Questions about Portable Oxygen Concentrators

This article was reviewed by Senior Director of Community Engagement and COPD360social Community Manager, Bill Clark, as well as certified staff Respiratory Therapists on January 23, 2020.

Dear COPD Coach,
I have been looking for a portable oxygen concentrator and have noticed that the continuous flow models are much larger, heavier, and have less battery time than the pulse models. My questions are, first why is this so, and second can anyone using oxygen use a pulse model?


Dear Confused,
You are correct when you say that continuous flow portable oxygen concentrators (POCs) tend to be significantly larger. There is a very good reason for this and it is really based on simple mechanics.

Oxygen concentrators all work pretty much the same. The ambient air we breathe contains about 78% nitrogen, 21% oxygen and 1% of other gasses. The concentrator has the job of taking as much of the nitrogen out of the air as is possible while leaving the oxygen. To do this, the concentrator draws in air through the inlet filter where a compressor compresses the air and puts it into the first of two cylinders called a zenolite tower which contains sieve beds. The sieve bed’s job is to become saturated by the nitrogen. A valve then opens (that’s the “poofing” noise you hear) and then the oxygen is pushed into a second zenolite tower where additional nitrogen is removed while the nitrogen in the sieve bed is released out of the unit. The oxygen, now at around 95% purity, also leaves the unit and travels to the user.

In order to produce large volumes of oxygen continuous flow models must have very large compressors and very large sieve beds to absorb enough nitrogen. In the case of a portable continuous unit it must have larger batteries in order to power the larger compressor. Pulse units have much smaller sieve beds and smaller compressors and therefore can use smaller batteries.

Continuous flow units put out a specific adjustable dose we measure in liters per minute. The oxygen put out by pulse units cannot be measured the same since it does not produce constant oxygen for one minute. The output of a pulse unit is determined by the size of the individual pulse (called a bolus) and is measured in milliliters per breath. The other thing that must be taken into account with pulse units is the number of pulses of oxygen they produce in a minute. It is very easy to “over-breathe” these units by trying to take more breaths than they are capable of producing.

Granted, much of the oxygen in a continuous flow unit is wasted simply because we pause between breaths. Most pulse units are designed to produce a pulse when it senses you are taking a breath (conservers work the same).

Another difference between pulse units is the purity of the oxygen and when and how the bolus is released. In some cases the bolus is released immediately when it senses a breath, and in other cases it is spread out longer or occurs later in the breathing cycle. All of this affects how you are saturated with oxygen. If the bolus is released late and you are taking short breaths, some of the oxygen could be wasted.

Talk to your doctor if you have more questions.

Battery technology is advancing at a rapid pace with batteries becoming smaller and lighter but with greater capacity. However the limiting factor with producing smaller continuous flow unit remains the size of the sieve beds and the size of the compressor needed to produce the large volume of air required. So, until the technology changes in those areas we will be left with larger and heavier continuous flow units. This is also why portable continuous flow units do not put out more than 3 liters per minute.

Before purchasing a unit you should consult with your pulmonologist to determine if a pulse unit is right for you. Remember also that most people requiring supplemental oxygen require more oxygen while exerting and that might be more than what the unit is capable of producing. Also, the numbers on a pulse unit are settings NOT liter flow, so don’t think that a setting of 3 is necessarily the same as 3 liters per minute on your continuous machine. The only way to determine if you are being properly saturated by a particular unit, be it pulse or continuous, is do check your saturations with a pulse oximeter during rest and exertion. You will most likely respond the same with different units. This is a test best left to a medical professional!

If you intend to travel with your pulse unit you have to consider that it might not be suitable for use while sleeping. Many supplemental oxygen users are “mouth breathers” (especially while sleeping) and pulse units are triggered by nasal inhalation. Therefore, the effectiveness of the sensitivity of the unit should be determined. if you intend to use it during while sleeping.

So, long story short, POCs are not a “one-size fits all” proposition. Make sure you speak with a medical professional prior to purchasing a unit, and don’t hesitate to return the unit if it is not keeping you properly saturated!

-The COPD Coach

Coaches Corner is aimed at providing information for individuals with COPD to take to your doctor, and is not in any way intended to be medical advice. If you would like to submit a question to the Coaches Corner email us at [email protected] We would love to hear your questions and comments. You can address your emails to The COPD Coach.


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