I recently had my RMR tested using a ventilator. The guy measured a baseline reading for maybe 5 minutes, then had me breathe into it for 20 minutes.
My RMR is a little over 10 calories per lb of bodyweight according to the device. That sounds about right, but when he factored in activity level, sounded high. Maybe his activity level info was high. I just know from personal experience, I maintain bodyweight at around 11-12 calories per lb, but he suggested I eat closer to 13-14 calories per lb. I am pretty sedentary due to some injuries limiting my activity level.
Anyway, what I’m wondering is how does the device account for things like hyperventilation? My understanding is they work by measuring how much CO2 you are producing. If you hyperventilate, that shouldn’t increase your CO2 as far as I know. Or do they measure O2? Or both? I don’t know.
Do they get a baseline measurement of the O2 and CO2 levels in the room, then compare how much CO2 you produce vs what is naturally occurring in the room? Or do they measure how much O2 you consume?
Ambient air is around 400ppm CO2, human exhalation is about 38,000 ppm CO2.
Basically what I’m asking is, my understanding is an RMR test will look at how much CO2 you produce to determine how many calories you are burning over the course of a day. Do things like hyperventilation while doing the test affect the results, or would your body not produce excess CO2 due to that since you aren’t actually doing excess activity?
I would assume/hope the device accurately measures the ambient O2 and CO2 content, then looks at how much O2 and CO2 you consume and produce.
But I think they just measure CO2. Do they measure both O2 and CO2?
So
Do they measure O2, CO2 or both?
Do they determine the baseline levels of O2 and CO2 in the room first?
If a person intentionally breathes heavily, rapidly or deeply, will that affect the readings or not?
I’ve never heard of RMR before, but I’d imagine that they can look at O2 in and O2 out (or O2 in and expected CO2 out, of maybe they even measure the CO2 in both directions, I really don’t know. If the amount of O2 or CO2 isn’t outside of the expected norms, I’d imagine that would be an indication of hyperventilating.
I’m guessing the machine also measures the volume of air and speed at which you’re breathing as well. If it notices shallow or quick breaths, it may make a note of that.
Also, and again, this is the first time I’m reading about the test, but from what I’m reading, you’re basically just sitting in a chair breathing into a mask for a few minutes. ISTM, if you’re hyperventilating while sitting down, they may want to address that first.
Lastly, regardless of what the machine says, I assume a pulmonogist looks at and interprets the data, so it may get picked up at that point.
Okay, some very quick googling (that I won’t stand behind, it’s just something I read and don’t fully understand) suggest that hyperventilating can invalidate the test. Some sites suggested that the patient has a few practice runs with the mask to get used to it, specfically to avoid hyperventilation.
When I was younger and more physically active by engaging in 3-5 hours a week of exercise combined with a few hours a week of walking (and more of my total bodyweight was lean skeletal tissue, also I was on a low dose of thyroid medication) my maintenance was around 16-18 calories per pound of bodyweight per day. Now that I’m older, much less active due to an injury, not on the medication, and a larger share of my total bodyweight is fat (which is less metabolically active) my maintenance is closer to 11-12 calories per pound. Back when I was younger, I aimed for 12 calories per lb when I was trying to lose weight, now that is where I aim for maintenance.
So I’m assuming my reading of about 10 calories per pound of total bodyweight as a RMR probably isn’t far off. It may be a little high, but probably only by a few hundred calories. I just didn’t agree with his assessment that a person should be eating 14 calories per lb per day based on my RMR readings and my activity level.
But as far as hyperventilation, I would assume the O2 isn’t converted into CO2 because your metabolism itself isn’t really going up by much.
I very well could be incorrect on this, but my understanding is that when you hyperventilate, the O2 doesn’t have enough time to get absorbed into your body. When you body notices the lack of O2 (or rather, the lack of CO2 I think) it makes you breathe faster to increase your O2, but that just makes problems worse. As they get worse your body sees even less CO2 and makes you breathe even faster and so on and so forth.
I believe that’s the reason that people say to breathe into a paper bag (or take long deep breaths) when you’re hyperventilating. It forces you to breathe in any CO2 you’ve expelled and helps to tell your body that it doesn’t have to breathe so fast.
But my understanding is that those devices work by measuring CO2 output. Atmospheric CO2 is about 400ppm but CO2 in a human exhale is about 38000ppm. So you’re converting a lot of O2 into CO2, and thats how they determine how many calories you’re burning.
If you hyperventilate, you breathe more but it isn’t like your metabolism is going much faster, and your body is producing more CO2.
I’d heard the same theory about breathing into a bag for anxiety. But its also my understanding that too much CO2 causes anxiety (which is why suicide by inert gas doesn’t cause anxiety the way suicide by suffocation does). I have no idea what the effects of too little CO2 are though.