Effect of hypoxia on metabolic rate in awake ponies.

The research investigates how low oxygen levels (hypoxia) affect the metabolic rate (oxygen use, VO2) in awake ponies. Key findings indicate that despite symptoms such as increased breathing and body temperature, acute hypoxia did not significantly reduce metabolic rate, unlike in smaller mammals.

Objective and setup of the research

• The study aimed to understand how low oxygen conditions, or hypoxia, impact the metabolic rate of ponies—a metabolic rate measurement referred to as VO2.
• The researchers performed tests on two different days, where ponies breathed room air for an hour and then were subjected to 5 hours of either hypoxic hypoxia or CO hypoxia.
• Hypoxic hypoxia was induced by reducing the fraction of oxygen concentration (inspired O2) to 0.126.

Results and observations

• The researchers monitored arterial PO2, which is the amount of oxygen present in arterial blood. Under normal conditions, PO2 recorded was 103 +/- 1.2 Torr. Within 5 minutes of hypoxic hypoxia, PO2 dropped to 53.1 +/- 1.8 Torr and further to 41.0 +/- 1.8 Torr after 5 hours.
• They noticed hypocapnia (decreased carbon dioxide in the blood), and alkalosis (increased blood pH)—both of which manifested over time during hypoxic hypoxia.
• Under CO hypoxia, levels of carboxyhemoglobin (a compound of hemoglobin and carbon monoxide, which reduces the oxygen-carrying capacity of blood) increased to 25% after 30 minutes and remained stable thereafter.

Impact on the metabolic rate

• There were no significant changes noted in VO2 during either form of hypoxia. This means that the ability of the ponies to utilize oxygen did not change significantly despite the hypoxic conditions.
• In 50% of the ponies, however, there were observable increases in VO2, lung ventilation, and rectal temperature, after 30 minutes of hypoxia. Some ponies also began to shiver.
• The peak values for increased pulmonary ventilation, VO2, and shivering were noted at approximately 2 hours, after which they returned towards control levels.

Conclusion

• The study concludes that unlike smaller animals, acute hypoxia doesn’t suppress a pony’s VO2.
• The symptoms such as hypermetabolism (increased metabolic rate) and hyperthermia (higher than normal body temperature) observed in some ponies during the extended hypoxic condition could indicate a temporary failure in their thermoregulation (body’s ability to control its internal temperature).