Noninvasive estimation of pharyngeal airway resistance and compliance in children based on volume-gated dynamic MRI and computational fluid dynamics

Computational fluid dynamics (CFD) analysis was used to model the effect of collapsing airway geometry on internal pressure and velocity in the pharyngeal airway of three sedated children with obstructive sleep apnea syndrome (OSAS) and three control subjects. Model geometry was reconstructed from volume-gated magnetic resonance images during normal tidal breathing at 10 increments of tidal volume through the respiratory cycle. Each geometry was meshed with an unstructured grid and solved using a low-Reynolds number k-ω turbulence model driven by flow data averaged over 12 consecutive breathing cycles. Combining gated imaging with CFD modeling created a dynamic three-dimensional view of airway anatomy and mechanics, including the evolution of airway collapse and flow resistance and estimates of the local effective compliance. The upper airways of subjects with OSAS were generally much more compliant during tidal breathing. Compliance curves (pressure vs. cross-section area), derived for different locations along the airway, quantified local differences along the pharynx and between OSAS subjects. In one subject, the distal oropharynx was more compliant than the nasopharynx (1.028 vs. 0.450 mm2/Pa) and had a lower theoretical limiting flow rate, confirming the distal oropharynx as the flow-limiting segment of the airway in this subject. Another subject had a more compliant nasopharynx (0.053 mm2/Pa) during inspiration and apparent stiffening of the distal oropharynx (C = 0.0058 mm2/Pa), and the theoretical limiting flow rate indicated the nasopharynx as the flow-limiting segment. This new method may help to differentiate anatomical and functional factors in airway collapse.

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Evaluation of human obstructive sleep apnea using computational fluid dynamics

Communications Biology ◽

10.1038/s42003-019-0668-z ◽

2019 ◽

Vol 2 (1) ◽

Cited By ~ 2

Author(s):

Shahab Taherian ◽

Hamid Rahai ◽

Samuel Lopez ◽

Jamie Shin ◽

Behrouz Jafari

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Obstructive Sleep Apnea ◽

Sleep Apnea ◽

3D Models ◽

Ct Scans ◽

Cfd Modeling ◽

Apnea Hypopnea Index ◽

Upper Airways ◽

Obstructive Sleep

AbstractObstructive sleep apnea (OSA) severity might be correlated to the flow characteristics of the upper airways. We aimed to investigate the severity of OSA based on 3D models constructed from CT scans coupled with computational fluid dynamics (CFD) simulations. The CT scans of seven adult patients diagnosed with OSA were used to reconstruct the 3D models of the upper airways and CFD modeling and analyses were performed. Results from the fluid simulations were compared with the apnea-hypopnea index. Here we show a correlation between a CFD-based parameter, the adjusted pressure coefficient (Cp*), and the respective apnea-hypopnea index (Pearson’s r = 0.91, p = 0.004), which suggests that the anatomical-based model coupled with CFD could provide functional and localized information for different regions of the upper airways.

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Computational fluid dynamics simulation of changes in the morphology and airflow dynamics of the upper airways in OSAHS patients after treatment with oral appliances

10.1101/688879 ◽

2019 ◽

Author(s):

