Smaller tube diameter = higher pressure?

Last night I tried the 15mm heated tube on my PRS1 and it seemed like the IPAP pressure was much higher than with the plain old 22mm.

The PRS1 automatically recognizes the 15T tube (and locks the setting). When I unplug it, the setting reverts to 22mm (which was the size of my regular hose). So it doesn't seem like it's an issue of incorrect settings.

The display still shows my expected EPAP/IPAP levels (5cm/9cm). But for some reason, IPAP seems much more forceful with the smaller tubing. (It makes leaks more of a problem.)

Is that normal? I can understand how it would need to blow faster through the narrower tube, but ultimately the volume of air delivered should (and the resulting pressure) be the same, right?

Check it with a manometer; maybe something is not working properly.

sawinglogz wrote:Last night I tried the 15mm heated tube on my PRS1 and it seemed like the IPAP pressure was much higher than with the plain old 22mm. ...

I went through the same thing - I was convinced the setting was wrong, double checked everything, switched hoses back and forth, etc. It just felt like a more forceful air flow. Finally I decided to "live with it" and within two days I couldn't tell the difference. I'm guessing that although the average pressure is the same, the increased velocity creates the sensation of slightly increased pressure which we are very sensitive to. It may also be more dramatic if flex or other "variable air flow" settings are used.

BTW, on the same day I changed the hose, I went from a Quattro to a Quattro AIr, and also got a new mattress! For two days my AHI jumped up over 5 (my highest ever) but then dropped steadily so I'm now feeling "dialed in."

That makes sense, Loki. The higher velocity would also dry out tissues more aggressively, making them even more sensitive to airflow.

CapnLoki wrote:It may also be more dramatic if flex or other "variable air flow" settings are used.

I'm on an ASV, so I'm getting bi-level flow with every breath. So it's quite dramatic.

What surprised me was how dramatic it was with a hybrid mask, since the increased air velocity is getting distributed over a pretty large area. I was tempted to drop my PSmin to 3, but I didn't want to mess with that in the middle of the night.

Oddly, I ended up with a better AHI than I'd had the previous few days, and my Zeo thought I slept great, but it sure didn't feel like one of my better nights. There was definitely more aerophagia/GERD going on than the previous few nights.

But thank you for weighing in with your experience; it makes me feel better.

Can anybody recommend a good source for a manometer? I'm just geeky enough (shock!) that I wouldn't mind having one on hand.

sawinglogz wrote:Can anybody recommend a good source for a manometer? I'm just geeky enough (shock!) that I wouldn't mind having one on hand.

Several forum members have made their own manometers. It has been discussed in the past...nothing real recent that I can remember. I imagine if you search the forum archives for "build your own manometer" you should find it.
Otherwise cpap.com sells them
They show 2 different models.
https://www.cpap.com/productSearch.php?query=manometer
$49 and $78...I imagine fairly available on the internet too.

Here is a page with a simple U-tube DIY one.
I couldn't find the Instructable.
http://www.komar.org/faq/manometer/