Higher pressure for longer hose?

otiose · Post by **otiose** » Sat Apr 26, 2008 4:02 am

I don't have any real world experience with pressurized hoses but I used to work with vacuum chambers.

What I found was a change in length of hose did not affect ultimate vacuum but did affect the time to reach it significantly. (inverse square?)

If the opposite is true, then maybe all you are doing by adding length to a apap hose is delaying the response time.

Engineers respond please.

roster · Post by **roster** » Sat Apr 26, 2008 5:45 am

[quote="otiose"]I don't have any real world experience with pressurized hoses but I used to work with vacuum chambers.

What I found was a change in length of hose did not affect ultimate vacuum but did affect the time to reach it significantly. (inverse square?)

If the opposite is true, then maybe all you are doing by adding length to a apap hose is delaying the response time.

Engineers respond please.

Guest · Post by **Guest** » Sat Apr 26, 2008 7:23 am

Got any clean 3yr old Subaru's for sale

otiose · Post by **otiose** » Sat Apr 26, 2008 7:25 am

OT: Why do I keep getting logged out?

RonS · Post by **RonS** » Sun Apr 27, 2008 1:57 pm

I can give you some information.

Longer hoses and other parts in the system will cause pressures to be lower during flow. Pressures are reduced by additional friction within the system.

According to a Respironics chart their machine (at least the version to which this chart applies) already compensates pressure for a "6 foot smooth bore tube." Adding a bacteria filter and/or a humidifier to the system causes an enlarging uncompensated drop in pressure which is based on flow rate.

According to their chart, at a flow rate of 50 LPM (about what a mask leaks) having a bacteria filter in place lowers the pressure by 1cm, having both a bacteria filter and a humidifier lowers the pressure by about 1.5cm.

So before you take a breath, the pressure at your mask is indeed lower when you add a lower hose, based upon the leak rate of the mask.

I don't know at what rate of LPM a person breathes, but assuming it is at least twice what a mask leaks, for sake of example, at 100LPM flow, pressure with the bacteria filter and humidifier causes a 3.5cm reduction in pressure.
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Sooooooo, when I put my mask to my face after adding another 6ft hose and a standalone humidifier and the pressure felt lower, I wasn't imagining things. I increased my machine's pressure setting by 1cm which was probably too little.

I can't wait for my smarter machine and card and card reader to arrive so that I can stop fumbling about in the dark.

zorrro13 · Post by **zorrro13** » Sun Apr 27, 2008 4:34 pm

Interesting that Resmed gives you a choice in hose selection. Do all machines have this option? I'm wondering why have the option unless your pressure is going to change

Goofproof · Post by **Goofproof** » Sun Apr 27, 2008 4:50 pm

zorrro13 wrote:Interesting that Resmed gives you a choice in hose selection. Do all machines have this option? I'm wondering why have the option unless your pressure is going to change

They must know the quality of their machines, maybe some day they will take into account how many of their users have the mask selection set wrong too. That shouldn't matter afterall we patients aren't supposed to know how our treatment is doing anyway. Jim

Needsdecaf · Post by **Needsdecaf** » Mon Apr 28, 2008 1:53 pm

DreamStalker wrote:
Already made the suggestion ... ditch the Swift and try one of the following:
Breeze (may need to modify headgear)
ComfortLIte II (may also need some modifiactions)
Opus (may need minimum of modifcation and most similar headgear to Swift)
Aura Headrest (may need to modify headgear)

Those are the most belly sleeping (toss-n-trun) friendly nasal pillow masks.

Ordered the Opus 360 today from my DME. I'm awaiting a call back to confirm the order but I was shocked that they didn't give me any BS like "We don't carry Fisher Paykel products.