Is acoustic analysis of snoring an alternative to sleep nasendoscopy?

Prediction of the obstruction sites in the upper airway in sleep-disordered breathing based on snoring sound parameters: a systematic review

BACKGROUND

Identification of the obstruction site in the upper airway may help in treatment selection for patients with sleep-disordered breathing. Because of limitations of existing techniques, there is a continuous search for more feasible methods. Snoring sound parameters were hypothesized to be potential predictors of the obstruction site. Therefore, this review aims to i) investigate the association between snoring sound parameters and the obstruction sites; and ii) analyze the methodology of reported prediction models of the obstruction sites.

METHODS

The literature search was conducted in PubMed, Embase.com, CENTRAL, Web of Science, and Scopus in collaboration with a medical librarian. Studies were eligible if they investigated the associations between snoring sound parameters and the obstruction sites, and/or reported prediction models of the obstruction sites based on snoring sound.

RESULTS

Of the 1016 retrieved references, 28 eligible studies were included. It was found that the characteristic frequency components generated from lower-level obstructions of the upper airway were higher than those generated from upper-level obstructions. Prediction models were built mainly based on snoring sound parameters in frequency domain. The reported accuracies ranged from 60.4% to 92.2%.

CONCLUSIONS

Available evidence points toward associations between the snoring sound parameters in the frequency domain and the obstruction sites in the upper airway. It is promising to build a prediction model of the obstruction sites based on snoring sound parameters and participant characteristics, but so far snoring sound analysis does not seem to be a viable diagnostic modality for treatment selection.

Sound frequency spectra of snore in relation to the site of obstruction among snorers

Objective

This study aimed to describe the sound frequency of snoring in relation to the site of upper airway vibration among snorers.

Methods

383 snores from 40 participants who complained of snoring were digitally recorded during natural and induced sleep using a level III polysomnography monitor with a built-in microphone. During drug-induced sleep endoscopy (DISE), the real-time site of upper airway obstruction was assessed, and the sound frequency of snoring was recorded synchronously.

Results

The mean peak of snoring frequency for unilevel palatal, oropharynx and epiglottis obstruction were 522.5, 482.4 and 300.0 Hz, respectively. Most participants showed multilevel obstruction at the palate and oropharynx, in which the mean for bi-peak snoring frequency were 402.90 Hz and 1086.96 Hz, respectively. Severity of OSA was significantly associated with multilevel obstruction.

Conclusions

There was a significant association between the snoring sound frequency and site of unilevel obstruction. Palatal or oropharyngeal obstruction produced sound at mid-frequency range, while the epiglottis produced a low frequency range. Multilevel obstruction documented a bi-peak snoring frequency.

Can Machine Learning Assist Locating the Excitation of Snore Sound? A Review

In the past three decades, snoring (affecting more than 30 % adults of the UK population) has been increasingly studied in the transdisciplinary research community involving medicine and engineering. Early work demonstrated that, the snore sound can carry important information about the status of the upper airway, which facilitates the development of non-invasive acoustic based approaches for diagnosing and screening of obstructive sleep apnoea and other sleep disorders. Nonetheless, there are more demands from clinical practice on finding methods to localise the snore sound's excitation rather than only detecting sleep disorders. In order to further the relevant studies and attract more attention, we provide a comprehensive review on the state-of-the-art techniques from machine learning to automatically classify snore sounds. First, we introduce the background and definition of the problem. Second, we illustrate the current work in detail and explain potential applications. Finally, we discuss the limitations and challenges in the snore sound classification task. Overall, our review provides a comprehensive guidance for researchers to contribute to this area.

A review on drug-induced sedation endoscopy - Technique, grading systems and controversies

Sleep disordered breathing (SDB) comprises a spectrum of disorders, ranging from simple snoring to severe obstructive sleep apnoea (OSA), with a significant burden to health care systems in high income countries. If left untreated, OSA has significant cumulative, long-term health consequences. In the 1990s drug induced sedation endoscopy (DISE) has been developed to become a primary tool in the diagnosis and management of OSA. It allows meticulous endoscopic evaluation of the airway and identifies areas of collapse, thereby informing both on the selection of surgical techniques, where efficacy depends entirely on success at relieving obstruction at a certain level and on the usefulness of conservative measures, such as mandibular advancement splints. This article provides a review of the literature on DISE, covering different grading systems and techniques, explaining different rationales and discussing controversies.

Numerical study of dynamic glottis and tidal breathing on respiratory sounds in a human upper airway model

BACKGROUND

Human snores are caused by vibrating anatomical structures in the upper airway. The glottis is a highly variable structure and a critical organ regulating inhaled flows. However, the effects of the glottis motion on airflow and breathing sound are not well understood, while static glottises have been implemented in most previous in silico studies. The objective of this study is to develop a computational acoustic model of human airways with a dynamic glottis and quantify the effects of glottis motion and tidal breathing on airflow and sound generation.

