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Comment by jvanderbot | Hacker News Reader

One interesting thing in the paper that I didn't think of, is that our breathing mechanism is tied to CO2 levels. And therefore, higher CO2 levels (not atmospheric high, but artificially high during studies), can trigger panic attacks and general stress. A slow suffocation hallucination, kind of. Even when there's still sufficient oxygen, your body doesn't "measure" oxygen!

I didn't know that!

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It's a factor in "shallow water blackout" a fairly common death for experienced swimmers. Caused by hyperventilating prior to a long breath hold flushing too much CO2 out of your blood, so your sense of needing to breathe is suppressed relative to your need for oxygen.

Yeah was going to hit on a similar point. When you hold your breath, that feeling that you need to breathe again isn't because you don't have enough oxygen, but because you have too much CO2. This is why things like hypoxia (lack of oxygen) can be so deadly in environments where it can be a thing (pilots, scuba, etc). Early onset symptoms include things like euphoria which isn't the most helpful warning from your body for 'death: imminent.'

This is the reason closed environments (e.g., space vehicles, submursibles, rebreathers) have CO2 scrubbers.

It's also the reason people pass out and die in high-nitrogen or helium environments. Your body can still exchange out CO2 (and O2 in really high concentrations) and you just carry on until you... Stop.

A couple of refrigeration engineers died near us at a poultry processing plant after it was found that the on-site liquid nitrogen tanks had a small leak. CCTV showed them just happily working in a room without ventilation and they just died. Was all very sad.

Correct. Depth and frequency of breathing is regulated 90% by arterial CO2 level due to a direct, potent servo feedback based on a sensor in the brain stem. The rest is due to O2 level. A fatal situation happens with low CO2 and low O2 that doesn't increase breathing. Pneumo doctors hate this and it's an absolute indication for intubation and mechanical breathing.

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