Retention of Teflon particles in hamster lungs: a stereological study

The significance of aerosols in medicine is increased when the distribution of inhaled aerosols in the different respiratory tract compartments and their interaction with lung structures are known. The aim of this study was to investigate the retention of the hydrophobic Teflon spheres used in human beings so as to analyze their regional distribution and to study their interaction with lung structures at the deposition site. Six intubated and anesthetized Syrian Golden hamsters inhaled aerosols of Teflon particles with an aerodynamic diameter of 5.5 microns by continuous negative-pressure ventilation adjusted to slow breathing. Lungs were fixed by intravascular perfusion within 21 minutes after inhalation was started, and tissue samples were taken and processed for light and electron microscopy. The stereological (fractionator) analysis revealed that particle retention was the greatest in alveoli (72.4%), less in intrapulmonary conducting airways (22.9%), and the least in extrapulmonary mainstem bronchi (0.3%) and trachea (4.4%). Particles were found submerged in the aqueous lining layer and in close vicinity to epithelial cells. In intrapulmonary conducting airways, 21.5% of Teflon particles had been phagocytized by macrophages. This study with highly hydrophobic Teflon particles clearly demonstrates that for spheres of this size, surface tension and line tension forces rather than the particles' surface free energy are decisive for the displacement of particles into the aqueous phase by surfactant. It was this displacement that enabled subsequent interaction with macrophages. Refined knowledge of particle retention may help us to better understand the biological response to inhaled particles.