Pulmonary absorption of instilled and inhaled DTPA in smokers

Pulmonary absorption of DTPA (diamine-triethylene-penta-acetic acid) has been widely adopted as an index of pulmonary epithelial permeability. The aim of this study was to analyse: (1) if measurements of pulmonary absorption are influenced by the amount of fluid being administered to the lungs together with the DTPA; and (2) if all DTPA administered to the lungs is equally accessible for pulmonary absorption. To this end DTPA was instilled into a lung segment of six smokers in association with a bronchoscopy. In six other subjects (five smokers and one ex-smoker) the DTPA was inhaled as an aerosol. Pulmonary absorption of DTPA was calculated from the plasma DTPA content, as determined for 4-10 h after the administration of the DTPA. We found that the mean transit time for the absorption of instilled DTPA, t(L), across the pulmonary membranes was significantly (P less than 0.05) longer (median 1498 min, range 955-2636 min) than the t(L) of the absorption of the inhaled DTPA (median 131 min, range 44-512 min). Pulmonary clearance of the inhaled aerosolized DTPA tended to be faster when determined by external detection for 4 h, than when estimated from plasma samples, suggesting that not all pulmonary DTPA may be equally accessible for absorption from the pulmonary lining fluids. We conclude that pulmonary absorption of DTPA is influenced by the volume of fluid being administered to the lungs in association with the measurements. Not all pulmonary DTPA, however, is equally accessible for absorption, rendering external detection of pulmonary clearance of DTPA sensitive to a variety of factors other than pulmonary absorption.