Genetic determinants of upper airway structures that predispose to obstructive sleep apnea

Genetic Overlap Between Obstructive Sleep Apnea and Ischemic Stroke: A Large-Scale Genome-Wide Cross-Trait Analysis

Background

To further understand the complex relationship between Obstructive Sleep Apnea (OSA) and ischemic stroke, this study explores the role of genetic factors in the comorbidity of these two conditions.

Methods

Based on large-scale available Genome-Wide Association Studies (GWAS) for OSA and ischemic stroke, we conducted a multi-level cross-trait analysis. First, we utilized Linkage Disequilibrium Score Regression (LDSC) to analyze the genetic correlation between the two diseases. Subsequently, we performed cross-trait analysis to identify pleiotropic Single Nucleotide Polymorphisms (SNPs) associated with both OSA and ischemic stroke. On this basis, we applied annotation and Multi-marker Analysis of GenoMic Annotation (MAGMA) analysis to examine results at the gene level. Finally, we conducted Transcriptome-Wide Association Studies (TWAS) to analyze gene expressions significantly related to both traits.

Results

The LDSC analysis revealed a significant positive genetic correlation between OSA and ischemic stroke. Cross-trait analysis identified a total of 90 pleiotropic SNPs, with rs78581380 being the most significant. Combining Functional Mapping and Annotation (FUMA) annotation and MAGMA analysis, we identified 83 genes in total. TWAS analysis discovered 23 gene expressions that were significantly associated with both OSA and ischemic stroke traits.

Conclusion

This study elucidates the shared genetic architecture between OSA and ischemic stroke, emphasizing the crucial role of genetic factors in the comorbidity of these two conditions.

A Comprehensive Review of Pediatric Obstructive Sleep Apnea: From Assessment to Intervention

Pediatric obstructive sleep apnea (OSA) is a prevalent sleep disorder characterized by upper airway obstruction during sleep, leading to oxygen desaturation and sleep disruptions. This comprehensive review examines the epidemiology, pathophysiology, clinical manifestations, diagnostic approaches, consequences, management strategies, challenges, and future directions of pediatric OSA. Prevalence rates vary globally, with notable associations found between OSA and obesity. The review explores the anatomical and neuromuscular factors contributing to airway obstruction, emphasizing the importance of timely identification and intervention to mitigate long-term health implications. Diagnostic tools such as polysomnography (PSG) are essential, although challenges in accessibility exist. Pediatric OSA is linked to various health issues, including cardiovascular complications, metabolic disturbances, and neurocognitive impairments. Treatment options range from surgical interventions like adenotonsillectomy to non-pharmacological therapies and pharmacotherapy. Challenges in diagnosis and treatment warrant research into innovative diagnostic approaches and refining clinical prediction rules. Addressing these areas will enhance clinical management and outcomes for children with OSA.

Effect of Orthodontic Treatment on Airway Dimensions in Patients with Obstructive Sleep Apnea: A Prospective Study

Background

Obstructive sleep apnea (OSA) is a common medical disorder characterized by recurrent instances of partial or total blockage of the upper airways while sleeping.

Materials and Methods

The trial included a cohort of 50 individuals, aged between 18 and 45, who were diagnosed with mild to moderate obstructive sleep apnea (OSA). The participants were split into two groups: Group A (n = 25) had orthodontic therapy that included expanding the upper jaw and advancing the mandible, whereas Group B (n = 25) acted as the control group and did not get any orthopedic intervention. Prior to and after therapy, the airway dimensions were evaluated using cone beam computed tomography (CBCT) at two time points: baseline and 12 months after treatment. In this study, the main outcome measures were the change in airway volume (measured in mm3) and the minimum cross-sectional area (measured in mm2). The secondary outcome measures consisted of alterations in the apnea-hypopnea index (AHI) and subjective sleep quality evaluated by the Epworth Sleepiness Scale (ESS).

Results

In comparison with baseline data, patients in Group A exhibited a statistically significant rise in airway volume (mean increase of 3500 mm3, P < 0.01) and minimum cross-sectional area (mean increase of 45 mm2, P < 0.01). In contrast, Group B exhibited no statistically significant alterations in these measures. A substantial decrease in AHI (mean reduction of 8 events/hour, P < 0.05) and an increase in ESS scores (mean improvement of 4 points, P < 0.05) were seen in Group A, suggesting improved sleep quality.

Conclusion

Orthodontic treatment, including maxillary expansion and mandibular advancement, positively affects airway dimensions in patients with OSA.

