? Accuracy of ResMed S9 AHI Readings

[larry2001]

Last night was my 1st night on CPAP ( ResMed S9 Elite, Nasal Pillow Swift Fx mask). I could not fall asleep with the device on and disconnected and turned off after 3 hours (I was clearly awake the entire time) for a variety of reasons.
I looked at the info for this 3 hour session and was shocked to find an AHI of 21.3 . The leak icon gave a "smiley" face.
Today, I sat in a chair reading (data had zeroed out after noon) and experimented, using the same set up.
To my dismay, in a 20 minute test, it was giving an AHI of 16 ! Bottom line, the machine registers apneic events while a person is fully awake and breathing normally.
I have not seen anyone on these forums check this device while awake. I did have problems with my mouth filling with air causing me to briefly exhale that air through my mouth. The mask leak was an acceptable but not great 15L/min.
The only way I can make sense of this is air going into the mouth is counted as an event.
Otherwise, the AHI readings would appear meaningless or I have an defective machine.
Does anyone have an explanation for this ?

larry2001

Posts: 1
Joined: Sun Dec 30, 2012 5:23 pm
Machine: ResMed S9 Elite
Mask: Swift FX
Humidifier: yes
Year Diagnosed: 2012

[ChicagoGranny]

An AHI of 16 for 20 minutes means 5 or 6 pauses or shallow breaths in twenty minutes - very common when awake (unless you are running a portion of a 5K during that 20 minutes ).

[VikingGnome]

No equipment will be accurate over short periods of time. That's because it's averaging ALL events over the time period you were hooked up to machine. The shorter the time, the higher your AHI will be because usually people have events while they settle down, get comfortable, and finally fall asleep. I notice that I get a CA event every time I turn over in bed or adjust my blanket. That's because we all tend to hold you breath briefly while doing something physical that is a bit strenuous. Lift a heavy box and see how you automatically hold your breath to exert more muscle power. Turning over in bed isn't as easy as you think.

AHI will drop as you spend more time on the machine. I wouldn't even bother looking at AHI until your able to sleep about 7 hours on CPAP. Then you will be getting meaningful numbers.

[HoseCrusher]

Sleep breathing is different from the way you breath while awake or while falling asleep. The machine is only somewhat accurate monitoring while you are sleeping.

If you take an extended amount of time to fall asleep, or slowly wake up, you will frequently find a cluster of events during those times.

[billbolton]

I have not seen anyone on these forums check this device while awake.

That's because all xPAP machine score AHI on the basis of autonomous sleep breathing behaviour (that is, breathing behaviour while you are truly asleep). Any data scored while you are not asleep is quite meainingless.

This has been discussed many, many times in the forum

Cheers,

Bill

[billbolton]

usually people have events while they settle down, get comfortable, and finally fall asleep

That's what ramp and settling time features on xPAP machines are for.... they will NOT score until the ramp or settling period is over.

Cheers,

Bill

[larry2001]

I have not seen anyone on these forums check this device while awake.

That's because all xPAP machine score AHI on the basis of autonomous sleep breathing behaviour (that is, breathing behaviour while you are truly asleep). Any data scored while you are not asleep is quite meainingless.

This has been discussed many, many times in the forum

Cheers,

Bill

Thank you, I have now found this elsewhere. However, if AHIs are being recorded while one is awake, it is highly questionable what the machine is calling an apnea or hypopnea while one is asleep. Clearly, you have no belts attached, no oximeter and no nasal cannula so no flow or effort is being measured by conventional means. Therefore, the machine has its own proprietary methods which you must "believe" in. Breathing patterns while awake and asleep are a continuum, not a phase transition. I would submit that this type of proprietary monitoring, with no external validation i am aware of, is not something that you want to stake your fate on. This is quite serious. Perhaps we would be better off with a recording oximeter , which would definitely not give sats <90% in a normal awake person at rest.

[chunkyfrog]

Any data collected while awake is meaningless, except to the insurance company.

