If I get a new mask - does anything on the machine need changing?

[cubes123]

I'm currently using the IQ mask given by Papworth but I was wondering if there was anything better out there.

It may be a silly question, but if I buy a new mask, will it be OK at the settings the machine is on now?

Thanks

[ElleCee]

Hi Cubes,
Different masks make a slight difference to the pressure but not really enough to worry about. As long as they fit your face and the machine it should be fine. As a rough guide the nasal masks seem to make the pressure a little higher but it is only a little. Ask at the Papworth if you want to make sure.

Oh and welcome to the forum

Lorraine

[Tigers Fan]

How on earth .......?

........ can a mask make the pressure higher - or lower, come to that?

A properly adjusted, leak free mask delivers the pressure created in the machine, less any friction losses in the hose.

Most interesting of all - to me - is how you would go about measuring the increase in pressure caused by a nasal mask.

Do you mean that nasal masks are less likely to leak? Not my experience. Do you mean there is a smaller volume within the mask - which would cause a quicker pressure drop on the inhale but a more rapid return to full pressure on the exhale?

????????????

TF

[ElleCee]

There are no holes for the air to escape therefore all the air goes into your lungs rather than a small loss expelled from the full face mask. Just put your hand infront of your mirrage quattro and feel the air escaping, that doesn't happen with my nasal mask.
Plus my technician told me, I think that James also said that in another thread.

Lorraine

[Tigers Fan]

Well! I stand corrected!

Hi Lorraine

That's me well and truly told! The Technician said so!

Or is that what you understood him to say?

My problem is that for "the nasal masks ...... make the pressure a little higher" we have to scrap the Laws of Physics.

Even if by "make the pressure a little higher" you actually mean "reduce the pressure losses", I still need a lot of convincing. When one considers the volume of the reservoir of compressd air inside the full face mask and the hose, along with the volume of air being constantly delivered compared to the loss through the vent, any pressure drop will be in the magnitude of small percentages of a micron of water. Then comes a great, big, fast asleep sucking in of breath and the full face will maintain pressure fractionally longer than the nasal because it has the greater reservoir. For the same reason it will take fractionally longer to re-pressurise. At that point, having EPR or not will affect the pressure far beyond the abilty of any mask shape or size. Then you turn over and nudge your mask, the resultant leak will probably knock your comparison into touch. de dah ad infinitum.

I wonder if it was the same technician who old Shuckie that CPAP is better than APAP?

Can you find James' reference?

In a strangely argumentative mood for such a fine Sunday morning - probably something to do with what the Chiefs did to us yesterday ......

TF

[ElleCee]

By 'make the pressure higher' I mean that due to less loss of pressure (Lack of escape holes) the resulting pressure is a little higher.

James, where are you?

[cubes123]

Thanks for the answers. I didn't think it would make much/any difference but wanted to make sure.

I'll have a look around for a mask and try one out.

Thanks!

[James @ Intus]

Here I am

It's not so much that nasal masks make a change over full face masks. It's to do with how fast the exhalation vents 'leak'.

Lorraine refers to my comments on her finding the SleepWeaver to give her more air, or a higher pressure, compared to the Quattro. Even with the machine at the same pressure.

So if it blows at the same rate, how can the end result be different?

TF forgot the CO2 exhalation port. An intentional leak to make sure CO2 washout is expelled from the mask (avoiding rebreathing) and that should the machine die when you have the mask on, you stay alive. You can just about get some air through the holes.

Rather than an industry standard "mask must leak at this Litre per Minute rate" all manufacturers and masks within their range seem to leak differently.

In Lorraine's case, we found that the Quattro leaks significantly more than the SleepWeaver, whilst the SleepWeaver leaks at the same rate as say a ComfortGel. Now remember, we're not talking accidental, annoying leaks form misfitting. We're talking intentional leaks through its exhalation holes/vent whatever you want to call them.

Where the quattro leaks at about 30-and a bit at 10hPa (cm/H2O) the Sleepweaver, at the same CPAP pressure, leaks at 25 LPM. That's quickly off the top of my head, we have a leak chart here on the SleepWeaver FAQ.

In all of ResMed's product manual PDFs, you will find a similar chart.

For example page 11:

http://www.resmed.com/us/assets/documents/product/mirage_quattro/user_guide/61843_mirage-quattro_user-guide_amer_eng.pdf

More in depth here:

http://www.resmed.com/assets/documents/service_support/pressure_flow_rates/1012648_pressure-vs-flow_usa_eng.pdf

Other manufacturers list similar info in their product material.

So if one mask intentionally leaks more air than another, the end therapeutic pressure can indeed vary slightly. Lorraine felt the SleepWeaver gave her more air, which wasn't a bad thing necessarily.

This is also why modern machines have mask settings, at least covering those masks by that manufacturer. Tell the machine which mask you are using and it will recalibrate to adjust for the change in leak rates/resistance whatever it takes into account.

So does anything need changing?

Most likely, no. It doesn't HAVE to. You may experience a bit more, or less, pressure than anticipated but an Auto will compensate for it to a degree and a fixed pressure machine is often set at an arbitrary level anyways. Unless it was properly titrated.

So the answer is, discuss it with the clinic, be aware of the possible changes, but don't worry about it too much as difference tend to be minimal.