Facial Contour Features Measured on CT Reflects Upper Airway Morphology in Patients With OSA

OBJECTIVE

To determine facial contour features, measured on computed tomography (CT), related to upper airway morphology in patients with obstructive sleep apnea (OSA); certain phenotype of facial abnormalities implying restriction of craniofacial skeleton and adipose tissue nimiety has predicted the value of the severity of OSA.

MATERIALS AND METHOD

Sixty-four male patients with OSA [apnea-hypopnea index (AHI) ≥10/h] who had upper airway CT were randomly selected to quantitatively measure indicators of facial contour and upper airway structures. Pearson correlation analyses were performed. Partial correlation procedure was used to examine correlations while controlling body mass index (BMI).

RESULTS

Upper airway anatomy can nearly all be reflected in the face, except retroglossal airway. Upper face width can be measured to assess the overall skeletal structures of the airway. Lower face width can be used to represent how much adipose tissue deposited. Hard palate, retropalatal, and hypopharyngeal airways have corresponding face indicators respectively. Midface width is a better predictor of AHI severity and minimum blood oxygen even than neck circumference because it contains the most anatomical information about the airway, including RP airway condition, soft palate length, tongue volume, etc. These correlations persisted even after correction for BMI.

CONCLUSIONS

All anatomical features of the upper airway except retroglossal airway can be reflected in the face, and midface width is the best predictor of AHI severity and minimum blood oxygen, even better than neck circumference and BMI.

Targeted Hypoglossal Nerve Stimulation for Patients With Obstructive Sleep Apnea: A Randomized Clinical Trial

Importance

Evidence is lacking from randomized clinical trials of hypoglossal nerve stimulation in obstructive sleep apnea (OSA).

Objective

To evaluate the safety and effectiveness of targeted hypoglossal nerve stimulation (THN) of the proximal hypoglossal nerve in patients with OSA.

Design, Setting, and Participants

This randomized clinical trial (THN3) was conducted at 20 centers and included 138 patients with moderate to severe OSA with an apnea-hypopnea index (AHI) of 20 to 65 events per hour and body mass index (calculated as weight in kilograms divided by height in meters squared) of 35 or less. The trial was conducted from May 2015 through June 2018. Data were analyzed from January 2022 through January 2023.

Intervention

Implant with THN system; randomized 2:1 to activation at month 1 (treatment) or month 4 (control). All received 11 months of THN with follow-up at months 12 and 15, respectively.

Main Outcomes and Measures

Primary effectiveness end points comprised AHI and oxygen desaturation index (ODI) responder rates (RRs). Treatment responses at months 4 and 12/15 were defined as a 50% or greater reduction in AHI to 20 or less per hour and an ODI decrease of 25% or greater. Coprimary end points comprised (1) month 4 AHI and ODI RR in the treatment greater than the control group and (2) month 12/15 AHI and ODI RR in the entire cohort exceeding 50%. Secondary end points included sleep apnea severity (AHI and ODI) and patient-reported outcomes (Epworth Sleepiness Scale, Functional Outcomes of Sleep Questionnaire, and EQ-5D visual analog scale).

Results

Among 138 participants, the mean (SD) age was 56 (9) years, and 19 (13.8%) were women. Month 4 THN RRs were substantially greater in those in the treatment vs control group (AHI, 52.3% vs 19.6%; ODI, 62.5% vs 41.3%, respectively) with treatment-control standardized mean differences of 0.725 (95% CI, 0.360-1.163) and 0.434 (95% CI, 0.070-0.843) for AHI and ODI RRs, respectively. Months 12/15 RRs were 42.5% and 60.4% for AHI and ODI, respectively. Improvements in AHI, ODI, Epworth Sleepiness Scale, Functional Outcomes of Sleep Questionnaire, and EQ-5D visual analog scale scores were all clinically meaningful (medium to large effect size). Two serious adverse events and 100 nonserious related adverse events were observed from the implant procedure or study protocol.

Conclusions and Relevance

This randomized clinical trial found that THN demonstrated improvements in sleep apnea, sleepiness, and quality of life in patients with OSAs over an extended AHI and body mass index range without prior knowledge of pharyngeal collapse pattern. Clinically meaningful improvements in AHI and patient-reported responses compared favorably with those of distal hypoglossal nerve stimulation trials, although clinically meaningful differences were not definitive for ODI.

Trial Registration

ClinicalTrials.gov Identifier: NCT02263859.

