Particle Transport from the Lower Respiratory Tract

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Abstract
Particle transport of monodisperse fused aluminosilicate particles and cobalt oxide particles was studied in beagle dogs for 1000 d after inhalation. Particle transport to the larynx and subsequently to the gastro-intestinal (GI) tract was determined from excretion analysis. However, dissolution of even so-called insoluble particles in the lungs over long periods of time cannot be neglected as was shown by urinary excretion analysis. Therefore, the particle fraction in fecal samples had to be distinguished from the non-particulate fraction transferred from blood to the GI tract. Long-term particle transport was very similar in all dogs starting with an initial rate of 0.05 ± 0.01 %/d of the contemporary lung burden and decreasing with a half-life of 170 ± 10 d. Although the initial rate is a factor of 5 less than in human volunteers, the exponential decrease is comparable in man and dogs. Kinetics of uptake and retention of particles in tracheobronchial and bifurcational lymph nodes was determined in individual dogs utilizing a gamma camera. Fraction and rate of uptake varies among different dogs. Broncho-alveolar lavages revealed phagocytized particles in alveolar macrophages from epithelial surfaces up to 500 days after inhalation.