Linear dimensions of the upper airway structure during development: assessment by magnetic resonance imaging

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.

Magnetic resonance imaging assessment of the velopharyngeal mechanism at rest and during speech in Chinese adults and children

PURPOSE

Recent applications of the magnetic resonance imaging (MRI) technique introduced accurate 3-dimensional measurements of the velopharyngeal mechanism. Further standardization of the data acquisition and analysis protocol was successfully applied to imaging adults at rest and during phonation. This study was designed to test and modify a noninvasive protocol for evaluating young children without using general anesthesia. In addition, the velopharyngeal structures and their maximal motion were compared between adults and children.

METHOD

MRI data were acquired in 12 young adults and 9 children at rest and during speech production. Multiple measurements were made on the velopharyngeal and craniofacial structures as well as on the levator veli palatini muscle.

RESULTS

Most of the ratio measurements of structural shape and maximal motion in the velopharyngeal and craniofacial regions were not significantly different between the adults and the children, despite the fact that the children had much smaller structures than the adults.

CONCLUSION

The proportion of the velopharyngeal mechanism remains stable in young children and adults so that the motions of the velum and pharyngeal walls are adequate to close the velopharyngeal port completely.

Decreasing incidence of adenotonsillar problems in Dutch general practice: real or artefact?

BACKGROUND

The incidence of hypertrophy and recurrent infections of the tonsils/adenoids appears to be decreasing in the Netherlands. It is uncertain whether this is a 'real' decrease in the incidence of disease or an 'artefact'.

AIM

To investigate possible causes of the decreasing incidence of adenotonsillar problems among Dutch children.

DESIGN OF STUDY

Observational.

SETTING

A nationally representative general practice database.

METHOD

Incidence rates were calculated over 2002-2005 among children aged 0-14 years. Multilevel Poisson regression analyses were used to examine the following possible causes of changing incidence rates: change in recording (more substitution codes), change in the demand for care (fewer visits to the GP), and change in the supply of care (fewer antibiotic prescriptions and referrals). Indications for a 'real' change in the incidence of disease were examined by calculating incidence rates of other clinical manifestations of microbial pathogens that may cause adenotonsillar problems.

RESULTS

The incidence rate decreased significantly (P = 0.017) from 3.0 to 1.3 per 1000 children per year. Correcting for demand for and supply of care led to a smaller decline in yearly incidence, from 2.9 to 1.7 per 1000 children per year (P = 0.105). No clearly similar trend was found in other clinical manifestations of viruses and bacteria that may cause adenotonsillar problems.

CONCLUSION

Part of the declining trend can be explained by a change in the demand for and supply of care, but no apparent causal clue emerged for the residual declining trend in the incidence of disease.

Age-Specific Size of the Upper Airway Structures in Children during Development

Objectives:

The purpose of this study was to establish the largest magnetic resonance imaging study so far, by including 292 cases in a prospective fashion, to investigate the normative values of the upper airway and surrounding tissues during development.

Methods:

We enrolled in the study 448 children who underwent cranial magnetic resonance imaging. We included 292 patients who had no sleep disorders or any associated symptom that could be related to breathing disorders. Using midsagittal and axial images, we evaluated the variations in size of the upper airway tissues.

Results:

On images from the midsagittal plane, the normative values of the length and the thickness of the soft palate, the length and height of the tongue, the distance between the mental spine and the clivus, the thickness of the adenoid pad and the nasopharyngeal area, the adenoid pad oblique width, the soft palate oblique width, and the tongue oblique width were obtained for several age groups. Using images from the axial plane at the level of maximal tonsillar cross-sectional area, we measured the normative values of the mean tonsillar width and intertonsillar space.

Conclusions:

Magnetic resonance imaging is an excellent method of assessing upper airway structures. Knowledge of variations in size of the upper airway and surrounding tissues is essential in determining the significance of incidental findings in this area.

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.

Tonsillar size in 2- to 14-year-old children with and without snoring

BACKGROUND

Few investigations have assessed tonsillar size in children of variable age, sleep-disordered breathing (SDB) status and degree of adiposity. This study evaluated the size of tonsils in young and older, lean and obese children, without or with snoring.

