上气道及部分支气管生物力学模型的数值研究

目的建立上气道、气管及部分支气管的生物力学模型,研究不同呼吸模式对气道内气流特性以及气道阻力的影响。方法根据CT扫描资料,建立包括鼻腔、口腔、咽、喉、气管和部分支气管在内的具有真实解剖结构形态的三维有限元呼吸道模型,针对现实中几种典型情况,数值模拟流经鼻、口的气流不同比例情况下气道内的气流特性。结果当仅有少量气流经由口腔吸入时,呼吸道内气流的分布规律以及各部位气道阻力的大小与完全经由鼻腔呼吸的情况相似。当口腔吸入或呼出大量气体,气流主要经由口腔与外界进行交换时,呼吸道内气流场、压力场和剪应力场分布规律明显不同,主要区别体现在鼻腔、口腔气道内。结论建立上气道与气管、支气管生物力学模型,可以从整体上了解呼吸过程中整个上气道至部分支气管中气流的分布情况,为了解与上气道结构相关疾病的发病机制建立数值研究平台。     

不同环境温度对人体呼吸道内颗粒物沉积规律的影响

目的 探究环境温度对人体呼吸道内气体流动和颗粒物沉积规律的影响。 方法 采用计算流体动力学(computational fluid dynamics,CFD)方法模拟具有黏液层的人体呼吸道内的气固两相流;考虑 6 种不同环境温度(-25、-15、0、15、26. 7、45 ℃ )和 8 种不同粒径(1~ 8 μm)的颗粒物。 结果 气流流速与 6 种温度下平均气流流速的差异可达 39. 42% ;气流湍流动能与 6 种温度下湍流动能平均值的差异可达到 11. 59% ;气流温度变化与 6 种温度下气流温度变化平均值的差异可高达 82. 4% 。 颗粒总沉积率与 6 种温度下总沉积率平均值的差异可达14. 72% ;颗粒局部沉积率与 6 种温度下局部沉积率平均值的差异可达到 37. 08% 。 结论 环境温度差异会影响人体呼吸道内部的气流流场性质,进而会影响颗粒物在呼吸道内的沉积规律。 因此,获得精准的颗粒物在人体呼吸道内的运动沉积规律,有必要考虑环境温度的影响。     

人体上呼吸道内气溶胶沉积的数值仿真研究

目的研究人体上呼吸道内气溶胶沉积规律,分析呼吸模式对气溶胶沉积规律的影响。方法建立人体上呼吸道计算机数值仿真模型,采用计算流体动力学方法对人体上呼吸道内的气溶胶沉积进行数值仿真,分析气溶胶在上呼吸道内的沉积规律。结果人体上呼吸道内不同部位气溶胶沉积率随惯性参数的增加而增加,人体上呼吸道内的呼吸流量和气溶胶性质对气溶胶在上呼吸道内的沉积模式影响较小,受到惯性碰撞和湍流扩散的影响致使在喉部气溶胶沉积最多。人体循环吸气模式下,气溶胶在人体上呼吸道内的沉积率高于稳态吸气模式下的气溶胶的沉积率。循环吸气模式下远大于循环呼气模式下气溶胶沉积率。结论惯性碰撞对于微尺度气溶胶沉积而言是主要的沉积机制,而湍流扩散、二次气流运动和环流气流运动对气溶胶在人体呼吸道内沉积同样具有重要的影响。     

