Tracheobronchial mucus viscoelasticity during environmental challenge in horses with recurrent airway obstruction

The goal of this study was to compare the rheological properties of mucus f rom horses with recurrent airway obstruction (RAO) to that from healthy con trols during environmental challenge by stabling in stalls with straw as be dding and hay as feed. We determined viscoelasticity (log G* dyn/cm(2), at 10 radian/s) and calculated mucociliary clearability index (MCI) and cough clearability index (CCI), which are derivative parameters of G* and the rat io of viscosity and elasticity measured at 1 and 100 radian/s, respectively , We also investigated the solids content of mucus, and cytology of broncho alveolar lavage fluid (BALF), Samples were obtained before (0 h) and 6, 24 and 48 h after environmental challenge. The central findings were rheologic al changes in airway mucus, which occurred over time in RAG-affected animal s, but not in controls, Mucus rheology was similar in both groups at 0 and 6 h, In RAO-affected horses, mucus viscoelasticity, as measured by log G*, increased from 2.49 +/- 0.18 dyn/cm(2) (mean +/- s.e.) at 0 h to 3.05 +/- 0 .13 dyn/cm(2) at 24 h after environmental challenge, and was accompanied by significant decreases in MCI and CCI, Percent solids of mucus did not diff er significantly between the 2 groups, nor over time. Rheological values di d not correlate with BALF cytology, We conclude that viscoelastic propertie s of tracheal mucus samples from RAO horses in remission do not differ from those of normal horses. However, environmental challenge causes clinical s igns of small airway disease and a concurrent increase in mucus viscoelasti city only in RAO horses, Therefore, we infer that unfavourable changes in m ucus rheology may contribute to stasis and accumulation of mucus in RAO hor ses in exacerbation, but not in clinical remission.