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Investigation of the defense system of the human lungs with ferrimagnetic particles.

Magnetic microparticles were used to investigate the defense system of the human lungs against foreign material. About 0.5 mg of spherical monodisperse magnetite particles were deposited in the alveolar region of the human lung by voluntary inhalation. After primary magnetization a remanent magnetic field (rmf) of the lung can be measured that allows estimation of the amount of dust retained in the lung. The decay of this rmf, called relaxation, results from a misalignment of the dipole particles due to the activity of pulmonary macrophages. This macrophage activity was characterized by a cell energy E z. With a secondary magnetization the lung can be remagnetized by rotation of the dipole particles. This allows estimation of the intracellular viscosity and motility of the alveolar macrophages in vivo. Secondary magnetization and relaxation curves of spherical monodisperse magnetite particles are presented. Intracelluar viscosity was estimated to be n approximately equal to 100 Paxs by a shear-rate near 0.01 s -1, macrophage activity was E z approximately equal to 5x10 -18 J. Aerosol exposure resulted in a faster relaxation, which was interpreted to be due to activation of the macrophages. The magnetite particles were cleared with a half-time of approximately equal to 110 days.