[foobarbecue]

Seems like the key thing would be to measure the concentration under mask during inhaling vs exhaling. Exhaled breath has many % CO2. The article references a whole table of articles measuring CO2 under masks. I haven't taken the time to check if they separate exhale vs inhale but would be curious to know.

[im3w1l]

Just thinking about the numbers. Exhaled air has 4% CO2, while fresh air has 0.04%. But if you inhale air with 3% CO2 that should add to those 4% yielding 7% exhale.

Now, in order to get 3% CO2 in your inhale this would mean that you would have to breathe in 42% stale air (with 7% CO2) mixed with 58% fresh air (~0 CO2).

I wonder if this 42-58 mix is plausible.

[kadoban]

That would mean that the volume of gas trapped in a mask is 42% of lung capacity? Seems extremely implausible to me.

[im3w1l]

A typical breath is much less than full lung capacity, but even then I don't think it adds up.

[foobarbecue]

I checked Roberge et al 2010 and it seems they don't separate inhalation from exhalation in the gas measurements under the mask.

I checked Sinkule et al 2012 and it's quite hard to tell how the review got those numbers from that paper.

Might check more when I have time later.

[kadoban]

Since the volume of gas trapped by a mask is miniscule compared to the lungs, I wonder if it even matters. Might be better to just try to measure blood concentrations.

[camgunz]

Yeah I was surprised they didn't measure blood concentrations--feels like the actual metric we should care about. I remember like, a lot of mic-drop social media posts about people being like "I wore a mask for 16 straight hours and my spo2 is 100% (or whatever), quit whining"