Pertechnegas lung clearance in different forms of interstitial lung disease

Interstitial lung diseases (ILD) are characterized by an acute or chronic inflammation of the alveolar capillary membrane, which affects the permeability of this membrane. A possible way to measure the permeability of the membrane is by radionuclide aerosol imaging. Pertechnegas, a gas composed of technetium-labelled carbon particles, has recently been proposed as a new ventilation agent to measure this lung clearance. The clearance by pertechnegas in the four most common forms of ILD (eight patients with connective tissue disease, 10 with hypersensitivity pneumonitis, nine with idiopathic interstitial pneumonia and 10 with sarcoidosis) was measured and compared with 10 nonactive smoking controls. Because forced vital capacity (FVC), total lung capacity (TLC) and carbon monoxide diffusing capacity of the lung (DL,CO) are used in the assessment of functional severity of the ILD, the pertechnegas clearance was correlated with these lung-function indices. It was found that the time to half clearance of pertechnegas of the lung is significantly decreased in idiopathic interstitial pneumonia (p<0.0001), hypersensitivity pneumonitis (p=0.0005) and connective tissue disease (p=0.002) but not in sarcoidosis when compared with 10 nonsmoking controls. A significant correlation is also found between time to half clearance and FVC (r=0.76; p<0.0001), TLC (r=0.63; p<0.0001) and DL,CO (r=0.75; p<0.0001) for all groups together. For all subjects as a group, the time to half clearance is shorter in the upper lung zones than in the lower zones (p<0.0001) and the ratio between both zones is not significantly different between the different types of disease. These results indicate that pertechnegas clearance is increased in idiopathic interstitial pneumonia, hypersensitivity pneumonitis and connective tissue disease, but not in sarcoidosis and is related to the functional severity of the disease.