[Consensus document on sleep apnea-hypopnea syndrome in children (full version). Sociedad Española de Sueño. El Área de Sueño de la Sociedad Española de Neumología y Cirugía Torácica(SEPAR)]

New Approaches to the Management of Cardiovascular Risk Associated with Sleep Respiratory Disorders in Pediatric Patients

Exposure to risk factors in youth can exacerbate the development of future cardiovascular disease (CVD). Obstructive sleep apnea (OSA), characterized by repetitive episodes of airway obstructions, could trigger said CVD acting as a modifiable risk factor. Measurements from echocardiography have shown impairments in the anatomy and function of the heart related to the severity of OSA. Therefore, the aim of this review was to propose a new clinical approach to the management of cardiovascular risk (CVR) in children based on treating OSA. The review includes studies assessing echocardiographic parameters for cardiac function and structure in pediatric OSA diagnosed using the apnea-hypopnea index (AHI) ≥ 1/h using polysomnography (PSG) and conducted within a year. Based on the reviewed evidence, in addition to PSG, echocardiography should be considered in OSA children in order to indicate the need for treatment and to reduce their future CVR. A follow-up echocardiography after treatment could be performed if impairments in the anatomy and function were found. Prioritizing parameters intimately connected to comorbidity could propel more effective patient-centered care. In conclusion, a reevaluation of pediatric OSA strategies should be considered, emphasizing comorbidity-related parameters in the cardiovascular field. Further studies are needed to assess this approach, potentially leading to enhanced protocols for more effective pediatric OSA treatment and CVR prevention.

Impact of obstructive sleep apnea in cardiovascular risk in the pediatric population: A systematic review

While the association of obstructive sleep apnea (OSA) with an increased cardiovascular risk (CVR) in the adult population is well known, there is insufficient evidence to affirm something similar in the pediatric population. On the other hand, adenotonsillectomy has been shown to be an effective treatment. Our objective was to evaluate the association of sleep respiratory disorders in children with increased CVR and the impact of adenotonsillectomy in the literature. To this aim, a literature search was conducted, between 2002 to the present. After carrying out a systematic review, the following results were provided: thoracic echocardiography after surgery found improvements in terms of cardiac function and structure; blood pressure (BP) measurement, verified a tendency to higher BP values in the OSA pediatric population, which improved after surgery; different biomarkers of CVR, were increased in OSA patients and improved after treatment and finally; some studies found endothelial dysfunction in pediatric OSA, a measurement of vascular system function, was reversible with adenotonsillectomy. Increases in BP parameters, biological markers related to CVR and alterations in cardiac function structure, have been reported in pediatric patients with OSA. At least, some of these parameters would be reversible after adenotonsillectomy, reflecting a possible reduction in CVR.

Sleep apnoea-hypopnoea syndrome in the obese and non-obese: Clinical, polysomnographical and clinical characteristics

INTRODUCTION

Sleep apnoea-hypopnoea syndrome (SAHS) and childhood obesity are two high prevalence conditions that represent a public health challenge.

OBJECTIVE

To analyse the association between both and comparing child groups that had or did not have both conditions.

PATIENTS AND METHODS

A prospective study in children (3-14 years), referred to the "Multidisciplinary Sleep Unit" due to suspected SAHS, between 1 November 2015 and 1 August 2017. The following parameters were evaluated: anthropometry, symptoms, blood pressure, ear, nose, and throat examination, polysomnography (nocturnal PSG) and laboratory tests.

RESULTS

A total of 67 children were evaluated (64% non-obese (NOb) and 36% obese (Ob). It was observed that the Ob were older (P < .001), slept less hours (P = .028), did less physical exercise (P = .029), ate less in the school dining room (P = .009), had la lower sleep efficiency, and had abnormal values in carbohydrate and lipid metabolism. The children with SAHS were younger (P = .010), a high percentage of daytime sleepiness (P = .001), and breathing through the mouth (P = .006), greater percentile of diastolic blood pressure (P = .019) and a lower IGF-1 (P = .003) than those that did not have SAHS. The comparison of the SAHS NOb and SAHS Ob groups, showed that the first group were younger (P = .010), snored more (P = .012), had a more severe SAHS (IAH 13.1 vs 5.4, P = .041), and a higher GOT (P < .001). In the second group, they slept less hours P = .038) and showed lower values of glucose (P = .039), insulin (P < .001), and HOMA (P < .001).

CONCLUSION

The behaviour of SAHS is different in obese children and non-obese children, with differences in age, clinical characteristics, severity of SAHS, and metabolic changes. The children diagnosed with SAHS were in the higher percentile of diastolic blood pressure. Obesity was associated with worse sleep quality, and changes in carbohydrate and lipid metabolism.

Is it necessary to perform a follow-up study after adenotonsillectomy in all children with moderate-severe obstructive sleep apnoea?

Hypertrophy of adenotonsillar tissue is the most common cause of OSAS in otherwise healthy children, and therefore adenotonsillectomy is the first line treatment. Scientific societies recommend nocturnal follow-up PSG to assess for residual OSAS in children with preoperative evidence for moderate to severe OSAS, obesity, craniofacial anomalies that obstruct the upper airway and neurological disorders, based on the increasing trend of publications reporting residual OSAS after adenotonsillectomy. Follow-up PSG values in children with a pre-operative diagnosis of severe OSAS were analysed retrospectively, and compared to the parents' impression after ENT surgery. The study population included 41 healthy children with severe OSAS and adenotonsillar surgery. The percentage of children with normal PSG parameters (AHI <2/h) after adenotonsillectomy was 80.48%. A very good correlation was observed between the parents' perception after treatment and the follow-up PSG parameters, specifically when the parents perceived that the patient had shown «complete resolution» (no snoring or apnoea), 90.62% of the children had an AHI <2/h in the follow-up PSG, the maximum residual AHI being 2.6/h. In healthy children with no underlying pathology, the information provided by the parents on clinical progression after surgery could be useful and might enable the selection of those patients who require a follow-up study, avoiding overload in sleep units.

