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Decreased tidal volume after switching machines

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HonestElephant +0 points · 7 months ago Original Poster

I have noticed on Oscar that my tidal volume during sleep has decreased by more than half (about 600 ml median volume per breath to 250 ml median volume per breath per night) since switching machines and raising pressure last year. I have had considerable anxiety this year as well as being tired in my muscles and I am wondering if it might be hypoventilation syndrome and if so, how to fix it. Hypoventilation syndrome is my Dr. Google diagnosis, not something that any professional has mentioned to me.

I just got my yearly checkup at the sleep doctor and he gave me an "A+" for using my sleep machine every night of 2021. I don't think he really looked at my numbers and I did not tell him of my anxiety and muscle pain because I did not think it could be related until I did some internet sleuthing.

Does anyone have any knowledge of this?

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Sierra +0 points · 7 months ago Sleep Patron

I don't really know what the significance of Tidal Volume is. Checking my records I seem to average about 350, and my wife averages about 400. On a simplistic basis I would have to think we get all the air we need or bad things happen. About all I can think of is that perhaps some people may be more efficient with the air they take in. They need a lower volume to get enough oxygen.... Not sure. I use a fixed pressure of 11 cm. My wife has her machine in Auto mode and uses a bit higher average pressure of 13.8 cm. Perhaps some others will have an explanation. Both my machine (AirSense 10) and my wife's (S9) are ResMed.

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PutSleepApneatoBed +0 points · 7 months ago Sleep Commentator

I don’t know much about tidal volume, either. And I’ve no idea of the degree to which it may be clinically important- or not.

However, I would purchase and use an overnight recording oximeter to check your O2 desaturation levels throughout the night. If you are desaturating for some reason, THAT could account for the anxiety levels increasing. And if you aren’t desaturating, at least you will know that your body is getting the O2 it needs.

Also, what machines did you switch from and to? If the machines/pressure settings are different, the expected tidal volumes may differ, too. Have you raised the question with the respective manufacturer(s)?

Also, one would think that, all other things being equal, there might be a relationship between pressure settings and expected tidal volumes, but that’s not something I’ve ever researched…

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CyrusManz +0 points · 7 months ago

Tidal Volume is a significant indicator for respiratory function and at 250 ml is what an 8 yr old female is at., so something is wrong here. An average North American (5'10" and at 170lb, should have a Tidal Volume of about 600-700ml. If you'd like to share what machine you used to use and what machine you have now and what software you use ti check your Tidal Volume, I may be able to help.

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HonestElephant +0 points · 7 months ago Original Poster

I have a Resmed Airsense 10 and I use Oscar.

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CyrusManz +0 points · 7 months ago

So at a tidal volume of 250ml and (assuming) a breath rate of 12/min, your Minute Ventilation should be (12x0.25 = 3l/min). Oscar should show a MV of average 3 L/Min and average adult MV is about 5 to 8 liters per minute. You either have a tremendous amount of circuit air leak overnight or your machine is faulty.

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HonestElephant +0 points · 7 months ago Original Poster

My MV is around 3.5l/m and my respiratory rate is about 15/minute. Does this still line up with your theory?

Thank you for your help

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CyrusManz +0 points · 7 months ago

That is not a theory, just calculations. Oscar doesn't get ALL the data it reports, from the machine memory card, but just SOME of the data like Flow Rate, Mask Pressure,Tidal Volume and it calculates the rest from these data sets. So if the machine reports a tidal volume of 0,.25 l/min (how much are displaces into your lungs at inspiration) and at a breath rate of 15 (how many times you breath per minute) then together with tidal volume, it can calculate other data like Minute Ventilation, such as 0.25 x 15 = 3.25 l.min (near enough to 3.5 l/min average Minute Ventilation that Oscar reports). So if the machine reports incorrect data such as tidal volume, then other data will also be incorrect because they strepulate from Minute ventilation. Now, we know your TD was twice as is now, before you changed the machine, so it must be the new machine that is producing faulty data. What machine did you have before?

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HonestElephant +0 points · 7 months ago Original Poster

I went from a Dreamstation (1) to this Resmed.

Well, here is the problem that I am worried about. The MV did not drop from high to low the day I got the new machine, there's a 2 month period where it sloped down from ~500 with the Dreamstation down to about ~300 with the Airsense. Then it slowly kept coming further down.

So the drop happened in real life, it would seem, and not on a microchip.

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CyrusManz +0 points · 7 months ago

Wow! That doesn't make much sense unless you have another respiratory condition that is affecting your tidal volume. With your TD that low, I suspect your Oxygen saturation would be low too. Have you been checking it? Also you definitely need to see a pulmonologist to test your lungs

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