Pulmonary function measurements during repeated environmental challenge of horses with recurrent airway obstruction (heaves)

Objectives-To evaluate the degree of reproducibility in clinical variables, blood gas measurements, and lung function variables, and the changes in these variables caused by exposure to moldy hay in naturally sensitized and control horses. Procedure-The magnitude of variation in arterial blood gas and pulmonary function measurements were evaluated in a model of naturally acquired heaves. Horses with heaves and similarly aged control horses were studied prior to moldy hay challenge and again after the horses with heaves manifested clinical signs oi airway obstruction. This cycle of testing was repeated 3 times to determine the variation of the before and after challenge measurements. Variables evaluated for repeatability included: clinical score; arterial O-2 and CO2 tensions; pulmonary function variables, such as breathing rate (f), tidal volumes, and flow rates; lung resistance (RL); dynamic compliance; and work of breathing (W-b). Results-Before challenge, significant differences observed between control horses and horses with heaves included clinical score, expiratory flow rate at near-end expiration, RL, and W-b. After exposure to moldy hay, variables measured in control horses were largely unchanged. However, in the afflicted horses, significant changes were observed for clinical score,arterial O-2 and CO2 tensions, breathing; rate, peak tidal inspiratory and expiratory flow rates, dynamic compliance, RL, and W-b, compared with prechallenge values and with control horses' postchallenge values. Analysis of the data revealed few statistically significant differences between repeats of challenges. Conclusion-Horses afflicted with heaves manifest air way obstruction that can be measured in repeatable fashion.