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Very low AHI

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Bundy +1 point · over 2 years ago Original Poster

Hi there, I'm new to getting apnea treatment. My sleep study results showed my AHI was 46 (severe). I started a trial straight away and immediately my AHI reduced to .6 and after a few weeks, I'm down to .2 or nothing at all. I am now on a set pressure of 4cmH20 and have purchased my own Auto/CPAP machine. Whilst I am extremely happy to have responded to the treatment so well, I am bothered by the thought that perhaps I don't have OSA at all and that the test was wrong. I did have a bit of a cold at the time, and in hindsight, I may have been better to wait. I would just get another sleep test done, but I can't afford one right now. Has anyone else experienced this or could shed some light on my situation? It would be much appreciated.

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snuzyQ +0 points · over 2 years ago Sleep Commentator

Hi Bundy and welcome to the forum.

There's some good news here: It doesn't even matter if you had a bit of a cold on the night of your sleep study. It's not possible for a cold to produce severe sleep apnea. An AHI of 46 is really pretty bad. You definitely have OSA. Waiting for your sleep test would not have improved your situation.

You are being treated with very light pressure. That's really OK if that's what you need to treat your condition. You can get the sleepyhead application for free online. You'll need an SD card and an SD card reader to interface with the application on your computer. Sleepyhead will allow you to view your own data on a daily basis to see whether your treatment is working for you or could be improved. You will get to see what kind and how many events you are having (which all affect your sleep architecture even though they are not all a part of the AHI). Good on 'ya for getting your own machine!

Please post next with type and model of your machine, mask and mode of treatment (Fixed CPAP or Auto CPAP or XPAP). View your own sleepyhead data and ask away. We're happy to help in any way we can.

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Sierra +0 points · over 2 years ago Sleep Patron

I will second what SnuzyQ has said. Tell us all the details on your machine. Download SleepyHead and have a look at your data. I'm suspicious that you must be getting a higher pressure than 4 cm. That is very low, and actually not that comfortable for most people. Here are some instruction on how to use SleepyHead.

Beginners Guide to SleepyHead

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wiredgeorge -1 point · over 2 years ago Sleep Enthusiast

Bundy, When you refer to a machine, you might actually mention the specific make and model. I can't see someone with a pressure of 4. You can check your pressure on a ResMed machine by looking at the menu using the right technique. I believe that the pressure is in the clinical menu.

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Bundy +0 points · over 2 years ago Original Poster

Hi snuzyQ, Sierra, and wiredgeorge, thanks for your replies. I tried the sleepyhead app and followed the instructions (thanks very much for that) but I couldn't get any data to transfer, I don't think the machine I'm using is supported. The machine I have purchased is a cheaper model, BMC Luna Auto CPAP, G2S A20/C20, and I use a nasal mask. During my trial under supervision with my local sleep specialists, I was using a Fisher and Paykel Sleep Style Auto CPAP with a nasal mask. After trialing Auto mode with consistently low AHI results and no other concerns except air leakage in the first two weeks, the technician set it down to CPAP at 4-6 (her words), for the third and fourth week (which is where I am at now). I have switched over to the BMC (only last few days) and set (yes in the clinical menu George) the machine to a set pressure of 4cmH2o with a result of 0.0 AHI. As you guys have mentioned, 4 does seem low and yes it is slightly uncomfortable but not nearly as uncomfortable as I found the pressure when it was set on auto. This is precisely the reason it makes me think the diagnosis was wrong. Getting results of 0.0 AHI though I would think it is best to leave the settings as they are? I am very new to this though and don't want to assume I have it figured out, your advice and opinions are appreciated.

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Sierra +1 point · over 2 years ago Sleep Patron

That is very puzzling. I am not at all familiar with that particular machine. I did find a brief clinical manual on line. It sounds like you have figured out how to set it up. I believe you are correct in that this machine is supported by SleepyHead. The F&P SleepStyle I don't believe is supported either. However the sleep specialists should be able to view the data from it. What they should look for is the maximum pressure reached and whether or not there were any apnea events.

