Have you ever dreamed of climbing one of the world’s highest peaks? I have. I used to shy from the notion and rationalize my shyness by branding peak-seekers as too goal oriented to appreciate the wilderness. And yet, two weeks ago I slept at 15,500 feet and listened to the sound of my climbing partner periodically stop breathing and vomit the many liters of water we had carried up on our backs.

Mountains have long occupied a place in our universal human mythology; they are where prophets go to speak to God, where spirits dwell, and where peasants go to become heroes. High altitudes and the lack of oxygen to the body caused by it, also take on a sort of aura of mystery in neuroscience and psychology. You may have heard about the horrors of deadly lung and brain hemorrhage, and edema that are never far from any story of success at the top of the world. These conditions (known as HAPE and HACE) are very real risks, and they represent conditions for which medicine still lacks a grasp on what is actually happening in the body. Some people go up and down unharmed, others perish. We don’t yet have a clear grasp on what differentiates those that make it and those that don’t.

Thus, climbing high mountains remains an almost existential pitting of oneself against whatever forces may or may not let you live.

As a brief introduction to high altitude: as you go up from sea level the barometric pressure gets gradually lower (basically all the molecules get further apart up there). Our lungs only have a set volume of air we can inhale in a breath, and at some point, because the oxygen molecules are so spread out, we can’t get as much oxygen in a single breath as we need. This is called hypoxia. It is actually a common misconception that there is simply “less oxygen” up there, whereas there is really the same amount, it’s just much more spread out.

Hypoxia causes all sorts of strange and unpleasant side effects, from head ache to more serious sickness which was what caused my partner to barf all over the rocks outside the shelter. Now the good news is that you can acclimatize to high altitudes. At some point you’ll get so high your body can’t catch up, but if you take it slow and give your body time you can get very high without serious issues. Unfortunately, the highest and most desirable peaks tend to be in that “can’t catch up” zone – the death zone.

So mountaineers everywhere experience all sorts of side effects of hypoxia and come home to report them. Anecdotal reports include things like strange “‘weird’ dreams” (Queiroz & Rapoport, 2007, p. 293). Sleep is a real chore at altitude – often times it just doesn’t come at all, and if it does it is plagued by episodes of wakefulness and vivid and strange dreams. Mountaineers will even experience periodic breathing. I laid there at 15,000 feet listening to the most eerie silence I could imagine, waiting for my partner to inevitably start breathing again. To listen to what periodic breathing can sound like listen HERE (Warning: content is somewhat disturbing). Periodic breathing is scary until you get used to hearing it, but it actually doesn’t mean anyone is dying. It’s a sign your body is trying to adapt to the altitude.

The breathing might be part of the reason that sleep is so fleeting at altitude, but I think there must be something more to it. Sleep comes in different stages, and they aren’t all equal. The ever-popular REM sleep, or Rapid Eye Movement sleep, is the most shallow stage of sleep and it is also the one during which dreaming occurs. Previous studies have shown that the deepest levels of sleep were less prevalent in people at altitude, but that REM was the same or greater. This might help explain why the sleep quality feels so poor; because we aren’t getting through a whole sleep cycle in the night. It might also help explain all the odd dream reports, because it might mean that individuals are waking up during REM sleep more often and thus recalling vivid dreams more.

Unfortunately, the theory can’t fit that well. A 2012 study by Aquino Lemos et al. indicated that REM sleep was also reduced along with the deeper levels at high altitude. In this complex puzzle, altitude neurology is not the only mysterious variable. There is still so much we don’t know about sleep itself. We aren’t even sure that it matters if mountaineers miss out on one stage of sleep or another, so it’s difficult to tease any cohesive meaning out of the research at this point. For now, the truth of sleep and the physical tests that big mountains send our way will remain somewhat elusive to us. But that doesn’t mean you shouldn’t consider some high dreams of your own. I must say, despite the misery of my summit attempt, something in me knows I will be back… if only to see if the mountain will have me.

References:
Aquino Lemos, V., Karen, H., Atunes, M., Vagner, R., dos Santos, T., Santos Lira, F.,  Tufik, S., & de Mello, M. (2012). High altitude exposure impairs sleep patterns, mood, and cognitive functions. Psychophysiology, 49, 1298–1306. doi: 10.1111/j.1469-8986.2012.01411.x