1. Wintergreenresearch. Oxygen Concentrators: Market Shares, Strategies, and Forecasts, worldwide, 2013 to 2018,http://www.wintergreenresearch.com/reports/oxygen%20concentrators.html.
2. Atlas, C. R., Bliss, P. L., Murdoch, R. W., and Halperin, S. C.Portable Oxygen Concentrator. U.S. Patent 0,227,360, 2007.
3. Dubois, A., Bodelin, P., and Vigor, X.Portable Oxygen Concentrator. U.S. Patent 6,520,176, 2003.
4. Ackley, M. and Zhong, G.Medical Oxygen Concentrator. U.S. Patent 6,551,384, 2003.