Changes in upper airway size during tidal breathing in children with obstructive sleep apnea syndrome

Are the severity of obstruction and the apnea-hypopnea index related to orofacial anatomy in children with obstructive sleep apnea? a kinetic MRI study

OBJECTIVES

The proportionality between anatomical characteristics and disease severity in children and adolescents with obstructive sleep apnea (OSA) has not been well characterized. The present study investigated the relationship between the dentoskeletal and oropharyngeal features of young patients with OSA and either the apnea-hypopnea index (AHI) or the amount of upper airway obstruction.

METHODS

MRI of 25 patients (8- to 18-year-old) with OSA (mean AHI = 4.3 events/h) was retrospectively analyzed. Sleep kinetic MRI (kMRI) was used to assess airway obstruction, and static MRI (sMRI) was used to assess dentoskeletal, soft tissue, and airway parameters. Factors related to AHI and obstruction severity were identified with multiple linear regression (significance level α = 0.05).

RESULTS

As evidenced by kMRI, circumferential obstruction was present in 44% of patients, while laterolateral and anteroposterior was present in 28%; as evidenced by kMRI, obstructions were retropalatal in 64% of cases and retroglossal in 36% (no nasopharyngeal obstructions); kMRI showed a higher prevalence of retroglossal obstructions compared to sMRI(p = 0.037); the main obstruction airway area was not related to AHI; the maxillary skeletal width was related to AHI (β = -0.512, p = 0.007) and obstruction severity (β = 0.625, p = 0.002); and the retropalatal width was related to AHI (β = -0.384, p = 0.024) and obstruction severity (β = 0.519, p = 0.006).

CONCLUSIONS

In children and adolescents, the severity of OSA and obstruction were inversely proportional to the maxillary basal width and retropalatal airway width. Further studies are needed to assess the benefits of targeted clinical treatments widening the transverse dimension of these structures.

Subtypes of obstructive sleep apnea in children and related factors

STUDY OBJECTIVES

To investigate the prevalence of positional obstructive sleep apnea (P-OSA) and rapid eye movement-related OSA (REM-OSA) in children with OSA and identify related factors.

METHODS

This was a cross-sectional study among children aged 2-12 years diagnosed with OSA using overnight polysomnography (PSG) between August 1, 2020, and July 31, 2021. Demographics, anthropometrics, PSG, and OSA-18 questionnaire data were recorded.

RESULTS

Data from a total of 474 children were available for analysis. Children had a median age of 4.8 (4.1, 6.4) years, 66.7% were male, and 23.2% were obese. The prevalence of P-OSA was 38.2% and that of REM-OSA was 43.0%. P-OSA was correlated with age and obstructive apnea-hypopnea index (OAHI; odds ratio [OR] = 1.172, 0.947; P = .005, < 0.001, respectively), but not sex, obesity, and adenoid and tonsil size (OR = 1.265, 0.785, 0.826, 0.989; P = .258, 0.327, 0.153, 0.905, respectively). REM-OSA was correlated with age, adenoid size, tonsil size, and OAHI (OR = 0.876, 1.320, 1.387, 1.021; P = .024, 0.040, 0.001, 0.042) but not with sex and obesity (OR = 0.910, 1.281; P = .643, 0.315).

CONCLUSIONS

The prevalence of P-OSA was 38.2% and that of REM-OSA was 43.0% in children with OSA. Age was correlated with both the prevalence of P-OSA and REM-OSA, with an increasing and decreasing prevalence as children grew older, respectively. The severity of OSA was significantly associated with the prevalence of both P-OSA and REM-OSA. Adenoid and tonsil size were correlated with the prevalence of REM-OSA but not P-OSA. Obesity and sex were not associated with the prevalence of P-OSA or REM-OSA.

CITATION

Wu Y, Zheng L, Cui G, Xu Z, Ni X. Subtypes of obstructive sleep apnea in children and related factors. J Clin Sleep Med. 2022;18(10):2397-2404.

Upper airway flow characteristics of childhood obstructive sleep apnea-hypopnea syndrome

Revealing the structural morphology and inner flow field of the upper airway is important for understanding obstructive sleep apnea-hypopnea syndrome (OSAHS) incidence phenomena and pathological diagnosis in children. However, prior work on this topic has been focused on adults and the findings cannot be directly extrapolated to children because of different inducing factors. Therefore, this paper employs a simulation method to investigate upper airway flow characteristics of childhood OSAHS. It is found that the Reynold number changes highly throughout the whole upper airway, and the laminar assumption is no longer suitable for low Reynold number flow, which is much unlike classic fluid mechanics. Turbulent models of Standard k-ω and Spalart-Allmaras were developed prior to suggestion. The simulation is validated by experiments with an error of approximately 20%. Additionally, carried out in this analysis is the influence of adenoidal hypertrophy with different narrow levels. The cross-sectional area, flow velocity, pressure drop and volume rate will change greatly when the narrow level is above 64% of the upper airway, which can be a quantitative explanation for medical intervention if adenoid hypertrophy blocks 2/3 of the upper airway in the common clinical judgment of otorhinolaryngology. It is expected that this paper can be a meaningful instruction on OSAHS surgery plan making as well as recovery evaluation postoperatively.

[Dimensions of the upper airways and its impact on the dentoalveolar system development]

Due to the high mobility and variability of bone structures and soft tissues surrounding the upper respiratory tract, the exact boundaries for measuring and normalizing the size of the respiratory tract have not yet been determined. Studies have determined the relationship between the narrowing of the upper jaw and a decrease in the transverse dimensions of the airways, as well as a positive effect in changing the size of the airways after orthodontic treatment and/or orthognathic surgery. Nevertheless, the results of research in this area may differ greatly from different specialists, which indicates that the topic is poorly studied and it is necessary to continue and expand the range of scientific works to assess the state of the upper respiratory tract and their relationship with the orthodontic status.

Pediatric Obstructive Sleep Apnea: What’s in a Name?

