Series distribution of mucociliary clearance of magnetized iron particles in anesthetized dogs

Clearance of magnetic iron particles placed in the trachea, peripheral airway and alveoli was studied in anesthetized dogs. A retrograde catheter was inserted into a peripheral airway 2 mm in diameter. A thin vynyl tube was inserted into the peripheral airway from the chest wall through the retrograde catheter and 0.05 ml of saline containing 30 mg of iron oxide (Fe₃O₄) was instilled into either the peripheral airway or the trachea. Further, 30 mg of Fe₃O₄ solution was instilled with an injection needle into the alveoli. After magnetization from outside the chest wall, remanent magnetic fields (RMF) generated in the trachea, peripheral airway and alveoli were subsequently measured with a flux-gate magnetometer. The decay of RMF immediately after sequential magnetization shows clearance of Fe₃O₄ particles. Relaxation of RMF just before sequential magnetization is related to random misalignment of the particles. The fastest clearance was observed in the trachea, followed by the peripheral airway and the slowest was that in the alveoli. Exposure to isoproterenol resulted in increased clearance in the trachea and peripheral airway. However, relaxation was of similar magnitude and was not altered by isoproterenol throughout the entire airway. These results suggest that mechanisms responsible for clearance and relaxation in vivo are different and that clearance accelerates toward the central airway from alveoli and relaxation may be due to properties of the airway surface lining layer.