Is AHI=0 actually a bad thing ?

[Diver71]

Just curious to see how others experiences mirror my own. Over the past 10 days I have had 6 nights with AHI's of zero and 4 with AHI's of between 0.6 and 1.3. After the nights with the 0 scores I have woken feeling like I haven't slept all that well yet the nights around 1 I wake feeling great.

Does anyone else experience this ...

[GumbyCT]

What are your leaks like? What is your setup?

[El Pap]

Your extremely low AHI on nights you feel less rested may be the effect, not the cause. Remember that most of us have the worst apnea symptoms during the deepest, most restorative stages of sleep and REM. So those ultra low AHI numbers may be happening on nights when you are spending less time in deep sleep. For me, I've noticed that any night that I'm under 0.5 I don't feel as alert as when my AHI is between .5 and 3.

[alnhwrd]

No matter how you feel, if your AHI is 0.0 that means your blood O2 levels are not dropping and you are probably not having blood pressure and heart rate spikes. Like El says though, it is possible you are not reaching the deep restful sleep that makes you feel better. I find I have better numbers with a FFM but I feel like I sleep better with a nasal and tape.

[tattooyu]

When my leak rate is very low (last two nights were 0.00 L/s), I find my AI and AHI go up just a bit, but I do feel more rested. I now average an AI of 0.5-0.8 and an HI of 3-4.5 with a lower leak rate. Before that I had AIs of 0.2-0.3 and HIs of 2-3 with leak rates between 0.1-0.25 L/s.

[GumbyCT]

Certainly the above is true and is part of the equation. However comma when the leaks are high the machine may just not detect many events and zero is therefore misleading. That means the blood O2 could be decreasing resulting in the poor feeling the next day. Never discount how you feel regardless of the numbers.

I have had setups where my hose was too long to detect events too. Which is why I asked those two Q?'s above.

So zero is not a bad thing but it's not the only thing either. Giving your stats without your pressure, mask, AND leak rate can also be misleading.

[tattooyu]

Certainly the above is true and is part of the equation. However comma when the leaks are high the machine may just not detect many events and zero is therefore misleading. That means the blood O2 could be decreasing resulting in the poor feeling the next day. Never discount how you feel regardless of the numbers.

I have had setups where my hose was too long to detect events too. Which is why I asked those two Q?'s above.

So zero is not a bad thing but it's not the only thing either. Giving your stats without your pressure, mask, AND leak rate can also be misleading.

Good point Gumby! While 0.1-0.2 L/s is still within the compensatory range of the Autoset II with the Swift LT, there could still be apneas happening when getting close to that 0.4 L/s leak threshold that aren't being recorded.

[Diver71]

Using the Quatro it is recording leak of - 31lpm which is actually less than what the predicted leak rate is supposed to be ....

I have no leakage issues at all ... my mask fits like a glove and no leakage.

Set-up is Covidien Sandman Info with humidifier at 9cmH2O using a 6ft hose. Hose is routed from the machine on my bedside table under the quilt and my arm up to the mask. I don't ramp and lately have managed 8hrs of continuous sleep with no waking for pee breaks or even itchy noses.

I have now been using this set-up for just over a month and in the past week my numbers all look great - no leaks, low AHI figures AHI between 0.0 and 1.3 HI between 0.3 and 1.3. No snoring and 20 flow restricted runs (as opposed to 30-50s before).

The only strange thing is that I feel better when I get AHIs of around 1 rather than when I get 0

[stuart1]

When my leak rate is very low (last two nights were 0.00 L/s), I find my AI and AHI go up just a bit, but I do feel more rested. I now average an AI of 0.5-0.8 and an HI of 3-4.5 with a lower leak rate. Before that I had AIs of 0.2-0.3 and HIs of 2-3 with leak rates between 0.1-0.25 L/s.

I'm confused about how it's possible to get a leak rate of 0.0. Since the masks have an exhalation port, isn't their leakage by design?

[tattooyu]

ResMed machines take into account vent flow rate already, so the "Leak Rate" is the amount of leak on top of that. Respironics (I believe) show a total of both, so you have to subtract the vent flow rate to get your actual leakage.

Please correct me if I'm mistaken.

