Mechanical properties of the lung in extrinsic allergic alveolitis.

The lung function of 14 patients with extrinsic allergic alveolitis caused by exposure to mouldy hay (farmer's lung) or to birds (bird fancier's lung) was studied one week and four to six weeks after the last exposure to antigen. These data, together with lung mechanics measured four weeks after antigen exposure, were compared with measurements in 34 healthy non-smoking control subjects. Shortly after exposure to antigen there were reduction in lung volumes, increased elastic recoil (reduced compliance), and varied effects on expiratory flow and reduced gas transfer. With time, lung volumes and gas transfer improved, but expiratory flow often remained decreased. The data on lung mechanics showed that reduced compliance was often found, but this increased recoil did not always produce high airflow indicating increased upstream airways resistance. Patients with a longer duration of the illness tended to have increased compliance (reduced recoil) and low airflow. These results show that the described pathological changes of airway involvement, fibrosis, and emphysema in allergic alveolitis are manifest in the lung function of patients with the disease.