Modeling of obstructive sleep apnea by fluid-structure interaction in the upper airways

Snoring is caused by the soft parts of the upper airways collapsing and preventing the air from flowing freely. In some cases, snoring is so severe that medical attention is required. The most severe, obstructive sleep apnea (OSA), affects 2-4 percent of the population. The disease is recognized by heavy snoring, frequent breathing stops, gasping for breath, and awakenings. OSA is the cause for low quality sleep and reduced oxygen uptake and is considered a major cause for reduced life quality and increased mortality in the modern society. There is a variety of available treatment options for OSA, but today there are no available methods for predicting the outcome of the treatment. A sizable portion of the patients don't improve - some even get worse. Thus, there is a demand for treating OSA in a more targeted way to allow for more predictable results and improved probability for choosing a successful form of therapy. Key to predicting the outcome of the treatment is full understanding of the physical mechanisms behind OSA. That is, we need improved understanding of the airflow in the upper airways and of the airway features and properties responsible for the problem. To achieve this, mathematical models play a crucial role. They can reveal causes and effects that are impossible to observe directly. To ensure successful application of mathematical models to predict or assess the effect of a treatment option, accurate, mathematical descriptions of the patient's upper airways are required. Medical imaging (e.g. CT, MRI, or ultrasound) can be used to "see" the airway. Based on the images, three-dimensional computer models can be constructed. These can be used to compute how the airflow behaves when the patient is breathing, how much force is required to cause an apnea, or how the soft tissue is vibrating due to breathing. In the future, we foresee that "virtual surgery" can be performed on such computer models to assess how surgery, or other types of therapy, can improve the patient's sleep apnea. Examples include the consequence of sleeping position, the effect of palatal implants or nasal surgery, or a combination of various treatment options. How can for example, a small surgical adjustment in the front of the nasal cavity affect airflow patterns that cause the soft palate to vibrate? And how does this connect with the altered oscillatory frequency due to palatal implants? To answer these and other related questions, three traditionally separate scientific fields must be joined: 1) Medical examination/interpretation and treatment of patients, 2) Structural dynamics, and 3) Fluid dynamics. In addition, the measurements of physical parameters and properties are crucial to support mathematical modelling activities. This project was conducted through the collaboration between medical experts from St. Olavs hospital, the university hospital of Trondheim, and the Faculty of medicine at NTNU and experts of various engineering fields at the Faculty of engineering at NTNU and SINTEF Industry. It is in the overlapping areas of these three scientific areas that the main challenges occur. But also the solutions. To ensure good quality in the interdisciplinary work, it is crucial to encourage close collaboration between the researchers from the different scientific disciplines. This can often be challenging due to the different "languages" of experts in different fields. The current project's success, in this regard, is documented through numerous cross-disciplinary publications and scientific results. A crucial ingredient in the collaboration has been the regular interdisciplinary workshops to disseminate and discuss scientific results and questions. There, we have become familiar with each other's jargon and methods bit by bit, and now we strive for further cooperation. The vision of the project team is to develop a commercial "design tool" that can be used in treatment planning. Such a tool has the potential to help reduce the waiting lists and costs in the health sector as well as reducing risk and inconvenience for patients. Moreover, it will enable increased patient participation in important decisions regarding the patient's health. This project brought us much closer to the vision. We have used patient specific, mathematical fluid flow and soft tissue models to study 1) the effect of nasal surgery on the airflow in the upper airways; and 2) the effect of palatal anatomy and surgery on the conditions for airway collapse. The project also established the statistical significance of nasal surgery on OSA - this was greater than anticipated. Today, the project holds a unique set of data that can be used for further investigation of the relationships between anatomy, treatment and OSA. To achieve full clinical value, however, additional groundbreaking research is required. We accept the challenge and look forward to the next project, for which we have applied funding.

The project aims at the heart of the Norwegian national strategy for biotechnology, by bridging the current gap between a major health issue in the population and technologically based diagnostics and decision making for medical personnel. Obstructive Sle ep Apnea Syndrome (OSAS) is caused by repetitive collapses of the pharyngeal walls during sleep resulting in oxygen desaturation and sleep disturbances. OSAS has a huge impact on global health; it is related to a range of modern society diseases. 4% and 2 % of the male and female population, respectively, and 2-3% of children suffer from OSAS. The treatment options for the conditions remain obscure, with surgery being one option. No accepted guidelines exist, however, on what type of nasal surgery to perf orm or in which subgroup of patients a positive outcome can be predicted. From a clinical point of view we need a new way of looking at the underlying mechanisms of OSAS, and there is a demand for treating OSAS in a more targeted way, to allow for a more predictable outcome of the treatment and improved chances of positive response to the treatment. The proposed project will demonstrate a new clinical tool to predict the response to OSAS surgery. The main hypothesis of the project is that by employing a c ombination of clinical examination and computer model investigation of fluid-structure interaction in the human upper airways, it is possible to evaluate the effect of surgery with respect to OSAS mitigation. Ultimately, the research activity will result in a tool that can be utilized by medical personnel in the planning stage of OSAS treatment. The project is multidisciplinary by nature and is organized in four work packages; clinical research; soft tissue modeling; mathematical modeling of fluid-struct ure interactions; and CFD modeling for prediction of the success of OSAS surgery. The main deliverable of the project is a method to perform patient specific cause-and-effect studies with respect to OSAS mitig