PULMONARY-FUNCTION MEASUREMENTS DURING REPEATED ENVIRONMENTAL CHALLENGE OF HORSES WITH RECURRENT AIRWAY-OBSTRUCTION (HEAVES)

Objectives-To evaluate the degree of reproducibility in clinical varia bles, blood gas measurements, and lung function variables, and the cha nges in these variables caused by exposure to moldy hay in naturally s ensitized 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 simila rly 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. Variable s evaluated for repeatability included: clinical score; arterial O-2 a nd CO2 tensions; pulmonary function variables, such as breathing rate (f), tidal volumes, and flow rates; lung resistance (RL); dynamic comp liance; and work of breathing (W-b). Results-Before challenge, signifi cant differences observed between control horses and horses with heave s included clinical score, expiratory flow rate at near-end expiration , RL, and W-b. After exposure to moldy hay, variables measured in cont rol horses were largely unchanged. However, in the afflicted horses, s ignificant changes were observed for clinical score,arterial O-2 and C O2 tensions, breathing; rate, peak tidal inspiratory and expiratory fl ow 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 repeat s of challenges. Conclusion-Horses afflicted with heaves manifest air way obstruction that can be measured in repeatable fashion.