METHODS

Children attending the Emergency Department or Pulmonology Clinic were recruited and tonsillar size was scored 1-4. Snoring >or=1 night/week was considered diagnostic of SDB and body mass index z-score >or=1.645 was defined as obesity. Age was analyzed as dichotomous variable (<or=7 years old vs. >7 years old).

RESULTS

362 children (2-14 years old) were recruited; 78 (21.5%) were obese and 108 (29.8%) had SDB. SDB-but not age or obesity-was significantly related to tonsillar size (P = 0.001). There was not enough evidence to support the presence of interactions between SDB and age or obesity regarding the size of tonsils (P = 0.157 and P = 0.978, respectively). Young subjects without SDB had larger tonsils than older subjects without SDB (1.9 +/- 0.7 vs. 1.7 +/- 0.8; P = 0.017), whereas age did not affect tonsillar size in children with SDB (P = 0.78).

CONCLUSIONS

Young and older children with SDB have similar tonsillar size. In contrast, older subjects without snoring have smaller tonsils than young subjects without snoring. Tonsillar enlargement in children with SDB probably occurs in early childhood without change in older age.

Palatine Tonsil Size and its Correlation with Subjective Tonsil Size in Patients with Sleep-Disordered Breathing

OBJECTIVE: To investigate the correlation of subjective tonsil size with real palatine tonsil size and to compare the differences of each parameter according to subjective tonsil size and between children and adults.

STUDY DESIGN: Prospective evaluation of subjective tonsil size (0–4+) and real palatine tonsil size, including tonsil height (TH), tonsil width (TW), tonsil thickness (TT), total tonsil volume (TTV), and embedded tonsil volume (ETV) within the tonsillar fossa.

SETTING: Tertiary-care rhinologic clinic.

SUBJECTS AND METHODS: We measured TH, TW, TT, TTV, and ETV in 277 children and 63 adults with sleep-disordered breathing (SDB).

RESULTS: In both children and adults, subjective tonsil size was significantly correlated with TTV, TH, TW, and TT (correlation coefficients 0.199–0.427 for children and 0.462–0.551 for adults). In children, TTV increased in proportion to subjective tonsil size, but about 45 percent and 34 percent of tonsils markedly deviated from the mean value of their TTV in size 2 and 3 groups, respectively. In adults, TTV of subjective tonsil size 3 and 4 groups was significantly larger than that of size 1 and 2 groups.

CONCLUSIONS: Real palatine tonsil size correlated with subjective tonsil size in both children and adults with SDB. Although there is a statistical correlation in children between TTV and subjective tonsil size, there is significant discordance in size 2 and 3 groups, thus greatly limiting the value of subjective tonsil size assessment in the majority of children. However, adult subjective tonsil size may reflect real palatine tonsil size and may help predict it preoperatively.

Age-related changes of the upper airway assessed by 3-dimensional computed tomography

The purposes of this study were to establish normative data for airway size and shape and to evaluate differences associated with age and sex using 3-dimensional (3-D) imaging. Patients being evaluated by computed tomography (CT) for pathologic conditions not related to the airway were included. Using 3-D Slicer (Harvard Surgical Planning Laboratory, Brigham and Women's Hospital, Boston, MA), a software program, digital 3-D CT reconstructions were made and parameters of airway size analyzed: volume (VOL), surface area (SA), length (L), mean cross-sectional area (mean CSA), minimum retropalatal (RP), minimum retroglossal (RG), minimum cross-sectional area (min CSA), and lateral (LAT) and anteroposterior (AP) retroglossal airway dimensions. Evaluation of airway shape included LAT/AP and RP/RG ratios, uniformity (U), and sphericity, a measure of compactness (Psi). Children were stratified by stage of dentition: primary, 0 to 5 years; mixed, 6 to 11 years; permanent, 12 to 16 years; and adults, older than 16 years. Differences in airway parameters by age and sex were analyzed. Forty-six CT scans (31 males) were evaluated. Adults had larger (VOL, SA, L, mean CSA, and LAT), more elliptical (increased LAT/AP, P = 0.01), less uniform (U, P = 0.02), and less compact (decreased Psi, P = 0.001) airways than children. Among children, those in the permanent dentition demonstrated greater VOL (P < 0.01), SA (P < 0.01), L (P < 0.01), and mean CSA (P < 0.01) than those in the primary dentition. There were no gender differences in airway parameters. Understanding differences in 3-D airway size and morphology by age may serve as a basis for evaluation of patients with obstructive sleep apnea and may help to predict and to evaluate outcomes of treatment.

