The portable oxygen concentrator has been in use since around 2000. These devices typically produce less than one LPM of oxygen and use a version of pulse flow or demand flow to deliver oxygen. The way this works is that the oxygen is not constantly flowing, only when the patient is inhaling is the flow working. The only draw back to this type
of device is that there are only a few portable oxygen concentrators that produce at least 3 LPM of continuous flow oxygen. However, with the
demand flow the device is able to either provide higher flows or are able to reduce power consumption. Portable oxygen concentrators typically use electricity from a wall outlet and can also run on batteries.
http://www.youtube.com/watch?v=Q4gIJjSMcCU
