10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Improved Prediction Of Intersubject Variability In Extrathoracic Aerosol Deposition
Conor A. Ruzycki, Michael Yang, Scott Tavernini, C. Paul Moore, Michelle L. Noga, Andrew R. Martin, Hak-Kim Chan, WARREN H. FINLAY, University of Alberta
Abstract Number: 52 Working Group: Aerosols in Medicine
Abstract Orally inhaled aerosols must pass through the extrathoracic region in order to deposit in the lungs. Variability in extrathoracic deposition between different subjects thus leads to variability in the dose delivered to the lungs. The ability to predict such intersubject variability is useful both for risk exposure assessment with inhaled environmental aerosols, as well as in the development of medical aerosol products. Traditional algebraic correlations that were first developed for radiological protection models have been used to predict intersubject variability in extrathoracic deposition. However, these correlations have recently been found to significantly underpredict intersubject variability in mouth-throat deposition. In order to provide more accurate estimates of intersubject variability, we have made use of in vitro data in which we have measured extrathoracic deposition in realistic replicas of the extrathoracic airways of several dozen subjects ranging in age from newborn infants to adults. From this dataset, a theoretical analysis based on uncertainty propagation was developed in order to predict in vivo intersubject variability. To examine the accuracy of these predictions, in vivo measurements of mouth-throat deposition in adults inhaling aerosol during tidal breathing were performed on an independent set of subjects using SPECT scintigraphy. Intersubject variability was found to be in good agreement with our predicted values. For a given aerosol, intersubject variability in extrathoracic deposition is caused by intersubject variations in inhalation flow rate, intersubject variations in geometry captured by a characteristic extrathoracic airway diameter dc, and intersubject variations caused by geometrical differences in the extrathoracic airways that are not captured by dc (i.e. geometric dissimilarity). All three factors are found to play a role in causing intersubject variability. The presented methods may be useful to those wanting to predict, understand and control the sources of extrathoracic intersubject variability with inhaled aerosols.