Oropharyngeal airway in children with Class III malocclusion evaluated by cone-beam computed tomography

INTRODUCTION

Upper airway size is increasingly recognized as an important factor in malocclusion. However, children with Class III malocclusion are somewhat neglected compared with those with a Class II skeletal pattern. Therefore, the purpose of this study was to establish the characteristic shape of the oropharyngeal airway (OA) in children with Class III malocclusion.

METHODS

The sample comprised 45 children (average age, 8.6 +/- 1.0 years) divided into 2 groups: 25 with Class I and 20 with Class III malocclusions. OA size of each group was evaluated by cone-beam computed tomography. Cluster analysis, based on OA shape, redivided the subjects into wide, square, and long types. The distributions of Class I and Class III subjects were compared among the types.

RESULTS

The Class III group showed statistically larger OA area and width compared with the Class I group. Area was positively correlated with Class III severity. The square type included 84% of the Class I malocclusions but only 30% of the Class III malocclusions, indicating that the OA in Class III malocclusion tends to be flat.

CONCLUSIONS

The Class III malocclusion is associated with a large and flat OA compared with the Class I malocclusion.

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.

Anatomic development of the oral and pharyngeal portions of the vocal tract: an imaging study

The growth of the vocal tract (VT) is known to be non-uniform insofar as there are regional differences in anatomic maturation. This study presents quantitative anatomic data on the growth of the oral and pharyngeal portions of the VT from 605 imaging studies for individuals between birth and 19 years. The oral (horizontal) portion of the VT was segmented into lip-thickness, anterior-cavity-length, oropharyngeal-width, and VT-oral, and the pharyngeal (vertical) portion of the VT into posterior-cavity-length, and nasopharyngeal-length. The data were analyzed to determine growth trend, growth rate, and growth type (neural or somatic). Findings indicate differences in the growth trend of segments/variables analyzed, with significant sex differences for all variables except anterior-cavity-length. While the growth trend of some variables displays prepubertal sex differences at specific age ranges, the importance of such localized differences appears to be masked by overall growth rate differences between males and females. Finally, assessment of growth curve type indicates that most VT structures follow a combined/hybrid (somatic and neural) growth curve with structures in the vertical plane having a predominantly somatic growth pattern. These data on the non-uniform growth of the vocal tract reveal anatomic differences that contribute to documented acoustic differences in prepubertal speech production.

Airway management

The pediatric airway and respiratory function differ from those in adults. Optimum management requires consideration of these differences, but the application of adult principles is usually sufficient to buy time in an emergency until specialist pediatric help is available. Simple airway opening techniques such as head tilt and jaw thrust are usually sufficient to open the child's airway, but there is now a range of equipment available to bypass supraglottic airway obstruction-the strengths and weaknesses of such devices are explored in this article. The role of endotracheal intubation is also discussed, along with the pros and cons of the use of cuffed endotracheal tubes in children, and methods of confirming tracheal placement of the tube.

Effects of head posture on the oral, pharyngeal and laryngeal axis alignment in infants and young children by magnetic resonance imaging

BACKGROUND

Objective anatomical studies supporting the different recommendations for laryngoscopy in infants and young children are scarce. The objective of this study was to measure by magnetic resonance imaging (MRI) the consequences of head extension on the oral, pharyngeal and laryngeal axes in infants and young children.

METHODS

Thirty patients (age: 33 +/- 28 months; weight 14 +/- 9 kg), under general inhalated anesthesia delivered via a laryngeal mask airway, were studied in two anatomic positions: head in the resting position and in simple extension. The following measurements were made on each scan: the face and the neck axes, the pharyngeal axis, the laryngeal axis, and the line of vision of glottis. The various angles between these axes were defined: delta angle between line of vision and laryngeal axis, and beta angle between pharyngeal axis and laryngeal axis. From an anatomical point of view, laryngoscopy and passage of a naso-tracheal tube would be facilitated if these angles are narrow.

RESULTS

Placing the patient from the resting position into extension led to a narrowing of the angle delta but a widening of the angle beta.

