ACCELERATED CLEARANCE OF SMALL SOLUTES FROM THE LUNGS IN INTERSTITIAL LUNG-DISEASE

Abstract

Solutions of 99mTc-diethylenetriaminepenta-acetate (99mTc-DTPA) and .**GRAPHIC**. were aerosolized and inhaled by subjects seated against a scintillation camera. Initial clearance rates of these radionuclides were determined over 6 posterior lung regions. Clearance of .**GRAPHIC**. MW 163 daltons) exceeded that of 99mTc-DTPA (MW 492 daltons) by an average factor of 3.3. Upper-lobe clearance of both radionuclides was greater than lower-lobe clearance in the normal subjects, but this gradient was abolished when the subjects exhaled against 7 cm of positive end-expiratory pressure. Patients [21] with clinical and roentgenographic evidence of interstitial lung disease (ILD) and diminished CO diffusion rates were studied with 99mTc-DTPA. Clearance of 99mTc-DTPA was increased in 5 patients with idiopathic pulmonary fibrosis, 4 of 8 with sarcoid, 2 of 5 with pneumoconiosis and 2 of 3 patients with other forms of ILD. Clearance of .**GRAPHIC**. was decreased in 4 patients with pulmonary alveolar proteinosis. No increase in 99mTc-DTPA clearance was found in 5 patients with chronic obstructive pulmonary disease. Apparently the initial clearance of these aerosolized hydrophilic radionuclides is accomplished in part by diffusion through the epithelium of alveoli and respiratory bronchioles. Whereas radionuclide clearance is impaired by the presence of precipitated protein in these structures in pulmonary alveolar proteinosis, clearance is accelerated in ILD. This may indicate increased epithelial permeability in ILD related to injury and increased retractile forces.