Numerical simulation of soft palate movement and airflow in human upper airway by fluid-structure interaction method

In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient with Obstructive Sleep Apnea-Hypopnea Syndrome （OSAHS）, three-dimensional models of upper airway cavity and soft palate are reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement of soft palate by fluid-structure interaction analysis. The reconstructed threedimensional models precisely preserve the original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate. The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function of the upper airway as well as in diagnosingdiseases related to anatomical structure and function of the upper airway.

Evaluation of Airway Obstruction at Soft Palate Level in Male Patients with Obstructive Sleep Apnea/Hypopnea Syndrome:Dynamic 3-Dimensional CT Imaging of Upper Airway

This study examined the dynamic characteristics of upper airway collapse at soft palate level in patients with obstructive sleep apnea/hypopnea syndrome（OSAHS） by using dynamic 3-Dimensional（3-D） CT imaging.A total of 41 male patients who presented with 2 of the following symptoms,i.e.,daytime sleepiness and fatigue,frequent snoring,and apnea with witness,were diagnosed as having OSAHS.They underwent full-night polysomnography and then dynamic 3-D CT imaging of the upper airway during quiet breathing and in Muller＇s maneuver.The soft palate length（SPL）,the minimal cross-sectional area of the retropalatal region（mXSA-RP）,and the vertical distance from the hard palate to the upper posterior part of the hyoid（hhL） were compared between the two breathing states.These parameters,together with hard palate length（HPL）,were also compared between mild/moderate and severe OSAHS groups.Association of these parameters with the severity of OSAHS [as reflected by apnea hypopnea index（AHI） and the lowest saturation of blood oxygen（LSaO2）] was examined.The results showed that 31 patients had severe OSAHS,and 10 mild/moderate OSAHS.All the patients had airway obstruction at soft palate level.mXSA-RP was significantly decreased and SPL remarkably increased during Muller＇s maneuver as compared with the quiet breathing state.There were no significant differences in these airway parameters（except the position of the hyoid bone） between severe and mild/moderate OSAHS groups.And no significant correlation between these airway parameters and the severity of OSAHS was found.The position of hyoid was lower in the severe OSAHS group than in the mild/moderate OSAHS group.The patients in group with body mass index（BMI）≥26 had higher collapse ratio of mXSA-RP,greater neck circumference and smaller mXSA-RP in the Muller＇s maneuver than those in group with BMI26（P0.05 for all）.It was concluded that dynamic 3-D CT imaging could dynamically show the upper airway changes at soft palate level in OSAHS patients.All the OSAHS patients had airway obstruction of various degrees at soft palate level.But no correlation was observed between the airway change at soft palate level and the severity of OSAHS.The patients in group with BMI≥26 were more likely to develop airway obstruction at soft palate level than those with BMI26.

Numerical analysis of respiratory flow patterns within human upper airway

A computational fluid dynamics （CFD） approach is used to study the respiratory airflow dynamics within a human upper airway. The airway model which consists of the airway from nasal cavity, pharynx, larynx and trachea to triple bifurcation is built based on the CT images of a healthy volunteer and the Weibel model. The flow character- istics of the whole upper airway are quantitatively described at any time level of respiratory cycle. Simulation results of respiratory flow show good agreement with the clinical mea- sures, experimental and computational results in the litera- ture. The air mainly passes through the floor of the nasal cavity in the common, middle and inferior nasal meatus. The higher airway resistance and wall shear stresses are distrib- uted on the posterior nasal valve. Although the airways of pharynx, larynx and bronchi experience low shear stresses, it is notable that relatively high shear stresses are distrib- uted on the wall of epiglottis and bronchial bifurcations. Besides, two-dimensional fluid-structure interaction models of normal and abnormal airways are built to discuss the flow-induced deformation in various anatomy models. The result shows that the wall deformation in normal airway is relatively small.

