Left-to-right asymmetry of aerosol deposition after shallow bolus inhalation depends on lung ventilation.

BACKGROUND: After shallow bolus inhalation of radiolabeled aerosols, gamma camera imaging has shown a left-right asymmetry, with a higher fraction of deposited particles in the left lung. It was not clear, however, whether this phenomenon was an effect of asymmetry in lung ventilation or aerosol deposition efficiency. METHODS: Lung ventilation and aerosol deposition was studied after shallow bolus inhalation and gamma camera imaging in nine healthy nonsmokers and 10 asymptomatic smokers. A 100-mL (81m)Kr-gas boli were administered within the Fowler and within the phase-1 dead space, respectively. In addition, 1-L full breaths of 81m-Kr-gas were inhaled. For aerosol deposition subjects inhaled 100-mL boli of 100-nm diameter radiolabeled carbon particles with shallow and deep penetration. Left-to-right (L/R) and central-to-peripheral (C/P) activity distribution of the lung was analyzed. RESULTS: None of the parameters analyzed were significantly different between nonsmokers and smokers. The full-breath 81m-Kr-gas inhalation revealed a similar activity distribution over the left and right lungs, according to their respective volumes (L/R ratio = 0.84 +/- 0.04; mean +/- SE). In contrast, the shallow bolus inhalation of 81m-Kr-gas to the phase-1 dead space revealed more activity in the left lung (L/R ratio = 1.49 +/- 0.15, normalized to full-breath Kr-gas L/R). This same left-right asymmetry was observed for the aerosol after shallow bolus inhalation (L/R ratio = 1.69 +/- 0.15), and there was no significant difference between Kr-gas and aerosol L/R ratio. C/P activity ratios of bolus inhalation to the phase-1 dead space were 1.71 +/- 0.19 and 1.79 +/- 0.15 (normalized to full-breath Kr-gas C/P) for gas and aerosol, respectively, and correlated with the L/R ratios. CONCLUSIONS: The data show that the asymmetry in shallow aerosol bolus deposition is primarily determined by lung ventilation. The reason for this asymmetry is unclear