多因素影响下的人体肺腺泡区吸入颗粒物沉积规律数值模拟研究

研究颗粒物在人体肺腺泡区的沉积规律对了解肺部疾病致病机制、促进肺部疾病的预防和治疗都有重要意义。现行研究大多关注颗粒物在人体肺腺泡区的最终沉积率,而对其沉积动态过程鲜有涉及。本文建立了G3～G7共五个多肺泡模型,引入颗粒物沉积速度评价参数1/4沉积时间,通过数值模拟研究了模型级数和结构、颗粒物粒径、呼吸模式等因素对0.1～5μm粒径范围内颗粒物沉积规律的影响,归纳总结了不同粒径颗粒物的沉积特点,为进一步了解人体肺腺泡区颗粒物的运动规律提供了新视角。结果表明:模型级数和结构是影响各粒径颗粒物沉积的重要因素。0.1μm颗粒物沉积受布朗力主导,沉积率高,沉积速度快,沉积曲线呈对数型分布;5μm颗粒物沉积受重力主导,沉积率高,沉积较快,沉积曲线呈"S"型分布;0.3～1μm颗粒物沉积则受惯性冲击影响较大,随着呼吸模式的改变沉积规律变化明显。本文的研究方法和结果能为进一步探究肺部疾病致病机制和肺部疾病的预防与治疗提供理论依据和数据支持。     

不同功能残气量对可吸入颗粒物在人体肺腺泡区沉积影响的实验研究

研究可吸入颗粒物在肺腺泡内的沉积规律对于明确肺气肿等常见呼吸系统疾病的诱因和发展,以及优化临床治疗和预防方案具有重要意义。本文建立了能够模拟终末细支气管和肺腺泡颗粒物沉积的体外实验模型,在不同功能残气量模式下研究了不同粒径的可吸入颗粒物在肺腺泡内的沉积率。结果表明,颗粒物直径是影响颗粒物在肺腺泡沉积的重要因素,1μm左右的颗粒物沉积率最高。功能残气量增大,颗粒物沉积率显著降低。本文研究结果为肺气肿和尘肺等疾病的靶向吸入治疗提供了数据支撑和优化途径,建立的模型也为研究可吸入颗粒物在肺腺泡内的沉积规律提供了一种可行的体外实验模型。     

人体肺腺泡区吸入颗粒物沉积状况数值模拟的研究进展

颗粒物的吸入和在人体肺腺泡区的沉积可能引发肺部疾病,采用数值模拟方法研究肺腺泡区吸入颗粒物的沉积状况,对肺部疾病的预防和临床治疗具有重要意义。本文从肺腺泡模型、模型运动方式、呼吸模式、颗粒物特性、肺部病变以及年龄等影响数值模拟结果的重要因素出发,分类总结了肺腺泡区数值模拟的研究进展,分析了现有研究的不足和局限,提出了未来发展重点研究的方向,以期为肺腺泡区数值模拟的进一步研究和应用提供参考和借鉴。     

鼻腔气道结构对鼻腔加温加湿功能影响的数值模拟

目的研究鼻腔气道结构的变化对鼻腔加温加湿功能的影响。方法选取9例正常人和2例鼻中隔偏曲患者(术前术后)作为研究对象,建立鼻腔的三维有限元模型,数值模拟鼻腔气道中的气流分布、气流温度和湿度,并对比正常人与病患、术前与术后的数值模拟结果。结果鼻腔气道宽敞一侧气流体积流率相对较大,加温加湿效果差;狭窄一侧加温效果相对较好。对于正常人,鼻腔对吸入气流加温加湿的部位主要位于前端;对于病患,则要取决于鼻腔的气道结构。结论鼻腔气道结构影响鼻腔对吸入气流的加温加湿效果,鼻腔气道结构的几何参数如鼻腔气道壁面积、鼻腔体积可以用来衡量鼻腔对气流的加温加湿效果。     

典型男性OSAHS患者上气道气流运动特性的数值模拟

目的 研究典型男性阻塞性睡眠呼吸暂停低通气综合症（OSAHS）患者在平静呼吸时上气道气流运动特性,以及气流对软腭和悬雍垂作用的动力特点。方法 基于患者CT影像数据建立可靠的上气道流场几何模型,以临床睡眠监测数据作为数值模拟边界条件的依据,采用低雷诺数的湍流模型计算获得一个完整呼吸周期内上气道气流运动规律。结果OSAHS患者在呼吸过程中,上气道气流流动形式有显著差异。在吸气阶段,上气道腔内流速可达9.808 m/s,最大负压可达-78.856 Pa,鼻腔顶部出现局部回流,软腭受到的最大气流压力为-10.884 Pa,悬雍垂受到的最大气流压力为-51.946 Pa,气流对软腭和悬雍垂造成的最大剪切应力分别为78和311 mPa。在呼气阶段,上气道腔内最大流速为10.330 m/s,最大负压为-51.921 Pa,口咽部和鼻腔顶部均出现局部回流,且口咽部顺时针回流现象显著,软腭受到的最大气流压力为2.603 Pa,悬雍垂受到的最大气流压力为-18.222 Pa,软腭和悬雍垂受到的最大剪切应力分别为51和508 mPa。结论 口咽部是易塌陷的部位,一个呼吸循环过程的数值模拟可以捕捉到上气道流场显著的回流特征,上气道回流直接影响软腭和悬雍垂所受的力,同时也关系到患者呼吸的流畅程度。     

