Narrowed Posterior Nasal Airway Limits Efficacy of Anterior Septoplasty

Background: Predicting symptomatic relief after septoplasty has been difficult. Minimal cross-sectional area (mCSA) measured by acoustic rhinometry and airflow resistance (R) measured by rhinomanometry have been used to select surgical candidates with mixed success. An important assumption is that mCSA and resistance are tightly coupled, but studies have reported weak or no correlation. Recently, we proposed the Bernoulli Obstruction Theory as an explanation, where tight coupling between mCSA and R is only predicted below a critical mCSA (A_crit). Methods: The nasal airway and septum of 10 healthy subjects were reconstructed from computed tomography scans. Simulated anterior septal deviations of increasing severity were created. Computational fluid dynamics simulations were performed to quantify mCSA, resistance, and flow in the healthy septum model and four simulated septal deviation models for each subject (total of 50 models). Results: A tighter coupling between mCSA and resistance was found below A_crit, estimated to be 0.20 cm² (a very severe deviation). Above A_crit, enlarging the mCSA had a smaller effect in patients with narrower cross-sectional area in the postvalve region (CSA_PV). Conclusions: Two patterns of flow increase are expected with septoplasty. Below A_crit, enlarging mCSA predictably increases flow. Above A_crit, the effect size of increasing mCSA depends on CSA_PV. Unrecognized small CSA_PV may explain persistent sensation of nasal obstruction after septoplasty. Our data suggest that inferior turbinate reduction ipsilateral to a septal deviation may amplify airflow benefits after septoplasty in patients with a narrow CSA_PV.