Heritability of cephalometric variables of airway morphology in twins with completed active growth

BACKGROUND

The interplay between genetic and environmental impacts on dental and facial morphology has been widely analyzed, but little is known about their relative contributions to airway morphology. The aim of this study was to evaluate the genetic and environmental influences on the cephalometric variables of airway morphology in a group of postpubertal twins with completed craniofacial growth.

MATERIALS AND METHODS

The materials comprised lateral head cephalograms of 94 pairs of twins (50 monozygotic, 44 dizygotic) with completed craniofacial growth. Zygosity was determined using 15 specific DNA markers. The computerized cephalometric analysis included 22 craniofacial, hyoideal, pharyngeal structural linear and angular variables. Genetic analysis and heritability estimation were performed using maximum likelihood genetic structural equation modeling (GSEM). Principal component analysis (PCA) was used to assess the correlations between cephalometric measurement variables.

RESULTS

Upper airway dimensions showed moderate to high genetic determination (SPPW-SPP and U-MPW: a2 = 0.64 and 0.5, respectively). Lower airway parameters showed only common and specific environmental determination (PPW-TPP a2 = 0.24, e2 = 0.38; LPW-V c2 = 0.2, e2 = 0.63; PCV-AH c2 = 0.47, e2 = 0.28). The relationship between the maxilla and the hyoid bone (for variables PNS-AH, ANS-AH d2 = 0.9, 0.92, respectively) showed very strong additive genetic determination. The size of the soft palate was affected by additive and dominant genes. Its length (SPL) was strongly influenced by dominant genes, while its width (SPW) showed a moderate additive genetic influence. Owing to correlations in the behavior of variables, the data could be expressed in 5 principal components that jointly explained 36.8% of the total variance.

CONCLUSIONS

The dimensions of the upper airway are strongly determined by genes, while the parameters of the lower airway depend mainly on environmental factors.

TRIAL REGISTRATION

The protocol has been approved by the Kaunas Regional Ethical Committee (No. BE - 2-41., May 13, 2020).

Association between body mass index and effectiveness of continuous positive airway pressure in patients with obstructive sleep apnea: a retrospective study

PURPOSE

Ineffective use of continuous positive airway pressure (CPAP) therapy can result in inconvenience and additional costs in patients with obstructive sleep apnea (OSA). This study investigated the predictive value of body mass index (BMI) to assess the efficacy of CPAP in patients with OSA.

METHODS

Data were extracted from a retrospective study performed in Silkeborg Hospital. The primary outcome was the improvement of Apnea-Hypopnea Index (AHI) after CPAP treatment. Association between BMI and improvement of AHI was assessed by multivariable linear regression. Interactions between BMI, baseline AHI severity (≥ 30 or < 30), and diabetes were also evaluated.

RESULTS

Four hundred eighty-one patients were included in the study. After adjusting for confounders, high BMI (coefficient [coef], 0.80; 95% confidence interval [CI], 0.59-1.00; p < 0.001) and high AHI severity (AHI ≥ 30) (coef, 29.2; 95% CI, 26.7-31.7; p < 0.001) were associated with greater improvement of AHI after CPAP treatment, while diabetes was associated with less improvement of AHI (coef, - 4.91; 95% CI, - 9.40 to - 0.42; p = 0.032). Baseline AHI severity, diabetes, and BMI showed significant interactions (p < 0.001). On subgroup analysis, the association between BMI and improvement of AHI remained significant only in patients belonging to high AHI severity subgroup (coef, 1.18; 95% CI, 0.8-1.49; p < 0.001) and that without diabetes (coef, 1.42; 95% CI, 1.11-1.72; p < 0.001).

CONCLUSIONS

Patients with OSA having high BMI, without diabetes, are more likely to benefit from CPAP therapy. Future studies should explore the predictors of the efficacy of CPAP in more depth.

Heritability of the pharyngeal airway volume and dimensions as assessed from siblings with overt malocclusions

OBJECTIVE

To quantify the relative contributions of genetic and environmental factors to airway volume and dimensions in orthodontic patients.

MATERIALS AND METHODS

One hundred and twenty-five siblings from 57 families were selected. Cone beam computed tomography scans were taken as part of the orthodontic records and the Dolphin3D © imaging software was used to determine airway volume and dimensions. SOLAR program was implemented to calculate heritability.

RESULTS

The heritability of the airway volume was negligible but increased significantly from 5% to 72% (95% confidence interval was 27% to 100%) when anterior-posterior (AP) dimension was controlled in the calculating model.

