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Objective—To investigate relationships between cough frequency and mucus accumulation, airway obstruction, and airway inflammation and to determine effects of dexamethasone on coughing and mucus score.
Animals—13 horses with recurrent airway obstruction( RAO and 6 control horses.
Procedure—6 RAO-affected and 6 control horses were stabled for 3 days. Coughing was counted for 4 hours before and on each day horses were stabled. Before and on day 3 of stabling, tracheal mucus accumulation was scored, airway obstruction was assessed via maximal change in pleural pressure (ΔPplmax), and airway inflammation was evaluated by use of cytologic examination of bronchoalveolar lavage fluid (BALF). Effects of dexamethasone (0.1 mg/kg, IV, q 24 h for 7 days) were determined in 12 RAO-affected horses.
Results—To assess frequency, coughing had to be counted for 1 hour. In RAO-affected horses, stabling was associated with increases in cough frequency, mucus score, and ΔPplmax. Control horses coughed transiently when first stabled. In RAO-affected horses, coughing was correlated with ΔPplmax, mucus score, and airway inflammation and was a sensitive and specific indicator of ΔPplmax > 6 cm H2O, mucus score > 1.0, and > 100 neutrophils/µL and > 20% neutrophils in BALF. Dexamethasone reduced cough frequency, mucus score, and ΔPplmax, but BALF neutrophil count remained increased.
Conclusions and Clinical Relevance—Because of its sporadic nature, coughing cannot be assessed accurately by counting during brief periods. In RAO-affected horses, coughing is an indicator of airway inflammation and obstruction. Corticosteroid treatment reduces cough frequency concurrently with reductions in ΔPplmax and mucus accumulation in RAO-affected horses. ( Am J Vet Res 2003;64:550–557)