Sleeping at high altitudes
What may feel miserable subjectively is objectively of sufficient quality
The glorious summit was happily conquered – but after what a night: horrible. “I couldn’t sleep at all and wouldn’t wish such a night on my worst enemy,” explained Michel-Gabriel Paccard in 1786, after having returned from his first ascent of Mont Blanc together with Jaques Balmat and for which the two had set up camp at 2300 meters above sea level. What is considered the birth of modern alpinism was also the beginning of a complaint that has united extreme mountaineers and recreational alpinists ever since: the complaint about miserable sleep.
“Paccard’s subjective impression has long shaped the scientific view,” explains sleep and altitude medicine specialist Nikolaus Netzer, who has been studying sleep at altitude for 30 years. “It was simply always assumed that you sleep very poorly at altitude. Intuitively, it’s also often the case. But, this reveals little about the objective quality of sleep.”
How well we sleep objectively remains a mystery to us.
The focus was on sleep, but not only sleep: a common assumption in high-altitude medicine was that poor sleep quality contributed to altitude sickness. However, the sleep quality of the expedition team on Aconcagua – three men and one woman – was “surprisingly good,” Netzer recalls. Good sleep means sufficient sleep duration and sufficient proportions of deep (delta) and dream (REM) sleep, he explains: “Both are necessary for physical and mental regeneration. Delta sleep serves to restore cells and organs and strengthen the immune system while REM sleep is necessary for mental performance.”
Subsequent studies, conducted at real and simulated altitudes, showed different results depending on variables such as acclimatization or exertion during the ascent, but generally came to the same conclusion: “Sleep quality at altitude is not nearly as bad as assumed, and is often even good.”
However, it is not surprising that it is usually perceived differently in a mountain hut or base camp: cold, high humidity, howling wind, tent mates, the worry of not making it to the summit the next day... many factors can contribute to the feeling of having had a lousy night
Breathing interruptions of ten to twelve seconds
“If sleep were as poor as people perceive, humans would not be able to climb to these heights.”
Nikolaus Netzer
In the 1980s, when modern polysomnographs were already available, experiments in US Air Force low-pressure chambers showed that the breathing pauses (apneas) during periodic high-altitude breathing provoke countless small, unconscious arousals – “and this seemed to prove once and for all that you can’t sleep well at altitude,” says Netzer. “But apparently, the human body can cope with these arousals.” This is not so surprising in view of our evolution: “Anyone who sleeps in a tree with tigers prowling below must always be in a kind of alert state. And you can train yourself to do this – if you do it often, you can cope with it better. You see this in extreme athletes, who are able to perform well even after very little sleep.”
Alpinists often describe high-altitude nights as miserable – “Sleeping was a big word for it,” wrote Steve House – but their performance proves otherwise. “If sleep were really as bad as it feels,” says Netzer, “alpinists couldn’t reach those heights at all.”
Once it had been clarified that periodic breathing does not completely ruin sleep, the interesting question remained: Would people sleep better without periodic breathing? This was investigated as part of a joint study between Eurac Research and the Medical University of Innsbruck in the terraXcube climate simulator. Sixteen test subjects spent two nights at a simulated altitude of 4000 meters: on one night, periodic breathing was allowed, and on the other, breathing was stimulated without the participants’ knowledge so that it proceeded normally. “However, this had no significant effect on sleep structure,” says Netzer, who was involved in the study. “The measurements in the terraXcube are limited, however, by the fact that the air flow generated by the vacuum pumps causes a certain amount of noise pollution.” But then, perhaps, the wind around the hut, here too.
The extent to which subjective sleep quality suffers from climatic conditions and other disruptive factors depends heavily on the individual and is difficult to determine, says Netzer. What can be assumed is that the expectation of sleeping poorly does not contribute to a restful night’s sleep. Knowing that the quality of sleep is not so bad should therefore have the opposite effect, says Netzer. Mountaineers, relax.
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