Baseline for Desaturations and Flow rates

[Tec5]

When AASM refers to a oxygen saturation baseline (to calculate or detect desaturations) I assume they are referring to the average oxygen saturation over some period of time prior.

What is that period of time?

Likewise when the CPaP algorithms refer to a flowrate baseline (to calculate or detect hypopneas), I assume they are referring to the average flow rate over some period of time prior.

What is that period of time?

Apologies if this question has been asked and answered previously, I've been unable to tease it out from the "search" function.

[ozij]

When AASM refers to a oxygen saturation baseline (to calculate or detect desaturations) I assume they are referring to the average oxygen saturation over some period of time prior.

You're assuming?
Why not google it and learn from a source you can rely on?
People could answer you based on their own assumptions - where will that get you?

Likewise when the CPaP algorithms refer to a flowrate baseline (to calculate or detect hypopneas), I assume they are referring to the average flow rate over some period of time prior.

What is that period of time?

Different companies, different machines, different algorithms, different time points, different patents.
Google and learn to your heart's content.

[Tec5]

When AASM refers to a oxygen saturation baseline (to calculate or detect desaturations) I assume they are referring to the average oxygen saturation over some period of time prior.

You're assuming?
Why not google it and learn from a source you can rely on?
People could answer you based on their own assumptions - where will that get you?

Likewise when the CPaP algorithms refer to a flowrate baseline (to calculate or detect hypopneas), I assume they are referring to the average flow rate over some period of time prior.

What is that period of time?

Different companies, different machines, different algorithms, different time points, different patents.
Google and learn to your heart's content.

People come to this forum to learn and be helped. Right?
I understand that among your forum participants are (were) Board Registered Polysomnographic Technologists - these people should know instantly.

When someone is referring to a baseline (of data), they generally mean an accumulation of data that establishes a baseline value. All I'm asking is how much data is required to establish that baseline.

If you don't know, just say so.
If you do know, but don't want to share that knowledge just say so.

[ozij]

People come to this forum to learn and be helped. Right?

Right. Your questions had nothing to do with being helped in your therapy. As a matter of fact, as of now, 29 Nov. 07:473UTC time zone, your profile doesn't even indicate which machine or mask you're using.

Your questions are academic, unfocused, and based on unchecked assumptions.
The best reliable replies to academic questions will be found by searching the internet for the info you want, and learning about about it from sources you trust.
I tried to help you focus your search by mentioning that you are making assumptions and that there are

• different companies,
• with different machines
• they have different algorithms
• and they change through time

.

I understand that among your forum participants are (were) Board Registered Polysomnographic Technologists - these people should know instantly.

Really? Since when do you trust anyone on our forum?

-------, the knowledgeable professional among us ....

Been lurking this thread, this is the first time I can recall that ------- has been described as the professional among us.

What is his profession and what are his credentials ?

Said person's name intentionally edited out of the quote.
Things known instantly can be used when trying to understand sleep reports and therapy charts.
They are not reliable info when given to others unless there's a prior basis for trust on a personal basis, or when accompanied by references.

If you don't know, just say so.

I doubt you don't know how to use google or google scholar. But just in case you don't, here's a link:
https://scholar.google.com/intl/en/scholar/help.html

[Tec5]

People come to this forum to learn and be helped. Right?

Right. Your questions had nothing to do with being helped in your therapy. As a matter of fact, as of now, 29 Nov. 07:473UTC time zone, your profile doesn't even indicate which machine or mask you're using.

Your questions are academic, unfocused, and based on unchecked assumptions.
The best reliable replies to academic questions will be found by searching the internet for the info you want, and learning about about it from sources you trust.
I tried to help you focus your search by mentioning that you are making assumptions and that there are

• different companies,
• with different machines
• they have different algorithms
• and they change through time

.

I understand that among your forum participants are (were) Board Registered Polysomnographic Technologists - these people should know instantly.

