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S9 central apnea detection
[parts of this thread were copied from our old forum]

It has been discussed that central detected by the S9 are not real centrals but ResMed assert that central are in fact central apnea as it conclude in the white paper of Central Sleep Apnea Detection and the Enhanced AutoSet Algorithm

The ability to detect central apneas is a useful addition to an automatic algorithm for the treatment of OSA. The ResMed AutoSet algorithm has recently been enhanced to include a Central Sleep Apnea Detector (CSAD). This paper describes the CSAD as part of the enhanced AutoSet algorithm on the S9 flow generator and documents the process of validation which included early human testing, bench testing and clinical trial results. The enhanced AutoSet algorithm and CSAD showed that it identified and appropriately treated the different types of apneas with a very high degree of accuracy leading to better overall therapy.

CSAD description
The enhanced AutoSet algorithm applies FOT (forced oscillation technique) only when an apnea is detected and turns it off once normal breathing has resumed. A 1 cm H2O amplitude sine wave at a frequency of 4Hz is superimposed on the current pressure and the resulting pressure and flow are measured within the device using a pneumotachograph.

The enhanced AutoSet algorithm on the S9 AutoSet now includes CSAD for the classification of apneas using the FOT. CSAD was extensively tested using patient simulators, normals simulating obstructive and central apneas and clinical trials. CSAD correctly identified and the enhanced AutoSet correctly treated obstructive, central and unknown apneas with a very high degree of accuracy. The enhanced AutoSet and CSAD algorithms have been shown to treat patients appropriately, including those with predominantly central apneas, and without causing disturbance to sleep.

jdireton wrote:
I think some people are putting too much stock in the Resmed, or any other manufacturers', information. If your AHI is pushing 20, you might want to talk with your doctor. If you're seeing Central hits, and have no history of them, you might want to talk with your doctor. This data should be more of a red flag and not considered in the same context as a sleep study.
I put APAP self titration in the same arena. Only a PS can give you real data. Everything else, while invaluable to give you a qualitative view of your therapy, is for reference only.

Netskier wrote:
PS = what?

greatunclebill wrote:
after reading it i think he's referring to PolySomnogram or sleep study.

jdireton wrote:
Thanks Uncle. Exactly right!

zonk wrote:
Enhanced AutoSet
S9's enhanced AutoSet algorithm now differentiates between Obstructive and Central Sleep Apnoeas and responds appropriately. You enjoy peace of mind because you know the right therapy is always delivered.
CSA detection
It uses the Forced Oscillation Technique (FOT) to determine whether the airway is open or closed during an apnoea. Small oscillations in pressure are added to the current device pressure. The CSA algorithm uses the resulting flow and pressures to measure whether the airway is open or closed.

archangle wrote:
I've heard that some true central apneas (no chest effort) also have a collapsed airway. These will probably not be graded as centrals by FOT.
The number suggested was up to 50%.
However, I still think flagging these as different from obstructive is a good idea. If it says "CA" instead of "OA," it's probably a "real" central apnea.
Of course, that leaves the concern about an "apnea" that isn't real because there's no O2 desat or EEG arousal.
We need to realize that all these catgories and measurements are just mental conveniences for simplifying a much more complicated set of events in the real world.

zonk wrote:
The S9 detects both obstructive and central sleep apneas and if CSA detected it,ll not respond by increasing pressure.

S9 manual:
Central sleep apnea
The S9 Series detects both obstructive and central sleep apneas (CSA). CSA detection uses the Forced Oscillation Technique (FOT) to determine the state of the patient's airway during an apnea. When an apnea has been detected, small oscillations in pressure (1 cm H2O peak-to-peak at 4 Hz) are added to the current device pressure. The CSA algorithm uses the resulting flow and pressure (determined at the mask) to measure the airway patency.

zimlich wrote:
"Of course, that leaves the concern about an "apnea" that isn't real because there's no O2 desat or EEG arousal."
This is not the definition of an apnea. " Apnea
A cessation of breathing/airflow lasting greater than 10 seconds."
I have very real apneas without O2 desats. I don't know about EEG arousals unless I'm in the sleep lab.
I used to be very resistant to the possibility that the S9 accurately diagnoses central events. Not so much anymore. I don't think people whould freak out over centrals when AHI is less than five.

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