METHODS

Large eddy simulation and FW-H models were adopted to compute airflows and respiratory sounds in an image-based mouth-lung model. User-defined functions were developed that governed the glottis kinematics. Varying breathing scenarios (static vs. dynamic glottis; constant vs. sinusoidal inhalations) were simulated to understand the effects of glottis motion and inhalation pattern on sound generation. Pressure distributions were measured in airway casts with different glottal openings for model validation purpose.

RESULTS

Significant flow fluctuations were predicted in the upper airways at peak inhalation rates or during glottal constriction. The inhalation speed through the glottis was the predominating factor in the sound generation while the transient effects were less important. For all frequencies considered (20-2500 Hz), the static glottis substantially underestimated the intensity of the generated sounds, which was most pronounced in the range of 100-500 Hz. Adopting an equivalent steady flow rather than a tidal breathing further underestimated the sound intensity. An increase of 25 dB in average was observed for the life condition (sine-dynamic) compared to the idealized condition (constant-rigid) for the broadband frequencies, with the largest increase of approximately 40 dB at the frequency around 250 Hz.

CONCLUSION

Results show that a severely narrowing glottis during inhalation, as well as flow fluctuations in the downstream trachea, can generate audible sound levels.

Spectral analysis of snoring events from an Emfit mattress

The aim of this study is to explore the capability of an Emfit (electromechanical film transducer) mattress to detect snoring (SN) by analyzing the spectral differences between normal breathing (NB) and SN. Episodes of representative NB and SN of a maximum of 10 min were visually selected for analysis from 33 subjects. To define the bands of interest, we studied the statistical differences in the power spectral density (PSD) between both breathing types. Three bands were selected for further analysis: 6-16 Hz (BW1), 16-30 Hz (BW2) and 60-100 Hz (BW3). We characterized the differences between NB and SN periods in these bands using a set of spectral features estimated from the PSD. We found that 15 out of the 29 features reached statistical significance with the Mann-Whitney U-test. Diagnostic properties for each feature were assessed using receiver operating characteristic analysis. According to our results, the highest diagnostic performance was achieved using the power ratio between BW2 and BW3 (0.85 area under the receiver operating curve, 80% sensitivity, 80% specificity and 80% accuracy). We found that there are significant differences in the defined bands between the NB and SN periods. A peak was found in BW3 for SN epochs, which was best detected using power ratios. Our work suggests that it is possible to detect snoring with an Emfit mattress. The mattress-type movement sensors are inexpensive and unobtrusive, and thus provide an interesting tool for sleep research.

Snoring Significance in Patients Undergoing Home Sleep Studies

OBJECTIVE: To analyze the impact of snoring, independent of obstructive sleep apnea syndrome on patients referred for home sleep studies and to report a new technology for the reporting of snoring, using sophisticated sound collection and noise-canceling technology.

STUDY DESIGN AND SETTING: A retrospective statistical review of consecutive anonymous data compiled from questionnaires and digital data of snoring loudness and duration measured at the upper lip during unattended home sleep studies in 4,860 patients referred for snoring and sleep-disturbed breathing.

RESULTS: A strong relationship exists between a history of snoring and complaints of daytime sleepiness (80%), obesity (73%), and chronic fatigue (78%) (all yield P < 0.001). By contrast, only 42% to 48% of patients without these symptoms complain of snoring. In 3 multiple-regression analyses, the percent of time snoring, average loudness, and peak loudness are all significantly predicted by the apnea hypopnea index (all P < 0.003), body mass index (all P < 0.001), and age ( P = 0.014). Daytime sleepiness was strongly predicted by percent time snoring ( P = 0.014), weakly by average loudness ( P = 0.046), and not at all by peak loudness (P = 0.303).

CONCLUSION: By using a pair of microphones placed at the upper lip, one that samples breath sounds and the other ambient sound and artifact noise, the NovaSOM QSG measures snoring while canceling ambient noise. The clinical impact of snoring on the patient as well as the bed partner, independent of obstructive sleep apnea syndrome, is an unrecognized factor in sleep-disturbed breathing.

SIGNIFICANCE: Measurable criteria to define snoring are suggested. Snoring loudness is not measured in most laboratory Polysomnograms.

EBM rating: B-3b

Evaluation of acoustic characteristics of snoring sounds obtained during drug-induced sleep endoscopy

INTRODUCTION

Snoring sounds are discussed to contain acoustic information about their geneses. Nocturnal snoring can easily be recorded acoustically but it is difficult to visually verify its genesis. Contrary, snoring patterns induced by drug-induced sleep endoscopy (DISE) can be visually differentiated. The aim of the study was to classify patterns of obstructions and vibration during DISE and to evaluate acoustic characteristics between these different patterns of snoring.

