Upper airway physiology and obstructive sleep-disordered breathing

Upper airway imaging and function in obstructive sleep apnea in people with and without HIV

Obstructive sleep apnea (OSA) is common in people living with human immunodeficiency virus (HIV) (PLWH), but the underlying mechanisms are unclear. With improved long-term survival among PLWH, aging and obesity are increasingly prevalent in this population. These are also strong risk factors for the development of obstructive sleep apnea. We used magnetic resonance imaging (MRI) to measure upper airway (UA) anatomy and tongue fat content in PLWH with OSA (PLWH + OSA, n = 9) and in age-, sex-, and body mass index (BMI)-matched OSA controls (OSA, n = 11). We also quantified change in UA dimension during tidal breathing (during wakefulness and natural sleep) at four anatomical levels from the hard palate to the epiglottis along with synchronous MRI-compatible electroencephalogram and nasal flow measurements. All participants underwent on a separate night a baseline polysomnogram to assess OSA severity and an additional overnight physiological sleep study to measure OSA traits. We found no difference between the PLWH + OSA and the OSA control group in UA volume [PLWH + OSA: 12.8 mL (10.1-17.0), OSA: 14.0 mL (13.3-17.9), median (IQR)] or tongue volume [PLWH + OSA: 140.2 mL (125.1-156.9), OSA: 132.4 mL (126.8-154.7)] and a smaller tongue fat content in PLWH + OSA [11.2% (10.2-12.4)] than in the OSA controls [14.8% (13.2-15.5), P = 0.046]. There was no difference in the dynamic behavior of the UA between the two groups. When pooled together, both static and dynamic imaging metrics could be correlated with measures of UA mechanical properties. Our data suggest similar underlying UA physiology in OSA in subjects with and without HIV.NEW & NOTEWORTHY Obstructive sleep apnea is common in people living with human immunodeficiency virus (HIV), but the underlying mechanisms are unclear. We did not find differences in upper airway morphology using magnetic resonance imaging (MRI) during wake and natural sleep between people living with HIV (PLWH) with obstructive sleep apnea (OSA) and age, gender, and body mass index (BMI)-matched people with OSA but without HIV. Nor were there differences in tongue volume or changes in airway size during inspiration and expiration. MRI-derived anatomy was correlated with measures of airway collapse.

The relationship between aerodynamic characteristics of the upper airway and severity of obstructive sleep apnea in adults

OBJECTIVE

To investigate the relationship between aerodynamic characteristics of the upper airway and severity of obstructive sleep apnea (OSA) in adults.

METHODS

Ninety-seven adult OSA patients underwent polysomnography and cone beam computed tomography (CBCT). The anatomical and aerodynamic characteristics were measured based on CBCT images and computational fluid dynamics modelling of the upper airway.

RESULTS

After controlling for patients' gender, age, and body mass index (BMI), the maximum velocity during inspiration (In-Vmax) led to the largest increase in the explanatory power of apnea-hypopnea index (AHI) variation. The In-Vmax was closely correlated with the minimum axial area, and their relationship was represented by an inversely proportional fitted curve.

CONCLUSIONS

The In-Vmax was the most relevant to OSA severity, and it could be used to assist in recognizing severe OSA patients and as a primary variable to evaluate treatment outcomes of OSA. The In-Vmax was closely related to the most constricted area of the upper airway.

What is the impact of distraction osteogenesis on the upper airway of hemifacial microsomia patient with obstructive sleep apnea: a case report

BACKGROUND

Current research about hemifacial microsomia (HFM) patients after distraction osteogenesis (DO) most emphasize the morphologic changes. This case report shows the outcome of DO on the upper airway of a HFM patient with obstructive sleep apnea (OSA) based on the use of computational fluid dynamics (CFD).

CASE PRESENTATION

An 11-year-old boy was diagnosed as HFM with OSA, and underwent unilateral DO. Polysomnography and CT scans were performed before and 6 months after treatment. After DO, lowest blood oxygen saturation increased from 81% to 95% and apnea and hypopnea index decreased from 6.4 events/hour to 1.2 events/hour. The oropharynx and nasopharynx were obviously expanded. We observed apparently increased average pressure, decreased average velocity and pressure drop in all cross-sections, and largely decreased airflow resistance and maximum velocity entirely in the airway.

CONCLUSIONS

The results suggest that DO might be effective for the treatment of OSA by expanding the upper airway and reducing the resistance of inspiration.

