Background

The higher incidence of obstructive sleep apnea (OSA) in men than in women has been attributed to the upper airway being longer in men. The Starling resistor is the paradigm biomechanical model of upper airway collapse in OSA where a collapsible tube (representing the pharynx) is located between two rigid tubes (representing the nasal cavity and trachea). While the Starling resistor has been extensively studied due to its relevance to many physiological phenomena, the effect of tube length on tube collapsibility has not been quantified yet.

Methods

Finite element analysis of a 3-dimensional collapsible tube subjected to a transmural pressure was performed in ANSYS Workbench. The numerical methods were validated with in vitro experiments in a silicone tube whose modulus of elasticity (361 ± 28 kPa) and dimensions (length = 100 mm, diameter = 22.2 mm, and wall thickness = 1.59 mm) were selected so that tube compliance was similar to pharyngeal compliance in humans during sleep. The buckling pressure (transmural pressure at which the tube collapses) was quantified in tubes of three different diameters (10 mm, 16 mm, and 22.2 mm) and ten length-to-diameter ratios ($\text{L}/\text{D}$ = 4 to 13), while keeping the wall-thickness-to-radius ratio constant at 0.143.

Results

The absolute value of the buckling pressure decreased from 4.7 to 3.3 cmH₂O (461–324 Pa) when $\text{L}/\text{D}$ increased from 4 to 13. The buckling pressure was nearly independent from tube length for $\text{L}/\text{D }>10$.

Conclusions

Our finding that longer tubes are more collapsible than shorter tubes is consistent with the higher incidence of obstructive sleep apnea in males than females.

中文翻译：

---

管长对伸缩管屈曲压力的影响

背景

男性阻塞性睡眠呼吸暂停 (OSA) 的发病率高于女性，这归因于男性的上呼吸道较长。Starling 电阻器是 OSA 中上气道塌陷的典型生物力学模型，其中可折叠管（代表咽）位于两个刚性管（代表鼻腔和气管）之间。虽然 Starling 电阻器由于与许多生理现象相关而被广泛研究，但管长度对管可塌陷性的影响尚未量化。

方法

在 ANSYS Workbench 中对承受跨壁压力的 3 维可折叠管进行有限元分析。数值方法在硅胶管的体外实验中得到验证，硅胶管的弹性模量 (361 ± 28 kPa) 和尺寸（长度 = 100 毫米，直径 = 22.2 毫米，壁厚 = 1.59 毫米）被选择，因此管的顺应性是类似于人类睡眠时的咽部顺应性。在三种不同直径（10 毫米、16 毫米和 22.2 毫米）和十个长径比（$\text{大号}/\text{D}$ = 4 到 13），同时保持壁厚与半径之比恒定为 0.143。

结果

屈曲压力的绝对值从 4.7 下降到 3.3 cmH ₂ O (461–324 Pa) 时$\text{大号}/\text{D}$从 4 增加到 13。屈曲压力几乎与管长度无关$\text{大号}/\text{D }>10$.

结论

我们发现较长的管子比较短的管子更容易折叠，这与男性阻塞性睡眠呼吸暂停的发生率高于女性是一致的。