Relationships between equine airway reactivity measured by flowmetric plethysmography and specific indicators of airway inflammation in horses with suspected inflammatory airway disease.

This research investigates the correlation between airway reactivity, determined by flowmetric plethysmography and histamine bronchoprovocation, and airway inflammation in horses suffering from suspected inflammatory airway disease (IAD). The study reveals a lack of significant agreement between these measurements in horses presented with unexplained poor performance or chronic cough, suggesting potential underdiagnosis of IAD if airway reactivity testing is not conducted.

Research Methodology and Sample

• The study was conducted as a prospective clinical trial, where 45 predominantly young Standardbred racehorses exhibiting unexplained poor performance or chronic cough were chosen.
• All selected horses underwent a series of tests, including endoscopic evaluation, tracheal wash, flowmetric plethysmography accompanied by histamine bronchoprovocation, and bronchoalveolar lavage (BAL).
• The response to histamine was gauged by computing PC35. This is the concentration of nebulized histamine provoking an increment of 35% in Δflow (change in airflow).

Key Findings

• No significant correlation was observed between the histamine response and cell populations in BAL cytology.
• When airway hyperreactivity (AHR) was defined as a Δflow increase of at least 35% at a histamine concentration of less than 6 mg/ml, 24 of the 45 horses, that is 53%, were identified as having AHR.
• Out of all the horses, 73% had either abnormal BAL cytology or AHR and were hence, diagnosed with IAD.
• For horses diagnosed with IAD, 27% had abnormal BAL, 33% had AHR, and 39% had both.”

Conclusions

• The research concluded that there was no parallelism between airway reactivity and BAL cytology in this specific group of horses suffering from unexplained poor performance and/or chronic cough.
• This indicates that a failure to consistenly include tests of airway reactivity while diagnosing could result in underdiagnosis of Inflammatory Airway Disease (IAD), particularly in young Standardbred racehorses that exhibit clinical signs indicative of IAD.