An oxygen concentrator is a medical device designed to provide a concentrated flow of oxygen to a patient. The air from an oxygen concentrator has a higher concentration of oxygen than the surrounding air, but the device does not rely on the use of oxygen tanks. There are a number of reasons for using an oxygen concentrator with a patient, and these devices are subject to varying degrees of regulation depending on where they are used. With an oxygen concentrator, the unit draws air into a chamber that absorbs nitrogen. The oxygen-rich air is led through a tube to the patient, while nitrogen is vented harmlessly. Depending on the size of the unit, it can filter and concentrate varying amounts of air per minute. Oxygen concentrators can be used instead, as seen in sick rooms, and several companies also make portable versions that can be used by people while traveling or wanting to stay up.