Lambeth C, Wang Z, Kairaitis K, Moshfegh A, Jabbarzadeh A, Amis TC. Modelling mucosal surface roughness in the human velopharynx: a computational fluid dynamics study of healthy and obstructive sleep apnea airways.
J Appl Physiol (1985) 2018;
125:1821-1831. [PMID:
30284517 DOI:
10.1152/japplphysiol.00233.2018]
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Abstract
We previously published a unique methodology for quantifying human velopharyngeal mucosal surface topography and found increased mucosal surface roughness in obstructive sleep apnea (OSA) patients. In fluid mechanics, surface roughness is associated with increased frictional pressure losses and resistance. This study used computational fluid dynamics (CFD) to analyse the mechanistic effect of different levels of mucosal surface roughness on velopharyngeal airflow.
METHODS
Reconstructed velopharyngeal models from OSA and Control subjects were modified, giving each model three levels of roughness, quantified by the curvature based surface roughness index (CBSRI0.6; range 24.8-68.6mm-1). CFD using the k-ω shear stress transport (SST) turbulence model was performed (unidirectional, inspiratory, steady state, 15l/min volumetric flow rate), and the effects of roughness on flow velocity, intraluminal pressure, wall shear stress and velopharyngeal resistance (Rv) were examined.
RESULTS
Across all models, increasing roughness increased maximum flow velocity, wall shear stress and flow disruption, while decreasing intraluminal pressures. Linear mixed effects modelling demonstrated a log-linear relationship between CBSRI0.6 and Rv, with a common slope (log(Rv)/CBSRI0.6) of 0.0079 (95%CI 0.0015-0.0143; p=0.019) for all subjects, equating to a 1.9-fold increase in Rv when roughness increased from Control to OSA levels. At any fixed CBSRI0.6, the estimated difference in log(Rv) between OSA and Control models was 0.9382 (95%CI 0.0032-1.8732; p=0.049), equating to an 8.7-fold increase in Rv.
CONCLUSION
This study supports the hypothesis that increasing mucosal surface roughness increases velopharyngeal airway resistance, particularly for anatomically narrower OSA airways, and may thus contribute to increased vulnerability to upper airway collapse in OSA patients.
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