A Convolutional Neural Network Architecture to Enhance Oximetry Ability to Diagnose Pediatric Obstructive Sleep Apnea

This study aims at assessing the usefulness of deep learning to enhance the diagnostic ability of oximetry in the context of automated detection of pediatric obstructive sleep apnea (OSA). A total of 3196 blood oxygen saturation (SpO2) signals from children were used for this purpose. A convolutional neural network (CNN) architecture was trained using 20-min SpO2 segments from the training set (859 subjects) to estimate the number of apneic events. CNN hyperparameters were tuned using Bayesian optimization in the validation set (1402 subjects). This model was applied to three test sets composed of 312, 392, and 231 subjects from three independent databases, in which the apnea-hypopnea index (AHI) estimated for each subject (AHICNN) was obtained by aggregating the output of the CNN for each 20-min SpO2 segment. AHICNN outperformed the 3% oxygen desaturation index (ODI3), a clinical approach, as well as the AHI estimated by a conventional feature-engineering approach based on multi-layer perceptron (AHIMLP). Specifically, AHICNN reached higher four-class Cohen's kappa in the three test databases than ODI3 (0.515 vs 0.417, 0.422 vs 0.372, and 0.423 vs 0.369) and AHIMLP (0.515 vs 0.377, 0.422 vs 0.381, and 0.423 vs 0.306). In addition, our proposal outperformed state-of-the-art studies, particularly for the AHI severity cutoffs of 5 e/h and 10 e/h. This suggests that the information automatically learned from the SpO2 signal by deep-learning techniques helps to enhance the diagnostic ability of oximetry in the context of pediatric OSA.

Effects of the Traditional Mediterranean Diet in Patients with Otitis Media with Effusion

INTRODUCTION

Otitis media with effusion (OME) is common in pediatric primary care consultations. Its etiology is multifactorial, although it has been proven that inflammation factors mediate and that immunity is in a phase of relative immaturity. The objective of this study was to assess the effects of the Traditional Mediterranean Diet (TMD) modulating inflammation and immunity in patients diagnosed with OME.

MATERIALS AND METHODS

A analysis as a single-group pre-test/post-test was conducted on 40 girls and 40 boys between 18 months and 5 years old. Tympanometry normalization was the main test to control the benefit of diet. Clinical and therapeutic variables were studied through evaluation questionnaires, a quality test of the diet, as well as various anthropometric parameters.

RESULTS

At the end of one year, tympanometry had normalized in 85% of patients. The remaining 15% had normal audiometry and/or associated symptoms had decreased. Likewise, episodes of recurrent colds decreased from 5.96 ± 1.41 to 2.55 ± 0.37; bacterial complications of 3.09 ± 0.75 to 0.61 ± 0.06 and persistent nasal obstruction of 1.92 ± 0.27 to 0.26 ± 0.05. The degree of satisfaction of the families with the program was very high.

CONCLUSIONS

The application of the Traditional Mediterranean Diet could have promising effects in the prevention and treatment of otitis media with effusion.

Wavelet Analysis of Overnight Airflow to Detect Obstructive Sleep Apnea in Children

This study focused on the automatic analysis of the airflow signal (AF) to aid in the diagnosis of pediatric obstructive sleep apnea (OSA). Thus, our aims were: (i) to characterize the overnight AF characteristics using discrete wavelet transform (DWT) approach, (ii) to evaluate its diagnostic utility, and (iii) to assess its complementarity with the 3% oxygen desaturation index (ODI3). In order to reach these goals, we analyzed 946 overnight pediatric AF recordings in three stages: (i) DWT-derived feature extraction, (ii) feature selection, and (iii) pattern recognition. AF recordings from OSA patients showed both lower detail coefficients and decreased activity associated with the normal breathing band. Wavelet analysis also revealed that OSA disturbed the frequency and energy distribution of the AF signal, increasing its irregularity. Moreover, the information obtained from the wavelet analysis was complementary to ODI3. In this regard, the combination of both wavelet information and ODI3 achieved high diagnostic accuracy using the common OSA-positive cutoffs: 77.97%, 81.91%, and 90.99% (AdaBoost.M2), and 81.96%, 82.14%, and 90.69% (Bayesian multi-layer perceptron) for 1, 5, and 10 apneic events/hour, respectively. Hence, these findings suggest that DWT properly characterizes OSA-related severity as embedded in nocturnal AF, and could simplify the diagnosis of pediatric OSA.

Bispectral analysis of overnight airflow to improve the pediatric sleep apnea diagnosis

Pediatric Obstructive Sleep Apnea (OSA) is a respiratory disease whose diagnosis is performed through overnight polysomnography (PSG). Since it is a complex, time-consuming, expensive, and labor-intensive test, simpler alternatives are being intensively sought. In this study, bispectral analysis of overnight airflow (AF) signal is proposed as a potential approach to replace PSG when indicated. Thus, our objective was to characterize AF through bispectrum, and assess its performance to diagnose pediatric OSA. This characterization was conducted using 13 bispectral features from 946 AF signals. The oxygen desaturation index ≥3% (ODI3), a common clinical measure of OSA severity, was also obtained to evaluate its complementarity to the AF bispectral analysis. The fast correlation-based filter (FCBF) and a multi-layer perceptron (MLP) were used for subsequent automatic feature selection and pattern recognition stages. FCBF selected 3 bispectral features and ODI3, which were used to train a MLP model with ability to estimate apnea-hypopnea index (AHI). The model reached 82.16%, 82.49%, and 90.15% accuracies for the common AHI cut-offs 1, 5, and 10 events/h, respectively. The different bispectral approaches used to characterize AF in children provided complementary information. Accordingly, bispectral analysis showed that the occurrence of apneic events decreases the non-gaussianity and non-linear interaction of the AF harmonic components, as well as the regularity of the respiratory patterns. Moreover, the bispectral information from AF also showed complementarity with ODI3. Our findings suggest that AF bispectral analysis may serve as a useful tool to simplify the diagnosis of pediatric OSA, particularly for children with moderate-to-severe OSA.

Surgical versus non-surgical treatment in the Obstructive Sleep Apnea-Hypopnea Syndrome

INTRODUCTION

The treatment of choice for pediatric OSAHS is surgical. However, its etiopathogenesis is multifactorial and surgery does not always solve it. Therefore, other modalities of treatment are used. The main objective of this study is to shed light on the efficacy of surgery compared to other treatments.

METHODS AND MATERIALS

Prospective cohort study with 317 children ages 1-13 years and apnea-hypopnea index (AHI) ≥3/h with no previous treatment. The treatment was organised into 3 categories: surgical (n = 201), medical (n = 75) and observation (n = 41). Quality of life and sleep was assessed by two validated questionnaires (PSQ & Esteller et al.) The upper airway was explored, and nocturnal polysomnography (PSG) performed in every patient. After 12 ± 3 months of treatment was completed, a new PSG and questionnaires were evaluated.

