Why is cognitive function impaired at high altitude?

It seems to me that metabolic state should also be taken into account.

A lower respiratory quotient for fat metabolism means expelled CO2 is much lower when utilising fat for energy (CO2 litres per kcal [0]), making respiration easier and requiring less tidal volume. A lower CO2 concentration in the alveolar space means O2 can be more effectively taken into the blood [1].

Hormonal disruptions also seem to play a role [2].

[0]: http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/metab.htm...

[1]: https://academic.oup.com/bjaed/article/13/1/17/281180

[2]: https://www.ncbi.nlm.nih.gov/pubmed/30008674

I had to do a session in an altitude chamber as part of training in my early military career. I remember how scary it was feeling like I had just sat down on the bench and been there for no more than 3-4 minutes tops when I was told time was up, but then watching the film of my session and realizing I had been in for 30 minutes and couldn’t perform the simplest tasks the trainers were instructing me to do.

>First, thin air alone doesn’t fully explain the cognitive deficits observed in mountain climbers, since the Kilimanjaro group fared worse than the altitude chamber group.

they should have made the chamber group doing heavy weight-lifting and treadmill running in the chamber (with thermostat set to -40 degrees) and i bet the results would be very close.

>And second, fatigue from prolonged exercise doesn’t explain the difference, since the ski touring group didn’t show any negative effects.

if anything, cross-country skiing pumps you up with energy and overall great feeling. Your brain works even better after that, and even of you get very tired, it isn't really a fatigue like you get during even modest mountain hiking (did Shasta once and it was pretty tough for me even just a bit beyond 4km - you feel really slow and remembering some stuff later with friends - happen to be more stupid than usual too). They should have tested super-marathon of 100mi instead of cross-country skiing.

The article somehow dances around obvious - oxygen insufficiency (like at high altitude) which naturally gets aggravated by heavy physical activity/exercise as well as cold which at the altitude slows down body energy production while taking its significant share of produced energy (at high altitudes there is also some effect that digesting food isn't energy efficient anymore or something like this).

Any one factor alone that they tested - like the chamber - may just not be enough to hit the threshold where oxygen insufficiency (more precisely - resulting balance of energy production and consumption in the body) starts to affect the brain. Especially given that our body prioritizes oxygen delivery to the brain (just look at the blood vessels diagram).

Relatedly, Destin from Smarter Every Day did a video about what happens with oxygen deprivation. https://www.youtube.com/watch?v=kUfF2MTnqAw

I participated in a trek in Nepal, the high point of which was ascending to the peak of Kala Patthar (chosen because of the great views of Everest it offers; we got great photos of an avalanche in progress there). It's 5,644.5 m (18,519 ft). We absolutely felt the lack of oxygen. It was a strange feeling, like nothing else I've experienced. I definitely wouldn't have had the competence to do much else than mindlessly climb up and mindlessly climb down again on the day we did the peak (other than snapping some photos)!

My wife is a retinal surgeon. She was interested in the effects high altitude on the retina, since the retina can, in some ways, almost be almost considered to be part of the brain. At a lower elevation than the top of Kala Patthar, she took out a magnification instrument and could spot some mild hemorrhaging on my retina. Not enough to worry about but enough that she could see it. It was interesting and a bit scary to think what could be going on in our brains.

I can't imagine how people climb Everest without oxygen. But one factor is that most of them probably take more time to acclimatize than we did. (It took us 2 weeks to trek to the peak.)

https://en.wikipedia.org/wiki/Kala_Patthar

It'd make sense that even if the human brain can cope on the oxygen available at higher altitudes (since versatility is kind of our thing), it might not do so well at high altitudes while also exercising vigorously, since then the brain and the muscles are competing for scarce oxygen.

I've climbed in the Andes in the past, getting as high as 6700m. I would really guess that poor sleep is the major factor aside from oxygen deprivation. It's very difficult to sleep at those altitudes, both from lack of oxygen and the difficult physical conditions.

The human body's breathing is controlled by CO2 in the blood. If you aren't getting a lot of oxygen, you aren't making enough CO2, so you are not breathing enough. This is the main cause behind altitude sickness. It takes time for your body to adjust its breathing rate.

This issue is worse at night. This is the reason behind an adage "climb high, sleep low." Many people even get Cheyne-Stokes breathing, which causes one to wake up hyperventilating kind of like sleep apnea.

I just got back from the Rockies. I noticed my usual anxiety at sea level was completely gone.

Because you don’t have enough oxygen getting to your brain cells?

“The most unambiguous—and unsurprising—finding is that the Kilimanjaro group had seriously impaired attentional capacity at the summit..”

You’re going to tell me that people might act distracted when trying to do some memory test while standing looking at the spectacular view in the blowing freezing wind on top of a mountain they just climbed? No way.

Next amazing result: people make 30% more errors on their tax returns while skydiving..