[idamtnboy]

However, if AHIs are being recorded while one is awake, it is highly questionable what the machine is calling an apnea or hypopnea while one is asleep. Clearly, you have no belts attached, no oximeter and no nasal cannula so no flow or effort is being measured by conventional means. Therefore, the machine has its own proprietary methods which you must "believe" in. Breathing patterns while awake and asleep are a continuum, not a phase transition. I would submit that this type of proprietary monitoring, with no external validation i am aware of, is not something that you want to stake your fate on. This is quite serious. Perhaps we would be better off with a recording oximeter , which would definitely not give sats <90% in a normal awake person at rest.

CPAP machines are amazingly sensitive. Once you get into a regular pattern of sleeping and look at your data you will see the machine very clearly detects when you are not breathing. You will also see there is a very clear difference in breathing pattern while asleep vs. awake. Contrary to your statement above, the transition is almost abrupt when you fall asleep. The definition of apnea is no breath for 10 seconds or longer. The 10 second threshold is a little bit arbitrary and there really is no great difference between a 9 second stoppage and an 11 second stoppage, but they are classified differently.

When it comes to sensing and scoring apneas CPAPs are exceedingly good. Where there is some debate is how reliable Resmed's scoring of Central Apneas is. I believe it is very good. Other manufacturers just classify them as Clear Airway Apneas.

[Boyce]

[
CPAP machines are amazingly sensitive. Once you get into a regular pattern of sleeping and look at your data you will see the machine very clearly detects when you are not breathing. You will also see there is a very clear difference in breathing pattern while asleep vs. awake. Contrary to your statement above, the transition is almost abrupt when you fall asleep. The definition of apnea is no breath for 10 seconds or longer. The 10 second threshold is a little bit arbitrary and there really is no great difference between a 9 second stoppage and an 11 second stoppage, but they are classified differently.

When it comes to sensing and scoring apneas CPAPs are exceedingly good.

That is what I thought from reading in the forum. I also can see the pattern change in the data when I fall asleep and when I wake up.

Thanks idmtnboy for confirming this.

[BlackSpinner]

This is quite serious. Perhaps we would be better off with a recording oximeter , which would definitely not give sats <90% in a normal awake person at rest.

Wrong. About 2 years ago I was in ER after an asthma event and spent about 3 hours hooked up to a machine which kept quite good track of my SPO2. Every time I bent over my food my O2 dropped. Now hospital food is notoriously bad but it was more about my sitting position, hunch over at an angle, that made breathing and eating a little difficult.

Breathing while asleep is quite different from breathing while awake. I used to do massage where one is supposed to follow peoples out breathe for the pressure. It is a real pain because most people when awake have erratic breathing patterns. One could feel as soon as they fell asleep that pattern changed to a slow deep form of breathing, only when they dropped into REM did that change. Just hold a baby and you will know when it falls a sleep in your arms just by its breathing. Sleep breathing comes from the diaphragm and is deep and rhythmic.

[larry2001]

This is quite serious. Perhaps we would be better off with a recording oximeter , which would definitely not give sats <90% in a normal awake person at rest.

Wrong. About 2 years ago I was in ER after an asthma event and spent about 3 hours hooked up to a machine which kept quite good track of my SPO2. Every time I bent over my food my O2 dropped. Now hospital food is notoriously bad but it was more about my sitting position, hunch over at an angle, that made breathing and eating a little difficult.

Breathing while asleep is quite different from breathing while awake. I used to do massage where one is supposed to follow peoples out breathe for the pressure. It is a real pain because most people when awake have erratic breathing patterns. One could feel as soon as they fell asleep that pattern changed to a slow deep form of breathing, only when they dropped into REM did that change. Just hold a baby and you will know when it falls a sleep in your arms just by its breathing. Sleep breathing comes from the diaphragm and is deep and rhythmic.

With all due respect, you were having or recently had an asthma attack. I was talking about people with a normal respiratory status, which you clearly did not have in the ER. When you are already marginal, various positions could certainly lower your O2 sat.