CONCLUSION

The capacity to maintain, rather than having proper AP dimension of the airway, seems to be the most critical mark of a proper airway volume.

Correlation between body mass index and obstructive sleep apnea severity indexes - A retrospective study

PURPOSE

To evaluate if Body Mass Index (BMI) is correlated to Apnea-Hypopnea Index (AHI), mean arterial oxygen saturation (SaO₂) and Nadir SaO₂, which are all indexes defining the severity of the respiratory stress associated with Obstructive Sleep Apnea (OSA).

MATERIALS AND METHODS

Seventy-five adult patients (mean age 51.4) referred for polysomnography were retrospectively recruited. BMI was calculated for each patient, as well as AHI, SaO₂, and Nadir SaO₂ recorded during polysomnography. Spearman's Rho test was used to evaluate if OSA severity was correlated to BMI values. First type error was set as p < 0.025.

RESULTS

No correlation was observed between BMI and AHI, and between BMI and SaO₂. A statistically significant negative correlation (r² = 0.424; p < 0.001) was found between the BMI index and the Nadir SaO₂.

CONCLUSIONS

Higher BMI values were correlated with lower Nadir SaO₂ during overnight polysomnography. Since hypoxia stress is a risk factor for cardiovascular diseases and alters the lipid metabolism, dietary consulting should be recommended in association with other treatment modalities for OSA.

Impact of Bariatric Surgery on Heme Oxygenase-1, Inflammation, and Insulin Resistance in Morbid Obesity with Obstructive Sleep Apnea

INTRODUCTION

Morbid obesity and obstructive sleep apnea (OSA) interact at an inflammatory level. Bariatric surgery reduces inflammatory responses associated with obesity. Heme oxygenase-1 (HO-1) is an enzyme with anti-inflammatory properties, which might be increased in morbid obesity or OSA. We studied morbidly obese patients with OSA to determine: (a) HO-1 plasma concentrations according to OSA severity and their relationship with insulin resistance and inflammation and (b) the impact of bariatric surgery on HO-1 and parameters of insulin resistance and inflammation.

MATERIAL AND METHODS

We analyzed the homeostasis model insulin resistance index (HOMA) and plasma concentrations of HO-1, tumor necrosis factor alpha, interleukin-6, interleukin-1-beta, C reactive protein (CRP), and adiponectin according to polysomnography findings in 66 morbidly obese patients before bariatric surgery and 12 months after surgery.

RESULTS

Before surgery, HO-1 plasma concentrations were similar in three groups of patients with mild, moderate, and severe OSA, and correlated with HOMA (r = 0.27, p = 0.02). Twelve months after surgery, low-grade inflammation and insulin resistance had decreased in all the groups, but HO-1 plasma concentration had decreased only in the severe OSA group (p = 0.02). In this group, the reduction in HO-1 correlated with a reduction in CRP concentrations (r = 0.43, p = 0.04) and with improved HOMA score (r = 0.37, p = 0.03).

CONCLUSIONS

Bariatric surgery decreases HO-1 concentrations in morbid obesity with severe OSA, and this decrease is associated with decreases in insulin resistance and in inflammation.

P4 medicine approach to obstructive sleep apnoea

P4 medicine is an evolving approach to personalized medicine. The four Ps offer a means to: Predict who will develop disease and co-morbidities; Prevent rather than react to disease; Personalize diagnosis and treatment; have patients Participate in their own care. P4 medicine is very applicable to obstructive sleep apnoea (OSA) because each OSA patient has a different pathway to disease and its consequences. OSA has both structural and physiological mechanisms with different clinical subgroups, different molecular profiles and different consequences. This may explain why there are different responses to alternative therapies, such as intraoral devices and hypoglossal nerve stimulation therapy. Currently, technology facilitates patients to participate in their own care from screening for OSA (snoring and apnoea apps) to monitoring response to therapy (sleep monitoring, blood pressure, oxygen saturation and heart rate) as well as monitoring their own continuous positive airway pressure (CPAP) compliance. We present a conceptual framework that provides the basis for a new, P4 medicine approach to OSA and should be considered more in depth: predict and prevent those at high risk for OSA and consequences, personalize the diagnosis and treatment of OSA and build in patient participation to manage OSA.