CONCLUSIONS

In infants and young children, under general anesthesia and with a laryngeal mask airway in place, just a slight head extension improves alignment of the line of vision of the glottis and the laryngeal axis (narrowing of angle delta) but worsened the alignment of the pharyngeal and laryngeal axes (widening of angle beta).

Obstructive sleep apnea in children: implications for the developing central nervous system

Recent increases in our awareness to the high prevalence of sleep disorders in general and of sleep-disordered breathing among children, in particular, has led to concentrated efforts aiming to understand the pathophysiological mechanisms, clinical manifestations, and potential consequences of such conditions. In this review, I will briefly elaborate on some of the pathogenetic elements leading to the occurrence of obstructive sleep apnea (OSA) in children, focus on the psychobehavioral consequences of pediatric OSA, and review the evidence on the potential mechanisms underlying the close association between central nervous system morbidity and the episodic hypoxia and sleep fragmentation that characterize OSA.

Puberty and upper airway dynamics during sleep

STUDY OBJECTIVES

The upper airway compensatory response to subatmospheric pressure loading declines with age. The epidemiology of obstructive sleep apnea suggests that sex hormones play a role in modulating upper airway function. Sex hormones increase gradually during puberty, from minimally detectable to adult levels. We hypothesized that the upper airway response to subatmospheric pressure loading decreased with increasing pubertal Tanner stage in males but remained stable during puberty in females.

DESIGN

Upper airway dynamic function during sleep was measured over the course of puberty.

PARTICIPANTS

Normal subjects of Tanner stages 1 to 5.

MEASUREMENTS

During sleep, maximal inspiratory airflow was measured while varying the level of nasal pressure. The slope of the upstream pressure-flow relationship (SPF) was measured.

RESULTS

The SPF correlated with age and Tanner stage. However, the relationship with Tanner stage became nonsignificant when the correlation due to the mutual association with age was removed. Females had a lower SPF than males.

CONCLUSIONS

In both sexes, the upper airway compensatory response to subatmospheric pressure loading decreased with age rather than degree of pubertal development. Thus, changes in sex hormones are unlikely to be a primary modulator of upper airway function during the transition from childhood to adulthood. Although further studies of upper airway structural changes during puberty are needed, we speculate that the changes in upper airway function with age are due to the depressant effect of age on ventilatory drive, leading to a decrease in upper airway neuromotor tone.

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.

Pediatric obstructive sleep apnea: complications, management, and long-term outcomes

Obstructive sleep apnea (OSA) in children has emerged not only as a relatively prevalent condition but also as a disease that imposes a large array of morbidities, some of which may have long-term implications, well into adulthood. The major consequences of pediatric OSA involve neurobehavioral, cardiovascular, and endocrine and metabolic systems. The underlying pathophysiological mechanisms of OSA-induced end-organ injury are now being unraveled, and clearly involve oxidative and inflammatory pathways. However, the roles of individual susceptibility (as dictated by single-nucleotide polymorphisms), and of environmental and lifestyle conditions (such as diet, physical, and intellectual activity), may account for a substantial component of the variance in phenotype. Moreover, the clinical prototypic pediatric patient of the early 1990s has been insidiously replaced by a different phenotypic presentation that strikingly resembles that of adults afflicted by the disease. As such, analogous to diabetes, the terms type I and type II pediatric OSA have been proposed. The different manifestations of these two entities and their clinical course and approaches to management are reviewed.

Cephalometric analysis of nonobese snorers either with or without obstructive sleep apnea syndrome

OBJECTIVE

To determine if there is an indicator on the lateral cephalometric radiograph that can be used for the differential diagnosis of severe obstruct sleep apnea syndrome and simple snoring in nonobese young male adults.

MATERIALS AND METHODS

The subjects were Taiwanese male patients with a complaint of snoring and/or sleep apnea, whose body mass index was less than 25 kg/m(2) and who were younger than 40 years old. Forty-six patients with severe obstructive sleep apnea and 36 patients with simple snoring were selected and underwent lateral cephalometric radiography, from which 24 linear and 34 angular measurements were calculated. Differences between the two groups were studied, and a discriminatory analysis was performed.

RESULTS

Soft palate length, mandibular body length, tongue size, and distance from the hyoid bone to the mandibular plane were significantly larger in patients with severe obstructive sleep apnea syndrome. Of the original grouped cases, 76.5% were correctly classified using these five variables. The position of the hyoid bone in simple snorers was near the straight line from the third vertebra to the menton, whereas the position of the hyoid bone in severe obstruct sleep apnea syndrome patients was far below the line from the third vertebra to the menton.

