Gas exchange during intense exercise in Standardbreds with earlier Rhodococcus equi pneumonia.

The research investigated the possible long-term effects of Rhodococcus equi pneumonia on pulmonary function and gas exchange in Standardbred horses during intense exercise. The study found that horses with a history of this pneumonia as foals showed no impairment in gas exchange during high-intensity exercises when compared to healthy Standardbreds.

Methodology

• The study involved seven Standardbred foals that had been diagnosed with R. equi pneumonia, which was treated successfully. When the horses reached three years of age and were undergoing professional training, they were made to perform an inclined treadmill exercise test that had four different speeds.
• Samples from the horses were collected when a steady state in the volume of oxygen consumed per unit during exercise (VO2) was achieved.”
• Several measurements were taken including:
  • The red cell volume, heart and respiratory rates, as well as systemic and pulmonary mean arterial pressures.
  • The oxygen and carbon dioxide tensions in both the arterial and mixed venous blood were also analysed.
• Additionally, the alveolar ventilation (the quantity of fresh air reaching the alveoli per minute) and the difference in oxygen tension between the alveoli and the artery were determined.

Results and Conclusions

• The pulmonary gas exchange, or the exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries, was assessed. The ventilation-perfusion distribution, or the distribution of ventilation and blood flow in the lung, was estimated using the multiple inert gas elimination technique.
• The degree of ventilation-perfusion mismatch (variation in the rate of ventilation relative to perfusion) and shunt (blood bypassing the lungs) were determined. Additionally, the degree of diffusion limitation or the hindrance in the exchange of gases across the alveolar capillary membrane was also calculated.
• It was found that the gas exchange in the Standardbred trotters that had previously been infected with R. equi and had been successfully treated, was not compromised during intense treadmill exercises, compared to reference values for healthy, fit Standardbreds.
• The study concludes that adult Standardbred trotters that had been diagnosed with R. equi pneumonia as foals are able to achieve adequate gas exchange even at a workload that is close to their peak volume of oxygen consumed per unit during exercise (VO2peak).