In reference to Regional peak mucosal cooling predicts the perception of nasal patency

We would like to comment on the recent article by Zhao et al. 1 comparing subjective and objective measures of nasal patency. In a cohort of 22 healthy individuals, Zhao et al. investigated whether the subjective perception of nasal patency (measured by a visual analog score) correlates with objective measures, such as mucosal cooling [measured by computational fluid dynamics (CFD)], nasal resistance (measured by rhinomanometry and CFD), and minimum cross-sectional area (measured by acoustic rhinometry). They found that “among all measured and computed variables, only CFD-simulated heat loss (...) significantly correlated with patency ratings.” This finding represents an important contribution to growing evidence that mucosal cooling plays an essential role in the sensation of nasal airflow. We commend the authors for conducting the first largescale comparison of CFD versus traditional measures of nasal patency (rhinomanometry and acoustic rhinometry). However, we are puzzled with the low correlation between the nasal resistances measured via CFD and rhinomanometry (Pearson correlation R 5 0.41; Table 1). We expected a much higher correlation (perhaps Pearson R> 0.8) between CFD-derived and rhinomanometry-derived nasal resistances given that both tools are well validated. For example, previous studies reported good agreement between the transnasal pressure drop computed by CFD and experimental measurements in plastic nasal replicas. In particular, Zhao and coworkers reported good agreement between CFD and rhinomanometry in one individual. One possible explanation for this surprising observation is that the CFD model had rigid walls, which do not account for tissue compliance in vivo. However, dynamic nasal valve collapse is not expected in a cohort of healthy individuals. Another possibility is that rhinomanometry evaluates nasal resistance at high pressure drops, whereas CFD-derived resistance reflects breathing at rest. But this also should have a minor effect given that nasal resistance is nearly a monotonic function of pressure. Finally, we speculate that this comparison may be confounded by the soft palate geometry, which shifts from a supine position (in which CFD models are based) to a sitting position (in which rhinomanometry is performed). We would appreciate if the authors could discuss this puzzling finding, which may have broad implications for the clinical assessment of nasal patency. In particular, a plot of CFD-derived versus rhinomanometry-derived nasal resistance would shine some light on this important issue.