Without being able to see the detailed data it is hard to figure out what is going on with your current machine. I guess one possibility is that the machine is not accurately reporting the AHI. Or, the other is that you were misdiagnosed. Perhaps you should ask for a retest at their cost...

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Bundy +0 points · over 2 years ago Original Poster

Thanks Sierra,

I think you're right, it's not likely both machines are incorrect which means I must be responding extremely well to using a machine or I have been misdiagnosed. I shall investigate further by going to a different clinic and doctor, and report back my findings. Thank-you. P.S. Thanks for the link, it's a replicate of what's in the manual they sent me.

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Sierra +0 points · over 2 years ago Sleep Patron

To put things in a bit of a perspective I was diagnosed with a home sleep study with an AHI of 34 or so. I now treat it with a min-max pressure of 11.2-12.6 cm. I get a very low obstructive index of less than 0.5, but my total AHI including the central apneas is closer to 3.0. My wife was diagnosed in the 70's for AHI, also with a home sleep study, and now uses a min-max pressure of 12-14.6 cm. She has very infrequent central apnea and regularly achieves less than 1.0 for AHI.

That is why I find it a bit strange that you could be diagnosed with an AHI of 46 and only need 4 cm pressure to treat it down to near zero.

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Bundy +0 points · over 2 years ago Original Poster

Yep, that's why I thought I'd ask around. Thanks, heaps for your input. I'm going to switch it back to auto for a couple of days and see what the results show.

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Sierra +0 points · over 2 years ago Sleep Patron

I was curious about your BMC machine as I had not heard of it before, and I did a little research on it. From what I can see it is made in China and the Luna model appears to be the latest and top of the line. The lower end model seems to include the RESmart Auto. I did find some information on the RESmart model in an older study which compared 11 different CPAP models. Here is the link to the study:

All APAPs are not Equivalent

The format of the study report is not exactly easy to read and interpret. But the BMC RESmart machine is designated as the "D2" machine. As a comparison the D8 machine is the more common ResMed S9 Auto. From what I can see in the testing, the BMC responds to obstructive apnea as one would expect, but it does not eliminate obstructive apnea as the ResMed machine does. The BMC responds somewhat to hypopnea, but not well compared to the ResMed. The BMC responds to snoring and in fact seems to be overly aggressive in raising pressure in response to snoring. Most surprising is that the BMC responds to central apnea or clear airway apnea by increasing pressure. That is not good if central apnea is an issue with the user. Pressure would be increased and it wouldn't be doing you any good. I suspect at least this RESmart machine is unable to determine the difference between obstructive and clear airway apnea, and blindly responds to them both in the same way. The reporting of the type of apnea event is likely compromised as well. The ResMed uses pressure and flow oscillation to distinguish between CAs and OAs, and only responds to the OAs. Last the BMC machine seems to over estimate the AHI remaining during treatment, while the ResMed under estimates it. So in your case that would seem to suggest the machine is not under reporting your events, and may if anything be over reporting. Not an explanation for what you are observing.

In my search I stumbled on a YouTube video on your machine which you may have found already. In any case the link is below. It outlines a method of extracting data from your machine if you have a smart phone. That may be very helpful in trying to figure out what is going on. This is the third of a 3 part series. I did not look at the other two, but this one seems good.

BMC Luna G2 Auto Clinical Settings and Icode Data Part 3 of 3

One of the things I saw in the video was that the machine has a sensitivity setting. If you find it is raising pressure too much when in Auto, you could try a lower setting to see if that helps...

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Sierra +0 points · over 2 years ago Sleep Patron

In thinking about your situation a bit more I have some further comments for consideration. Your comment that you found the fixed pressure of 4 cm more comfortable than the 4-6 which I presume is a minimum of 4 cm and max of 6 cm in auto mode, is interesting. This would seem to suggest the machine was detecting some issues and was increasing pressure potentially to the maximum 6 cm (which is still very low). I couldn't find much detailed information on your machine, but in general these things respond to more than obstructive apnea. They typically do not respond to clear airway apnea at all as pressure does not help an airway that is already open. However they typically do respond to snoring, flow limitations, and possibly hypopnea. So while you may be getting low AHI, the machine may be detecting these other issues and is increasing pressure to address them. Flow limitations and snoring don't count in the AHI index.