METHODS

DISE was performed in 41 male patients with sleep-disordered breathing. The recorded video sequences (n = 108) were classified visually at a mute mode in different patterns of snoring (velar, velar obstructive, tonsillar, post-apnoeic). The sound tracks of these subgroups were analysed and compared with regard to the parameters sound pressure level, loudness, sharpness, roughness, fluctuations strength and centre frequency.

RESULTS

Obstructive snoring patterns revealed a higher loudness than non-obstructive patterns (>25 sone). Velar snoring showed more roughness (>150 cAsper) than tonsillar and post-apnoeic snoring and revealed the lowest centre frequency (<3000 Hz) of all patterns. Tonsillar snoring presented the highest sharpness (>1.6 acum) whereas post-apnoeic snoring revealed the largest fluctuation strength (>50 cVacil).

CONCLUSION

Different snoring patterns induced by DISE can be classified visually, and an approach to differentiate them acoustically by means of psychoacoustic analyses is demonstrated. On the basis of these results, nocturnal snoring might also be differentiated by psychoacoustic algorithms which could be implemented in acoustic polygraphic screening devices in the future.

[Sk2 guidelines"diagnosis and therapy of snoring in adults" : compiled by the sleep medicine working group of the German Society of Otorhinolaryngology, Head and Neck Surgery]

These guidelines aim to facilitate high quality medical care of adults with snoring problems. The guidelines were devised for application in both in- and outpatient environments and are directed primarily at all those concerned with the diagnosis and therapy of snoring. According to the AWMF three-level concept, these represent S2k guidelines.A satisfactory definition of snoring does not currently exist. Snoring is the result of vibration of soft tissue structures in narrow regions of the upper airway during breathing while asleep. Ultimately, these vibrations are caused by the sleep-associated decrease in muscle tone in the area of the upper airway dilator muscles. A multitude of risk factors for snoring have been described and its occurrence is multifactorial. Data relating to the frequency of snoring vary widely, depending on the way in which the data are collected. Snoring is usually observed in middle-aged individuals and affected males predominate. Clinical diagnosis of snoring should comprise a free evaluation of the patient's medical history. Where possible this should also involve their bed partner and the case history can be complimented by questionnaires. To determine the airflow relevant structures, a clinical examination of the nose should be performed. This examination may also include nasal endoscopy. Examination of the oropharynx is particularly important and should be performed. The larynx and the hypopharynx should be examined. The size of the tongue and the condition of the mucous membranes should be recorded as part of the oral cavity examination, as should the results of a dental assessment. Facial skeleton morphology should be assessed for orientation purposes. Technical examinations may be advisable in individual cases. In the instance of suspected sleep-related breathing disorders, relevant comorbidities or where treatment for snoring has been requested, an objective sleep medicine examination should be performed. Snoring is not-at least as we currently understand it-a disease associated with a medical threat; therefore there is currently no medical necessity to treat the condition. All overweight patients with snoring problems should strive to lose weight. If snoring is associated with the supine position, positional therapy can be considered. Some cases of snoring can be appropriately treated using an intraoral device. Selected minimally invasive surgical procedures on the soft palate can be recommended to treat snoring, provided that examinations have revealed a suitable anatomy. The choice of technique is determined primarily by the individual anatomy. At an appropriate interval after the commencement or completion a therapeutic measure, a follow-up examination should be conducted to assess the success of the therapy and to aid in the planning of any further treatments.

European position paper on drug-induced sedation endoscopy (DISE)

BACKGROUND

Although drug-induced sedation endoscopy (DISE) represents the most widespread diagnostic tool for upper airway endoscopic evaluation of snoring and obstructive sleep apnea hypopnea syndrome (OSAHS), many controversies exist about how to perform the sedation, the indications for DISE, and how to report DISE findings. The present position paper reports on a consensus as proposed by a group of European experts in the field of DISE after discussion during a recent dedicated meeting.

METHODS

The authors have evaluated all the available evidence reported in the literature and have compared experience among various departments in leading European centers in order to provide a standardization of the DISE procedure and an in-depth insight in the main aspects of this technique.

RESULTS

A proposal of the DISE procedure standardization has been achieved with a general agreement concerning the terminology, indications, contraindications, required preliminary examinations, setting, technical equipment required, staffing, local anesthesia and nasal decongestion, patient positioning, basis and special diagnostic maneuvers, and the applied sedation drugs and observation windows. Otherwise, no consensus has been reached on a scoring and classification system.

