BRONCHIAL AIRWAY DEPOSITION AND RETENTION OF PARTICLES IN INHALED BOLUSES - EFFECT OF ANATOMIC DEAD SPACE

The fractional deposition of particles in boluses delivered to shallow lung depths and their subsequent retention in the airways may depend on the relative volume and size of an individual's airways. To evaluat e the effect of variable anatomic dead space (ADS) on aerosol bolus de livery we had healthy subjects inhale radiolabeled, monodisperse aeros ol (Tc-99m-iron oxide, 3.5 mu m mean mondispersed aerosol diameter) bo luses (40 mi) to a volumetric front depth of 70 mi into the lung at a lung volume of 70% total lung capacity end inhalation. By using filter techniques, aerosol photometry, and gamma camera analysis, we estimat ed the fraction of the inhaled boluses deposited in intrathoracic airw ays (IDF). ADS by single-breath Nz washout was also measured from 70% total lung capacity. Results showed that among all subjects IDF was va riable (range = 0.04-0.43, coefficient of variation = 0.54) and increa sed with decreasing ADS (r = -0.76, P = 0.001, n = 16). We found signi ficantly greater deposition in the left (L) vs. right (R) lungs; mean L/R (ratio of deposition in L lung to R lung, normalized to ratio of L -to-R lung volume) was 1.58 +/- 0.42 (SD; P < 0.001 for comparison wit h 1.0). Retention of deposited particles at 2 h was independent of ADS or IDF. There was significant retention of particles at 24 h postdepo sition (0.27 +/- 0.05) and slow clearance of these particles continued through 48 h postdeposition. Finally, analysis of central-to-peripher al ratios of initial deposition and 24-h-retention gamma-camera images suggest significant retention of insoluble particles in large bronchi al airways at 24 h postdeposition (i.e., 24 h central-to-peripheral ra tio = 1.40 +/-: 0.44 and 1.82 +/- 0.54 in the R and L lung, respective ly; P < 0.02 for comparison with 1.0). These data may prove useful for 1) designing aerosol delivery techniques to target bronchial airways and 2) understanding airway retention of inhaled particles.