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A good seal isn't needed with a Respironics delivery device? Huh??
#1
So I'm watching a Philips video on the Amara mask, and the last sentence is a short reminder that you don't "have to seal every mask leak if you have a PR delivery device". Say what??? I've been beating my brains out trying to stop leaks for most of the night thinking they're compromising the therapy, not to mention they're noisy and irritating.

Admittedly I'm only four months into this, but could you folks enlighten me as to where I took a wrong turn?
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#2
Ignore, for a moment, noise and air blowing into your eyes. Strictly speaking, that does not interfere with your treatment, even though it would interfere with your sleep so you'll want to correct the issue.

This question also relates to why the mask has an intentional leak vent, so I'll address both.

The important thing to remember is that CPAP treatment is predicated on pressure in the airway. It is the pressure in the airway that splints the airway open, not the airflow. So, let's ignore for a moment the complicating issues of that mask vent and the complicating issue of breathing. [ I promise we'll get back to them. ]

Assuming a perfect seal between the mask and the face, all the CPAP device would have to do is create airflow until the appropriate airway pressure is maintained, then stop the blower. Just like filling a car tire, pump it with air, then it is pressurized and stays pressurized (more or less).

Ok, now let's talk about breathing. Again, assuming a perfect seal in the pressure system, inhaling will require the CPAP device to pump some more air into the system to compensate for the inhaled air. Then, when you exhale, the CPAP device would simply remove the amount of air that you exhale to keep the pressure constant. Sounds great, except for one little problem. You are constantly breathing your own exhaled air. The medical term for the eventual result of this is called "death". Back to the drawing board!

So, let's add a vent in the mask to introduce an intentional leak in the system. Just like a slow leak in a car tire, the CPAP device can keep the system pressurized by simply pumping in air at the same rate that it is leaking out. When you inhale, the device pumps in more air, and when you exhale, it pumps in less air. This means that you are always inhaling fresh air from the machine because your exhaled air is going out the mask vent.

[ The following paragraph was edited based on input from Sleepster, below. ]

So what's the catch? It turns out that the CPAP device has a finite limit on the airflow it can deliver. If the total leakage exceeds the airflow that the device can deliver, it cannot maintain the treatment pressure. And if the total leakage gets close to the airflow that the device can deliver, the extra airflow required for an inhale may push it over the edge, causing the inhale to not be detected.

So, the overall leakage rate wants to be kept within reasonable limits. However, the mask leak rate is _well_ below those limits. That means that there's some room for more leakage without the system getting confused. And that's where unintentional leaks come in. As long as the total leak rate is within reason, the machine doesn't care whether the system leakage happens because of the mask vent or because of unintentional leaks. It's still just leaks to the machine. It simply compensates.

And that's why "small" unintentional leaks do not _have_ to be fixed. The machine can deal with it.

To put some numbers into the mix, ResMed devices consider that an unintentional leak rate of less than 24 L/min (liters per minute) is an acceptable seal. Intentional mask leak rates through the vent will vary with the mask and with the pressure, but they are around 35-ish L/min.

Does that explain it for you?
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#3
Wow Ron, it certainly does, and in spades to boot!

Again, I'm a rookie and only just beyond the "casual observer" level, but it has seemed to me that my worst nights AHI-wise are somewhat coincidental with higher large leak numbers. Admittedly I don't know what constitutes a "large leak", but it would seem that a higher % number is worse. Therefore, at least part of my efforts to stem all leaks are founded here.

I remember that strangely "way back when" I first started therapy in mid-April I got some of my best nightly numbers. But at the time I didn't know what the numbers were, I was just trying to comply best I could and be comfortable and quiet. Now that I know a little more about it and can read the numbers on my info screen, and am trying to learn SleepyHead it seems that the good numbers are a little more elusive!

Thanks for the enlightenment.
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#4
[ This first paragraph was edited based in feedback from Sleepster, below. ]

A "large leak" is a leak at which the total airflow is at or near the limit that the device can provide. AHI numbers during large leak periods are not reliable. They may or may not have been real events.

To keep mask leaks under control, try sleeping at the edge of your pillow so the mask is not being pushed aside by the pillow. Try to "pre-compensate" with the mask straps so that the tension is correct once you have settled into the pillow. Starting with the mask skewed and "sliding" into position to center the mask seems to work for me.

DO NOT OVER TIGHTEN YOUR MASK STRAPS. That will have two bad effects: one, it will be uncomfortable and may prompt anxiety (go ahead, ask me how I know this for a fact), and the second is that it may actually make the leaks worse. Many masks have a silicone "flap" that acts sort of like a hovercraft skirt. It actually uses the air pressure itself to create a seal with your face, so over tightening the straps totally eliminates that effect.

Oils from your skin will interfere with getting a good seal, so try cleaning just the cushions and flaps of your mask as well as washing your face just before bed.

It may be that your mask cushions have worn out. They might not be as good at creating a seal as they used to be. Fortunately, you can buy just the cushions/flaps for most masks without $pending lot$ of $$ getting a whole new ma$k.
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#5
Maintaining the pressure is the critical issue. Your machine can maintain the pressure while leaking -- up to a point. That's why it's important to make sure you're not leaking too much. And yes it's true that PR machines can tolerate some leaks. It's also true that all other machines can, too.

So while the manufacturer's claim is true, it's what's known as a vacuous truth.
Sleepster
Apnea Board Moderator
www.ApneaBoard.com


INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#6
Ditto on the face washing before bed as I have oily skin , it really helps . I went from the amara to the mirage quattro , I like the latter better.
I did have to wash the cushions in dawn every day to get the oil off for a better seal. But I went to mask liners from pad a cheek and I only have to wash both once a week . They feel and work beautifully for me. Reduced leaks for me too. Seems to reduce mask sliding on face.
Some people make their own liners out of old t- shirts, I'm not Betsy Ross ,so I buy them.
I also got the hose strain off the mask by using a hose hanger at the head board using an 18 inch short hose with swivel connector coupling. I sleep with my head near the end of the pillow so the mask is hanging over the edge. This allows me freedom to turn from side to side all night long . It also stopped my sore neck due to hose weight.
I think you need to change cushions on the mask every couple of months anyway.
We all have our tricks, I have learned not to worry about small leaks . I keep my eye on nightly numbers on sleepyhead .
good luck hunting a good nights sleep.
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#7
Thinking about it some more, Sleepster has it right. It is not the sensor noise that is the issue with large leaks. If that were the case, we would see the sensor noise in the data plots.

The issue with large leaks must be that the CPAP machine can only generate a certain amount of airflow. If the leakage exceeds the airflow the CPAP machine can generate, it cannot maintain the treatment pressure. If the leakage is close to the airflow the CPAP machine can generate, inhaling may push the airflow over the edge and the inhale is simply not detected. Either way, apnea events during large leak periods are still suspect.

Thanks for the clarification Sleepster. I have edited my previous posts accordingly.
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#8
The data reported by a CPAP machine (AHI, etc) is totally unreliable if the leak rate is too high. In other words, the CPAP machine cannot correctly determine if you are having an apnea, or what kind of apnea you are having, if the leak rate is too high.

More importantly, the CPAP machine cannot reliably maintain the pressure needed to keep your airway from collapsing. And that's the only reason you have a CPAP machine!

So, getting the leak rate under control is first and foremost when it comes to CPAP therapy. This is one of the reasons we hate bricks so much. They can't report your leak rate.

Sleepster
Apnea Board Moderator
www.ApneaBoard.com


INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#9
"you don't have to seal every mask leak if you have a PR delivery device".

Sounds like a load of industrial jive to me.

Tongue
"With ordinary talent and extraordinary perseverance, all things are attainable." - Thomas Foxwell Buxton

Cool
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#10
All good info. Thanks.
Mike
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