RESULTS

The surgical group improved significantly both subjectively and objectively. Mean AHI decreased from 7.95/h to 2.57/h and T 90 (time spent with arterial oxygen saturation <90%) from 0.49 to 0. AHI of the medical group decreased only from 5.09/h to 4.9/h. Subjective parameters improved less than in the surgical group. Persistence after surgery was 31%, 50% following medical treatment, and after observation 75%. There were no differences in age and BMI between groups. Age or obesity showed no relationship with treatment success or failure.

CONCLUSIONS

The best results were achieved in surgically treated children. However, 31% of those operated had OSAHS persistence, which means a combination of treatments may be the most appropriate strategy.

Childhood Obesity and its Influence on Sleep Disorders: Kids-Play Study

Background: Sleep disorders are associated with overweight and obese children, and could decrease life quality with limitations to normal daily activities. The purpose of the study is to describe the prevalence of sleep disorders in a cohort of overweight/obese children using respiratory polygraphy. Methods: A descriptive cross-sectional study was conducted in Granada (Spain) on a sample of 98 children with overweight or obesity. The presence of sleep disorders was determined by respiratory polygraphy. Results: Regarding apnoea–hypopnea-index (AHI) results, 44% of affected children had severe sleep apnoea–hypopnea syndrome (SAHS), and the remaining 56% had a mild form of the disorder. With respect to oxygen-desaturation index, 56% of the same group had severe SAHS, 32% had mild SAHS, and the remaining 12% did not suffer from SAHS. Among participants, average scores of 13.8 obstructive apnoea, 7.7 central apnoea, and 13.6 hypopnoea were recorded. Conclusions: Respiratory polygraphy can provide conclusive results in the diagnosis of SAHS in overweight/obese children. Interventional programmes designed and implemented to reduce overweight and obesity can improve quality of sleep and life in children.

[Sleep apnoea-hypopnoea syndrome in the obese and non-obese: clinical, polysomnographical and clinical characteristics]

INTRODUCTION

Sleep apnoea-hypopnoea syndrome (SAHS) and childhood obesity are la high prevalence conditions that represent a public health challenge.

OBJECTIVE

To analyse the association between both and comparing child groups that had or did not have both conditions.

PATIENTS AND METHODS

A prospective study in children (3-14 years), referred to the "Multidisciplinary Sleep Unit" due to suspected SAHS, between 1 November 2015 and 1 August 2017. The following parameters were evaluated: anthropometry, symptoms, blood pressure, ear, nose, and throat examination, polysomnography (nocturnal PSG) and laboratory tests.

RESULTS

A total of 67 children were evaluated (64% non-obese and 36% obese. It was observed that the obese were older (P<.001), slept less hours (P=.028), did less physical exercise (P=.029), ate less in the school dining room (P=.009), had la lower sleep efficiency, and had abnormal values in carbohydrate and lipid metabolism. The children with SAHS were younger (P=.010), a high percentage of daytime sleepiness (P=.001), and breathing through the mouth (P=.006), greater percentile of diastolic blood pressure (P=.019) and a lower IGF-1 (P=.003) than those that did not have SAHS. The comparison of the SAHS non-obese and SAHS obese groups, showed that the first group were younger (P=.010), snored more (P=.012), had a more severe SAHS (IAH 13.1 vs. 5.4, P=.041), and a higher GOT (P<.001). In the second group, they slept less hours P=.038) and showed lower values of glucose (P=.039), insulin (P<.001), and HOMA (P<.001).

CONCLUSION

The behaviour of SAHS is different in obese children and non-obese children, with differences in age, clinical characteristics, severity of SAHS, and metabolic changes. The children diagnosed with SAHS were in the higher percentile of diastolic blood pressure. Obesity was associated with worse sleep quality, and changes in carbohydrate and lipid metabolism.

Preliminary results on the impact of simultaneous palatal expansion and mandibular advancement on the respiratory status recorded during sleep in OSAS children

INTRODUCTION

The study aimed to evaluate the evolution of the respiratory status during sleep of OSAS children treated with a custom-made device combining maxillary expansion and mandibular advancement.

MATERIAL AND METHODS

Sleep studies were performed before and after the treatment for 103 children presenting an initial OSAS and Class II malocclusion. Sleep questionnaires were also addressed to parents several years after the end of the treatment to evaluate its long-term effects.

RESULTS

After nine months of treatment, the sleep breathing quality significantly improved: the Apnea/Hypopnea Index systematically decreased ≤5. According to the sleep questionnaires results, 84% of the patients did not show any loud or troubled breathing several years after the end of the treatment.

DISCUSSION

Simultaneous maxillary expansion and mandibular advancement induced an increase of the oral space in the three spatial dimensions, helping in the significant improvement of the OSAS symptoms, with long-terms effects on the sleep breathing quality.

Combined Surgical and Orthodontic Treatments in Children with OSA: A Systematic Review

Obstructive sleep apnea (OSA) is a sleeping breathing disorder. In children, adenotonsillar hypertrophy remains the main anatomical risk factor of OSA. The aim of this study was to assess the current scientific data and to systematically summarize the evidence for the efficiency of adenotonsillectomy (AT) and orthodontic treatment (i.e., rapid maxillary expansion (RME) and mandibular advancement (MA)) in the treatment of pediatric OSA. A literature search was conducted in several databases, including PubMed, Embase, Medline, Cochrane and LILACS up to 5th April 2020. The initial search yielded 509 articles, with 10 articles being identified as eligible after screening. AT and orthodontic treatment were more effective together than separately to cure OSA in pediatric patients. There was a greater decrease in apnea hypoapnea index (AHI) and respiratory disturbance index (RDI), and a major increase in the lowest oxygen saturation and the oxygen desaturation index (ODI) after undergoing both treatments. Nevertheless, the reappearance of OSA could occur several years after reporting adequate treatment. In order to avoid recurrence, myofunctional therapy (MT) could be recommended as a follow-up. However, further studies with good clinical evidence are required to confirm this finding.

