A field guide to DIY altitude science
I don’t think you need to be a geek or a scientist to enjoy collecting data during your vacation. Our ability to adapt to foreign environments such as high altitude is a testament to the wonder of the human body. Quantifying it will help you see and appreciate your body more. Plus, monitoring your blood oxygen level (SpO2) during high altitude trekking can literally save your life!
My data from Everest Base Camp Trekking can be found here.
Contribute Your Data!
If you would like to contribute your data to my Science with a Little Altitude project, please fill out this questionnaire:
Once you share your data with me, I can share my analysis of your data. With enough data, we can compare you against others and hopefully discover new science to share with the larger scientific and quantified self communities.
What to track?
If you are traveling to a “very high altitude” location, anything higher than 11,500 ft or 3,500 meters e.g. Mt Whitney, Nepal, Machu Picchu, Jungfrau, or Kilimanjaro, there are a few experiments you can try…
How your SpO2 drops as the altitude rises may be determined by your genetics and may predict if you will get altitude sickness. I found that most informative times to measure SpO2 are:
On arrival at your resting point (e.g. campground, lodge)
Morning, within the first 1 hr of waking up
This data will allow you to see how your SpO2 drops as the elevation increases and if you stay at one elevation for a few days, you can also see the effect of acclimatization. You will also want to make note of if or when you experience symptoms of altitude sickness.
Figure 1A: SpO2 (gray line) decreased as the elevation (blue line) increased. Symptoms of altitude sickness such as headache, blurry vision, and sleeplessness were experienced when SpO2 dropped below 80, between Day 5 and Day 8.
Figure 1B: SpO2 measured in Namche Bazaar (11,286 ft) on three different days show improved SpO2 over time. Acclimatization is real and measurable.
Exertion vs rest SpO2
It’s been known that at altitude your blood oxygen level drops noticeably during physical exertion [Pandolf and Burr 2002]. This includes walking, which is what you will be doing most of the time during your trekking trip. The SpO2 during exercise may be a better predictor of your risk of altitude sickness [Karinen et al, 2010]. I did a small experiment comparing my SpO2 during exercise and after 1-2 minutes of rest and found that my SpO2 during the walk is ~10 points lower than resting (76 walking vs 88 resting), and a short (1-2 mins) rest helps recover SpO2 to the “safe zone” (>80).
Figure 2: Effect of short rest on SpO2 and heart rate.
If you are going to a moderately high altitude location (4,900-11,500 ft or 1,500–3,500 meters), such as Aspen or Lake Tahoe, it is less likely that you will experience altitude sickness at this altitude, but you may observe changes in your physiology especially during an exercise. You might consider doing some strenuous exercise such as a sprint and measure your SpO2. You might be surprised by how low it can get.
You will need …
Pulse oximeter. There are several brands. The one I used is iHealth Air Pulse Oximeter available on Amazon.
Fitness tracker. E.g. Fitbit, Apple Watch, Withings. There are several acceptable, each with its own features and quirks. I use Fitbit Charge HR, mostly for the balance between price and features. Make sure it has continuous heart rate monitor and accelerometer (for steps and elevation gain estimate).
Heating bag or patch for warming your hand. You might also find it useful in your sleeping bag when it’s below freezing outside.
Skin temperature sensor or thermometer. I didn’t try this, but research suggests that skin temperature indicates blood flow rate and hydration level.
What is ‘normal’ SpO2 at different altitude?
94-99% at sea-level is considered normal.
<85% you may experience symptoms of altitude sickness
Make sure to use Oximeter correctly
Finger/hand temperature. Blood flow reduces at lower temperature. Warm your hand before you use Oximeter.
Ambient light. Because Oximeter works on light sensor, bright ambient light will affect the reading. Find shade or cover your finger inside the jacket.
Positioning your fingers. Make sure to use the same finger and position throughout the experiment. I find that my middle fingers consistently give higher SpO2 reading than my index fingers.
Be systematic. SpO2 measurement fluctuate more at high altitude. It is important to take a few (3-5) replicates per measurement. Also, because the SpO2 reading may not “converge” to a stable number, to get an unbiased reading, leave the Oximeter on your finger for the same amount of time every measurement (I used 10 seconds).