CONCLUSION

The position of the hyoid bone relative to the line from the third vertebra to the menton can be used as an indicator for a diagnosis of severe obstruct sleep apnea syndrome in nonobese young male Taiwanese adults.

Vowel acoustic space development in children: a synthesis of acoustic and anatomic data

PURPOSE

This article integrates published acoustic data on the development of vowel production. Age specific data on formant frequencies are considered in the light of information on the development of the vocal tract (VT) to create an anatomic-acoustic description of the maturation of the vowel acoustic space for English.

METHOD

Literature searches identified 14 studies reporting data on vowel formant frequencies. Data on corner vowels are summarized graphically to show age- and sex- related changes in the area and shape of the traditional vowel quadrilateral.

CONCLUSIONS

Vowel development is expressed as follows: (a) establishment of a language-appropriate acoustic representation (e.g., F1-F2 quadrilateral or F1-F2-F3 space), (b) gradual reduction in formant frequencies and F1-F2 area with age, (c) reduction in formant-frequency variability, (d) emergence of male-female differences in formant frequency by age 4 years with more apparent differences by 8 years, (e) jumps in formant frequency at ages corresponding to growth spurts of the VT, and (f) a decline of f0 after age 1 year, with the decline being more rapid during early childhood and adolescence. Questions remain about optimal procedures for VT normalization and the exact relationship between VT growth and formant frequencies. Comments are included on nasalization and vocal fundamental frequency as they relate to the development of vowel production.

Adiposity in relation to age as predictor of severity of sleep apnea in children with snoring

Correlation between obesity and obstructive sleep apnea has been documented in both adults and children. This investigation evaluated importance of body mass index (BMI) in relation to age as predictor of severity of obstructive sleep-disordered breathing (SDB). Children with habitual snoring referred for polysomnography were recruited. BMI Z score (> or =1.036 vs <1.036, i.e. at risk for overweight or overweight vs normal) was assessed as predictor of severity of SDB (apnea-hypopnea index [AHI] >five vs < or =five episodes per hour) at different ages (< or =6 vs >6 years). Two hundered eighty-four participants were recruited: 75 young children (4.6 +/- 1 years) with high BMI (1.9 +/- 0.7); 95 young subjects (4.5 +/- 1.1 years) with low BMI (-0.2 +/- 1.3); 55 older children (9.2 +/- 1.8 years) with high BMI (1.8 +/- 0.5); and 59 older participants (9.7 +/- 2.2 years) with low BMI (-0.2 +/- 1.1). Odds ratios for AHI >5 in young/high BMI children, young/low BMI subjects, and older/high BMI subjects relative to older/low BMI participants were: 6.5 (95% confidence interval 2.1-19.9), 7.3 (2.4-22) and 2 (0.6-7.3), respectively. Large tonsil size was associated with young age (odds ratio 1.97; 1.2-3.3). Among children with habitual snoring, adiposity does not predict severity of obstructive SDB in early childhood probably due to the prominent role of adenotonsillar hypertrophy. However, it may have a more important contribution to severity of SDB in older children.

Obesity and obstructive sleep apnea in children

The prevalence and severity of obesity in children and adolescent is dramatically increasing worldwide with a corresponding increase in the prevalence of obesity-associated morbidities particularly those involving OSAS and metabolic and cardiovascular sequelae. Obstructive sleep apnea and obesity hypoventilation syndrome are important and serious consequences of obesity, and may in fact mediate components of the association between obesity and metabolic and cardiovascular morbidities, most likely via potentiation of inflammatory cascades. It is anticipated that the increased prevalence of obesity in children and adolescents in our society will be accompanied by a steady increase in the incidence of OSAS. In this review, we will examine our current understanding of sleep-disordered breathing and associated morbidities in obese children, and summarize the range of therapeutic modalities currently available for this high-risk population.