Home Respiratory Polygraphy is Useful in the Diagnosis of Childhood Obstructive Sleep Apnea Syndrome

The utility of home respiratory polygraphy (HRP) was assessed as an alternative to polysomnography (PSG) in the diagnosis of childhood obstructive sleep apnea syndrome (OSAS). PSG was indicated only in patients with concomitant disease or where HRP results were questionable. The follow-up period was 1 year. We recorded clinical and anthropometric data, physical examination findings, respiratory variables, severity level and choice of therapy. We assessed 121 children, 70 boys and 51 girls, with mean age 7 ± 4 years, mean body mass index (BMI) 19 ± 5 kg/m², and mean BMI percentile 62 ± 38%. We included 104 HRP and 24 PSG recordings. Of the latter, 7 were preceded by HRP (false negatives) and 17 were indicated as the first-choice method owing to concomitant disease. Of the initial HRP recordings, 93% were technically valid. All technically valid HRPs and 96% of PSGs resulted in a diagnosis of OSAS (apnea-hypopnea index 9.5 ± 9.1/h). Thirty-three percent of cases were moderate and 22% severe. Apnea-hypopnea index showed no correlation with BMI or BMI percentile. Adenotonsillectomy was indicated in 93 patients (77%), conservative treatment in 17 (14%), and conservative treatment combined with CPAP/BiPAP in 11 (9%). There were no significant differences between children diagnosed by HRP and by PSG in terms of treatment choice. The prevalence of OSAS in our sample was 96.7%. In conclusion, when the probability of OSAS is high, HRP is usually sufficient for diagnosing the syndrome and establishing therapy in children. PSG is advisable in complex or questionable cases.

Treatment of Obstructive Sleep Apnea in Children: Handling the Unknown with Precision

Treatment approaches to pediatric obstructive sleep apnea (OSA) have remarkably evolved over the last two decades. From an a priori assumption that surgical removal of enlarged upper airway lymphadenoid tissues (T&A) was curative in the vast majority of patients as the recommended first-line treatment for pediatric OSA, residual respiratory abnormalities are frequent. Children likely to manifest persistent OSA after T&A include those with severe OSA, obese or older children, those with concurrent asthma or allergic rhinitis, children with predisposing oropharyngeal or maxillomandibular factors, and patients with underlying medical conditions. Furthermore, selection anti-inflammatory therapy or orthodontic interventions may be preferable in milder cases. The treatment options for residual OSA after T&A encompass a large spectrum of approaches, which may be complementary, and clearly require multidisciplinary cooperation. Among these, continuous positive airway pressure (CPAP), combined anti-inflammatory agents, rapid maxillary expansion, and myofunctional therapy are all part of the armamentarium, albeit with currently low-grade evidence supporting their efficacy. In this context, there is urgent need for prospective evidence that will readily identify the correct candidate for a specific intervention, and thus enable some degree of scientifically based precision in the current one approach fits all model of pediatric OSA medical care.

Usefulness of Spectral Analysis of Respiratory Rate Variability to Help in Pediatric Sleep Apnea-Hypopnea Syndrome Diagnosis

The sleep apnea-hypopnea syndrome (SAHS) is a chronic respiratory disorder of high prevalence among children (up to 4%). Nocturnal polysomnography (PSG) is the gold standard method to diagnose SAHS, which is a complex, expensive, and time-consuming test. Consequently, alternative simplified methods are demanded. We propose the analysis of the respiratory rate variability (RRV) signal, directly obtained from the airflow (AF) signals. The aim of our study is to evaluate the usefulness of the spectral information obtained from RRV in the diagnosis of pediatric SAHS. A database composed of 946 AF and blood oxygen saturation (SpO2) recordings from children between 0 and 13 years old was used. Our database was divided into four severity groups according to the apnea-hipopnea index (AHI): no-SAHS (AHI <; 1 events/h), mild (1 events/h ≤ AHI <; 5 events/h), moderate (5 events/h ≤ AHI <; 10 events/h), and severe SAHS (AHI ≥ 10 events/h). RRV and 3% oxygen desaturation index (ODI3) were obtained from AF and SpO2 recordings, respectively. A spectral band of interest was determined (0.09-0.20 Hz.) and a total of 12 spectral features were extracted. Nine of these features showed statistically significant differences (p-value <; 0.05) among the four severity groups. The spectral features from RRV along with ODI3 were used as inputs to binary logistic regression (LR) classifiers. The diagnostic performance of LR models were evaluated for the AHI cut-off points of 1, 5, and 10 e/h, achieving 66.5%, 84.0%, and 88.5% accuracy, respectively. These results outperformed those obtained by single ODI3. The joint use of the spectral information from RRV and ODI3 achieved a high diagnostic capability in the most severely-affected children, thus showing their complementarity. These results suggest that the information contained in RRV spectrum together with ODI3 is useful to help identify moderate-to-severe SAHS.

Usefulness of recurrence plots from airflow recordings to aid in paediatric sleep apnoea diagnosis

BACKGROUND AND OBJECTIVE

In-laboratory overnight polysomnography (PSG) is the gold standard method to diagnose the Sleep Apnoea-Hypopnoea Syndrome (SAHS). PSG is a complex, expensive, labour-intensive and time-consuming test. Consequently, simplified diagnostic methods are desirable. We propose the analysis of the airflow (AF) signal by means of recurrence plots (RP) features. The main goal of our study was to evaluate the utility of the information from RPs of the AF signals to detect paediatric SAHS at different levels of severity. In addition, we also evaluated the complementarity with the 3% oxygen desaturation index (ODI₃).

METHODS

946 AF and blood oxygen saturation (SpO₂) recordings from children ages 0-13 years were used. The population under study was randomly split into training (60%) and test (40%) sets. RP was computed and 9 RP features were extracted from each AF recording. ODI₃ was also calculated from each SpO₂ recording. A feature selection stage was conducted in the training group by means of the fast correlation-based filter (FCBF) methodology to obtain a relevant and non-redundant optimum feature subset. A multi-layer perceptron neural network with Bayesian approach (BY-MLP), trained with these optimum features, was used to estimate the apnoea-hypopnoea index (AHI).

RESULTS

8 of the RP features showed statistically significant differences (p-value <0.01) among the SAHS severity groups. FCBF selected the maximum length of the diagonal lines from RP, as well as the ODI₃. Using these optimum features, the BY-MLP model achieved 83.2%, 78.5%, and 91.0% accuracy in the test group for the AHI thresholds 1, 5, and 10 events/h, respectively. Moreover, this model reached a negative likelihood ratio of 0.1 for 1 event/h and a positive likelihood ratio of 13.7 for 10 events/h.

