Measuring untreated AHI with APAP machine?

[DougalMcDougal]

Is it possible to perform a limited home sleep study by setting my APAP machine pressure to its minimum e.g. if I set minimum and maximum pressure to 1 (assuming it can be set that low) for a night will that give me an accurate estimate of my untreated AHI?

My original home sleep study provided an RDI measurement but no AHI and I am also interested in determining my untreated AHI at home again but do not want the hassle/expense of another formal sleep study?

[LSAT]

Lowest machine setting is 4

[-tim]

It is the Heisenberg Uncertainty Principle in the real world. You can measure it with an APAP machine but your measurement will change the results.

Your APAP will give an general indication of an AHI chance it you set it to the lowest level (which will be 4 except for some special units for pediatric use). Lets assume you have one of these devices and try... If weight more than about 60 pounds, the hose would restrict your breathing causing a higher AHI than without it.

What sort of level do you use your machine at? If your running 6->15, then you could run it 6->10 and show that your AHI went way up and that is bad. If you set it to 6->7 in that case you would have a bad night.

You also need to know that AHI is sort of an odd number. If you sleep for just one hour and have one 60 second event, that is an AHI of 1.0. Now if your APAP improves things so that same 60 second event is broken into 2, such as a 20 second event and a 20 second recovery followed by a 20 second event, your AHI has gone to 2.0. While it looks worse, your SpO2 level will be much higher. Even if you have a 11 second event followed 40 seconds later by another 11 second event your AHI is also 2.0 yet your oxygen levels will stay every higher.

[Pugsy]

Your machine won't go below 4 cm. 4 cm does offer some therapy value so it can and will prevent some events from happening. How many it prevents you won't ever know but you could find out how many it doesn't prevent and it might be a large number or it might be a small number. If you can be comfortable breathing at 4 cm all night...go for it.
I never could go that low with my pressure as it would feel too stifling but I did discover that even with my pressure at 8 cm I had double digit AHI.

[johnthomasmacdonald]

I did this with running my apap machine as cpap at a setting of four to give me a background number to see if my dental appliance was working at all. At a setting of 4, the machine recorded the exact same ahi number as my home sleep test had - 21. Using the dental appliance with the machine at four, my ahi was 0.6 last night - the best ever.

[old64mb]

My original home sleep study provided an RDI measurement but no AHI and I am also interested in determining my untreated AHI at home again but do not want the hassle/expense of another formal sleep study?

It's certainly possible to set up xPAP to not provide you sufficient pressure and attempt to let it record its definition of events. However, keep in mind that on an event-by-event basis (especially with centrals and to a lesser degree hypopneas and flow limitations) the machine is entirely capable of misinterpreting what's going on and flagging something that wouldn't qualify as an event in a lab. On a longer term basis this is not all that important - longitudinal xPAP results can be quite useful for gauging the overall efficacy of therapy even if they're off slightly day-to-day - but as a test it may not be that accurate.

More importantly, as has been discussed on other threads, the problem is that you already have an additional sleep disorder (longstanding insomnia) comorbid with obstructive sleep apnea, and based on your test RDI versus your recorded apneas and hypopneas, you may have other things going on too.

All this would tend to point out that professional intervention is not just reasonable but necessary. The Woolcock Institute is probably the world's second best research hub (after Stanford) for respiratory and sleep disorders, and it just happens to be located in Sydney.

[DougalMcDougal]

Thanks for the tip about the Wollcock institute - I didn't know about it but will get an appointment

Can you recommend any specific Dr's there?

[old64mb]

Peter Liu is one of the few endocrinologists on the planet who actually has a clue about sleep and hormones, but he's in the wrong field as you're going to want someone who deals with primarily general sleep stuff with possibly pulmonary if you've got other stuff going on.

You should be fine with describing your diagnosis and continuing problems and trusting in the clinic people to refer you to someone for a general consult there, since the nice part about going to major research centers is even throwing a dart at the wall generally works out well.

http://www.woolcock.org.au/Default.aspx?tabid=59 even has a referral form for your GP.