Obstructive sleep apnea is a highly prevalent disease across the lifespan and imposes substantial morbidities, some of which may become irreversible if the condition is not diagnosed and treated in a timely fashion. Here, we focus on the clinical and epidemiological characteristics of pediatric obstructive sleep apnea, describe some of the elements that by virtue of their presence facilitate the emergence of disrupted sleep and breathing and its downstream consequences, and also discuss the potential approaches to diagnosis in at-risk children.

Effect of sleep on upper airway dynamics in obese adolescents with obstructive sleep apnea syndrome

STUDY OBJECTIVES

The biomechanical basis of obstructive sleep apnea syndrome (OSAS) may influence upper airway dynamics. In this study, we investigate dynamic changes during respiration in wakefulness and sleep in obese adolescents with and without OSAS.

METHODS

Respiratory-gated dynamic magnetic resonance imaging (MRI) at the retropalatal and retroglossal regions was performed with simultaneous measurement of SpO2 and nasal-oral mask airflow and pressure. Airway cross-sectional area (CSA) was determined using AMIRA. Percent change in CSA was calculated from five continuous tidal breaths in states of wakefulness and sleep. Mixed effects models were used to evaluate interactions between group (OSAS/control), site (retropalatal/retroglossal), and stage (wake/sleep).

RESULTS

We studied 24 children with OSAS (mean age 15.49 ± 2.00 years, mean apnea-hypopnea index [AHI] 16.53 ± 8.72 events/h) and 19 controls (mean age 14.86 ± 1.75 years, mean AHI 2.12 ± 1.69 events/h). Groups were similar in age, sex, height, weight, and BMI Z-score. Participants with OSAS had a 48.17% greater increase in percent change of airway CSA during sleep than controls (p < 0.0001), while there was no difference between groups during wakefulness (p = 0.6589). Additionally, participants with OSAS had a 48.80% increase in percent change of airway CSA during sleep as compared with wakefulness (p < 0.0001), whereas no such relationship was observed in controls (p = 0.5513).

CONCLUSIONS

This study demonstrates significant effects of sleep on upper airway dynamics in obese children with OSAS. Dynamic MRI with physiological data can potentially provide further insight into the biomechanical basis of OSAS and assist in more effective management.

Effect of adenoids and tonsil tissue on pediatric obstructive sleep apnea severity determined by computational fluid dynamics

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is a respiratory disorder caused by the obstruction of the upper airway during sleep. The most common cause of pediatric OSA is adenotonsillar hypertrophy. Adenotonsillectomy is the first-line treatment for pediatric OSA; however, OSA persists in a significant number of patients due, in part, to the method of evaluating enlarged adenoids and tonsil tissue. The reason for these effects on OSA severity is not clear. This study aimed to establish a method to diagnose the need for adenoidectomy or tonsillectomy.

METHODS

Twenty-seven Japanese children (mean age 6.6 years) participated in this study, undergoing polysomnography and computed tomography examination. Pharyngeal airway morphology (adenoids and tonsil tissue size, volume, and cross-sectional area [CSA]) and pressure on the upper airway were evaluated at each site using computational fluid dynamic analysis.

RESULTS

Apnea-hypopnea index (AHI) showed a strong linear association with maximum negative pressure (P_max) (AHI = -0.055* events/h P_max -1.326, R² = .805). The relationship between minimum CSA (CSA_min) and P_max was represented by an inversely proportional fitted curve (P_max = -4797/CSA_min -5.1, R² = .507). The relationship between CSA_min and AHI was also represented by an inversely proportional fitted curve (AHI = 301.6 events/h/CSA_min ^1.22, R² = .680). P_max greatly increased if CSA_min became ≤ 30 mm². The negative pressure of each site increased when CSA measured ≤ 50 mm².

CONCLUSIONS

In children, when the CSA for each site is ≤ 50 mm², AHI is likely to be elevated, and the patient may require tonsillectomy or adenoidectomy.

The effect of airway motion and breathing phase during imaging on CFD simulations of respiratory airflow

RATIONALE

Computational fluid dynamics (CFD) simulations of respiratory airflow can quantify clinically useful information that cannot be obtained directly, such as the work of breathing (WOB), resistance to airflow, and pressure loss. However, patient-specific CFD simulations are often based on medical imaging that does not capture airway motion and thus may not represent true physiology, directly affecting those measurements.

OBJECTIVES

To quantify the variation of respiratory airflow metrics obtained from static models of airway anatomy at several respiratory phases, temporally averaged airway anatomies, and dynamic models that incorporate physiological motion.

METHODS

Neonatal airway images were acquired during free-breathing using 3D high-resolution MRI and reconstructed at several respiratory phases in two healthy subjects and two with airway disease (tracheomalacia). For each subject, five static (end expiration, peak inspiration, end inspiration, peak expiration, averaged) and one dynamic CFD simulations were performed. WOB, airway resistance, and pressure loss across the trachea were obtained for each static simulation and compared with the dynamic simulation results.

RESULTS

Large differences were found in the airflow variables between the static simulations at various respiratory phases and the dynamic simulation. Depending on the static airway model used, WOB, resistance, and pressure loss varied up to 237%, 200%, and 94% compared to the dynamic simulation respectively.

CONCLUSIONS

Changes in tracheal size and shape throughout the breathing cycle directly affect respiratory airflow dynamics and breathing effort. Simulations incorporating realistic airway wall dynamics most closely represent airway physiology; if limited to static simulations, the airway geometry must be obtained during the respiratory phase of interest for a given pathology.

