Sleep magnetic resonance imaging: Dynamic characteristics of the airway during sleep in obstructive sleep apnea syndrome

Estimating the severity of obstructive sleep apnea during wakefulness using speech: A review

Obstructive sleep apnea (OSA) is a chronic breathing disorder during sleep that affects 10-30% of adults in North America. The gold standard for diagnosing OSA is polysomnography (PSG). However, PSG has several drawbacks, for example, it is a cumbersome and expensive procedure, which can be quite inconvenient for patients. Additionally, patients often have to endure long waitlists before they can undergo PSG. As a result, other alternatives for screening OSA have gained attention. Speech, as an accessible modality, is generated by variations in the pharyngeal airway, vocal tract, and soft tissues in the pharynx, which shares similar anatomical structures that contribute to OSA. Consequently, in this study, we aim to provide a comprehensive review of the existing research on the use of speech for estimating the severity of OSA. In this regard, a total of 851 papers were initially identified from the PubMed database using a specified set of keywords defined by population, intervention, comparison and outcome (PICO) criteria, along with a concatenated graph of the 5 most cited papers in the field extracted from ConnectedPapers platform. Following a rigorous filtering process that considered the preferred reporting items for systematic reviews and meta-analyses (PRISMA) approach, 32 papers were ultimately included in this review. Among these, 28 papers primarily focused on developing methodology, while the remaining 4 papers delved into the clinical perspective of the association between OSA and speech. In the next step, we investigate the physiological similarities between OSA and speech. Subsequently, we highlight the features extracted from speech, the employed feature selection techniques, and the details of the developed models to predict OSA severity. By thoroughly discussing the current findings and limitations of studies in the field, we provide valuable insights into the gaps that need to be addressed in future research directions.

Mechanical mechanism to induce inspiratory flow limitation in obstructive sleep apnea patients revealed from in-vitro studies

Inspiratory flow limitation means that when the flowrate reaches a certain value, it no longer increases, or even decreases, which is called negative effort dependence flow limitation, even if the inspiration effort is increased. This occurs often in obstructive sleep apnea patients, but its mechanism remains unclear. To reveal the mechanism of inspiratory flow limitation, we constructed a unique partially collapsible in-vitro upper airway model of obstructive sleep apnea patients to observe the change of airway resistance with inspiratory driving pressure. The important findings demonstrate that with the increase of inspiratory effort, the driving pressure increases faster than the airway resistance in the early stages, and then the reverse occurs as the airway becomes narrower. The airway collapse caused by the transmural pressure can lead to a rapid increase in downstream resistance with the increase of inspiratory effort, which is the key reason causing the flow reduction and the formation of typical negative effort dependence flow limitation. The mechanical mechanism revealed in this study will lead to fully new insights into the study and treatment of obstructive sleep apnea.

Dynamic sleep MRI in obstructive sleep apnea: a systematic review and meta-analysis

PURPOSE

The objective of this study is to systematically review the international literature for dynamic sleep magnetic resonance imaging (MRI) as a diagnostic tool in obstructive sleep apnea (OSA), to perform meta-analysis on the quantitative data from the review, and to discuss its implications in future research and potential clinical applications.

STUDY DESIGN

A comprehensive review of the literature was performed, followed by a detailed analysis of the relevant data that has been published on the topic.

METHODS

Clinical key, Uptodate, Ovid, Ebscohost, Pubmed/MEDLINE, Scopus, Dynamed, Web of Science and The Cochrane Library were systematically searched. Once the search was completed, dynamic sleep MRI data were analyzed.

RESULTS

Nineteen articles reported on 410 OSA patients and 79 controls that underwent dynamic sleep MRI and were included in this review. For meta-analysis of dynamic sleep MRI data, eight articles presented relevant data on 160 OSA patients. Obstruction was reported as follows: retropalatal (RP) 98%, retroglossal (RG) 41% and hypopharyngeal (HP) in 5%. Lateral pharyngeal wall (LPW) collapse was found in 35/73 (48%) patients. The combinations of RP + RG were observed in 24% and RP + RG + LPW in 16%. If sedation was used, 98% of study participants fell asleep compared to 66% of unsedated participants.

CONCLUSIONS

Dynamic sleep MRI has demonstrated that nearly all patients have retropalatal obstruction, retroglossal obstruction is common and hypopharyngeal obstruction is rare. Nearly all patients (98%) who are sedated are able to fall asleep during the MRI. There is significant heterogeneity in the literature and standardization is needed.

Novel non-invasive assessment of upper airway inflammation in obstructive sleep apnea using positron emission tomography/magnetic resonance imaging

PURPOSE

To develop a novel non-invasive technique to quantify upper airway inflammation using positron emission tomography/magnetic resonance imaging (PET/MRI) in patients with obstructive sleep apnea (OSA).

