Fluid Structure Interaction Study of the Obstructive Sleep Apnea and Surgical Treatment Using Suture-~Patch Device on the Patient’s Tongue
Up to 14% of the U.S. population is estimated to have obstructive sleep apnea (OSA) related to obesity, and there is increased incidence occurring worldwide. While treatment with continuous positive airway pressure (CPAP) resolves airway obstruction, patient compliance is relatively low. Alternative interventions are available to treat OSA patients; however, their outcomes have had variable results. For example, current technologies have demonstrated an inability to define and treat the specific anatomical site(s) causing the obstruction, resulting in suboptimal modifications of the airway and poor control of OSA.
In the current study, a three-dimensional (3-D) fluid-structure interaction (FSI) numerical simulation has been applied to simulate upper airway (UA) collapse, without considering the individual muscles. The objective of this study is to demonstrate how to use the two-way FSI numerical simulation to study the characteristics of and identify the precise location of an upper airway collapse on female and male patients with OSA. This task was accomplished using Simpleware®, which is medical image processing software, and ANSYS® Fluent, which is computational fluid dynamics (CFD) and structural software. Simpleware® is able to process a patient’s 3-D computed tomography (CT) scan image and render this airway image to ANSYS® Fluent in order to generate the computational domains of fluid and structure. During FSI numerical simulation, areas that are prone to collapse and precipitate apneic episodes were identified at the tip of the soft palate and the base of the tongue, with intrathoracic pressures as low as -1370 Pa. These results are consistent with anatomical structures that are currently indicated and targeted in the treatment of OSA. The negative pressure is similar to previous values reported in human esophageal pressure measurements in UA resistance syndrome. This improved two-way FSI numerical simulation, which is the first to accurately model the UA geometry in OSA, can allow virtual modification of the airway before actual clinical treatment by ear, nose, and throat (ENT) medical doctors.
The improved two-way FSI numerical simulation was later used to model and simulate a unique suture-patch device, which can be used to virtually apply force to the tongue. Based on the numerical simulation results, this device can effectively reduce the risk of UA occlusion and open up the UA at the pharynx 92% of its original area under the peak inhale volume for a specific patient. This provides a possible treatment for the patient, instead of conducting tissue removal or requiring use of a CPAP mask. Three locations to put the suture-patch device on the patient’s tongue were compared in the study, and the suture-patch at location 2 is recommended. Next, the bisection method is used to find the minimum force needed to open up the airway from occlusion. The results show that 1.25 N is the recommended force.
Both male and female OSA patients were studied and compared in three different aspects: geometry, flow field, and tissue movement. The results from this case study show that tissue movement does not depend only on the apnea and hypopnea index (AHI). They show that classic symptoms, like snoring, should not be the only diagnosis of OSA. Anyone with restless sleep or daytime fatigue, with snoring syndrome, should visit an ENT doctor and have a clinical sleep test in order to find out whether he or she has OSA.
Using the current FSI development, a patient-specific numerical simulation can be carried out prior to surgery to virtually audit different treatments, when the patient is diagnosed with severe OSA and needs surgical treatment. Then the ENT doctor can discuss the best treatment with the patient based on the simulation results. Moreover, ENT doctors and patients will be able to visualize the outcome of virtual surgery from numerical simulations. This will give patients more confidence and help to alleviate their trepidation about treatment options. Moreover, the patient-specific numerical simulations can be used to compare different OSA cases to study the characteristics they have in common. Therefore, patients can understand more about OSA, and ENT doctors can determine the possible ways to conduct the best treatment in the near future.