CONCLUSIONS

Although consensus has been reached on several aspects of the DISE procedure, some topics remain open to future research, such as a better analysis of the importance of positional aspects during DISE and a further comparison of the differences in degree, level and pattern of upper airway collapse observed during DISE versus during natural sleep and awake endoscopy. Finally, a universally accepted scoring and classification system is lacking.

Modeling the pharyngeal anatomical effects on breathing resistance and aerodynamically generated sound

The objective of this study was to systematically assess the effects of pharyngeal anatomical details on breathing resistance and acoustic characteristics by means of computational modeling. A physiologically realistic nose-throat airway was reconstructed from medical images. Individual airway anatomy such as the uvula, pharynx, and larynx was then isolated for examination by gradually simplifying this image-based model geometry. Large eddy simulations with the FW-H acoustics model were used to simulate airflows and acoustic sound generation with constant flow inhalations in rigid-walled airway geometries. Results showed that pharyngeal anatomical details exerted a significant impact on breathing resistance and energy distribution of acoustic sound. The uvula constriction induced considerably increased levels of pressure drop and acoustic power in the pharynx, which could start and worsen snoring symptoms. Each source anatomy was observed to generate a unique spectrum with signature peak frequencies and energy distribution. Moreover, severe pharyngeal airway narrowing led to an upward shift of sound energy in the high-frequency range. Results indicated that computational aeroacoustic modeling appeared to be a practical tool to study breathing-related disorders. Specifically, high-frequency acoustic signals might disclose additional clues to the mechanism of apneic snoring and should be included in future acoustic studies.

Diagnosis and treatment of snoring in adults-S2k Guideline of the German Society of Otorhinolaryngology, Head and Neck Surgery

OBJECTIVES

This guideline aims to promote high-quality care by medical specialists for subjects who snore and is designed for everyone involved in the diagnosis and treatment of snoring in an in- or outpatient setting.

DISCUSSION

To date, a satisfactory definition of snoring is lacking. Snoring is caused by a vibration of soft tissue in the upper airway induced by respiration during sleep. It is triggered by relaxation of the upper airway dilator muscles that occurs during sleep. Multiple risk factors for snoring have been described and snoring is of multifactorial origin. The true incidence of snoring is not clear to date, as the incidence differs throughout literature. Snoring is more likely to appear in middle age, predominantly in males. Diagnostic measures should include a sleep medical history, preferably involving an interview with the bed partner, and may be completed with questionnaires. Clinical examination should include examination of the nose to evaluate the relevant structures for nasal breathing and may be completed with nasal endoscopy. Evaluation of the oropharynx, larynx, and hypopharynx should also be performed. Clinical assessment of the oral cavity should include the size of the tongue, the mucosa of the oral cavity, and the dental status. Furthermore, facial skeletal morphology should be evaluated. In select cases, technical diagnostic measures may be added. Further objective measures should be performed if the medical history and/or clinical examination suggest sleep-disordered breathing, if relevant comorbidities are present, and if the subject requests treatment for snoring. According to current knowledge, snoring is not associated with medical hazard, and generally, there is no medical indication for treatment. Weight reduction should be achieved in every overweight subject who snores. In snorers who snore only in the supine position, positional treatment can be considered. In suitable cases, snoring can be treated successfully with intraoral devices. Minimally invasive surgery of the soft palate can be considered as long as the individual anatomy appears suitable. Treatment selection should be based on individual anatomic findings. After a therapeutic intervention, follow-up visits should take place after an appropriate time frame to assess treatment success and to potentially indicate further intervention.

[Drug-induced sleep videoendoscopy: clinical usefulness and literature review]

Fiberoptic examination of the pharynx under drug-induced sleep is a test that helps to detect the areas of vibration and collapse in patients with sleep-disordered breathing. This article is a review of the available literature on the subject, aimed at helping otolaryngologists to understand the procedure and to resolve some controversies surrounding it.

Evaluation of upper airway obstruction in snoring patients using digital video stroboscopy

Stroboscopy is routinely used in voice disorder clinics but its use in studying the mechanisms of upper airway obstruction in patients who snore has not yet been described. This study combines the use of stroboscopy during sleep nasendoscopy to evaluate the oscillations and vibrations observed during snoring in slow motion. In addition, we utilised the multi-dimensional voice programme simultaneously to study some of the acoustic parameters of snoring whilst visualising the dynamics of the upper airway. Forty-five patients with primary snoring or mild obstructive sleep apnoea were recruited at two different centres and underwent sleep nasendoscopy. The simultaneous use of acoustic analysis was included to ascertain whether sound analysis alone could replace the need for using the sedation endoscopy in these patients. The use of a stroboscopic light source indeed enhanced the visualisation during the procedure and some subtle aspects of the mechanisms of upper airway obstruction, such as vibrations of the posterior pharyngeal wall and mucosal waves were identified. Most of the patients in this study exhibited multilevel obstruction and thus acoustic analysis alone would not be sufficient in accurately locating the site of upper airway obstruction in snorers.