METHODS

Patients with treatment naïve moderate-to-severe OSA underwent [18F]-fluoro-2-deoxy-D-glucose (FDG) PET/MRI. Three readers independently performed tracings of the pharyngeal soft tissue on MRI. Standardized uptake values (SUV) were generated from region of interest (ROI) tracings on corresponding PET images. Background SUV was measured from the sternocleidomastoid muscle. SUV and target-to-background (TBR) were compared across readers using intraclass correlation coefficient (ICC) analyses. SUV from individual image slices were compared between each reader using Bland-Altman plots and Pearson correlation coefficients. All tracings were repeated by one reader for assessment of intra-reader reliability.

RESULTS

Five participants completed our imaging protocol and analysis. Median age, body mass index, and apnea-hypopnea index were 41 years (IQR 40.5-68.5), 32.7 kg/m² (IQR 28.1-38.1), and 30.7 event per hour (IQR 19.5-48.1), respectively. The highest metabolic activity regions were consistently localized to palatine or lingual tonsil adjacent mucosa. Twenty-five ICC met criteria for excellent agreement. The remaining three were TBR measurements which met criteria for good agreement. Head-to-head comparisons revealed strong correlation between each reader.

CONCLUSIONS

Our novel imaging technique demonstrated reliable quantification of upper airway FDG avidity. This technology has implications for future work exploring local airway inflammation in individuals with OSA and exposure to pollutants. It may also serve as an assessment tool for response to OSA therapies.

Role of dynamic sleep MRI in obstructive sleep apnea syndrome

PURPOSE

To identify obstruction sites of the upper airway during sleep in patients with obstructive sleep apnea syndrome (OSAS) under dynamic conditions and improve knowledge to guide surgical treatment and advancements.

MATERIALS AND METHODS

The study included 15 patients (5 females and 10 males) who were diagnosed as having OSAS. Overall mean age was 40.2 years (± 7.01 years). All the patients underwent drug-induced sleep endoscopy (DISE) and dynamic sleep MRI. The presence, location, and direction of airway collapse were assessed. Dynamic MRI findings were correlated to DISE. Data of the site and direction of airway collapse were correlated with those of endoscopic findings and interobserver agreement was done.

RESULTS

The dynamic images in sagittal section showed collapse of the upper airway at retropalatal level in 14 patients (93.33%) and at retroglossal level in seven patients (46.7%) and of these 14 patients; seven had combined retropalatal and retroglossal collapse. These findings were highly correlated with DISE findings with an excellent interobserver agreement for retropalatal and retroglossal levels (Kappa = 1 and 0.867, P value = 0.000), respectively. Objective measurements of the direction of collapse in axial dynamic sleep MRI images showed significant statistical correlation with endoscopic findings regarding retropalatal anteroposterior and circumferential collapse (Kappa = 0.58 and 0.52, P value = 0.02 and 0.03, respectively).

CONCLUSION

Dynamic sleep MRI can reliably characterize the actual site of dynamic airway obstruction and has the potential of improving predictions of successful surgical outcomes in OSAS patients.

TORS for OSA: a practice, pitfalls and literature review

PURPOSE

Trans-oral robotic surgery (TORS) is increasingly employed in obstructive sleep apnoea (OSA) management. Objective outcomes are generally assessed through polysomnography. Pre-operative magnetic resonance imaging (MRI) can be a useful adjunct in objective upper airway assessment, in particular the tongue base, providing useful information for surgical planning and outcome assessment, though care must be taken in patient positioning during surgery. The purpose of this paper is to identify pitfalls in this process and suggest a protocol for pre-operative MRI scanning in OSA.

DESIGN/METHODOLOGY/APPROACH

This study is a four-patient prospective case-series and literature review. Outcome measures include pre- and post-operative volumetric changes in the pharynx as measured on MRI and apnoea-hypopnea indices (AHI), with cure being OSA resolution or a 50 per cent reduction in AHI.

FINDINGS

All patients achieved AHI reduction and/or OSA cure following TORS, despite a decrease in pharyngeal volume measurements at the tongue base level. This study and others lacked standardisation in the MRI scanning protocol, which resulted in an inability to effectively compare pre- and post-operative scans. Pitfalls were related to variation in head/tongue position, soft-tissue marker usage and assessed area boundary limits.

PRACTICAL IMPLICATIONS

TORS appears to be effective in OSA management. A new protocol for patient positioning and anatomical landmarks is suggested.

ORIGINALITY/VALUE

The findings could provide directly comparable data between scans and may allow correlation between tongue base volumetric changes and AHI through subsequent and historical study meta-analysis.

Point-of-Care Ultrasound for Obstructive Sleep Apnea Screening: Are We There Yet? A Systematic Review and Meta-analysis

BACKGROUND

Perioperative diagnosis of obstructive sleep apnea (OSA) has important resource implications as screening questionnaires are overly sensitive, and sleep studies are expensive and time-consuming. Ultrasound (US) is a portable, noninvasive tool potentially useful for airway evaluation and OSA screening in the perioperative period. The objective of this systematic review was to evaluate the correlation of surface US with OSA diagnosis and to determine whether a point-of-care ultrasound (PoCUS) for OSA screening may help with improved screening in perioperative period.

