Ferrimagnetic particles in the lung. Part II: The relaxation process.

Abstract

After ferrimagnetic particles in the lung have been magnetized and aligned by an external magnetic field which is then removed, they undergo relaxation. In this process the remanent magnetic field at the chest produced by the aligned particles decreases in time, typically by a factor of five in the first hour; this is the result of misalignments of the particles caused by random, physiological impulses. The purpose here is to consolidate previous and new relaxation curves (the decreasing field versus time), due to Fe3O4 particles in the human lung, and to interpret the curves. They are shown as a function of the magnetizing field strength, of the dust residence time in the lung, of smoking, and of the breathing pattern. Curves of ?Fe2O3 in the hamster lung are also presented, showing the change due to death. The curves are qualitatively explained by the same physics model used in Part I, where single-domain and multidomain particles residing in a viscous fluid are subjected to random impulses. Although the physiological sources of the impulses are not directly considered here, the curves suggest that one cause of relaxation is elasticity of the fluid. Also, the curves indirectly support the findings by others that the physiological sources of the impulses are within macrophages.