Oxidant stress and inflammation in the snoring child: confluent pathways to upper airway pathogenesis and end-organ morbidity

Snoring in children is increasingly being recognized as a highly prevalent condition, and indicates the presence of heightened upper airway resistance during sleep. In this paper, we present evidence to support the hypothesis that local inflammatory processes within the upper airway contribute to the pathophysiology of adenotonsillar hypertrophy and altered reflexes potentially leading to increased propensity for upper airway obstruction during sleep. Furthermore, the cumulative evidence supporting multiorgan morbidity for sleep-disordered breathing (SDB) is reviewed, and a unified hypothesis of a triple risk model proposing oxidative-inflammatory mechanisms as mediating the morbid consequences of SDB is presented. This hypothetical working model incorporates both dose-dependent disease severity components, as well as environmental and genetic elements of susceptibility.

Computational fluid dynamics modeling of the upper airway of children with obstructive sleep apnea syndrome in steady flow

Computational fluid dynamic (CFD) analysis was used to model the effect of airway geometry on internal pressure in the upper airway of three children with obstructive sleep apnea syndrome (OSAS), and three controls. Model geometry was reconstructed from magnetic resonance images obtained during quiet tidal breathing, meshed with an unstructured grid, and solved at normative peak resting flow. The unsteady Reynolds-averaged Navier-Stokes equations were solved with steady flow boundary conditions in inspiration and expiration, using a two-equation low-Reynolds number turbulence model. Model results were validated using an in-vitro scale model, unsteady flow simulation, and reported nasal resistance measurements in children. Pharynx pressure drop strongly correlated to airway area restriction. Inspiratory pressure drop was primarily proportional to the square of flow, consistent with pressure losses due to convective acceleration caused by area restriction. On inspiration, in OSAS pressure drop occurred primarily between the choanae and the region where the adenoids overlap the tonsils (overlap region) due to airway narrowing, rather than in the nasal passages; in controls the majority of pressure drop was in the nasal passages. On expiration, in OSAS the majority of pressure drop occurred between the oropharynx (posterior to the tongue) and overlap region, and local minimum pressure in the overlap region was near atmospheric due to pressure recovery in the anterior nasopharynx. The results suggest that pharyngeal airway shape in children with OSAS significantly affects internal pressure distribution compared to nasal resistance. The model may also help explain regional dynamic airway narrowing during expiration.

Platelet endothelial cell adhesion molecule-1 is expressed in adenoidal crypt epithelial cells

The adenoidal epithelial crypt is a potential site of antigen transport from pharyngeal lumen to adenoidal tissue. The base of the crypt is consistently infiltrated with leucocytes, forming a reticular lymphoepithelial structure. To evaluate mechanisms that possibly mediate leucocyte infiltration, expressions of leucocyte adhesion molecules, such as platelet endothelial cell adhesion molecule-1 (PECAM-1) (CD31), vascular cell adhesion molecule-1 (VCAM-1) (CD106) and intercellular adhesion molecule-1 (ICAM-1) (CD54), were studied in the adenoidal epithelial crypt. Epithelial cells in the outer opening of the adenoidal crypt were positive for VCAM-1, whereas epithelial cells at the base of the crypt were positive for PECAM-1. Isolated ICAM-1-expressing cells were found throughout the epithelial crypt. Double immunofluorescence staining revealed that the epithelial cells positive for PECAM-1 or VCAM-1 were positive for cytokeratin. The expression of PECAM-1 in the base and VCAM-1 at the orifice of the adenoidal epithelial crypt implies that the base and the orifice of the crypt have a distinct ability to recruit leucocytes. Epithelial cells expressing PECAM-1 may have a role in the formation of the reticular lymphoepithelial structure in the epithelial crypt.

Development, structure and function of the upper airways

The upper airways play an essential role in the conduction of air into the lungs, and influence the properties of the inhaled air by both the anatomical structure and the functional properties of the mucosa, cartilages and neural and lymphatic tissues. The upper airways also play an important role in the protection of the lower airways, in the formation of the sound and host the sense of olfaction. Main events in the development of the upper airways happen during early embryonic periods. Postnatally, the growth of the airways follows the growth of the skeleton of the head and of the neck and thorax. Growth is accelerated mainly during the first 2 years of life; thereafter, it linearly follows the growth of the body. For a profound understanding of the function of the upper airways, it is important to understand the main developmental events during both prenatal and postnatal periods.

Obstructive sleep apnea in children: do intranasal corticosteroids help?

