Effects of airway obstruction induced by asthma attack on particle deposition

Two computational models of the airway tree up to six generations deep were reconstructed from computed tomography scans from a single patient. The first scan was taken a day after an acute asthma episode while the second scan was taken 30 days later when the patient had recovered. The reconstructed models were used to investigate the effects of acute asthma on realistic airway geometry, the airflow patterns, the pressure drop, and the implications it has on targeted drug delivery. Comparisons in the geometry found that in general the average increase in diameter was larger in the right airway the airway is larger in diameter than the left side. The average airway branch difference from the Asthma Model to the Recovered Model was found to be 10.4% in the right airway and 4.8% in the left airway; however the airway dilation during the recovery stage was not consistent through the entire branch airway. Instead there were local branches that exhibited a very high local dilation recovery (≈30% recovery). This inconsistent dilation recovery makes it difficult to predict where and how much each branch will recover from an asthma episode. In terms of targeted drug delivery studies in the lung airways, the deposition patterns will be under-predicted for airway models that are reconstructed from a healthy or non-asthma affected lung airway. The discrepancy may reach as high as 13% between the two models for particles ≥10 μm under a turbulent flow. For particles <10 μm, the discrepancy reduces to 1% as the particle size reduces to 1 μm under a turbulent flow. This means that drug delivery studies in the lung airway should consider the effects of airway narrowing and that if a recovered or a healthy airway is used, then the deposition fraction and efficiencies are expected to be under-predicted.