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

Abstract

Effect of head and neck position on intrathoracic pressure and arterial blood gas values in Dutch Warmblood riding horses during moderate exercise.
Janneke Sleutjens, DVM; Esmee Smiet, DVM; René van Weeren, DVM, PhD; Johannes van der Kolk, DVM, PhD; Willem Back, DVM, PhD; Inge D. Wijnberg, DVM, PhD
Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, NL-3584 CM, The Netherlands. (Sleutjens, Smiet, van Weeren, van der Kolk, Back, Wijnberg)
Presented in abstract form at the World Equine Airway Symposium, Bern, Switzerland, August 2009.

The authors thank Anna Elgersma for designing the analytic software, Freek Heuyerjans for help with equations, and Hans Vernooij for statistical advice.

Objective - To evaluate the effect of various head and neck positions on intrathoracic pressure and arterial oxygenation during exercise in horses.
Animals - 7 healthy Dutch Warmblood riding horses.

Procedures - The horses were evaluated with the head and neck in the following predefined positions: position 1, free and unrestrained; position 2, neck raised with the bridge of the nose aligned vertically; position 4, neck lowered and extremely flexed with the nose pointing toward the pectoral muscles; position 5, neck raised and extended with the bridge of the nose in front of a vertical line perpendicular to the ground surface; and position 7, neck lowered and flexed with the nose pointing towards the carpus. The standard exercise protocol consisted of trotting for 10 minutes, cantering for 4 minutes, trotting again for 5 minutes, and walking for 5 minutes. An esophageal balloon catheter was used to indirectly measure intrathoracic pressure. Arterial blood samples were obtained for measurement of Pao2, Paco2, and arterial oxygen saturation.

Results - Compared with when horses were in the unrestrained position, inspiratory intrathoracic pressure became more negative during the first trot (all positions), canter and second trot (position 4), and walk (positions 4 and 5). Compared with when horses were in position 1, intrathoracic pressure difference increased in positions 4, 2, 7, and 5; Pao2 increased in position 5; and arterial oxygen saturation increased in positions 4 and 7.

Conclusions and Clinical Relevance - Position 4 was particularly influential on intrathoracic pressure during exercise in horses. The effects detected may have been caused by a dynamic upper airway obstruction and may be more profound in horses with upper airway disease.