Regional deposition and retention of particles in shallow, inhaled boluses: effect of lung volume

The regional deposition of particles in boluses delivered to shallow lung d epths and their subsequent retention in the airways may depend on the lung volume at which the boluses are delivered. To evaluate the effect of end-in spiratory lung volume on aerosol bolus delivery, we had healthy subjects in hale radiolabeled, monodisperse aerosol (Tc-99m-iron oxide, 3.5-mu m mass m edian aerodynamic diameter) boluses (40 ml) to a volumetric front depth of 70 ml into the lung at lung volumes of 50, 70, and 85% of total lung capaci ty (TLC) end inhalation. By gamma camera analysis, we found significantly g reater deposition in the left (L) vs. right (R) lungs at the 70 and 85% TLC end inhalation; ratio of deposition in L to R lung, normalized to L-to-R r atio of lung volume (mean L/R), was 1.60 +/- 0.45 (SD) and 1.96 +/-. 0.72, respectively (P < 0.001 for comparison to 1.0) for posterior images. Howeve r, at 50% TLC, L/R was 1.23 +/- 0.37, not significantly different from 1.0. These data suggest that the L and R lungs may be expanding nonuniformly at higher lung volumes. On the other hand, subsequent retention of deposited particles at 2 and 24 h postdeposition was independent of L/R at the variou s lung volumes. Thus asymmetric bolus ventilation for these very shallow bo luses does not lead to significant increases in peripheral alveolar deposit ion. These data may prove useful for 1) designing aerosol delivery techniqu es to target bronchial airways and 2) understanding airway retention of inh aled particles.