CONCLUSIONS

RP analysis enables extraction of useful SAHS-related information from overnight AF paediatric recordings. Moreover, it provides complementary information to the widely-used clinical variable ODI₃. Thus, RP applied to AF signals can be used along with ODI₃ to help in paediatric SAHS diagnosis, particularly to either confirm the absence of SAHS or the presence of severe SAHS.

Postoperative complications after adenotonsillectomy in two paediatric groups: Obstructive sleep apnoea syndrome and recurrent tonsillitis

INTRODUCTION AND OBJECTIVES

Adenotonsillectomy is a surgery to treat recurrent tonsillitis or obstructive sleep apnoea syndrome (OSAS). It is considered a safe procedure, with few complications. Moreover, patients over 3 years and without comorbidities do not present a higher rate of respiratory adverse events after the immediate postoperative period, and do not need systematic admission to a paediatric intensive care unit (PICU), regardless of their OSAS severity. The aim of this study is to reanalyse the situation, including patients under the age of 3 years, for whom there are fewer available data, to confirm that this trend has not changed.

METHODS

A retrospective observational study was performed, including all adenotonsillectomised children in our hospital over 5 years.

RESULTS

418 adenotonsillectomised children were included, 56.7% due to recurrent tonsillitis, and 43.3% because of OSAS. Only 24 patients (5%7%) experienced adverse events, of whom 1.2% had vomiting, 3.1% bleeding, and 1.4% respiratory events. All the respiratory events occurred in the operating theatre or in the post-anaesthetic unit, most frequently in children with severe OSAS, while the tonsillitis group had more bleeding (P=.046). No differences in complications were observed according to age (P=0.174), but the group of patients under three years was relatively small.

CONCLUSIONS

No differences were found in the percentage of complications between the two groups. Although the OSAS group exhibited more respiratory events, these occurred in the immediate postoperative period; otherwise, there was a higher risk of bleeding in the tonsillitis group. These results support the findings indicating that routine PICU admission is not required for these patients.

Drug-induced sleep endoscopy in children

This document is intended as a guide for Spanish ENT specialists who want to perform drug-induced sleep endoscopy. Indications, sedation method and important findings are discussed to unify criteria and methodology.

Outcome of drug-induced sleep endoscopy-directed surgery for persistent obstructive sleep apnea after adenotonsillar surgery

PURPOSE

Drug-induced sleep endoscopy (DISE) is suitable for evaluating persistent obstructive sleep apnea syndrome (OSAS) after adenotonsillar surgery as a means to guide surgical intervention, yet few studies demonstrate its usefulness in resolving the syndrome. We describe our experience of DISE-directed surgery in children with persistent OSAS by analysing objective and subjective outcomes of this treatment.

METHODS

Prospective study of 20 otherwise healthy 2-12 year-old children with OSAS persisting after adenotonsillar surgery. All patients underwent DISE-directed surgery and were followed up clinically and with a polysomnogram at 12 ± 3 months.

RESULTS

All 20 children had an apnea-hypopnea index (AHI) score ≥1 (mean: 6.1 ± 4.9) and 75% had AHI>3 before surgery. We performed a total of 14 total tonsillectomies (70%), 7 with associated pharyngoplasties; 5 radiofrequency turbinate reductions (25%); 7 radiofrequency lingual tonsil reductions (35%); and 10 revision adenoidectomies (50%). No surgery-related complications were observed. AHI scores at follow-up were significantly lower than AHI scores before surgery (1.895 ± 1.11 vs 6.143 ± 4.88; p < 0.05) and, in 85% (n = 17) of patients, AHI was below 3. There was a significant reduction in the number of children with AHI>3 in follow-up at 12 ± 3 months (15%; n = 3) compared to before surgery (75%; n = 15) (p < 0.005).

CONCLUSION

DISE-directed surgery for otherwise healthy children with persistent OSAS is a useful and safe technique to decide a therapeutic strategy and to obtain good objective and subjective results regarding resolution of the syndrome.

Wavelet analysis of oximetry recordings to assist in the automated detection of moderate-to-severe pediatric sleep apnea-hypopnea syndrome

BACKGROUND

The gold standard for pediatric sleep apnea hypopnea syndrome (SAHS) is overnight polysomnography, which has several limitations. Thus, simplified diagnosis techniques become necessary.

OBJECTIVE

The aim of this study is twofold: (i) to analyze the blood oxygen saturation (SpO2) signal from nocturnal oximetry by means of features from the wavelet transform in order to characterize pediatric SAHS; (ii) to evaluate the usefulness of the extracted features to assist in the detection of pediatric SAHS.

METHODS

981 SpO2 signals from children ranging 2-13 years of age were used. Discrete wavelet transform (DWT) was employed due to its suitability to deal with non-stationary signals as well as the ability to analyze the SAHS-related low frequency components of the SpO2 signal with high resolution. In addition, 3% oxygen desaturation index (ODI3), statistical moments and power spectral density (PSD) features were computed. Fast correlation-based filter was applied to select a feature subset. This subset fed three classifiers (logistic regression, support vector machines (SVM), and multilayer perceptron) trained to determine the presence of moderate-to-severe pediatric SAHS (apnea-hypopnea index cutoff ≥ 5 events per hour).

RESULTS

The wavelet entropy and features computed in the D9 detail level of the DWT reached significant differences associated with the presence of SAHS. All the proposed classifiers fed with a selected feature subset composed of ODI3, statistical moments, PSD, and DWT features outperformed every single feature. SVM reached the highest performance. It achieved 84.0% accuracy (71.9% sensitivity, 91.1% specificity), outperforming state-of-the-art studies in the detection of moderate-to-severe SAHS using the SpO2 signal alone.

CONCLUSION

Wavelet analysis could be a reliable tool to analyze the oximetry signal in order to assist in the automated detection of moderate-to-severe pediatric SAHS. Hence, pediatric subjects suffering from moderate-to-severe SAHS could benefit from an accurate simplified screening test only using the SpO2 signal.

Cloud algorithm-driven oximetry-based diagnosis of obstructive sleep apnoea in symptomatic habitually snoring children

The ability of a cloud-driven Bluetooth oximetry-based algorithm to diagnose obstructive sleep apnoea syndrome (OSAS) was examined in habitually snoring children concurrently undergoing overnight polysomnography.