流固耦合作用下真实人体上呼吸道气溶胶扩散沉积的仿真与实验

通过构建真实人体上呼吸道三维规范模型,运用大涡模拟数值方法和Lagrangian随机轨道模型,对考虑流固耦合作用时循环呼吸模式下上呼吸道内气溶胶的扩散沉积进行数值仿真,分析气流涡结构演化对气溶胶扩散的影响,并通过实验对气溶胶在人体上呼吸道的沉积率进行测量,验证仿真方法的正确性。结果表明:循环吸气时,0.3 μm气溶胶颗粒比6.5 μm气溶胶颗粒更容易通过上呼吸道而进入更深层次的支气管;循环呼气时,部分进入上呼吸道的颗粒在呼出气流夹带下,在气道中折返、回旋、沉积,而有些则从口腔中呼出;0.3和6.5 μm气溶胶颗粒在咽、喉以及气管内沉积较多,而在口腔内沉积较少;6.5 μm气溶胶颗粒在上呼吸道不同部位的沉积率明显高于0.3 μm气溶胶;流固耦合作用时咽部、喉部的壁面形变可缓冲气流冲击,气溶胶颗粒在咽喉部位的沉积率有所下降;大粒径气溶胶颗粒沉积受惯性碰撞影响较大,而小粒径气溶胶颗粒沉积受湍流扩散及涡流夹带的影响较大。     

急性呼吸窘迫综合征患者下呼吸道内气流运动特性

目的应用计算流体动力学(computational fluid dynamics,CFD)技术对急性呼吸窘迫综合征(acute respiratory distress syndrome,ARDS)患者不同程度呼吸窘迫状态时下呼吸道内气流运动特性进行模拟研究。方法基于CT影像数据建立真实健康人体下呼吸道三维模型。采用标准k-ε湍流模型对下呼吸道内的气体流动进行数值模拟,分析下呼吸道内气流的速度、流量、压力以及壁面剪切应力等参数分布特点。结果拟合下呼吸道空气流动阻力与呼吸强度的函数关系;得到下呼吸道内空气流速、压力、壁面剪切应力的分布特点以及空气流量在各肺及各叶支气管的分配情况。结论通过CFD模拟分析可以获得更为详细的下呼吸道流场相关数据,为ARDS患者的临床治疗提供理论依据。     

Nasal dosimetry of inhaled gases and particles: where do inhaled agents go in the nose?

The anatomical structure of the nasal passages differs significantly among species, affecting airflow and the transport of inhaled gases and particles throughout the respiratory tract. Since direct measurement of local nasal dose is often difficult, 3-dimensional, anatomically accurate, computational models of the rat, monkey, and human nasal passages were developed to estimate regional transport and dosimetry of inhaled material. The computational models predicted that during resting breathing, a larger portion of inspired air passed through olfactory-lined regions in the rat than in the monkey or human. The models also predicted that maximum wall mass flux (mass per surface area per time) of inhaled formaldehyde in the nonsquamous epithelium was highest in monkeys (anterior middle turbinate) and similar in rats and humans (dorsal medial meatus in the rat and mid-septum in the human, near the squamous/nonsquamous epithelial boundary in both species). For particles that are 5 microm in aerodynamic diameter, preliminary simulations at minute volume flow rates predicted nasal deposition efficiencies of 92%, 11% and 25% in the rat, monkey, and human, respectively, with more vestibular deposition in the rat than in the monkey or human. Estimates such as these can be used to test hypotheses about mechanisms of toxicity and supply species-specific information for risk assessment, thus reducing uncertainty in extrapolating animal data to humans.     

