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Questions about Portable Oxygen Concentrators

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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

Ask the Expert 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 We would love to hear your questions and comments. You can address your emails to any of the following: COPD Coach, Caregiver Coach, COPD Doctor or COPD RT.


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  • I've just moved from using a continuous oxygen in large bottles and a home concentrator to using a portable pulse oxygen concentrator and despite trying to breath normally and also when the breath symbol is shown, my oxygen saturation is dropping a lot more than usual; into the low 70s and high 60s. I then need to stop walking or sit down frequently to get my O2 back up to 88%. I have been running at 4 liters continuous when walking and 2 liters continuous when sitting and able to keep my O2 up to 94% most the time; except for long distances walking. I know the portable pulse oxygen concentrators just give a pulse of air every 10 seconds or so, vs continuous oxygen, but apparently I'm not breathing at the right time sometimes or too often and missing some of the puffs of O2, as my O2 saturation doesn't recover or even keep up as high as with continuous oxygen. What am I doing wrong?
    • Sounds like your portable is just not putting out the volume that you need. You can try pursed lip breathing to get the maximum that your machine can provide but you don't need to time your breathing to the pulse noise the machine is making. The pulse you are hearing is the machine filling the tank so there is O2 there when you need it. If the tank isn't large enough to supply your needs, or the compressor isn't filling the tank fast enough [That's the pulse sound you hear.] you are simply "over breathing the machine"! [Read the above post again carefully.] Check with your provider to insure that you have the correct machine for your needs. You are not doing anything wrong!
    • You are doing nothing wrong. Just breath normally and your mobile oxygen bottle or device senses the right moment to give an oxygen pulse. That is just a split-second after you started breathing in.
      So your device synchronizes with you, not the other way around.
  • I have a question.. What is the lifetime of oxygen concentrator?

    • I am not 100% positive, but I have heard that it's unusual for a POC to last for 5 years without needing to have the sieve beds refurbished.

      I hope that someone with more knowledge will see this and respond.

  • My first POC gave up the ghost after a little over three years. I was very pleased that the company honored the warrantee even though I was over by about three weeks. Because I was travelling again almost immediately, I bought another and had the first one repaired and refurbished. Now I have two, and keep both pretty busy traveling. I used mine hard, and still do.

    Partha, I agree with the Professor. I doubt that you are doing anything wrong; your machine just doesn't have the "oomph" you need. I would refer you to the following website:

    This review of POC's should explain what the problem is with the POC you have.

  • I hope you can help!

    My dad has IPF and uses oxygen normally on 4lpm... Or at least that's what we think, as i get confused between the difference of flow and lpm. He has the devilbiss poc and normally puts it on a 3-4 setting. We are trying to buy a poc that he can travel with and use outside of the house. I understand that they don't come over 3lpm continuous, can you help guide a little on which are the better ones to use? With as long battery life as possible?


    • The two I am aware of that gave the highest continuous setting at 3 liters are the SeQual Eclipse and the eQuinox. You should ask his O2 provider if he could try both. Also, sometimes if a conserved or oximiser device is used, a patient can get more O2 at the same setting.

      For higher flow rates, liquid or tank systems are the only equipment that can deliver higher than 3 liters/minute continuous flow.
  • I have heard that an oxygen concentrator should not be laid on its side--something about mixing up the cystals inside? Is that true? If so, is it the same for portable concentrators?


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