A preliminary study on the role of the equine guttural pouches in selective brain cooling.

The research paper explores a hypothesis that horses use their guttural pouches as a mechanism to cool their brains during strenuous activity. Through a series of experiments on cadavers and a live, anaesthetized horse, the study demonstrates that ventilating these pouches does, in fact, significantly lower the temperature of the blood in the horse’s internal carotid arteries (ICA), which supply blood to the brain.

Study Background

• The paper begins by noting that horses lack a well-known, robust mechanism for cooling their brains. However, the researchers propose a theory that horses use their guttural pouches—a large air-filled section of the horse’s auditory tube—for this purpose.
• This preliminary study examines the effect of ventilating the guttural pouches on the temperature of the horse’s internal carotid arteries (ICA), which supply blood to the brain.

Methodology

• The team carried out initial experiments on nine horse cadavers. They simulated blood flow using warmed saline pumped through the body.
• Subsequent experiments were conducted on an anaesthetized live horse, in which the researchers ventilated the guttural pouch and monitored the ICA temperatures.

Results and Interpretation

• The results showed that whenever the guttural pouch was ventilated using cooled or warmed air, or warmed humidified air, the temperature within the ICA dropped considerably in both the cadavers and the anaesthetized horse. The temperature drops ranged from 0.4 to 5 degrees Celsius, depending on the conditions.
• When the team simulated respiration, there were ICA temperature drops of 0.9-2.3 degrees Celsius in two out of five cadavers tested. This showed that the large pharyngeal orifices of the guttural pouches can let enough respiratory air to ventilate the pouch.
• The researchers noted that a single, unbranching 13cm portion of the ICA is exposed on the wall of each guttural pouch.
• The findings of this study suggest that when horses exercise heavily, they could utilize their guttural pouches to cool blood within the ICA, which is then sent to the brain.