Mechanical properties of the lungs and experimental asthma in conscious allergic dogs

Three allergic dogs were trained to swallow an esophageal balloon, breathe through a tracheostomy tube, and stand quietly in a wooden stall. The mechanical properties of their lungs were measured reproducibly over many months. Average values were: pulmonary resistance 1.33 cmH2O/l per s, static lung compliance 104 ml/cmH2O, and functional residual capacity 982 ml. In two dogs inhalation of histamine aerosol caused a 374% increase in resistance; inhalation of Ascaris suum aerosol caused a 307% increase in resistance. The increased resistance was associated with mild-to-moderate respiratory distress and slightly increased functional residual capacity. Aerosols of isoproterenol or atropine sulfate inhibited the increased resistance. We conclude that the conscious allergic dog is a suitable subject for the long-term study of asthma. Our present results are consistent with our earlier findings in anesthetized dogs, that a vagal reflex is involved in acute bronchomotor responses to inhalation of histamine as well as specific antigen.