The overall and regional clearance of an inhaled isotope labelled solute from the lungs was examined on the basis of a 15 minute period of data collection, for which a technique was developed that does not require intravenous injection to correct for blood-tissue background activity. The technique was applied to 52 normal subjects (31 non-smokers and 21 smokers) and to 37 patients with asbestosis (21 non-smokers and 16 smokers). In normal smokers solute clearance was faster in the upper and middle zones, with a mean ratio of T1/2 LB (half time solute clearance from lungs to blood) in the upper two thirds to the lower one third of the lungs of 0.66 (0.28-1.33), compared with 1.24 (0.43-2.77) in normal non-smokers (p less than 0.002). In patients with asbestosis solute clearance was accelerated throughout the lungs even though radiographic abnormalities were limited to lower or lower to middle zones. Regional distribution of clearance was not affected by posture in normal subjects. Overall solute clearance was significantly faster in normal current smokers and in patients with asbestosis than in normal non-smokers (p less than 0.001 respectively). Among patients with asbestosis, smokers had faster overall clearance than non-smokers (p less than 0.01). Among normal non-smokers T1/2 LB was not significantly different between those who had never smoked and ex-smokers. Regional abnormalities in pulmonary epithelial permeability may offer insight into the pathogenesis of interstitial lung diseases and smoking related disorders.
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