Snoring Imaging: Could Bernoulli Explain It All?

doi:10.1378/chest.128.2.896

Chest

Volume 128, Issue 2, August 2005, Pages 896-901

https://doi.org/10.1378/chest.128.2.896 Get rights and content

Study objectives

To identify upper airway changes in snoring using CT scanning, to clarify the snoring mechanism, and to identify the key structures involved

Participants

Forty patients underwent CT examination of the head and neck region according to snoring habits; patients were classified into nonsnoring (n = 14), moderately loud snoring (n = 13), and loud snoring (n = 13) groups

Design

Comparative analysis

Measurements

Using CT images, areas, the anteroposterior and transversal distances of the pharyngeal space at different levels, and the thickness and length of the soft palate and uvula and their angle against the hard palate were measured; evidence of impaired nasal passages was noted; the extent of pharyngeal inspiratory narrowing was the ratio between the area at the hard palate level and most narrow area; and expiratory narrowing was the ratio between the area behind the root of the tongue and the most narrow area

Results

Greater pharyngeal inspiratory narrowing (p = 0.0015) proportional to the loudness of snoring (p = 0.0016), and a longer soft palate with uvula (p = 0.0173) were significant for snoring. Impaired nasal breathing was significantly related (p = 0.029) only to the loud snoring group. The body mass index and age of snoring persons were also significantly higher

Conclusions

Snoring is associated with typical changes that can be revealed by CT scanning. Greater pharyngeal narrowing is the most important factor. Given the “Venturi tube” shape of the pharynx, the Bernoulli pressure principle plays a major role in snoring. The key structure in snoring is the soft palate: it defines the constriction and is sucked into vibrating by negative pressure that develops at this site. Its repetitive closures present an obstruction to breathing, producing the snoring sound, and should therefore be the target for causal treatment of snoring. Obstacles in the upper airway that increase negative inspiratory pressure could not be confirmed as important for the development of snoring, although they may increase its loudness

Section snippets

Materails and Methods

Forty patients undergoing CT examination of the head and neck region—in most cases (n = 34) for carotid angiography—were included in the study. Mean age was 61.8 years (SD, 15.3 years), and 24 of the patients were men. In the course of the CT scanning, the patients were awake and lying in the supine position.

The participants and their spouses answered a questionnaire about their snoring habits, any stops of breathing experienced, daytime sleepiness, and impaired nose breathing. They estimated

Results

Results are presented in Table 1 and Figure 1. measured parameters are presented in Figure 2

Discussion

At the beginning of our study, we wanted to check the presence of clinically recognized reasons for snoring, such as obstacles in the nose, a narrow pharynx (in obese persons), backward displacement of the soft palate, enlarged tonsils, and a voluminous root of the tongue in snoring persons.⁷ In CT images, these factors should appear as identifiable and measurable constrictions.

In our study, there were 24 persons with objective and/or subjective nasal breathing impairment. Contrary to our

Conclusion

The study showed that snoring is associated with typical changes in the upper airway and that they can be presented by CT scanning in awake individuals. We must realize that these are in fact the changes that trigger the real snoring alteration in sleep. They are not very evident and cannot be seen and measured directly from CT images but must be calculated. The increased degree of pharyngeal narrowing determined by the ratio between the area at the hard palate level and the most narrow area

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From simple snoring to sleep apnea syndrome: clinical spectrum
Ther Umsch
(2000)

There are more references available in the full text version of this article.