Morphologic and Aerodynamic Changes of Upper Airway in Pediatric Hemifacial Microsomia Patients Undergoing Distraction Osteogenesis

Current studies on hemifacial microsomia (HFM) patients undergoing unilateral distraction osteogenesis (DO) mainly confined to description of facial morphology. This study was to investigate the effect of unilateral DO on upper airway in pediatric HFM patients using computational fluid dynamics. The investigators implemented the present retrospective study composed of 20 patients (age 9.5 ± 2.5 years, 11 males, 9 females) with moderate HFM performed unilateral DO on the ramus of mandible. Computational fluid dynamics models of the upper airway were obtained based on the computed tomography data sets which were taken before and 6 months after distraction. Morphologic and aerodynamic parameters were respectively computed and compared at peak inspiration. Paired t-tests were used to compare the differences between the before and after parameters with the significance set at P < 0.05. The authors observed that after DO, oropharynx and nasopharynx were the major expanded regions, average pressure increased in all cross-sections, average velocity decreased significantly except in the superior border of the epiglottis plane, and the airflow resistance significantly reduced in the whole upper airway (P < 0.05). The results indicate that unilateral DO may expand the constricted oropharynx and nasopharynx, obtain a relatively symmetrical airway shape and decrease the airflow resistance which consequently reduce the workload necessary for breathing and facilitate inspiration.

Computational fluid dynamics simulation of changes in the morphology and airflow dynamics of the upper airways in OSAHS patients after treatment with oral appliances

OBJECTIVES

To explore the changes of morphology and internal airflow in upper airways (UA) after the use of oral appliances (OAs) in patients with obstructive sleep apnea hypopnea syndrome (OSAHS), and investigate the mechanisms by which OAs function as a therapy for OSAHS.

METHODS

Eight OSAHS patients (all male, aged 37-58, mean age 46.25) underwent CT scans before and after OA use. Then, computational fluid dynamics(CFD) models were built on the base of the CT scans using Mimics and ANSYS ICEM CFD software. The internal airflow of the upper airways was simulated using ANSYS-FLUENT and the results were analyzed using ANSYS-CFD-Post. The data were analyzed to identify the most important changes of biomechanical properties between patients with and without OA intervention. Upper airway morphology and the internal airflow changes were compared using t-tests and Spearman correlation coefficient analysis.

RESULTS

The narrowest area of upper airways was found to be located in the lower bound of velopharynx, where the volume and pressure were statistically significantly increased (P<0.05) and the air velocity was statistically significantly decreased (P<0.05) in the presence of the OA(P<0.05). After wearing OA, pharyngeal resistance was significantly decreased (P<0.05), from 290.63 to 186.25Pa/L, and the airflow resistance of the pharynx has reduced by 35.9%.

CONCLUSION

The enlargement of the upper airway after wearing the OA changed its airflow dynamics, which decreased the negative pressure and resistance in narrow areas of the upper airways. Thus, the collapsibility of the upper airways was reduced and patency was sustained.

Computational fluid dynamics analysis of H-uvulopalatopharyngoplasty in obstructive sleep apnea syndrome

PURPOSE

To explore the impact of H-uvulopalatopharyngoplasty (H-UPPP) in obstructive sleep apnea syndrome (OSAS) and gain insights into the potential mechanism underlying improvement by H-UPPP.

METHODS

In a cohort of 11 OSAS patients, computational fluid dynamics (CFD) models of the upper airway were obtained using commercial software from computed tomography (CT) datasets before and after H-UPPP. Morphological and numerical parameters were respectively computed and compared during the peak tidal inspiratory flow. The correlations among polysomnography endpoints, airway dimensions, and pre- and post-operative airflow properties were analyzed with Spearman's rank correlation.

RESULTS

The preoperative minimum cross-sectional area was significantly increased by 89.56% (p < .05), with a positive correlation to the apnea hypoapnea index (AHI) (r = 0.974). However, the capacity of all pharyngeal regions was not significantly altered (p > .05). Following H-UPPP, we observed a significant increase in pressure and reduction of velocity (p < .05) in the previously constricted areas. The change in pressure and velocity were significantly correlated with AHI (r = 0.922 and r = 0.946, respectively). In addition, the pressure drop in the constricted area, oropharynx, and hypopharynx were also significantly decreased (p < .05).

CONCLUSIONS

H-UPPP is capable of expanding the constricted region of the velopharynx and can decrease the airway resistance which will in turn decrease the workload necessary for breathing and facilitate inspiration.

Upper airway dynamic imaging during tidal breathing in awake and asleep subjects with obstructive sleep apnea and healthy controls

We used magnetic resonance imaging (MRI) to quantify change in upper airway dimension during tidal breathing in subjects with obstructive sleep apnea (OSA, N = 7) and BMI-matched healthy controls (N = 7) during both wakefulness and natural sleep. Dynamic MR images of the upper airway were obtained on a 1.5 T MR scanner in contiguous 7.5 mm-thick axial slices from the hard palate to the epiglottis along with synchronous MRI-compatible electroencephalogram and nasal/oral flow measurements. The physiologic data were retrospectively scored to identify sleep state, and synchronized with dynamic MR images. For each image, the upper airway was characterized by its area, and linear dimensions (lateral and anterior-posterior). The dynamic behavior of the upper airway was assessed by the maximum change in these parameters over the tidal breath. Mean upper airway caliber was obtained by averaging data over the tidal breath. There was no major difference in the upper airway structure between OSA and controls except for a narrower airway at the low-retropalatal/high-retroglossal level in OSA than in controls. Changes in upper airway size over the tidal breath ((maximum - minimum)/mean) were significantly larger in the OSA than in the control group in the low retropalatal/high retroglossal region during both wakefulness and sleep. In the four OSA subjects who experienced obstructive apneas during MR imaging, the site of airway collapse during sleep corresponded to the region of the upper airway where changes in caliber during awake tidal breathing were the greatest. These observations suggest a potential role for dynamic OSA imaging during wakefulness.

