Measurement, Reconstruction, and Flow-Field Computation of the Human Pharynx With Application to Sleep Apnea

Abstract

Repetitive closure of the upper airway characterizes obstructive sleep apnea. It disrupts sleep causing excessive daytime drowsiness and is linked to hypertension and cardiovascular disease. Previous studies simulating the underlying fluid mechanics are based upon geometries, time-averaged over the respiratory cycle, obtained usually via MRI or CT scans. Here, we generate an anatomically correct geometry from data captured in vivo by an endoscopic optical technique. This allows quantitative real-time imaging of the internal cross section with minimal invasiveness. The steady inhalation flow field is computed using a k-ω shear-stress transport (SST) turbulence model. Simulations reveal flow mechanisms that produce low-pressure regions on the sidewalls of the pharynx and on the soft palate within the pharyngeal section of minimum area. Soft-palate displacement and side-wall deformations further reduce the pressures in these regions, thus creating forces that would tend to narrow the airway. These phenomena suggest a mechanism for airway closure in the lateral direction as clinically observed. Correlations between pressure and airway deformation indicate that quantitative prediction of the low-pressure regions for an individual are possible. The present predictions warrant and can guide clinical investigation to confirm the phenomenology and its quantification, while the overall approach represents an advancement toward patient-specific modeling.

Computational fluid dynamics endpoints for assessment of adenotonsillectomy outcome in obese children with obstructive sleep apnea syndrome

“…Decreases in both dP TAmax and PQR TAmax were correlated to AHI decrease. These correlations are consistent with CFD studies of adults (Cisonni et al, 2013; Lucey et al, 2010; Vos et al, 2007) and children (Van Holsbeke et al, 2013; Wootton et al, 2014) correlating pharyngeal pressure drops to OSAS severity. The strong correlation between dP TAmax and AHI decreases support further development of patient-specific CFD as a potential clinical tool for surgical planning in patient populations where residual OSAS is more common, such as obese patients.…”

Effect of the velopharynx on intraluminal pressures in reconstructed pharynges derived from individuals with and without sleep apnea

“…4 and 5). For all subjects, strong cross-flow pressure gradients appeared in this region of the pharynx as has been previously demonstrated by Lucey et al (2010). The pressure gradients were stronger for OSA subjects since the difference between the mean values of the minimum and the maximum pressures within the velopharynx was larger for the OSA group (4.3 Pa) than for the control group (2.8 Pa).…”

Passive movement of human soft palate during respiration: A simulation of 3D fluid/structure interaction

“…Three dimensional (3D) modeling and simulation of airflow in realistic human upper airway could be implemented with the current state-of-the-art computational fluid dynamics (CFD) (Lucey et al, 2010;Mihaescu et al, 2008;Shome et al, 1998;Sung et al, 2006;Xu et al, 2006). Two dimensional (2D) fluid-structure interaction (FSI) pharyngeal models have been reconstructed to study the compliant pattern of surrounded soft tissues especially the human tongue and soft palate (Chouly et al, 2009;Chouly et al, 2008), the effects of anatomical manipulations on pharyngeal collapse (Huang et al, 2005b) and the upper airway variation with contraction of genioglossal muscle at wake/sleep state (Huang et al, 2005a).…”