I’m interested in a compact CPAP unit for travel. ResMed’s Air Mini seems like a pretty good choice, but I’m trying to understand the humidification system. My current home CPAP has a tank that you fill with distilled water for humidification, but the Air Mini uses a cartridge placed in the hose just upstream of the mask that somehow captures the moisture of your exhaled air and puts it back into the fresh air you then inhale. The cartridges are a consumable item: once you open the sealed wrapper, you’re supposed to discard the cartridge within 30 days.
I thought maybe the 30-day time limit was a sanitary thing, because from what I’ve read, they’re not washable. But now I’m reading some user reviews that claim the cartridges actually stop working effectively after some period of time (anywhere from 1-3 months). This implies some kind of chemical activity taking place, with reactants getting consumed over time.
Anyone have an idea of how these little humidifier cartridges work?
The Resmed site calls it a small “heat and moisture exchanger”, which appears to be a term of art. Wikipedia has a short article on them:
There are also various NIH papers on the subject:
I’m guessing the HumidX device is probably the hydroscopic type, with calcium chloride salts embedded in paper. I looked for a patent on it, but couldn’t find one, possibly indicating that this is very standard and unpatentable technology.
The salts themselves shouldn’t chemically degrade. But the paper matrix would only last so long in that environment. It’s also possible the salts wash away over time, or migrate in a way that makes them less effective.