Obstructive sleep apnea (OSA) is a common condition of childhood, and is associated with significant morbidity. Prevalence of the condition peaks during early childhood, due in part to adenoidal and tonsillar enlargement within a small pharyngeal space. The lymphoid tissues regress after 10 years of age, in the context of ongoing bony growth, and there is an associated fall in the prevalence of OSA. Obstruction of the nasopharynx by adenoidal enlargement promotes pharyngeal airway collapse during sleep, and the presence of large tonsils contributes to airway obstruction. Administration of systemic corticosteroids leads to a reduction in the size of lymphoid tissues due to anti-inflammatory and lympholytic effects. However, a short course of systemic prednisone has been demonstrated not to have a significant effect on adenoidal size or the severity of OSA, and adverse effects preclude the long-term use of this therapy. Intranasal corticosteroids are effective in relieving nasal obstruction in allergic rhinitis, and allergic sensitization is more prevalent among children who snore than among those who do not snore. Intranasal corticosteroids have also been demonstrated to reduce adenoidal size, independent of the individual's atopic status. There is preliminary evidence of an improvement in the severity of OSA in children treated with intranasal corticosteroids, but further studies are needed before such therapy can be routinely recommended. Prescribing clinicians should take into account the potential benefits to the patient, the age of the child, the presence of comorbidities such as allergic rhinitis, the agent used, and the dose and duration of treatment when considering such therapy.

Diagnostic studies in the assessment of pediatric sleep-disordered breathing: techniques and indications

In summary, SDB is a common condition in children that can have serious complications if left undiagnosed and untreated. OSA is the most commonly recognized form of SDB in children. The history and physical have limitations in their capacity to determine which children have SDB. Abbreviated or screening techniques, such as audio- or videotaping, oximetry studies, nap studies, or home studies, tend to be helpful if the results are positive but have a poor predictive value if the results are negative. Overnight polysomnography is the gold standard for the diagnosis of SDB in children. It is important that children are studied in laboratories that have expertise with children. Often, children with SDB have associated nonrespiratory or behavioral sleep disorders that also must be evaluated and addressed.

Sleep-disordered breathing, pharyngeal size and soft tissue anatomy in children

We tested the hypothesis that pharyngeal geometry and soft tissue dimensions correlate with the severity of sleep-disordered breathing. Magnetic resonance images of the pharynx were obtained in 18 awake children, 7-12 yr of age, with obstructive apnea-hypopnea index (OAHI) values ranging from 1.81 to 24.2 events/h. Subjects were divided into low-OAHI (n = 9) and high-OAHI (n = 9) groups [2.8 +/- 0.7 and 13.5 +/- 4.9 (SD) P < 0.001]. The OAHI correlated positively with the size of the tonsils (r2 = 0.42, P = 0.024) and soft palate (r2 = 0.33, P = 0.049) and inversely with the volume of the oropharyx (r2 = 0.42, P = 0.038). The narrowest point in the pharyngeal airway was smaller in the high-compared with the low-OAHI group (4.4 +/- 1.2 vs. 6.0 +/- 1.3 mm; P = 0.024), and this point was in the retropalatal airway in all but two subjects. The airway cross-sectional area (CSA)-airway length relation showed that the high-OAHI group had a narrower retropapatal airway than the low-OAHI group, particularly in the retropalatal region where the soft palate, adenoids, and tonsils overlap (P = 0.001). The "retropalatal air space," which we defined as the ratio of the retropalatal airway CSA to the CSA of the soft palate, correlated inversely with the OAHI (r2 = 0.49, P = 0.001). We conclude that 7- to 12-yr-old children with a narrow retropalatal air space have significantly more apneas and hypopneas during sleep compared with children with relatively unobstructed retropalatal airways.

Snoring in preschoolers: associations with sleepiness, ethnicity, and learning

Sleep-disordered breathing (SDB) in children is associated with poor school performance, with minority children being at increased risk for both conditions. The latter have been attributable to low socio-economic status (SES). To further study these relationships, the contribution of SES to SDB and learning was examined in 1,010 validated questionnaires collected from parents of both white and African-American low-SES preschoolers. Twenty-two percent of disadvantaged preschoolers were reported to be at risk for SDB. These children were more likely to be African American, and had a higher incidence of daytime sleepiness, lower academic performance, and hyperactivity. Maternal education level did not account for these differences.

