We are now posting some of the results that we found from our altitude investigation on Mount Kilimanjaro. For the purpose of explaining these results to the lay-person, a colleague of mine has given his own interpretation of the results (why the graphs below look the way they do) and his own experience at altitude intermixed with my writing below.
Phil: Some of the early results of our altitude experiment are illustrated in the following plots. Essentially, the data speak to the idea that what I would call "intense" pressure breathing and rest stepping contributes to larger SPO2 levels than moderate to no pressure breathing. Note that this assumes that all persons from whom data were collected are somewhat similar in physiology related to oxygen transport from the atmosphere into the blood. The data collected are from males between the ages of 35 and 57 years of age. (No significant correlation of hiking SPO2 with age was found (corr=-0.72 n=4; -0.95 would be required for n=4 at p=0.05). Measurements were taken so as to not distract (too much) from their hiking experience although each time a measurement was taken, that hiker was informed of their SPO2 level and heart rate and encouraged to keep their SPO2 numbers high. You will note in Figure 1 that a different number of measures were taken each day. The values in Figure 2 were calculated using a daily average (for each of days 2, 3, and 4) so as not to weight one day more than another in the statistics derived. Hiking SPO2 data were not recorded for day 1 or our final ascent on the summit (day 5).
While being "in an experiment" mode I really did consciously change my breathing to bring my SPO2 levels up. Two reasons - I'm a bit competitive in a team environment AND I wanted to avoid the experience of suffering AMS again. In the end I really believe that my rest-stepping and increased breathing helped get me comfortably to the summit. Those techniques helped me feel more in control of the outcome rather than wondering if I was going to one of those who arbitrarly gets dragged off the mountain.
The first graph (fig 1) moves up and down depending on the steepness of the trail (if I remember correctly) and, for me, what was going on in my head at the time. Distractions meant lower breathing rate, which is my natural tendancy. The lines heading down to lower SPO2 levels with higher altitude make sense. Our scientist's encouragement to stay above 80 finally sunk in on summit day for me. Before then I felt strong and capable on my own. On summit day I knew that any tool which increased the odds of making it to the top without getting AMS was worth adopting.
BTW I finally figured out what "pressure breathing" was (for me) on the way DOWN from the summit. Before then I was just breathing as deep as I could. I'm not yet sure how to describe it in words. I do know it sounds like what I imagine a steam engine sounds like. More to come on that later.
Phil: SPO2 stands for "Saturation (peripheral) of haemoglobin with oxygen" which is a percentage ratio compared to fully saturated haemoglobin. Basically, it is how filled your red bloods cells are with oxygen. At our home altitude (sea-level) we measure approximately 98%. Of course, these meters often have a error of 2%. At any rate, we're close to complete saturation at our home altitude.
On our final ascent towards the summit of Kilimanjaro I distinctly recall 2 things: some people being helped down the mountain by their guides, and every once and a while reminding the team about their oxygen levels. On our training hike to the summit of White Mountain Peak, I recalled that SPO2 levels below 60% were definitely bad news (at least for us tourists at altitude). Again, on that particular ascent I wanted to look after myself so I worked to maintain an SPO2 above 86%. That said, I picked that number because I seemed to be OK there. I don't know if it is a good guideline; we will get more data on this topic. What I have noticed for us is that levels in the 80% seem to relate to some mild cognitive changes (we joke around a little more, things are funnier, my sense of time is way off), in the 70s there is some distinct drunkenness (altitude drunk), loss of balance, and loss of body awareness, and in the 60s loss of color in the skin and look a bit ill. After we got back to Victoria from White Mountain Peak, I found this information about SPO2 levels on the internet (http://www.anesthesiaweb.org/hypoxia.php; I have not verified the information at this link). The information on this site seems a bit arbitrary because they have put the boundaries of the altitude effects on body function in steps of 10%. Still, it supports the idea that we want to keep our oxygen levels high.
I noticed that if I got into a conversation with someone while hiking, my oxygen levels would drop quite quickly. I talked to one of our guides for a while in French and it seemed really easy (I speak terrible French at sea-level; presumably it was equally terrible at altitude). It is easy and even fun to get 'distracted' from breathing. On one of the days I borrowed a porter's radio, gave him my camera to make video recordings, and then rocked-out to Shaggy for a good 10 minutes (or something like that; remember that I seem to have poor sense of time at altitude). While I was up to these antics, I was not pressure breathing (or taking measurements). That said, I did this for a relatively short amount of time.
The descent at the end of the day as the sun was falling was 'interesting'. I remember measuring some "too low" oxygen levels and noticing the temperature fall. I was genuinely concerned about getting back. And we did- we did get back to our camp and crashed-out in our chairs for dinner. The guides and our support team did a fantastic job getting us down safely and supporting our recovery.