False Positives for OA and H

[Jason S.]

I've noticed my data recorded some OA and H during a time I know I was awake. Knowing this, doesn't it call into question the validity of the data which records events when I'm sleeping? How do I know if the OA's and H's actually occurred or are just another false positive? Last night I scored an AHI of 2.0, but 3 of the 7 OA's I know for a fact were false positives in the first 15 minutes of CPAP.

[roster]

Well, when I first started with the Respironics machine and Encore software, I was sure it was often recording false positives. As I gained more experience my opinion began to change.

We are looking at the data the morning after and relying on our memory of when we were awake and when we were asleep. I don't think our memory of those two conditions and the time of those two conditions is anywhere near good. In fact I think it is not possible to accurately recollect times of awake and times of sleep.

Reviewing the results of my first sleep study the doc asked me some questions about when I was awake and when asleep. After I answered he showed me the sleep stages in the EEG. It was obvious I did not have a good recollection of sleep/awake times.

Now I trust my data nearly 100%. Part of my evidence against false positives is the many nights when I record no apneas and no hypopneas.

[fuzzy96]

i have apneas while awake!!!!!!!!!
seems my breathing style is rather shallow and if i'm just lounging i've cought myself not breathing for short periods

i could be wrong but the higher the pressure it takes less airflow to trigger the sensors.

so if you mask up with the ramp on (lower presure)if a machine were to give false positives this would be the time it does it.
i pay little attention to the first 15-30 minutes knowing that the deeper sleep is the better sleep and it takes a while to get there.

[Velbor]

I've noticed my data recorded some OA and H during a time I know I was awake. Knowing this, doesn't it call into question the validity of the data which records events when I'm sleeping? How do I know if the OA's and H's actually occurred or are just another false positive? Last night I scored an AHI of 2.0, but 3 of the 7 OA's I know for a fact were false positives in the first 15 minutes of CPAP.

Many important issues here.

First, breathing while awake can be very irregular. It's no big deal to hold our breaths, either intentionally or unknowingly, for 10 seconds or more, while awake. While moving. While daydreaming. There is no a priori reason to doubt the machine sensors. The machine doesn't know our state or depth of sleep. It just records and analyzes and reports pressure and flow patterns.

There is nothing in this which calls into question the "validity" of data recorded while sleeping.

As to "false positive" results, the question is, false positive WHAT? If we expect that the numbers churned out by the machinery reflect ONLY events DURING SLEEP, then indeed we are setting ourselves up to be misinformed. We have to acknowledge that the numbers reflect events for the ENTIRE PERIOD that the blower is on, which includes everything from awakeness to light sleep to deep sleep to REM sleep, each present multiple times through the night, and likely different each night. There's something not quite right in selectively tossing out "awake" data at the beginning of the night, when there is likely more "awake" data as the night progresses that we're not aware of and don't remember in the morning.

It's our expectations that need to be clarified! The scientist faced with anomalous data questions their own assumptions first. The possibility of lab equipment error must always be considered, but that's usually rather far down the list.

Good observation. Velbor

[ywp]

I need some honest second opions on a recent event.

I decieded to change a setting on my apap. I used an oximeter with the same report as above. In the middle of the night I had a 40 min. episode of 70 to 80 % o2 saturation. Heart showed some slight spikes at first then normal. Then back to normal?

This freaked me out, so I recorded the next two nights, same conditions. the episode did not repeat. Kinda normal reading for me.

My question is should I call this an oximeter false reading. Or do I have monster apnea events on a weekly instead of nightly cycle.

[jinroh]

I need some honest second opions on a recent event.

I decieded to change a setting on my apap. I used an oximeter with the same report as above. In the middle of the night I had a 40 min. episode of 70 to 80 % o2 saturation. Heart showed some slight spikes at first then normal. Then back to normal?

This freaked me out, so I recorded the next two nights, same conditions. the episode did not repeat. Kinda normal reading for me.

My question is should I call this an oximeter false reading. Or do I have monster apnea events on a weekly instead of nightly cycle.

Could you recommend an affordable oximeter which can record data for later analysis? Thank you

[roster]

I need some honest second opions on a recent event.

I decieded to change a setting on my apap. I used an oximeter with the same report as above. In the middle of the night I had a 40 min. episode of 70 to 80 % o2 saturation. Heart showed some slight spikes at first then normal. Then back to normal?

This freaked me out, so I recorded the next two nights, same conditions. the episode did not repeat. Kinda normal reading for me.

My question is should I call this an oximeter false reading. Or do I have monster apnea events on a weekly instead of nightly cycle.

First, I always recommend getting a CPAP with software so you can see what happened with your breathing minute by minute.

Regarding the 40 minute episode, have you considered positional sleep apnea (PSA)?

From another thread:

............
I would like to make you aware of "positional sleep apnea" (PSA). Maybe 40% or more of patients have PSA.

PSA means the apnea is much worse in one sleeping position (on the back) compared to other sleeping positions. For example, my sleep apnea is very severe when I am sleeping on my back.

For people with PSA, the sleeping position can have a big effect on CPAP pressure requirements. For example, I have been titrated in a sleep lab and at home have confirmed my pressure requirements for different positions. On my back I require a pressure of 19 cm (Yow!). On my side or stomach, a pressure of 8.5 cm is sufficient. So I have some devices and train myself to sleep only on side or stomach and use pressure of 8.5 cm.

