How does ResMed S9 machine differentiate OA and CA?

[jcarerra]

Does anybody know how the ResMed S9 machines decide an apnea is a cenral rather than an obstructive?
Obviously it has no input to"see" if chest is "trying" to breathe--so how does it decide that a central is happening?

This document may answer some of your questions:
Central Sleep Apnea Detection and the Enhanced AutoSet Algorithm
http://www.resmed.com/fr/assets/document...-paper.pdf

Yes. Very good.

[Robert6]

Maybe if I tried the ASV Auto mode on my machine, it [forced oscillation technique (FOT)] might be there because the machine may then need the FOT to find the EPAP automatically.

...
Yes, that would be an interesting experiment. Perhaps you could change to ASVauto mode with Min EPAP of 9.0 and Max EPAP only slightly higher, like perhaps 9.2 or so.
...

I tried the ASVauto mode and I had two short apneas, both indicated with red flags, which is supposed to mean obstructive apnea events. In the ASV (not ASVauto) mode that I had always used, the flags were always red, i.e. supposedly obstructive apnea events. Note that my sleep study before I got the ResMed machine indicated predominantly central events (or maybe all, just going by my memory here).

I then tried to look at the corresponding detailed data graphs of flow and pressure near the time of one of the apneas and wasn't able to see the oscillations of the FOT. That might be from not setting the graph scales for best viewing or limitations of the ResScan software or computer that I have. Not sure what's going on.

Examples of the FOT in action are shown on pages 41 and 42 at ww.apneaboard.com/ResScan_Interpretation-Guide.pdf . Note in those examples that the tiny oscillations aren't always present but kick in after 4 seconds of an apnea.

By the way, your Min PS setting is maxed out as high as your machine allows (6). That may be a little too high. I suggest wearing a recording Pulse Oximeter ocassionally while sleeping, to verify your average saturation percentage of oxygen (SpO2) is not higher than around 96% or so. 94-96 is considered ideal, and 90-93 is probably fine, too. Less than 89 is considered low. Less than 75% is considered severely low. An average of 97% or higher (not counting the occasional short dips caused by apneas), if lasting for hours on end, may be unhealthful and can lead to dangerous conditions.

Hyperoxia is something I hadn't considered so I'll look into it. So far I have seen the range 94–96% mentioned as you suggested, but I'm not sure about that. For example, at the Mayo Clinic website the pulse oximeter normal range is given as 95–100%. See ww.mayoclinic.org/symptoms/hypoxemia/basics/definition/sym-20050930
"An approximate blood oxygen level can also be estimated using a pulse oximeter — a small device that clips on your finger. Though the pulse oximeter actually measures the saturation of oxygen in your blood, the results are often used as an estimate of blood oxygen levels. Normal pulse oximeter readings range from 95 to 100 percent, under most circumstances."

I checked my levels with a non-recording pulse oximeter a few times while in bed last night and got 96–98%. I also checked it while writing this message and I got 98%. So for me, the pulse oximeter reading being at or above 96% may be normal, which is consistent with the Mayo Clinic article.

Regards, Bob

P.S. I left out a "w" in each of the two urls in my message because of this board's rules for new members. If this was improper, please make appropriate modifications. Thanks.

[vsheline]

Hyperoxia is something I hadn't considered so I'll look into it. So far I have seen the range 94–96% mentioned as you suggested, but I'm not sure about that. For example, at the Mayo Clinic website the pulse oximeter normal range is given as 95–100%. See ww.mayoclinic.org/symptoms/hypoxemia/basics/definition/sym-20050930
"An approximate blood oxygen level can also be estimated using a pulse oximeter — a small device that clips on your finger. Though the pulse oximeter actually measures the saturation of oxygen in your blood, the results are often used as an estimate of blood oxygen levels. Normal pulse oximeter readings range from 95 to 100 percent, under most circumstances."

I checked my levels with a non-recording pulse oximeter a few times while in bed last night and got 96–98%. I also checked it while writing this message and I got 98%. So for me, the pulse oximeter reading being at or above 96% may be normal, which is consistent with the Mayo Clinic article.

Hi Bob.

Most Oximeters are accurate +/- 2%, and maybe yours reads slightly higher than the actual SpO2 percentage.

I recommend looking over the following discussions about the dangers of too much O2.

http://www.emsworld.com/article/10915304...uch-oxygen

http://www.ems1.com/columnists/mike-mcev...ygen-hurt/

http://www.webmm.ahrq.gov/case.aspx?caseID=172

Take care,
-- Vaughn

Added:

By the way, to convert between mmHg, cmH2O, kPa and PSI we can use this handy online calculator:
http://www-users.med.cornell.edu/~spon/p...essure.htm

[Robert6]

Vaughn, Thanks for the links and the concern. I read them and noted that they were about giving oxygen to ill people. I don't think this applies to my case of VPAP where I don't use supplemental oxygen. Air has about 20% oxygen and 80% nitrogen. I think the air pressures for VPAP and CPAP are benign with respect to oxygen. For example, if someone was using a PAP device that got up to 30 cm H2O, that would correspond to 22 mm Hg (using your link for conversion, thanks). This is less of a pressure increase than someone who lives at an altitude of 1000 ft going down to the seashore at 0 ft. See for example (w) ww.sablesys.com/baro-altitude.html .

Regards, Bob