{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,8]],"date-time":"2025-12-08T10:51:11Z","timestamp":1765191071843,"version":"3.46.0"},"reference-count":57,"publisher":"MDPI AG","issue":"24","license":[{"start":{"date-parts":[[2025,12,7]],"date-time":"2025-12-07T00:00:00Z","timestamp":1765065600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100008794","name":"Research Manitoba","doi-asserted-by":"publisher","award":["5792"],"award-info":[{"award-number":["5792"]}],"id":[{"id":"10.13039\/100008794","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100004489","name":"Mathematics of Information Technology and Complex Systems","doi-asserted-by":"publisher","award":["IT39986"],"award-info":[{"award-number":["IT39986"]}],"id":[{"id":"10.13039\/501100004489","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Diagnostics"],"abstract":"<jats:p>Background: Tracheal breathing sounds (TBS) have demonstrated strong potential as a non-invasive, wakefulness-based diagnostic tool for obstructive sleep apnea (OSA); yet the relationship between specific upper airway anatomical features and the resulting TBS spectra remains insufficiently understood. This study aims to enhance the diagnostic utility of TBS in OSA by investigating how the upper airway anatomy influences TBS spectral characteristics. Method: Patient-specific computational models of the upper airway were reconstructed from high-resolution CT scans of a healthy subject and an individual with OSA. Additional variants were generated with targeted constrictions at the velopharynx, oropharynx, and trachea, based on clinically reported anatomical ranges. Airflow dynamics were simulated using Large Eddy Simulation (LES), and the resulting acoustic responses were computed via Lighthill\u2019s acoustic analogy within a hybrid aero-acoustic framework. Results: Oropharyngeal constriction generated the most spatially concentrated vorticity patterns among single-region constricted models. Airway Resistance analysis revealed that severe velopharyngeal and oropharyngeal constrictions contributed most to regional airway resistance. Spectral analysis showed that velopharyngeal narrowing produced a progressive downward shift in the third resonance peak (1000\u20131700 Hz), while oropharyngeal narrowing induced an upward shift of the third peak and a downward shift of the fourth peak (1700\u20132500 Hz). These frequency shifts were attributed to the effective role of acoustic mass and airway compliance. Conclusions: Anatomical modifications of the upper airway produce region-specific changes in both flow and acoustic responses. These findings support the use of TBS spectral analysis for non-invasive localization of airway obstructions in OSA.<\/jats:p>","DOI":"10.3390\/diagnostics15243108","type":"journal-article","created":{"date-parts":[[2025,12,8]],"date-time":"2025-12-08T09:17:36Z","timestamp":1765185456000},"page":"3108","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Anatomical Determinants of Tracheal Breathing Sounds: A Computational Study of Airway Narrowing and Obstructive Sleep Apnea"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1593-6285","authenticated-orcid":false,"given":"Walid","family":"Ashraf","sequence":"first","affiliation":[{"name":"Biomedical Engineering Program, University of Manitoba, Winnipeg, MB R3T 2N2, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jeffrey J.","family":"Fredberg","sequence":"additional","affiliation":[{"name":"Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9202-949X","authenticated-orcid":false,"given":"Zahra","family":"Moussavi","sequence":"additional","affiliation":[{"name":"Biomedical Engineering Program, University of Manitoba, Winnipeg, MB R3T 2N2, Canada"},{"name":"Department of Electrical and Computer Engineering, University of Manitoba, Winnipeg, MB R3T 2N2, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,12,7]]},"reference":[{"key":"ref_1","first-page":"104","article-title":"Computerized Respiratory Sounds in Patients with COPD: A Systematic Review","volume":"12","author":"Marques","year":"2015","journal-title":"COPD J. Chronic Obstr. Pulm. Dis."