Shouldn't the APAP blow if I hold my breath?

SailorBoy · Post by **SailorBoy** » Mon Apr 25, 2005 8:18 am

Just thinking here.

If I hold my breath, which I would think to be simulating an apnea, shouldn't the 420e kick up the pressure? You know, so I breathe?

Hmmm.

Liam1965 · Post by **Liam1965** » Mon Apr 25, 2005 9:15 am

In theory, yes. However, holding your breath behaves more like a central apnea than an obstructive apnea (in that you don't start breathing with the application of pressure, and probably in other ways as well).

SOME of the algorithms take into account centrals, and because they can actually be INDUCED by higher pressures, attempt to differentiate. In that case, you might be surprised to find the machine trying higher pressure for a bit and then backing off, or perhaps backing off from the start, if there are different characteristics (pressure sensing wise) between an obstructive and a central apnea.

My guesses only.

Liam, not a PAP scientist.

wading thru the muck! · Post by **wading thru the muck!** » Mon Apr 25, 2005 9:17 am

SB,

No, The APAP algorithm is more sophisticated than that. It senses your breathing patterns and recognizes when your sleeping or not.

Hugh Jass · Post by **Hugh Jass** » Mon Apr 25, 2005 10:27 am

No, The APAP algorithm is more sophisticated than that. It senses your breathing patterns and recognizes when your sleeping or not.

Sorry Mr. Wader, have to politely disagree.

I know of no CPAP that can recognize when you are actually asleep. It
would have to measure your brain waves to do that. Some people can fall asleep within a minute or two after hitting the pillow, and start SDB shortly thereafter. Others require longer. XPAP needs to respond to both situations.

An APAP should increase the pressure, but my experience with such a test is that you need to breath fairly regular for about 4-5 minutes. Afterwards, you need to hold your breath after inhalation and hold it more than 10 seconds. (Remember it's not considered APNEA unless you stop breathing for more than that.)

If I hold my breath for ten seconds on exhalation, it sometimes will not increase the pressure.

It all has to do with those fancy algorithms, I suppose.

(It was by doing this test that I discovered my rental unit was defective, one week after using it ...)

Regards

cktan · Post by **cktan** » Mon Apr 25, 2005 10:53 am

How about this ?

The pressure supply by the APAP is actually "Low", from 4cmH2O to 20cmH2O only. The machine actually produce a continous flow once it is started.

When you purposely "resist" the flow to produce "an apnea", it will just need 4cmH2O to stop the flow,(If you set the minimal pressure at 4), which you probably unaware of.

Now you can try this, set the pressure to 20cmH2O(make it as a CPAP), then you have to produce a pressure of 20cmH2O to counteract the blower of the machine to stop the flow in your airway. And now, you might feel that the machine is actually "trying to blow" all the time. You produce the "apnea" by purposely impose a greater pressure to counteract it, and divert the flow.

Shouldn't the APAP blow if I hold my breath?
In brief, the APAP actually blow continously, but your breath-holding resist and divert the flow.

wading thru the muck! · Post by **wading thru the muck!** » Mon Apr 25, 2005 12:20 pm

OK, Hugh Jass,

It does not actually "know" whether you are asleep or not. It doesn't actually "know" anything, but it does limit it's reaction to circumstances unless it has recognized an extended period of sleep related breathing patterns.

If you were to block off the hose, both the PB 420E and the REMstar auto will back off the pressure so that the blower will be damaged.

The best way to see how the machine reacts is to read the data collected on the smart card.

Hugh Jass · Post by **Hugh Jass** » Mon Apr 25, 2005 1:18 pm

If you were to block off the hose, both the PB 420E and the REMstar auto will back off the pressure so that the blower will be damaged.

I assume that this would happen only after a blockage is perceived and lasts for mnore than a minute or so, otherwise CPAP therapy wouldn't work. Blocking the hose, the same as when one's throat collapses, actually increases the pressure to open the blockage in the circuit. (Our lungs actually form part of the circuit, and as such become an extension of "the hose."