You may want to make some observations about the possibility of PSA in your case. There may be information from your lab PSG also.

.............

[ywp]

Thanks

I think now those oximeters squeeze my finger too hard. Maybe it can cut down blood flow in the finger and give false readings ?
I got my encore printed out and it did not show any 40 minute episode. I have never been able to relate the oximeter data to the APAP data.

[DoriC]

FWIW, I can speak from experience. My husband told me he didn't fall asleep for a long time the other night so I asked him if he had heard the loud thunder and lightening not long after he went to bed, he said "No". As a non-cpapper, I sometimes swear the same thing also, but my TV sleep timer is set for 30mins and I don't remember it shutting off.

[Silver Pelt]

I have suspected false positives, both awake and asleep. My suspicions were first aroused by the strong correlation between changes in leak rate and OA/H flags in the respironics reports.

I bought an inexpensive oximeter and confirmed that it showed real apnea events. Then I compared the data it recorded to the respironics data and found a large number of flags that did not correspond to any desaturation in my oxygen levels.

At least some CPAP machines lie. You can spend a lot of time pursuing perfect scores, just as you can spend a lot of time getting high scores in a video game. In both cases, a lot of time invested. In both cases, the health benefits are questionable. I'm looking to make my therapy effective, not to score a great number on some self-interested xPAP vendor's machine.

[roster]

..........I bought an inexpensive oximeter and confirmed that it showed real apnea events. Then I compared the data it recorded to the respironics data and found a large number of flags that did not correspond to any desaturation in my oxygen levels.

........

1) An oximeter does not detect apnea events. It only measures blood-oxygen levels (plus pulse rate with most oximeters).

2) Apneas can occur without causing oxygen desaturations.

I remain unconvinced that my Respironic machine records false positive apneas. The fact that I occasionally get a night when there are no apneas is part of the evidence I rely on.

If you are awake and hold your breathe for ten seconds, the machine is not recording a false positive.

The machine is dumb, but it can measure air flow, absence of air flow and elapsed time. It is not a very big challenge for the machine to record lack of air flow for 10 seconds or more.

[DoriC]

Rooster, I love that explanation of how these "dumb" machines work, it teaches me a lot. Thanks.

[Silver Pelt]

1) An oximeter does not detect apnea events. It only measures blood-oxygen levels (plus pulse rate with most oximeters).

The standard definition of any apneic event includes a minimum 10 second interval between breaths, with either a neurological arousal (a 3-second or greater shift in EEG frequency, measured at C3, C4, O1, or O2), a blood oxygen desaturation of 3-4% or greater, or both arousal and desaturation.

http://en.wikipedia.org/wiki/Sleep_apnea

So I must disagree. An oximeter plus a breathing monitor can be used to detect apnea events, neither alone will suffice. Absent any other health issues, desaturation will only occur as a result of a sleep apnea event. While the oximeter does not detect the 10-second pause in breathing, it does detect desaturation. Ideally, the combination of xPAP machine events and oximeter desaturation events would produce a reliable record of apneas. I'm working to combine the two.

2) Apneas can occur without causing oxygen desaturations.

It may be possible to have a 10-second pause in breathing with neurological arousal but less than 3% blood oxygen desaturation, so this statement is correct. However clever the machines may be, they are NOT detecting neurological arousal. They are only detecting 10-second intervals. The machines cannot detect apnea by themselves.

The definition is clear: both the pause AND (desaturation OR neurological arousal.)

I remain unconvinced that my Respironic machine records false positive apneas. The fact that I occasionally get a night when there are no apneas is part of the evidence I rely on.

I am quite certain that the machines produce apnea "markers" when in fact the definition of pause AND desaturation is not satisfied.

The machine is dumb, but it can measure air flow, absence of air flow and elapsed time. It is not a very big challenge for the machine to record lack of air flow for 10 seconds or more.

The machine is dumb, and it makes the measurements you claim. However, detecting abnormal changes in breathing by measuring changes in airflow against the background of inhalation, exhalation, steady-state leaks from the mask, PLUS variable leaks from imperfect and changing seals is quite challenging. The machines fail to do this well. My research suggests that the machines are biased to produce false positives, probably to decrease the incidence of false negatives, when the machines fails to detect and respond to an event.

If it pleases you to strive for perfect scores, suit yourself. Some people enjoy spending time perfecting video game scores. I'm trying to understand, assess, and improve the effectiveness of my therapy. Flags caused by changing leaks concern me not because they cause the machine to mark apnea events when none have occurred, but because it means I can't rely on the machine score alone to make progress towards my goals.

[roster]

SP,

I agree with what you posted, which was to much greater level of detail than what we were discussing. Your post will add to the knowledge level of those who take the time to read it.

........If it pleases you to strive for perfect scores, suit yourself. ........

I don't know why you summed up your nice post with that paragraph. None of the posters in this thread, either directly or by implication, advocated this approach. You introduced the concept earlier in the thread.

In case someone was misled by my posts, I don't advocate or practice this approach. My settings haven't been changed in months and certainly most nights there are "apnea events as recorded by Encore Pro".

[Silver Pelt]

I apologize if the phrasing caused offense. Keyboard communications strip away nuances and frequently doesn't communicate what was intended.

My intent was to say that each person can, and should, manage their therapy as they see fit. If getting good machine scores works for you, by all means use that. It doesn't work for me, so I'm trying something different.