0460 Upper Airway Flow Characteristics of Obstructive Sleep Apnea Patients who underwent Uvulopalatopharyngoplasty

Abstract

Introduction: Obstructive sleep apnea(OSA) is one of most common sleep breathing disorders. Surgeries, such as uvulopalatopharyngoplasty( UPPP), maxillomandibular advancement(MMA), are perceived as effective treatment to anatomy abnormality due to their success in enlarging velopharyngeal region. But from our clinical samples, we found that UPPP sometimes may induce new narrowing in the retroglossal and epiglottal regions. In this study, we use computational fluid dynamics(CFD) simulation to capture the flow patterns of OSA patients who underwent UPPP. Contrary to previous CFD studies on OSA, this study shows that even the minimum wall pressure is lower after UPPP, the apnea hypopnea index(AHI) could be reduced. Thus, we combine fluid mechanics and muscular physiology to raise a new perspective to explain pathology of OSA and evaluate efficiency of UPPP. Methods: Seven OSA patients were selected randomly form Beijing Tsinghua Changgung Hospital with one-night polysomnography(PSG) before and after UPPP. 3D upper airway structures were reconstructed from CT scan of each patient. We used a commercial CFD software( CFX, ANSYS) to simulate the airflow for a given respiratory condition. Correlation analysis was performed among CFD data and clinical data, such as maximum velocity, minimum wall pressure, apnea hypopnea index(AHI). We calculated average wall pressure around velopharyngeal region and introduced a new parameter, which equals average wall pressure divided by total pressure loss. Results: The result shows no significant correlation(p>;0.05) between AHI and conventional flow parameters that had been used in previous study. But ratio of the new parameter pre- and post UPPP shows strong correlation(p<0.01) with ratio of AHI pre- and post UPPP for each patient. Conclusion: The parameter we firstly introduced here represents an effort that the muscle around velopharyngeal region must make to keep upper airway open. The higher this parameter is, the more collapsible the upper airway will be when a patient is asleep due to the damped muscular activity. Thus, it can be seen as a compensatory coefficient that is correlated with anatomy abnormality which can be corrected by UPPP.