Obesity and perceived severity of obstructive sleep apnea-related conditions

This study examined risk factors and perceived severity of obstructive sleep apnea-related conditions among college students based on weight categories. Data collected from 1399 college students were analyzed using multinomial and binary logistic regressions. Overweight and obese participants were more likely to snore and report familial risk for cardiovascular disease compared with their normal weight counterparts. Relative to normal weight participants, obese participants perceived snoring (odds ratio [OR] = 1.10), irritability (OR = 1.16), and high blood pressure (OR = 1.21) as more severe; they perceived erectile dysfunction (OR = 0.89) and cardiovascular disease (OR = 0.71) as less severe. Efforts are needed to identify obstructive sleep apnea risk and create systems for weight loss interventions, screening, and diagnosis.

Facial phenotyping by quantitative photography reflects craniofacial morphology measured on magnetic resonance imaging in Icelandic sleep apnea patients

STUDY OBJECTIVES

(1) To determine whether facial phenotype, measured by quantitative photography, relates to underlying craniofacial obstructive sleep apnea (OSA) risk factors, measured with magnetic resonance imaging (MRI); (2) To assess whether these associations are independent of body size and obesity.

DESIGN

Cross-sectional cohort.

SETTING

Landspitali, The National University Hospital, Iceland.

PARTICIPANTS

One hundred forty patients (87.1% male) from the Icelandic Sleep Apnea Cohort who had both calibrated frontal and profile craniofacial photographs and upper airway MRI. Mean ± standard deviation age 56.1 ± 10.4 y, body mass index 33.5 ± 5.05 kg/m(2), with on-average severe OSA (apnea-hypopnea index 45.4 ± 19.7 h(-1)).

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Relationships between surface facial dimensions (photos) and facial bony dimensions and upper airway soft-tissue volumes (MRI) was assessed using canonical correlation analysis. Photo and MRI craniofacial datasets related in four significant canonical correlations, primarily driven by measurements of (1) maxillary-mandibular relationship (r = 0.8, P < 0.0001), (2) lower face height (r = 0.76, P < 0.0001), (3) mandibular length (r = 0.67, P < 0.0001), and (4) tongue volume (r = 0.52, P = 0.01). Correlations 1, 2, and 3 were unchanged when controlled for weight and neck and waist circumference. However, tongue volume was no longer significant, suggesting facial dimensions relate to tongue volume as a result of obesity.

CONCLUSIONS

Significant associations were found between craniofacial variable sets from facial photography and MRI. This study confirms that facial photographic phenotype reflects underlying aspects of craniofacial skeletal abnormalities associated with OSA. Therefore, facial photographic phenotyping may be a useful tool to assess intermediate phenotypes for OSA, particularly in large-scale studies.

Pharyngeal wall fold influences on the collapsibility of the pharynx

Obstructive sleep apnoea (OSA) is a disease that is characterised by recurrent pharyngeal obstruction during sleep. The pharynx is a hollow muscular tube lined with epithelium that performs the competing functions of breathing, where it is required to be open and swallowing where it is required to close. The mechanical process by which these large changes in luminal dimensions occur have not been considered, however in other biological tubes such as the oesophagus and the bronchial airways narrowing and closure occurs via folding of the mucosal surface. The transmural pressure (P) required to collapse a tube is related to the number of folds (n) formed during collapse by the equation P=n(2)-1, so that the more folds formed during narrowing and closure, the greater the transmural pressure required to collapse the tube. In biomechanical models, the bronchial airway is modelled as a 2-layer tube with an inner epithelial lining and an outer layer of muscle. These models predict that fold numbers will be reduced with thickening and stiffening of the outer layer, accompanied by an increase in collapsibility. We hypothesise that, similar to other biological tubes the pharynx narrows and closes via folding of the surface of the tube, and that the pharynx can also be modelled as a 2-layer tube. We further hypothesise that when compared to healthy subjects, subjects with OSA will have less pharyngeal wall folds during narrowing and closure, and that this reduction in fold numbers will contribute to an increase in pharyngeal collapsibility. In the absence of muscle activity, subjects with OSA have increased pharyngeal collapsibility when compared with healthy subjects, supporting an anatomical contribution to pharyngeal collapse. Histopathological studies of the pharyngeal epithelium in subjects with OSA demonstrate that, compared with age matched subjects, there is thickening of the epithelial surface with oedema of the submucosal layer, with a loss of tethering of the epithelium to the submucosal layer. These changes would tend to decrease fold numbers. There are no measurements of pharyngeal folds, however previous imaging data supports that narrowing of the pharynx occurs via folding. This hypothesis defines a novel anatomical risk for OSA. It also suggests a new therapeutic paradigm for the treatment of OSA, aimed at increasing the folds formed during narrowing and closure.

