and hemoglobin saturation during incremental exercise in horses.

The research explores the factors contributing to increased oxygen consumption and hemoglobin saturation during progressive exercise in horses. The study shows that boosts in cardiac output, hemoglobin concentration, and oxygen extraction are key to enhancing oxygen consumption during exercise. Additionally, the research finds pH decrease appears to be accountable for necessary shifts in oxygen-hemoglobin binding, permitting optimal oxygen extraction during exercise.

Methodology

• This study was conducted on seven unfit adult mares.
• The horses performed one preliminary exercise test and two experimental exercise tests.
• Arterial and mixed venous blood samples were obtained, along with hemodynamic measurements, during the last half minute of every exercise test step. This allowed for measurements of variables such as oxygen pressure, hemoglobin concentration, hemoglobin saturation, and determinants of acid-base state including protein concentration, electrolyte concentration, and carbon dioxide pressure.

Results

• The study found that increased oxygen consumption during exercise was facilitated by significant increases in cardiac output, hemoglobin concentration, and the expansion of the arteriovenous difference in oxygen.
• During exercise, arterial and venous pH, partial pressure of oxygen in arteries and veins decreased, while the arterial carbon dioxide partial pressure, bicarbonate concentrations decreased significantly. On the other hand, venous carbon dioxide pressure increased.
• Arterial and venous sodium and potassium concentrations, strong ion difference, and venous lactate concentration significantly increased during exercise.

Conclusions

• Increases in cardiac output, hemoglobin concentration, and oxygen extraction were found to contribute equally to increased oxygen consumption during exercise.
• A higher carbon dioxide pressure did not independently contribute to a shift in the oxyhemoglobin dissociation curve in venous blood, but a lower partial pressure of carbon dioxide in the arteries helped facilitate oxygen loading.
• The shift of the oxyhemoglobin dissociation curve had minimal effect on oxygen extraction due to its convergence at lower values of oxygen pressure.
• The decrease in pH was found to be responsible for the rightward shift of the oxyhemoglobin dissociation curve, which might be necessary to allow optimal oxygen extraction at high blood flows achieved during exercise.