下颌逐步前伸对阻塞性睡眠呼吸暂停低通气综合征患者腭咽部形态影响的三维有限元分析
【摘要】
阻塞性睡眠呼吸暂停低通气综合征（obstructive sleep apnea hypopnea syndrome，OSAHS）是一种以睡眠中反复出现呼吸暂停、血氧饱和度下降、上气道阻塞为特征的复杂综合征。成年人OSAHS的发病率为2%～4%[1]。它是高血压发病的危险因素，可导致心血管疾病以及白天嗜睡、生活质量下降等严重后果。OSAHS发病机制目前尚不明确，多数学者认为其与上气道阻塞相关。导致上气道阻塞的主要原因是咽气道解剖和神经肌肉功能异常[2]，其中以上气道解剖性狭窄为重要因素[3-6]。因此，上气道解剖结构成为研究OSAHS发生机制的重要方面。
对OSAHS患者上气道形态的研究多采用影像学手段[7-12]，如X线头影测量法、计算机体层扫描技术（CT）和磁共振技术（MRI）等。但是CT、MRI技术只是OSAHS的一种影像学诊断技术，如果要研究OSAHS患者上气道的受力变化、应力分布等情况，有限元法无疑具有更大的优越性。其优越性在于[13]：不仅能够提供直观、数字化的三维影像，还能利用相关软件对所获得的三维影像进行三维有限元分析，从而提供动态解剖、功能学以及生物力学方面的信息。
本研究通过对OSAHS患者上气道拍摄螺旋CT，获得DICOM格式的图像信息，运用医学建模软件Mimics、逆向工程软件Imageware和有限元分析软件Ansys建立准确、可灵活模拟操作的OSAHS患者上气道及其周围结构的三维有限元模型。通过对有限元模型下颌骨前伸位移载荷分析，对OSAHS患者上气道及其周围结构进行生物力学分析，以期深入了解OSAHS的发生机制以及为口腔矫治器治疗提供理论依据，同时探索一种新的方法，为今后研究提供一种新的思路。
目的：建立OSAHS患者上气道及其周围结构的三维有限元模型，通过加载下颌逐步前伸，观察OSAHS患者腭咽部生物力学和形态学改变，为口腔矫治器治疗提供理论依据。
方法：对OSAHS患者上气道行薄层CT扫描，获得患者上气道DICOM格式的图像信息，采用Mimics三维建模软件、Imageware逆向工程软件、Ansys有限元分析软件建立上气道及其周围结构的三维有限元模型，然后通过加载下颌骨逐步前伸，观察腭咽部生物力学和形态学的变化及其规律。
结果：建立了OSAHS患者上气道及其周围结构的三维有限元模型，规定采用10节点Solid 92四面体单元划分网格，按要求划分网格后，骨、肌肉、气道得到的单元数和节点数分别为：214725、38826、22590个单元，317305、60018、30720个节点。通过逐步前伸下颌骨，腭咽部软腭末端横截面发生形态变化，主要表现为：截面位移增加最大出现在下颌前伸8 mm时，其中横径缩小而矢状径呈增大趋势；随着下颌逐步前伸，加载模型（后）的平均应力变化不大，分布均匀；随着位移载荷增加，S1主应力有增加的趋势，但其分布位置未发生明显改变。
结论：应用螺旋CT技术联合使用Mimics三维建模软件、Imageware逆向工程软件、Ansys有限元分析软件建立OSAHS患者上气道及其周围结构的三维有限元模型，证实通过CT建立准确、可灵活模拟操作的OSAHS患者上气道及其周围结构三维有限元模型的方法，建模效率高、速度快，模型的几何相似性较好，使用灵活；通过下颌逐步前伸，对OSAHS腭咽部有限元模型进行载荷分析，有效展示下颌骨前伸与腭咽部之间的关系，为下颌前伸矫治器治疗OSAHS提供理论依据，同时为后续患者上气道生物力学研究打下良好的基础。
【关键词】阻塞性睡眠呼吸暂停低通气综合征；下颌前伸；上气道腭咽；三维有限元法
The three-dimensional Finite Element analysis of an Obstructive Sleep Apnea Hypopnea Syndrome Patient’s palatopharyngeal part with the titrated mandibular advancement(https://www.daowen.com)
ABSTRACT
Obstructive sleep apnea hypopnea syndrome（OSAHS）is a complex syndrome characterized by collapsed upperairway resulting recurring sleep apnea，oxygen desaturation.The Morbidity rate of OSAHS in adult is to 2%～4%[1].OSAHS is a risk factor of hypertension.In the long run，the OSAHS can lead to cardiovascular disease and daytime somnolence，affect one’s living mass greatly.The pathogenesis of OSAHS is not yet very clear，generally considered it is related to the collapse of the upper airway.Abnormalities of the upper airway morphology and surrounding tissue defunction can result in the collapse of the upper airway[2].Upper airway anatomic factors are thought to play a critical role[3-6].Therefore，to study the upper airway anatomic structure become an important aspect of the pathogenesis study of OSAHS.
