Effects of Size on Ovoid Anterior Septal Perforations: Physiologic Modeling With Computational Fluid Dynamics




Farzal, Zainab

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BACKGROUND: Nasal septal perforations (NSPs) often cause bleeding, crusting, obstruction, and/or whistling. Exposed cartilage along the perimeter of the perforation prolongs healing time. The perforation perimeter lies in the path of nasal airflow which could exacerbate these effects. Understanding the interaction of airflow with perforation edges can lead to better treatments for perforation symptoms. OBJECTIVE: To analyze the impact of NSP size on nasal physiology including its effects on airflow, heat and water vapor transport, wall shear, resistance, and humidification using computational fluid dynamics (CFD). METHODS: A 3-dimensional model of the nasal cavity was constructed from a radiologically normal CT scan using MimicsTM 17.0 imaging software (Materialise, Plymouth, MI). Ovoid anterior NSPs that were 0.5, 1, 2, and 3 cm long anterior-to-posteriorly were virtually created in the septum of the model. Perforation walls were divided into ventral, dorsal, anterior, and posterior regions in ICEM-CFDTM 15.0 (ANSYS, Canonsburg, PA). Planar surfaces at the nostrils and trachea were constructed for specifying inlet and outlet conditions on simulated airflow. Computational meshes of the airspaces, consisting of approximately 4 million unstructured, graded tetrahedral elements, were created. Steady-state inspiratory airflow, heat, and water vapor transport were simulated using FluentTM CFD softwareTM15.0 (ANSYS, Inc., Canonsburg, PA). Air crossover through the perforation, wall shear, heat flux, water vapor flux, resistance, and humidification were analyzed. RESULTS: Air crossover increased with perforation size with the highest crossover rate of 12.2% through the 3 cm NSP. Regionally, wall shear and heat and water vapor flux were highest along the posterior region and lowest anteriorly (p<0.05). Wall shear stress averaged over the entire perforation increased with NSP size. The highest heat and water vapor flux averaged over the entire perforation occurred in the 2 cm NSP. Dorsal and ventral values for wall shear stress and heat and water vapor flux did not correlate with size. Resistance decreased by 5% or more from normal only in the 3 cm perforation case. No change in humidification with perforation size was evident. CONCLUSION: High wall shear and heat and water vapor flux in posterior perforation regions may explain the crusting most commonly noted on posterior edges of NSPs. This study suggests that smaller NSPs may not grossly affect nasal resistance or humidification, and that perforation size effects on individual airflow patterns may be important in dorsal and ventral perforation regions. Further studies will correlate these findings with clinical implications.

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