The retention of particles in large airways of the respiratory tract

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Abstract
After the intra-tracheal injection in the conscious rat of 133 BaSO 4 particles suspended in 2.5 μI isotonic mannitol, only approximately 80% were rapidly removed from the distal trachea by mucociliary clearance. Some 20% were cleared with a mean half-time of 16 h, and approximately 1% remained in the tracheal tissue for at least 30 d. Such retention could be a basis for effects of inhaled toxic particles on the large airways. Mucus was collected from the trachea of the conscious rat and shown to exhibit shear-thinning. When BaSO 4 particles suspended in the mucus were injected into another rat, clearance kinetics over 2 d were similar to those for particles suspended in mannitol.