Changes in nasal airflow and heat transfer correlate with symptom improvement after surgery for nasal obstruction

Abstract

Surgeries to correct nasal airway obstruction (NAO) often have less than desirable outcomes, partly due to the absence of an objective tool to select the most appropriate surgical approach for each patient. Computational fluid dynamics (CFD) models can be used to investigate nasal airflow, but variables need to be identified that can detect surgical changes and correlate with patient symptoms. CFD models were constructed from pre- and post-surgery computed tomography scans for 10 NAO patients showing no evidence of nasal cycling. Steady-state inspiratory airflow, nasal resistance, wall shear stress, and heat flux were computed for the main nasal cavity from nostrils to posterior nasal septum both bilaterally and unilaterally. Paired t-tests indicated that all CFD variables were significantly changed by surgery when calculated on the most obstructed side, and that airflow, nasal resistance, and heat flux were significantly changed bilaterally as well. Moderate linear correlations with patient-reported symptoms were found for airflow, heat flux, unilateral allocation of airflow, and unilateral nasal resistance as a fraction of bilateral nasal resistance when calculated on the most obstructed nasal side, suggesting that these variables may be useful for evaluating the efficacy of nasal surgery objectively. Similarity in the strengths of these correlations suggests that patient-reported symptoms may represent a constellation of effects and that these variables should be tracked concurrently during future virtual surgery planning.

Keywords: Computational fluid dynamics; Nasal heat flux; Nasal resistance; Numerical modeling; Patient symptoms.

Fig. 1

Three-dimensional reconstructions of the external nose before (PRE) and after (POST) surgery for nasal airway obstruction in four subjects, with axial images from pre- and post-surgery CT scans. Arrows indicate level of scan image.

Fig. 2

Lateral views of pre- and post-surgery 3D reconstructions of the nasal passages of subject 1 showing division between main nasal cavity (light gray) and nasopharynx (dark gray) at the level of the posterior end of the nasal septum.

Fig. 3

Method for setting comparable steady-state, inspiratory airflow rates in pre- and post-operative states for an individual. Step 1: In the Post-Surgery CFD model, pressure drop from nostrils to outlet (Overall Pressure-Drop) was fitted to target flow rate for normal resting breathing. Step 2: Pressure drop from nostrils to posterior end of nasal septum (PSP Pressure-Drop) was calculated from the Post-Surgery CFD model. This value was called “Post PSP-PD”. Step 3: In the Pre-Surgery CFD model, Overall Pressure-Drop fitted so that PSP Pressure-Drop=“Post PSP-PD” value.

Fig. 4

Survey results. Average pre- and post-surgery survey scores and average pairwise differences between pre- and post-surgery values. Error bars indicate one sample standard deviation. Asterisks indicate statistically significant differences. (A) NOSE scores. (B) VAS scores on the most obstructed side. (C) VAS scores on the less unobstructed side.

Fig. 5

Bilateral variable results. Average pre-surgery and post-surgery biophysical variables measured bilaterally from the nostrils to the posterior end of the nasal septum, and average pairwise differences between pre- and post-surgery values. Error bars indicate one sample standard deviation. Asterisks indicate statistically significant differences. (A) Total inspiratory airflow rate (Airflow-Bilateral). (B) Bilateral nasal resistance (CFDNR-Bilateral). (C) Total heat flux per unit surface area (Heat Flux-Bilateral). (D) Average shear stress on the walls of the nasal cavity (Wall Shear-Bilateral).

Fig. 6

Unilateral variable results on the most obstructed side. Pre-surgery and post-surgery biophysical variables measured from the nostrils to the posterior end of the nasal septum in the most obstructed nasal side, and average pairwise differences between pre- and post-surgery values. Error bars indicate one sample standard deviation. Asterisks indicate statistically significant differences. (A) Unilateral inspiratory airflow rate (Airflow-OS). (B) Unilateral nasal resistance (CFDNR-OS). (C) Total heat flux per unit surface area (Heat Flux-OS). (D) Average shear stress on the walls of the nasal cavity (Wall Shear-OS).

Fig. 7

Unilateral variable results on the less obstructed side. Pre-surgery and post-surgery biophysical variables measured from the nostrils to the posterior end of the nasal septum in the less obstructed nasal side, and average pairwise differences between pre- and post-surgery values. Error bars indicate one sample standard deviation. Pairwise differences between pre-surgery and post-surgery values were not statistically different. (A) Unilateral inspiratory airflow rate (Airflow-US). (B) Unilateral nasal resistance (CFDNR-US). (C) Total heat flux per unit surface area (Heat Flux-US). (D) Average shear stress on the walls of the nasal cavity (Wall Shear-US).

Fig. 8

Correlations among subjective and objective measures of nasal airflow. (A) NOSE scores plotted against unilateral airflow on the most obstructed side (Airflow-OS). (B) Visual analog scale (VAS) scores plotted against Airflow-OS. (C) NOSE scores vs. unilateral heat flux on the most obstructed side (Heat Flux-OS). (D) VAS scores vs. Heat Flux-OS. (E) NOSE scores plotted against unilateral nasal resistance ratio on the most obstructed side (CFDNR Ratio-OS). (F) VAS scores plotted against CFDNR Ratio-OS.