A computer program for the simulation of fiber deposition in the human respiratory tract

As inhaled fibers may lead to a variety of lung diseases, detailed information on their deposition in the human respiratory tract is an indispensable requirement in medical science. In the work presented here, a Visual Basic((R)) computer program, termed FIBROS, is described which enables the simulation of fibrous particle deposition in both the extrathoracic region and different parts of the lung itself, including the results of published numerical studies on inertial/interceptional as well as diffusional and gravitational deposition. The input window of FIBROS includes the selection of specific breathing conditions by variation of the tidal volume and breathing cycle. Furthermore, the user is able to determine fiber properties such as diameter, aspect ratio, specific weight, and fiber orientation with respect to the air stream in the upper and lower airways of the lungs. Besides the offer of various deposition formulae for each region of the respiratory tract, thereby also allowing a distinction between mouth and nose breathing, the user may select between different morphometric datasets of the lung and respective airway scaling procedures. Analysis routines of FIBROS include the estimation of regional deposition fractions, thereby distinguishing between extrathoracic, bronchial, and acinar compartments, and a calculation of generation-by-generation deposition probabilities within tubular and alveolar structures. Preliminary results presented here should demonstrate the effects on fiber deposition due to variations of the breathing behaviour and the particle properties.     

Behavior of submicrometer particles in periodic alveolar airflows

Here, we report a numerical experiment in which submicrometer particle entrainment in a periodic flow that matches those existing in the alveolus in the human lung was simulated for both sedentary and light activity. A spherical cavity with a prescribed velocity profile at the inlet was used to simulate the time-dependent periodical flow of air in the alveolus. Expansion and contraction of the alveolus were simulated by setting a conceptual permeable wall as the outer surface of the model and adjusting the boundary conditions in order to match the continuity of the flow. The simulations were conducted for breathing periods of 5 and 3 s, which match sedentary and light activity conditions, respectively, and the results were extrapolated to the real lung. It was found that, most of the particles mainly followed a straightforward path and reached the opposite side of the alveolar wall in both breathing conditions. The concentration patterns obtained are consistent with the fact that the flow within the alveolus is mainly diffusive and does not greatly depend on the flow velocity. It was found that the particles which are heavier than air move out of phase with the periodic airflow that crosses the alveolus entrance, and that these particles are significantly caught within the alveolus. Particle entrapment increases with breathing rate in accordance with experimental values and indicates that increase in breathing frequency in environments with high concentration of submicrometer particles has the consequence of increasing particle entrapment by several times with respect to normal breathing rate.     

Aerosol deposition and clearance in the human upper airways

The human upper respiratory tract, defined here as the airways above the trachea, is the portal of entry for airborne particles. Whether inhaled particles reach the bronchial or alveolated airways or are deposited in the upper airways (nasal or oral passage) depends upon a number of factors which are discussed in this paper. These factors can be divided into two groups: those which relate to the air flow properties and those which relate to the particles. If these factors are known to a sufficient degree, the regional deposition efficiency of the inhaled particles can be estimated. Particles once deposited in the upper airway are cleared by one of several mechanisms depending on the type of particle, site of deposition and functional state of the airway surface. The clearance processes and their importance for various particles are discussed. Supported by NIH Grant HL-19715 and NIEHS Grant EHS-00454.     