Really? Since when do you trust anyone on our forum?

-------, the knowledgeable professional among us ....

Been lurking this thread, this is the first time I can recall that ------- has been described as the professional among us.

What is his profession and what are his credentials ?

Said person's name intentionally edited out of the quote.
Things known instantly can be used when trying to understand sleep reports and therapy charts.
They are not reliable info when given to others unless there's a prior basis for trust on a personal basis, or when accompanied by references.

If you don't know, just say so.

I doubt you don't know how to use google or google scholar. But just in case you don't, here's a link:
https://scholar.google.com/intl/en/scholar/help.html

So all this to say that you, personally, object to the question even being asked — so noted.

[Wondering1]

Really? Since when do you trust anyone on our forum?

What ????

Nobody on this forum can be trusted ???? Really ?

Now, back to the topic......

[Wondering1]

So how is this a hypopnea:



It maybe a reduction in flow of 30% but compared to what?

Inquiring minds would like to know.

[ChicagoGranny]

Something smells of alter egos.

[Wondering1]

Something smells of alter egos.

So Tec5 asked a question that I'm also interested in (since he raised the topic).

Can you answer ANY of the questions ?
(either his or mine)

[chunkyfrog]

Let's just stop feeding it.
Maybe it will go away . . .

[robysue1]

When AASM refers to a oxygen saturation baseline (to calculate or detect desaturations) I assume they are referring to the average oxygen saturation over some period of time prior.

What is that period of time?

Likewise when the CPaP algorithms refer to a flowrate baseline (to calculate or detect hypopneas), I assume they are referring to the average flow rate over some period of time prior.

What is that period of time?

The only relevant description for establishing baseline oxygenation and breathing amplitude (i.e. flow rate amplitude) for in-lab PSG I could find is in Rules for Scoring Respiratory Events in Sleep: Update of the 2007 AASM Manual for the Scoring of Sleep and Associated Events, available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3459210/, and which was published in 2012. It would not surprise me if further updates have left this basic discussion of "baseline breathing amplitude" (i.e. flow rate amplitude) and "baseline oxygenation" were pretty much unchanged:

The 2007 scoring manual states that the event duration for scoring either apnea or hypopnea is measured from the nadir preceding the first breath that is clearly reduced to the beginning of the first breath that approximates baseline breathing amplitude. The only recommended revision to the 2007 scoring manual is to explicitly mention the recommended signal to be used for measurement. For apnea duration, the oronasal thermal sensor signal (diagnostic study) or PAP device flow signal (PAP titration study) should be used to determine the event duration [Recommended] (Consensus). For hypopnea event duration, the nasal pressure signal (diagnostic study) or PAP device flow signal (PAP titration study) should be utilized [Recommended] (Consensus). If the recommended sensor fails or the signal is inaccurate an alternative sensor signal can be used. The ability to determine baseline breathing is a problem in patients that have nearly continuous events. The AASM “Chicago consensus paper” states, “Baseline is defined as the mean amplitude of stable breathing and oxygenation in the 2 minutes preceding onset of the event (in individuals who have a stable breathing pattern during sleep) or the mean amplitude of the 3 largest breaths in the 2 minutes preceding onset of the event (in individuals without a stable breathing pattern).” The 2007 scoring manual states, “When baseline breathing amplitude cannot be easily determined (and when underlying breathing variability is large), events can be terminated when either there is a clear and sustained increased in breathing amplitude, or in the case where an oxygen desaturation has occurred, there is event-associated oxygen re-saturation of at least 2%.” The task force recommends that the 2007 manual guideline for determining baseline breathing be upheld [Recommended] (Consensus).

The italicized and bold parts of this quote answer your questions as they pertain to in-lab PSGs scored using AASM criteria.

When a person has stable sleep breathing and oxygenation, the baseline respiration amplitude and oxygenation are based on the the last two minutes of stable sleep breathing before the start of the event.

