Project Summary/Abstract This proposed project relates to the development and evaluation of a novel closed-loop long-term oxygen therapy control system that includes an innovative smartphone-based companion software application. We hypothesize that such a system will optimize oxygen delivery in mobile patients, minimize hypoxemia and air hunger during physical exertion, avoid hyperoxia and improve patient health-related quality of life. More than 1.5 million Americans are currently receiving long-term oxygen therapy. Drawbacks to long-term oxygen therapy include significant limitations to patient physical activity, a heightening of social isolation and decline in emotional well-being. Improved mobile technology is needed to address these drawbacks and improve patient outcomes. A production prototype system will be designed, built, and evaluated.