Identification of upper airway anatomic risk factors for obstructive sleep apnea with volumetric magnetic resonance imaging

We used sophisticated volumetric analysis techniques with magnetic resonance imaging in a case-control design to study the upper airway soft tissue structures in 48 control subjects (apnea-hypopnea index, 2.0 +/- 1.6 events/hour) and 48 patients with sleep apnea (apnea-hypopnea index, 43.8 +/- 25.4 events/hour). Our design used exact matching on sex and ethnicity, frequency matching on age, and statistical control for craniofacial size and visceral neck fat. The data support our a priori hypotheses that the volume of the soft tissue structures surrounding the upper airway is enlarged in patients with sleep apnea and that this enlargement is a significant risk factor for sleep apnea. After covariate adjustments the volume of the lateral pharyngeal walls (p < 0.0001), tongue (p < 0.0001), and total soft tissue (p < 0.0001) was significantly larger in subjects with sleep apnea than in normal subjects. These data also demonstrated, after covariate adjustments, significantly increased risk of sleep apnea the larger the volume of the tongue, lateral pharyngeal walls, and total soft tissue: (1) total lateral pharyngeal wall (odds ratio [OR], 6.01; 95% confidence interval [CI], 2.62-17.14); (2) total tongue (OR, 4.66; 95% CI, 2.31-10.95); and (3) total soft tissue (OR, 6.95; 95% CI, 3.08-19.11). In a multivariable logistic regression analysis the volume of the tongue and lateral walls was shown to independently increase the risk of sleep apnea.

System for upper airway segmentation and measurement with MR imaging and fuzzy connectedness

RATIONALE AND OBJECTIVES

The purpose of this study was to evaluate whether a computerized system developed to help delineate the upper airway and surrounding structures with magnetic resonance (MR) imaging was effective for aiding in the diagnosis of upper airway disorders in children.

MATERIALS AND METHODS

The authors performed axial T2-weighted MR imaging to gather information about different aspects of the airway and its surrounding soft-tissue structures, including the adenoid and palatine tonsils, tongue, and soft palate. Images were processed and segmented to compute the architectural parameters of the airway (eg, surface description, volume, central [medial] line, and cross-sectional areas at planes perpendicular to the central line). The authors built a software package for the visualization, segmentation, registration, prefiltering, interpolation, standardization, and quantitative analysis of the airway and tonsils.

RESULTS

The system was tested with 40 patient studies. For every study, the system segmented and displayed a smooth three-dimensional rendition of the airway and its central line and a plot of the cross-sectional area of the airway orthogonal to the central line as a function of the distance from one end of the central line. The precision and accuracy for segmentation was 97%. The mean time taken per study was about 4 minutes and included the operator interaction time and processing time.

CONCLUSION

This method provides a robust and fast means of assessing the airway size, shape, and level of restriction, as well as a structural data set suitable for use in modeling studies of airflow and mechanics.

Upper airway size analysis by magnetic resonance imaging of children with obstructive sleep apnea syndrome

Detailed analysis of the upper airway has not been performed in children with obstructive sleep apnea. We used magnetic resonance imaging and automatic segmentation to delineate the upper airway in 20 children with obstructive sleep apnea and in 20 control subjects (age, 3.7 +/- 1.4 versus 3.9 +/- 1.7 years, respectively). We measured mean and minimal cross-sectional area, length, and volume of: (1) the total airway; (2) regions along the adenoid, tonsils, and where adenoid and tonsils overlap; and (3) 10 segments at 10% increments along the airway. The mean cross-sectional area of the total airway of the obstructive sleep apnea group was significantly smaller in comparison with the control group, 28.1 +/- 12.6 versus 47.1 +/- 18.2 mm2, respectively (p < 0.0005). Minimal cross-sectional area and airway volume were smaller in this group, 4.6 +/- 3.3 versus 15.7 +/- 12.7 mm2 (p < 0.0005), and 1,129 +/- 515 versus 1,794 +/- 846 mm3 (p < 0.005), respectively. Regional analysis suggested that the upper airway in children with obstructive sleep apnea is most restricted where adenoid and tonsils overlap. Segmental analysis demonstrated that the upper airway is restricted throughout the initial two-thirds of its length and that the narrowing is not in a discrete region adjacent to either the adenoid or tonsils, but rather in a continuous fashion along both.