Category Archives: Altitude

Predicting altitude sickness?


Source: National Park Service

At the time this paper was written (1995), we did not have a good way to predict which people would likely develop acute mountain sickness. We still don’t have a good way, but that isn’t keeping investigators from trying to find one thankfully. The extremes of HACE and HAPE can cause expeditions to fail and have cost overruns, so any method that allows us easily predict those most likely to need help is well received.

What they did was follow 2 separate groups from New Zealand during a trip to Nepal. Maximum altitude of the trip was 5640 m. Prior to ascending, they took baseline measurements of breath holding, hyperventilation, and gag reflex. Gag reflex was measured as0 being no gag, 3 being gagged just looking at the wooden spatula they were using for the test. Let’s hope they had a way to clean the spatula between the 40 different test subjects, but this being 1992-3 climbing seasons I’m doubting it. Hyperventilation was quantified by the test subject on how dizzy they got with rapid breathing, in a 1-4 scale.

Twice daily during the trip they measured breath holding and had them take a general high altitude questionnaire (a variant not shown in the methods).  AMS was diagnosed if they scored above 15 on the test. One climber required evacuation to Kathmandu after scoring 69, but was still included in the data.

All of the climbers who scored 2 or 3 on the gag test, and all that scored 3 on the hyperventilation/dizziness test developed AMS. The authors take this to mean that ability to not develop AMS has something to do with ability to tolerate hypocapnea as well as some degree of pharyngeal nerve input. They were still unable to get above 85% prediction rate by combining variables, but for tests that are free and only mildly invasive, it’s worth a shot.


The brain wants oxygen

It goes without saying that the body is designed to work aerobically.  The mind therefore, follows the same pattern.  This essay by Rodway shows historical data and research about the changes in cognition as one goes further up into thin air.  This is important, because they conjecture that many of the problems climbers face are so serious that they have life or death implications, and thus the brain cannot process them as it should, leading to fatal errors.

“Mountaineers have often observed a lack of clarity in their mental state at high altitudes; it is difficult for the stupid mind to observe how stupid it is.”               George Leigh Mallory 1922

He further explains how this is likely a combination of sleeplessness due to periodic breathing as well as hypoxia due to the altitude.  Interestingly, one of the references (Richalet) showed that psychomotor performance and mental efficiency declined progressively with altitudes above 5500m, but differences did not reach statistical significance until 8000m.  Another reference (Waters) in the same paper describes the neuropsychological effects of sleep loss. They include: sleep loss effects both cognitive functions as well brain regions that support cognitive performance; decreased processing speed is most reliable finding after sleep loss; and peformance decreases appear in a dose dependent manner with sleep debt accumulation.

Thus, be aware (and self aware as best as possible) to the problems associated with cognitive function with high altitude climbing. You wouldn’t let a drunk drive you home, don’t let one hold the rope that keeps you alive.

“Decision making at extreme altitude: Has anyone seen my executive function lately?”