METHODS

A search of all electronic databases including Medline, Embase, and Cochrane Database of Systematic Reviews was conducted from database inception to September 2017. Inclusion criteria were observational cohort studies and randomized controlled trials of known or suspected OSA patients undergoing surface US assessment. Article screening, data extraction, and summarization were conducted by 2 independent reviewers with ability to resolve conflict with supervising authors. Diagnostic properties and association between US parameters (index test) and OSA diagnosis using sleep study (reference standard) were evaluated. The US parameters were divided into airway and nonairway parameters. A random-effects meta-analysis was planned, wherever applicable.

RESULTS

Of the initial 3865 screened articles, 21 studies (7 airway and 14 nonairway) evaluating 3339 patients were included. Majority of studies were conducted in the general population (49%), respirology (23%), and sleep clinics (12%). No study evaluated the use of US for OSA in perioperative setting. Majority of included studies had low risk of bias for reference standard and flow and timing. Airway US parameters having moderate-good correlation with moderate-severe OSA were distance between lingual arteries (DLAs > 30 mm; sensitivity, 0.67; specificity, 0.59; 1 study/66 patients); mean resting tongue thickness (>60 mm; sensitivity, 0.85; specificity, 0.59; 1 study/66 patients); tongue base thickness during Muller maneuver (MM; sensitivity, 0.59; specificity, 0.78; 1 study/66 patients); and a combination of neck circumference and retropalatal (RP) diameter shortening during MM (sensitivity, 1.0; specificity, 0.65; 1 study/104 patients). Nonairway US parameters having a low-moderate correlation with moderate-severe OSA were carotid intimal thickness (pooled correlation coefficient, 0.444; 95% confidence interval [CI], 0.320-0.553; P value = .000, 8 studies/727 patients) and plaque presence (sensitivity, 0.24-0.75; specificity, 0.13-1.0; 4 studies/1183 patients).

CONCLUSIONS

We found that a number of airway and nonairway parameters were identified with moderate to good correlation with OSA diagnosis in the general population. In future studies, it remains to be seen whether PoCUS screening for a combination of these parameters can address the pitfalls of OSA screening questionnaires.

Upper Airway Narrowing during Central Apnea in Obese Adolescents

RATIONALE

The use of real-time magnetic resonance imaging (MRI) for the evaluation during sleep-related respiratory events can lead to better understanding of airway dynamics.

OBJECTIVES

To investigate the dynamic anatomy of the upper airway during central apnea.

METHODS

The study included obese adolescents who snore and were otherwise healthy. Subjects underwent an overnight baseline polysomnogram. Subjects slept during a 24-minute real-time upper airway MRI scan wearing a full face mask attached to a pneumotach. Sleep versus wakefulness during the MRI was inferred from the heart rate and respiratory patterns. Central apneas were scored using tracings of facemask airflow and abdominal bellows. The cross-sectional area of the upper airway before, during, and after each central apnea event was recorded.

RESULTS

Eight subjects were studied and 57 central apnea events were observed during real-time MRI scanning during natural sleep. The median age of subjects was 14.0 years (interquartile range [IQR], 13.5 to 15.5). The median average reduction in cross-sectional area during central apnea events was -38% (IQR, -27 to -51) for primary snorers and -45% (IQR, -40 to -54) for subjects with obstructive sleep apnea. The percentage decrease in cross-sectional area of upper airway during a central apnea event was positively correlated to the length of the central apnea (ρ = 0.389; r² = 0.152; P = 0.003).

CONCLUSIONS

We observed that there is upper airway narrowing during central apneas during natural sleep in obese adolescent subjects, using real-time MRI.

State-dependent changes in the upper airway assessed by multidetector CT in healthy individuals and during obstructive events in patients with sleep apnea

Objective:

To determine whether airway narrowing during obstructive events occurs predominantly at the retropalatal level and results from dynamic changes in the lateral pharyngeal walls and in tongue position.

Methods:

We evaluated 11 patients with severe obstructive sleep apnea (OSA) and 7 healthy controls without OSA during wakefulness and during natural sleep (documented by full polysomnography). Using fast multidetector CT, we obtained images of the upper airway in the waking and sleep states.

Results:

Upper airway narrowing during sleep was significantly greater at the retropalatal level than at the retroglossal level in the OSA group (p < 0.001) and in the control group (p < 0.05). The retropalatal airway volume was smaller in the OSA group than in the control group during wakefulness (p < 0.05) and decreased significantly from wakefulness to sleep only among the OSA group subjects. Retropalatal pharyngeal narrowing was attributed to reductions in the anteroposterior diameter (p = 0.001) and lateral diameter (p = 0.006), which correlated with an increase in lateral pharyngeal wall volume (p = 0.001) and posterior displacement of the tongue (p = 0.001), respectively. Retroglossal pharyngeal narrowing during sleep did not occur in the OSA group subjects.

