Effects of soft palate and tongue collapse on upper airway flow field under progressive muscle tone loss: a fluid-structure interaction study

Abstract

Background: Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent upper airway collapse during sleep, yet the relative contributions of soft palate versus tongue collapse remain poorly quantified. Methods: Three-dimensional numerical models of the upper airway, soft palate, and tongue were reconstructed from computed tomography (CT) images. A transient bidirectional fluid-structure interaction (FSI) method was employed to determine the ventilation pressure required to maintain a prescribed inspiratory flow across progressively reduced artificial support loads applied to the soft palate and tongue (0–100% of the calibrated reference loads). Results: Isolated soft palate collapse exerted minimal effect on the required ventilation pressure. Obstruction severity was predominantly governed by tongue behavior: Below approximately 93% reduction of the reference tongue supported load, and airflow dynamics remained largely unchanged (maximum velocity ≤ 15.6 m/s, ventilation pressure ≤ 94 Pa). Beyond this level, appreciable tongue–soft palate compression was established and a marked nonlinear transition occurred: The ventilation pressure required to maintain the prescribed flow increased by approximately 806% (to 852 Pa), and the maximum velocity reached 46.3 m/s. Joint collapse analysis confirmed that tongue behavior, rather than soft palate status, is the primary determinant of flow obstruction in this model. Conclusions: In this single-subject model and under the selected artificial support loads, appreciable tongue–soft palate compression produces a marked nonlinear increase in the pressure required to maintain a prescribed flow, occurring at approximately 93% reduction of the reference tongue support load. This contact transition is model-specific and should not be interpreted as a universal neuromuscular threshold. The findings provide proof-of-concept evidence for a biomechanical mechanism of tongue-driven obstruction that warrants validation in multi-subject, clinically characterized cohorts.

Keywords

obstructive sleep apnea / upper airway / tongue collapse / fluid-structure interaction / ventilation pressure / tongue–soft palate contact transition

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