Elliot Eliyahu Greenblatt1,2, Tilo Winkler2, Robert Scott Harris2, Vanessa Jane Kelly2, Mamary Kone2, Ira Katz3,4, Andrew R Martin5, George Caillibotte3, Jose Venegas2. 1. 1 Department of Mechanical Engineering, Massachusetts Institute of Technology , Boston, Massachusetts. 2. 2 Massachusetts General Hospital and Harvard Medical School , Boston, Massachusetts. 3. 3 R&D Medical , Air Liquide Santé International, Les-Loges-en-Josas, France . 4. 4 Department of Mechanical Engineering, Lafayette College , Easton, Pennsylvania. 5. 5 Department of Mechanical Engineering, University of Alberta , Edmonton, Alberta, Canada .
Abstract
BACKGROUND: A previous PET-CT imaging study of 14 bronchoconstricted asthmatic subjects showed that peripheral aerosol deposition was highly variable among subjects and lobes. The aim of this work was to identify and quantify factors responsible for this variability. METHODS: A theoretical framework was formulated to integrate four factors affecting aerosol deposition: differences in ventilation, in how air vs. aerosol distribute at each bifurcation, in the fraction of aerosol escaping feeding airways, and in the fraction of aerosol reaching the periphery that is exhaled. These factors were quantified in 12 of the subjects using PET-CT measurements of relative specific deposition sD*, relative specific ventilation sV* (measured with dynamic PET or estimated as change in expansion between two static HRCTs), average lobar expansion FVOL, and breathing frequency measured during aerosol inhalation fN. RESULTS: The fraction of the variance of sD* explained by sV* (0.38), by bifurcation effects (0.38), and by differences in deposition along feeding airways (0.31) were similar in magnitude. We could not directly estimate the contribution of aerosol that was exhaled. Differences in expansion did not explain any fraction of the variability in sD* among lobes. The dependence of sD* on sV* was high in subjects breathing with low fN, but weakened among those breathing faster. Finally, sD*/sV* showed positive dependence on FVOL among low fN subjects, while the dependence was negative among high fN subjects. CONCLUSION: The theoretical framework allowed us to analyze experimentally measured aerosol deposition imaging data. When considering bronchoconstricted asthmatic subjects, a dynamic measurement of ventilation is required to evaluate its effect on aerosol transport. The mechanisms behind the identified effects of fN and FVOL on aerosol deposition need further study and may have important implications for aerosol therapy in subjects with heterogeneous ventilation.
BACKGROUND: A previous PET-CT imaging study of 14 bronchoconstricted asthmatic subjects showed that peripheral aerosol deposition was highly variable among subjects and lobes. The aim of this work was to identify and quantify factors responsible for this variability. METHODS: A theoretical framework was formulated to integrate four factors affecting aerosol deposition: differences in ventilation, in how air vs. aerosol distribute at each bifurcation, in the fraction of aerosol escaping feeding airways, and in the fraction of aerosol reaching the periphery that is exhaled. These factors were quantified in 12 of the subjects using PET-CT measurements of relative specific deposition sD*, relative specific ventilation sV* (measured with dynamic PET or estimated as change in expansion between two static HRCTs), average lobar expansion FVOL, and breathing frequency measured during aerosol inhalation fN. RESULTS: The fraction of the variance of sD* explained by sV* (0.38), by bifurcation effects (0.38), and by differences in deposition along feeding airways (0.31) were similar in magnitude. We could not directly estimate the contribution of aerosol that was exhaled. Differences in expansion did not explain any fraction of the variability in sD* among lobes. The dependence of sD* on sV* was high in subjects breathing with low fN, but weakened among those breathing faster. Finally, sD*/sV* showed positive dependence on FVOL among low fN subjects, while the dependence was negative among high fN subjects. CONCLUSION: The theoretical framework allowed us to analyze experimentally measured aerosol deposition imaging data. When considering bronchoconstricted asthmatic subjects, a dynamic measurement of ventilation is required to evaluate its effect on aerosol transport. The mechanisms behind the identified effects of fN and FVOL on aerosol deposition need further study and may have important implications for aerosol therapy in subjects with heterogeneous ventilation.
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