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. Since patients only inhale oxygen when they breathe in, when exhaling oxygen is wasted. By having the machine work with the patients breathing cycle, only providing oxygen when necessary, the system keeps 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.
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.
Read more about this topic: Portable Oxygen Concentrator
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