I see that the machine has a exhale pressure relief feature called Reslex. Pressure while you are inhaling helps you breath easier and most find it very comfortable. However pressure when you exhale is what many may find uncomfortable. The Reslex feature reduces pressure during the exhale only. While this feature can reduce treatment effectivness it seems you do not need much. My suggestion for setup in Auto would be to set the Maximum pressure at say 7 cm, and the minimum at 6 cm and turn on the Reslex with a setting of 3. That should provide maximum comfort and a reasonable degree of treatment. But, it sure would be helpful to be able to view or at least see what the maximum pressure it is going to during your sleep. That way you can determine if the maximum pressure needs to be adjusted.

Hope that helps some.

Edit: One more thought. Air leakage may be masking some of your apnea events, if leakage is an issue. The ResMed in some situations does not report apnea if leakage is high.

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Bundy +0 points · over 2 years ago Original Poster

Hi Sierra, I was not clear relating to finding the pressure of 4cm (fixed) more comfortable than the alternative setting of 4-6. The technician I was seeing said the set pressure was 4-6 which I thought was odd and now that I've had a play around with the settings realize she may have misspoken or been referring so something else. I meant to say I found the set pressure more comfortable than the automatic pressure (the range of which I was not informed so it could have been anything). I found the sleep technician very uninformative and even when I would ask a question she would just respond with "yes". I have received much more in-depth and helpful information from you which I truly appreciate, it is obvious from your responses you're an educated person. Thanks for the link to the article, I hadn't thought of checking journal articles so that is very helpful indeed although I'm not very good yet at reading reports so I appreciated your interpretation. Also, I'm pretty much stuck with the machine I have either way. The reason I purchased an inferior machine was purely financially motivated as it was all I could afford. Another bothersome result of seeing the sleep technician is they seemed to be very secretive (and understandably so) about how they set up and adjust everything so that the customer relies on coming back to them and also to purchase one of their top of the line but also overpriced machines. So I'll do the best with what I have. I had looked at that youtube link that's how I figured out how to adjust the settings, it was very helpful. My sleep study reports my obstructive events were predominately hypopnoeic in type, so I'm not sure if that would influence what I would adjust my settings to. Last night I set it on an auto range of 4cm to 12cm, and the results were P95=8.5, Pmean=6.5, AHI=.02, SNI=2.3, and Leak=3.1. I found this comfortable enough without any concerns except I can hear the machine a little in comparison to no noise at all on set pressure. I had the Reslex turned off, but I will adjust to 3 as suggested. I know it's only one day's data so I'll leave the other settings until I hear back from you. I don't mind using the auto pressure, I had already ordered this machine before the sleep technician informed me I was showing consistent enough results to try a set pressure. Either way, I'd rather have it set on whatever is best when I can figure out what that is. It's much more complicated than I would have thought, thanks again for your input it is much appreciated.

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Sierra +0 points · over 2 years ago Sleep Patron

Just heading out to dinner, and I will give you a more detailed response later. For tonight I would set the auto range at 6 minimum rather than 4 cm. Reslex at 3 is good. 12 cm is fine for max. I think your machine is going to do OK for you. It would be nice to know what the max pressure is during the night, but the 95% number is going to be close, so as long as you know that, you should be fine.

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Bundy +0 points · over 2 years ago Original Poster

Thanks Sierra. I made the adjustments and give it a test. Reslex at 3 was quite uncomfortable so I've put it at 1 for now which felt fine. I hope you have a nice dinner.

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Sierra +0 points · over 2 years ago Sleep Patron

I don't know much about the specifics of Reslex compared to the EPR of ResMed and Flex of Phillips. How they can differ is in how they switch from exhale to inhale. The ResMed senses the patient initiation of a change, probably from flow. The Phillips (Dreamstation) tries to time it. I did my trial after the sleep study with a F&P SleepStyle. I'm sure it was using the timed approach, as at time I felt rushed into taking the next breath, and as a result they turned the setting down for me. I will include a link to an article on how the various systems work, but little information on the 3B Reslex system.

