Assessment of regional deposition of inhaled particles in human lungs by serial bolus delivery method. J. Appl. Physiol. 81(5): 2203-2213, 1996.-Detailed regional deposition of inhaled particles was investigated in young adults (n 5 11) by use of a serial bolus aerosol delivery technique. A small bolus (45 ml half-width) of monodisperse aerosols [1-, 3-, and 5-µm particle diameter (D p )] was delivered sequentially to a specific volumetric depth of the lung (100-500 ml in 50-ml increments), while the subject inhaled clean air via a laser aerosol photometer (25-ml dead volume) with a constant flow rate (Q 5 150, 250, and 500 ml /s) and exhaled with the same Q without a pause to the residual volume. Deposition efficiency (LDE) and deposition fraction in 10 local volumetric regions and total deposition fraction of the lung were obtained. LDE increased monotonically with increasing lung depth for all three D p . LDE was greater with smaller Q values in all lung regions. Deposition was distributed fairly evenly throughout the lung regions with a tendency for an enhancement in the distal lung regions for D p 5 1 µm. Deposition distribution was highly uneven for D p 5 3 and 5 µm, and the region of the peak deposition shifted toward the proximal regions with increasing D p . Surface dose was 1-5 times greater in the small airway regions and 2-17 times greater in the large airway regions than in the alveolar regions. The results suggest that local or regional enhancement of deposition occurs in healthy subjects and that the local enhancement can be an important factor in health risk assessment of inhaled particles.

Detailed regional deposition of inhaled particles in the human lung is calculated for individual airway generations. The calculations are based on Landahl's deposition model as applied to the morphometric lung model of Weibel. We consider primarily deposition patterns of iron oxide particles with diameters ranging between 1 and 10 micrometers, but we also calculate patterns of deposition for bis(2-ethylhexyl) sebacate particles with diameters as small as 0.2 micrometers. We obtain good agreement between predicted values and observed values for alveolar retention of inhaled iron oxide particles with 64 and 20% of total deposition predicted to occur in nonciliated airways for 2- and 5-micrometer particles, respectively. This is compared with 48 +/- 9 and 27 +/- 10% for the measured values. Calculated values for total lung deposition of small bis(2-ethylhexyl) sebacate particles agree well with experimental data. The calculations show a minimum in deposition occurring for particle diameters of 0.5 micrometers, which is in agreement with observations. A calculation of surface concentration of deposited 7.9-micrometer aerodynamic particles reveals a very large concentration occurring at airway generation four. This observation is considered in light of observations that bronchial carcinomas occur in this vicinity of the lung.

No abstract