<P> The United States Federal Aviation Administration (FAA) has approved the use of portable oxygen concentrators on commercial airlines . However, users of these devices should check in advance as to whether a particular brand or model is permitted on a particular airline . Unlike in commercial airlines, users of aircraft without cabin pressurization need oxygen concentrators which are able to deliver enough flowrate even at high altitudes, such as OXYFLY . </P> <P> Usually, "demand" or pulse - flow oxygen concentrators are not used by patients while they sleep . There have been problems with the oxygen concentrators not being able to detect when the sleeping patient is inhaling . Some larger portable oxygen concentrators are designed to operate in continuous - flow mode in addition to pulse - flow mode . Continuous - flow mode is considered safe for night use when coupled with a CPAP machine . </P> <P> Common models retail at around $2500 . Leasing arrangements may be available through various medical - supply companies and / or insurance agencies . </P> <P> Military aircraft sometimes use oxygen concentrators to supply the aircrew with oxygen at high altitudes . Otherwise, supplies of compressed or liquefied oxygen are used . </P>

Home o2 can be supplied by which of the following systems