Children clinically referred for overnight in-laboratory polysomnographic evaluation for suspected OSAS were simultaneously hooked to a Bluetooth oximeter linked to a smartphone. Polysomnography findings were scored and the apnoea/hypopnoea index (AHIPSG) was tabulated, while oximetry data yielded an estimated AHIOXI using a validated algorithm.

The accuracy of the oximeter in identifying correctly patients with OSAS in general, or with mild (AHI 1–5 events·h−1), moderate (5–10 events·h−1) or severe (>10 events·h−1) OSAS was examined in 432 subjects (6.5±3.2 years), with 343 having AHIPSG >1 event·h−1. The accuracies of AHIOXI were consistently >79% for all levels of OSAS severity, and specificity was particularly favourable for AHI >10 events·h−1 (92.7%). Using the criterion of AHIPSG >1 event·h−1, only 4.7% of false-negative cases emerged, from which only 0.6% of cases showed moderate or severe OSAS.

Overnight oximetry processed via Bluetooth technology by a cloud-based machine learning-derived algorithm can reliably diagnose OSAS in children with clinical symptoms suggestive of the disease. This approach provides virtually limitless scalability and should alleviate the substantial difficulties in accessing paediatric sleep laboratories while markedly reducing the costs of OSAS diagnosis.

Detrended fluctuation analysis of the oximetry signal to assist in paediatric sleep apnoea-hypopnoea syndrome diagnosis

OBJECTIVE

To evaluate whether detrended fluctuation analysis (DFA) provides information that improves the diagnostic ability of the oximetry signal in the diagnosis of paediatric sleep apnoea-hypopnoea syndrome (SAHS).

APPROACH

A database composed of 981 blood oxygen saturation (SpO₂) recordings in children was used to extract DFA-derived features in order to quantify the scaling behaviour and the fluctuations of the SpO₂ signal. The 3% oxygen desaturation index (ODI3) was also computed for each subject. Fast correlation-based filter (FCBF) was then applied to select an optimum subset of relevant and non-redundant features. This subset fed a multi-layer perceptron (MLP) neural network to estimate the apnoea-hypopnoea index (AHI).

MAIN RESULTS

ODI3 and four features from the DFA reached significant differences associated with the severity of SAHS. An optimum subset composed of the slope in the first scaling region of the DFA profile and the ODI3 was selected using FCBF applied to the training set (60% of samples). The MLP model trained with this feature subset showed good agreement with the actual AHI, reaching an intra-class correlation coefficient of 0.891 in the test set (40% of samples). Furthermore, the estimated AHI showed high diagnostic ability, reaching an accuracy of 82.7%, 81.9%, and 91.1% using three common AHI cut-offs of 1, 5, and 10 events per hour (e h^-1), respectively. These results outperformed the overall performance of ODI3.

SIGNIFICANCE

DFA may serve as a reliable tool to improve the diagnostic performance of oximetry recordings in the evaluation of paediatric patients with symptoms suggestive of SAHS.

Obstructive sleep apnea syndrome and growth failure

Obstructive sleep apnea syndrome is a common problem among children and is recognized as a cause of significant medical morbidity. Since the 1980s, it has been suggested that obstructive sleep apnea syndrome is a risk factor for growth failure in children. In many cases, it has been shown that growth failure is reversible once the obstructive sleep apnea syndrome is resolved. The objectives of this study were to analyze and compare growth failure prevalence in a Mediterranean population of children with obstructive sleep apnea syndrome and healthy children matched in age and sex, and to assess the effectiveness of tonsillectomy and adenoidectomy in resolving growth retardation. We compared 172 children with obstructive sleep apnea syndrome (apnea-hypopnea index ≥ 3) who had undergone tonsillectomy and adenoidectomy with 172 healthy controls in terms of key anthropometric parameters. Most of the criteria used for growth failure were higher to a statistically significant degree in the study group vs the control group: height-for-age ≤ 3rd percentile (7.56% vs 2.91%; p = 0.044), weight-for-age ≤ 5th percentile (9.30% vs 2.33%; p = 0.005), weight-for-age ≤ 3rd percentile (8.14% vs 2.33%; p = 0.013) and height and/or weight for-age ≤ 5th percentile (13.95% vs 5.81%; p = 0.009). The height-for-age ≤ 5th percentile was almost at the limit of statistical significance (8.72% for the study group vs 4.65% for the control group; p = 0.097). At one-year post-surgery follow-up, 10 of 15 children with height-for-age ≤ 5th percentile had achieved catch-up growth (66.6%), and 14 of 24 children with height- and/or weight-for-age ≤ 5th percentile had normalized growth (58.33%). For children with failure to thrive or who have growth failure, physicians should consider the possibility of obstructive sleep apnea. A significant number of children with obstructive sleep apnea concurrent with growth failure could benefit from tonsillectomy and adenoidectomy to recover and normalize their growth rate.

Utility of bispectrum in the screening of pediatric sleep apnea-hypopnea syndrome using oximetry recordings

BACKGROUND AND OBJECTIVE

The aim of this study was to assess the utility of bispectrum-based oximetry approaches as a complementary tool to traditional techniques in the screening of pediatric sleep apnea-hypopnea syndrome (SAHS).

METHODS

298 blood oxygen saturation (SpO₂) signals from children ranging 0-13 years of age were recorded during overnight polysomnography (PSG). These recordings were divided into three severity groups according to the PSG-derived apnea hypopnea index (AHI): AHI < 5 events per hour (e/h), 5 ≤ AHI < 10 e/h, AHI ≥ 10 e/h. For each pediatric subject, anthropometric variables, 3% oxygen desaturation index (ODI3) and spectral features from power spectral density (PSD) and bispectrum were obtained. Then, the fast correlation-based filter (FCBF) was applied to select a subset of relevant features that may be complementary, excluding those that are redundant. The selected features fed a multiclass multi-layer perceptron (MLP) neural network to build a model to estimate the SAHS severity degrees.

RESULTS

An optimum subset with features from all the proposed methodological approaches was obtained: variables from bispectrum, as well as PSD, ODI3, Age, and Sex. In the 3-class classification task, the MLP model trained with these features achieved an accuracy of 76.0% and a Cohen's kappa of 0.56 in an independent test set. Additionally, high accuracies were reached using the AHI cutoffs for diagnosis of moderate (AHI = 5 e/h) and severe (AHI = 10 e/h) SAHS: 81.3% and 85.3%, respectively. These results outperformed the diagnostic ability of a MLP model built without using bispectral features.

