ReMed Airsense software/firmware

[Ralph436]

let's start at the beginning

[Ralph436]

opps sorry about that,

@Muggzy, Dataq1, Boxcar, Pholynyk

 Let's step back for a moment, when I first posted my question on the Resmed's   criteria for Hypopnea it was based on matrix you cited above:
( see next post)

That seems to read 12 seconds of RMS data (of something) followed by 10 seconds (of something) that is 25-50% less than the  prior 12 seconds. 

and (additionally for S-10 software package) at least one obstructed breath.

1) am I misreading that?

2) Do you suppose that the "12 s" should (in actuality) be 120 seconds ?

3) Do you guess that the "of something" is ventilation  or volume (expressed in liters)  or is it Flow Rate (expressed in L/min)

   I just averaged the flow rates for a three minute segment and because there are both positive and negative values the resultant average is zero (for all intents and         purposes).

[Ralph436]

Here is the criteria I'm referring to:
   

[Muggzy]

1) Seems like a reasonable reading, but I'm having trouble believing that's the complete criteria because apnea scoring just doesn't work with such short windows normally (see the AASM for instance)

2) Maybe? Hard to say as I can't find any errata to check, but that would make sense and be more in line with AASM guidelines.

3) Root Mean Squares of the variance of the Absolute value of the (filtered) flow rate for whichever time period they're working with. So basically the average of the absolute flow rate for a given time period.

[dataq1]

Agree, That is how I'd read it.

12 seconds doesn't seem long enough to safely set a baseline to be used for comparison purposes.

My recollection is that the comparison should be based on ventilation (volume); to obtain volume the flow rate curve should be integrated (that is calculation of the area between the flow rate curve and zero line (where there is no flow and no flow rate)

[Ralph436]

@Muggzy, Dataq1, Boxcar, Pholynyk

Further information from the article "Treatment of Sleep-disordered breathing with positive airway pressure devices: technology update":

ResMed’s RMS method determines ventilation from variance of the flow throughout the entire breath by comparing individual  flow  points  to  the  mean  airflow  over  a  defined time  period.  The  mean  airflow  is  the  zero-point  between inspiration  and  expiration,  thus  variance  from  this  mean divided by two equals the amplitude of the inspiratory flow. By taking the square root of the variance squared, outlying values receive less weight. A moving short time period (eg, one breath or 2 seconds) can be compared to a moving longer period (eg, 5 minutes) to evaluate for apnea or hypopnea. Apneas and hypopneas are typically defined as a reduction in ventilation below a percentage of recent breathing for at least 10   seconds,  with  varying  methods  used  by  different devices

Two inferences I can draw from this:
 1) baseline, however it is computed is typically longer than 12 seconds.
 2) the comparative values are typically ventilation or volume and not simply rate of flow. This suggests that the flow-rate curve be integrated to determine the volume. 

[BoxcarPete]

It's possible that the 12 second time span we are all arguing about is the timescale used to set the average, or zero point, for flow analysis.

[dataq1]

I hope that we are not arguing about  the "12s", but are trying to achieve some clarity re what is being compared and over what period of time.
I certainly don't think of this discussion as an argument.

Having said that, could you explain what you mean by a "12s time scale"?

[BoxcarPete]

Hyperbolically arguing, but yes, discussing with intent to clarify. The only place it seems to make sense for a 12s time span is to seek the average flow to compensate for leaks. It's far too short to use as a baseline to compare against apnea or hypopnea, as those events tend to go on longer than 12s most of the time, but too long to use to score such an event because a qualifying event could be shorter than the 12s itself.

[Ralph436]

I wrote to the author of the article (the Technology Update) asking for a clarification of the “12s” reference - specifically if that is a typo.

BTW, the author, Dr Johnson, is a practicing sleep specialist who has been in the speciality for 21 years. So contrary to a persistent narrative in both this forum as well as the a DME-owned forum , there are some sleep docs that are really knowledgable.