Backing off on the pressure when the "hose is blocked" would make CPAP therapy totally useless, and if the blower was damaged because of blockages, the manufacturers would probably make more money from repairs than they do from selling the machine.

Regards

-SWS · Post by **-SWS** » Mon Apr 25, 2005 1:27 pm

Recall that as soon as you turn on any AutoPAP it incurs a "settling period". During that initial time frame the Remstar Auto will not react to sleep events, genuine or artificial (with the possible exception of snore, which is highly indicative of sleep). I believe the Remstar Auto's settling period is defined by some quantified sequence of respiratory cycles (perhaps with additional respiratory criteria thrown in as well---I actually forgot) as opposed to the 420e or Spirit. These latter two models define a settling period simply using the criteria of time alone.

The Remstar Auto also has a variable breathing controller which can detect a change in the cadence or rhythm of breathing. The variable breathing controller will first try to normalize the respiratory rate, then it will go into a fifteen minute "sit out" period in which it will not address any sleep events, genuine or artificial. The breathing pattern changes that occur during the transition from sleep to wake just may be enough to trigger that variable breathing controller as Wader suggests. Or highly variable breathing that might occur while awake regardless of prior sleep may be enough to trigger that variable breathing controller. In either case simulated apneas will not trigger the machine.

I would expect the 420e likely employs some kind of similar algorithmic controller that cautiously suspends pressure increases when irregular or highly variable breathing is present. If so, that controller or even the 420e's fifteen-minute settling period would be potential impediments to fooling the 420e with an artificial apnea.

notbigenuf1 · Post by **notbigenuf1** » Mon Apr 25, 2005 10:12 pm

If i hold my breath it feels like mine keeps cycling air

Guest · Post by **Guest** » Mon Apr 25, 2005 10:26 pm

It's supposed to.

-SWS · Post by **-SWS** » Mon Apr 25, 2005 10:40 pm

notbigenuf1 wrote:If i hold my breath it feels like mine keeps cycling air

It's supposed to either: 1) increase pressure if no algorithmic safety guards are in place, 2) maintain pressure if the settling period is still in effect, or 3) vary pressure in an attempt to normalize respiration rate before "sitting out" from pressure increases for a while. The impeller always rotates to generate static pressure as it facilitates patient regulated/sourced airflow. Even without patient-sourced airflow of any kind, the impeller will spin to maintain either a set or algorithmically determined pressure.

These are positive pressure machines that deliver pressures to achieve target air flows.

SailorBoy · Post by **SailorBoy** » Tue Apr 26, 2005 7:05 am

Well, I am extremely hapy with the thing, and do not know what drives me to fiddle. but fiddle i shall.

I suspect that breathe regularly/settling time thing is what inhibits the initial response.

More experimentation to come.

JRM · Post by **JRM** » Tue Apr 26, 2005 7:44 am

Try remembering when you wake up in the morning to hold your breath for 10 seconds or more. You will notice a 1 cmH20 increase in pressure unless the machine pressure is already at the set level where there are no pressure commands on apnea (default value is 10 cmH20). I've tried this--it works.

The other option is to stay awake and try this 15 minutes after the machine has been on. . .

-John

-SWS · Post by **-SWS** » Tue Apr 26, 2005 8:15 am

Interesting thought about these algorithmic safety controllers that are supposed to detect highly irregular breathing patterns: How many times have we read posts where a poster complains that when they wake up their AutoPAP is blowing at an elevated pressure and won't adjust the pressure downward, despite being wide awake with no apneas.

I wonder if these are instances where that particular person triggered a variable breathing safety controller. Then by the time they woke, their pressure refused to budge because the algorithm was in the middle of a safety "sit out" period.

christinequilts · Post by **christinequilts** » Tue Apr 26, 2005 5:53 pm

The only machine you can 'test out' by holding your breath are BiPAP ST because they are set to kick in and try to get you to breath when you stop for Central Sleep Apnea. I have to admitt for the first few months on my BiPAP ST I tested it every night just to make sure it would work...I don't do it anymore unless I switch machines or settings. I can totally understand why autoPAP users would want to be able to test their machines too.

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