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Comment by hourislate | Hacker News Reader

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>My wife is an Ironman as well (Muskoka, Tremblant and Penticton). . She's been using Zwift since last year. Great way to train btw and great idea but. My concern would be a collapsed lung(s) if this wasn't calibrated correctly. To each their own, but stressing your lungs and diaphragm this much isn't a great idea.

In a lab they can at least make sure you don't hurt yourself.

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I see where you're coming from I assume that you are talking about the device resistance when breathing in and you're worried that the adhesion between the lung sac and the cavity wall breaks.

You can pull a pretty good vacuum with just your lungs, so I'm not overly worried about that. And pressure is not a problem unless you have a weak spot in your lung.

But still, it's a good point to make and maybe the author could measure the flow resistance in both directions and optimize for that to ensure that it never becomes a problem, even in people that might have a hidden defect.

But the device resistance won't be very big, would it? If I understand correctly, you are just breathing through a tube, and this device measures the flow through the tube. Or is there something in the tube that would cause a lot of resistance?

Adding some resistance is typically how you measure flow.

How would you get a collapsed lung from using this? And how does its calibration influence whether you get a collapsed lung? This device doesn't interfere with inspiration, and a large breath of air inflates your alveoli.

Pulling a vacuum against your lung can break adhesion when done from the lung cavity.

Questions like this are why people should not be building medical devices at home. Your average athlete interested in this may lack the necessary medical knowledge to understand that a collapsed lung is a possibility when using this device, and cause themselves serious bodily harm.

How could it cause one’s lungs to collapse? Isn’t the idea of measuring VO2 max that a tight seal is formed and all input and output is measured for O2 and CO2? It isn’t pressurizing or depressurizing.

It is pressurizing on output due to the flow through the device, the same thing causes some underpressure when breathing in.

But I doubt it is enough to draw a vacuum strong enough to break adhesion. Still, better safe than sorry, it would be good to read the instruction manual of a professional unit to see what kind of failure modes they have listed there.

I read a lot of stuff back in 2020 because I was going to be coding up controls for an emergency ventilator... you would not believe just how little pressure difference it takes to permanently ruin your lungs... less than 1 PSI if I recall correctly.

1psi is actually quite a lot.

Standard CPAP machines max out at just over 0.25psi, and even ventilators usually max out about 0.4-0.5psi.

You really don't want to over-pressure your lungs with 1 PSI, that's huge for tissue. For a regular party balloon that you blow up the pressure is less than 0.5 psi. But a flow meter in a sports measurement device should be a fraction of that, after all, the back pressure is going to take away effort that should go into providing work.

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