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"481","DOI":"10.1152\/jappl.1984.57.2.481","article-title":"Measurement and Theory of Wheezing Breath Sounds","volume":"57","author":"Gavriely","year":"1984","journal-title":"J. Appl. Physiol."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1087","DOI":"10.1007\/s11517-010-0674-2","article-title":"Sleep Apnea Monitoring and Diagnosis Based on Pulse Oximetery and Tracheal Sound Signals","volume":"48","author":"Yadollahi","year":"2010","journal-title":"Med. Biol. Eng. Comput."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"e37","DOI":"10.1183\/20734735.008817","article-title":"The Use of Tracheal Sounds for the Diagnosis of Sleep Apnoea","volume":"13","author":"Penzel","year":"2017","journal-title":"Breathe"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1217","DOI":"10.1164\/rccm.2109080","article-title":"Epidemiology of Obstructive Sleep Apnea: A Population Health Perspective","volume":"165","author":"Young","year":"2002","journal-title":"Am. J. Respir. Crit. Care Med."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"279","DOI":"10.1164\/ajrccm.154.2.8756795","article-title":"Recognition of Obstructive Sleep Apnea","volume":"154","author":"Strohl","year":"1996","journal-title":"Am. J. Respir. Crit. Care Med."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"2076","DOI":"10.1007\/s00134-008-1180-y","article-title":"Sleep Monitoring in the Intensive Care Unit: Comparison of Nurse Assessment, Actigraphy and Polysomnography","volume":"34","author":"Beecroft","year":"2008","journal-title":"Intensive Care Med."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"American Society of Anesthesiologists Task Force on Perioperative Management of patients with obstructive sleep apnea (2014). Practice Guidelines for the Perioperative Management of Patients with Obstructive Sleep Apnea. Anesthesiology, 120, 268\u2013286.","DOI":"10.1097\/ALN.0000000000000053"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Elwali, A., and Moussavi, Z. (2019). A Novel Decision Making Procedure during Wakefulness for Screening Obstructive Sleep Apnea Using Anthropometric Information and Tracheal Breathing Sounds. Sci. Rep., 9.","DOI":"10.1038\/s41598-019-47998-5"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1493","DOI":"10.1378\/chest.110.6.1493","article-title":"Posture-Dependent Change of Tracheal Sounds at Standardized Flows in Patients with Obstructive Sleep Apnea","volume":"110","author":"Pasterkamp","year":"1996","journal-title":"Chest"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"111021","DOI":"10.1016\/j.apacoust.2025.111021","article-title":"Aeroacoustics of Breath Sounds in Trachea and Upper Airway","volume":"241","author":"Ashraf","year":"2026","journal-title":"Appl. Acoust."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1139","DOI":"10.1378\/chest.122.4.1139","article-title":"Sites of Obstruction in Obstructive Sleep Apnea","volume":"122","author":"Rama","year":"2002","journal-title":"Chest"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1350","DOI":"10.1016\/j.joms.2013.12.006","article-title":"Velopharyngeal Anatomy in Patients with Obstructive Sleep Apnea versus Normal Subjects","volume":"72","author":"Finkelstein","year":"2014","journal-title":"J. Oral Maxillofac. Surg."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"230","DOI":"10.1111\/j.1365-2869.2008.00647.x","article-title":"Evaluation of Pharyngeal Shape and Size Using Anatomical Optical Coherence Tomography in Individuals with and without Obstructive Sleep Apnoea","volume":"17","author":"Walsh","year":"2008","journal-title":"J. Sleep Res."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"19","DOI":"10.1016\/j.sleep.2016.01.022","article-title":"Three-Dimensional Imaging of the Upper Airway Anatomy in Obstructive Sleep Apnea: A Systematic Review","volume":"21","author":"Chen","year":"2016","journal-title":"Sleep Med."