Sidestream smoke inhalation decreases respiratory clearance of Tc-99m-DTPA acutely

Background: The permeability of the alveolar-capillary barrier to an inhaled aerosol of technetium (99m) labelled diethylenetriamine penta-acetate (Tc-99m-DTPA) is used as an index of alveolar epithelial injury. Permeability, is greatly increased in active smokers. Aims: To determine the effect of sidestream smoke inhalation on permeability as this has not been described previously. Methods: We measured lung clearance of inhaled (TC)-T-99m-DTPA aerosol in 20 normal nonsmoking subjects before and after exposure to one hour's sidestream smoke inhalation. Results: Measured carbon monoxide (CO) levels rose to a maximum of 23.5 +/- 6.2 ppm (mean +/- SD) from baseline values of 0.6 +/- 1.3 (p<0.001) and plasma cotinine levels to a maximum of 9.5 +/- 4.5 nmol/L (mean +/- SD). The half time (T1/2 in minutes) for Tc-99m-DTPA clearance rose from baseline 69.1 +/- 15.6 (mean +/- SD) to 77.4 +/- 17.8 (p<0.05) after smoke exposure. No effect of Tc-99m-DTPA scanning or of sidestream smoke was demonstrated on lung function. Conclusions: We conclude that low level sidestream smoke inhalation decreases (TC)-T-99m-DTPA clearance acutely in humans. The mechanism of this unexpected result is not established but may include differences in constituents between sidestream and mainstream smoke, alterations in pulmonary microvascular blood flow, or changes in surfactant due to an acute phase irritant response.