Conclusions:

In patients with OSA, upper airway narrowing during sleep occurs predominantly at the retropalatal level, affecting the anteroposterior and lateral dimensions, being associated with lateral pharyngeal wall enlargement and posterior tongue displacement.

Sagittal Measurement of Tongue Movement During Respiration: Comparison Between Ultrasonography and Magnetic Resonance Imaging

The tongue makes up the anterior pharyngeal wall and is critical for airway patency. Magnetic resonance imaging (MRI) is commonly used to study pharyngeal muscle function in pharyngeal disorders such as obstructive sleep apnoea. Tagged MRI and ultrasound studies have separately revealed ∼1 mm of anterior tongue movement during inspiration in healthy patients, but these modalities have not been directly compared. In the study described here, agreement between ultrasound and MRI in measuring regional tongue displacement in 21 healthy patients and 21 patients with obstructive sleep apnoea was evaluated. We found good consistency and agreement between the two techniques, with an intra-class correlation coefficient of 0.79 (95% confidence interval: 0.75-0.82) for anteroposterior tongue motion during inspiration. Ultrasound measurements of posterior tongue displacement were 0.24 ± 0.64 mm greater than MRI measurements (95% limits of agreement: 1.03 to -1.49). This may reflect the higher spatial and temporal resolution of the ultrasound technique. This study confirms that ultrasound is a suitable method for quantifying inspiratory tongue movement.

Three-dimensional volumetric magnetic resonance imaging (MRI) analysis of the soft palate and nasopharynx in brachycephalic and non-brachycephalic dog breeds

The purpose of this study was to use magnetic resonance imaging (MRI) to compare the volumes and three-dimensional configurations of the soft palate and nasopharynx in non-brachycephalic and brachycephalic dogs with different body weights, and infer which factors influence nasopharyngeal volume. This was a retrospective observational study. The brain MRI medical records of all dogs referred to the Veterinary Medical Center, Chungbuk National University, between 2013 and 2016, for evaluation of intracranial disease were reviewed. There was a significant difference in the two-dimensional parameters including soft palate length/skull length ratio (P<0.01) and maximum soft palate thickness (P<0.01), and three-dimensional parameters which included soft palate volume (P<0.01), nasopharyngeal volume (P<0.01), soft palate/total upper airway volume ratio (P<0.01), and nasopharyngeal volume/total upper airway volume ratio (P<0.01), between brachycephalic and non-brachycephalic dog breeds. Nasopharyngeal volume correlated positively with the maximum soft palate thickness and body weight in all breeds. The three-dimensional morphologic grades of soft palate were significantly different between the two groups. In brachycephalic breeds, Grade 3 was observed in 33% of cases but was absent in non-brachycephalic breeds, where Grade 1 was present in 85% of the cases. We can conclude that three-dimensional morphology and upper airway volume are significantly different between brachycephalic and non-brachycephalic breeds, and body weight and maximum soft palate thickness are the key factors associated with a decreased nasopharyngeal volume.

Skeletal Surgery for Obstructive Sleep Apnea

Multilevel surgery has been established as the mainstay of treatment for the surgical management of obstructive sleep apnea (OSA). Combined with uvulopalatopharyngoplasty, tongue-base surgeries, including the genioglossus advancement (GA), sliding genioplasty, and hyoid myotomy and suspension, have been developed to target hypopharyngeal obstruction. Total airway surgery consisting of maxillomandibular advancement (MMA) with/without GA has shown significant success. Skeletal procedures for OSA with or without a palatal procedure is a proven technique for relieving airway obstruction during sleep. A case study demonstrating the utility of virtual surgical planning for MMA surgery is presented.

Fluid structure interaction simulations of the upper airway in obstructive sleep apnea patients before and after maxillomandibular advancement surgery

INTRODUCTION

The purpose of this study was to analyze pharyngeal airflow using both computational fluid dynamics (CFD) and fluid structure interactions (FSI) in obstructive sleep apnea patients before and after maxillomandibular advancement (MMA) surgery. The airflow characteristics before and after surgery were compared with both CFD and FSI. In addition, the presurgery and postsurgery deformations of the airway were evaluated using FSI.

METHODS

Digitized pharyngeal airway models of 2 obstructive sleep apnea patients were generated from cone-beam computed tomography scans before and after MMA surgery. CFD and FSI were used to evaluate the pharyngeal airflow at a maximum inspiration rate of 166 ml per second. Standard steady-state numeric formulations were used for airflow simulations.

RESULTS

Airway volume increased, pressure drop decreased, maximum airflow velocity decreased, and airway resistance dropped for both patients after the MMA surgery. These findings occurred in both the CFD and FSI simulations. The FSI simulations showed an area of marked airway deformation in both patients before surgery, but this deformation was negligible after surgery for both patients.