It would be interesting if someone can work out the difference in end pressure in hPa hectopascals when a mask leaks say 15% more air in LPM, litres per minutes. Engineers like TF may fancy that equation, I haven't been able to come up with a meaningful explanation myself as hectopascals and water pressure (when measuring air) is too scientific for me!

[Tigers Fan]

Oh, no I didn't!

Hi James and Lorraine

TF did not forget the CO2 exhalation port, I called it a vent, as in "the volume of air being constantly delivered compared to the loss through the vent".

I also acknowledge that indeed we could expect a slight pressure drop in LOrraine's Quattro compered to her unvented Sleepweaver but that it would be in the order of small percentages of a micron of water - say 10%, that is 1/10 of 1/1000 of 1/10 of a cm H2O which by my reckoning is one millionth of 1 cm H2O.

So when we say Lorrane felt she was getting a higher pressure, we are definately talking subjective experience and not science.

Now I will take a leap into the unknown (to me). As we can calibrate some machines for different masks, I'm going to argue that the differences are due to the rate of flow of which the mask is capable - the rate at which the mask is able to pass air at whatever pressure from the hose/machine to the patient's lungs. The nasal mask has smaller holes through which the air must pass to get to the patient than a mouth breathing Quattro user. The nasal mask user will require a slightly higher pressure than the Quattro user to inhale the same volume of air (given the same pair of lungs breathing in for the same amount of time) and therein lies the calibration of the machine per mask.

Imagine if you will, the air pressure curve over several cycles of breathing. Let's sart with the machine pumped up and the user holding his/her breath with full lungs - just momentarily to get a start point. Take out EPR for simplicity. The machine is supplying massively, your lungs are supplying massively - are a few teensy CO2 vent holes going to make any difference compared to the exhalation port opening. Not a measurable bit! Pause betweeen breaths, the pressure builds and wallop! the user breaths in. Sleepweaver has to suck through nasal prongs, I suck in through my large, gaping mouth. CO2 vent hoes make no difference in the Sleepweaver 'cos there aren't any. Compare a few teensy vent holes to my gaping jaw and are they going to make any difference whatever? With a moiuth even bigger than my ego - nah! they're not.

Even in a static situation, compare the area of the cross-section of the hose to the total area of the CO2 vent holes, add a constant pressure air supply and you're going to need a magnifying glass over the miniscii of your U-tube to see the difference between CO2 vent open and CO2 vent sellotaped over (do NOT do that at home, children!!).

ANyway, th real question is: how big a hole do you have to dig to distract attention from what the Chiefs did to us yesterday? Is this one big enough yet?

TF

[ElleCee]

TF,
Please tell me, what did the Chiefs do?

[James @ Intus]

Yes but no but yes but no but... The SleepWeaver does have a decent set of vent holes. You just can't see them in most pictures. They're in the cloth, not on the elbow. Only NIV masks haven't got any, as the ventilator will take care of the exhalation part. All CPAP masks and most BiPAP masks have to have CO2 vent holes/exhalation port.

But yes, flow rate will probably also have to do with it.

I'll see if I can ask some of the manufacturers about what influences it most. Their view will definitely trump my attempt at coming to a logical conclusion.

[Tigers Fan]

Stop digging!

I woke last night and remembered to feel the air flow from the vent of my Quattro. It was a large flow at 17 cm!! In fact, feed sleepy dust or fine sand into it and my partner could exfoliate themself!!

Before now, I have only felt the start-of-ramp flow - not much at all. Where it counts, at full pressure, the flow is considerable. I was surprised.

However, the restriction to flow caused by nasal prongs compared to a gaping yaw would, I still believe/guess, effect delivered pressure more.

And isn't that the poiint - delivered pressure to give a lower AHI? I fitted a Whisperer to my 'M' Series and perceived a small pressure drop. I didn't bother measuring the effect on my AHI (would involve changing machines), I just noted two poorer night's sleep and increased the set pressure a half cm to compensate. What I'm saying here is that surely one's AHI is the low constant we seek rather than calibrating machines to deliver a set pressure no matter the mask - and ignoring AHI.

Lorraine - I can't say the words about what the Chiefs did to us. Maybe a CHiefs fan will tell you - in which case it wasn't as bad as s/he says. Failing that - http://blogs.bettor.com/Aviva-Premie...s-scare-a26764 . They won League 1 last season and we won the Premiership, as we so often do - so we were supposed to wup their newly promoted arses. We took a bonus point in the end but only after they wupped us good for a while - a long while!! The entire first half, in fact! Here it comes - I can say it! - they ran in three tries against us! Three!!!

TF

[James @ Intus]

The set pressure is designed to eliminate, or keep within a tolerable level, the AHI. So yes, the AHI is the goal, the pressure the means. If a change of mask changes the pressure, it most likely also changes the AHI. Indeed, the AHI will be the more important figure, in the end.

[Tigers Fan]

Oops!

They won the Championship, not League 1.

[James @ Intus]

As the TF & James debate is over...

It may be a silly question, but if I buy a new mask, will it be OK at the settings the machine is on now?

It's certainly not a silly question and yes, it will be OK, bearing in mind the discussion in this thread. Ideally, you have a machine that has nice reporting features, so you can keep an eye on any changes that may happen.

Oh and welcome to the forums by the way!

I bet you didn't see such a long, part-technical response coming Sorry if it was a tad overwhelming. It's not always like this, sometimes we do just say yes, or no.