The body at altitude
Sleeping at this elevation is an interesting experience: The lack of oxygen up here means your lungs have to work a lot harder (i.e. take a lot more breaths) to get the required O2 in. This has the side effect of blowing out a greater amount of carbon dioxide. As it turns out, CO2 concentration helps dictate your breathing rate. So the lack of CO2 because of excessive breathing causes you to subsequently slow your breathing, or even breath-hold, until the point where you become hypoxic. At this point your O2 chemoreceptors finally kick in as a kind of override and cause you to hyperventilate to resupply your body with O2. This blows off more CO2, and so this crazy oscillation repeats. Trevor made the analogy that it’s like that shower mixer at the motel that you can never quite get to be the right temperature – it’s always overshooting and making things too hot or too cold.
It means that your sleep is quite interrupted, as you are constantly waking up not being able to breath. Soon enough the hyperventilating starts but it is a bit disconcerting and makes for a pretty poor night’s sleep. By the time we’d hit Gorek Shep this was in full effect. Fun times.
Now for acute mountain sickness: this is the strangest thing. It presents as a number of symptoms: headache, dizziness, lethargy, lack of appetite, gastro problems. If not kept in check (usually by descending) it can evolve into cerebral or pulmonary oedema which is life-threatening. Nobody really knows how or why it manifests like it does – it does so in some people but not others – although it is thought exertion, hydration, food intake, genetics and rate of ascent are all factors. The above sleep apneoa may be causal to AMS, but may also just be an artifact of the condition.
Every day we have been required to rank the above symptoms on a scale and add up these numbers to get a final tally. This score is an indicator of the severity of our AMS. Typically we have been seeing quite low numbers across the group because we have been ascending gradually and not over-exerting ourselves. However at Gorek Shep (over 5000 metres altitude) some people’s scores really ramped up. The worst was David and he got extremely sick. His blood oxygen saturation percentage also plummeted into the 60s (a healthy acclimatized individual has a saturation level in the high 90s). We got him on bottled oxygen and with some others who were feeling poorly, he started making the walk back down the hill. Remarkably he had recovered by lunchtime.
While his case was very acute (equally rapid onset and recovery), others had a gradual degradation of health. Trevor, I think, had a pretty rough time of it, with a crook guts adding to things, but in typical Trevor fashion, he remained constantly upbeat. He’s a legend.
The flip side to this is that most of us acclimatized rather well to being five kilometres up in the air, and when we began our descent, every 100 metre drop made us feel that much stronger. Combined with a general increase in fitness due to all the walking, I was feeling like superman as we trekked down to Lukla, something that took us only a few days.