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I read some articles that suggested that even moderately high altitudes can lead to some irreversible brain damage. Thus, I was wondering whether that is actually possible and what is its likelihood?

I have done that once and I was wondering if there's a realistic chance that I caused myself brain damage. I usually live at 500ft (~150m) and I did a hike to a summit which is at 9,600ft (~2900m). We spent a night at 7,000ft (~2100m) and then on the next day climbed the peak and went back to 500ft. Thus, we spent around 5-6 hours at above 9,000ft elevation.

I never felt any discomfort or any worrisome symptoms and I was 18 at the time.

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    This is a bit like asking "Can you break your arm from running? I went running once when I was 18 and I didn't notice anything wrong but now I wonder if my arm is ok." The answer is, well, yes, you could have broken your arm, but you would have noticed falling over, feeling a lot of pain at the time, and almost certainly would have received medical treatment. – foobarbecue Oct 29 '17 at 5:22
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    When skiing I would spend most of the time between 2500 and 3300m. The first days you get out of breath fast, but you get used to it. – user276648 Oct 29 '17 at 6:13
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    Probably not. You might be suffering from acute hypochondria, though. – Eric Duminil Oct 29 '17 at 12:23
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    @TodorPetrov Sorry, I was being flippant. I think you get my drift -- I'm saying that brain damage from being at altitude happens through HACE, and you would know if you experienced HACE. Charlie Brumbaugh's Everest citation below surprises me, but that's three times the altitude you're talking about. I've climbed lots of mountains, up to 19,900ft, and despite experiencing some severe AMS, I /think/ my brain is still working ok! – foobarbecue Oct 29 '17 at 21:56
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    Millions of people smoke, drink and appear healthy. It took us very long time to realize not only the extent of damage it does to human body, but the mere fact that there is any. – Agent_L Oct 30 '17 at 12:32
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TLDR: Yes, it can happen at that altitude, but the odds are extremely low.

Long answer

High-altitude cerebral edema has happened at lower than 10,000 ft.

The condition is seldom seen below 3,000 metres (9,800 ft),2 but in some rare cases it has developed as low as 2,500 metres (8,200 ft).

Source

To give an idea of how rare those rare cases are, consider

HACE occurs in 0.5% to 1% of people who climb or trek between 4,000 metres (13,000 ft) and 5,000 metres (16,000 ft).

Source

It's worth noting that while HACE is rare it also an extremely serious situation that will end fatally without treatment.

Although AMS is not life-threatening, HACE is usually fatal within 24 hours if untreated. Without treatment, the patient will enter a coma and then die. In some cases, patients have died within a few hours, and a few have survived for two days. Descriptions of fatal cases often involve climbers who continue ascending while suffering from the condition's symptoms.

Source

The damage caused by HACE is long lasting,

"It was previously thought that HACE did not leave any traces in the brains of survivors," said Dr. Michael Knauth, PhD, director of the University Medical Center Department of Neuroradiology in Göttingen. "Our studies show that this is not the case. For several years after, microhemorrhages or microbleeds are visible in the brains of HACE survivors."

...

Survivors of the most clinically severe cases of HACE had the most prominent evidence of microhemorrhages on MRI, according to the research group. The bleeds were found predominantly in the corpus callosum, which consists of densely packed nerve fibers connecting the two brain hemispheres, and they showed a characteristic distribution different from other vascular diseases such as vasculitis.

Source

For much higher peaks, their is a real risk of permanent brain damage and that is without showing signs of altitude sickness.

METHODS:

We recruited 35 climbers consecutively (12 were professional and 23 were amateur) in 4 expeditions without supplementary oxygen: 12 professionals and one amateur went up to Mt. Everest (8848 m), 8 amateurs to Mt. Aconcagua (6959 m), 7 amateurs to Mont Blanc (4810 m), and 7 amateurs to Mt. Kilimanjaro (5895 m). The mean age was 33.8 years (range: 22-46). All of them underwent general medical examination, standard blood tests, and MRI of the brain after the expeditions. MRI also was carried out in a control group of 20 healthy subjects. Single-voxel MR spectroscopy was carried out in 14 amateur subjects after the expeditions and in 10 healthy controls. As outcome measures, we evaluated changes in the hematocrit value, presence of cerebral lesions on MRI, as well as atrophy and dilatation of Virchow-Robin spaces, and differences in the metabolite ratios obtained from brain MRS in comparison with controls.

