|Year : 2022 | Volume
| Issue : 1 | Page : 2-5
The complicated simple snoring
Esther Tin Wing Cheng
Department of Paediatrics, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China
|Date of Submission||10-Dec-2021|
|Date of Decision||20-Feb-2022|
|Date of Acceptance||08-May-2022|
|Date of Web Publication||02-Jan-2023|
Ms. Esther Tin Wing Cheng
Department of Paediatrics, Chinese University of Hong Kong, 6/F, Clinical Sciences Building, Prince of Wales Hospital, Shatin, Hong Kong Special Administrative Region
Source of Support: None, Conflict of Interest: None
Primary snoring, also known as simple snoring, was historically regarded as a benign entity on the sleep-disordered breathing spectrum until recently, when more and more evidence suggested the otherwise. This article aims to provide an overview on the research directions of primary snoring and their relevant clinical significance.
Keywords: Cognition, hypertension, obstructive sleep apnoea, primary snoring
|How to cite this article:|
Cheng ET. The complicated simple snoring. Pediatr Respirol Crit Care Med 2022;6:2-5
| A Continuum of Snoring?|| |
Primary snoring (PS), also known as simple or non-apneic snoring, is a relatively common condition characterized by habitual snoring (HS) >3 nights per week and normal conventional polysomnography (PSG). Current estimation reported that 7.2% and 4.8% of children in Hong Kong suffered from HS and obstructive sleep apnoea (OSA) respectively., Positioned at the milder end of sleep-disordered breathing (SDB) spectrum,, PS was historically regarded as a benign entity without causing significant medical consequences for the snorer and co-snorer until recently. As accumulating evidence has identified PS as an independent risk factor for complications described originally for OSA, such as poorer neurocognitive-behavioral function and higher cardiovascular risks, an urgent need for a paradigm shift in the current clinical thinking and management strategy of PS is hence required.
| Definition of PS|| |
Despite the high prevalence in the general population, currently, we see a lack of consensus regarding the cut-off and occasional requirements of PS. The distinction between PS and other sleep disorders is, conceptually and originally, based on the absence of clinical consequences. Previously, the 2005 American Academy of Sleep Medicine (AASM) International Classification of Sleep Disorders (ICSD-2) was amongst the most commonly cited definition of PS. It defined PS as loud upper airway breathing sounds in sleep without episodes of apnoea or hypoventilation. In 2014, the update by ICSD-3 recognized that an absolute absence of apnoea is not essential to delineate the difference in clinical outcomes of PS and other sleep disorders. Since then, <1 apnoea/hypopnoea events per hour of sleep on the Apnoea-Hypopnoea Index (AHI) in the absence of any clinical consequences was commonly used to identify PS in research settings. It is also worth noticing that this working definition is arbitrary, without reliable clinical validation, and varies between studies.
Meanwhile, it is clear that AHI alone may not be sufficient to define PS. In 2016, Kryger redefined PS based on the duration, oxygen saturation, airflow limitation, and the level of anatomical obstruction in the hopes to model the absence of any physical implications due to PS. For the psychological aspect, i.e., to study the disturbance to patients and possibly the co-sleepers, a noise approach that looks into sound patterns and cut-offs of specific acoustic parameters may be appropriate. The limitation of such an approach, however, lies in the subjectivity of individuals’ perception of snoring, making objective quantification of nuisance from PS extremely difficult. Considering the dyadic nature of sleep, recent studies, such as the one by Genlyd et al. on noise exposure, promote the assessment of ‘noise annoyance level’ that include aspects such as ‘daytime sleepiness’ and ‘tiredness’ in the paired comparison.