CONCLUSIONS

Our results suggest that bispectrum provides additional information to anthropometric variables, ODI3 and PSD regarding characterization of changes in the SpO₂ signal caused by respiratory events. Thus, oximetry bispectrum can be a useful tool to provide complementary information for screening of moderate-to-severe pediatric SAHS.

Nocturnal Oximetry-based Evaluation of Habitually Snoring Children

RATIONALE

The vast majority of children around the world undergoing adenotonsillectomy for obstructive sleep apnea-hypopnea syndrome (OSA) are not objectively diagnosed by nocturnal polysomnography because of access availability and cost issues. Automated analysis of nocturnal oximetry (nSp_O2), which is readily and globally available, could potentially provide a reliable and convenient diagnostic approach for pediatric OSA.

METHODS

Deidentified nSp_O2 recordings from a total of 4,191 children originating from 13 pediatric sleep laboratories around the world were prospectively evaluated after developing and validating an automated neural network algorithm using an initial set of single-channel nSp_O2 recordings from 589 patients referred for suspected OSA.

MEASUREMENTS AND MAIN RESULTS

The automatically estimated apnea-hypopnea index (AHI) showed high agreement with AHI from conventional polysomnography (intraclass correlation coefficient, 0.785) when tested in 3,602 additional subjects. Further assessment on the widely used AHI cutoff points of 1, 5, and 10 events/h revealed an incremental diagnostic ability (75.2, 81.7, and 90.2% accuracy; 0.788, 0.854, and 0.913 area under the receiver operating characteristic curve, respectively).

CONCLUSIONS

Neural network-based automated analyses of nSp_O2 recordings provide accurate identification of OSA severity among habitually snoring children with a high pretest probability of OSA. Thus, nocturnal oximetry may enable a simple and effective diagnostic alternative to nocturnal polysomnography, leading to more timely interventions and potentially improved outcomes.

Circulating exosomes in obstructive sleep apnea as phenotypic biomarkers and mechanistic messengers of end-organ morbidity

Obstructive sleep apnea (OSA), the most severe form of sleep disordered breathing, is characterized by intermittent hypoxia during sleep (IH), sleep fragmentation, and episodic hypercapnia. OSA is associated with increased risk for morbidity and mortality affecting cardiovascular, metabolic, and neurocognitive systems, and more recently with non-alcoholic fatty liver disease (NAFLD) and cancer-related deaths. Substantial variability in OSA outcomes suggests that genetically-determined and environmental and lifestyle factors affect the phenotypic susceptibility to OSA. Furthermore, OSA and obesity often co-exist and manifest activation of shared molecular end-organ injury mechanisms that if properly identified may represent potential therapeutic targets. A challenge in the development of non-invasive diagnostic assays in body fluids is the ability to identify clinically relevant biomarkers. Circulating extracellular vesicles (EVs) include a heterogeneous population of vesicular structures including exosomes, prostasomes, microvesicles (MVs), ectosomes and oncosomes, and are classified based on their size, shape and membrane surface composition. Of these, exosomes (30-100nm) are very small membrane vesicles derived from multi-vesicular bodies or from the plasma membrane and play important roles in mediating cell-cell communication via cargo that includes lipids, proteins, mRNAs, miRNAs and DNA. We have recently identified a unique cluster of exosomal miRNAs in both humans and rodents exposed to intermittent hypoxia as well as in patients with OSA with divergent morbid phenotypes. Here we summarize such recent findings, and will focus on exosomal miRNAs in both adult and children which mediate intercellular communication relevant to OSA and endothelial dysfunction, and their potential value as diagnostic and prognostic biomarkers.

Pediatric OSA Syndrome Morbidity Biomarkers: The Hunt Is Finally On!

Since initial reports 40 years ago on pediatric OSA syndrome (OSAS) as a distinct and prevalent clinical entity, substantial advances have occurred in the delineation of diagnostic and treatment approaches. However, despite emerging and compelling evidence that OSAS increases the risk for cognitive, cardiovascular, and metabolic end-organ morbidities, routine assessment of such morbidities is seldom conducted in clinical practice. One of the major reasons for such discrepancies resides in the relatively labor-intensive and onerous steps that would be required to detect the presence of any of such morbidities, further adding to the already elevated cost of diagnosing the disorder. To circumvent these obstacles, the search for biomarker signatures of pediatric OSA and its cognitive and cardiometabolic consequences was launched, and considerable progress has occurred since then. Here, we review the current evidence for the presence of morbidity-related biomarkers among children with OSAS, and explore future opportunities in this promising arena.

Surgical treatment for childhood obstructive sleep apnoea: Cold-knife tonsillar dissection versus bipolar radiofrequency thermal ablation

INTRODUCTION AND OBJECTIVE

Adenotonsillectomy for treatment of childhood obstructive sleep apnoea is effective. The uncomfortable postoperative period and possible complications have significantly increased the use of partial techniques, seeking to improve these aspects while achieving the same results in resolving sleep apnoea. The aim was to present the experience with 2 consecutive groups of patients, comparing total tonsillectomy to bipolar radiofrequency ablation (RFA).

METHOD

A group of 96 children that underwent total tonsilloadenoidectomy using cold dissection were compared to another group of 101 children that underwent RFA. In all cases, polysomnography was performed before and 1 year after surgery. The percentage of cases with persistent disease (apnea-hypopnea index ≥ 3) and the improvement of clinical symptoms at one year were evaluated. The percentages of surgical and anaesthetic complications in both groups were also compared.

RESULT

The persistence of the syndrome was comparable in both groups: 25% in the cold dissection and 22.77% in the radiofrequency ablation group. Anaesthetic complications (5% in the group where cold dissection was used and 4.2% in the radiofrequency ablation group) and postoperative bleeding rates were very low and statistically comparable with both techniques.

CONCLUSION

In the treatment of childhood obstructive sleep apnoea syndrome, both extracapsular surgery using cold scalpel and bipolar radiofrequency tunnelling techniques are safe. Likewise, results as to resolution of the syndrome show no statistically significant differences.