},{"key":"ref_16","first-page":"719","article-title":"Pharyngeal Size and Shape During Wakefulness and Sleep in Patients with Obstructive Sleep Apnoea","volume":"72","author":"Horner","year":"1989","journal-title":"QJM Int. J. Med."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"79","DOI":"10.1183\/09031936.01.17100790","article-title":"Magnetic Resonance Imaging of the Pharynx in OSA Patients and Healthy Subjects","volume":"17","author":"Ciscar","year":"2001","journal-title":"Eur. Respir. J."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"775","DOI":"10.1148\/radiology.171.3.2717750","article-title":"Obstructive sleep apnea: Diagnosis with ultrafast CT","volume":"171","author":"Galvin","year":"1989","journal-title":"Radiology"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"311","DOI":"10.1007\/s11325-008-0191-9","article-title":"Upper Airway Length May Be Associated with the Severity of Obstructive Sleep Apnea Syndrome","volume":"12","author":"Segal","year":"2008","journal-title":"Sleep Breath."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"354","DOI":"10.1016\/j.joms.2009.09.087","article-title":"Three-Dimensional Computed Tomographic Analysis of Airway Anatomy in Patients With Obstructive Sleep Apnea","volume":"68","author":"Abramson","year":"2010","journal-title":"J. Oral Maxillofac. Surg."},{"key":"ref_21","first-page":"840","article-title":"Dimensions of the Growing Trachea Related to Body Height. Length, Anteroposterior and Transverse Diameters, Cross-Sectional Area, and Volume in Subjects Younger than 20 Years of Age","volume":"131","author":"Griscom","year":"1985","journal-title":"Am. Rev. Respir. Dis."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1083","DOI":"10.1164\/ajrccm\/148.4_Pt_1.1083","article-title":"Tracheal Sound Spectra Depend on Body Height","volume":"148","author":"Sanchez","year":"1993","journal-title":"Am. Rev. Respir. Dis."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"295","DOI":"10.1016\/S0034-5687(97)00113-8","article-title":"Effects of Breathing Pathways on Tracheal Sound Spectral Features","volume":"111","author":"Kraman","year":"1998","journal-title":"Respir. Physiol."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"605","DOI":"10.1152\/jappl.1993.75.2.605","article-title":"Detection of Tracheal Stenosis by Frequency Analysis of Tracheal Sounds","volume":"75","author":"Yonemaru","year":"1993","journal-title":"J. Appl. Physiol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"423","DOI":"10.2147\/NSS.S397196","article-title":"Sleep Apnea Detection by Tracheal Motion and Sound, and Oximetry via Application of Deep Neural Networks","volume":"15","author":"Ghahjaverestan","year":"2023","journal-title":"Nat. Sci. Sleep"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Mu\u00f1oz Rojo, M., Pramono, R.X.A., Devani, N., Thomas, M., Mandal, S., and Rodriguez-Villegas, E. (2024). Validation of Tracheal Sound-Based Respiratory Effort Monitoring for Obstructive Sleep Apnoea Diagnosis. J. Clin. Med., 13.","DOI":"10.3390\/jcm13123628"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"959","DOI":"10.1152\/japplphysiol.01033.2018","article-title":"Computational Analysis of Airflow Dynamics for Predicting Collapsible Sites in the Upper Airways: Machine Learning Approach","volume":"127","author":"Yeom","year":"2019","journal-title":"J. Appl. Physiol."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"463","DOI":"10.1007\/s11325-017-1588-0","article-title":"Numerical Study of Dynamic Glottis and Tidal Breathing on Respiratory Sounds in a Human Upper Airway Model","volume":"22","author":"Xi","year":"2018","journal-title":"Sleep Breath."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1038\/srep25730","article-title":"A Subject-Specific Acoustic Model of the Upper Airway for Snoring Sounds Generation","volume":"6","author":"Saha","year":"2016","journal-title":"Sci. Rep."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1116","DOI":"10.1016\/j.neuroimage.2006.01.015","article-title":"User-Guided 3D Active Contour Segmentation of Anatomical Structures: Significantly Improved Efficiency and Reliability","volume":"31","author":"Yushkevich","year":"2006","journal-title":"Neuroimage"},{"key":"ref_31","first-page":"564","article-title":"On Sound Generated Aerodynamically I. General Theory","volume":"211","author":"Lighthill","year":"1952","journal-title":"Proc. R. Soc. London. Ser. A. Math. Phys. Sci."