Acoustical flow estimation in patients with obstructive sleep apnea during sleep

Tracheal respiratory sound analysis is a simple and non-invasive way to study the pathophysiology of the upper airways; it has recently been used for acoustical flow estimation and sleep apnea diagnosis. However in none of the previous studies, the accuracy of acoustical flow estimation was investigated neither during sleep nor in people with obstructive sleep apnea (OSA). In this study, we recorded tracheal sound, flow rate and head position from 11 individuals with OSA during sleep and wakefulness. We investigated two approaches for calibrating the parameters of acoustical flow estimation model based on the known data recorded during wakefulness and sleep. The results show that the acoustical flow estimation parameters change from wakefulness to sleep. Therefore, if the model is calibrated based on the data recorded during wakefulness, although the estimated flow follows the relative variations of the recorded flow, the quantitative flow estimation error would be high during sleep. On the other hand, when the calibration parameters are extracted from tracheal sound and flow recordings during sleep, the flow estimation error is less than 5%. These results confirm the reliability of acoustical methods for estimating breathing flow during sleep and detecting the partial or complete obstructions of the upper airways during sleep.

Acoustic characteristics of snoring according to obstruction site determined by sleep videofluoroscopy

CONCLUSION

Acoustic characteristics of snoring sound, such as pitch and formant, differed according to the site of upper airway obstruction determined by sleep videofluoroscopy (SVF). Snoring sound analysis can complement determination of the site of obstruction in snoring and sleep apnea patients.

OBJECTIVES

The aim of this study was to evaluate the acoustic characteristics of snoring according to obstruction site determined by SVF.

METHODS

Ninety patients who underwent simultaneous snoring sound recording during SVF were included in this study. Acoustic parameters of snoring such as pitch (min, mean, max) and formant (1,2) were analyzed. Site of obstruction was determined by SVF and classified according to anatomic structure and level of obstruction.

RESULTS

Mean value of peak frequency showed significant difference between soft palate and isolated tongue base or epiglottis obstruction and combined obstruction involving soft palate and tongue base or epiglottis. Peak frequency of velopharyngeal obstruction showed difference only with hypopharyngeal obstruction. First formant showed similar results in the structure classification whereas velopharyngeal obstruction showed significant difference compared with other levels of obstruction. Other parameters (intensity, jitter, shimmer) did not show significance according to site of obstruction.

One hundred consecutive patients undergoing drug-induced sleep endoscopy: results and evaluation

OBJECTIVES/HYPOTHESIS

Polysomnography (PSG) is mandatory in the diagnostic workup of obstructive sleep apnea (OSA); drug-induced sleep endoscopy (DISE) is a valid addition. DISE is a dynamic, safe, easy-to-perform technique that visualizes the anatomic sites of snoring or apneas and guides the making of a tailor-made treatment plan in individual cases. The aim of this prospective study was to document the results of 100 consecutive DISE procedures and investigate associations between PSG and DISE findings.

STUDY DESIGN

This prospective, single-center, observational study enrolled 100 consecutive patients between June and August 2010.

METHODS

All 100 patients eligible for sleep surgery or a mandibular repositioning appliance (MRA) underwent PSG and DISE (using midazolam or propofol). DISE findings were reported using the VOTE classification system; site, degree of airway narrowing, and configuration of obstruction were reported. Associations were analyzed between PSG results, patient characteristics, and DISE findings.

RESULTS

Our results suggest that a multilevel collapse, a complete collapse, and a tongue-base collapse are statistically significantly associated with higher apnea hypopnea index values. A tongue base collapse or epiglottal collapse is associated with positional OSA. Complete concentric collapse is statistically significantly associated with an increased body mass index.

CONCLUSIONS

The results of this small-scale study help us understand the pathogenesis of OSA and the various associations between PSG outcomes and DISE results, as well as assisting the sleep surgeon in tailoring surgery for the patient.

Continuous analysis and monitoring of snores and their relationship to the apnea-hypopnea index

OBJECTIVES/HYPOTHESIS

We used a new automatic snoring detection and analysis system to monitor snoring during full-night polysomnography to assess whether the acoustic characteristics of snores differ in relation to the apnea-hypopnea index (AHI) and to classify subjects according to their AHI.

STUDY DESIGN

Individual Case-Control Study.

