Nasal physiology and septal perforations
Reviewed by Suki Ahluwalia

This interesting article from North Carolina and New York aims to assess the impact of anterior septal perforations on nasal physiology, using computational fluid dynamics and computer simulation. A computerised 3D model was constructed of a normal patient aged 37, from CT scans using Mimics Imaging software. The nostrils, nasal cavity, turbinates and nasopharynx were modelled, but not the sinuses. Different sized ovoid nasal septal perforations were virtually introduced of varying sizes: 0.5x0.3cm, 1x0.6cm, 2x1cm and 3x1.3cm width x height, with width being in the anteroposterior plane of the septum. Round perforations of 0.5 and 1cm were also created, to study the effect of shape, always maintaining 1cm from the columella. The edges of each perforation were divided into four regions; anterior, posterior, dorsal and ventral. With computer-aided design and mesh generating software, ICEM-CFD, the 3D models of each situation were created and then analysed using a computational fluid dynamics package, Fluent. Inspiratory air flow, heat and water vapour transport were simulated and also crossover of air through the perforation, wall shear stress, heat flux, water vapour flux, resistance and humidification were all analysed. A small right-sided predominance was found in inspiratory air flow and this increased with size of perforation, particularly in the ovoid which was perhaps the more clinically relevant group. Airflow crossover rate was defined as the net percentage increase in air flow at the left choana, after air had passed from the right to the left cavity via the perforation. This increased with size of defect with the highest being 12% with a 3cm ovoid perforation. Flow velocity magnitude was higher in the centre to posterior perforation regions for smaller defects and for the larger perforations, flow was highest near the centre. Velocity seemed to increase after crossing the posterior border of the perforation. Wall shear stress, which may be related to feelings of blockage despite good airflow, was highest at the posterior edge of perforations and lowest at the anterior edge. This increased with perforation size, however the biggest increase was seen between 0.5 and 1.0cm ovoid perforations. Heat and water vapour flux were again highest at the posterior edge of perforations, although there was not much difference between sides or with perforation size from normal. Total nasal cavity humidification and posterior choanal temperature did not seem to vary much with size of perforation, however water content of air measured in cross-section seemed to be higher posteriorly in larger perforations. High wall shear stresses, heat and vapour flux at the posterior margin of the perforation may explain the occurrence of bleeding and crusting in this region of a perforation. There’s a large amount of data here and it’s an interesting read. Of course, it’s not in vivo physiology, but it’s the best we have.

A computational fluid dynamics analysis of the effects of size and shape of anterior nasal septal perforations.
Farzal Z, Del Signore A, Zanation A, et al.
RHINOLOGY
2019;57(2):153-9.