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1179","DOI":"10.1121\/10.0000785","article-title":"Hybrid Aeroacoustic Approach for the Efficient Numerical Simulation of Human Phonation","volume":"147","author":"Schoder","year":"2020","journal-title":"J. Acoust. Soc. Am."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"99","DOI":"10.1175\/1520-0493(1963)091<0099:GCEWTP>2.3.CO;2","article-title":"General Circulation Experiments with the Primitive Equations: I. The Basic Experiment","volume":"91","author":"Smagorinsky","year":"1963","journal-title":"Mon. Weather Rev."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"633","DOI":"10.1063\/1.858280","article-title":"A Proposed Modification of the Germano Sugrid-Scale Closure Method","volume":"4","author":"Lilly","year":"1992","journal-title":"Phys. Fluids A"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1016\/j.rmed.2018.01.013","article-title":"Pleural Manometry\u2013Historical Background, Rationale for Use and Methods of Measurement","volume":"136","author":"Krenke","year":"2018","journal-title":"Respir. Med."},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Vara Almirall, B., Calmet, H., Ang, H.Q., and Inthavong, K. (2025). Flow Behavior in Idealized & Realistic Upper Airway Geometries. Comput. Biol. Med., 194.","DOI":"10.1016\/j.compbiomed.2025.110449"},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Lancmanov\u00e1, A., and Bodn\u00e1r, T. (2025). Numerical Simulations of Human Respiratory Flows: A Review, Springer International Publishing.","DOI":"10.1007\/s42452-025-06617-x"},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Caro, S., Ploumhans, P., and Gallez, X. (2004, January 10\u201312). Implementation of Lighthill\u2019s Acoustic Analogy in a Finite\/Infinite Elements Framework. Proceedings of the 10th AIAA\/CEAS Aeroacoustics Conference, Manchester, UK.","DOI":"10.2514\/6.2004-2891"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"2021","DOI":"10.5664\/jcsm.8736","article-title":"Effect of Adenoids and Tonsil Tissue on Pediatric Obstructive Sleep Apnea Severity Determined by Computational Fluid Dynamics","volume":"16","author":"Iwasaki","year":"2020","journal-title":"J. Clin. Sleep Med."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"2427","DOI":"10.1152\/jappl.1989.67.6.2427","article-title":"Glottic and Cervical Tracheal Narrowing in Patients with Obstructive Sleep Apnea","volume":"67","author":"Rubinstein","year":"1989","journal-title":"J. Appl. Physiol."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"433","DOI":"10.1016\/j.sleep.2012.12.005","article-title":"Functional Respiratory Imaging as a Tool to Assess Upper Airway Patency in Children with Obstructive Sleep Apnea","volume":"14","author":"Vos","year":"2013","journal-title":"Sleep Med."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"A3645","DOI":"10.1164\/ajrccm.2025.211.Abstracts.A3645","article-title":"Aero-Acoustic Simulation of Patient-Specific Breathing Sounds in Obstructive Sleep Apnea Versus Healthy Airways","volume":"211","author":"Ashraf","year":"2025","journal-title":"Am. J. Respir. Crit. Care Med."},{"key":"ref_43","unstructured":"Foucart, M. (2015). Aeroacoustic Investigation of a Stridor Patient\u2019s Upper Respiratory System. [Master Thesis, TU Delft]."},{"key":"ref_44","first-page":"505","article-title":"The Influence of Solid Boundaries upon Aerodynamic Sound","volume":"231","author":"Curle","year":"1955","journal-title":"Proc. R. Soc. London. Ser. A. Math. Phys. Sci."},{"key":"ref_45","unstructured":"Blackstock, D.T. (2000). Fundamentals of Physical Acoustics, John Wiley & Sons."