Only 1 in 13 of the Everest climbers had a normal MRI; the amateur showed frontal subcortical lesions, and the remainder had cortical atrophy and enlargement of Virchow-Robin spaces but no lesions. Among the remaining amateurs, 13 showed symptoms of high-altitude illness, 5 had subcortical irreversible lesions, and 10 had innumerable widened Virchow-Robin spaces. Conversely, we did not see any lesion in the control group. We found no significant differences in the metabolite ratios between climbers and controls.

https://www.ncbi.nlm.nih.gov/pubmed/16443427

  • Thank you for your answer. Is there a way to suffer permanent brain damage without HACE or any noticeable symptoms at that altitude (<10,000ft)? – Todor Petrov Oct 28 '17 at 17:54
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    if it's fatal without treatment, is it safe to assume that since the OP is still alive, there was no damage caused by the one day exposure? – Kate Gregory Oct 28 '17 at 18:31
  • @KateGregory The part about HACE is just to show that the title question is within the realm of possibility. There is no indication that I can see that the OP had any altitude sickness. – Reinstate Monica Oct 28 '17 at 18:56
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    @Qudit Yes, see updated answer – Reinstate Monica Oct 28 '17 at 22:25
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    Note that the studies that exist can't tell you if you will suffer X, but can give only a statistical likelihood. If neither you, nor your parents, nor your friends, nor your teachers noticed any cognitive decline in the days, weeks and months after your trip, the answer most likely is that your brain is firing away as briskly as it ever did. Statistics again (and informal to boot), but the group I was with at Lawrence Berkeley Lab never mentioned cognitive decline as a problem with our frequent hiking trips in the Sierra. And we would have noticed. – ab2 ReinstateMonicaNow Oct 29 '17 at 5:44
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No, you certainly have not suffered any damage. But there are several aspects:

  • Regarding HACE and HAPE: It's extremely rare below 3000 meters, but there is no way to predict which person will suffer from it. The only way to prevent it is staying well-hydrated, and to ascend not too fast (i.e. lengthen the ascent by making some overnight stays). If it occurs, descend as fast as possible.
  • Oxygen supply: The untrained, not acclimatized person will get enough oxygen for consciousness at 6000-7000 meters, but you will not be able to do any meaningful work. You'll feel quite drowsy. A person who lives near sea level (e.g. below 500 meters) has only half the muscular strength at 3500 meters. It's an effect every mountaineer knows.

As a comparison: Passenger aircraft are pressurized to the same pressure that occurs at around 2000 to 2400 meters - this is to relieve stress on the airframe. So you get from near sea level to 2400 meters in a very short time, and you will notice a certain drop in alertness and muscular power.

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    I've been on a flight from La Paz, 13,325ft, 4,061m, to Lima. The passengers were not on oxygen, but oxygen is required for the pilots during pre-flight checks and takeoff. Even at that altitude there is enough loss of skill and concentration to increase the risk of pilot error. Finding ones seat, sitting down, and fastening the seat belt is a less demanding task. – Patricia Shanahan Oct 30 '17 at 13:44
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If there were any serious likelyhood of brain damage due to exposure to 10,000 feet or more altitude for just a day, then the city of Cusco would be full of brain-damaged zombies.

There are nearly half a million people living in Cusco, for long periods, even their whole lives, at over 10,000 feet. The city has been continuously inhabited for 100s of years, perhaps nearly 1000 years. If there were significant brain damage from this, I expect it would be well known by now.

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    Ever heard of survivor bias? – Eric Duminil Oct 29 '17 at 16:41
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    Most of us (including me) are talking outside of our biological and medical expertise here, but three points against this being too casual an answer to the question: (1) People whose ancestors have been living at altitude for centuries probably have some genetic adaptations to altitude. I remember an article from Science magazine on this point for Tibetan people; (2) The article I mentioned above in N Eng Jour Med takes the possibility of "impaired neurological function" for permanent residents at high altitude very seriously; continued – ab2 ReinstateMonicaNow Oct 29 '17 at 19:13
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    continued (3) brain damage doesn't necessiarily mean the affected people are zombies. The damage could be subtle and possibly not even noticed until later in life, and even then as a small statistical difference between otherwise similar groups. – ab2 ReinstateMonicaNow Oct 29 '17 at 19:17
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    The German language wikipedia page on altitude sickness says that atlitude sickness is a permanent problem for many inhabitants of high-altitude cities in the Andes (as opposed to Tibetans). Also "perinatal and neonatal mortality is presently still high at elevated altitudes, even after taking into account socio-economic status." (Gonzales Respir Physiol Neurobiol. 2007,158(2-3):172-9.PubmedID 17482897) that's a very literal survivorship bias. But statistical survivorship bias can also happen if people who are sensitive to altitude do not move to high altitude and/or move to lower altitude... – cbeleites supports Monica Oct 30 '17 at 20:32
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    ... and thereby avoid permanent damage. So your observation may only be saying that those who do fine, do fine. In other words, 3000m is not general death zone for humans - but that we knew already. (I am aware that altitude sickness is not a good surrogate for altitude-caused permanent brain damage - I just want to point out that survivorship bias is not something to be waved away in your "proposed study design"). – cbeleites supports Monica Oct 30 '17 at 20:43

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