Comparing Expiratory Relief Systems

The thing to keep in mind with this feature is that it is for your comfort only. At least in theory breathing out against less pressure should feel better. But exactly how they do it, may negate the benefits. It depends on the individual. It is something you may get used to, or not.

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Bundy +0 points · over 2 years ago Original Poster

Also, I have the latest model that was just released here, it's BMC Luna IQ so I'm hoping it performs a little better than the other models but I've failed to find any further information than what is on the previous G2 models.

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Sierra +0 points · over 2 years ago Sleep Patron

I can't find much detail on how the Luna is different from the ReSmart machines. I kind of think it is mainly in the wireless features and app to report sleep data to a smart device. I see that ResMed and 3B Medical (US arm of the China company) have been in a legal battle over patent infringements. ResMed attempted to ban sales in the US but eventually lost. Now 3B is paying royalties to ResMed, and are continuing sales. There did not seem to be much detail on what specifically was said to be copied or infringed on. But, there must be some similarities between the two machines.

ResMed Dispute

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Sierra +0 points · over 2 years ago Sleep Patron

The overall objective in setting Auto CPAP pressures is to get AHI under 5 as a minimum, and as much as possible under that while maintaining sleeping comfort. Normally you start with a wide pressure range, and narrow it up. You will get the most benefit from increasing the minimum pressure. The last step is to reduce the maximum so it is not going too high unnecessarily. From your data of "P95=8.5, Pmean=6.5, AHI=.02, SNI=2.3, and Leak=3.1" I would set your minimum at 6 cm or possibly even 6.5 or 7 cm, and your maximum at 9 cm. You may find you can reduce that maximum to as low as 8 cm. A final setting may be as narrow as a minimum of 7 cm and maximum of 8 cm. The other aspect of the minimum pressure is comfort. If it is too low like 4 cm you can feel starved for air when you are trying to go to sleep. That will all depend on you and your mask to some degree. So factor in your own comfort.

I'm guessing that SNI may be a snoring index? If so that may be what is driving your pressure up. So when reducing maximum pressure you should keep an eye on it as well as the AHI. That article I gave you a link to, suggests this machine may be overly aggressive in increasing pressure in response to snoring. So, you may want to control that by reducing max pressure until you see the SNI start go up.

Hope that helps some,

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Bundy +0 points · over 2 years ago Original Poster

That does help, thank you. I found the settings quite comfortable and had an AHI of zero. I don't mind increasing the minimum pressure, but would that be for the best if it's not uncomfortable? I would have thought the lower the pressure the better. But I've also considered just because it doesn't bother me doesn't mean it's providing me with the best quality of sleep. Overall though, I did find starting at six more comfortable with a great result. That's a great tip with the SNI (yes snoring index) I think I'll reduce the max to ten. So 6-9 for now and close that a little (maybe 7-8 as suggested) until I find it right. Thank-you. I think the lack of quality in the machine is evident with the Reslex setting, it does not correctly adjust to the inhale-exhale rate as is my understanding to reduce the pressure of exhaling, instead, it is mistimed and has increased pressure at the pause in-between exhale and inhale and the result is a slight rush of uncomfortable pressure before inhale. However, set on 1 (out of 5) was fine. The other setting which may fine-tune things a bit is the sensitivity (1-5). I think this responds to how many or severity of API before increasing pressure. If the machine unnecessarily responds to snoring this may be the best way to adjust it. I currently have it set at three but perhaps lowering it might be better? I guess at the end of the day you have helped me with my initial concern that a set flow of 4 didn't feel right. Also, whilst misdiagnoses are possible, I did have severe symptoms associated with OSA and feel a degree of relief at times since starting treatment. I still have an upcoming final report with the doctor in a few weeks when he's available - not the sleep study technician - so with the new data/report which I will provide it'll be interesting to get his updated analysis. My primary concern was compliance so that I didn't have my license completely restricted. I do hope you and your wife continue to have success with your OSA, your support and assistance have been invaluable and very much appreciated.