Evaluation and Management of Children with Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) is a common pediatric disorder characterized by recurrent events of partial or complete upper airway obstruction during sleep which result in abnormal ventilation and sleep pattern. OSAS in children is associated with neurobehavioral deficits and cardiovascular morbidity which highlights the need for prompt recognition, diagnosis, and treatment. The purpose of this state-of-the-art review is to provide an update on the evaluation and management of children with OSAS with emphasis on children with complex medical comorbidities and those with residual OSAS following first-line treatment. Proposed treatment strategies reflecting recommendations from a variety of professional societies are presented. All children should be screened for OSAS and those with typical symptoms (e.g., snoring, restless sleep, and daytime hyperactivity) or risk factors (e.g., neurologic, genetic, and craniofacial disorders) should undergo further evaluation including referral to a sleep specialist or pediatric otolaryngologist and overnight polysomnography, which provides a definitive diagnosis. A cardiology and/or endocrinology evaluation should be considered in high-risk children. For the majority of children, first-line treatment is tonsillectomy with or without adenoidectomy; however, some children exhibit multiple levels of airway obstruction and may require additional evaluation and management. Anti-inflammatory medications, weight loss, and oral appliances may be appropriate in select cases, particularly for mild OSAS. Following initial treatment, all children should be monitored for residual symptoms and polysomnography may be repeated to identify persistent disease, which can be managed with positive airway pressure ventilation and additional surgical approaches if required.

Primary site identification in children with obstructive sleep apnea by computational fluid dynamics analysis of the upper airway

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is a respiratory disorder caused by the obstruction of the upper airway during sleep. The identification of the primary site of OSA is essential to determine treatment strategy. This study aimed to establish computational fluid dynamics (CFD) analysis for determining the clinical severity of OSA and the primary site of OSA.

METHODS

Twenty children (mean age, 6 years) were divided into OSA and control groups according to their apnea-hypopnea index. Three-dimensional airways were constructed from computed tomography data. The pharyngeal airway morphology and the pressure and velocity of the upper airway were evaluated using CFD analysis.

RESULTS

The maximum velocity and negative pressure of the upper airway in the OSA group were significantly correlated with the severity of OSA (r_s = .741, P < .001; r_s = -.653, P = .002). A velocity higher than 12 m/s indicated the primary site of OSA. In addition, we found that the primary site of OSA is not necessarily the same as the collapsible conduit site.

CONCLUSIONS

CFD analysis allows both the evaluation of the disease severity of OSA and the identification of the primary site of OSA in children. The primary site of OSA is not necessarily the same as the collapsible conduit site; therefore, CFD analysis can be used to identify the appropriate intervention for treating OSA.

Sleep-disordered breathing and comorbidities: role of the upper airway and craniofacial skeleton

Obstructive sleep-disordered breathing (SDB), which includes primary snoring through to obstructive sleep apnea syndrome (OSAS), may cause compromise of respiratory gas exchange during sleep, related to transient upper airway narrowing disrupting ventilation, and causing oxyhemoglobin desaturation and poor sleep quality. SDB is common in chronic disorders and has significant implications for health. With prevalence rates globally increasing, this condition is causing a substantial burden on health care costs. Certain populations, including people with sickle cell disease (SCD), exhibit a greater prevalence of OSAS. A review of the literature provides the available normal polysomnography and oximetry data for reference and documents the structural upper airway differences between those with and without OSAS, as well as between ethnicities and disease states. There may be differences in craniofacial development due to atypical growth trajectories or extramedullary hematopoiesis in anemias such as SCD. Studies involving MRI of the upper airway illustrated that OSAS populations tend to have a greater amount of lymphoid tissue, smaller airways, and smaller lower facial skeletons from measurements of the mandible and linear mental spine to clivus. Understanding the potential relationship between these anatomical landmarks and OSAS could help to stratify treatments, guiding choice towards those which most effectively resolve the obstruction. OSAS is relatively common in SCD populations, with hypoxia as a key manifestation, and sequelae including increased risk of stroke. Combatting any structural defects with appropriate interventions could reduce hypoxic exposure and consequently reduce the risk of comorbidities in those with SDB, warranting early treatment interventions.

[Orthodontic management of obstructive sleep-disordered respiratory disorders]

Through his/her knowledge of cranio-facial growth, the orthodontist plays a leading role within the multidisciplinary team that tracks and treats sleep-disordered breathing (SDB) in children. Correction of craniofacial risk factors (maxillary deficiency and retrognathia) is commonly used by practitioners alongside orthodontic treatment such as OMA and RME in the optimal conditions afforded by childhood growth. Myofunctional therapies are performed to restore correct stomatognathic function and play a central role in the management of SDB in children. The orthodontist is therefore a key player in the medical treatment chain of these children.

Ultrasonographic Evaluation of Upper Airway Structures in Children With Obstructive Sleep Apnea

Importance

Adenotonsillar hypertrophy is an important cause of obstructive sleep apnea (OSA) in children. However, residual OSA and abnormal polysomnographic findings have been reported in up to 75% of cases after adenotonsillectomy. Other anatomical and functional factors that influence upper airway structures, including the lateral pharyngeal wall, have rarely been studied in children with OSA.

Objective

To determine whether the upper airway structures can be evaluated using head and neck ultrasonography and if there is an association between the ultrasonographic measurements for these structures and severity of OSA seen on polysomnography in children.

Design, Setting, and Participants

Prospective, single-center, observational study of 82 children younger than 18 years with a diagnosis of sleep-disordered breathing (20 with primary snoring, 62 with OSA, as determined by the apnea-hypopnea index) and admitted to a tertiary teaching hospital for adenotonsillectomy.

Exposures

Ultrasonography and polysomnography.

Main Outcomes and Measures

Ultrasonographic measurements of upper airway structures.

Results

Of the 82 children studied, 62 (76%) were boys; mean (SD) age, 7.7 (6.2). There was no significant difference found in tonsillar dimensions or volume between the children with OSA and those with primary snoring. However, the mean (SD) total lateral pharyngeal wall and the total neck thicknesses at the retropalatal level were both greater in children with OSA than in those with primary snoring at rest (24.9 [4.4] mm vs 21.3 [2.6] mm; difference, 3.61 mm; 95% CI of difference, 1.48-5.74 mm for lateral pharyngeal wall; and 59.9 [14.4] mm vs 49.9 [11.2] mm; difference, 10.9 mm, 95% CI of difference, 3.8-17.9 mm for the total neck).

Conclusions and Relevance

Estimated tonsillar volume measured using ultrasonography had no relationship with the apnea-hypopnea index in childhood sleep-disordered breathing. However, the lateral pharyngeal wall was significantly thicker in children with OSA than in those with primary snoring at rest.

