Submitted on June 17, 2003
Accepted on February 9, 2004
Energetic cost of breathing, body composition, and pulmonary function in horses with recurrent airway obstruction
Melissa R Mazan1*, Edward F Deveney2, Shane DeWitt1, Daniela Bedenice1, and Andrew Hoffman1
1 Clinical Sciences, Tufts University School of Veterinary Medicine, N. Grafton, MA, USA
2 Physics Department, Bridgewater State College, Bridgewater, MA, USA
* To whom correspondence should be addressed. E-mail: melissa.mazan{at}tufts.edu.
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, 3) have significantly decreased REE after bronchodilation and therefore, 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-hour intervals for a 24-hour period. Body condition scoring was performed, and an estimate of fat mass was determined using 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 v. 6.4 ± 1.2), and significantly greater VO2 than controls (4.93±1.30 mls/kg/min v. 2.93 ± 0.70). After bronchodilation, there was no significant difference in VO2 between RAO horses and controls, although there remained evidence of residual airway obstruction. There was a strong correlation between oxygen consumption and indices of airway obstruction. Xylazine sedation was not associated with changes in pulmonary function, but did result in markedly decreased REE in controls.
