Coughing, mucus accumulation, airway obstruction, and airway inflammation in control horses and horses affected with recurrent airway obstruction.

This study explores the relationships between coughing frequency, mucus buildup, airway blockage, and inflammation in both healthy horses and those suffering from recurrent airway obstruction (RAO). It also examines the impacts of the drug dexamethasone on these symptoms. The results showed that in RAO-affected horses, stabling increased symptoms, including coughing, mucus accumulation, and airway obstruction. Additionally, while dexamethasone helped to reduce symptoms, it did not impact the elevated neutrophil count in bronchoalveolar lavage fluid, a marker of inflammation.

Research Methodology

• The researchers involved 13 horses diagnosed with recurrent airway obstruction (RAO) and 6 healthy horses (controls).
• Half of the RAO-affected and control horses were stabled for three days, and their coughing was monitored for four hours before and on each day they were stabled.
• At the start and on day 3 of stabling, the horses had their tracheal mucus accumulation scored, airway obstruction assessed via maximal change in pleural pressure (deltaPpl(max)), and airway inflammation measured using cytologic examination of bronchoalveolar lavage fluid (BALF).
• Additionally, they studied the effects of dexamethasone (administered at 0.1 mg/kg, IV, every 24 hours for seven days) on 12 RAO-affected horses.

Findings

• Researchers found that for an accurate assessment of coughing frequency, it needs to be counted for at least one hour.
• Stabling of RAO-affected horses led to increased cough frequency, higher mucus scores, and surge in deltaPpl(max) values.
• In contrast, control horses only exhibited transient coughing when first stabled.
• Coughing in RAO-affected horses showed correlation with deltaPpl(max), mucus score, and airway inflammation.
• Moreover, coughing was a sensitive and specific indicator for increases in deltaPpl(max), mucus score, and inflammation markers measured in the BALF (neutrophils >100/microL and >20%).
• Dexamethasone treatment reduced cough frequency, mucus score, and deltaPpl(max), but it did not lead to a decrease in BALF neutrophil count.

Conclusion

• The findings demonstrated that due to its intermittent nature, accurate assessment of coughing can’t be achieved during brief periods.
• For RAO-affected horses, coughing is an indicator of airway inflation and obstruction.
• The treatment with corticosteroids like dexamethasone can mitigate symptoms like cough frequency, mucus accumulation, and airway obstruction but it does not significantly reduce airway inflammation as indicated by the persistently high neutrophil count in BALF.