Computational Fluid Dynamics Simulation of the Upper Airway of Obstructive Sleep Apnea Syndrome by Muller Maneuver

This study aimed to use computer simulation to describe the fluid dynamic characteristics in patients with obstructive sleep apnea syndrome（OSAS） and to evaluate the difference between during quiet respiration and the Muller maneuver（MM）. Seven patients with OSAS were involved to perform computed tomographic（CT） scanning during quiet respiration and the MM. CT data in DICOM format were transformed into an anatomically three-dimensional computational fluid dynamics（CFD） model of the upper airway. The velocity magnitude, relative pressure, and flow distribution were obtained. Numerical simulation of airflow was performed to discuss how the MM affected airflow in the upper airway. To measure the discrepancy, the SPSS19.0 software package was utilized for statistic analysis. The results showed that the shape of the upper airway became narrower, and the pressure decreased during the MM. The minimal cross-sectional area（MCSA） of velopharynx was significantly decreased（P〈0.05） and the airflow velocity in MCSAs of velopharynx and glossopharynx significantly accelerated（P〈0.05） during the MM. This study demonstrated the possibility of CFD model combined with the MM for understanding pharyngeal aerodynamics in the pathophysiology of OSAS.

Computational Analysis of Airflow in Upper Airway under Light and Heavy Breathing Conditions for a Realistic Patient Having Obstructive Sleep Apnea

Background:Obstructive sleep apnea is a sleeping disorder that has troubled a sizeable population.There is an active area of research on obstructive sleep apnea that intends to better understand airflow behaviors and therefore treat patients more effectively.This paper aims to investigate the airflow characteristics of the upper airway in an obstructive sleep apnea(OSA)patient under light and heavy breathing conditions by using Turbulent Kinetic Energy(TKE),an accurate method in expressing the flow concentration mechanisms of sleeping disorders.It is important to visualize the concentration of flow in the upper airway in order to identify the severity level of the obstruction during sleep.Methods:Computational fluid dynamic(CFD)analysis was used as a solution tool to evaluate the airflow during light and heavy breathing conditions.A medical imaging technique was used to extract the 3D model from the CT scan images.Additionally,mesh generation and simulation were carried out via CFD software to evaluate the light and heavy breathing characteristics related to obstructive sleep apnea.Steady state Reynold’s averaged Navier-Stoke(RANS)with the k-ωshear stress transport(SST)turbulence model was utilized.The airflow characteristics were quantified using parameters such as pressure distribution,skin friction coefficient,velocity profile,Reynolds number,turbulent Reynolds number and turbulence kinetic energy.Results:Contour plots at different planes were used to visualize the airflow distribution as it passed through different cross-sectional areas of the airway.The results revealed that the presence of a smaller cross-sectional area of the airway caused an increase in airflow parameters,especially during heavy breathing.Furthermore,turbulent airflow conditions along the airway were noticed during heavy breathing.The severity of OSA could be measured by the turbulent kinetic energy which is able to show the behavior and concentration of mean flow.This study is expected to provide crucial and important results by visualizing the concentration of airflow mechanisms and characteristics of a patient’s airway during light and heavy breathing. These findings enable TKE to be used as a new tool for characterizing theseverity of obstructive sleep apnea in the upper airways of patients.

Upper Airway Changes after Maxillary Distraction Osteogenesis in Cleft Lip and Palate Patients

Purpose: To measure the upper airway changes associated with maxillary distraction osteogenesis in cleft lip and palate patients in the immediate post operative period and 12 months later. Materials and Methods: Seven patients with repaired cleft lip and palate (CLP) presented with severe maxillary hypoplasia. They were examined initially at T1 predistraction phase. Records taken included radiographs (orthopantograms OPG, lateral cephalometric, posteroanterior). Cephalometric analysis was done to evaluate the upper airway. Mean age is 17 years and the reverse overjet > 6 mm. They underwent maxillary Le Fort I distraction using external rigid distracters (RED). Cephalometric analysis to evaluate the upper airway was repeated at the end of the consolidation phase T2 and twelve months after distractor removal T3. Results: The range of maxillary advancement was between 8 - 15 mm (mean 9 mm). The anteroposterior distance of the superior velopharynx (PPS) and middle velopharynx (SPPS) increased at T2. A small amount of reduction in these values was recorded at T3. The inferior velopharynx (MPS) and the oropharynx (IPS, EPS) showed minimum increase in anteroposterior distance in only two patients at T2 and no change at T3. Conclusion: All seven patients showed clinical improvement in the upper airway and an increase in the upper airway values on lateral cephalometric radiographs.