Pharyngeal airway dimension in patients before and after treatment of myofascial pain syndrome

Objective: This study aimed: (1) to assess the localization of the anatomic landmarks of the pharyngeal airway on cone beam computed tomography (CBCT) images; and (2) to evaluate if resolution of myofascial pain syndrome (MPS) changed the airway dimensions.Methods: Twenty-nine patients with pre- and post-treatment CBCT scans were randomly selected to locate five landmarks twice, with a two-week interval. The same landmarks were used to measure the airway volume and minimal cross-sectional area (CSA_min).Results: The intra-observer reliability (ICC) was 0.99-1.00 for volumetric and CSA_min measurements, based on the five landmarks used. The paired t test showed no significant difference in the airway volume (p = 0.68) and CSA_min (p = 0.96).Discussion: The outcomes showed that the landmarks used had excellent ICCs for the volumetric and CSA_min measurements. There was no change in volume and CSA_min of the pharyngeal airway after resolution of MPS.

Airway dimensions from fetal life to adolescence-A literature overview

BACKGROUND

Data on airway dimensions in pediatric patients are important for proper selection of pediatric airway equipment such as endotracheal tubes, double-lumen tubes, bronchial blockers, or stents. The aim of the present work was to provide a synopsis of the available data on pediatric airway dimensions.

METHODS

A systematic literature search was carried out in the PubMed database, Scopus, Embase, Web of Science, Prisma, and Google Scholar and secondarily completed by a reference search. Based on inclusion and exclusion criteria, a final selection of 109 studies with data on pediatric airway dimensions published from 1923 to 2018 were further analyzed.

RESULTS

Six different airway measurement methods were identified. They included anatomical examinations, chest X-ray, computed tomography, magnetic resonance tomography, bronchoscopy, and ultrasound. Anatomical studies were more abundant compared to other methods. Data provided were very heterogeneously presented and powered. In addition, due to different study conditions, they are hardly comparable. Among all, anatomical and computer tomography studies are thought to provide the most reliable data. Ultrasound is an upcoming technique to estimate airway parameters of fetus and premature infants. There was, in general, a lack of comprehensive studies providing a complete range of airway dimensions in larger groups of patients from birth to adolescence.

CONCLUSIONS

This work revealed a large heterogeneity of studies providing data on pediatric airway dimensions, making it impossible to compare, or assemble them to normograms for clinical use. Comprehensive studies in large population of children are needed to provide full range nomograms on pediatric airway dimensions.

Influence of pharyngeal airway respiration pressure on Class II mandibular retrusion in children: A computational fluid dynamics study of inspiration and expiration

OBJECTIVES

To examine the influence of negative pressure of the pharyngeal airway on mandibular retraction during inspiration in children with nasal obstruction using the computational fluid dynamics (CFD) method.

SETTING AND SAMPLE POPULATION

Sixty-two children were divided into Classes I, II (mandibular retrusion) and III (mandibular protrusion) malocclusion groups.

MATERIAL AND METHODS

Cone-beam computed tomography data were used to reconstruct three-dimensional shapes of the nasal and pharyngeal airways. Airflow pressure was simulated using CFD to calculate nasal resistance and pharyngeal airway pressure during inspiration and expiration.

RESULTS

Nasal resistance of the Class II group was significantly higher than that of the other two groups, and oropharyngeal airway inspiration pressure in the Class II (-247.64 Pa) group was larger than that in the Class I (-43.51 Pa) and Class III (-31.81 Pa) groups (P<.001). The oropharyngeal airway inspiration-expiration pressure difference in the Class II (-27.38 Pa) group was larger than that in the Class I (-5.17 Pa) and Class III (0.68 Pa) groups (P=.006).

CONCLUSION

Large negative inspiratory pharyngeal airway pressure due to nasal obstruction in children with Class II malocclusion may be related to their retrognathia.

Multi-modal anatomical Optical Coherence Tomography and CT for in vivo Dynamic Upper Airway Imaging

We describe a novel, multi-modal imaging protocol for validating quantitative dynamic airway imaging performed using anatomical Optical Coherence Tomography (aOCT). The aOCT system consists of a catheter-based aOCT probe that is deployed via a bronchoscope, while a programmable ventilator is used to control airway pressure. This setup is employed on the bed of a Siemens Biograph CT system capable of performing respiratory-gated acquisitions. In this arrangement the position of the aOCT catheter may be visualized with CT to aid in co-registration. Utilizing this setup we investigate multiple respiratory pressure parameters with aOCT, and respiratory-gated CT, on both ex vivo porcine trachea and live, anesthetized pigs. This acquisition protocol has enabled real-time measurement of airway deformation with simultaneous measurement of pressure under physiologically relevant static and dynamic conditions- inspiratory peak or peak positive airway pressures of 10-40 cm H₂O, and 20-30 breaths per minute for dynamic studies. We subsequently compare the airway cross sectional areas (CSA) obtained from aOCT and CT, including the change in CSA at different stages of the breathing cycle for dynamic studies, and the CSA at different peak positive airway pressures for static studies. This approach has allowed us to improve our acquisition methodology and to validate aOCT measurements of the dynamic airway for the first time. We believe that this protocol will prove invaluable for aOCT system development and greatly facilitate translation of OCT systems for airway imaging into the clinical setting.

Investigation of the Upper Airway Anatomy With Ultrasound

OBJECTIVE

The aims of this study were to describe the relationship between the scanning planes and appearance of the upper airway on sonography and to demonstrate the reliability and reproducibility of sonographic measurements of the upper airway.

METHODS

Airway sonoanatomy was recognized by comparing the airway images and the corresponding cadaver's anatomical specimens. Systemic sonographic examination of 267 healthy volunteers was conducted to obtain the sonographic measurement of airway lumen. The reliability and reproducibility studies were conducted in 40 healthy volunteers.