Comparison of micron- and nanoparticle deposition patterns in a realistic human nasal cavity

Knowledge regarding particle deposition processes in the nasal cavity is important in aerosol therapy and inhalation toxicology applications. This paper presents a comparative study of the deposition of micron and submicron particles under different steady laminar flow rates using a Lagrangian approach. A computational model of a nasal cavity geometry was developed from CT scans and the simulation of the fluid and particle flow within the airway was performed using the commercial software GAMBIT and FLUENT. The air flow patterns in the nasal cavities and the detailed local deposition patterns of micron and submicron particles were presented and discussed. It was found that the majority of micron particles are deposited near the nasal valve region and some micron particles are deposited on the septum wall in the turbinate region. The deposition patterns of micron particles in the left cavity are different compared with that in the right one especially in the turbinate regions. In contrast, the deposition for nanoparticles shows a moderately even distribution of particles throughout the airway. Furthermore the particles releasing position obviously influences the local deposition patterns. The influence of the particle releasing position is mainly shown near the nasal valve region for micron particle deposition, while for submicron particles deposition, both the nasal valve and turbinate region are influenced. The results of the paper are valuable in aerosol therapy and inhalation toxicology.     

Substance deposition assessment in obstructed pulmonary system through numerical characterization of airflow and inhaled particles attributes

Background

Chronic obstructive pulmonary disease (COPD) and asthma are considered as the two most widespread obstructive lung diseases, whereas they affect more than 500 million people worldwide. Unfortunately, the requirement for detailed geometric models of the lungs in combination with the increased computational resources needed for the simulation of the breathing did not allow great progress to be made in the past for the better understanding of inflammatory diseases of the airways through detailed modelling approaches. In this context, computational fluid dynamics (CFD) simulations accompanied by fluid particle tracing (FPT) analysis of the inhaled ambient particles are deemed critical for lung function assessment. Also they enable the understanding of particle depositions on the airways of patients, since these accumulations may affect or lead to inflammations. In this direction, the current study conducts an initial investigation for the better comprehension of particle deposition within the lungs. More specifically, accurate models of the airways obstructions that relate to pulmonary disease are developed and a thorough assessment of the airflow behavior together with identification of the effects of inhaled particle properties, such as size and density, is conducted. Our approach presents a first step towards an effective personalization of pulmonary treatment in regards to the geometric characteristics of the lungs and the in depth understanding of airflows within the airways.

Methods

A geometry processing technique involving contraction algorithms is established and used to employ the different respiratory arrangements associated with lung related diseases that exhibit airways obstructions. Apart from the normal lung case, two categories of obstructed cases are examined, i.e. models with obstructions in both lungs and models with narrowings in the right lung only. Precise assumptions regarding airflow and deposition fraction (DF) over various sections of the lungs are drawn by simulating these distinct incidents through the finite volume method (FVM) and particularly the CFD and FPT algorithms. Moreover, a detailed parametric analysis clarifies the effects of the particles size and density in terms of regional deposition upon several parts of the pulmonary system. In this manner, the deposition pattern of various substances can be assessed.

Results

For the specific case of the unobstructed lung model most particles are detected on the right lung (48.56% of total, when the air flowrate is 12.6 L/min), a fact that is also true when obstructions arise symmetrically in both lungs (51.45% of total, when the air flowrate is 6.06 L/min and obstructions occur after the second generation). In contrast, when narrowings are developed on the right lung only, most particles are pushed on the left section (68.22% of total, when the air flowrate is 11.2 L/min) indicating that inhaled medication is generally deposited away from the areas of inflammation. This observation is useful when designing medical treatment of lung diseases. Furthermore, particles with diameters from 1 μm to 10 μm are shown to be mainly deposited on the lower airways, whereas particles with diameters of 20 μm and 30 μm are mostly accumulated in the upper airways. As a result, the current analysis indicates increased DF levels in the upper airways when the particle diameter is enlarged. Additionally, when the particles density increases from 1000 Kg/m³ to 2000 Kg/m³, the DF is enhanced on every generation and for all cases investigated herein. The results obtained by our simulations provide an accurate and quantitative estimation of all important parameters involved in lung modeling.

Conclusions

The treatment of respiratory diseases with inhaled medical substances can be advanced by the clinical use of accurate CFD and FPT simulations and specifically by evaluating the deposition of inhaled particles in a regional oriented perspective in regards to different particle sizes and particle densities. Since a drug with specific characteristics (i.e. particle size and density) exhibits maximum deposition on particular lung areas, the current study provides initial indications to a qualified physician for proper selection of medication.