Exploration on the Treatment of Upper Airway Cough Syndrome Based on the Pathogenesis of Hidden Pathogen(Evil)

Upper airway cough syndrome refers to a clinical syndrome with chronic cough as the main manifestation caused by the reverse flow of secretions from various upper airway diseases such as allergic rhinitis,rhino-sinusitis,adenoid hypertrophy and other parts of the nose and pharynx.Professor Yin Dan believes that the main disease of upper airway cough syndrome is due to cold fluid retained in lung,blood stasis endogenous,compound feeling of wind evil.The pathogenesis is external wind evil and the hidden pathogen together to cause the disease.In the treatment,the warm cold fluid retention is the core,accompanied by the activation of blood and wind,so that the wind evil can go away,the cold evil can be warmed,the phlegm can be removed,and the blood stasis can be dispersed,so as to achieve the purpose of treating the upper airway cough syndrome of the children’s cold fluid retention in lung.

Control mechanism for the upper airway collapse in patients with obstructive sleep apnea syndrome: a finite element study

Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent collapses of the upper airway, which lead to repetitive transient hypoxia, arousals and finally sleep fragmentation. Both anatomical and neuromuscular factors may play key roles in the pathophysiology of OSAS. The purpose of this paper was to study the control mechanism of OSAS from the mechanical point of view. A three-dimensional finite element model was developed, which not only reconstructed the realistic anatomical structure of the human upper airway, but also included surrounding structures such as the skull, neck, hyoid, cartilage and soft tissues. The respiration process during the normal and apnea states was simulated with the fluid-structure interaction method (FSI) and the computational fluid dynamics method (CFD). The airflow and deformation of the upper airway obtained from the FSI and the CFD method were compared and the results obtained under large negative pressure during an apnea episode were analyzed. The simulation results show that the FSI method is more feasible and effective than the CFD method. The concave configuration of the upper airway may accelerate the collapse of the upper airway in a positive feedback mechanism, which supplies meaningful information for clinical treatment and further research of OSAS.

Evaluating the effect of midpalatal corticotomy-assisted rapid maxillary expansion on the upper airway in young adults using computational fluid dynamics

Midpalatal corticotomy-assisted rapid maxillary expansion(MCRME)is a minimally invasive treatment of maxillary transverse deficiency(MTD)in young adults.However,the effect of MCRME on respiratory function still needs to be determined.In this study,we evaluated the changes in maxillary morphology and the upper airway following MCRME using computational fluid dynamics(CFD).Twenty patients with MTD(8 males,12 females;mean age 20.55 years)had cone-beam computed tomography(CBCT)images taken before and after MCRME.The CBCT data were used to construct a threedimensional(3 D)upper airway model.The upper airway flow characteristics were simulated using CFD,and measurements were made based on the CBCT images and CFD.The results showed that the widths of the palatal bone and nasal cavity,and the intermolar width were increased significantly after MCRME.The volume of the nasal cavity and nasopharynx increased significantly,while there were no obvious changes in the volumes of the oropharynx and hypopharynx.CFD simulation of the upper airway showed that the pressure drop and maximum velocity of the upper airway decreased significantly after treatment.Our results suggest that in these young adults with MTD,increasing the maxillary width,upper airway volume,and quantity of airflow by MCRME substantially improved upper airway ventilation.

Numerical Study on the Effect of Nerve Control on Upper Airway Collapse in Obstructive Sleep Apnea

Obstructive sleep apnea syndrome （OSAS） is a respiratory disease characterized by the upper airway collapses and reopens repeatedly during sleep. Though the nerve control plays a key role in the upper airway collapse, it has been considered in previous studies only with lumped parameter models. Based on a finite element model including airway and surrounding structures, the effect of nerve control on the upper airway collapse was studied with fluid-structure interaction method. Spring elements were used to simulate the function of the muscle group. The simulation results show that the nerve control reduces the deformation of airway successfully and avoids the risk of OSAS.