RESULT

The air-filled upper airway appeared as a bright heterogeneous hyperechoic line. During deep inspiration, the upper airway lumen expanded to the highest anterior-posterior dimension, whereas during deep expiration, the lateral dimension tended to increase. The sonographic measurements had good reproducibility, with intraclass correlation coefficient ranging from 0.722 to 0.887 and 0.727 to 0.882 for interobserver and intraobserver reliability, respectively.

CONCLUSIONS

Ultrasonography can determine the anatomy of the upper airway and perform the quantitative analysis of the upper airway lumen during respiration. The results were encouraging and support the utility of ultrasonography in future airway disorder studies.

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 3-D MR Visualization and Detection of Upper Airway Obstruction During Sleep Using Region-Growing Segmentation

GOAL

We demonstrate a novel and robust approach for visualization of upper airway dynamics and detection of obstructive events from dynamic 3-D magnetic resonance imaging (MRI) scans of the pharyngeal airway.

METHODS

This approach uses 3-D region growing, where the operator selects a region of interest that includes the pharyngeal airway, places two seeds in the patent airway, and determines a threshold for the first frame.

RESULTS

This approach required 5 s/frame of CPU time compared to 10 min/frame of operator time for manual segmentation. It compared well with manual segmentation, resulting in Dice Coefficients of 0.84 to 0.94, whereas the Dice Coefficients for two manual segmentations by the same observer were 0.89 to 0.97. It was also able to automatically detect 83% of collapse events.

CONCLUSION

Use of this simple semiautomated segmentation approach improves the workflow of novel dynamic MRI studies of the pharyngeal airway and enables visualization and detection of obstructive events.

SIGNIFICANCE

Obstructive sleep apnea (OSA) is a significant public health issue affecting 4-9% of adults and 2% of children. Recently, 3-D dynamic MRI of the upper airway has been demonstrated during natural sleep, with sufficient spatiotemporal resolution to noninvasively study patterns of airway obstruction in young adults with OSA. This study makes it practical to analyze these long scans and visualize important factors in an MRI sleep study, such as the time, site, and extent of airway collapse.

The Relationship Between Volume Overload in End-Stage Renal Disease and Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is common, underdiagnosed, and undertreated among patients with end-stage renal disease (ESRD). As in all cases, pathogenesis of OSA is related to repeated upper airway (UA) occlusion or narrowing, but in ESRD, additional contributory factors likely include uremic destabilization of central respiratory control and anatomic changes in the UA related to fluid status. Pulmonary congestion is common in acute and chronic kidney failure and is a consequence of cardiomyopathy and fluid overload, two potentially reversible risk factors. Emerging evidence suggests that volume overload also reduces the UA caliber. The diminution in UA area as well as destabilization of ventilatory control in ESRD have been postulated as causes of increased OSA prevalence and severity in these patients, and creates a vicious cycle wherein OSA exacerbates fluid overload disorders such as in congestive heart failure (CHF) and ESRD, which then further worsen OSA. Dialysis modalities may differ in their effects on volume status, the accumulation of uremic toxins, and acid-base status, and as a consequence, on the emergence and severity of OSA. Given the contribution of excess fluid to both the severity of nocturnal hypoxia and UA narrowing, establishing and maintaining dry weight is of particular importance when managing OSA in ESRD. Clinical trials to determine the extent to which more aggressive fluid removal in ESRD patients may alleviate OSA are needed.

Quantitative tissue velocity imaging evaluation of ventricular function in obstructive sleep apnoea-hypopnoea syndrome in children

This study aimed to evaluate the changes in left and right ventricular functions of children with obstructive sleep apnoea-hypopnoea syndrome (OSAHS) and to determine the efficacy of surgical treatment for OSAHS in children. The subjects included 20 normal controls and 55 children of OSAHS with adenoid and/or tonsil hypertrophy diagnosed by polysomnography (PSG). We divided the children with OSAHS into the mild group, moderate group and severe group of OSAHS according to the condition of apnoea-hypopnoea index (AHI) and the lowest of oxygen saturation (LSaO₂). In mitral annulus,the Va values were increased in moderate and severe OSAHS (P > 0.05), and the Ve/Va values were decreased in the severe group (P > 0.05), while the Vs values were not changed (P > 0.05). In tricuspid annulus, the Vs values were decreased in moderate and severe OSAHS (P < 0.05), while the Ve, Va and Ve/Va values were not changed (P > 0.05). Six months after adenoidectomy and/or tonsillectomy, mitral Va values were decreased and tricuspid Vs values were increased significantly (P < 0.05), and AHI was decreased and LSaO₂ was significantly increased (P < 0.05). Compared with the control group, no difference was found in the above parameters (P > 0.05). The left ventricular diastolic function and the right ventricular systolic function of children with moderate to severe OSAHS are decreased to varying degrees at an early stage. Mitral annular and tricuspid annular velocity detected by quantitative tissue velocity imaging (QTVI) could sensitively reflect the early changes of left and right ventricular function. Adenoidectomy and/or tonsillectomy were effective methods to treat childhood OSAHS, which could reverse myocardial dysfunction.

Nasal versus oral aerosol delivery to the "lungs" in infants and toddlers

OBJECTIVES

The oral route has been considered superior to the nasal route for aerosol delivery to the lower respiratory tract (LRT) in adults and children. However, there are no data comparing aerosol delivery via the oral and nasal routes in infants. The aim of this study was to compare nasal and oral delivery of aerosol in anatomically correct replicas of infants' faces containing both nasal and oral upper airways.

METHODS

Three CT-derived upper respiratory tract ("URT") replicas representing infants/toddlers aged 5, 14 and 20 months were studied and aerosol delivery to the "lower respiratory tract" (LRT) by either the oral or nasal route for each of the replicas was measured at the "tracheal" opening. A radio-labeled (99mDTPA) normal saline solution aerosol was generated by a soft-mist inhaler (SMIRespimat® Boehringer Ingelheim, Germany) and aerosol was delivered via a valved holding chamber (Respichamber® TMI, London, Canada) and an air-tight mask (Unomedical, Inc., McAllen, TX). A breath simulator was connected to the replicas and an absolute filter at the "tracheal" opening captured the aerosol representing "LRT" dose. Age-appropriate mask dimensions and breathing patterns were employed for each of the airway replicas. Two different tidal volumes (V_t ) were used for comparing the nasal versus oral routes.

