Effect of upper airway CO2 on breathing in awake ponies.

This research investigates whether the carbon dioxide concentration in the upper airways of ponies can influence their breathing patterns, particularly during periods of increased inspired CO2 or higher environmental temperatures. Using a group of six ponies, the study found that increasing upper airway CO2 can reduce breathing frequency in conditions of elevated temperature, suggesting the existence of a CO2-H+ sensory mechanism in the pony’s respiratory system.

Study Design and Procedures

• The study involved six ponies that had chronic tracheostomies a month prior.
• Two protocols were used. In the first protocol, the ponies breathed room air through a cuffed endotracheal tube, with an additional smaller tube directing a mixture of prepared gases into the upper airway to artificially alter the CO2 concentration.
• In the second protocol, the ponies breathed a 6% CO2 gas mixture normally through either the entire airway or through the cuffed endotracheal tube.
• Researchers then monitored how different CO2 concentrations and environmental temperatures affected the ponies’ breathing frequency.

Findings

• Researchers found that under neutral environmental temperatures and a regular breathing frequency of 8 breaths per minute, increasing the CO2 concentration in the upper airway up to 18-20% had no effect on the ponies’ breathing frequency.
• However, when the environmental temperature was increased by 20 degrees Celsius, which raised the ponies’ breathing frequency to 50 breaths per minute, then increasing the upper airway CO2 concentration to either 6% or 18-20% significantly reduced their breathing frequency. This provides evidence that there could be a CO2-H+ sensory mechanism in the ponies’ upper airways.

Conclusion and Implications

• The research concludes that upper airway CO2 concentration can influence breathing frequency, particularly under conditions of increased environmental temperature.
• This could provide useful insights into the understanding and treatment of breathing-associated disorders in horses such as asthma and other respiratory conditions, since the CO2-H+ sensory mechanism could potentially serve as a therapeutic target.