Hyperventilation in ponies at the onset of and during steady-state exercise.

This research studied how alveolar ventilation (breathing rate) relates to the delivery of CO2 from the lungs to the blood during exercise in ponies, and found that these factors are not closely matched during activity or transition between different types of activity. Exercise influenced the levels of CO2 in the ponies’ arterial blood and affected other health indicators, such as arterial pH.

Study Methodology

• The study involved monitoring the blood gases in ponies during moderate treadmill exercise. Exercise speeds studied were 1.8, 3, or 6 mph.
• The primary focus of the study was alveolar ventilation (VA), the process by which air is inhaled into the alveoli in the lungs, and the exchange of O2 and CO2 between the fresh air and the blood.
• The researchers also monitored aspects such as partial pressure of CO2 and O2 in arterial blood (PaCO2 and PaO2, respectively) and arterial pH (pHa), as well as mixed venous CO2 partial pressure (PVCO2).
• The study also investigated the effects of carotid body denervation (CBD), a process that removes the function of the carotid bodies, in ponies in both acute (2-4 weeks) and chronic (1-2 years) stages.

Key Findings

• Across all exercise intensities, the partial pressure of CO2 in arterial blood decreased significantly during the initial moments of exercise and remained lower than the resting rate during steady-state (continuous) exercise.
• Similar trends were observed with regard to arterial pH and O2 partial pressure in arterial blood, indicating hyperventilation in the ponies during exercise.
• Mixed venus CO2 partial pressure also saw a significant decrease within the first 30 seconds of 3 and 6 mph exercise.
• In ponies with carotid body denervation, the decrease in CO2 pressure was greater than in normal ponies but less than in acute CBD ponies.

Conclusions

• The research concluded that in ponies, the alveolar ventilation is not tightly matched to pulmonary CO2 delivery during exercise. This discrepancy is particularly noticeable during transitional periods between different levels of activity.
• Hyperpnea (abnormally deep or rapid breathing) during exercise is not mediated by the levels of CO2 in arterial or mixed venous blood.
• In normal ponies, carotid bodies can mitigate the drive for alveolar ventilation during transitional phases of exercise, thereby reducing arterial hypocapnia (a state of reduced carbon dioxide in the blood).