Particle Retention in Airways Estimated by Unbiased Stereology and Photometry

ABSTRACT

The retention pattern of 6 (μm polystyrene particles at two breathing modes was studied by unbiased stereology in hamster airways (trachea, main bronchi and intrapulmonary conducting airways) and in the inhalation cannula. In addition, the total particle number estimated by stereology was compared with total deposition by laser photometry. Seven Syrian Golden hamsters which were artificially ventilated with continuous-negative-pressure ventilation inhaled the aerosol through an intratracheal cannula. Four of them were ventilated with a tidal volume V_t = 1.0 ml and a breathing frequency f of 60 min⁻¹ (group A), three of them with V_t=0.5 ml and the same f (group B). Immediately after inhalation, the lungs of all animals were fixed by intravascular perfusion, sampled and processed for stereologic fractionator analysis on light microscopic sections. The inhalation cannula was rinsed and particles counted in a hemocytometer. The total particle numbers by stereology were not found to be significantly different from total deposition data by laser photometry in group A (V_t=1.0 ml) animals, whereas they were different (lower) in group B animals. Differences in the patterns of particle retention were observed and biologic differences were apparent, although not statistically significant. In the short time of 20 minutes from the beginning of the inhalation to the beginning of fixation, a significant, but variable number of particles was found phagocytized by airway macrophages, indicating the importance of airway macrophages in particle clearance. This study shows the application and the limitation of hitherto conventional systematic sampling for particle distribution analyses in conducting airways of small rodents and of photometric measurements.