Airflow dynamics in obese minipigs with obstructive sleep apnea

Zi-Jun Liu,Tiffany Do,Hanson Fong

doi:10.1016/j.heliyon.2020.e05700

Zi-Jun Liu, Tiffany Do + Show 1 more

Open Access

https://doi.org/10.1016/j.heliyon.2020.e05700

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Abstract

ObjectivesObstructive sleep apnea (OSA) is associated with anatomical restrictions of pharyngeal airway, but the mechanism of airflow dynamics in OSA is largely unknown. This study utilized computational flow dynamics (CFD) to build a 3D model of the pharynx and to test the hypothesis that an increased restriction in the pharynx in OSA/obese minipigs leads to higher resistance, which in turn creates turbulence to induce temporary blockage of pharyngeal airway patency. DesignOf five 9-11-months-old Yucatan minipigs, 3 were non-obese (BMI<35) and two obese (BMI>51). After natural sleep monitoring using BioRadio system, pigs were sedated to collect MRI images and airflow parameters. The MRI images were processed to create 3D configurations of pharynx. These 3D configurations were meshed to create finite element models (FEM) of CFD. The obtained airflow parameters were input into the configurations to identify turbulent airflow and its location. ResultsHeavy snoring and multiple >5s hypopnea/apnea episodes (AHI = 32–35) were identified in both obese minipigs during sleep. Compared to the non-obese/non-OSA controls, obese/OSA minipigs showed much lower respiratory tidal volumes and inspiratory airflow speed. FEM simulation found that turbulence was not present in the pharynx in either model. However, a 25% increase of airflow velocity was observed at the narrowest part of the nasal pharynx in the obese/OSA minipig model. ConclusionsDespite the narrower pharyngeal airway and the higher velocity of airflow, FEM simulation indicated that turbulence was not produced in the obese/OSA minipigs.

Highlights

Obstructive sleep apnea (OSA) is characterized by the repeated narrowing of the pharyngeal airway during sleep
Through finite element modeling (FEM), computational fluid dynamics (CFD) can be used to simulate airflow dynamics and pressure distributions in a 3D format to understand the biomechanical properties of airway involved in OSA and to evaluate the various treatment outcomes on airway restriction of OSA (Mylavarapu et al 2009, 2013; Zhao et al, 2013)
In the obese/OSA minipig, the range was -10% to þ25% of V0's, where the 25% increase was observed at the narrowest part of the airflow pathway located in the end of nasal pharynx, as indicated by the vertical arrows (Figure 6)

Summary

Introduction

Obstructive sleep apnea (OSA) is characterized by the repeated narrowing of the pharyngeal airway during sleep. One of the biggest risk factors of OSA is obesity, as it contributes to expanding the mass of structures around the pharyngeal airway and in turn, narrowing the airway passage. Both animal and clinical studies have revealed that obesity increase the sizes, and accumulates adipose tissue in the tongue and soft palate, which positively correlates with the severity of OSA (Brennick et al, 2014; Kim et al, 2014; Schwartz et al, 2008). A decrease in the volume of pharyngeal airway passages is believed to increase the airway resistance and pressure that would cause a disruption the inspiratory laminar airflow as it enters the airway, causing the airflow

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