[qlm]

If this was enough to temporarily replace breathing I wonder how that would feel if you were otherwise healthy. I imagine not breathing would instinctively feel quite strange and even distressing.

[goodells]

It would be quite distressing because of the accumulation of CO2 in the blood, even with completely adequate oxygenation delivered intrarectally. The slight change in acid-base balance is what makes a person feel the need to breathe, and CO2 is an acidic byproduct of metabolism. This is why people with metabolic acidosis (e.g. in diabetic ketoacidosis or sepsis) have an increased respiratory rate.

[eszed]

Would CO2 still build up if someone isn't breathing at all? I'm guessing so, since you say CO2 is a byproduct of metabolism. Alternatively, could respiration exhaust enough CO2 even in a situation where the lungs are too damaged to take in sufficient oxygen?

All that apart, I'm guessing this would be used in emergency situations, where a patient is likely already unconscious and could be kept under sedation until transferred to ECMO. Is CO2 buildup dangerous on its own? If so, in what kind of time-frame? What's the upper limit on the additional minutes this therapy could buy?

[dillydogg]

In my thoracic surgery rotations in med school I was taught that the strongest stimulus for increasing the respiratory drive was the acidification of cerebrospinal fluid. Which, of course, correlates with the blood pH. This information comes from some studies in the 60s with goats, and the old guard are happy to hang their hat on it.

There are also chemoreceptors for oxygen concentration in the circulatory system as well.

I think everything you have said is correct, I just wanted to add a few more details for anyone who is interested.

[hifikuno]

From the littlei know from a breath holding workshop I did awhile ago (for trying to get into freediving) it's the carbon dioxide build up in our blood that gives us the urge to breath, and not the lack of oxygen. If this method allowed for the removal of carbon dioxide from the blood then holding your breath might not even be discomforting.

Edit: goodells explained it better!

[not_a_bot_4sho]

I'm scuba certified.

Now I'm wondering if I should get certified to dive with an anal rebreather too.

[dillydogg]

The acid base balance of the cerebrospinal fluid is the primary driver of the respiratory drive, like allude to with your comment on the CO2. I did want to add that the lack of oxygen can affect respiration, which is detected by the peripheral chemoreceptors, like in the carotid bodies.

Additionally, the thoracic stretch receptors are important for respiratory drive, where the lack of expansion of the chest will promote respiration. When a healthy young person holds their breath for short periods, say 30 seconds or so, their blood CO2 and O2 are not much different, but they still will have to fight the instinct to breathe!