Effect of head and neck position on intrathoracic pressure and arterial blood gas values in Dutch Warmblood riding horses during moderate exercise.

The research investigates how different head and neck positions affect the intrathoracic pressure (pressure within the chest cavity), and blood oxygenation levels in Dutch Warmblood riding horses when they’re exercising moderately.

Research Methodology

• Seven healthy Dutch Warmblood riding horses were involved in the study. The horses were studied in five distinct head and neck positions: unrestrained, raised neck with vertical snout alignment, lowered and flexed neck with snout towards pectoral muscles, raised and stretched neck with snout in front of a vertical line perpendicular to the ground, lowered and flexed neck with snout towards the carpus.
• The horses were given a standard exercise regimen that involved 10 minutes of trotting, 4 minutes of cantering, 5 minutes of trotting again, and afterward 5 minutes of walking.
• Intrathoracic pressure (pressure within the chest or thoracic cavity) was measured indirectly using an esophageal balloon catheter.
• Arterial blood samples were taken to measure Pao(2), Paco(2), and arterial oxygen saturation. Pao(2) represents oxygen partial pressure, Paco(2) represents carbon dioxide partial pressure, and arterial oxygen saturation refers to the degree of oxygen-bound haemoglobin in the blood.

Research Findings

• They found that compared to when horses were in the unrestrained position, the intrathoracic pressure decreased (became more negative) during the first trot (all positions), canter, and second trot (when the neck was lowered and extremely flexed), and walk (when the neck was raised, extended or lowered, and flexed). This means there was a drop in the pressure in the horse’s chest cavity during these exercises.
• They established that when compared to the unrestrained position, the intrathoracic pressure difference expanded in certain postures; Pao(2) increased when the neck was raised and extended, while arterial oxygen saturation increased when the neck was lowered and either extremely flexed or flexed towards the carpus.

Conclusions

• The study concluded that the most pronounced changes in intrathoracic pressure during exercise were observed when the horse’s neck was lowered and extremely flexed (position 4).
• The variations noted might be due to a dynamic upper airway obstruction, which implies the horse’s breathing may be hindered during exercise in certain head and neck positions. This could potentially have more severe implications for horses with pre-existing upper airway diseases.