Endonasal thermal imaging in the assessment of nasal obstruction and airflow

Background: Objective tests that measure nasal resistance, peak flow, and cross-sectional area correlate poorly with the subjective perception of nasal breathing. Airflow perception is thought to be mediated by changes in mucosal temperature from radiant cooling from airflow rather than the direct sensation of the airflow. Changes in nasal mucosal temperature may better predict the subjective perception of nasal breathing. This study aims to develop the endonasal thermal image of the nasal passage and assess the intranasal mucosal temperature with the subjective perception of nasal breathing and objective measurement of nasal airflow. Methods: A cross-sectional analysis of a single cohort of consecutively recruited and clinically evaluated patients with nasal obstruction at a tertiary rhinology center between August 2022 and February 2023 were recruited. Intranasal mucosal temperatures were extracted from the thermal endonasal image of the nasal passage generated from the infrared radiometric thermal camera (FILR VS290). The mid-expiration and mid-inspiration temperature data [internal nasal valve area, nasal cavity area, inferior turbinate area, and overall airway (mean value)] were compared to the patient-reported nasal breathing [visual analog scale (VAS), Nasal Obstruction Symptom Evaluation (NOSE) scale] and nasal airway resistance (NAR) pre-and post-decongestion. Results: Thirty-three patients (age 33.94±11.65 years, 39.4.% female, 66 nasal cavities) were included. The NOSE scale (0–100), VAS (0–100), and NAR were 59.85±26.65, 57.03±28.35 mm, and 0.67±0.62 Pa/cm³/s (normal <0.25 Pa/cm³/s), respectively. VAS improved pre-post decongestion (57.03±28.35 vs. 33.30±24.16 mm, P<0.001). Mid-expiration temperature (ExT) of all areas were higher than mid-inspiration temperature (InT) at both pre- and post-decongestion states. ExT post-decongestion of three areas and overall airway were lower than ExT pre-decongestion. No statistically significant correlations were found between intranasal mucosal temperature, subjective perception of nasal breathing, and objective measurement of nasal airflow at pre-and post-decongestion states. Conclusions: Endonasal thermal imaging can accurately measure intranasal mucosal temperature in patients with nasal obstruction. The lower intranasal mucosal temperature during inspiration pre- and post-decongestion and expiration post-decongestion are consistent with mucosal cooling and critical in the perception of nasal breathing. However, more precise imaging of the nasal passage and data acquisition is likely to be required before the clinical use of mucosal temperature as an objective measure of nasal obstruction.