Song Baolong ◽

Li Yibo ◽

Sun Jianwei ◽

Qi Yizhe ◽

Li Peng ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Upper Airway ◽

Biomechanical Properties ◽

Dynamics Simulation ◽

Ct Scans ◽

Oral Appliances ◽

Upper Airways ◽

Obstructive Sleep ◽

Airway Morphology

AbstractObjectivesTo explore the changes of morphology and internal airflow in upper airways (UA) after the use of oral appliances (OAs) in patients with obstructive sleep apnea hypopnea syndrome (OSAHS), and investigate the mechanisms by which OAs function as a therapy for OSAHS.MethodsEight OSAHS patients (all male, aged 37-58, mean age 46.25) underwent CT scans before and after OA use. Then, computational fluid dynamics(CFD) models were built on the base of the CT scans using Mimics and ANSYS ICEM CFD software. The internal airflow of the upper airways was simulated using ANSYS-FLUENT and the results were analyzed using ANSYS-CFD-Post. The data were analyzed to identify the most important changes of biomechanical properties between patients with and without OA intervention. Upper airway morphology and the internal airflow changes were compared using t-tests and Spearman correlation coefficient analysis.ResultsThe narrowest area of upper airways was found to be located in the lower bound of velopharynx, where the volume and pressure were statistically significantly increased (P<0.05) and the air velocity was statistically significantly decreased (P<0.05) in the presence of the OA(P<0.05). After wearing OA, pharyngeal resistance was significantly decreased (P<0.05), from 290.63 to 186.25Pa/L, and the airflow resistance of the pharynx has reduced by 35.9%.ConclusionThe enlargement of the upper airway after wearing the OA changed its airflow dynamics, which decreased the negative pressure and resistance in narrow areas of the upper airways. Thus, the collapsibility of the upper airways was reduced and patency was sustained.

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Computational Fluid Dynamics Modeling of Upper Airway During Tidal Breathing Using Volume-Gated MRI in OSAS and Control Subjects

ASME 2011 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2011-53311 ◽

2011 ◽

Author(s):

Steven C. Persak ◽

Sanghun Sin ◽

Raanan Arens ◽

David M. Wootton

Keyword(s):

Fluid Dynamic ◽

Sleep Apnea Syndrome ◽

Three Dimensional ◽

Upper Airway ◽

Magnetic Resonance Images ◽

Dynamics Modeling ◽

Tidal Breathing ◽

Pharyngeal Airway ◽

Cross Section Area ◽

Obstructive Sleep

Three-dimensional (3D) computational fluid dynamic (CFD) analysis was used to model the effect of collapsing airway geometry on internal pressure and velocity in the pharyngeal airway of sedated obese children with and without obstructive sleep apnea syndrome (OSAS). Geometry was reconstructed from volume-gated magnetic resonance images during normal tidal breathing of the respiratory cycle and solved using flow data averaged over 12 consecutive breathing cycles. In the OSAS subject, collapse initiated in the proximal nasopharynx and continued downstream into the oropharynx, while the control experienced negligible collapse. Tube laws (pressure vs. cross-section area) derived for the nasopharynx and oropharynx, indicated the oropharynx in the OSAS subject more compliant than the nasopharynx (1.028 mm2/Pa vs. 0.449 mm2/Pa) and had a lower theoretical limiting flow rate, confirming the oropharynx as the flow-limiting segment of the airway in this subject. This new method may help to differentiate anatomical and functional factors in airway collapse.

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Numerical and Experimental Analysis of Inhalation Airflow Dynamics in a Human Pharyngeal Airway

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph17051556 ◽

2020 ◽

Vol 17 (5) ◽

pp. 1556

Author(s):

Yaming Fan ◽

Jingliang Dong ◽

Lin Tian ◽

Kiao Inthavong ◽

Jiyuan Tu

Keyword(s):