Relationship between surface facial dimensions and upper airway structures in obstructive sleep apnea

STUDY OBJECTIVES

We hypothesized that the facial phenotype is closely linked to upper airway anatomy. The aim of this study was to investigate the relationship between surface facial dimensions and upper airway structures using magnetic resonance imaging (MRI) in subjects with obstructive sleep apnea (OSA).

DESIGN

Cohort study.

SETTING

Sleep investigation unit.

PATIENTS

Sixty-nine patients (apnea-hypopnea index > or = 10/h) underwent MRI as part of a study of upper airway anatomy in oral appliance therapy.

INTERVENTIONS

Measurements of a range of surface facial dimensions and upper airway soft tissue volumes were performed on the MR images using image-analysis software. Pearson correlation analyses were performed.

MEASUREMENTS AND RESULTS

Significant correlations were identified between a number of surface facial dimensions and neck circumference. Significant positive correlations were demonstrated between surface facial dimensions (including facial widths, facial heights, nose width, interocular and intercanthal widths) and upper airway structures. The strongest associations were between the tongue volume and the midface width (r = 0.70, P < 0.001), and lower-face width (r = 0.60, P <0.001). Surface facial dimensions in combination were also strong determinants for tongue volume (r2 = 0.69). Correlations between surface soft tissue thickness and upper airway soft tissue volumes occurred at the level of the midface but not at the level of the lower face.

CONCLUSIONS

This study demonstrates that there is a relationship between surface facial dimensions and upper airway structures in subjects with OSA. These findings support the potential role of surface facial measurements in anatomic phenotyping for OSA.

Mouth breathing children have cephalometric patterns similar to those of adult patients with obstructive sleep apnea syndrome

OBJECTIVE

To determine whether mouth breathing children present the same cephalometric patterns as patients with obstructive sleep apnea syndrome (OSAS).

METHOD

Cephalometric variables were traced and measured on vertical lateral cephalometric radiographs. The cephalometric measurements of 52 mouth and 90 nose breathing children were compared with apneic patients. The children had not undergone adenoidectomy or tonsillectomy and had not had or were not receiving orthodontic or orthopedic treatment.

RESULTS

Mouth breathing children showed same cephalometric pattern observed in patients with OSAS: a tendency to have a retruded mandible (p=0.05), along with greater inclination of the mandibular and occlusal planes (p<0.01) and a tendency to have greater inclination of the upper incisors (p=0.08). The nasopharyngeal and posterior airway spaces were greatly reduced in mouth breathing children, as observed in patients with apnea (p<0.01).

CONCLUSION

Mouth breathing children present abnormal cephalometric parameters and their craniofacial morphology resembles that of patients with OSAS.

Clinical assessment of the obstructive sleep apnoea/hypopnoea syndrome

This review focuses on the clinical presentation of the obstructive sleep apnoea/hypopnoea syndrome in adults. Features consistent with the diagnosis are described. A brief discussion of the objective measurement of sleep-disordered breathing, largely in the form of overnight monitoring, is undertaken.

Altered upper airway and soft tissue structures in the New Zealand Obese mouse

RATIONALE

The effect of obesity on upper airway soft tissue structure and size was examined in the New Zealand Obese (NZO) mouse and in a control lean mouse, the New Zealand White (NZW).

OBJECTIVES

We hypothesized that the NZO mouse has increased volume of neck fat and upper airway soft tissues and decreased pharyngeal airway caliber.

METHODS

Pharyngeal airway size, volume of the upper airway soft tissue structures, and distribution of fat in the neck and body were measured using magnetic resonance imaging (MRI). Dynamic MRI was used to examine the differences in upper airway caliber between inspiration and expiration in NZO versus NZW mice.

MEASUREMENTS AND MAIN RESULTS

The data support the hypothesis that, in obese NZO versus lean NZW mice, airway caliber was significantly smaller (P < 0.03), with greater parapharyngeal fat pad volumes (P < 0.0001) and a greater volume of other upper airway soft tissue structures (tongue, P = 0.003; lateral pharyngeal walls, P = 0.01; soft palate, P = 0.02). Dynamic MRI showed that the airway of the obese NZO mouse dilated during inspiration, whereas in the lean NZW mouse, the upper airway was reduced in size during inspiration.

