Lung Clearance of the Rats Estimated by Ferrimagnetic Particles (1)

Abstract

This report presents the lung clearance of the rats measured by the technique of “the magnetopneumography”in order to evaluate effects of the xposure to air pollutants on the small animals.
Ferrimagnetic Fe₃0₄particles (1 pm diam.) of 0.3mg/100 g body wt which was suspended into 0.4 ml of sterile physiological saline was transorally instilled into trachea of anesthetized male Wistar rats (12 weeks old, N=9). Rats were exposed to magnetic field of 800 Gauss for periods of 30 seconds to magnetize the particles and then transferred into the shields made of double cylinders of Permalloy. The remanent field from the lungs was measured by a flux gate magnetometer, which probe was installed inside the cylinder.
A gradual decrease was observed in the remanent magnetic field and called “relaxation phenomenon”. The first one minute of the relaxation curve was fitted to the exponential function, Y=ae^-bX, where “X” is the time (sec) after the external magnetic field was turned off, “Y” is the field strength at timeX, “a” (initial field strength, obtained by extrapolation) is the field strength at timeX=0, and “b” is the relaxation rate for the first one minute. The above measurements were carried out every during the first 4 days and then every one or two week up to the 9th week after the particle instillation. The normalized clearance curve which was drawn using the time-“a” relation were shown to have two components, the first one decreased rapidly during the first 2 weeks (T_1/2= 16.2 days) and the second one decreased more gradually (T_1/2= 52.3 days). Nine weeks after the instillation, 65% of the particles in the lungs had been cleared.
The relaxation rate for the first 30 seconds period increased the most rapidly the forth day after the instillation.
The clearance curve estimated by this technique was similar to that of well-characterized radiologicaldetection method and this relatively inexpensive and noninvasive technique was suggested to be suitable for studying the efffects of the exposure to air pollutants on the lung clearance of small animals.