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Heart Rate Variability - Anyone looked into this?
I am curious about something called "Heart Rate Variability". It seems there are some studies that can use this to determine REM sleep, etc. There are also apps, but I don't know how well they work? Evidently you need a chest strap monitor (which I happen to have a Polar H7 handy).


Any thoughts on this?
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Yes, this is a known thing in medicine, but how it makes difference to you personally is not clear to me. Did you suffer an Mi at any time? It describes how in various stages of sleep, the vagal system overtakes the control of heart rhythm, and how, in the case of an MI, that dominance may not occur, which may explain sudden sleep death phenomena. But this is only of importance to someone who has cardiac damage of a specific kind, and to date, there is nothing you could do about it. What it does not mention is that certain kinds of pacemakers negate the problem to some extent, but only for specific conditions. You would ave to take it up with your cardiologist.

As for using it to determine REM sleep, it is a possible method, but still a poor one at the moment, compared to other methods. In theory, a recording pulse-ox would do the trick, since different sleep phases are also visible (vaguely) by your resting pulse rate.
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Great info. No MI here. Any thoughts on this software?


Here is my data with pulse from an oximeter (2nd post). Can anything be interpreted about REM (or other sleep stages) from that? What are you looking for? I am not aware of this method.

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The software is a very rudimentary version of the sort of belt we use in sleep studies, how accurate it is I can't say, but it will be about as accurate as an unsecured pulse-ox IMHO - in short, prone to a lot of data noise that will be then need to be filtered out to understand the core data. If they have their own filter algorithm, it may or may not make it more accurate - we tend to look at the raw data and can more easily screen noise than machines can, but since is meant for non-medical types it probably tries to filter and interpret the data for you.

As for reading sleep phases on the pulse-ox, I would need to combine it with the rest of the CPAP read-out, but basically, because when you enter REM stage, your brain sends signals to induce a form of sleep paralysis, and in this stage, with muscle tone having gone smooth, your heart rate will dip a bit compared to non-REM phases. All sleep phases will show slowed respiration, which is why combining the data from the pulse-ox and the CPAP's night chart is needed to better determine the time and length of the various cycles. However, this is a rough and dirty method used when EEG data is not available. But it does work. It takes a practised eye to eyeball it and suss it out quickly, but with practice one can do it well enough. Is it a 100% accurate method? no, not at all, but I doubt if it is far less accurate than the sleep tracking device you mention.

On your posted pulse-ox print-outs, there are some small stable dips that last several minutes every hour or so that indicate the onset of sleep induced limb paralysis, which would then point to REM sleep - mostly where you bottom out at around 45 bpm. However, with the print-outs you posted, not easy to really get more than that - the scale is too compressed, and it is not coupled with respiration data that would confirm it. The spikes indicate strong arousal, it seems from O2 deprivation.
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For the SleepRate app, you use a chest strap heart rate monitor that connects via bluetooth (Polar H7). Evidently this gives quite a bit better info for HRV than a pulse oximeter would. At this point, I don't have a CPAP machine. In fact, I don't even think I have sleep apnea (seeing a doctor in a few days to discuss further). But I am a researcher (another field) and curious about these sorts of things. So it got me wondering how much information could I collect on my own to (a) understand the quality of my sleep (b) make improvements if necessary and © track sleep patterns after changing things like supplements, etc.

Thanks for having a look at my graphs. You are correct about the arousals. I work up a few times so I think that is what is going on.

Here is another print out from the first 3 hours from last night. I was able to find out how to rework the scales a bit better. Any comments on this?

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You have a few low stable sections that indicate a likelihood of REM sleep, none longer than 20 minutes, but again, this is just a rough look and not enough to go on. There is considerable controversy surrounding the idea that BPM alone can indicate sleep phase, and the method, looking at the differences between phases of BPM is championed by some (anaesthesiologists, for example) and derided by others, mostly sleep neurologists, and rightly so, for they want accurate and as I said, this isn't - it is last century methods when we have better ways today - it works in a pinch, but not enough to hand a diagnosis on these days, just enough to spot trends that warrant further investigation.
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Thanks again. That is great info!

In your opinion, is there anything else that can be done to monitor sleep at home? It seems SpO2 data is useful and an APAP machine can generate useful data. But aside from pulse, motion, and noise...is there anything else more "sophisticated" for at home use? It is sort of a curiosity of mine at this point. I am wondering if something like a small motion sensor placed on the eyelids exists for home use? I doubt it, but curious.
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I haven't heard of one, but that doesn't mean one doesn't exist. There was a headband for a while that took a primitive EEG, I forget the name, some members here had them and liked them very much, but the company went out of business. It more or less could show your state of sleep/arousal, I don't know if could track down to the various forms of REM and NREM sleep. In a pinch, a recording pulse-ox is method to make a first rough assessment if someone suffers from clinical level sleep apnoea in the sense that it will show desaturations of sO2 levels, which is a primary part of sleep apnoea, however it is not enough for final diagnostic, partly because knowing that one has desaturations does not indicate how and why the desaturations take place, and therefore a proper treatment solution cannot be determined. Certain wrist band pulse-ox devices now come with a cannula to monitor respiration levels and flow rates, so come even closer to a home polysomnograph, and there are hand held cardiac monitors that can take recordings of up to six hours, enough for a night's sleep, but they only follow one lead, so you would have to choose your electrode placement wisely (V3 or V4 would be my first choice - nice, clear, juicy P and T waves, clear recovery phases and an easily recognisable QRS complex, which is easier for amateurs to interpret). Please note the pule recordings on a pulse-ox are not enough to do any clear heart diagnostic, as they only record the beat and not the electrical activity of the heart. At most it can indicate a fast or slow beat or a skipped beat, but they give no indication as to what exactly is happening in the heart at all. As such, it is far easier to determine state of sleep from an EKG than a pulse-ox, and of course, an EEG will tell you pretty much exactly where you are, within reason.

