Zeolite Zeolite-based oxygen concentrator systems are widely used to produce medical-grade oxygen. The zeolite is used as a molecular sieve to create purified oxygen from air using its ability to trap impurities, in a process involving the adsorption of nitrogen, leaving highly purified oxygen and up to 5% argon Zeolites are the aluminosilicate members of the family of microporous solids known as "molecular sieves." The term molecular sieve refers to a particular property of these materials, i.e., the ability to selectively sort molecules based primarily on a size exclusion process http://en.wikipedia.org/wiki/Zeolite
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 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 effective as a continuous flow oxygen concentrator. On-demand devices are not suitable for sleep for patients with the sleeping disorder sleep apnea.
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