[feeling_better]

Diver71,

1. How much total sleep are you getting on those good/bad days? If I do not sleep at all my AHI would be 0 too

2. Most of us cpap users get so cpap centric (yes, cpap has an easy way to get to our mind), we tend to think every life experience is some how only related to cpap usage or lack thereof . Yes, I have to catch myself when I think this way. While getting AHI of 0 is excellent by itself, I am thinking about your not feeling well 'only after those' nights? What is the day time activity variations? Exercise, drinking, stress, social life, work life, ...

3. Is there a small chance you do not need the machine at all on some days, are you only very low apneaic? What was your AHI untreated? Perhaps you can get away with lower pressure and still have very low AHI? I do not know your machine; many machine sw has bugs and counts items unreliably. Whenever a measurement over a long period like 8 hours in a natural phenomenon shows up with a value of 0, I always suspect the measurement -- I get Hs invariably as I fall asleep and after I wake up even in the best of nights. My AHI is typically below 2 most nights; but I have never ever once seen below 0.3 or so.

[LinkC]

I find I have better numbers with a FFM but I feel like I sleep better with a nasal and tape.

Wow! My experience exactly! But I thought it was just the sleep deprivation talkin'...

[Diver71]

Pre CPAP AHI was 67.1 and my lifestyle isn't really a factor ... work stress is even, diet doesnt vary much and I am not much of a drinker.

Leak rate of zero is shown in the software readout it confused me a little too ...

I have also noted that the nights of less sleep are lower AHIs (obviously) but the ones I am commenting on all came from nights of 6+ hours and my average sleep per night is around 7 hours.

I no longer even wake for a toilet break in the early hours (pre CPAP averaged about 4-5 toilet trips a night)

No real issue with anything ... as they say if it aint broke .... but was simply curious why I seemed to feel better when the numbers were showing that the incident count was actually worse. Anyway thanks for all your suggestions and comments ... I am off for a dive

[feeling_better]

Pre CPAP AHI was 67.1 and my lifestyle isn't really a factor ... work stress is even, diet doesnt vary much and I am not much of a drinker.

Leak rate of zero is shown in the software readout it confused me a little too ...

I have also noted that the nights of less sleep are lower AHIs (obviously) but the ones I am commenting on all came from nights of 6+ hours and my average sleep per night is around 7 hours.

I no longer even wake for a toilet break in the early hours (pre CPAP averaged about 4-5 toilet trips a night)

The last item above is a well documented (good) effect of better uninterrupted sleep. I have also been sleeping without getting up for 7+ hours every night, safter my cpap therapy stabilized. My own guess of the cause is that body naturally reduces urine production rate during good sleep -- perhaps to allow uninterrupted longer sleep?

No real issue with anything ... as they say if it aint broke .... but was simply curious why I seemed to feel better when the numbers were showing that the incident count was actually worse. Anyway thanks for all your suggestions and comments ... I am off for a dive

Diver, with all your answers put together, your experience has started to become a bit puzzling to me too. But your last sentence... Just curious... Have you already taken out any possible variation from diving too, especially if you dive often enough? Based on your previous responses, I would guess the answer is affirmative for that too BTW, give the outside chance the effects of diving may continue to span over more than one day.

OK, then let me continue with secondary factors ... When you see 0 leaks, being a measurement expert, I get a bit uneasy... I do not know your machine, but does it show negative leak rate sometimes? If not, you are definitely losing some information sometimes. You see, your machine has to assume a 'standardized leak rate' depending on the pressure variations, based on the type of mask you entered into your machine. But the actual leak for your own particular mask may be indeed be less than that standardized or spec value. Search for my posts in other threads about 6 months ago on detailed study and analysis of possible actual leak value difference from the 'average published spec curve'. If your machine does not show negative leaks ever, it is highly likely that even when your report is showing 0 leaks, there is some leaks over the intended normal leak thru the outports! This convenience of automatically subtracting spec value is really resulting in some information loss This is why I like better, what many users may think of as stupid, Repironic's reporting of the total leak, you can always see the variations even when the leak is small. Hope you followed this somewhat long explanation of a possible error in leak reporting...

Assuming the above, a possible explanation is that you are actually getting leak variations even when you see 0 every night; and the higher leaks may be reducing the cpap effectiveness on some nights. Of course that also assumes that the software algorithms detecting the Hs and As are at best not accurate; but bugs in software alogrithms, especially in these complex and 'closed proprietary' systems is more the norm than the exception For whatever it is worth, I spent my lifetime in high end scientific/research software.

Now I eagerly look forward to your response. Diver, I hope you had an excellent dive!