Continuous flow vs pulse dose

Oxygen concentrators deliver in one of two ways, and the difference changes how long a battery lasts, how heavy the machine is, and whether it suits you at all. It is the second-biggest sorting question after concentration, and unlike concentration it is often not stated clearly in listings.

Continuous flow

A continuous-flow machine produces a steady, uninterrupted stream of oxygen. Set it to 3 litres per minute and it delivers 3 litres per minute, while you inhale, while you exhale, while you talk, while you sleep. The stream never stops.

This is the simpler behaviour, and it is what most home machines do. Because the output is constant, the compressor has to run constantly too, which is why these units are larger, heavier, plugged into the wall, and usually sold on casters rather than a shoulder strap.

The trade-off: a lot of the oxygen is produced during the part of your breathing cycle when you are not inhaling, and simply vents away. That is inefficient, but it is also predictable, and predictability is exactly what you want from a machine that runs all night.

Pulse dose

A pulse-dose machine waits. It senses the small pressure drop at the start of an inhale and releases a measured burst of oxygen at that moment, then stops until the next breath.

Because it only produces oxygen when you are actually breathing in, a pulse machine does far less work for the same delivered dose. That is what allows portable concentrators to be small enough to carry and to run on a battery for hours.

The trade-offs are real:

• The machine has to detect your breath. Shallow breathing, mouth breathing, or a poorly seated cannula can mean missed triggers.
• Settings are not litres per minute. A pulse machine's setting 3 is a bolus size, not a flow rate, and it does not translate directly to 3 L/min of continuous flow.
• Most manufacturers do not rate pulse machines for sleeping, because breathing changes during sleep and missed triggers become more likely.

Which delivery type suits which situation

• Continuous flow suits use at home, extended sessions, and any situation where you need a known, steady rate. It is what you want if a clinician has specified litres per minute.
• Pulse dose suits going out, where weight and battery life decide whether the machine comes with you at all.

Some people end up with both, a larger machine at home and a portable one for leaving the house. That is a real expense, and worth planning for rather than discovering after you have bought the wrong single machine.

How to tell which a listing is describing

• Units. 1 to 5 L/min is continuous flow. A bare 1 to 5 settings with no unit is usually pulse dose.
• Power. If a machine runs on an internal battery for hours, it is almost certainly pulse dose. Continuous-flow machines draw too much to do that.
• Weight. Continuous-flow home units generally run well into double-digit pounds. Machines light enough to carry on a strap are typically pulse.
• Overnight rating. If a listing says the machine is rated for 24-hour operation, it is continuous flow.

If you cannot tell from the listing, that is a reasonable question to put to the seller before buying. We would rather answer it than have the machine come back.

A note on our own range

The machines we sell are continuous-flow units, quoted in litres per minute. We do not currently stock pulse-dose portables. Where a machine is battery-capable, it says so on its product page; where it is not, it runs from mains power.

We would rather tell you plainly that we do not sell something than let you assume we do.

Talk to your doctor about this specifically

If you are considering supplemental oxygen for a health reason, delivery type is worth raising explicitly. A clinician who has told you 2 litres is describing continuous flow, and a pulse machine set to 2 is not the same thing. People get this wrong, and it is an easy thing to get wrong.

Take the specification page of whatever machine you are considering to the appointment. It is a two-minute conversation that avoids an expensive mistake.

Long Breeze machines are intended for general wellness and everyday breathing comfort. They are not intended to diagnose, treat, cure, prevent, or relieve any disease or symptom, and they are not a substitute for professional medical care or for oxygen therapy prescribed by your physician. Talk to your doctor before use if you have a medical condition. Statements on this site have not been evaluated by the Food and Drug Administration.