Life Threatening Stridor Due to Primary Laryngeal Tuberculosis

Tuberculosis is a potentially serious infectious disease. In otorhinolaryngology practice, lymph node infection is the most common site of predilection followed by the larynx. Laryngeal tuberculosis (LTB) typically presents with dysphagia, odynophagia and hoarseness. We reported a case of primary LTB presenting with acute upper airway obstruction and respiratory distress mimicking acute supraglottitis which requires emergency tracheostomy. Therefore, in acute upper airway obstruction, the appropriate initial investigation should be done to rule out TB to make sure early treatment can be given and it may prevent complications of disease to the patient. .

Drinking a Structured Water Product on Markers of Hydration,Airway Health and Heart Rate Variability in Thoroughbred Racehorses:a Small-scale,Clinical Field Trial

Racehorses in training are in situations of repeated stress that may have effects on hydration and health.It was hypothesized that daily consumption of a structured water(SW)product for 4 weeks will result in improved hydration,improved upper airway health and increased heart rate variability.Two groups of Thoroughbred racehorses matched for physiological,training and racing attributes were studied for 4 weeks.One group(n=17)received 10 L(about 15%)of their daily water as SW(followed by ad libitum filtered deep well water)and the control group(n=15)only filtered deep well water.Blood samples and bioelectrical impedance analysis(BIA)measures were obtained at baseline,2 and 4 weeks.Hydration was assessed using BIA.The upper airway was assessed by nasopharyngeal endoscopy at baseline and weekly within 60 minutes of breezing.On weekly breeze days heart rate was recorded at rest,during exercise and recovery and data were analysed for heart rate variability.Compared to controls,horses drinking SW showed increased hydration improved upper airway health post-breezing and increased heart rate variability.It is concluded that drinking 10 L daily of SW increased hydration and may have conferred some wellness benefits.

Nasogastric tube syndrome induced by an indwelling long intestinal tube

The nasogastric tube(NGT) has become a frequently used device to alleviate gastrointestinal symptoms. Nasogastric tube syndrome(NTS) is an uncommon but potentially life-threatening complication of an indwelling NGT. NTS is characterized by acute upper airway obstruction due to bilateral vocal cord paralysis. We report a case of a 76-year-old man with NTS, induced by an indwelling long intestinal tube. He was admitted to our hospital for treatment of sigmoid colon cancer. He underwent sigmoidectomy to release a bowel obstruction, and had a long intestinal tube inserted to decompress the intestinal tract. He presented acute dyspnea following prolonged intestinal intubation, and bronchoscopy showed bilateral vocal cord paralysis. The NGT was removed immediately, and tracheotomy was performed. The patient was finally discharged in a fully recovered state. NTS be considered in patients complaining of acute upper airway obstruction, not only with a NGT inserted but also with a long intestinal tube.

Assessment of Intranasal Steroid ,Effect in Management of Adenoid Hypertrophy in Children between 2-11 Years Old

Adenoid hypertrophy associated with high morbidity in children. However, in severe cases surgery recommended, some medical treatments are effective too. This study is based on effect of nasal steroid spray, mometasone, in decreasing upper airway obstruction and other symptoms of adenoid hypertrophy. In a clinical trial study 51 children with adenoid hypertrophy divided in two groups： 2-4 years old and 5-11 years old. Each patient receive nasal momethasone （one puff each nostril twice a day） for 3 months and their symptoms evaluated before treatment, 3 months after treatment initiation and 3 months after stop it with questionnaire and lateral neck radiography. Decreasing in all symptoms score and upper airway obstruction was statistically significant in both groups 3 months after treatment and its effect maybe stable for next 3 months. Nasal momethasone spray is effective in decreasing adenoid size and severity of symptoms of adenoid hypertrophy and this response is more obvious in 2-4 years old children.

