Objective: Nasal airflow is essential for delivering odorants to the olfactory epithelium. With increasing evidence demonstrating a strong link between nasal airflow and olfaction, we conducted a large multicenter retrospective study to further examine if nasal airflow can influence olfactory recovery in patients with COVID-19-related olfactory dysfunction (C19OD). Methods: Patients with reported C19OD received Sniffin' Sticks extended set, peak nasal inspiratory flow (PNIF), and VAS for smell (sVAS) at baseline (T0). Subjects with a confirmed OD at T0 were offered a second follow-up, averaged at 6 months (T1). All tests were repeated at T1. Results: Two hundred and five patients (median age 46) with a median length of OD of 1.1 years were seen at T0. One hundred and eleven dysosmics at T0 were seen at T1. At T1 43 patients (38.7%) recovered their sense of smell. A statistically significant improvement was observed for PNIF (p = 0.001) and sVAS (p < 0.001) in the whole population at T1. A statistically significant difference was noted for all the olfactory scores and sVAS (p < 0.001 for all) between normosmic and dysosmic subjects at T1. When we looked at changes in the scores between T0-T1, statistically significant correlations were observed between changes (Δ) in PNIF and Δthreshold (rho = 0.24 and p = 0.015), ΔPNIF and ΔTDI (rho = 0.22 and p = 0.021). An increase in ΔPNIF of 77.4 L/min corresponded to a 65% probability of reaching the normosmic level, with olfactory threshold being the more sensitive to PNIF changes. Conclusion: Improvement in nasal airflow can have a positive impact on smell recovery and on olfactory threshold in particular, highlighting its importance in persistent C19OD. Level of evidence: 3.
