The airway response of horses with recurrent airway obstruction (heaves) to aerosol administration of ipratropium bromide.

The airway response to aerosol administration of the anticholinergic agent ipratropium bromide was determined in 8 horses with recurrent airway obstruction (heaves). The reversibility of airway obstruction was confirmed by measuring lung function before and during stabling; and by determining the response to atropine administration (0.02 mg/kg bwt intravenously). The dose-response to ipratropium bromide was determined using a Williams square design experiment in which 25, 50 or 75 micrograms ipratropium bromide/ml (4 ml/100 kg bwt) or the same volume of vehicle was administered to each horse by nebulisation. Lung function was measured before and 1 and 4 h after nebulisation. Vehicle had no effect on lung function. Ipratropium decreased the maximal change in pleural pressure during tidal breathing (delta Pplmax) and pulmonary resistance (RL) and increased dynamic compliance (Cdyn). At the 1 h measurement period, the effect on RL and Cdyn was dose-dependent. A separate experiment demonstrated that the duration of action of ipratropium was between 4 and 6 h.