     

Breathing Resistance and Ultrafine Particle Deposition in Nasal–Laryngeal Airways of a Newborn, an Infant, a Child, and an Adult

As a human grows from birth to adulthood, both airway anatomy and breathing conditions vary, altering the deposition rate and pattern of inhaled aerosols. However, deposition studies have typically focused on adult subjects, results of which may not be readily extrapolated to children. This study numerically evaluated the age-related effects on the airflow and aerosol dynamics in image-based nose?Cthroat models of a 10-day-old newborn, a 7-month-old infant, a 5-year-old child, and a 53-year-old adult. Differences in airway physiology, breathing resistance, and aerosol filtering efficiency among the four models were quantified and compared. A high-fidelity fluid-particle transport model was employed to simulate the multi-regime airflows and particle transport within the nasal?Claryngeal airways. Ultrafine particles were evaluated under breathing conditions ranging from sedentary to heavy activities. Results of this study indicate that the nasal?Claryngeal airways at different ages, albeit differ significantly in morphology and dimension, do not significantly affect the total deposition fractions or maximum local deposition enhancement for ultrafine aerosols. Further, the deposition partitioning in the sub-regions of interest is different among the four models. Results of this study corroborate the use of the in vivo-based diffusion parameter (D ^0.5 Q ^?0.28) over the replica-based parameter in correlating nasal?Claryngeal depositions of ultrafine aerosols. Improved correlations have been developed for the four age groups by implementing this in vivo-based diffusion parameter as well as the Cunningham correction factor.     

基于PIV技术的人体上呼吸道流场测量实验装置的构建

目的针对人体上呼吸道气流运动形成涡结构、流动分流、二次流等特点,研制基于粒子图像测速（particle image velocimetry, PIV）技术的人体上呼吸道流场测量实验装置,为开展人体上呼吸道流场特性实验研究提供平台。方法 基于完整人体上呼吸道医学扫描图像制备透明的实物模型,通过选择合适的气路系统,结合二维PIV系统搭建整套实验装置,并利用该装置对人体上呼吸道流场速度进行初步实验,将实验结果和数值仿真结果进行对比。结果呼吸流量为30 L/min稳态呼吸模式下,实验装置测得的气流在口腔上部有涡结构的形成,口腔下部贴近舌苔上部及口腔中部的气流速度较高,其他部位气流速度较低,与数值仿真结果较为一致。结论 基于PIV技术的人体上呼吸道流场测量实验装置合理可行,运行可靠,可用于人体上呼吸道内气流组织形式和涡量分布等测量,并能够实现对数值仿真的验证。     

Micro and nanoparticle deposition in human nasal passage pre and post virtual maxillary sinus endoscopic surgery

Realistic 3-D models of the human nasal passages were developed pre and post virtual uncinectomy and Middle Meatal Antrostomy. A 3-D computational domain was constructed by a series of coronal CT scan images from a healthy subject. Then a virtual uncinectomy intervention and maxillary antrostomy were performed on the left nasal passage by removing the uncinate process and exposing the maxillary sinus antrum. For several breathing rates corresponding to low or moderate activities, the airflows in the nasal passages were simulated numerically pre and post virtual routine maxillary sinus endoscopic surgery. The airflow distribution in the nasal airway, maxillary and frontal sinuses were analyzed and compared between pre and post surgery cases. A Lagrangian trajectory analysis approach was used for evaluating the path and deposition of microparticles in the nasal passages and maxillary sinuses. A diffusion model was used for nanoparticle transport and deposition analysis. The deposition rate of the inhaled micro and nanoparticles in the sinuses were evaluated and compared for pre and post operation conditions. The results showed that after maxillary sinus endoscopic surgery, the inhaled nano and microparticles can easily enter this sinus due to penetration of the airflow into the sinus cavity. This was in contrast to the preoperative condition in which almost no particles entered the sinuses. These results could be of importance for a better understanding of the effect of sinus endoscopic surgery on patient exposure to particulate pollution and inhalation drug delivery. The significantly higher airflow rate and particle deposition in the sinus could be a reason for the discomfort reported by some patient after maxillary sinus endoscopic surgery.