CONCLUSIONS

Both CFD and FSI simulations produced airflow results that indicated less effort was needed to breathe after MMA surgery. The FSI simulations demonstrated a substantial decrease in airway deformation after surgery. These beneficial changes positively correlated with the large improvements in polysomnography outcomes after MMA surgery.

Imaging of adult obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is characterised by recurrent upper airway collapse during sleep resulting in chronic and repetitive hypoxia, hypercapnia, subsequent arousal and fragmented sleep. Symptoms are insidious and diagnosis is usually delayed. Moderate to severe OSA has serious health implications with significant increase in all causes of mortality in patients with the condition as compared with unaffected individuals. The prevalence of OSA in the 30-70 year age group is estimated at 27% of males and 11% of females and it increases with age. 80% of affected individuals are obese and as obesity rates rise, so has the prevalence of OSA. An overnight polysomnogram (PSG) is required for a definitive diagnosis of OSA. Imaging has played a fundamental role in the evaluation of the anatomical factors associated with recurrent upper airway collapse and the pathogenesis of OSA. The upper airway is frequently imaged by radiologists, providing an opportunity to detect features that are strongly associated with unsuspected OSA and to raise the possibility of this diagnosis. The gold standard of treatment is continuous positive airway pressure (CPAP) which acts as a pneumatic splint for the upper airway. However, efficacy is frequently limited by poor tolerance; clinicians and patients are increasingly opting for one of a range of surgical procedures. Dedicated imaging protocols can be performed for evaluation of the upper airway to aid surgical planning.

Tracking Dynamic Tongue Motion in Ultrasound Images for Obstructive Sleep Apnea

Obstructive sleep apnea (OSA), a breathing disorder characterized by repetitive collapse of the pharyngeal airway during sleep, can cause intermittent hypoxemia and frequent arousal. The evaluation of dynamic tongue motion not only provides the biomechanics and pathophysiology for OSA diagnosis, but also helps doctors to determine treatment strategies for these patients with OSA. The purpose of this study was to develop and verify a dedicated tracking algorithm, called the modified optical flow (OF)-based method, for monitoring the dynamic motion of the tongue base in ultrasound image sequences derived from controls and patients with OSA. The performance of the proposed method was verified by phantom and synthetic data. A common tracking method, the normalized cross-correlation method, was included for comparison. The efficacy of the algorithms was evaluated by calculating the estimated displacement error. All results indicated that the modified OF-based method exhibited higher accuracy in verification experiments. In the human subject experiment, all participants performed the Müller maneuver (MM) to simulate the contour changes of the tongue base with a negative pharyngeal airway pressure in sleep apnea. Ultrasound image sequences of the tongue were obtained during 10 s of a transition from normal breathing to the MM, and these were measured using the modified OF-based method. The results indicated that the displacement of the tongue base during the MM was larger in the controls than in the patients with OSA (p < 0.05); the calculated areas of the tongue in the controls and patients with OSA were 24.9 ± 3.0 and 27.6 ± 3.3 cm², respectively, during normal breathing (p < 0.05), and 24.7 ± 3.6 and 27.3 ± 3.8 cm², respectively, at the end of the MM. The percentage changes in the tongue area were 2.2% and 1.3% in the controls and patients with OSA, respectively. We found that quantitative assessment of tongue motion by ultrasound imaging is suitable for evaluating pharyngeal airway behavior in OSA patients with minimal invasiveness and easy accessibility.

Evaluation of upper airway collapsibility using real-time MRI

PURPOSE

To develop and demonstrate a real-time MRI method for assessing upper airway collapsibility in sleep apnea.

MATERIALS AND METHODS

Data were acquired on a clinical 3 Tesla scanner using a radial CAIPIRIHNA sequence with modified golden angle view ordering and reconstructed using parallel imaging and compressed sensing with temporal finite difference sparsity constraint. Segmented airway areas together with synchronized facemask pressure were used to calculate airway compliance and projected closing pressure, Pclose , at four axial locations along the upper airway. This technique was demonstrated in five adolescent obstructive sleep apnea (OSA) patients, three adult OSA patients and four healthy volunteers. Heart rate, oxygen saturation, facemask pressure, and abdominal/chest movements were monitored in real-time during the experiments to determine sleep/wakefulness.

RESULTS

Student's t-tests showed that both compliance and Pclose were significantly different between healthy controls and OSA patients (P < 0.001). The results also suggested that a narrower airway site does not always correspond to higher collapsibility.

CONCLUSION

With the proposed methods, both compliance and Pclose can be calculated and used to quantify airway collapsibility in OSA with an awake scan of 30 min total scan room time. J. Magn. Reson. Imaging 2016;44:158-167.

