Investigation of the Defense System of the Human Lungs With Ferrimagnetic Particles

Abstract

ABSTRACT

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 the 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 η ≈ 100 Pa•s by a shear-rate near 0.01 s⁻¹, macrophage activity was E_Z = 5•10₋₁₈ 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 ≈ 110 days.