Why standard home test said AHI 8 (twice) but WatchPAT said AHI 46

[Fabrice01]

Hospital's respiratory department had me do the same standard home test once in 2017 and again in 2022. There's a little thingy going in the nostrils (presumably to check breathing), an electrode to be taped on the chest and a finger probe. All of this to be worn the whole night once. In 2017 it yielded AHI = 8, and in 2022 almost the same thing. On that basis I was prescribed CPAP machine with set pressure 10 which didn't help at all (no sleep improvement).

Then a few months ago I did a WatchPAT test which yielded AHI = 46. This was requested by a neuropsychiatrist who asked my GP to refer me back to the respiratory department.

To be sure, my symptoms are consistent with severe OSA which tends to give the WatchPAT results more credence.

Anyway my question is: why the test discrepancy? I heard the WatchPAT is more sensitive than the standard test - is that true?

[SarcasticDave94]

When there's different test brands or types, it added variables to the test results. Different years can as well.

The test is also a one night snapshot of Apnea. If you were to look at your OSCAR charts, each night is a little different. You could in theory retest the sleep study every night for a year, and it'll give different numbers.

Which of these 3 is more accurate? I don't know. Do you feel like your untreated AHI is closer to 8 or 46?

[THEVGE]

Without showing the reports hard to say anything useful.....

[greatunclebill]

watchpat looks like an o2 sensor. o2 sensors show o2 drops or desats. give a thought to maybe the desats are not strictly apnea related. maybe you have something else going on. without seeing oscar it makes the most sense to me. maybe you also need a pulmonologist and an in lab sleep test.

[Fabrice01]

Thanks all.

@SarcasticDave94 : my symptoms are severe - chronic mild shortness of breath that goes up if I slept less hours than I need + constant heavy fatigue. I feel like an anaemic 100 years old man (I'm 45). For years I've been wondering what on earth is causing this. Undetected severe sleep apnea is the only explanation that makes sense to me.

Will sleep with machine on as soon as I can to produce data and see what's going on.

[DaveSkvn]

Hi Fabrice,

I saw someone posting about a WatchPAT test a few weeks ago and had a look at it then. It seems to be based on a "Peripheral Arterial Tone (PAT®)" which is a "proprietary technology used to identify respiratory events" (i.e. its not used by anyone else). It seems to assume OSA events are directly linked to a particular change in blood flow. The result doesn't seem to include any measure of air flow (it does have some measure of chest motion). I would say it shows there is an issue but I would be reluctant to conclude it is OSA given the previous two results.

You mention a "neuropsychiatrist". Is it the one at the top of Harley St? If it is (that's were I got my initial diagnosis), I'm surprised he would rely on it.

OSA is typically associated with "oxygen desaturations". You can buy an oximeter that records your blood oxygen level whist you sleep and download it to create a report. I've got a Contec CMS-50E. It seems to still be available online in the UK for a shade under £100. You can use it for as many nights as you want and have a good look at the data. If you have AHI of 46 the graph will "go nuts". Using CPAP for a few nights and uploading the SD card to Oscar will do much the same.

You mention "shortness of breath". Have you considered something like "atrial fibrillation"? My mother had it. She felt she just couldn't exert any force / got out of breath very easily. I guess there are a number of more heart/blood related issues that might confound a WatchPAT - and cause poor sleep. I see there is a crowd called Vista Health that do ECG testing ("physiological measurements" -> "ECG 12L ECG") for £75 in London and Liverpool. That might be worth a shot. 

Good luck getting to the bottom of it.

[Fabrice01]

Hi Dave,

If it's not OSA then it has to be a magical curse because nothing else makes sense: waking up 5x a night + constant disabling fatigue, no depression or anxiety disorder. Thanks for suggesting atrial fibrillation but it really doesn't match my experience.

Anyway I was thinking about an oximeter actually. I was wondering, why nobody ever suggest to combine this with CPAP data? But you're saying CPAP data includes the information provided by an oximeter? If so, how so?

I don't have £100 for an oximeter but I could buy a cheap one that pairs with a phone app to record data during the night.

Also I'm in Birmingham not in London

[SarcasticDave94]

There's threads here on Apnea Board that do discuss using a recording pulse oximeter. With the right model, it can load the oximeter data into OSCAR, combining it with CPAP data.

[DaveSkvn]

The key question is whether your AHI is 8 or 46. 

As @SarcasticDave94 says you can use the oximeter to record SpO2 and then upload it into Oscar with data from the CPAP's SD card - as I've been doing for the last couple weeks! For example, here is my plot from last Friday.

   

The Flow rate, flow limits and respiratory rate data comes from CPAP. The blue line SpO2 data comes from the Oximeter. The light blue vertical lines in the flow rate graph are where the CPAP machine detected and recorded Apnea events. The dark blue vertical lines are the less severe Hypopneas. As you can see the SpO2 graph drops where the CPAP machine detects apenas.

If you are willing to use the CPAP for a few nights and upload the data to Oscar you'll get the flow rate graph with the blue vertical lines showing the apneas. That will give you a very good idea if your AHI is closer to 8 or 46. There is no need for the oximeter. It would just give you another option if you don't feel like using the CPAP machine / Oscar.

In my case the graphs show the respiratory rate heading away from the expected 12 and records flow limitations at the same time which would indicate my problem is more UARS than OSA. As you can see the SpO2 shows absolutely nothing whilst that is going on which shows the limitation of oximeter data. My Apenas are clustered together indicating "positional apena" - in my case on my back - which doesn't tend to respond to air pressure - great!. If you can, I'd use CPAP and upload it to Oscar - its much more useful.

Others can pile in here but I personally don't associate OSA with "shortness of breath" during waking hours at all (hence my suggestion to keep an open mind). The CPAP data will reveal all!

[PeaceLoveAndPizza]

Whether your AHI is 8 or 46 the result is the same. You are exhibiting the symptoms of SDB/OSA. 

Any idea why they gave you an ST model? In one of your earlier posts it sounded like they gave it to you because they did not have a Vauto, which seems like it should be the machine for you to use.