RESULTS

Nasal delivery to the LRT exceeded that of oral delivery in the 5- and 14-month models and was equivalent in the 20-month model. Differences between nasal and oral delivery diminished with "age"/size. Similar findings were observed with lower and higher tidal volumes (V_t ).

CONCLUSION

Nasal breathing for aerosol delivery to the "LRT" is similar to, or more efficient than, mouth breathing in infant/toddler models, contrary to what is observed in older children and adults. Pediatr Pulmonol. 2015; 50:276-283. © 2014 Wiley Periodicals, Inc.

Influence of rostral fluid shift on upper airway size and mucosal water content

STUDY OBJECTIVE

Fluid displacement from the legs during recumbency while in bed might narrow the upper airway (UA) in association with nuchal fluid accumulation that may contribute to the pathogenesis of obstructive sleep apnea (OSA). The aim of this study was to test the hypothesis that rostral fluid displacement from the legs causes a greater decrease in UA cross-sectional area (UA-XSA) and a greater increase in UA mucosal water content (UA-MWC) and internal jugular venous volume (IJVVol) in subjects with OSA than in those without OSA.

METHODS

Subjects underwent baseline assessment of leg fluid volume (LFV) measured by bio-electrical impedance, as well as UA-XSA and UA-MWC by magnetic resonance imaging. They were then randomly assigned to a 20-min period either with or without application of lower body positive pressure (LBPP) of 40 mm Hg, followed by a 15-min washout period, after which they crossed over to the other arm of the study. Measurements of LFV, UA-MWC, and UA-XSA were repeated after each arm of the study.

RESULTS

In 12 subjects without sleep apnea, UA-XSA increased and UA-MWC decreased significantly, whereas in 12 subjects with OSA, UA-XSA decreased and UA-MWC increased significantly in response to LBPP. The changes in UA-XSA and UA-MWC in response to LBPP differed significantly between the 2 groups (p = 0.006 and p < 0.001, respectively), despite similar changes in LFV and IJVVol.

CONCLUSIONS

Our results suggest that rostral fluid shift may contribute to the pathogenesis of OSA at least partly through narrowing of the UA due to transudation of fluid into the UA mucosa.

The effect of rapid maxillary expansion on pharyngeal airway pressure during inspiration evaluated using computational fluid dynamics

INTRODUCTION

Recent evidence suggests that rapid maxillary expansion (RME) is an effective treatment of obstructive sleep apnea syndrome (OSAS) in children with maxillary constriction. Nonetheless, the effect of RME on pharyngeal airway pressure during inspiration is not clear. The purpose of this retrospective study was to evaluate changes induced by the RME in ventilation conditions using computational fluid dynamics.

METHODS

Twenty-five subjects (14 boys, 11 girls; mean age 9.7 years) who required RME had cone-beam computed tomography (CBCT) images taken before and after the RME. The CBCT data were used to reconstruct 3-dimensional shapes of nasal and pharyngeal airways. Measurement of airflow pressure was simulated using computational fluid dynamics for calculating nasal resistance during exhalation. This value was used to assess maximal negative pressure in the pharyngeal airway during inspiration.

RESULTS

Nasal resistance after RME, 0.137 Pa/(cm(3)/s), was significantly lower than that before RME, 0.496 Pa/(cm(3)/s), and the maximal negative pressure in the pharyngeal airway during inspiration was smaller after RME (-48.66 Pa) than before (-124.96 Pa).

CONCLUSION

Pharyngeal airway pressure during inspiration is decreased with the reduction of nasal resistance by the RME. This mechanism may contribute to the alleviation of OSAS in children.

Computational fluid dynamics endpoints to characterize obstructive sleep apnea syndrome in children

Computational fluid dynamics (CFD) analysis may quantify the severity of anatomical airway restriction in obstructive sleep apnea syndrome (OSAS) better than anatomical measurements alone. However, optimal CFD model endpoints to characterize or assess OSAS have not been determined. To model upper airway fluid dynamics using CFD and investigate the strength of correlation between various CFD endpoints, anatomical endpoints, and OSAS severity, in obese children with OSAS and controls. CFD models derived from magnetic resonance images were solved at subject-specific peak tidal inspiratory flow; pressure at the choanae was set by nasal resistance. Model endpoints included airway wall minimum pressure (Pmin), flow resistance in the pharynx (Rpharynx), and pressure drop from choanae to a minimum cross section where tonsils and adenoids constrict the pharynx (dPTAmax). Significance of endpoints was analyzed using paired comparisons (t-test or Wilcoxon signed rank test) and Spearman correlation. Fifteen subject pairs were analyzed. Rpharynx and dPTAmax were higher in OSAS than control and most significantly correlated to obstructive apnea-hypopnea index (oAHI), r = 0.48 and r = 0.49, respectively (P < 0.01). Airway minimum cross-sectional correlation to oAHI was weaker (r = -0.39); Pmin was not significantly correlated. CFD model endpoints based on pressure drops in the pharynx were more closely associated with the presence and severity of OSAS than pressures including nasal resistance, or anatomical endpoints. This study supports the usefulness of CFD to characterize anatomical restriction of the pharynx and as an additional tool to evaluate subjects with OSAS.

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.

Functional respiratory imaging as a tool to assess upper airway patency in children with obstructive sleep apnea

OBJECTIVE

We aim to investigate if anatomical and functional properties of the upper airway using computerized 3D models derived from computed tomography (CT) scans better predict obstructive sleep apnea (OSA) severity than standard clinical markers.

METHODS

Consecutive children with suspected OSA underwent polysomnography, clinical assessment of upper airway patency, and a CT scan while awake. A three-dimensional (3D) reconstruction of the pharyngeal airway was built from these images, and computational fluid dynamics modeling of low inspiratory flow was performed using open-source software.

