Higher pressure for longer hose?

Needsdecaf · Post by **Needsdecaf** » Thu Apr 24, 2008 1:30 pm

Well on that subject, I have a question being new....what is the drawback to upping the pressure 1/2 or 1 cm? Is there anything other than discomfort and the potential for more leaks? Or do you run the risk of physical harm?

Just asking. You guys who run APAP must have pressures all over the place vs. your titration, no?

-SWS · Post by **-SWS** » Thu Apr 24, 2008 1:55 pm

On the subject on pressure drop. Here's a post where dsm measures a 1 cm pressure drop at the mask with his humidifier, hose, etc.:
viewtopic.php?t=30283&start=30

Not such a big deal with AutoPAP, since the algorithm strives to simply deliver "enough" pressure to keep obstructive events at bay (regardless of reported pressure measurements). But a 1 cm pressure drop for someone using fixed BiLevel of fixed CPAP can be slightly suboptimal in some cases. Machines measuring pressure at the mask are not susceptible to this problem.

Needsdecaf wrote: Well on that subject, I have a question being new....what is the drawback to upping the pressure 1/2 or 1 cm? Is there anything other than discomfort and the potential for more leaks? Or do you run the risk of physical harm?

No significant risk of physical harm IMO. I personally think either incrementation method is viable. If you're "fine tuning" then 0.5 cm increments make sense to me. If you're searching for a quick pattern then 1 cm or even greater increments make sense to me as well. I've done it both ways over the years with no problems.

So far the only problem I've encountered is radon in the basement... And I didn't even realize this CPAP caveat until Jim recently pointed it out! .

TerryB · Post by **TerryB** » Thu Apr 24, 2008 1:59 pm

The APAP doesn't get as wild as you might imagine. I usually set the hi and lo limits within a couple cm of my current running CPAP pressure. That just gives the machine a little wiggle room on the high side in case it needs it to open an event. On the other end, if I set the bottom too low, I know I am going to have obstructions. And those cause disturbances which I try to avoid. So I just see if giving it more latitude indicates I could lower my AHI by raising my running pressure. A couple of times, it has shown me that is the case so I tweaked up. I have run around 0.7 to 1.3 for most of my 2+ years.

TerryB

Snoredog · Post by **Snoredog** » Thu Apr 24, 2008 2:09 pm

[quote="TerryB"]The APAP doesn't get as wild as you might imagine. I usually set the hi and lo limits within a couple cm of my current running CPAP pressure. That just gives the machine a little wiggle room on the high side in case it needs it to open an event. On the other end, if I set the bottom too low, I know I am going to have obstructions. And those cause disturbances which I try to avoid. So I just see if giving it more latitude indicates I could lower my AHI by raising my running pressure. A couple of times, it has shown me that is the case so I tweaked up. I have run around 0.7 to 1.3 for most of my 2+ years.

TerryB

DreamStalker · Post by **DreamStalker** » Thu Apr 24, 2008 2:27 pm

Needsdecaf wrote:...
I didn't mean to come off as being pompous by giving the "I am an engineer comment" ...

No biggie .... could have been worse. Like ... "Trust me, I'm a certified DME!"

GeneS · Post by **GeneS** » Thu Apr 24, 2008 8:46 pm

I am a Civil Engineer too. I think flow formulas help understand cpap flow such as why airway and lung pressure goes negative when you breath in thru your mouth with cpap. Pressure loss per foot increases as air flow or velocity increases with increased cpap pressure settings. It helps explain how the vent acts as an orifice and how it affects the circuit flow rate at a given pressure. Berneule's sp? law and pv=nrt are two formulas that help explain circuit flow. It would be interesting to try to make a mathematical model of cpap flow. I do not have the time to do it.
GeneS

Needsdecaf · Post by **Needsdecaf** » Fri Apr 25, 2008 7:40 am

[quote="GeneS"]I am a Civil Engineer too. I think flow formulas help understand cpap flow such as why airway and lung pressure goes negative when you breath in thru your mouth with cpap. Pressure loss per foot increases as air flow or velocity increases with increased cpap pressure settings. It helps explain how the vent acts as an orifice and how it affects the circuit flow rate at a given pressure. Berneule's sp? law and pv=nrt are two formulas that help explain circuit flow. It would be interesting to try to make a mathematical model of cpap flow. I do not have the time to do it.
GeneS

DreamStalker · Post by **DreamStalker** » Fri Apr 25, 2008 7:48 am

[quote="Needsdecaf"][quote="GeneS"]I am a Civil Engineer too. I think flow formulas help understand cpap flow such as why airway and lung pressure goes negative when you breath in thru your mouth with cpap. Pressure loss per foot increases as air flow or velocity increases with increased cpap pressure settings. It helps explain how the vent acts as an orifice and how it affects the circuit flow rate at a given pressure. Berneule's sp? law and pv=nrt are two formulas that help explain circuit flow. It would be interesting to try to make a mathematical model of cpap flow. I do not have the time to do it.
GeneS

RonS · Post by **RonS** » Fri Apr 25, 2008 8:31 am

It would seem to me, as a non-engineer but scientifically minded person , that one could measure the pressure in one's cpap system rather effectively with some water and a ruler, making a quick and dirty analog manometer.