Treatment outcomes of obstructive sleep apnoea in obese community-dwelling children: the NANOS study

The first line of treatment of obstructive sleep apnoea syndrome (OSAS) in children consists of adenotonsillectomy (T&A). The aim of the present study was to evaluate treatment outcomes of OSAS among obese children recruited from the community.A cross-sectional, prospective, multicentre study of Spanish obese children aged 3-14 years, with four groups available for follow-up: group 1: non-OSAS with no treatment; group 2: dietary treatment; group 3: surgical treatment; and group 4: continuous positive airway pressure treatment.117 obese children (60 boys, 57 girls) with a mean age of 11.3±2.9 years completed the initial (T0) and follow-up (T1) assessments. Their mean body mass index (BMI) at T1 was 27.6±4.7 kg·m(-2), corresponding to a BMI Z-score of 1.34±0.59. Mean respiratory disturbance index (RDI) at follow-up was 3.3±3.9 events·h(-1). Among group 1 children, 21.2% had an RDI ≥3 events·h(-1) at T1, the latter being present in 50% of group 2, and 43.5% in group 3. In the binary logistic regression model, age emerged as a significant risk factor for residual OSAS (odds ratio 1.49, 95% confidence interval 1.01-2.23; p<0.05) in obese children surgically treated, and RDI at T0 as well as an increase in BMI emerged as significant risk factors for persistent OSAS in obese children with dietary treatment (OR 1.82, 95% CI 1.09-3.02 (p<0.03) and OR 8.71, 95% CI 1.24-61.17 (p=0.03)).Age, RDI at diagnosis and obesity are risk factors for relatively unfavourable OSAS treatment outcomes at follow-up.

Reliability of home respiratory polygraphy for the diagnosis of sleep apnea in children

OBJECTIVE

The objective of this study was to evaluate the diagnostic reliability of home respiratory polygraphy (HRP) in children with a clinical suspicion of OSA-hypopnea syndrome (OSAS).

METHODS

A prospective blind evaluation was performed. Children between the ages of 2 to 14 years with clinical suspicion of OSAS who were referred to the Sleep Unit were included. An initial HRP followed by a later date, same night, in-laboratory overnight respiratory polygraphy and polysomnography (PSG) in the sleep laboratory were performed. The apnea-hypopnea index (AHI)-HRP was compared with AHI-PSG, and therapeutic decisions based on AHI-HRP and AHI-PSG were analyzed using intraclass correlation coefficients, Bland-Altman plots, and receiver operator curves (ROCs).

RESULTS

Twenty-seven boys and 23 girls, with a mean age of 5.3 ± 2.5 years, were studied, and 66% were diagnosed with OSAS based on a PSG-defined obstructive respiratory disturbance index ≥ 3/h total sleep time. Based on the availability of concurrent HRP-PSG recordings, the optimal AHI-HRP corresponding to the PSG-defined OSAS criterion was established as ≥ 5.6/h The latter exhibited a sensitivity of 90.9% (95% CI, 79.6%-100%) and a specificity of 94.1% (95% CI, 80%-100%).

CONCLUSIONS

HRP recordings emerge as a potentially useful and reliable approach for the diagnosis of OSAS in children. However, more research is required for the diagnosis of mild OSAS using HRP in children.

Effects of adenotonsillectomy on plasma inflammatory biomarkers in obese children with obstructive sleep apnea: A community-based study

Background

Obesity and obstructive sleep apnea syndrome (OSA) are highly prevalent and frequently overlapping conditions in children that lead to systemic inflammation, the latter being implicated in the various end-organ morbidities associated with these conditions.

Aim

To examine the effects of adenotonsillectomy (T&A) on plasma levels of inflammatory markers in obese children with polysomnographically diagnosed OSA who were prospectively recruited from the community.

Methods

Obese children prospectively diagnosed with OSA, underwent T&A and a second overnight polysomnogram (PSG) after surgery. Plasma fasting morning samples obtained after each of the 2 PSG were assayed for multiple inflammatory and metabolic markers including interleukin-6 (IL-6), IL-18, plasminogen activator inhibitor-1 (PAI-1), monocyte chemoattractant protein-1 (MCP-1), matrix metalloproteinase- (MMP-9), adiponectin, apelin C, leptin and osteocrin.

Results

Out of 122 potential candidates, 100 obese children with OSA completed the study with only 1/3 exhibiting normalization of their PSG after T&A (i.e., AHI≤1/hrTST). However, overall significant decreases in MCP-1, PAI-1, MMP-9, IL-18 and IL-6, and increases in adropin and osteocrin plasma concentrations occurred after T&A. Several of the T&A responsive biomarkers exhibited excellent sensitivity and moderate specificity to predict residual OSA (i.e., AHI≥/hrTST).

Conclusions

A defined subset of systemic inflammatory and metabolic biomarkers is reversibly altered in the context of OSA among community-based obese children, further reinforcing the concept on the interactive pro-inflammatory effects of sleep disorders such as OSA and obesity contributing to downstream end-organ morbidities.

[Obstructive sleep apnea-hypopnea syndrome in children: beyond adenotonsillar hypertrophy]

The prevalence of obstructive sleep apnea-hypopnea syndrome in the general childhood population is 1-2% and the most common cause is adenotonsillar hypertrophy. However, beyond adenotonsillar hypertrophy, there are other highly prevalent causes of this syndrome in children. The causes are often multifactorial and include muscular hypotonia, dentofacial abnormalities, soft tissue hypertrophy of the airway, and neurological disorders). Collaboration between different specialties involved in the care of these children is essential, given the wide variability of conditions and how frequently different factors are involved in their genesis, as well as the different treatments to be applied. We carried out a wide literature review of other causes of obstructive sleep apnea-hypopnea syndrome in children, beyond adenotonsillar hypertrophy. We organised the prevalence of this syndrome in each pathology and the reasons that cause it, as well as their interactions and management, in a consistent manner.

Home ventilation therapy in obstructive sleep apnea-hypopnea syndrome

Obstructive sleep apnea-hypopnea is a highly prevalent disease that is often underdiagnosed at present. It has a significant economic and social welfare impact, accounting for a large part of the resources assigned to home respiratory therapies. As part of the 2014 SEPAR Year of the Chronic Patient and Domiciliary Respiratory Care sponsored by the Spanish Society of Pulmonology and Thoracic Surgery, this article reviews the most recent publications on the indications and controversial issues in the treatment of sleep apnea, the latest evidence for indication of various positive pressure devices, and adjustment modes, ranging from the use of empirical formulae or mathematical estimations to modern auto-CPAP equipment, while not forgetting the gold standard of manual titration. Emphasis is placed on the need for monitoring required by patients to ensure treatment adherence and compliance. Finally, other therapies that are not the object of this article are briefly reviewed.