Simulation of upper airway occlusion without and with mandibular advancement in obstructive sleep apnea using fluid-structure interaction Moyin Zhao a,n , Tracie Barber a , Peter A. Cistulli b,c , Kate Sutherland b,c , Gary Rosengarten a,d,nn a School of Mechanical Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia b Department of Respiratory and Sleep Medicine, Royal North Shore Hospital, and University of Sydney, NSW, Australia c NHMRC Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney and Woolcock Institute of Medical Research, Australia d School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, VIC 3053, Australia article info Article history: Accepted 20 August 2013 Keywords: OSA Upper airway MAS MRI CFD FSI Airway occlusion abstract Obstructive Sleep Apnea (OSA) is a common sleep disorder characterized by repetitive collapse of the upper airway (UA). One treatment option is a mandibular advancement splint (MAS) which protrudes the lower jaw, stabilizing the airway. However not all patients respond to MAS therapy and individual effects are not well understood. Simulations of airway behavior may represent a non-invasive means to understand OSA and individual treatment responses. Our aims were (1) to analyze UA occlusion and flow dynamics in OSA using the fluid structure interaction (FSI) method, and (2) to observe changes with MAS. Magnetic resonance imaging (MRI) scans were obtained at baseline and with MAS in a known treatment responder. Computational models of the patients' UA geometry were reconstructed for both conditions. The FSI model demonstrated full collapse of the UA (maximum 5.83 mm) pre-treatment (without MAS). The UA collapse was located at the oropharynx with low oropharyngeal pressure ( À51.18 Pa to À39.08 Pa) induced by velopharyngeal jet flow (maximum 10.0 m/s). By comparison, simulation results from the UA with MAS, showed smaller deformation (maximum 2.03 mm), matching the known clinical response. Our FSI modeling method was validated by physical experiment on a 1:1 flexible UA model fabricated using 3D steriolithography. This is the first study of airflow dynamics in a deformable UA structure and inspiratory flow. These results expand on previous UA models using computational fluid dynamics (CFD), and lay a platform for application of computational models to study biomechanical properties of the UA in the pathogenesis and treatment of OSA. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Obstructive sleep apnea (OSA) is a rapidly increasing sleep disorder affecting at least 17% of adults and 2% of children (Young et al., 1993, Ali et al., 1993, Young et al., 2005). It is characterized by repetitive episodes of complete (apnea) or partial (hypopnea) collapse of the upper airway during sleep (Force, 1999). A range of treatment modalities is available to treat the disorder, including weight loss, continuous positive airway pressure (CPAP), and various types of surgery (eg. uvulopalato- haryngoplasty, maxillomandibular advancement) (Riley et al., 1989, Croft and Golding-Wood, 1990, Sher et al., 1996, Barnes et al., 2004). Mandibular Advancement Splints (MAS) are an alternative approach for OSA treatment. MAS devices hold the lower jaw in a protruded position and help to prevent the upper airway (UA) from occluding (Cistulli et al., 2004). MAS have a high acceptance as they are comparatively easy to use, but have similar health benefits com- pared to CPAP, which is attributable to better treatment adherence (Gotsopoulos et al., 2002, Ng et al., 2003, Phillips et al., 2013). Although 60–70% of patients benefit clinically from MAS, a complete treatment to OSA (apnea-hypopnea index (AHI) o5/h after treat- ment) is achieved in 35–40% of patient (Chan et al., 2010). The mechanisms of UA collapse in OSA, and why some patients respond to MAS treatment while others do not, are not well understood. A key unresolved issue is the factors that influence treatment out- come, and whether it is feasible to predict treatment response before implementation of treatment. Computational modeling shows promise as a method to understand treatment responses in OSA. Computational fluid dynamics (CFD) has recently been introduced in OSA research by modeling the UA flow. Compared with idealized Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics 0021-9290/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jbiomech.2013.08.010 n Corresponding author. Tel.: þ61 4305 71593. nn Corresponding author. Tel.: þ61 3 9925 8020. E-mail addresses: zhaomoyin@hotmail.com (M. Zhao), gary.rosengarten@rmit. edu.au (G. Rosengarten). Journal of Biomechanics 46 (2013) 2586–2592