ASSESSMENT OF REGIONAL DEPOSITION OF INHALED PARTICLES IN HUMAN LUNGSBY SERIAL BOLUS DELIVERY METHOD

Detailed regional deposition of inhaled particles was investigated in young adults (n = 11) by use of a serial bolus aerosol delivery techni que. A small bolus (45 mi half-width) of monodisperse aerosols [1-, 3- , and 5-mu m particle diameter (D-p)] was delivered sequentially to a specific volumetric depth of the lung (100-500 mi 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 = 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 volu metric 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. Depos ition was distributed fairly evenly throughout the lung regions with a tendency for an enhancement in the distal lung regions for D-p = 1 mu m Deposition distribution was highly uneven for D-p = 3 and 5 mu m, a nd the region of the peak deposition shifted toward the proximal regio ns with increasing D-p. Surface dose was 1-5 times greater in the smal l airway regions and 2-17 times greater in the large airway regions th an in the alveolar regions. The results suggest that local or regional enhancement of deposition occurs in healthy subjects and that the loc al enhancement can be an important factor in health risk assessment of inhaled particles.