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Sierra +0 points · over 2 years ago Sleep Patron

"I don't mind increasing the minimum pressure, but would that be for the best if it's not uncomfortable?"

In some people more pressure can increase the frequency of central apnea (clear airway) events. Your low numbers would suggest you are not in that category. One benefit of increased minimum pressure is that it makes it easier to breathe in. The negative is that it makes it harder to breathe out. That is the reason that the expiratory pressure relief can be helpful. But if you find it annoying then it is not. In the bigger picture breathing out against 6 cm is not that hard. Many people are forced to breathe out against pressures as high as 20 cm or even higher in some cases. The ResMed machines allow you to use the EPR relief feature on the ramp only, so that is what I do. I have a ramp start pressure of 8.4 cm because that is what I find comfortable and then use an EPR of 3. That means I get 8.4 cm in inhale and 5.4 cm on exhale. For me that is very comfortable. Once I go to sleep the machine detects that and turns off the EPR. I have a minimum of 11.4 cm and a maximum of 12.6 cm, and I seem to be able to handle breathing out against that while sleeping.

The other benefit of increasing the minimum is to stop the apnea before it happens. The auto CPAP is a reaction based machine. It has to detect apnea before it increases pressure. If you have your minimum high enough then it may not need to increase very often if at all during the night. That can improve comfort levels by maintaining a more constant pressure level during sleep rather than having one that is jerking pressure up and down as the machine responds to events or lack of events.

But it is all personal. Do what works best for you. Your numbers look very good.

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Bundy +0 points · over 2 years ago Original Poster

Thanks again, very helpful.

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sleeptech +0 points · over 2 years ago Sleep Enthusiast

I don't have time to read the many pages of text in this thread, so I hope my comment hasn't been covered elsewhere. Just because your OSA is being really well treated at 4 cmH2O doesn't mean that it's not real. There is little relation between AHI and the pressure required to treat it. Some people have horrendous OSA and are fixed the moment the CPAP is turned on at 4. Others have mild OSA are still not entirely stable at 20 cmH2O. People are different - they're annoying like that. If you had a proper in lab study that was scored by a human then a positive result is very reliable. Having a cold would not generate a false positive. If you really want to you could get a repeat study, but it's probably not worth it. As an alternative, you could ask your doc to show you the results of your study, and even a little of the raw data. It's not that hard to read the basics with a little guidance, and it might help you understand the situation better. Just be happy that your treatment was relatively easy, and at a pressure of 4 you should have few mask leak problems.

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Bundy +0 points · over 2 years ago Original Poster

Thanks sleep tech, that makes perfect sense, I hadn't really considered the human difference component as much at first. I did an at-home study but I have made a personal adjustment for comfort and now use a pressure of 6-8cm with a result of 0.0 AHI and a mask leak of only 2 liters per hour, so I'm pretty happy with that. I now have the raw data as suggested (I was shown but have little understanding of the implications), the interesting part I've noticed is I only had 2 obstructive events but 253 hypopnea events. Perhaps this means I would respond better in a certain way to air pressure? Thank-you for your input, it's much appreciated.

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Sierra +0 points · over 2 years ago Sleep Patron

Out of curiosity what types of events does your machine report? Does it give you a number for clear airway or central apnea?

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Bundy +0 points · over 2 years ago Original Poster

No, unfortunately, it only gives me an output for AHI, snoring index, and mask leakage. Also, I didn't notice before on the sleep study data, for events there were 2 obstructive, 0 central, 0 mixed, 2 total apnea, and 253 hypopnea.

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Sierra +0 points · over 2 years ago Sleep Patron

That seems unusual to have so many hypopnea events compared to central and obstructive. Hypopnea is an interesting measure, and is more complex than it first appears. It is a reduction of air flow of 50% or more but not 100%. It can happen due to physical obstruction or blockage. Or it can happen due to your body simply deciding to breathe more shallow. The former hypopnea is an obstructive apnea that does not full develop into an apnea. The latter is a central apnea that does not develop into a full stoppage of air flow. One has the airway blocked, and the other the airway open. CPAP pressure does not help when the airway is already open. This would seem to suggest since low pressure is so effective in your case, that your problem is partial obstruction. Perhaps that is why you had such a high total index at diagnosis, but now it is so easy to treat. With most people the condition progresses to full blockage at least some of the time.