Currently, to distinguish PS from other sleep disorders, overnight PSG is the only currently available definitive investigation. Diagnosis is made based on clinical history, the number of respiratory events per hour of sleep on PSG, and the corresponding physiological consequences in terms of gas exchange abnormalities and arousals. Some authors choose a composite respiratory disturbance score to diagnose PS based on several factors such as the extent of SpO2 desaturation and respiratory arousals.,
| Risk Factors of HS and PS Progression|| |
To the best of our knowledge, no studies have evaluated the risk factors of PS thus far. Studies reporting risk factors for HS may provide clues for the predictor of PS development. A large cohort across the Asia Pacific showed a higher prevalence of HS in males and Caucasians, most probably due to their genetically determined craniofacial structure. Nonetheless, prematurely born children may be at a higher risk for snoring and SDB as well. Additionally, the severity can be made significantly lower by breastfeeding for at least 2 months according to one study.
Studies examining the natural history of PS are also scarce. Whether PS is associated with the development of other more severe sleep disorders, for example, OSA remains unclear. In a community-based follow-up study by Li et al, persistent snoring and overweight or obesity were found to be the risk factors for PS progression. Persistent snoring, with its relatively high negative predictive value, can hence be used as a guide for SDB progression. Meanwhile, weight reduction may play an important role in the management of PS. In addition, puberty has no significant effect on PS progression, suggesting that changes in sex hormones were not a primary modulator of upper airway function during puberty. Neither sex nor adenotonsillar hypertrophy was identified as a significant predictor.
| Cardiovascular Impacts of PS|| |
Emerging evidence has shown that childhood PS has adverse effects on the cardiovascular system, rendering the need to identify and treat as soon as possible.
A local cross-sectional study by Li et al. published in 2009 was among the very few who first provided evidence on the potential cardiovascular risks in PS children. By demonstrating that PS was an aspect of the dose-response relationship between SDB and blood pressure (BP), it provided a new insight contrary to the universal belief that PS was entirely benign. Nighttime BP particularly was found to be significantly higher in the PS cohort after adjusting for age, sex, and body mass index (BMI). The findings carry prominent significance in the sense that elevated childhood BP is associated with increased carotid intima-media thickness (cIMT) and arterial thickness, which are the preceding markers of atherosclerosis. With a similar elevation in BP level during childhood, it predicts a worse prognosis of future cardiovascular adverse events, adult hypertension, and metabolic syndrome.
The association between PS and endothelial function was first proposed by the same author in 2011, which showed a significantly reduced flow-mediated vasodilation (FMD) among PS children independent of body size and OAHI. Unlike OSA, the mechanism underlying PS and impaired endothelial function is not associated with hypoxia, oxidative stress, and frequent arousals, as reflected by the insignificant differences in all respiratory parameters, arousal indexes, and sleep architecture between PS and controls in the same study. These results, inspiringly, provided grounds on the possibility that PS may not simply be a milder form of OSA, but a part of a more complex phenotype that is yet to be determined.
The causal association between childhood PS and undesirable cardiovascular outcomes is further supported by a recent longitudinal study by Au et al. Predictive markers of cardiovascular disease (CVD), namely reduced FMD, increased cIMT, and elevated BP remained significant at 5-year follow-up of PS subjects aged 6 to 18 irrespective to the change of OSA severity. Strategies to alleviate upper airway narrowing and the resultant CVD burden should, therefore, not be overlooked. Though a proven treatment for childhood snoring is not currently available besides nasal steroids,, the study highlighted the clinical importance of regular monitoring for children with PS on their SDB and cardiovascular status.
| Neurocognitive and Behavioral Impacts of PS|| |
There is growing evidence that children with PS exhibit cognitive and behavioral deficits equivalent to children with OSA when compared to non-snoring controls.,
In a pioneer study by Blunden et al. published in 2000, a significant difference in cognitive functioning was accidentally found between snoring children and controls. The unexpected finding sparked much intrigue surrounding the morbidity of PS. Subsequently, cognitive outcomes, such as IQ score, memory, attention, executive function, organization ability, motor coordination, verbal ability, and fluency, were investigated by various studies.,,, The observation of deficit in PS children is not universal. It is noted that in the majority of studies, results of cognitive assessment in PS subjects, even if found to be significantly lower than controls, still fall within normative limits. This highlights that whether snoring is associated with cognitive impairment later in life still requires further investigation. However, the adverse effect of PS on cognitive functioning is still undeniable if we compare the percentage of PS children labelled with impaired cognition and those who are carefully matched to control.
Studies have consistently shown behavioral impairment in children with PS., Most commonly reported deficits include hyperactivity, inattention, and somatic complaints. A surprising finding was found in the Jackman et al. study in which the PS group exhibited the greatest deficit in a majority of the behavioral domains, followed by the mild OSA group. Another cross-sectional study by Brockman et al. also reported that children with PS had a higher risk of inattentive behavior than those with OSA. A 10-fold increase in sleepiness was observed as well in PS children compared to a 5-fold increase in the OSA group. All evidence seems to be hinting that PS may not simply be a milder form of OSA at the SDB spectrum.
| Proposed Mechanistic Pathways|| |
Currently, the clinical outcomes of OSA are explained by the hypoxic insult to the developing brain and sleep disruption due to repeated arousals. There has been an endeavor to evaluate if those physiological stresses also account for the deficit in PS. However, current data cannot depict the association. It is possible that the subtle differences in oxygen level and sleep parameters could be missed using the conventional protocol. Measures of cerebral oxygenation in response to a respiratory event may be inaccurately reflected at the periphery and that excessive daytime sleepiness may not be a fit measurement for arousals. More objective assessments, such as differences in cerebral blood flow velocity and sleep latency test, may hence be required for further investigation.
Some of the neurocognitive and cardiovascular impacts of PS, nonetheless, can be explained by a large community-based study by Zhu et al. in 2014 consisting of 619 subjects. Compared to non-snoring children, the percentage of slow-wave sleep (SWS) decreased significantly in the prepubertal PS group. SWS is associated with better neurocognitive functioning. Meanwhile, the percentage of non-rapid eye movement stage 1 (N1) sleep as well as wake after sleep onset (WASO), a representation of sleep deficiency, were both significantly elevated in the pubertal sub-group. With less N1 sleep, impacted learning and memory are explained. Along with a study by Zhang et al. which showed the direct correlation between lower sleep efficiency (i.e. higher WASO) and increased sympathetic activity as reflected by a higher 24-hour urinary catecholamine level, the critical role of PS in mediating cardiovascular complications is also conjointly manifested.
| Treatment of PS|| |
PS management can be conservative or non-conservative, depending on the associated underlying conditions. For snorers with obesity and orofacial myofunctional disorders (OMDs), for instance, weight loss and myofunctional therapy would be the first-line treatment respectively. The AASM also recommends oral appliance (OA) therapy for PS in general. There is currently no consensus on the optimal design of OAs but the therapeutic outcome in term of AHI and oxygen desaturation index (ODI) appear to be better if the device is custom-made. It is worth noted that OAs, though effective, are associated with low compliance. Meanwhile, surgical approaches like uvulopalatopharyngoplasty (UPPP) and adenotonsillectomy, though radical, are also available for patients with associated obstructed upper airway due to craniofacial anomalies as well as adenotonsillar hypertrophy. Till date, there are no drugs available for treating the primary pathology of PS.
| Conclusion|| |
PS is a relatively common sleep disorder amongst the paediatric population. Although the original definition aims to delineate PS from OSA based on the absence of clinical consequences, increasing evidence revealed that snoring, even without associated changes in respiratory markers, may be associated with extensive cardiovascular and neurocognitive outcomes. More studies are required to elucidate the effects of PS on various disease development and appropriate action may be required to prevent these adverse outcomes.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Li AM, Sadeh A, Au CT, Goh DY, Mindell JA. Prevalence of habitual snoring and its correlates in young children across the Asia pacific. J Paediatr Child Health 2013;49:E153-9.
Li AM, So HK, Au CT, Ho C, Lau J, Ng SK, et al
. Epidemiology of obstructive sleep apnoea syndrome in Chinese children: A two-phase community study. Thorax 2010;65:991-7.
Marcus CL. Sleep-disordered breathing in children. Am J Respir Crit Care Med 2001;164:16-30.
Anstead M, Phillips B. The spectrum of sleep-disordered breathing. Respir Care Clin N Am 1999;5:363-77, viii.
Marcus CL, Brooks LJ, Draper KA, Gozal D, Halbower AC, Jones J, et al
; American Academy of Pediatrics. Diagnosis and management of childhood obstructive sleep apnea syndrome. Pediatrics 2012;130:e714-55.
Horne RSC. Childhood snoring has long-term adverse effects on cardiovascular health. Respirology 2021;26:725-6.
De Meyer MMD, Jacquet W, Vanderveken OM, Marks LAM. Systematic review of the different aspects of primary snoring. Sleep Med Rev 2019;45:88-94.
Medicine AAoS. International classification of sleep disorders. Diagnostic and coding manual 2005:51-5.
Sateia MJ. International classification of sleep disorders-third edition: Highlights and modifications. Chest 2014;146:1387-94.
Kryger MH. Sleep and Breathing Disorders. E-Book. Elsevier Health Science; 2016. pp. 126-39.
Michael H, Andreas S, Thomas B, Beatrice H, Werner H, Holger K. Analysed snoring sounds correlate to obstructive sleep disordered breathing. European Archives of Oto-Rhino-Laryngology 2008;265:105-13.
Peterson TH. The “Genlyd” Noise Annoyance Model. Delta Report, 2007.
O’Brien LM, Mervis CB, Holbrook CR, Bruner JL, Klaus CJ, Rutherford J, et al
. Neurobehavioral implications of habitual snoring in children. Pediatrics 2004;114:44-9.
Honaker SM, Gozal D, Bennett J, Capdevila OS, Spruyt K. Sleep-disordered breathing and verbal skills in school-aged community children. Dev Neuropsychol 2009;34:588-600.
Montgomery-Downs HE, Crabtree VM, Sans Capdevila O, Gozal D. Infant-feeding methods and childhood sleep-disordered breathing. Pediatrics 2007;120:1030-5.
Li AM, Zhu Y, Au CT, Lee DLY, Ho C, Wing YK. Natural history of primary snoring in school-aged children: A 4-year follow-up study. Chest 2013;143:729-35.
Deary V, Ellis JG, Wilson JA, Coulter C, Barclay NL. Simple snoring: Not quite so simple after all? Sleep Med Rev 2014;18:453-62.
Li AM, Au CT, Ho C, Fok TF, Wing YK. Blood pressure is elevated in children with primary snoring. J Pediatr 2009;155:362-8.e1.
Li S, Chen W, Srinivasan SR, Bond MG, Tang R, Urbina EM, et al
. Childhood cardiovascular risk factors and carotid vascular changes in adulthood: The Bogalusa heart study. JAMA 2003;290:2271-6.
Verdecchia P, Schillaci G, Borgioni C, Ciucci A, Battistelli M, Bartoccini C, et al
. Adverse prognostic significance of concentric remodeling of the left ventricle in hypertensive patients with normal left ventricular mass. J Am Coll Cardiol 1995;25:871-8.
Li AM, Au CT, Chook P, Lam HS, Wing YK. Reduced flow-mediated vasodilation of brachial artery in children with primary snoring. Int J Cardiol 2013;167:2092-6.
Au CT, Chan KC, Chook P, Wing YK, Li AM. Cardiovascular risks of children with primary snoring: A 5-year follow-up study. Respirology 2021;26:796-803.
Vlahandonis A, Walter LM, Horne RS. Does treatment of Sdb in children improve cardiovascular outcome? Sleep Med Rev 2013;17:75-85.
Leung TN, Cheng JW, Chan AK. Paediatrics: How to manage obstructive sleep apnoea syndrome. DIC 2021;10:1-14.
Bourke R, Anderson V, Yang JS, Jackman AR, Killedar A, Nixon GM, et al
. Cognitive and academic functions are impaired in children with all severities of sleep-disordered breathing. Sleep Med 2011;12:489-96.
Miano S, Paolino MC, Urbano A, Parisi P, Massolo AC, Castaldo R, et al
. Neurocognitive assessment and sleep analysis in children with sleep-disordered breathing. Clin Neurophysiol 2011;122:311-9.
Blunden S, Lushington K, Kennedy D, Martin J, Dawson D. Behavior and neurocognitive performance in children aged 5–10 years who snore compared to controls. J Clin Exp Neuropsyc 2000;22:554-68.
Beebe DW, Wells CT, Jeffries J, Chini B, Kalra M, Amin R. Neuropsychological effects of pediatric obstructive sleep apnea. J Int Neuropsychol Soc 2004;10:962-75.
O’Brien L, Mervis C, Holbrook C, Bruner J, Klaus C, Rutherford J, et al
. Neurobehavioral implications of habitual snoring in children. Pediatrics 2004;114:44-9.
Beebe DW, Ris MD, Kramer ME, Long E, Amin R. The association between sleep disordered breathing, academic grades, and cognitive and behavioral functioning among overweight subjects during middle to late childhood. Sleep 2010;33:1447-56.
Biggs SN, Nixon GM, Horne RS. The conundrum of primary snoring in children: What are we missing in regards to cognitive and behavioural morbidity? Sleep Med Rev 2014;18:463-75.
Jackman AR, Biggs SN, Walter LM, Embuldeniya US, Davey MJ, Nixon GM, et al
. Sleep-disordered breathing in preschool children is associated with behavioral, but not cognitive, impairments. Sleep Med 2012;13:621-31.
Brockmann PE, Urschitz MS, Schlaud M, Poets CF. Primary snoring in school children: Prevalence and neurocognitive impairments. Sleep Breath 2012;16:23-9.
Halbower AC, Mahone EM. Neuropsychological morbidity linked to childhood sleep-disordered breathing. Sleep Med Rev 2006;10:97-107.
Hill CM, Hogan AM, Onugha N, Harrison D, Cooper S, McGrigor VJ, et al
. Increased cerebral blood flow velocity in children with mild sleep-disordered breathing: A possible association with abnormal neuropsychological function. Pediatrics 2006;118:e1100-8.
Gozal D, Wang M, Pope DW Jr. Objective sleepiness measures in pediatric obstructive sleep apnea. Pediatrics 2001;108:693-7.
Zhu Y, Au CT, Lam HS, Chan CC, Ho C, Wing YK, et al
. Sleep architecture in school-aged children with primary snoring. Sleep Med 2014;15:303-8.
Kaemingk KL, Pasvogel AE, Goodwin JL, Mulvaney SA, Martinez F, Enright PL, et al
. Learning in children and sleep disordered breathing: Findings of the tucson children’s assessment of sleep apnea (tucasa) prospective cohort study. J Int Neuropsychol Soc 2003;9:1016-26.
Zhang J, Ma RC, Kong AP, So WY, Li AM, Lam SP, et al
. Relationship of sleep quantity and quality with 24-hour urinary catecholamines and salivary awakening cortisol in healthy middle-aged adults. Sleep 2011;34:225-33.
Camacho M, Guilleminault C, Wei JM, Song SA, Noller MW, Reckley LK, et al
. Oropharyngeal and tongue exercises (myofunctional therapy) for snoring: A systematic review and meta-analysis. Eur Arch Otorhinolaryngol 2018;275:849-55.
Ramar K, Dort L, Katz S, Lettieri C, Harrod C, Thomas S, et al
. Clinical practice guideline for the treatment of obstructive sleep apnea and snoring with oral appliance therapy: An update for 2015. J Clin Sleep Med 2015;11:773-827.
Ilea A, Timuș D, Höpken J, Andrei V, Băbțan AM, Petrescu NB, et al
. Oral appliance therapy in obstructive sleep apnea and snoring - systematic review and new directions of development. Cranio 2021;39:472-83.
De Meyer MMD, Vanderveken OM, De Weerdt S, Marks LAM, Cárcamo BA, Chavez AM, et al
. Use of mandibular advancement devices for the treatment of primary snoring with or without obstructive sleep apnea (Osa): A systematic review. Sleep Med Rev 2021;56:101407.
Achuthan S, Medhi B. A systematic review of the pharmacological approaches against snoring: Can we count on the chickens that have hatched? Sleep Breath 2015;19:1035-42.