HUMAN DEPOSITION AND CLEARANCE OF 6-MU-M PARTICLES INHALED WITH AN EXTREMELY LOW-FLOW RATE

In human experimental data, tracheobronchial deposition reaches its ma ximum for particles of about 6 mu m inhaled at 0.5 L/s. The purpose of the present study was to investigate if tracheobronchial deposition o f 6-mu m particles could be increased, especially in the smaller bronc hi, using an extremely slow inhalation rate. Six healthy nonsmokers in haled monodisperse 6-mu m (aerodynamic diameter) Teflon particles labe led with In-111 at 0.04 L/s. Radioactivity in mouth and throat, lung, and stomach was measured immediately after inhalation by profile scann ing and in the lung also after 24, 48, 72, and 96 h. There was a subst antial clearance between 24 and 72 h; around 20% of the total clearanc e occurred between 24 and 72 h. This is in contrast to earlier studies in which only around 1% of 6-mu m particles inhaled at 0.5 L/s cleare d 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 tracheobron chial deposition was 50%, compared to about 30% when particles were in haled at 0.5 L/s. These findings could be of therapeutic use. They als o implicate the possibility of developing a diagnostic model that can separate between bronchial reactivity in large and small bronchi.