METHODS

Thirty-seven snorers (12 females and 25 males; ages 40-65 years; body mass index (BMI), 29.65 +/- 4.7 kg/m(2)) participated. Subjects were divided into three groups: G1 (AHI <5), G2 (AHI >or=5, <15) and G3 (AHI >or=15). Snore and breathing sounds were recorded with a tracheal microphone throughout 6 hours of nighttime polysomnography. The snoring episodes identified were automatically and continuously analyzed with a previously trained 2-layer feed-forward neural network. Snore number, average intensity, and power spectral density parameters were computed for every subject and compared among AHI groups. Subjects were classified using different AHI thresholds by means of a logistic regression model.

RESULTS

There were significant differences in supine position between G1 and G3 in sound intensity; number of snores; standard deviation of the spectrum; power ratio in bands 0-500, 100-500, and 0-800 Hz; and the symmetry coefficient (P < .03). Patients were classified with thresholds AHI = 5 and AHI = 15 with a sensitivity (specificity) of 87% (71%) and 80% (90%), respectively.

CONCLUSIONS

A new system for automatic monitoring and analysis of snores during the night is presented. Sound intensity and several snore frequency parameters allow differentiation of snorers according to obstructive sleep apnea syndrome severity (OSAS). Automatic snore intensity and frequency monitoring and analysis could be a promising tool for screening OSAS patients, significantly improving the managing of this pathology.

Assessment of obstruction level and selection of patients for obstructive sleep apnoea surgery: an evidence-based approach

Introduction:

Obstructive sleep apnoea has long been recognised as a clinical syndrome; however, high quality evidence on the effects of surgery for this condition is still missing. Despite this, a consensus seems to be evolving, albeit based on limited evidence, that surgery should be offered as a second line treatment to suitable patients with obstructive sleep apnoea.

Aims:

This article aims to assess the different methods of investigating upper airway obstruction in patients with obstructive sleep apnoea, in respect to these methods' relevance to surgical treatment, via a systematic review of the literature.

Methods:

The Cochrane Controlled Trials Register, Medline and EMBASE were searched from 1966 onwards. The search was performed in August 2008. A total of 2001 citations were retrieved.

Results and conclusion:

There is not yet a generally accepted way to assess surgical candidacy based on the level of obstruction. Better organised clinical studies with well defined endpoints are needed. In the meanwhile, it appears that sleep nasendoscopy, acoustic reflectometry and pressure catheters can all provide useful information, and their use may be decided upon based on the experience and resources available in individual departments.

The acoustics of snoring

Snoring is a prevalent disorder affecting 20-40% of the general population. The mechanism of snoring is vibration of anatomical structures in the pharyngeal airway. Flutter of the soft palate accounts for the harsh aspect of the snoring sound. Natural or drug-induced sleep is required for its appearance. Snoring is subject to many influences such as body position, sleep stage, route of breathing and the presence or absence of sleep-disordered breathing. Its presentation may be variable within or between nights. While snoring is generally perceived as a social nuisance, rating of its noisiness is subjective and, therefore, inconsistent. Objective assessment of snoring is important to evaluate the effect of treatment interventions. Moreover, snoring carries information relating to the site and degree of obstruction of the upper airway. If evidence for monolevel snoring at the site of the soft palate is provided, the patient may benefit from palatal surgery. These considerations have inspired researchers to scrutinize the acoustic characteristics of snoring events. Similarly to speech, snoring is produced in the vocal tract. Because of this analogy, existing techniques for speech analysis have been applied to evaluate snoring sounds. It appears that the pitch of the snoring sound is in the low-frequency range (<500 Hz) and corresponds to a fundamental frequency with associated harmonics. The pitch of snoring is determined by vibration of the soft palate, while nonpalatal snoring is more 'noise-like', and has scattered energy content in the higher spectral sub-bands (>500 Hz). To evaluate acoustic properties of snoring, sleep nasendoscopy is often performed. Recent evidence suggests that the acoustic quality of snoring is markedly different in drug-induced sleep as compared with natural sleep. Most often, palatal surgery alters sound characteristics of snoring, but is no cure for this disorder. It is uncertain whether the perceived improvement after palatal surgery, as judged by the bed partner, is due to an altered sound spectrum. Whether some acoustic aspects of snoring, such as changes in pitch, have predictive value for the presence of obstructive sleep apnea is at present not sufficiently substantiated.

Sleep Endoscopy Versus Modified Mallampati Score in Sleep Apnea and Snoring

OBJECTIVES/HYPOTHESIS

The aim of this study is to quantify the correlation between a large tongue classified by the modified Mallampati score (MMS) and obstruction at the tongue base observed during sleep endoscopy in patients with socially unacceptable snoring (SUS) and obstructive sleep apnea syndrome (OSAS).

STUDY DESIGN

Prospective.