Dynamic upper airway collapse observed from sleep MRI: BMI-matched severe and mild OSA patients

Dynamic magnetic resonance imaging (MRI) allows real-time characterization of upper airway collapse in sleeping subjects with obstructive sleep apnea (OSA). The aim of our study was to use sleep MRI to compare differences in upper airway collapse sites between BMI-matched subjects with mild OSA and severe OSA. This is a prospective, nested case-control study using dynamic sleep MRI to compare 15 severe OSA subjects (AHI >40) and 15 mild OSA (AHI <10) subjects, who were matched for BMI. Upper airway imaging was performed on sleeping subjects in a 3.0 T MRI scanner. Sleep MRI movies were used by blinded reviewers to identify retropalatal (RP), retroglossal (RG), and lateral pharyngeal wall (LPW) airway collapse. Mean AHI in the severe OSA group was 70.3 ± 23 events/h, and in the mild group was 7.8 ± 1 events/h (p < 0.001). All mild and severe OSA subjects demonstrated retropalatal airway collapse. Eighty percent in the mild group showed single-level RP collapse (p < 0.001). All subjects in the severe group showed multi-level collapse: RP + LPW (n = 9), RP + RG + LPW (n = 6). All severe OSA subjects showed LPW collapse, as compared with three subjects in the mild group (p < 0.001). LPW collapse was positively associated with AHI in simple regression analysis (β = 51.8, p < 0.001). In conclusion, severe OSA patients present with more lateral pharyngeal wall collapse as compared to BMI-matched mild OSA patients.

Static craniofacial measurements and dynamic airway collapse patterns associated with severe obstructive sleep apnoea: a sleep MRI study

OBJECTIVES

Using sleep MRI, we aimed to identify static craniofacial measurements and dynamic upper airway collapse patterns associated with severe obstructive sleep apnoea (OSA) during natural sleep in age and BMI-matched patients.

DESIGN

Nested case-control study.

SETTING

Sleep MRI images (3.0 Tesla scanner) and synchronised acoustic recording were used to observe patterns of dynamic airway collapse in subjects with mild and severe OSA. Midsagittal images were also used for static craniofacial measurements.

PARTICIPANTS

Fifteen male subjects with severe OSA (mean AHI 70.3 ± 23 events/h) were matched by age and BMI to 15 subjects with mild OSA (mean AHI 7.8 ± 1.4 events/h). Subjects were selected from a consecutive sleep MRI study cohort.

MAIN OUTCOME MEASURES

Static craniofacial measurements selected a priori included measurements that represent maxillomandibular relationships and airway morphology. Axial, sagittal and coronal views of the airway were rated for dynamic collapse at retropalatal, retroglossal and lateral pharyngeal wall regions by blinded reviewers. Bivariate analysis was used to correlate measures associated with severity of OSA using AHI. Statistical significance was set at P < 0.01.

RESULTS

Lateral pharyngeal wall collapse from dynamic sleep MRI (β = 51.8, P < 0.001) and upper airway length from static MRI images (β = 27.2, P < 0.001) positively correlated with severity of OSA.

CONCLUSIONS

Lateral pharyngeal wall collapse and upper airway length are significantly associated with severe OSA based on sleep MRI. Assessment of these markers can be readily translated to routine clinical practice, and their identification may direct targeted surgical treatment.

Diagnostic Role of Magnetic Resonance Imaging in Obstructive Sleep Apnea Syndrome

We aim to review the diagnostic role of magnetic resonance (MR) imaging in obstructive sleep apnea syndrome (OSAS). Basic background about sleep apnea, MR anatomy of the pharyngeal airway, and MR imaging sequences applied in obstructive sleep apnea are discussed. Static and dynamic MR imaging is used in the assessment of patients with OSAS. Magnetic resonance imaging can detect the level, degree, and cause of obstruction in the upper airway that guide the clinical diagnosis and treatment. Imaging is used for prediction of treatment outcome and monitoring and follow-up of patients with OSAS after therapy.

Compliance Measurements of the Upper Airway in Pediatric Down Syndrome Sleep Apnea Patients

Compliance of soft tissue and muscle supporting the upper airway are two of several factors contributing to pharyngeal airway collapse. We present a novel, minimally invasive method of estimating regional variations in pharyngeal elasticity. Magnetic resonance images for pediatric sleep apnea patients with Down syndrome [9.5 ± 4.3 years (mean age ± standard deviation)] were analyzed to segment airways corresponding to baseline (no mask pressure) and two positive pressures. A three dimensional map was created to evaluate axial and circumferential variation in radial displacements of the airway, dilated by the positive pressures. The displacements were then normalized with respect to the appropriate transmural pressure and radius of an equivalent circle to obtain a measure of airway compliance. The resulting elasticity maps indicated the least and most compliant regions of the pharynx. Airway stiffness of the most compliant region [403 ± 204 (mean ± standard deviation) Pa] decreased with severity of obstructive sleep apnea. The non-linear response of the airway wall to continuous positive airway pressure was patient specific and varied between anatomical locations. We identified two distinct elasticity phenotypes. Patient phenotyping based on airway elasticity can potentially assist clinical practitioners in decision making on the treatments needed to improve airway patency.

