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Some interesting differences between PAP resultes and sleep study results
#1
This article mentions the differences in how AHI numbers are calculated, why they may differ from machine to machine, and why they will be different between a CPAP and a sleep study:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3274337/

I'm sure there are other explanations, but I came across this first while looking for something.

A PSG will also use oxygen levels for part of the formula to determine an AH event. A CPAP can't do that, so it has to estimate. This probably can lead to brand to brand differences. Also, a PSG scores only the AH events that occur after sleep begins, and a CPAP scores events that occur after the machine is turned on.

Automatic Event Detection (AED) from CPAPs was compared to manually scored events during a sleep study.

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"The results of our study show that the AED tended to overestimate the AHI when the manually scored AHI was low and underestimate the AHI when the manually scored AHI was high."
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#2
Almost all of the difference was in hypopneas, due to things the CPAP can not measure and differences in definition. Even the article says,"Differences between manually scored and AED events were primarily due to different criteria for hypopnea detection". So if one compares AI to AI it should be pretty close.

Best Regards,

PaytonA
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#3
I've not read the whole article but read this and stopped wasting my time ....
Subjects enrolled in the parent study were randomized to one of three treatment arms: CPAP at the pressure determined by the titration PSG; APAP using a form of flexible positive pressure (A-Flex™), or APAP for 2 wks followed by CPAP treatment based on the results of the 2 wks of APAP treatment (pressure below which the patient spent 90% of the time). The same study device was used for all participants (REMstar Auto M-Series, Philips-Respironics, Murrysville PA) functioning in the CPAP, APAP, or AFlex™ modes10. The pressure range on the APAP units was set at 4 cm H2O to 20 cm H2O.
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Older machine used in a wide range settings ...
To get a better idea, they'll need to repeat the study using ResMed "AirSense 10 AutoSet and DreamStation Auto
Machines can distinguish between obstructive and clear airways events
For some people, pressure relief can skew AHI results somewhat and I have no faith in factory default pressure settings
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#4
Yeah, I noticed this near the end:

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DISCLOSURE STATEMENT

This study was sponsored by Philips-Respironics.
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#5
The training and experience of the Tech reading the PSG make all the difference in the world. If a Tech doesn't know the difference between Obstructive Hypopneas and Central Hypopneas the diagnosis can be completely wrong.

Rich
Apnea Board Member RobySue has posted a Beginners Guide to Sleepyhead Software here:  http://www.apneaboard.com/wiki/index.php...SleepyHead

Download Sleepyhead
Organize your Sleepyhead Charts
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