METHODS

One hundred twenty-seven patients with obstructive sleep apnea and SUS underwent sleep endoscopy. Patients were classified into four specific groups according to their MMS. After intravenous administration of midazolam, obstructive events in the upper airway were classified. The level of obstruction was expressed as palatal (2), palatal and to a lesser degree base of the tongue/laryngeal level (2), tongue base/laryngeal level and to a lesser degree palatal (3), and tongue base/laryngeal level (3). The degree of correlation between the level of obstruction and the MMS was analyzed by means of Spearman's rank-order correlation.

RESULTS

No linear association between the level of obstruction and MMS could be found. A large tongue (MMS 3 or 4) does not predict obstruction at the base of the tongue. Patients classified as MMS 1 or 2 did not frequently show obstruction at the base of the tongue (9 of 38, 23,6%). The majority of the population showed retropalatal obstruction. A large tongue (MMS 3 or 4) was often accompanied by retropalatal obstruction, 76% of the cases (64 of 89).

CONCLUSIONS

No positive correlation exists between a large tongue and obstruction at tongue base level. In both groups, retropalatal obstruction occurred more often than retrolingual obstruction. Sleep endoscopy provides qualitative insight into important changes during sleep in patients with SUS and OSAS. In addition, anatomic aberrations are clearly visualized in a dynamic setting. Classification of the size of the tongue, as assessed by the MMS, may be of great importance as well.

Is sleep nasendoscopy a valuable adjunct to clinical examination in the evaluation of upper airway obstruction?

The objective of the study is to assess the correlation between outpatient department (OPD) assessment and sleep nasendoscopy (SNE) in treatment planning for sleep related breathing disorders. The study design includes a blinded, cohort study comparing the treatment prediction based on OPD clinical evaluation with SNE in consecutive, adult patients by a single clinician with a specialist interest in snoring related disorders. Patients with moderate to severe obstructive sleep apnoea and those who had undergone previous treatment were excluded. The study was conducted in Royal National Throat, Nose and Ear Hospital, London and Queen's Hospital, Romford. Ninety-four patients were recruited as participants for the study. The main outcome measures include site of obstruction and treatment planning. The results show no significant correlation between the two groups with SNE recommending less surgical intervention and a choice of surgical and non-surgical management in greater number of patients. In conclusion, even in experienced hands, clinical prediction is significantly modified by SNE findings. The addition of SNE to the diagnostic pathway, to assess the three-dimensional dynamic anatomy of the upper airway, provides a valuable adjunct to the OPD assessment of upper airway collapse. This affords the clinician a greater accuracy of diagnosis and the patient a more focussed management strategy with increased choice of modality of treatment.

Investigation of sequential properties of snoring episodes for obstructive sleep apnoea identification

In this paper, 'snore regularity' is studied in terms of the variations of snoring sound episode durations, separations and average powers in simple snorers and in obstructive sleep apnoea (OSA) patients. The goal was to explore the possibility of distinguishing among simple snorers and OSA patients using only sleep sound recordings of individuals and to ultimately eliminate the need for spending a whole night in the clinic for polysomnographic recording. Sequences that contain snoring episode durations (SED), snoring episode separations (SES) and average snoring episode powers (SEP) were constructed from snoring sound recordings of 30 individuals (18 simple snorers and 12 OSA patients) who were also under polysomnographic recording in Gülhane Military Medical Academy Sleep Studies Laboratory (GMMA-SSL), Ankara, Turkey. Snore regularity is quantified in terms of mean, standard deviation and coefficient of variation values for the SED, SES and SEP sequences. In all three of these sequences, OSA patients' data displayed a higher variation than those of simple snorers. To exclude the effects of slow variations in the base-line of these sequences, new sequences that contain the coefficient of variation of the sample values in a 'short' signal frame, i.e., short time coefficient of variation (STCV) sequences, were defined. The mean, the standard deviation and the coefficient of variation values calculated from the STCV sequences displayed a stronger potential to distinguish among simple snorers and OSA patients than those obtained from the SED, SES and SEP sequences themselves. Spider charts were used to jointly visualize the three parameters, i.e., the mean, the standard deviation and the coefficient of variation values of the SED, SES and SEP sequences, and the corresponding STCV sequences as two-dimensional plots. Our observations showed that the statistical parameters obtained from the SED and SES sequences, and the corresponding STCV sequences, possessed a strong potential to distinguish among simple snorers and OSA patients, both marginally, i.e., when the parameters are examined individually, and jointly. The parameters obtained from the SEP sequences and the corresponding STCV sequences, on the other hand, did not have a strong discrimination capability. However, the joint behaviour of these parameters showed some potential to distinguish among simple snorers and OSA patients.

