Human Deposition and Clearance of 6-μm Particles Inhaled with an Extremely Low Flow Rate

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Abstract
In human experimental data, tracheobronchial deposition reaches its maximum for particles of about 6 μm inhaled at 0.5 L/s. The purpose of the present study was to investigate if tracheobronchial deposition of 6-μm particles could be increased, especially in the smaller bronchi, using an extremely slow inhalation rate. Six healthy nonsmokers inhaled monodisperse 6-μM (aerodynamic diameter) Teflon particles labeled with 111in at 0.04 L/s. Radioactivity in mouth and throat, lung, and stomach was measured immediately after inhalation by profile scanning and in the lung also after 24, 48, 72, and 96 h. There was a substantial clearance between 24 and 72 h; around 20% of the total clearance occurred between 24 and 72 h. This is in contrast to earlier studies in which only around 1% of 6-μm particles inhaled at 0.5 L/s cleared between 24 and 72 h. This indicates a markedly higher deposition in the smaller bronchi at 0.04 L/s than at 0.5 L/s. The total tracheobronchial deposition was 50%, compared to about 30% when particles were inhaled at 0.5 L/s. These findings could be of therapeutic use. They also implicate the possibility of developing a diagnostic model that can separate between bronchial reactivity in large and small bronchi.