We propose to develop a system for natural sleep endoscopy (NSE) - the direct visual examination of the pharynx during natural sleep – to define the anatomical pattern of obstruction for individual patients and guide treatment selection in obstructive sleep apnea (OSA). OSA is a disorder of repeated upper airway obstruction during sleep that is associated with substantial cardiovascular morbidity and mortality, endocrine disturbances, daytime somnolence, decreased quality of life, and motor vehicle crashes. About 25-40% of OSA patients cannot tolerate first-line treatment (positive airway pressure) and may consider other options. Oral appliances, surgery, and hypoglossal nerve stimulation offer substantial benefit for selected patients, albeit with associated risks, expense. Outcomes are often unpredictable but are associated with an individual patient’s pattern of airway obstruction. Current approaches of determining pattern of obstruction have important limitations related to validity, feasibility, and cost. NSE is the most likely gold standard, but it has been limited to small studies in the research laboratory or hospital without widespread use, for multiple reasons: trained personnel required, lack of appropriate video recording equipment, substantial cost, and arousal when moving the endoscope to visualize the two major regions of the pharynx. Drug-induced sleep endoscopy incorporates unconscious sedation, avoiding the latter issue but adding risks of administering sedation and validity concerns because unconscious sedation is not natural sleep. Our strategy for meeting this challenge is an endoscopic system for NSE: two cameras incorporated into an endoscopic catheter, microphone, accelerometer (head position), and the embedded system to record the audiovisual and position data in a patient-worn system mounting device. This Phase I SBIR proposal includes developing the endoscopic system and performing a limited evaluation of safety and feasibility. Aim 1: Design and manufacture dual camera endoscopic catheter. The catheter will incorporate two existing cameras with an integrated lens, light source, and sheath. The catheter will provide signal output to a patient- worn system mounting device for data capture during sleep. Aim 2: Design and manufacture patient-worn system mounting device. The head-worn system mounting device will include a microphone, accelerometer, power source, and data recording capability. Aim 3: Perform pilot safety and feasibility study. We will enroll 10 study participants with mild to moderate OSA who will undergo polysomnography and simultaneous evaluation with the NSE system. Adverse events (epistaxis, pain), usability, and acceptance will be measured. Efficacy will be examined.