Is brain damage really involved in the pathogenesis of obstructive sleep apnea?

Obstructive sleep apnea (OSA) syndrome is a surprisingly complex and highly individualized disease, with different factors contributing toward the disease process. Many factors can induce OSA disease, such as hypertrophy uvula, adenoidectomy, tonsil caused by mechanical obstruction of the airway, airway obstruction on obesity cause of decubitus, etc.; in addition, abnormal structure and function of the central nervous system (CNS) is also one of the important factors. This paper examines the relationship of the CNS with the onset of OSA. Evidence has shown that dysfunction of the CNS may be related to the occurrence of OSA. Although modification of the behaviors of the motor neurons may offer a potentially interesting means of controlling the airway, human afferent and motor pathways that regulate eupnea are still poorly understood. Combining some clinical phenomena of patients with cerebral hemorrhage or brain trauma at the temporal lobe, it seems that no close relation with OSA has been observed in clinical work and animal experiments; however, CNS damage at the temporal lobe is involved in the pathogenesis of OSA. This article examines the role of the CNS in the pathogenesis of OSA and its mechanisms. We have summarized previous findings of OSA-related brain damage, which were obtained by brain functional MRI, clinical, and animal experiment data to better understand the roles of the CNS in the pathogenesis of OSA. More specifically, this review summarizes how altered activity of the limbic system and its related structures could be associated with the occurrence of OSA. This conclusion may contribute toward our understanding of nosogenesis and the treatment of OSA.

Interrater reliability of sleep videofluoroscopy for airway obstruction in obstructive sleep apnea

OBJECTIVES/HYPOTHESIS

Sleep videofluoroscopy (SVF) has been introduced to identify upper airway obstruction. This study was aimed to determine the interrater reliability of SVF in patients with obstructive sleep apnea (OSA).

STUDY DESIGN

A retrospective analysis.

METHODS

On the basis of apnea-hypopnea index in full-night attended polysomnography, 374 consecutive OSA patients who underwent SVF were enrolled in this study. The SVF was evaluated by three independent reviewers. Interrater reliabilities were assessed by evaluating agreement of the obstructive anatomic structures (soft palate, tongue base, tonsils, and epiglottis) and airway levels (velopharynx, oropharynx, and hypopharynx) between the reviewers.

RESULTS

In a comparison between an unblinded and a blinded well-experienced sleep surgeons, the interrater reliability for the presence of obstruction was the highest for the soft palate at the level of the velopharynx (Cohen's kappa value, 0.919) and the lowest for the soft palate at the level of the oropharynx (Cohen's kappa value, 0.757). In a blind comparison between a well-experienced and less-experienced sleep surgeons, the interrater reliability for the presence of obstruction was also the highest for the soft palate at the level of the velopharynx (Cohen's kappa value, 0.938) and the lowest for the palatine tonsils at the level of the oropharynx (Cohen's kappa value, 0.635).

CONCLUSION

This study showed that SVF was a diagnostic modality that can be used to evaluate upper airway obstruction without significant interrater disagreements.

Real-time 3D magnetic resonance imaging of the pharyngeal airway in sleep apnea

PURPOSE

To investigate the feasibility of real-time 3D magnetic resonance imaging (MRI) with simultaneous recording of physiological signals for identifying sites of airway obstruction during natural sleep in pediatric patients with sleep-disordered breathing.

METHODS

Experiments were performed using a three-dimensional Fourier transformation (3DFT) gradient echo sequence with prospective undersampling based on golden-angle radial spokes, and L1-norm regularized iterative self-consistent parallel imaging (L1-SPIRiT) reconstruction. This technique was demonstrated in three healthy adult volunteers and five pediatric patients with sleep-disordered breathing. External airway occlusion was used to induce partial collapse of the upper airway on inspiration and test the effectiveness of the proposed imaging method. Apneic events were identified using information available from synchronized recording of mask pressure and respiratory effort.

RESULTS

Acceptable image quality was obtained in seven of eight subjects. Temporary airway collapse induced via inspiratory loading was successfully imaged in all three volunteers, with average airway volume reductions of 63.3%, 52.5%, and 33.7%. Central apneic events and associated airway narrowing/closure were identified in two pediatric patients. During central apneic events, airway obstruction was observed in the retropalatal region in one pediatric patient.

CONCLUSION

Real-time 3D MRI of the pharyngeal airway with synchronized recording of physiological signals is feasible and may provide valuable information about the sites and nature of airway narrowing/collapse during natural sleep.

Deep cervical lymph node hypertrophy: a new paradigm in the understanding of pediatric obstructive sleep apnea

OBJECTIVES/HYPOTHESIS

To determine if adenotonsillar hypertrophy is an isolated factor in pediatric obstructive sleep apnea (OSA), or if it is part of larger spectrum of cervical lymphoid hypertrophy.

STUDY DESIGN

Prospective case control study.