But all this gear together costs more money than a sleep test, especially a hospital guided home test. And you get the experts to interpret it then, to boot. Far better choice, even if you are not certain you have sleep apnoea, as it can at least clearly eliminate one avenue of enquiry and give some nice indication as to other things (for instance, part of a sleep test is wearing a portable EKG device called a Holter device so you get nice, clear 3D indication as to the state of the heart's health for a good six or seven hours worth of recording, which is nice, as it gives plenty of time for anomalies to show up) so my advice is to get thee to thy physician and get the process going.

As for using the pulse-ox to tell if you hit REM sleep, it takes a practised eye to make anything of that at all - sleep medicine was still in early stages when I was in med school, back when dinosaurs ruled the earth, and we used to, more or less for a lark, try out different methods of seeing what stage of sleep the patient was in, so we got very practised in "black-box" methods. Younger doctors never got that practice, I am afraid - technology had by then advanced and taken over (and became more accurate) but if we were stranded on a desert island, I would have a better change at doing my job than a lot of the young whipper-snappers today. Most of the kids today would not know how to make a cat-gut suture at all (no, you don't' need cats for it - a bit of a mis-nomer, I am afraid, but cows or sheep are a must). So most docs today will tell you that you can't do it with a pulse-ox, which is true, but what they mean is you can't get better than a decent guess with a pulse-ox, which is more to the point. I don't think it is a useful avenue to pursue in, for instance, developing a "state of sleep" indicator that has any clinical value.
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That all makes sense. Thanks so much for sharing. A few comments:

- Do you know the actual equipment that can be purchased? While an APAP is an option, a nasal canula seems easier and doesn't require an adjustment period.
- One of the reasons I wanted to acquire some home gear was to monitor myself at various times. Plus some guys actually get sleep apnea after starting testosterone (which I am about to do). So I may another test down the road...potentially.
- Also, I would like to be able to help my friends do some checks (share equipment).
- I gave data using the CMS50D+ so far. I just received the CMS50I and it is showing the SpO2 to be a little different (will put up some graphs after a few days). The CMS50I has a "purfusion index" but I don't know how valuable that is, except for that supposedly units with this have more accurate SpO2 results. But either way, I was pretty disappointed to see a decent amount of difference (about 3-5%) which makes me wonder if the previous data was useful.
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The thing is, in the three postings of data you put up, none show a significant desaturation, certainly none that would put you in anything even vaguely a sleep apnoea range. For that reason alone, a proper sleep study with an EEG, etc will be necessary to determine if you have any sleep problems, home kits won't work (no EEG, you see, so a lab study is probably necessary) - at a glance at the posted data, it probably is not apnoea, at least in a classic sense. While it is true that not all cases of apnoea show a desaturation to 88% or below for every event, normally there has to be some sort of desaturation, and you never drop below the the norms for waking or healthy sleep. Desaturation to around 92-93% is perfectly within a normal human level, usually caused by nasal wall collapse, mouth breathing (far less efficient at O2 exchange than the nose) a skipped breath, a choke on some mucus, slowed respiration, or other normal causes.

Without an EEG, it will be very difficult to determine if you really are passing through all the sleep phases and or how long. Basing it on muscle tone alone is not enough, which is why a pulse-ox is at best a quick, dirty and inaccurate method, even in the hands of an expert diagnostician like me, since there are conditions where the patient enters into REM sleep but does not have the concomitant sleep paralysis, which is a potentially dangerous condition and needs a proper sleep lab to diagnose. So again, get thee to thy physician. this isn't something you can reasonably do at home.

All the equipment I mentioned is discussed elsewhere on this forum, particularly in the equipment review sections - do a bit of digging and you will find it all.

Don't share equipment that you can insert in your nose, etc, unless you have medical grade cleaning methods, and disposable cannulae. Too easy to share "other things" as well. Even the pulse-ox should be wiped down with medical grade alcohol before using on someone else, and immediately after use as well.

One more thing - while over the years we have put tremendous emphasis on REM sleep, and assumed it is the only state where one dreams, we are now learning that non REM sleep is as vital if not more vital and also produces dreams. There is considerable evidence coming to light that different states of sleep produce different dreams and reflect different emotional states - REM sleep seems associated with negative dreams, NREM with positive,and since you remember your last dreams before waking, it will depend on which state of sleep you are in before waking that will tell you what your dreams were - nightmares are there because you woke directly from a REM state. As such, what we are learning is that you need a complete sleep cycle or culture in order to have a healthy sleep - the question of REM or not is simply now considered insufficient to get a complete picture. As an interesting factoid, all mammals experience REM sleep, lizards and reptiles do not. I would assume it has to do with the brain structures.
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