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The medical records and video recordings of awake flexible endoscopic examination of patients with history of OSA who presented to the sleep apnea clinic in a tertiary referral medical center between June 2022 and December 2022, were reviewed. All patients had filled the STOP-BANG questionnaire and had intermediate/high risk of having OSA. A group of patients matched by age and gender and with no history of OSA were used as controls.
A total of 95 patients, 64 with a history of OSA and 31 with no history of OSA, were included. Among the study group, 37.5% (n = 24) had a STOP-BANG score between 3 and 4 and were considered to be at an intermediate risk of OSA while the remaining had a score more than 5 and were considered to be at high risk of OSA. There was a significant difference in the prevalence of ACC between the study group and controls (32.8% vs 12.9%, respectively, P < 0.001).
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Impact of sleep posture and breathing pattern on soft palate flutter and pharynx vibration in a pediatric airway using fluid–structure interaction
2023, Journal of Biomechanics
Snoring is a common condition in the general population, and the management of snoring requires a better understanding of its mechanism through a fluid–structure interaction (FSI) perspective. Despite the recent popularity of numerical FSI techniques, outstanding challenges are accurately predicting airway deformation and its vibration during snoring due to complex airway morphology. In addition, there still needs to be more understanding of snoring inhibition when lying on the side, and the possible effect of airflow rates, as well as nose or mouth-nose breathing, on snoring remains to be investigated. In this study, an FSI method verified against in vitro models was introduced to predict upper airway deformation and vibration. The technique was applied to predict airway aerodynamics, soft palate flutter, and airway vibration in four sleep postures (supine, left/right lying, and sitting positions) and four breathing patterns (mouth-nose, nose, mouth, and unilateral nose breathing). It was found that, at given elastic properties of soft tissues, the evaluated flutter frequency of 19.8 Hz in inspiration was in good agreement with the reported frequency of snoring sound in literature. Reduction in flutter and vibrations due to the mouth-nose airflow proportion changes were also noticed when having side-lying and sitting positions. Breathing through the mouth results in larger airway deformation than breathing through the nose or mouth-nose. These results collectively demonstrate the potential of FSI for studying the physics of airway vibration and clarify to some degree the reason for snoring inhibition during sleep postures and breathing patterns.
Prediction of the obstruction sites in the upper airway in sleep-disordered breathing based on snoring sound parameters: a systematic review
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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.
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.
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%.
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.
Impact of upper airway configuration on CPAP titration assessed by CT during Müller's maneuver in OSA patients
2021, Respiratory Physiology and Neurobiology
Citation Excerpt :
It has been suggested that UAL plays an important role in the assessment of pharyngeal collapse, whereby reduced UAL would improve the severity of OSA [(Kim et al., 2011; Segal et al., 2008; Sutherland et al., 2011)]. The relationship between UAL and the collapsibility of the pharynx could be interpreted by Bernoulli's law, which states that an inviscid fluid flowing through a tube is susceptible to an increase in velocity and a decrease in pressure [(Fajdiga, 2005)]. Because the pharynx lacks rigid bony structures, it is more prone to collapse when UAL is longer, based on the rules of buckling of cylindrical shells.
Continuous positive airway pressure (CPAP) is the current gold-standard treatment for moderate to severe obstructive sleep apnea (OSA), and upper airway anatomy plays an increasingly important role in evaluating the efficacy of CPAP therapy. The aim of this observational study was to investigate the influence of upper airway anatomy on CPAP titration in OSA patients assessed by computed tomography (CT) during Müller's maneuver.
Consecutive patients under investigation for OSA by undergoing polysomnography and CT scan of the upper airway while awake were enrolled. Successful full-night manual titration was performed to determine the optimal CPAP pressure level for OSA patients in supine position using a nasal mask.
A total of 157 subjects (134 males and 23 females) were included. Both apnea–hypopnea index (AHI) and LaSO2 significantly correlated with CPAP titration level, upper airway length (UAL), distance from mandibular plane to hyoid bone (MPH), and neck circumference (all p < 0.05). There were significant positive correlations between CPAP titration level and UAL (r = 0.348, p = 0.000) and MPH (r = 0.313, p = 0.002). Stepwise multiple linear regression analyses were performed to evaluate the independent predictors of AHI, LaSO2, and CPAP titration level. CPAP titration level was identified as an independent explanatory variable for AHI and LaSO2 after adjustment for confounders. Multiple linear regression analyses also indicated that body mass index (BMI) and UAL were independently associated with CPAP titration level (all p < 0.05).
