Analysis and assessment for the intrapulmonary kinetics of N-isopropyl-I-123-p-iodoamphetamine (IMP) in diffuse respiratory diseases

We investigated intrapulmonary kinetics of N-isopropyl-I-123-p-iodoamphetamine (IMP) in patients with diffuse respiratory diseases. Subjects studied were 4 healthy nonsmoking controls (age≥40), 3 young healthy nonsmokers (age<40), 4 healthy smokers, 8 patients with idiopathic pulmonary fibrosis (IPF), 2 with sarcoidosis, and 4 with chronic pulmonary emphysema (CPE). All studies were performed after obtaining informed consent. Ages were matched among the groups except the group of young healthy nonsmokers. We calculated the lung initial extraction fraction (E value) of IMP using Tc-99m human serum albumin as an intravascular reference tracer with deconvolution method. We also analyzed the lung IMP washout curve by a two-compartmental model. The mean E value for the nonsmoking controls was 0.977, indicating almost all IMP injected was taken up by the lungs at the initial passage. There was no difference in the E value among the groups. With regard to the lung IMP washout analysis, the distribution to the fast compartment (A1) was smaller than that to the slow compartment (A2). There was no difference in the A1 to A2 ratio among the groups. We then analyzed the slopes of the fast and slow compartments (k1, k2). There was no difference in k1 among the groups. On the other hand, k2 was larger in young healthy nonsmokers and smaller in healthy smokers, the patients with IPF, sarcoidosis and CPE than k2 in nonsmoking controls. Furthermore, k2 decreased in inverse proportion to age. We concluded that k2 could be a valuable index to detect changes of IMP, a lipophilic amine, metabolism in the lungs. (author)