Numerical simulation of pharyngeal airflow applied to obstructive sleep apnea: effect of the nasal cavity in anatomically accurate airway models

Abstract

Repetitive brief episodes of soft-tissue collapse within the upper airway during sleep characterize obstructive sleep apnea (OSA), an extremely common and disabling disorder. Failure to maintain the patency of the upper airway is caused by the combination of sleep-related loss of compensatory dilator muscle activity and aerodynamic forces promoting closure. The prediction of soft-tissue movement in patient-specific airway 3D mechanical models is emerging as a useful contribution to clinical understanding and decision making. Such modeling requires reliable estimations of the pharyngeal wall pressure forces. While nasal obstruction has been recognized as a risk factor for OSA, the need to include the nasal cavity in upper-airway models for OSA studies requires consideration, as it is most often omitted because of its complex shape. A quantitative analysis of the flow conditions generated by the nasal cavity and the sinuses during inspiration upstream of the pharynx is presented. Results show that adequate velocity boundary conditions and simple artificial extensions of the flow domain can reproduce the essential effects of the nasal cavity on the pharyngeal flow field. Therefore, the overall complexity and computational cost of accurate flow predictions can be reduced.

Detailed computational analysis of flow dynamics in an extended respiratory airway model

“…By incorporating subject-specific geometric models derived from clinical images, personalised computer models are increasingly used among respiratory modelling studies (Dong et al, 2018;Inthavong et al, 2017;Shang et al, 2018). Previous numerical simulations in pulmonary health have focused mainly on two aspects: establishing particle dosimetry model for inhalation toxicology (Koullapis et al, T 2016;Luo and Liu, 2009) or drug delivery purposes (Inthavong et al, 2011;Kenjereš and Tjin, 2017;Yousefi et al, 2015;Yousefi et al, 2017); and understanding the airway structural effect on airflow dynamics (Inthavong et al, 2009), such as sleep apnoea associated with obstructions in extra-thoracic airways (Cisonni et al, 2015) or airway obstructions in the intrathoracic airway (Sul et al, 2014). In particular, progress has been made in the area of lung model reconstruction.…”

Upper airway reconstruction using long‐range optical coherence tomography: Effects of airway curvature on airflow resistance

“…LR‐OCT reconstructions could also be used for computational fluid dynamics (CFD) simulations of airflow through upper airways to quantify airflow characteristics such as resistance and wall shear. .…”

Effects of replacing the nasal cavity with a simple pipe like structure in CFD simulations of the airflow within the upper airways of OSA patients with patient individual flow rates

“…It is important to validate the effects of omitting the nasal cavity on the flow features in the pharynx, especially on the acting pressure forces. In [8] it has been shown, that omitting the nasal cavity decreases the precision of flow modelling in the pharyngeal part, but replacing the nasal cavity by a simple pipe results in neglectable changes of the flow patterns in the pharynx. But, the numerical simulations in [8] were performed with steady flow conditions and a nonpatient-specific inflow rate of 21.2 L min -1 equally distributed through both nostrils, although nasal obstructions have been identified as predisposing factor for OSA [9].…”

“…In [8] it has been shown, that omitting the nasal cavity decreases the precision of flow modelling in the pharyngeal part, but replacing the nasal cavity by a simple pipe results in neglectable changes of the flow patterns in the pharynx. But, the numerical simulations in [8] were performed with steady flow conditions and a nonpatient-specific inflow rate of 21.2 L min -1 equally distributed through both nostrils, although nasal obstructions have been identified as predisposing factor for OSA [9]. The investigation misses the patient-specific contributions of individual flow rates especially for significant differences in left to right nostril ventilation typical for nasal obstructions.…”

“…In the present study, the investigation of simplifying the nasal cavity by pipes from [8] is extended to one subject with patient specific inspiratory flow rates that are significantly different from the left to the right side. This is performed by analysing the results of steady numerical simulations in the patient-specific upper airway geometry including the nasal cavity with patient individual different left and right nostril inspiratory flow rates in comparison to the anatomically accurate pharyngeal and laryngeal parts extended by a simple pipe structure replacing the nasal cavity and using the sum of each nostril flow rate as inlet boundary condition.…”