Upper airway abnormalities combined with anthropometric parameters play important roles in CPAP titration for OSA patients, providing additional insight into the factors influencing OSA treatment strategies. UAL and BMI should be taken into consideration when choosing CPAP titration level to improve CPAP compliance.
Computational analysis of a flapping uvula on aerodynamics and pharyngeal wall collapsibility in sleep apnea
2019, Journal of Biomechanics
Citation Excerpt :
Besides the aforementioned mechanical/neuromuscular and anatomical causes, the flow-induced aerodynamic loads in human upper airway have been proven to be an important factor affecting snoring and OSA by extensive experimental (Ayappa and Rapoport, 2003) and computational fluid dynamics (CFD) studies (Mihaescu et al., 2011; Pirnar et al., 2015). Though Bernoulli’s principle was found to be the major cause of reduced aerodynamic pressure in the pharynx (Fajdiga, 2005), enriched flow physics other than laminar flow happens in the processes of snoring and OSA, suggesting more complex pathological mechanisms driven by aerodynamics. Specifically, flow separation and recirculation can happen due to the irregular shape of human airway, even at its static condition, causing secondary and highly turbulent flows.
Studying the airflows and the resultant aerodynamic pressure/force in the pharyngeal airway is critical for understanding the pathophysiology of snoring and sleep apnea. In this work, an experiment-driven computational study was conducted to examine the aerodynamics in human pharyngeal airway. An anatomically accurate pharynx model associated with different uvula kinematics was reconstructed from human magnetic resonance image (MRI) and high-speed photography. An immersed-boundary-method (IBM)-based direct numerical simulation (DNS) flow solver was adopted to simulate the corresponding unsteady flows in all their complexity. Analyses were performed on vortex dynamics and pressure fluctuations in the pharyngeal airway and force oscillations on the pharyngeal wall under the influence of varying airway obstructions, uvula flapping mode, and uvula flapping frequencies. It was found the vortex formation, aerodynamic pressure, and pharyngeal wall force were significantly affected by the width of the pharyngeal airway. By contrast, the influences from the uvula flapping mode were insignificant when other parameters were similar. Fast Fourier transformation (FFT) and continuous wavelet transform (CWT) analysis of the pressure time history revealed the existence of higher order harmonics of base frequency with significant pressure amplitudes and energy intensities. It was also found the airway pressure and pharyngeal wall force oscillate more dramatically at higher uvula flapping frequencies, which tends to promote the collapse of pharyngeal wall and initiates sleep apnea.
Exercise inducible laryngeal obstruction: diagnostics and management
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Citation Excerpt :
Thus, there is a large gap in knowledge that needs to be filled. The Bernoulli principle states that increasing airflow through a tube creates increasing negative pressures within the tube [59]. Depending on airflow velocity, turbulence and the strength of the supporting structures, sooner or later the tube will yield to these forces.
Obstruction of the central airways is an important cause of exercise-induced inspiratory symptoms (EIIS) in young and otherwise healthy individuals. This is a large, heterogeneous and vastly understudied group of patients. The symptoms are too often confused with those of asthma. Laryngoscopy performed as symptoms evolve during increasing exercise is pivotal, since the larynx plays an important role in symptomatology for the majority. Abnormalities vary between patients, and laryngoscopic findings are important for correct treatment and handling. The simplistic view that all EIIS is due to vocal cord dysfunction [VCD] still hampers science and patient management. Causal mechanisms are poorly understood. Most treatment options are based on weak evidence, but most patients seem to benefit from individualised information and guidance. The place of surgery has not been settled, but supraglottoplasty may cure well-defined severe cases. A systematic clinical approach, more and better research and randomised controlled treatment trials are of utmost importance in this field of respiratory medicine.

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The work was performed at the University Clinic for Otorhinolaryngology and Cervicofacial Surgery and Clinical Institute for Radiology, University Medical Centre, Ljubljana, Slovenia.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml)

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Chest

Impact of Basic Research on TomorrowSnoring Imaging: Could Bernoulli Explain It All?

Study objectives

Participants

Design

Measurements

Results

Conclusions

Section snippets

Materails and Methods

Results

Discussion

Conclusion

Chest

Ann Allergy Asthma Immunol

From simple snoring to sleep apnea syndrome: clinical spectrum

Ther Umsch

Impact of Basic Research on Tomorrow
Snoring Imaging: Could Bernoulli Explain It All?