Numerical simulation for the upper airway flow characteristics of Chinese patients with OSAHS using CFD models

OSAHS is a common disease with many factors related to the etiology. Airflow plays an important role in the pathogenesis of OSAHS. Previous research has not yielded a sufficient understanding of the relationship between airflow in upper airway and the pathophysiology of OSAHS. Therefore, a better understanding of the flow inside the upper airway in an OSAHS patient is necessary. In this study, ten Chinese adults with OSAHS were recruited. We used the software MIMICS 13.1 to construct 3-dimensional (3-D) models based on the computer tomography scans of them. The numerical simulations were carried out using the software ANSYS 12.0. We found that during the inhalation phase, the vortices and turbulences were located in both the anterior part of the cavity and nasopharynx. But there is no vortex in the whole nasal cavity during the expiratory phase. The airflow velocity is much higher than that of the normal models. The distributions of pressure and wall shear stress are different in two phases. The maximum velocity, pressure and wall shear stress (WSS) are located in velopharynx. It is notable that a strong negative pressure region is found in pharyngeal airway. The maximum velocity is 19.26 ± 12.4 and 19.46 ± 13.1 m/s; the average pressure drop is 222.71 ± 208.84 and 238.5 ± 218.56 Pa and the maximum average WSS is 0.72 ± 0.58 and 1.01 ± 0.61 Pa in inspiratory and expiratory, respectively. The changes of airflow due to the structure changes play an important role in the occurrence of collapse and obstruction of the upper airway, especially, the abnormal pressure changes in velopharyngeal during both inspiratory and expiratory phases. We can say that the airway narrowing in the pharynx may be one of the most important factors driving airway collapse. In addition, the most collapsible region of the pharyngeal airway of the patient with OSAHS may be the velopharynx and oropharynx. In spite of limitations, our results can provide a basis for the further research. On this basis, more about the secret of the pathogenesis of the OSAHS will be revealed.

The relationships between cephalometric parameters and severity of obstructive sleep apnea

OBJECTIVE

To verify the relationships between cephalometric parameters and apnea hypopnea index (AHI) in snoring patients in Chiang Mai University Hospital.

METHODS

Fifty patients who attend ENT snoring clinic, Faculty of Medicine, Chiang Mai University Hospital during 1 October, 2007 to 31 October, 2008 were enrolled. All subsequently underwent overnight polysomnography by SOMNOCHECK(®) V2.04 and lateral cephalometric radiographs.

RESULTS

Of the 50 patients, 78% were men (n=39) and 22% were women (n=11). Ages ranged from 31 to 65 years. Average apnea hypopnea index (AHI)=18.4 ± 18.2 events/h. Body mass index (BMI)=27.2 ± 3.3 kg/m². The mean sella-nasion-subspinale (SNA)=84.1 ± 4.3°. Sella-nasion-supramental (SNB)=81.8 ± 3.4°. Posterior airway space (PAS)=14.9 ± 4.3mm. Distance between mandibular plane and hyoid (MP-H)=27.7 ± 5.6 mm. Distance between posterior nasal spine and tip of soft palate (PNS-P)=42.5 ± 5.4mm. Using Pearson's correlation analysis of BMI, the cephalometric parameters from all subjects with AHI revealed BMI, PAS and MP-H had significant correlation with AHI; p=0.009, p=0.003, and p=0.005, respectively. BMI, MP-H, and PAS were correlated with AHI. The multiple regression model for the effects of BMI, PAS, and MP-H on AHI is AHI=2.090(BMI)-1.953(PAS)+1.1333(MP-H)-40.54.

CONCLUSION

The model seems to be useful as a screening tool to assess the severity of obstructive sleep apnea in snoring patients.

Numerical investigation on the flow characteristics and aerodynamic force of the upper airway of patient with obstructive sleep apnea using computational fluid dynamics

Developing a mathematical model to predict the abnormal flow characteristics that are produced by obstructive sleep apnea is an important step in learning the pathophysiology of the obstructive sleep apnea (OSA) disease. The present study provides detailed calculations of flow in the pharyngeal airway of a patient with obstructive sleep apnea. To achieve this goal, a computational fluid dynamics model was constructed using raw data from three-dimensional computed tomogram (CT) images of an OSA patient. To reproduce the important transition from laminar to turbulent flow in the pharyngeal airway, the low Reynolds number k-epsilon model was adopted and successfully validated using previous open literature. The results show that the flow in the pharyngeal airway of patients with OSA comprises a turbulent jet formed by area restriction at the velopharynx. This turbulent jet causes higher shear and pressure forces in the vicinity of the velopharynx. From the results, It may be deduced that the most collapsible area in the pharyngeal airway of OSA patients is the velopharynx where minimum intraluminal pressure and maximum aerodynamic force lie.