Snore site discrimination using statistical moments of free field snoring sounds recorded during sleep nasendoscopy

The non-invasive measurement of free field snoring sounds to estimate the site of snoring is an important development in the diagnosis, treatment and management of sleep-related breathing disorders. We investigated characteristics of the probability density function by testing the sensitivity of the statistical moments to amplitude patterns in the snoring acoustic signal. Snoring sounds from 15 patients were recorded whilst performing sleep (under anaesthetic) nasendoscopy evaluation. We demonstrated, using a fuzzy 2-means clustering method, that a combination of the statistical dimensionless moment coefficients of skewness and kurtosis could discriminate between pure palatal and non-palatal snoring subject groups.

Sleep nasendoscopy: a 10-year retrospective audit study

Sleep nasendoscopy was conceived at the Royal National Throat, Nose and Ear Hospital, UK in 1991, and has remained fully implemented in patient selection for targeted treatment of the spectrum of sleep-disordered breathing. The senior authors (B.T.K. and P.B.) have been performing sleep nasendoscopy together for over 10 years, and we look back at their decade's experience. A retrospective audit study based on case notes was performed over a 10-year period (1995-2005) in a tertiary-referral practice setting. Case notes were retrieved on all patients who had undergone sleep nasendoscopy during the study period, and agreed data were extracted and analyzed. A total of 2,485 sleep nasendoscopies were performed in patients with a mean age of 44.1 years, a 4:1 male preponderance, and a mean body mass index of 27.3 kg m(-2). Sleep nasendoscopy grading correlated well with apnoea-hypopnoea index and mean oxygen desaturation. Such grading helped us define and discuss treatment options with patients. After a median follow-up period of 518 days, 72% of patients reported feeling better; 26% of patients reported no change; and only 2% of patients reported feeling worse after treatment. Sleep nasendoscopy has proved to be a useful adjunctive method to identify the anatomical site of snoring, not to mention upper airway collapse, and remains integral to our tertiary-referral practice. It has allowed us quality assessment of the dynamic anatomy of sleep-disordered breathing that most closely and cost-effectively simulates the natural situation of patients. And for targeted treatment, such assessment has been fundamental.

Automatic detection, segmentation and assessment of snoring from ambient acoustic data

Snoring is a prevalent condition with a variety of negative social effects and associated health problems. Treatments, both surgical and therapeutic, have been developed, but the objective non-invasive monitoring of their success remains problematic. We present a method which allows the automatic monitoring of snoring characteristics, such as intensity and frequency, from audio data captured via a freestanding microphone. This represents a simple and portable diagnostic alternative to polysomnography. Our system is based on methods that have proved effective in the field of speech recognition. Hidden Markov models (HMMs) were employed as basic elements with which to model different types of sound by means of spectrally based features. This allows periods of snoring to be identified, while rejecting silence, breathing and other sounds. Training and test data were gathered from six subjects, and annotated appropriately. The system was tested by requiring it to automatically classify snoring sounds in new audio recordings and then comparing the result with manually obtained annotations. We found that our system was able to correctly identify snores with 82-89% accuracy, despite the small size of the training set. We could further demonstrate how this segmentation can be used to measure the snoring intensity, snoring frequency and snoring index. We conclude that a system based on hidden Markov models and spectrally based features is effective in the automatic detection and monitoring of snoring from audio data.

Acoustic Analysis of Snoring Sounds by a Multidimensional Voice Program

OBJECTIVES

This prospective study aimed to determine whether the acoustic characteristics of snoring sounds differed between simple snorers and patients with obstructive sleep apnea syndrome (OSAS) by using a multidimensional voice program (MDVP) that analyzes various aspects of voice.

METHODS

Fifty-eight patients (48 men, 10 women) with a history of snoring were included in the study. All patients underwent conventional polysomnography (PSG). Twelve subjects were diagnosed as simple snorers and 46 subjects were diagnosed with OSAS. The mean body mass index (BMI) of simple snorers was 24.7 kg/m and that of patients with OSAS was 25.8 kg/m. Natural overnight snoring was recorded from each subject while they slept during PSG. Using the multiple token protocols of MDVP, 30 snores from each subject were analyzed automatically. For data analysis, four markers were used: peak frequency, soft phonation index (SPI), noise to harmonics ratio (NHR), and power ratio.

RESULTS

The Mann-Whitney U test revealed significant differences between the SPI, NHR, and power ratio of simple snorers and patients with OSAS. Simple snorers had a high SPI value. OSAS-related snorers demonstrated a high NHR and low power ratio.

CONCLUSIONS

MDVP can be used for snoring sound analysis as a noninvasive examination of sleep-related breathing disorders for differential diagnosis. However, a suitable option that is rapid and has an easy-to-use interface would be more advantageous for analyzing snoring sounds.