CONCLUSIONS

In addition to the increased volume of pharyngeal soft tissue structures, direct fat deposits within the tongue may contribute to airway compromise in obesity. Pharyngeal airway dilation during inspiration in NZO mice compared with narrowing in NZW mice suggests that airway compromise in obese mice may lead to muscle activation to defend upper airway patency during inspiration.

Mass loading of the upper airway extraluminal tissue space in rabbits: effects on tissue pressure and pharyngeal airway lumen geometry

Lateral pharyngeal fat pad compression of the upper airway (UA) wall is thought to influence UA size in patients with obstructive sleep apnea. We examined interactions between acute mass/volume loading of the UA extra-luminal tissue space and UA patency. We studied 12 supine, anesthetized, spontaneously breathing, head position-controlled (50 degrees ), New Zealand White rabbits. Submucosal extraluminal tissue pressures (ETP) in the anterolateral (ETPlat) and anterior (ETPant) pharyngeal wall were monitored with surgically inserted pressure transducer-tipped catheters (Millar). Tracheal pressure (Ptr) and airflow (V) were measured via a pneumotachograph and pressure transducer inserted in series into the intact trachea, with hypopharyngeal cross-sectional area (CSA) measured via computed tomography, while graded saline inflation (0-1.5ml) of a compliant tissue expander balloon in the anterolateral subcutaneous tissue was performed. Inspiratory UA resistance (Rua) at 20 ml/s was calculated from a power function fitted to Ptr vs. V data. Graded expansion of the anterolateral balloon increased ETPlat from 2.3 +/- 0.5 cmH(2)O (n = 11, mean +/- SEM) to 5.0 +/- 1.1 cmH(2)O at 1.5-ml inflation (P < 0.05; ANOVA). However, ETPant was unchanged from 0.5 +/- 0.5 cmH(2)O (n = 9; P = 0.17). Concurrently, Rua increased to 119 +/- 4.2% of baseline value (n = 12; P < 0.001) associated with a significant reduction in CSA between 10 and 70% of airway length to a minimum of 82.2 +/- 4.4% of baseline CSA at 40% of airway length (P < 0.05). We conclude that anterolateral loading of the upper airway extraluminal tissue space decreases upper airway patency via an increase in ETPlat, but not ETPant. Lateral pharyngeal fat pad size may influence UA patency via increased tissue volume and pressure causing UA wall compression.

Abdominal fat and sleep apnea: the chicken or the egg?

Obstructive sleep apnea (OSA) syndrome is a disorder characterized by repetitive episodes of upper airway obstruction that occur during sleep. Associated features include loud snoring, fragmented sleep, repetitive hypoxemia/hypercapnia, daytime sleepiness, and cardiovascular complications. The prevalence of OSA is 2-3% and 4-5% in middle-aged women and men, respectively. The prevalence of OSA among obese patients exceeds 30%, reaching as high as 50-98% in the morbidly obese population. Obesity is probably the most important risk factor for the development of OSA. Some 60-90% of adults with OSA are overweight, and the relative risk of OSA in obesity (BMI >29 kg/m(2)) is >or=10. Numerous studies have shown the development or worsening of OSA with increasing weight, as opposed to substantial improvement with weight reduction. There are several mechanisms responsible for the increased risk of OSA with obesity. These include reduced pharyngeal lumen size due to fatty tissue within the airway or in its lateral walls, decreased upper airway muscle protective force due to fatty deposits in the muscle, and reduced upper airway size secondary to mass effect of the large abdomen on the chest wall and tracheal traction. These mechanisms emphasize the great importance of fat accumulated in the abdomen and neck regions compared with the peripheral one. It is the abdomen much more than the thighs that affect the upper airway size and function. Hence, obesity is associated with increased upper airway collapsibility (even in nonapneic subjects), with dramatic improvement after weight reduction. Conversely, OSA may itself predispose individuals to worsening obesity because of sleep deprivation, daytime somnolence, and disrupted metabolism. OSA is associated with increased sympathetic activation, sleep fragmentation, ineffective sleep, and insulin resistance, potentially leading to diabetes and aggravation of obesity. Furthermore, OSA may be associated with changes in leptin, ghrelin, and orexin levels; increased appetite and caloric intake; and again exacerbating obesity. Thus, it appears that obesity and OSA form a vicious cycle where each results in worsening of the other.

