Inflammatory airway disease (IAD) describes a condition of non-septic inflammation of the lower airways in horses. The disease occurs principally in adult horses and has an apparent worldwide distribution. The most common clinical signs of IAD include poor athletic performance, cough, and/or increased tracheobronchial secretions. Inconsistencies in disease definition, sampling methods and laboratory techniques have limited comparisons between studies.
Essential criteria for diagnosis of IAD, as stated by the 2007 ACVIM consensus statement, include documentation of non-septic inflammation or pulmonary dysfunction based on evidence of lower airway obstruction, airway hyperresponsiveness, or impaired blood gas exchange at rest or during exercise. A definitive diagnosis is currently based on bronchoalveolar lavage fluid (BALF) cytology and/or pulmonary function testing (PFT).
The correlation between BALF cytology and pulmonary function testing (PFT) has been poorly defined. The primary aim of this study was to characterise the relationship between BALF cytology and PFT with histamine bronchoprovocation methods in a population of sedentary asymptomatic horses. The principal hypothesis was that a strong association exists between these two diagnostic methods.
On the basis of BALF cytology the majority of horses in this study had lower airway inflammation as defined by published criteria. The study thus highlights that normal values for cell proportions in BALF might vary between populations of horses.
Despite an obvious overlap between inflammatory BALF cytological profiles and airway hyperresponsiveness, no statistical association between these two diagnostic methods was found in this population of horses. The secondary aim was to assess the reliability of the Open Pleth™ PFT system Acceptable reliability {ICC: 0.655 (95% CI: 0.098, 0.952; significance: 0.011)}) was demonstrated using the Flowmetrics Plethysmography™ system with histamine bronchoprovocation.
In conclusion, airway inflammation and airway hyperreactivity are loosely related to each other in this population of horses. The presence of inflammatory cells does not necessarily predict airway hyperresponsiveness on the basis of histamine bronchoprovocation. Likewise, airway hyperresponsiveness can occur in the absence of a BALF inflammatory profile. Further investigation of other potential factors such as inherited abnormalities of smooth muscle contractility, airway wall remodelling, autonomic dysfunction, and the presence of inflammatory cell mediators in bronchoalveolar lavage fluid are warranted
