Effect of upper airway carbon dioxide on ventilation and blood gases in the awake pony.

The research paper investigates the impact of increased carbon dioxide concentrations in the respiratory tract on the breathing and arterial blood gases of an awake pony. Results show that the increased carbon dioxide levels mildly changed the breathing pattern and enhanced arterial oxygen pressure.

Experiment Methodology

• The study primarily focused on evaluating the effects of increased upper airway Carbon dioxide (CO2) on the pulmonary and cardiovascular health of ponies. Ponies were chosen based on their availability and the researchers’ experience working with them.
• Researchers increased CO2 concentrations during the exhalation phase in the upper half of the trachea, pharynx, and nasal sinuses of the ponies.
• To execute this, pure CO2 (100%) was injected into the mid-part of the trachea by using a chronically implanted transcutaneous cannula. This was done during the initial part of the pony’s expiration.
• This method was designed to avoid any exogenous CO2 from reaching the lungs and absorbing into the arterial blood, consequently elevating upper airway CO2 during exhalation.
• The testing phase consisted of twelve experiments performed on six ponies. They monitored the effects of elevated upper airway CO2 of 2%, 4%, and 6% above the standard CO2 levels during expiration.

Findings

• The study showed that the size of the breath (tidal volume) increased relative to the increase in CO2 levels in the upper airway. This reflected a change in breathing pattern during the CO2 exposure.
• However, despite an increased tidal volume, the total amount of air inhaled and exhaled within one minute (total ventilation) remained unchanged from the baseline measures that were recorded while the pony was breathing normal room air, suggesting that even though the breathing pattern might have been altered slightly, the overall intake and output of air was the same.
• An unexpected outcome from the study was that the pressure of oxygen in arterial blood (arterial PO2) also rose during the administration of CO2 in the upper airway, with a mean increase of 6 Torr at the +6% CO2 exposure. This suggests a possible enhancement in the oxygenation of blood under these increased CO2 conditions.

Conclusions

• The research concluded that the elevated levels of CO2 in the upper airway led to slight alterations in a pony’s breathing pattern by increasing the tidal volume.
• Additionally, the arterial blood gases were affected, resulting in an increase in arterial PO2, suggesting enhanced oxygenation during increased CO2 exposure.
• However, the total ventilation or the overall amount of air inhaled and exhaled by the ponies within a minute remained unaffected.