Growth velocity predicts recurrence of sleep-disordered breathing 1 year after adenotonsillectomy

RATIONALE

Adenotonsillectomy, the first line of treatment of sleep-disordered breathing (SDB), is the most commonly performed pediatric surgery. Predictors of the recurrence of SDB after adenotonsillectomy and its impact on cardiovascular risk factors have not been identified.

OBJECTIVES

Demonstrate that gain velocity in body mass index (BMI) defined as unit increase in BMI/year confers an independent risk for the recurrence of SDB 1 year after adenotonsillectomy.

METHODS

Children with SDB and hypertrophy of the tonsils and a comparison group of healthy children were followed prospectively for 1 year.

MEASUREMENTS AND MAIN RESULTS

Serial polysomnographies, BMI, and blood pressure were obtained before adenotonsillectomy and 6 weeks, 6 months, and 1 year postoperatively. Gain velocity in BMI, BMI and being African American (odds ratios, 4-6/unit change/yr; 1.4/unit and 15, respectively) provided equal amounts of predictive power to the risk of recurrence of SDB. In the group that experienced recurrence, systolic blood pressure at 1 year was higher than at baseline and higher than in children who did not experience recurrence.

CONCLUSIONS

Three clinical parameters confer independent increased risk for high recurrence of SDB after adenotonsillectomy: gain velocity in BMI, obesity, and being African American. A long-term follow-up of children with SDB and monitoring of gain velocity in BMI are essential to identifying children at risk for recurrence of SDB and in turn at risk for hypertension.

Neurotrophins and tonsillar hypertrophy in children with obstructive sleep apnea

Enlarged adenotonsillar tissue (AT) is a major determinant of obstructive sleep apnea (OSA) severity in children; however, mechanisms of AT proliferation are poorly understood. We hypothesized that early exposure to respiratory syncytial virus (RSV) may modify AT proliferation through up-regulation of nerve growth factor (NGF)-neurokinin 1 (NK1) receptor dependent pathways. AT harvested from 34 children with OSA and 25 children with recurrent tonsillitis (RI) were examined for mRNA expression of multiple growth factors and their receptors. In addition, NK1 receptor expression and location, and substance P tissue concentrations were compared in AT from OSA and RI children. NGF mRNA and its high-affinity tyrosine kinase receptor (trkA) expression were selectively increased in OSA (p<0.001). NK1 receptor mRNA and protein expression were also enhanced in OSA (p<0.01), and substance P concentrations in OSA patients were higher than in RI (p<0.0001). AT from OSA children exhibit distinct differences in the expression of NGF and trkA receptors, NK1 receptors, and substance P. The homology between these changes and those observed in the lower airways following RSV infection suggests that RSV may have induced neuro-immunomodulatory changes within AT, predisposing them to increased proliferation, and ultimately contribute to emergence of OSA.

Diagnostic and therapeutic approach to nonsleepy apnea

Epidemiological and observational studies suggest that sleep-disordered breathing is associated with the subsequent development of hypertension and ultimately with cardiovascular consequences. It may therefore be assumed that continuous positive airway pressure (CPAP) not only avoids sleep-related symptoms but could also mitigate cardiovascular consequences. Short-term studies have revealed a drop in blood pressure, especially in more severe, symptomatic cases of obstructive sleep apnea. Two recent studies have reported that nonsleepy obstructive sleep apnea is associated with an absence of reduced blood pressure after CPAP treatment. This suggests that this group of patients is less susceptible to the consequences of apneas, even those with mild-moderate hypertension or other cardiovascular disorders. However, in patients with severe cardiovascular disease or a higher number of obstructive events, CPAP treatment should be seriously considered.

Genetic susceptibility to obstructive sleep apnea in the obese child

The etiology of obstructive sleep apnea (OSA) is multifactorial, consisting of a complex interplay between anatomic and neuromuscular factors and an underlying genetic predisposition toward this disease. Several of the factors that have been reported to play a role in the pathogenesis of OSA can serve as intermediate phenotypes in investigations targeting genetic susceptibility to OSA. A precise underpinning of the genetic basis of OSA has been thus far difficult because it is still unknown whether or not the recognized candidate genes for OSA are directly causal to the phenotype, or whether their effects on OSA are mediated through the intermediate phenotypes of OSA. Future studies utilizing phenotypically homogenous groups such as those with childhood OSA and technological advances such as haplotype analysis in a case control design are extremely promising. Developing predictive models that incorporate genetic and phenotypic markers will enable early diagnosis and, therefore, intervention, ultimately resulting in reduction of morbidity and of the public health concerns associated with OSA in obese children.