Deposition and clearance of inhaled ¹⁸FDG powder in patients with chronic obstructive pulmonary disease

As freon is limited in its use as a generator for aerosol inhalation, powder particles are used as an alternative for inhalation therapy. The pulmonary deposition and clearance of inhaled powder particles was studied by positron emission tomography (PET) in ten patients with chronic obstructive pulmonary disease (COPD) and in five normal controls. The powder, 5 μm in mean diameter, was water soluble and labelled with 2-deoxy-2-[¹⁸F]-fluoro- D-glucose (¹⁸FDG). Powder inhalation was done with single deep inspiration from residual volume to total lung capacity. The initial deposition ratio in the right or left lung field to total inhaled dose, measured by an anteroposterior rectilinear scan, did not differ between normals and COPD patients. Ratios of radioactivity detected within the central and peripheral regions (the central to peripheral ratio) measured by the PET scan was not significantly different between COPD patients (4.8±2.6, mean±SD) and normals (2.6±0.8, mean±SD). However, the regional powder deposition in peripheral lung fields measured by the PET scan was significantly more uneven in COPD patients than in normal patients. The clearance rate of ¹⁸FDG, defined as the retention ratio of ¹⁸FDG activity to the initially deposited ¹⁸FDG at 60 and 120 min after inhalation, in the trachea, large bronchi or peripheral lung fields measured by tomographic scan showed a wider variation in COPD patients than in normals. To conclude, inhaled powder tended to be deposited more centrally and was distributed more unevenly in the peripheral lung in chronic obstructive pulmonary disease patients than in normals. This could be a limitation of powder inhalation used for therapy in chronic obstructive pulmonary disease patients.