When the person's sleep breathing is not stable, the baseline respiration amplitude is based on the mean (average) amplitude of the 3 largest breaths in the last 2 minutes before the start of the event.

And when lots of events are happening on top of each other, it can be difficult to establish the baselines. (This is more relevant for detecting hypopneas than apneas, since a near or complete cessation of air flow---i.e. a breathing amplitude of essentially 0---is not that difficult to detect.)

Additional information about the difficulties of establishing oxygenation baselines in individuals who are experiencing multiple events in a very, very short time is discussed in Section 3.1.5 of the same article.

As for xPAP machines, each manufacturer has had to program ways for the machine to compute "baseline" flow rate amplitude and how much the flow rate must decrease before an apnea or a hypopnea can be flagged. Clearly certain types of wake breathing patterns can trick these algorithms into flagging things that would clearly not be scored on an in-lab sleep test. Likewise, certain kinds of breathing patterns can also lead to things in the flow rate curve that look like they ought to have been flagged, but they weren't flagged for some reason. (No algorithm is perfect and no computer program implementation of an algorithm is perfect.)

For Resmed AirSense 10 and AirCurve 10 machines, the event detection criteria are found in the clinical manuals for the machines. A apnea is flagged "when the respiratory flow decreases by more than 75% for at least 10 sec". A hypopnea is flagged "when the respiratory flow decreases to 50% for at least 10 sec." The manual does not specify how the baseline flow is determined and I have not been able to find that out with Google tonight.

For PR DreamStations, the event detection criteria is found in the clinical manuals for the machines. A apnea is flagged " when there is an 80% reduction in airflow from baseline for at least 10 seconds or if there is no airflow detected for 10 seconds." A hypopnea is flagged "when there is an approximately 40% reduction in airflow from baseline for at least 10 seconds." The manual does not specify how the baseline flow is determined and I have not been able to find that out with Google tonight.

In both Resmed and PR machines, I would assume that the baseline flow rate is computed over approximately a 2 minute window of stable breathing or some kind of an average of "largest breaths" over a 2 minute period if the breathing is not particularly stable.

[Tec5]

To Robysue1, Thank you so much for your very through reply to me. Suffice it to say, that just the reading of the 2007 AASM guides leaves the novice with more unanswered questions, because I lack the practical context of how the "words" are applied. It is that area that I expected that forum participants would be able to "translate" for the newcomer.
To that end, you've assisted me greatly.

I don't really have the time right now (today) to digest everything you said, but I will be trying to get a better grasp. Hopefully I can get back to you if there are further clarifications needed.

So...... long-winded.... but a note of gratitude to you !

At this stage, I'd have to say that the direct answer is...... "it's tricky". Tricky in the sense that one has to evaluate the prior moments as to stability (that could well be subjective).

For now, my appreciation and thanks.

[Wondering1]

Above I posted a flowrate curve with a flagged hypopnea, in considering what Robsue1 posted, is it best to examine the tidal volume / time graph to understand why a hypopnea was flagged?
Here is the same flowrate curve, but with the tidal volume curve added.
It would seem that the average tidal volume for a couple of minutes prior to the H flag was approximately 470.
After what appears to be a deep breath, approaching 639ml, the next few breaths dropped to approximately 330 ml.
Since 330 ml is just 70% of the 470 (baseline?) it meets the criteria of hypopnea, and was so flagged.

Should it have been flagged? It actually looks like 2, maybe three, sub optimal breaths, taken after a deep breath.

But my main question is this..... when examining these charts for hypopneas, should the tidal volume chart be used for guidance?

[Rubicon]

But my main question is this..... when examining these charts for hypopneas, should the tidal volume chart be used for guidance?

I think you should blow up the chart if you want to measure what seems to ne a marginal hypopnea. Single channel, 60 second window, fit to window like:

[Rubicon]

Meanwhile, consider why all those areas that should have hypopneas scored, don't: