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Obstruction always associated with increase in leak graph
#1
This might be a silly question but when I have an event (ex. an obstruction) it is almost always associated at the same time with an increase in not only pressure which makes sense but with an increase in the same time frame with an increase in leaks.  Is this always the case?  If not what are the factors that cause this.
Sorry if this has been asked before.
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#2
The machine attempts to increase volume in an effort to maintain pressure, not to increase it.  In the process of increasing volume, more air is escaping the leak ostensibly, and the machine might be assigning a quality to the leak based on the presumed increase flow out of it.
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#3
A little confused because the machine does increase the pressure after an obstruction.
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#4
It's normal for the leaks to increase as the pressure increases in response to obstructions. More pressure causes more volume of air to escape which increases the leak rate.
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#5
Got it, thanks WW.
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#6
edit: posted before seeing WW's reply which helps but I'm a little slow so still not entirely clear to me.

"The machine attempts to increase volume in an effort to maintain pressure, not to increase it." mesenteria

I think this has been explained to me before but sadly I still don't understand it. mesenteria, I assume you're saying there's a difference between amount of air - volume - in mL/min(?) and pressure or force(?) of air in cmw? like psi/cfm or volts/amps (or is one of those watts?). not sure I have these right either but am vaguely aware of the concept.

we routinely refer to machine settings as pressure settings. if an apap is set to say, 10-20 cmw , running at 10, and it responds to an obstruction, doesn't it raise pressure to 11 then 12 etc.? it feels like it's blowing harder (higher pressure?) and maybe it's blowing more air (volume?) but I'm not certain of that. is it mistaken to call moving from 10 to 12 cmw an increase in pressure? doesn't that increase in pressure follow through the hose and mask and is applied to the airway? if I want to blow the dust off my keyboard, the harder I blow and the smaller the orifice through which I blow produces more force and (I think) volume. doesn't it? IDK. we see volume in expressing leaks but how does it apply to inspiration? it sounds like you're saying pressure is a constant when intuitively it seems like more pressure is necessary as the strength or totality or duration of the obstruction increases.

clearly I'm confused. thanks in advance for straightening me out.

yankees, it makes sense to me that any increase in pressure also increases the potential for leak. we see it all the time. I think I raised a similar question some time back: if you stop breathing during an event and the air from the machine is insufficient to keep the airway open, where does the air continuously blowing through your mask go? I thought it would have to leak but I think I was told the exhalation port on masks are designed to dispel / release as much air (pressure? volume?) as the machine can dispense. (but if that was strictly true, why do we ever get mask leaks?) so while higher pressure might cause leaks, I think it was explained to me that obstructions don't. now that I've muddied the water with more questions than answers, I hope somebody can explain this in terms that are easy to understand.
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#7
The obstruction doesn't cause the mask leak. A poor seal is the cause. The increase in pressure just forces more air out the existing leak. The machines are designed to maintain pressure while accounting for the mask vent rate. However if you have a mask leak and it's large enough it will exceed the machines capability to maintain pressure. The more common problem though is because of large leaks the machine can't get an accurate measurement of the air flow and so it can't sense the events and respond correctly.
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Membership in the Advisory Members group does not imply medical expertise or qualification for advising Sleep Apnea patients concerning their treatment.



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#8
Let's start with a basic CPAP machine.  A basic CPAP machine maintains a constant pressure to splint open the airway.  Volume has nothing to do with it.  Auto CPAP and even your ASV are based on this principle.  When you inhale the CPAP will increase speed to compensate for the slight pressure drop caused by your inhalation.  Should a leak develop, the CPAP will increase speed to compensate for the pressure drop caused by the leak.  Yes, the increase in speed can be associated with an increased volume coming out of the CPAP.

Remember that every CPAP mask is designed to leak to maintain the proper amount of CO2 in your blood so there is ALWAYS some flow of air thru the system.

Auto CPAPs, your ASV included, will modify pressures (or not) based on an algorithm that senses slight differences in pressures and flow to head off disruptive events such as hypopnea, Obstructive Apneas, flow limits, and even Central Apneas / Clear Airway events.  Different manufacturers have different algorithms and different class machines (BiPAP/Bilevel ST, and ASV have different algorithms.  

I hope this helps some
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#9
(10-11-2018, 07:51 PM)bonjour Wrote: Let's start with a basic CPAP machine.  A basic CPAP machine maintains a constant pressure to splint open the airway.  Volume has nothing to do with it.  Auto CPAP and even your ASV are based on this principle.  When you inhale the CPAP will increase speed to compensate for the slight pressure drop caused by your inhalation.  Should a leak develop, the CPAP will increase speed to compensate for the pressure drop caused by the leak.  Yes, the increase in speed can be associated with an increased volume coming out of the CPAP.

Remember that every CPAP mask is designed to leak to maintain the proper amount of CO2 in your blood so there is ALWAYS some flow of air thru the system.

Auto CPAPs, your ASV included, will modify pressures (or not) based on an algorithm that senses slight differences in pressures and flow to head off disruptive events such as hypopnea, Obstructive Apneas, flow limits, and even Central Apneas / Clear Airway events.  Different manufacturers have different algorithms and different class machines (BiPAP/Bilevel ST, and ASV have different algorithms.  

I hope this helps some

As good an explanation as any.
There is a designed leak on the mask to get rid of co2 in the form of a vent.
Leaks can show up as a larger leak, if it was leaking in the first place.
Confusion can occur if you wake up and the mask is leaking, in which case you do start to wonder if it was the leak that caused to machine to raise in pressure or did it rise in pressure cause the leak.  Does it matter really, the machine has compensated for it.
This will only confuse!
The machine has pressure sensors inside the machine.  If the pressure drops, there is a leak, increase pressure to compensate.
If the pressure rises, the flow of air has been blocked, so increase pressure until there is a drop, patient is breathing again, so drop pressure slowly.
That is as near to how it works as you will get.
I have had a machine in bits and repaired it, only thing inside was pressure transducers a circuit board and a motor.  More or less anyway.
So how it reacts is down to the software installed.
It was an APAP I took to bits as it was just doing CPAP and not reacting.
Now works fine, though it is a bit old and noisy.
>^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^<
I am NOT a doctor.  I try to help, but do not take what I say as medical advice.

I am just a long term user of c.p.a.p. and therefore I have some experience in using these machines and equipment.

However, I am NOT an expert, so advice given should be taken as given in good faith only and NOT medical advice.

Every journey, however large or small starts with the first step.   Coffee
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#10
Now I am confused!!!    Huh

Lolabove   Not really   Big Grin
>^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^<
I am NOT a doctor.  I try to help, but do not take what I say as medical advice.

I am just a long term user of c.p.a.p. and therefore I have some experience in using these machines and equipment.

However, I am NOT an expert, so advice given should be taken as given in good faith only and NOT medical advice.

Every journey, however large or small starts with the first step.   Coffee
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