Forced expiration: a test for airflow obstruction in horses

The purpose of this study was to assess whether our method of inducing forc ed expiration detects small airway obstruction in horses. Parameters derive d from forced expiratory flow-volume (FEFV) curves were compared with lung mechanics data obtained during spontaneous breathing in nine healthy horses , in three after histamine challenge, and in two with chronic obstructive p ulmonary disease (COPD) pre- and posttherapy with prednisone. Parameters me asured in the healthy horses included forced vital capacity (FVC = 41.6 +/- 5.8 liters; means +/- SD) and forced expiratory flow (FEF) at various perc entages of FVC (range of 20.4-29.7 l/s). Histamine challenge induced a dose -dependent decrease in FVC and FEF at low lung volume. After therapy, lung function of the two COPD horses improved to a point where one horse had nor mal lung mechanics during tidal breathing; however, FEF at 95% of FVC (4.9 Vs) was still decreased. We concluded that FEFV curve analysis allowed the detection of induced or naturally occurring airway obstruction.