Airflow Characteristics of Empty Nose Syndrome: Insights From Patient-Specific Computational Modeling of Airflow Distribution Patterns and Nasal Air-Conditioning.

Background: Computational fluid dynamics (CFD) is increasingly used to investigate the complex pathophysiology of empty nose syndrome (ENS). Although previous CFD studies reported middle-meatus-dominant airflow and reduced air-mucosal interaction in ENS, whether airflow distribution alone explains symptoms or impaired nasal physiology remains unclear. Methods: Patient-specific CFD simulations were performed in 14 ENS patients using nasal cavity models reconstructed from computed tomography. Airflow distribution, nasal resistance, air temperature, relative humidity, and surface area-to-volume ratio (SAVR) were analyzed. Ten non-ENS subjects with nasal septal deviation (NSD) without prior nasal surgery and five normal subjects were analyzed for comparison. Results: Airflow distributions in ENS were heterogeneous, consisting of middle-meatus-dominant (9/14), inferior-meatus-dominant (4/14), and mixed (1/14) patterns. ENS6Q scores tended to be higher in the inferior-meatus-dominant group, whereas other variables did not differ between patterns. NSD subjects showed similarly diverse distributions (3/10, 3/10, and 4/10, respectively), indicating that skewed airflow distribution is not unique to ENS, although middle-meatus-dominant airflow was more frequent in ENS. All normal subjects exhibited mixed distributions. ENS subjects showed lower and more variable choanal relative humidity than normal subjects, and relative humidity correlated positively with SAVR in ENS and NSD, suggesting that nasal air-conditioning may be related to residual mucosal surface geometry. No parameter differed significantly between ENS and NSD or correlated with ENS6Q scores. Conclusion: ENS is not characterized by a single airflow pattern but represents a heterogeneous spectrum of airflow characteristics, with similar phenotypes also occurring in non-ENS subjects. Airflow distribution pattern alone was insufficient to explain ENS symptoms, and none of the evaluated global CFD parameters correlated significantly with ENS6Q scores, although the small sample precludes firm exclusion of clinically relevant associations. Preservation of mucosal surface area may nevertheless play an important role in nasal air-conditioning. These findings support a physiology-based and patient-specific understanding of ENS.