Currently scholars often use imaging methods to study the upper airway of OSAHS patient[7-12]，including X cephalometric method，computer tomography technology（CT）and magnetic resonance imaging（MRI），but CT and MRI are only imaging diagnosis method.Absolutely，the finite element analysis（FEA）have more superiority，if the stress analysis of the upper airway was demanded.FEA can supply not only visualized digital threedimensional image，but also analysis to the three-dimensional image with relative software，and the information about dynamic anatomy，functional morphology and biomechanics[13].
This study obtained the accurate DICOM format of the image information of OSAHS patient’s upper airway by using spiral CT scan and establish an model by using Mimics、Imageware and Ansys software，which can simulate OSAHS patient’s upper airway accurately and flexiblely.Through the load analysis of finite element model，lay the foundation for the biomechanical analysis of the OSAHS patient’s upper airway，in order to understand the pathogenesis of OSAHS，and provid a theoretical basis OSAHS therapy with Oral appliance while explor a new method of OSAHS research which can provide a new idea for future research of OSAHS.
Objective：Construct a three-dimensional finite element model of the Upper airway and adjacent structure of an Obstructive sleep apnea hypopnea syndrome patient for OSAHS biomechanical analysis.And then with titrated mandibular advancement，the biomechanics and morphologic changes of the palatopharyngeal part can be observed.
Methods：DICOM format image information of an OSAHS patient’s upper airway obtained by thin-section CT scanning and digital image processing were utilized to construct a three-dimensional finite element model by Mimics、Imageware and Ansys software.And then titrated mandibular advancement，the changes and the law of glossopharyngeal part observed by biomechanics and morphologic.
Results：A case of OSAHS and the adjacent upper airway structure of three-dimensional finite element model is constructed.The model is formed by solid 92 tetrahedral which unit is 10-node mesh.Then the model has bone：214725 elements，317305 nodes；muscle：38826 elements，60018 nodes；upper airway：22590 elements，30720 nodes.With titrated mandibular advancement，glossopharyngeal part of three-dimensional finite element of OSAHS change signficately，The main manifestations are：After loading model，The cross-sectional area of palatopharyngealparts was increased Largest when mandibular advanced at 8 mm.The sagittal diameter of palatopharyngeal were increased significantly，Although the transverse diameter was decreased correspondingly.With titrated mandibular advancement，the palatopharyngeal stress did not change significantly.The frist principal stress（S1）is increased，with the increasing of distance，but the location of frist principal stress concentration did not change significantly.
Conclusion：The joint use of spiral CT technology and Mimics software，Imageware software，Ansys software on the establishment of upper airway and vicinity structure of OSAHS patient，which confirmed by CT to establishment accurate，flexible threedimensional finite element model of the upper airway and vicinity structure of an OSAHS patient.The model has good geometric similarity and good efficiency.Through titrated mandibular advancement，do load analysis to the finite element model of OSAHS palatopharyngeal part，show the relationship between mandibular advancement and the palatopharyngeal part effectively，which confirming that the study is feasibility，providing a theoretical basis for treatment of OSAHS with Mandibular advancement appliance and laying a good foundation for the follow-up study of upper airway in OSAHS patients with biomechanical analysis.
Key words：Obstructive sleep apnea hypopnea syndrome；mandibular advancement；palatopharyngeal part of upper airway；three-dimensional finite element method