Fluid Dynamics ◽

Secondary Flow ◽

Flow Patterns ◽

Cross Sectional ◽

Pharyngeal Wall ◽

High Tendency ◽

Flow Acceleration ◽

Pharyngeal Airway ◽

Airway Collapse ◽

Obstructive Sleep

This paper presents a computational and experimental study of steady inhalation in a realistic human pharyngeal airway model. To investigate the intricate fluid dynamics inside the pharyngeal airway, the numerical predicted flow patterns are compared with in vitro measurements using Particle Image Velocimetry (PIV) approach. A structured mesh with 1.4 million cells is used with a laminar constant flow rate of 10 L/min. PIV measurements are taken in three sagittal planes which showed flow acceleration after the pharynx bend with high velocities in the posterior pharyngeal wall. Computed velocity profiles are compared with the measurements which showed generally good agreements with over-predicted velocity distributions on the anterior wall side. Secondary flow patterns on cross-sectional slices in the transverse plane revealed vortices posterior of pharynx and a pair of secondary flow vortexes due to the abrupt cross-sectional area increase. Finally, pressure and flow resistance analysis demonstrate that greatest pressure occurs in the superior half of the airway and maximum in-plane pressure variation is observed at the velo-oropharynx junction, which expects to induce a high tendency of airway collapse during inhalation. This study provides insights of the complex fluid dynamics in human pharyngeal airway and can contribute to a reliable approach to assess the probability of flow-induced airway collapse and improve the treatment of obstructive sleep apnea.

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Herbst appliance effects on pharyngeal airway ventilation evaluated using computational fluid dynamics

The Angle Orthodontist ◽

10.2319/080616-603.1 ◽

2017 ◽

Vol 87 (3) ◽

pp. 397-403 ◽

Cited By ~ 10

Author(s):

Tomonori Iwasaki ◽

Hideo Sato ◽

Hokuto Suga ◽

Ayaka Minami ◽

Yuushi Yamamoto ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Three Dimensional ◽

Control Group ◽

Herbst Appliance ◽

Oropharyngeal Airway ◽

Pharyngeal Airway ◽

Obstructive Sleep ◽

Before And After ◽

Computational Fluid Dynamics Cfd

ABSTRACT Objective: To evaluate the effect of a Herbst appliance on ventilation of the pharyngeal airway (PA) using computational fluid dynamics (CFD). Materials and Methods: Twenty-one Class II patients (10 boys; mean age, 11.7 years) who required Herbst therapy with edgewise treatment underwent cone-beam computed tomography (CBCT) before and after treatment. Nineteen Class I control patients (8 boys; mean age, 11.9 years) received edgewise treatment alone. The pressure and velocity of the PA were compared between the groups using CFD based on three-dimensional CBCT images of the PA. Results: The change in oropharyngeal airway velocity in the Herbst group (1.95 m/s) was significantly larger than that in the control group (0.67 m/s). Similarly, the decrease in laryngopharyngeal airway velocity in the Herbst group (1.37 m/s) was significantly larger than that in the control group (0.57 m/s). Conclusion: The Herbst appliance improves ventilation of the oropharyngeal and laryngopharyngeal airways. These results may provide a useful assessment of obstructive sleep apnea treatment during growth.

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Computational Fluid Dynamics Modeling of Rotating Annular VUV/UV Photoreactor for Water Treatment

Processes ◽

10.3390/pr9010079 ◽

2020 ◽

Vol 9 (1) ◽

pp. 79

Author(s):

Minghan Luo ◽

Wenjie Xu ◽

Xiaorong Kang ◽

Keqiang Ding ◽

Taeseop Jeong

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Water Treatment ◽

Cfd Modeling ◽

Flow Mode ◽

Oh Radicals ◽

Dynamics Modeling ◽

Rotational Movement ◽

Contaminant Degradation ◽

Wide Range

The ultraviolet photochemical degradation process is widely recognized as a low-cost, environmentally friendly, and sustainable technology for water treatment. This study integrated computational fluid dynamics (CFD) and a photoreactive kinetic model to investigate the effects of flow characteristics on the contaminant degradation performance of a rotating annular photoreactor with a vacuum-UV (VUV)/UV process performed in continuous flow mode. The results demonstrated that the introduced fluid remained in intensive rotational movement inside the reactor for a wide range of inflow rates, and the rotational movement was enhanced with increasing influent speed within the studied velocity range. The CFD modeling results were consistent with the experimental abatement of methylene blue (MB), although the model slightly overestimated MB degradation because it did not fully account for the consumption of OH radicals from byproducts generated in the MB decomposition processes. The OH radical generation and contaminant degradation efficiency of the VUV/UV process showed strong correlation with the mixing level in a photoreactor, which confirmed the promising potential of the developed rotating annular VUV reactor in water treatment.

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