Effects of airway obstruction on transmural pulmonary artery pressure in exercising horses

Objective To determine whether laryngeal hemiplegia would increase transmural pulmonary artery pressure (TPAP). Animals 6 horses. Design Horses were studied under 5 conditions: control conditions, after induction of left laryngeal hemiplegia, during obstruction of the left nostril, after placement of an instrumented tracheostomy, and after placement of an open tracheostomy. Horses were evaluated after being given saline solution and after being given furosemide. Procedures Horses were exercised on a high speed treadmill, using a maximum speed of 13 m/s. During each exercise, airway pressures, airflow, esophageal and pulmonary artery pressures, and blood gas partial pressures were measured. Results When adjusted for horse, speed, and obstruction condition, mean TPAP (pulmonary artery pressure – esophageal pressure) and minimum TPAP were significantly lower after administration of furosemide than after administration of saline solution. In horses given saline solution, respiratory obstruction that increased intrapleural pressure significantly increased mean TPAP, and respiratory obstruction that decreased intrapleural pressure significantly decreased minimum TPAP. Conclusions Changes in intrapleural pressure appear to play an important role in pulmonary artery pressure and TPAP. Clinical Relevance Because induction of laryngeal hemiplegia did not increase TPAP, laryngeal hemiplegia is unlikely to contribute to development of exercise-induced pulmonary hemorrhage. (Am J Vet Res 1997;58:897–903)