RESULTS

Thirty-three children were included (23 boys; mean age, was 6.0±3.2y). OSA was diagnosed in 23 patients. Children with OSA had a significantly lower volume of the overlap region between tonsils and the adenoids (median volume, 1408 mm compared to 2173 mm; p=0.04), a lower mean cross-sectional area at this location (median volume, 69.3mm(2) compared to 114.3mm2; p=0.04), and a lower minimal cross-sectional area (median volume, 17.9 mm2 compared to 25.9 mm2; p=0.05). Various significant correlations were found between several imaging parameters and the severity of OSA, most pronounced for upper airway conductance (r=-0.46) (p<0.01) for correlation between upper airway conductance and the apnea-hypopnea index. No differences or significant correlations were observed with clinical parameters of upper airway patency. Preliminary data after treatment showed that none of the patients with residual OSA had their smallest cross-sectional area located in segment 3, and this frequency was significantly lower than in their peers whose sleep study normalized (64%; p=0.05).

CONCLUSION

Functional imaging parameters are highly correlated with OSA severity and are a more powerful correlate than clinical scores of upper airway patency. Preliminary data also showed that we could identify differences in the upper airway of those subjects who did not benefit from a local upper airway treatment.

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.

Relationship of pharyngeal water content and jugular volume with severity of obstructive sleep apnea in renal failure

BACKGROUND

In patients with end-stage renal disease (ESRD), fluid overload may contribute to their high prevalence of obstructive sleep apnea (OSA) by increasing the amount of fluid displaced from the legs into the neck overnight, and possibly compressing the upper airway (UA). Indeed, in ESRD patients, the amount of overnight rostral fluid displacement from the legs is related to the frequency of apneas and hypopneas per hour of sleep (apnea-hypopnea index, AHI). We, therefore, hypothesized that in ESRD patients, the greater the UA-mucosal water content (UA-MWC) and internal jugular vein volume (IJVVol), the higher the AHI.

METHODS

We studied 20 patients with ESRD on thrice weekly hemodialysis who had undergone diagnostic polysomnography (age 41.0 ± 12.3 years, with a body mass index (BMI) of 25.8 ± 6.3 kg/m(2) and an AHI of 20.2 ± 26.8). The leg fluid volume (LFV) was measured by bioelectric impedance. The IJVVol and MWC were measured by UA magnetic resonance imaging (MRI).

RESULTS

The only significant independent correlates of the AHI were IJVVol (r = 0.801, P < 0.0001) and UA-MWC (r = 0.720, P = 0.0005) which together explained 72% of its variability.

CONCLUSIONS

These data suggest that fluid overload via increased IJVVol, and UA-MWC, contributes to the pathogenesis of OSA in patients with ESRD. These findings help us to explain the high prevalence of OSA in ESRD patients, and attenuation of OSA in association with nocturnal dialysis. They also suggest the need for randomized trials to determine whether more aggressive fluid removal in ESRD patients will alleviate OSA.

Noninvasive estimation of pharyngeal airway resistance and compliance in children based on volume-gated dynamic MRI and computational fluid dynamics

Computational fluid dynamics (CFD) analysis was used to model the effect of collapsing airway geometry on internal pressure and velocity in the pharyngeal airway of three sedated children with obstructive sleep apnea syndrome (OSAS) and three control subjects. Model geometry was reconstructed from volume-gated magnetic resonance images during normal tidal breathing at 10 increments of tidal volume through the respiratory cycle. Each geometry was meshed with an unstructured grid and solved using a low-Reynolds number k-ω turbulence model driven by flow data averaged over 12 consecutive breathing cycles. Combining gated imaging with CFD modeling created a dynamic three-dimensional view of airway anatomy and mechanics, including the evolution of airway collapse and flow resistance and estimates of the local effective compliance. The upper airways of subjects with OSAS were generally much more compliant during tidal breathing. Compliance curves (pressure vs. cross-section area), derived for different locations along the airway, quantified local differences along the pharynx and between OSAS subjects. In one subject, the distal oropharynx was more compliant than the nasopharynx (1.028 vs. 0.450 mm(2)/Pa) and had a lower theoretical limiting flow rate, confirming the distal oropharynx as the flow-limiting segment of the airway in this subject. Another subject had a more compliant nasopharynx (0.053 mm(2)/Pa) during inspiration and apparent stiffening of the distal oropharynx (C = 0.0058 mm(2)/Pa), and the theoretical limiting flow rate indicated the nasopharynx as the flow-limiting segment. This new method may help to differentiate anatomical and functional factors in airway collapse.

Update on pediatric sleep-disordered breathing

Pediatric sleep-disordered breathing (SDB) includes an increasingly recognized, highly prevalent, yet still underdiagnosed spectrum of respiratory disorders, the most common and clinically significant of which is obstructive sleep apnea. SDB is linked with significant end-organ dysfunction across various systems, particularly with cardiovascular, neurocognitive, and metabolic consequences. This review summarizes recent advances in understanding of pediatric SDB and discusses the challenges inherent in diagnosing and treating children with SDB.

Urinary proteins for the diagnosis of obstructive sleep apnea syndrome

Approximately 2-3% of all children in the United States suffer from obstructive sleep apnea (OSA). This condition is characterized by repeated events of partial or complete obstruction of the upper airways during sleep leading to recurring episodes of hypercapnia, hypoxemia, and arousal throughout the night as well as snoring, which afflicts 7-10% of all children. Since clinical history and physical examination are unreliable in the differentiation between children with OSA and children with primary snoring (PS) who have no apparent alteration in sleep architecture, current diagnostic approaches for OSA require an overnight sleep study (ONP). ONP is onerous, relatively unavailable, labor intensive, and inconvenient, leading to long waiting periods and unnecessary delays in diagnosis and treatment. Development of noninvasive biomarker(s) capable of reliably distinguishing children with PS from those with OSA would greatly facilitate timely screening and diagnosis of OSA in children. Therefore, we hypothesized that proteomic strategies in the urine may permit the identification of biomarker(s) that reliably screen for OSA. In this study, time-of-flight mass spectrometry was used to profile proteins in the first morning void urines from children. We discovered that urocortins are increased in OSA and provide a noninvasive approach for quick and convenient diagnosis otf OSA in snoring children.

