Effects of extrathoracic airway obstruction on intrathoracic pressure and pulmonary artery pressure in exercising horses

Objective-To determine whether dorsal displacement of the soft palate (DDSP ) results in pulmonary artery hypertension and leads to increases in transm ural pulmonary artery pressure (TPAP); to determine whether pulmonary hyper tension can be prevented by prior administration of furosemide; and to dete rmine whether tracheostomy reduces pulmonary hypertension. Animals-7 healthy horses. Procedure-Horses were subjected to 3 conditions (control conditions, condit ions after induction of DDSP, and conditions after tracheostomy). Horses we re evaluated during exercise after being given saline (0.9% NaCl) solution or furosemide. Results-Controlling for drug, horse, and speed of treadmill, DDSP-induced i ncrease in intrathoracic pressure was associated with a significant increas e in minimum (36 mm Hg), mean (82 mm Hg), and maximum (141 mm Hg) pulmonary artery pressure, compared with values for control horses [30, 75, and 132 mm Hg, respectively). Increases in pulmonary artery pressure did not induce concomitant increases in TPAP. Tracheostomy led to a significant reduction of minimum (53 mm Hg), and mean (79 mm Hg) TPAP pressure, compared with va lues for control horses (56 and 83 mm Hg, respectively). When adjusted for horse, speed of treadmill, and type of obstruction, all aspects of the pulm onary artery and TPAP curves were significantly decreased after administrat ion of furosemide, compared with those for horses given saline (0.9% NaCl) solution. Conclusions-DDSP was associated with increases in pulmonary artery pressure but not with increases in TPAP. Clinical Relevance-Expiratory obstructions such as DDSP are likely to resul t in pulmonary hypertension during strenuous exercise, but may not have a r ole in the pathogenesis of exercise-induced pulmonary hemorrhage.