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Energetic cost of breathing, body composition, and pulmonary function in horses with recurrent airway obstruction

¹Department of Clinical Sciences, Tufts University School of Veterinary Medicine, North Grafton 01536, and ²Physics Department, School of Arts and Sciences, Bridgewater State College, Bridgewater, Massachusetts 02325

Submitted 17 June 2003 ; accepted in final form 9 February 2004

This study was conducted to determine whether horses with naturally occurring, severe chronic recurrent airway obstruction (RAO) 1) have a greater resting energy expenditure (REE) than control horses, 2) suffer body mass depletion, and 3) have significantly decreased REE after bronchodilation and, therefore, also 4) whether increased work of breathing contributes to the cachexia seen in some horses with RAO. Six RAO horses and six control horses underwent indirect calorimetric measures of REE and pulmonary function testing using the esophageal balloon-pneumotachograph method before and after treatment with ipratropium bromide, a parasympatholytic bronchodilator agent, at 4-h intervals for a 24-h period. Body condition scoring was performed, and an estimate of fat mass was determined via B-mode ultrasonography. O₂ and CO₂ fractions, respiratory airflow, respiratory rate, and pleural pressure changes were recorded, and O₂ consumption, CO₂ production, REE, pulmonary resistance, dynamic elastance, and tidal volume were calculated. In addition, we performed lung function testing and calorimetry both before and after sedation in two control horses. RAO horses had significantly lower body condition scores (2.8 ± 1.0 vs. 6.4 ± 1.2) and significantly greater O₂ consumption than controls (4.93 ± 1.30 vs. 2.93 ± 0.70 ml·kg^–1·min^–1). After bronchodilation, there was no significant difference in O₂ consumption between RAO horses and controls, although there remained evidence of residual airway obstruction. There was a strong correlation between O₂ consumption and indexes of airway obstruction. Xylazine sedation was not associated with changes in pulmonary function but did result in markedly decreased REE in controls.

indirect calorimetry; naturally occurring disease; resting energy expenditure; oxygen consumption; ipratropium bromide