The pulmonary epithelial permeability of 99mTc-DTPA (
diethylene triamine penta acetate) was assessed in patients with
interstitial lung diseases including
radiation pneumonitis,
idiopathic interstitial pneumonia/
pulmonary fibrosis,
sarcoidosis, unclassified
interstitial pneumonia, and in healthy subjects. Pulmonary epithelial permeability was estimated by the rate constant (kep) of inhaled 99mTc-DTPA clearance from the lungs. Healthy nonsmokers had a mean kep value of 0.82 +/- 0.26% min, and their kep values were constant irrespective of age or sex. Of healthy smokers, 53% showed an increase in kep. This increase correlated with their cigarette consumption per day, but was reversible after cessation of smoking. The provocative concentration of
histamine to decrease FEV 1.0 by more than 20% caused an increase in epithelial permeability. However, its effect on permeability was transient, limited, and not dose-dependent. During lung inflation by continuous external negative pressure or by
positive end-expiratory pressure, pulmonary 99mTc-DTPA clearance was increased, suggesting changes in epithelial permeability. The patients with diffuse
interstitial lung diseases also showed increased permeability compared with healthy nonsmokers. In the patients with pre-existing
radiation pneumonitis, the mean kep value obtained from the area with infiltration on chest
X-ray films was significantly higher than that from the opposite lung. In the prospective study, 3 of 11 patients developed
radiation pneumonitis during the course of
radiation therapy. The mean kep value obtained in the 3 patients who developed
radiation pneumonitis increased just before onset, and further increased when the disease manifested clinically. We believe that 99mTc-DTPA
aerosol inhalation is a sensitive test for the detection of inflammatory changes in the bronchioalveolar epithelium.