Developmental aspects of the upper airway: report from an NHLBI Workshop, March 5-6, 2009

The upper airway serves three important functions: respiration, swallowing, and speech. During development it undergoes significant structural and functional changes that affect its size, shape, and mechanical properties. Abnormalities of the upper airway require prompt attention, because these often alter ventilatory patterns and gas exchange, particularly during sleep when upper airway motor tone and ventilatory drive are diminished. Recognizing the relationship of early life events to lung health and disease, the National Heart, Lung, and Blood Institute (NHLBI), with cofunding from the Office of Rare Diseases (ORD), convened a workshop of extramural experts, from many disciplines. The objective of the workshop was: (1) to review the state of science in pediatric upper airway disorders; (2) to make recommendations to the Institute to fill knowledge gaps; (3) to prioritize new research directions; and (4) to capitalize on scientific opportunities. This report provides recommendations that could facilitate translation of basic research findings into practice to better diagnose, treat, and prevent airway compromise in children.

Evaluation of the human airway using cone-beam computerized tomography

OBJECTIVE

The goal of this project was to define and measure human airway space with radiographic volumetric 3-dimensional imaging and digital reconstruction of the pharynx using cone-beam computerized tomography.

STUDY DESIGN

This was a randomized retrospective study. Ten patient scans were selected randomly from a pool of 196 subjects seeking dental treatment at the University of California, San Francisco. Digital Imaging and Communications in Medicine-format volume images were captured using a low-radiation rapid-scanning cone-beam computerized tomography system (Hitachi MercuRay).

RESULTS

Detailed progressive rostrocaudal cross-sectional area histograms indicated that 8 of the 10 subjects demonstrated a region of maximum constriction near the oropharynx level. The most restricted cross-sectional area varied from 90 mm(2) to 360 mm(2).

CONCLUSIONS

The maximum constriction of the airway in 10 subjects quietly breathing for 10 seconds indicated variation in the level of the pharynx and the extent of the rostrocaudal zone of restriction.

Respiratory gating of anatomical optical coherence tomography images of the human airway

Anatomical optical coherence tomography (aOCT) is a long-range endoscopic imaging modality capable of quantifying size and shape of the human airway. A challenge to its in vivo application is motion artifact due to respiratory-related movement of the airway walls. This paper represents the first demonstration of respiratory gating of aOCT airway data, and introduces a novel error measure to guide appropriate parameter selection. Results indicate that at least four gates per respiratory cycle should be used, with only minor improvements as the number of gates is further increased. It is shown that respiratory gating can substantially improve the quality of aOCT images and reveal events and features that are otherwise obscured by blurring.

Effect of body posture on pharyngeal shape and size in adults with and without obstructive sleep apnea

STUDY OBJECTIVES

In patients with obstructive sleep apnea (OSA), the severity and frequency of respiratory events is increased in the supine body posture compared with the lateral recumbent posture. The mechanism responsible is not clear but may relate to the effect of posture on upper airway shape and size. This study compared the effect of body posture on upper airway shape and size in individuals with OSA with control subjects matched for age, BMI, and gender.

PARTICIPANTS

11 males with OSA and 11 age- and BMI-matched male control subjects.

RESULTS

Anatomical optical coherence tomography was used to scan the upper airway of all subjects while awake and breathing quietly, initially when supine, and then in the lateral recumbent posture. A standard head, neck, and tongue position was maintained during scanning. Airway cross-sectional area (CSA) and anteroposterior (A-P) and lateral diameters were obtained in the oropharyngeal and velopharyngeal regions in both postures. A-P to lateral diameter ratios provided an index of regional airway shape. In equivalent postures, the ratio of A-P to lateral diameter in the velopharynx was similar in OSA and control subjects. In both groups, this ratio was significantly less for the supine than for the lateral recumbent posture. CSA was smaller in OSA subjects than in controls but was unaffected by posture.

CONCLUSIONS

The upper airway changes from a more transversely oriented elliptical shape when supine to a more circular shape when in the lateral recumbent posture but without altering CSA. Increased circularity decreases propensity to tube collapse and may account for the postural dependency of OSA.

Pathophysiology of pediatric obstructive sleep apnea

Sleep-disordered breathing is a common and serious cause of metabolic, cardiovascular, and neurocognitive morbidity in children. The spectrum of obstructive sleep-disordered breathing ranges from habitual snoring to partial or complete airway obstruction, termed obstructive sleep apnea (OSA). Breathing patterns due to airway narrowing are highly variable, including obstructive cycling, increased respiratory effort, flow limitation, tachypnea, and/or gas exchange abnormalities. As a consequence, sleep homeostasis may be disturbed. Increased upper airway resistance is an essential component of OSA, including any combination of narrowing/retropositioning of the maxilla/mandible and/or adenotonsillar hypertrophy. However, in addition to anatomic factors, the stability of the upper airway is predicated on neuromuscular activation, ventilatory control, and arousal threshold. During sleep, most children with OSA intermittently attain a stable breathing pattern, indicating successful neuromuscular activation. At sleep onset, airway muscle activity is reduced, ventilatory variability increases, and an apneic threshold slightly below eupneic levels is observed in non-REM sleep. Airway collapse is offset by pharyngeal dilator activity in response to hypercapnia and negative lumenal pressure. Ventilatory overshoot results in sudden reduction in airway muscle activation, contributing to obstruction during non-REM sleep. Arousal from sleep exacerbates ventilatory instability and, thus, obstructive cycling. Paroxysmal reductions in pharyngeal dilator activity related to central REM sleep processes likely account for the disproportionate severity of OSA observed during REM sleep. Understanding the pathophysiology of pediatric OSA may permit more precise clinical phenotyping, and therefore improve or target therapies related to anatomy, neuromuscular compensation, ventilatory control, and/or arousal threshold.