Hold end 1/3 of tubing in horseshoe-like U shape, fill half way with water. Turn CPAP on. Measure height difference of water levels in centimeters.

This should be fine for measuring static pressure -- no leaks and no breathing going on. At least it should be able to check if your machine is calibrated properly.

I think that the problem is that the cpap must maintain constant pressure during variable flow rates. It would be interesting to poke some holes in the hose before the water and see if pressure holds... maybe when I have a spare hose or two.

A long ribbed hose probably wouldn't reduce static pressure by much, but it might have a very significant impact on pressure when there is a flow.

IM(non-engineer)HO

Panhandler · Post by **Panhandler** » Fri Apr 25, 2008 8:54 am

Two quick observations.

The hose coupler with an oxygen port and a few feet of clear tubing from the hardware store makes an easy way to make a manometer.

I use the F&P Infinity (which is being phased out) and the NasalAire II. Both are nasal prong systems that fit into the nares, and both are very stable for sleeping on my stomach. Once I figured out the right size, both are very comfortable.

oceanpearl · Post by **oceanpearl** » Fri Apr 25, 2008 9:12 am

Hose length cannot possibly have an effect on pressure. Pressure is constant in a vessel!!!

Needsdecaf · Post by **Needsdecaf** » Fri Apr 25, 2008 9:16 am

[quote="oceanpearl"]Hose length cannot possibly have an effect on pressure. Pressure is constant in a vessel!!!

Needsdecaf · Post by **Needsdecaf** » Fri Apr 25, 2008 9:24 am

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.

Saw your suggestions before, but did not connect them to belly sleeping. I guess that you've got your face on it's side on the pillow so more or less the same.

Opus is what I am thinking is my choice.

Breeze looks a bit on the scary side. Is all that headgear comfortable? Doesn't look it. I'll have to research the mods you mentioned.

Comfort Lite II - that just looks REALLY uncomfortable.

Ditto on the Aura.

I'm a minimalist kind of guy, the Opus would be be my first choice.

Does anyone sleep with the Opus and is both a side and back sleeper? I am primarily a back sleeper but like to flip around as well. I'm happy with my current hose management rig, it'll pretty much adapt to anything.

_________________

CPAPopedia Keywords Contained In This Post (Click For Definition): breeze, nasal pillow, swift, Aura

DreamStalker · Post by **DreamStalker** » Fri Apr 25, 2008 9:48 am

Needsdecaf wrote:
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.
Saw your suggestions before, but did not connect them to belly sleeping. I guess that you've got your face on it's side on the pillow so more or less the same.

Opus is what I am thinking is my choice.

Breeze looks a bit on the scary side. Is all that headgear comfortable? Doesn't look it. I'll have to research the mods you mentioned.

Comfort Lite II - that just looks REALLY uncomfortable.

Ditto on the Aura.

I'm a minimalist kind of guy, the Opus would be be my first choice.

Does anyone sleep with the Opus and is both a side and back sleeper? I am primarily a back sleeper but like to flip around as well. I'm happy with my current hose management rig, it'll pretty much adapt to anything.

I agree. The Opus 360 would be a very good first choice. Mkae sure it is the newer "360" version as there are still versions of the introductory model being sold on the auction site and other vendors. The newer "360" version fixed several design flaws from introductory model that came out about a year ago.

The Breze headgear is not just scary, it is actually a torure device and I'm sure Cheney and comapany are using it on prisoners at Gitmo. However, you can totally redesign the headgear and make it a very effective and comfortable mask interface as I did about a year and a half ago. Used it very successfully for over a year but have recently started using the newer Opus 360 and I think I now prefer it to the Breeze.

RonS · Post by **RonS** » Fri Apr 25, 2008 10:31 am

Well, I tried my quick and dirty manometer.

My CPAP is set at 10 with a ramp starting pressure of 5.

I took the hose off my mask and held it in a U shape.

I poured about 8 oz of water into the hose and adjusted so that the water levels were approximately half way up the legs of the "U".

I turned on the cpap and hit the ramp button.

I did not precisely measure the height differential of the water, but it was approximately 2 inches.

I then turned the machine off and on to get the 10cm pressure and the height differential appeared to double to about 4 inches.

All of this took less than 2 minutes, probably closer to 1.
I could have simply marked the two water levels on the wall with a pencil and measured accurately, but it was just a quick-and-dirty proof-of-concept for a quick-and-dirty manometer.

As a side note: Turn off the cpap before pouring out the water or you'll be wiping water off the wall.

Like me.