Modeling micro-particle deposition in human upper respiratory tract under steady inhalation

A representative human upper respiratory tract （URT） with idealized oral region and asymmetric tracheo- bronchial （TB） airway has been modeled, and laminar-to-turbulent airflow for typical inhalation modes as well as micro-particle transport and deposition has been simulated using CFX10.0 software from Ansys Inc. on a personal computer. The asymmetric TB airway could not be replaced by an extended straight tube as outlet of the oral region while investigating the tracheal airflow field and particle deposition. Compared to an idealized oral airway with an extended straight tube, several differences could be noted： （i） The laryngeal jet extends further down the trachea and inclines towards the anterior wall; （ii） the turbulence level in trachea is less and decays more quickly; （iii） three recirculation zones are visible with intense adverse current after the glottis; （iv） deposition of small particles in trachea is reduced due to lower turbulence. Refined unstructured mesh with densified boundary layer mesh could be a proper substitute for the structured mesh in the human URT model with asymmetric TB airway. Based on the refined unstructured mesh, the physiological structure of uvula in the soft palate is properly simulated in the present human URT model.

Deposition of non-spherical microparticles in the human upper respiratory tract

We investigated the deposition pattern of microparticles with different particle diameters, shape factors, and initial flow conditions in a realistic human upper respiratory tract model. We identified a close relationship between the deposition fraction and the particle shape factor. The deposition fraction of the particles decreased sharply with increasing particle shape factor because of the decreasing drag force. We also found that the deposition varied at different positions in the upper respiratory tract. At low shape factors, the highest fraction of particles deposited at the mouth and pharynx. However, with increasing shape factor, the deposition fraction in the trachea and lungs increased. Moreover, for a given shape factor, larger particles deposited at the mouth and pharynx, which indicates that the deposition fraction of microparticles in the human upper respiratory tract is affected first and foremost by particle inertia as well as by the drag force.

Evaluation of neuromuscular activity in patients with obstructive sleep apnea using chin surface electromyography of polysomnography

Background It is believed that defects in upper airway neuromuscular control play a role in sleep apnea pathogenesis. Currently, there is no simple and non-invasive method for evaluating neuromuscular activity for the purpose of screening in patients with obstructive sleep apnea. This study was designed to assess the validity of chin surface electromyography of routine polysomnography in evaluating the neuromuscular activity of obstructive sleep apnea subjects and probe the neuromuscular contribution in the pathogenesis of the condition. Methods The chin surface electromyography of routine polysomnography during normal breathing and obstructive apnea were quantified in 36 male patients with obstructive sleep apnea. The change of chin surface electromyography from normal breathing to obstructive apnea was expressed as the percent compensated electromyography value, where the percent compensated electromyography value = （normal breath surface electromyography - apnea surface electromyography）/normal breath surface electromyography, and the percent compensated electromyography values among subjects were compared. The relationship between sleep apnea related parameters and the percent compensated electromyography value was examined. Results The percent compensated electromyography value of the subjects varied from 1% to 90% and had a significant positive correlation with apnea hypopnea index （R2=0.382, P 〈0.001）. Conclusions Recording and analyzing chin surface electromyography by routine polysomnography is a valid way of screening the neuromuscular activity in patients with obstructive sleep apnea. The neuromuscular contribution is different among subjects with obstructive sleep apnea.

Hypoglossal nerve stimulation for obstructive sleep apnea:A review of the literature

Objective:To review the indications and clinical evidence supporting hypoglossal nerve stimulation (HNS) therapy for the treatment of moderate-to-severe obstructive sleep ap-nea (OSA). Methods:Peer reviewed literature on hypoglossal nerve stimulation therapy for obstructive sleep apnea from 2001 to 2016. Results:The only currently FDA-approved HNS device for the treatment of moderate-to-severe OSA is produced by Inspire Medical Systems, which recently published its 36-month outcomes data from its Stimulation Therapy for Apnea Reduction (STAR) trial. HNS therapy is currently indicated for moderate-to-severe OSA patients who are CPAP-intolerant, have a body mass in-dex <32, apnea-hypopnea index <50, and without a concentric pattern of upper airway collapse on sleep endoscopy. Conclusions:Data from the STAR trial suggests that a subset of OSA patients can achieve a sig-nificant therapeutic response from hypoglossal nerve stimulation. However, these results may be limited in their generalizability to the broader OSA population.