In my case I have concluded from looking at the detail in SleepyHead that my hypopnea is actually partially developed central apnea. Increased pressure in my case is not very effective in reducing hypopnea as it is not a blockage issue, but really a breathing control system problem.

I think the conclusion in your case is that it is probably real, and easily treated. It must have something to do with your physical anatomy. Any other breathing issues like COPD, or smoking?

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Bundy +0 points · over 2 years ago Original Poster

No COPD fortunately, I smoked heavily for ten years but have ceased smoking for two or three years now. My guess is the huge amount of weight I put on since I stopped smoking (30kg), but I did have weight issues before that (was 110kg). I am going through insurance, currently going through the waiting period for bariatric surgery next year. Fingers crossed that may eliminate all apnea.

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Sierra +0 points · over 2 years ago Sleep Patron

I think what this experience shows is that the AHI is not a perfect measure of apnea severity. If you google the subject one can find may papers criticizing the AHI system, but it seems to never get changed. Currently it is just a count of the total apnea and hypopnea events divided by the sleeping hours. So, it assumes all events are of an equal weight in the overall severity. Seems to me that hypopnea events which are a flow reduction of 50% should only be given a 50% or so weight compared to a full apnea. And currently apnea duration is not considered. It would seem that apnea and hypopnea events should also be weighted by their duration. I can see in the old days this might be a little more difficult, but this is 2018 and with computer technology this is not very hard. It would seem to be time to make a change to the severity weighting system. In your case it would bring the number down, but it would seem you still do have an issue with flow restriction, and CPAP is a very effective treatment.

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Bundy +0 points · over 2 years ago Original Poster

I totally agree Sierra. Thankfully I've had the opportunity to chat here and now have a much better understanding of sleep apnea. I don't agree with my case being in the "severe" category, and it also explains why I haven't had a vast improvement in my alertness during the day, although I am experiencing a noticeable improvement. I would be interested in your thoughts on minimum pressure; It appears to me that a simple addition of pressure is opening the airway sufficiently to not allow any events to occur, by that reasoning, would an increase in minimum pressure further decrease flow restriction and provide a better quality sleep environment. Or, might it be better to have the minimum pressure set as low as possible that would still produce near-zero AHI so that I'm relying as little as possible on the machine support?

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Sierra +0 points · over 2 years ago Sleep Patron

Without being able to see the actual flow waveforms in SleepyHead it is hard to say what the benefit of more minimum pressure would be. What I see in my wife's SleepyHead reports is that it takes more pressure to reduce flow limitation and snoring than it does to stop apnea and hypopnea events. I am kind of the other way around. When I have my pressure high enough to stop the apnea events my flow limitation and snoring is zero.

With your machine you are kind of flying blind. That comparison study of various brands of CPAP machine shows that your machine may be over reacting to snoring, and under reacting to hypopnea. Perhaps it does not even detect hypopnea and that is your main issue. Don't know. Just guessing. However it only reports snoring to you and not hypopnea, so it is really hard to tell what is going on. Probably the best you can do is limit pressure to the point where the snoring index is not further improved. On minimum pressure it would really seem to be mainly a comfort factor. If you feel comfortable and are getting enough air, then what feels good and keep the snoring index and AHI index in control, should be good too.

The other issue is just pressure variation during the night. Say for example you need a pressure of 8 cm to control snoring and going above that does not do any more good, it would make sense to set max pressure at 8. If you find that the machine is going up to 8 cm and back down frequently during the night you can minimize that variation by moving the minimum pressure up.

Hope that helps some,

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Sierra +0 points · over 2 years ago Sleep Patron

I keep thinking that this thread has come to a conclusion, but as I thought about this more during the US Open tennis match today (excellent tennis by the way), I decided that there may still be a bit more to it.

If we make some assumptions which may or may not be true, there seems to be another conclusion that has not been identified so far.

