Computational fluid dynamics (CFD) was used to simulate air flow changes in reconstructed nasal passages based on magnetic resonance imaging (MRI) data from a previous clinical study of 0.05% Oxymetazoline (Vicks Sinex Micromist®). Total-pressure boundary conditions were uniquely applied to accommodate low patency subjects. Net nasal resistance, the primary simulation outcome, was determined using a parallel-circuit analogy and compared across treatments. Relative risk (RR) calculations show that for a 50% reduction in nasal resistance, subjects treated with Sinex® are 9.1 times more likely to achieve this after 8 hr, and 3.2 times more likely after 12 hr compared to Sham.