},{"key":"ref_46","doi-asserted-by":"crossref","unstructured":"Ashraf, W., Alqudah, A., Band, M., Zhao, L., Lithgow, B., and Elwali, A. (2025). Developing an Empirical Acoustic Transfer Function Model for the Upper Airway. Ann. Biomed. Eng., 1\u201314.","DOI":"10.1007\/s10439-025-03883-z"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"519","DOI":"10.1016\/S0892-1997(01)00052-2","article-title":"Acoustic Interpretation of Resonant Voice","volume":"15","author":"Titze","year":"2001","journal-title":"J. Voice"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"637","DOI":"10.1016\/j.medengphy.2006.08.017","article-title":"Numerical Investigation on the Flow Characteristics and Aerodynamic Force of the Upper Airway of Patient with Obstructive Sleep Apnea Using Computational Fluid Dynamics","volume":"29","author":"Jeong","year":"2007","journal-title":"Med. Eng. Phys."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"1385","DOI":"10.1164\/ajrccm\/148.5.1385","article-title":"Dynamic Upper Airway Imaging during Awake Respiration in Normal Subjects and Patients with Sleep Disordered Breathing","volume":"148","author":"Schwab","year":"1993","journal-title":"Am. Rev. Respir. Dis."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"740","DOI":"10.1164\/ajrccm.162.2.9908123","article-title":"Physical Findings and the Risk for Obstructive Sleep Apnea: The Importance of Oropharyngeal Structures","volume":"162","author":"Schellenberg","year":"2000","journal-title":"Am. J. Respir. Crit. Care Med."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"431","DOI":"10.5664\/jcsm.8224","article-title":"Primary Site Identification in Children with Obstructive Sleep Apnea by Computational Fluid Dynamics Analysis of the Upper Airway","volume":"16","author":"Sugiyama","year":"2020","journal-title":"J. Clin. Sleep Med."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"623","DOI":"10.1164\/ajrccm\/136.3.623","article-title":"Pharyngeal Size and Resistance in Obstructive Sleep Apnea","volume":"136","author":"Stauffer","year":"1987","journal-title":"Am. Rev. Respir. Dis."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"302","DOI":"10.1378\/chest.97.2.302","article-title":"Pulmonary Function in Obstructive Sleep Apnea. Relationships to Pharyngeal Resistance and Cross-Sectional Area","volume":"97","author":"Stauffer","year":"1990","journal-title":"Chest"},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1371\/journal.pone.0219642","article-title":"Computational Fluid Dynamics Simulation of Changes in the Morphology and Airflow Dynamics of the Upper Airways in OSAHS Patients after Treatment with Oral Appliances","volume":"14","author":"Song","year":"2019","journal-title":"PLoS ONE"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1186\/s12931-020-01532-8","article-title":"Upper Airway Lengthening Caused by Weight Increase in Obstructive Sleep Apnea Patients","volume":"21","author":"Lin","year":"2020","journal-title":"Respir. Res."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"670","DOI":"10.1111\/joor.12298","article-title":"Anatomy of the Larynx and Pharynx: Effects of Age, Gender and Height Revealed by Multidetector Computed Tomography","volume":"42","author":"Inamoto","year":"2015","journal-title":"J. Oral Rehabil."},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"72.e9","DOI":"10.1016\/j.amjmed.2005.01.077","article-title":"Aging Influences on Pharyngeal Anatomy and Physiology: The Predisposition to Pharyngeal Collapse","volume":"119","author":"Malhotra","year":"2006","journal-title":"Am. J. Med."}],"container-title":["Diagnostics"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2075-4418\/15\/24\/3108\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,12,8]],"date-time":"2025-12-08T10:47:26Z","timestamp":1765190846000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2075-4418\/15\/24\/3108"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,12,7]]},"references-count":57,"journal-issue":{"issue":"24","published-online":{"date-parts":[[2025,12]]}},"alternative-id":["diagnostics15243108"],"URL":"https:\/\/doi.org\/10.3390\/diagnostics15243108","relation":{},"ISSN":["2075-4418"],"issn-type":[{"type":"electronic","value":"2075-4418"}],"subject":[],"published":{"date-parts":[[2025,12,7]]}}}