Respiratory mechanics of horses during stepwise treadmill exercise tests, and the effect of clenbuterol pretreatment on them.

This research article studies the effects of physical exercise and clenbuterol, a bronchodilator, on the respiratory mechanics of horses. Utilizing a stepwise treadmill exercise, it also explores the correlation between the changes in gas exchange, resistance, dynamic compliance, and inertance of the horses’ respiratory systems during exercise.

Exercise Test and Measurements

• The study used Normal Standardbred horses as subjects, these were put through an exercise test on a horizontal treadmill. The progression of the exercise test was divided into the speeds of – 2.4 m/sec (walk), 4.5 m/sec (slow trot), 7.0 m/sec (fast trot) and 10 m/sec (gallop) with each lasting for 2 minutes.
• Various parameters such as airflow, tidal volume, respiratory frequency, certain pressures, and arterial blood gas tensions were measured at rest and after 1 min of exercise at each step.

Effect of Clenbuterol

• Subsequently, the horses were treated with an intravenous injection of clenbuterol (0.8 microgram/kg). The same exercise test and set of measurements were performed again 10 minutes after the injection of clenbuterol.

Findings from the Experiment

• In response to exercise, there was an appreciable increase in tidal volume, respiratory frequency, airflow and pressures. Moreover, exercise resulted in decreased upper airway resistance while total pulmonary resistance remained unaltered.
• Exercise did not make a difference to inertance or dynamic compliance. Interestingly though, horses became hypoxaemic, and while galloping at 10 m/sec, they developed hypercarbia.

Clenbuterol’s Influence on Exercise Response

• Contrary to what might be expected, the treatment with clenbuterol did not change any of these measurements in response to exercise.

Conclusions and Implications

• The findings of the research hint at the occurrence of upper airway dilation during exercise. They also highlight the importance of inertial forces in the respiratory processes of horses when they perform strenuous exercises.
• This implies that these inertial forces can impact the accuracy of dynamic compliance determinations at high levels of exercise intensities.

Please note that as this study was based on a small sample size and only one drug, further research is needed to confirm and expand on these findings.