Portable oxygen concentrator
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# Overview
A portable oxygen concentrator, (POC) also called a portable concentrator is a portable device used to provide oxygen therapy to a patient at substantially higher concentrations than the levels of ambient air. It is very similar to a home oxygen concentrator, but it smaller in size and more mobile. The portable oxygen concentrator makes it easy for patients to travel freely; they are small enough to fit in a car and most of the major concentrators are now FAA-approved.

# Development
Portable oxygen concentrators have been around for decades; but the older versions were bulky, not reliable, and were not permitted on airplanes. Since 2000, a number of manufactures have improved their reliability and they now produce anywhere between 1 and 6 liters per minute (LPM) of oxygen. There are versions that provide pulse or continuous flow. The portable concentrators plug directly into a regular house outlet for charging at home or hotel; but they came with a power adapter that can usually be plugged into a vehicle DC adapter. They have the ability to operate from the battery power as well for either ambulatory use, or away from a power source, or on an airplane.

# How does it work?
The technology behind a Portable Oxygen Concentrator is based on the same principle as a home domestic concentrator. Air at barometric pressure contains 21% Oxygen combined with Nitrogen and a mixture of other gases. A miniaturised compressor inside the machine will pressurise this air through a system of chemical filters known as a molecular sieve. This chemical filter is made up of silicate granules called Zeolite. The Zeolite will sieve the nitrogen out of the "air" concentrating the Oxygen. Part of the produced Oxygen is delivered to the patient; part is fed back into the sieves to clear the system from the accumulated nitrogen, making it ready for the next cycle. Through this process, this system is capable of producing medical grade oxygen of up to 96% consistently. The latest models can be powered from mains electricity supply, 12v DC (Car/Boat etc..) & battery packs making the patient free from relying on using cylinders & other current solutions that put a restriction on time, weight & size.
Most of the portable oxygen concentrator systems available today provide oxygen on a pulse (on-demand) delivery in order to maximise the purity of the oxygen.

# The difference between on-demand & continuous flow
Most portable oxygen concentrators are built from the size of a binocular case and weigh less than a couple of bags of sugar. The reason for this is because of the on-demand system. It allows the concentrator to be built with smaller components than that of a domestic concentrator. Because the patient only inhales oxygen when they breathe in, when exhaling oxygen is wasted. Therefore what manufacturers decided to do is build a machine that works on your breathing... only providing oxygen when necessary, keeping wasted oxygen to a minimum.
Most on-demand portable oxygen concentrators work on settings which are very much equivalent to a specific LPM (Litre per minute). To determine this, the machine works on a bolus system. The bolus size is measured in millilitres and is the "shot" of oxygen released upon inhalation. The size of the bolus on each setting is worked out based on the amount of oxygen inhaled if the patient was on continuous flow oxygen. Since oxygen isn't required when we exhale, oxygen is normally wasted; hence the reason behind the this type of technology.
Technology has progressed in a way so that boluses can be made variable based on the patients breathing rate. This is particularly useful for using an on-demand machine whilst sleeping. Naturally the breathing rate slows whilst sleeping. A machine with a variable bolus detects a slower breathing rate; adjusting the bolus size so that its a longer shot of oxygen upon inhalation, but still maintaining the patients prescription of x amount of litres per minute.
It is not usually recommended that an on-demand device be used during sleep, however clinical studies have found that some on-demand portable oxygen concentrators are just as affective as a continuous flow oxygen concentrator. On-demand devices are not suitable for sleep for patients with the sleeping disorder sleep apnea.

# FAA approval
On July 12, 2005 the American FAA approved the use of portable oxygen concentrator for use on commercial airlines. This Special Federal Aviation Regulation (SFAR) will permit passengers to use certain portable oxygen concentrator devices on aircraft, provided certain conditions in this SFAR are satisfied. The SFAR includes a POC preparation requirement for carry-on baggage transport, and a battery-packaging standard necessary for the safe carriage of extra POC batteries in carry-on baggage. This rulemaking action was deemed necessary to address the traveling needs of people on oxygen therapy.