METHODS

A total of 70 screened patients (mean age 7.47 years) underwent polysomnography to confirm OSA, and then underwent MRI of the upper airway. Seventy-six matched controls (mean age 8.00 years) who already had an MRI underwent polysomnography. Volumetric analysis of lymphoid tissue volumes was carried out. Chi-square analysis and Student's t test were used to compare demographic data and lymph node volumes between cohorts. Fisher's Exact test and Chi-square analysis were used to compare sleep data.

RESULTS

Patients and controls demonstrated no significant difference in mean age (7.47 vs. 8.00 yrs), weight (44.87 vs. 38.71 kg), height (124.68 vs. 127.65 cm), or body-mass index (23.63 vs. 20.87 kg/m(2)). OSA patients demonstrated poorer sleep measures than controls (P < 0.05) in all polysomnography categories (sleep efficiency, apnea index, apnea-hypopnea index, baseline SpO2, SpO2 nadir, baseline ETCO2, peak ETCO2 , and arousal awakening index). Children with OSA had higher lymphoid tissue volumes than controls in the retropharyngeal region (3316 vs. 2403 mm(3), P < 0.001), upper jugular region (22202 vs. 16819 mm(3), P < 0.005), and adenotonsillar region (18994 vs. 12675 mm(3), P < 0.0001).

CONCLUSIONS

Children with OSA have larger volumes of deep cervical lymph nodes and adenotonsillar tissue than controls. This finding suggests a new paradigm in the understanding of pediatric OSA, and has ramifications for future research and clinical care.

Novel retrospective, respiratory-gating method enables 3D, high resolution, dynamic imaging of the upper airway during tidal breathing

PURPOSE

A retrospective, respiratory-gated technique for measuring dynamic changes in the upper airway over the respiratory cycle was developed, with the ultimate goal of constructing anatomically and functionally accurate upper airway models in obstructive sleep apnea patients.

METHODS

Three-dimensional cine, retrospective respiratory-gated, gradient echo imaging was performed in six adolescents being evaluated for polycystic ovary syndrome, a disorder with a high obstructive sleep apnea prevalence. A novel retrospective gating scheme, synchronized to flow from a nasal cannula, limited image acquisition to predefined physiological ranges. Images were evaluated with respect to contrast, airway signal leakage, and demonstration of dynamic airway area changes.

RESULTS

Two patients were diagnosed with obstructive sleep apnea. Motion artifacts were absent in all image sets. Scan efficiency ranged from 48 to 88%. Soft tissue-to-airway contrast-to-noise ratio varied from 6.1 to 9.6. Airway signal leakage varied between 10 and 17% of soft tissue signal. Automated segmentation allowed calculation of airway area changes over the respiratory cycle. In one severe apnea patient, the technique allowed demonstration of asynchronous airway expansion and contraction above and below a severe constriction.

CONCLUSIONS

Retrospective, respiratory gated imaging of the upper airway has been demonstrated, utilizing a gating algorithm to ensure acquisition over specified ranges of respiratory rate and tidal volume.

A trial of drug-induced sleep endoscopy in the surgical management of sleep-disordered breathing

OBJECTIVES/HYPOTHESIS

To determine the reliability and validity of drug-induced sleep endoscopy (DISE) for patients undergoing surgery for sleep-disordered breathing (SDB).

STUDY DESIGN

Non-randomized, prospective clinical trial.

METHODS

Patients with sleep-disordered breathing were evaluated for multi-level upper airway surgery by awake and drug-induced sleep endoscopy to identify levels and degree of airway collapse. The reliability of a drug-induced sleep endoscopy rating index was assessed by comparing scores of three blinded investigators. The validity was assessed by comparison of drug-induced sleep endoscopy index scores from awake and drug-induced sleep endoscopy; correlation between drug-induced sleep endoscopy scores and Apnea-Hypopnea Index; and determination whether drug-induced sleep endoscopy affected the original surgical plan.

RESULTS

Thirty-eight patients (22 M, 16 F) underwent preoperative assessment with awake and drug-induced sleep endoscopy. Drug-induced sleep endoscopy was successfully performed in all but one patient (97%) who became combative during propofol infusion. Using an internal airway grading scale, drug-induced sleep endoscopy demonstrated more severity of collapse than awake endoscopy (P = 0.0001). The surgical plan was changed after drug-induced sleep endoscopy in 23 (62%) cases and unchanged in 14 (38%). The majority (73%) had multi-segmental airway collapse with fewer having single-level palatal (16%) or tongue base (11%) collapse. Scoring of drug-induced sleep endoscopy videos demonstrated good intrarater (κ 0.61) and interrater (κ 0.65) correlation.

CONCLUSIONS

Drug-induced sleep endoscopy provides more clinical information to assess airway function and collapse than awake endoscopy alone and assists in the surgical planning. Additional investigation is needed to standardize drug-induced sleep endoscopy techniques, training, and interpretation.