  Airway constriction and blockage in obstructive lung diseases create barriers
to effective drug deposition by altering how different regions of the lungs are
ventilated. Established computational particle deposition models have not
accounted for these impacts of disease. We present a new particle deposition
model that calculates ventilation based on the resistance of each airway, such
that ventilation patterns respond to airway constriction. We incorporate distal
airway constrictions representative of cystic fibrosis, and assess the
resulting impact on deposition down to the single-airway scale. We demonstrate
how constriction reduces deposition in the airways directly distal and proximal
to the affected airways. When multiple constrictions are clustered together,
deposition in the central airways proximal to the constrictions is more
strongly reduced, and deposition in the other central airways is generally
increased. This results in more uneven deposition in both the central and
distal airways, even when constrictions affect only the distal airways. We use
our model to calculate lung clearance index (LCI), a clinical measure of
ventilation heterogeneity, in lungs with constrictions of various severities
localised to one lobe. We find an increase in LCI coinciding with a significant
drop in deposition throughout the affected lobe.