Assumptions:

  1. The Luna machine you are using behaves like the RESmart Auto machine tested in the study I posted earlier.
  2. The sleep study you had done is accurate and your apnea is nearly 100% hypopnea

If the assumptions are correct what does that mean? First the machine may not be detecting hypopnea and as a result may not be responding to it. And further, it may not be including hypopnea in the AHI reported. What does that result in? Well, it would mean it would take minimal pressure to produce a very low AHI, which is your basic original question. Why? In fact it kind of validates what you have observed which is a high AHI at diagnosis, but almost no pressure to reduce it to a very low AHI.

If this is in fact true, what can you do about it considering that you bought this machine to minimize costs for a CPAP? The first thing to keep in mind is that while there are many different CPAP machines with all kinds of bells and whistles, at the end of the day, they only do one thing. That is to provide pressure to keep the airway open. This machine can certainly do that. Your only problem is making the machine do that, while at the same time, it may not be detecting your basic problem in Auto, which is hypopnea. Contrary to what I have said in previous posts, the easiest way to do that is to let it provide a higher pressure.

A second thing to keep in mind is that CPAP therapy operates on various pressure levels. In my opinion less than 10 cm is low pressure. 10-15 cm is moderate pressure, and 15+ is high pressure. The pressure you need to treat the condition that your CPAP may not even be detecting is likely in the low pressure range, with minimal if any side effects of using it.

So my conclusion (for today) is that you may be better to error on the higher side for pressure than on the lower side, when using this specific machine.

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Bundy +0 points · over 2 years ago Original Poster

Thanks Sierra, that does make sense. Again, much appreciated. All the facts aside, my gut feeling is that whilst 4cm was sufficient on both a high quality and my personal machine, it may only be just doing enough to not count as an "event". However, I'm just going to set it on 5-9 for a few weeks and take how I feel post sleep as an indicator. I don't know why, but while I recently had it on 6-8 I felt fatigued even though the results were the same (low). I'm currently feeling quite fatigued during the day again but have put this down to a cold I have for the time being, so I will update again as things improve.

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sleeptech +0 points · over 2 years ago Sleep Enthusiast

The reason that all apnoeas and hypopnoeas are weighted equally is that, while the duration and degree of oxygen desaturation can be of significance, most of the damage is caused by the arousal process which is the same for all of them. Also, whether an events is a an apnoea or a hypopnoea has little bearing on its duration or degree of desaturation. The difference between the an apnoea and a hypopnoea is very arbitrary. To be an apnoea there must be a 90% or greater reduction in respiratory air flow compared to baseline. If the reduction is 89% it's a hypopnoea. In either case you don't get enough air and it's causing damage to your body. AHI is not a perfect measure, and in the realm of medicine very few measures are perfect, but it is a pretty reasonable indication.

The other thing, of course, is that AHI should not be considered in isolation, but rather as part of a full suite of data from a properly performed, monitored and scored sleep study. It is very easy for people (including doctors) to fall into the trap of just looking at the AHI and nothing else. Care and should be taken by all sleep professionals to take each patient's individual situation into account. An AHI reported by a CPAP machine is far more reliable when a patient has had sleep study to assess the nuances of their particular situation and their response to treatment. We can be far more confident a machine returning a low AHI is providing effective treatment when we know what duration and severity of events are at different stages of sleep and how they responded to CPAP. In most cases we can be pretty confident that if the machine-reported AHI is low then a patient's oxygen levels are high and stable when we've already seen that this is the case in a titration study. Conversely, if we know that someone still has low oxygen levels, even though their respiration is stable, then we know that the AHI is not telling us the full story.

AHI is a useful tool, and like all tool it only works when used correctly. There is no substitute for good quality, conscientious, compassionate medical care.

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Bundy +0 points · over 2 years ago Original Poster

Thanks sleeptech, that's very helpful, it's good to understand that it all is seriously damaging. I think for the time being I shall make do with the machine I have, I think if it's set to return a low AHI reading that might have to suffice for now, and investigated further down the track when I can again afford it. I think my medical care was poorly constructed with rushed sessions and only liaising with the diagnosing doctor once via video link. Unfortunately, that's the best we have here, living remotely.

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