Regional Ventilation and Aerosol Deposition with Helium-Oxygen in Bronchoconstricted Asthmatic Lungs

Abstract

Background: Theoretical models suggest that He-O₂ as carrier gas may lead to more homogeneous ventilation and aerosol deposition than air. However, these effects have not been clinically consistent and it is unclear why subjects may or may not respond to the therapy. Here we present 3D-imaging data of aerosol deposition and ventilation distributions from subjects with asthma inhaling He-O₂ as carrier gas. The data are compared with those that we previously obtained from a similar group of subjects inhaling air. Methods: Subjects with mild-to-moderate asthma were bronchoconstricted with methacholine and imaged with PET-CT while inhaling aerosol carried with He-O₂. Mean-normalized-values of lobar specific ventilation sV∗ and deposition sD∗ were derived and the factors affecting the distribution of sD∗ were evaluated along with the effects of breathing frequency (f) and regional expansion (FVOL). Results: Lobar distributions of sD∗ and sV∗ with He-O₂ were not statistically different from those previously measured with air. However, with He-O₂ there was a larger number of lobes having sV∗ and sD∗ closer to unity and, in those subjects with uneven deposition distributions, the correlation of sD∗ with sV∗ was on average higher (p < 0.05) in He-O₂ (0.84 ± 0.8) compared with air (0.55 ± 0.28). In contrast with air, where the frequency of breathing during nebulization was associated with the degree of sD∗-sV∗ correlation, with He-O₂ there was no association. Also, the modulation of f on the correlation between FVOL and sD∗/sV∗ in air, was not observed in He-O₂. Conclusion: There were no differences in the inter-lobar heterogeneity of sD∗ or sV∗ in this group of mild asthmatic subjects breathing He-O₂ compared with patients previously breathing air. Future studies, using these personalized 3D data sets as input to CFD models, are needed to understand if, and for whom, breathing He-O₂ during aerosol inhalation may be beneficial.