A question about blood oxygen levels

[zippetydude]

Hey, I've been fiddling around with a heart monitor for some time, but I have no experience with a blood oxygen monitor (%spO2 is what it says on it).

Anybody out there with mountaineering experience (or more knowledge than me on exercise physiology) know how to interpret levels from this little critter? Maybe Ellen? bcox? Alan? Anyone?

z

[Ellen]

Howdy Z

I think you're referring to the percent of oxygen saturation of the blood. At sea level, the percent saturation is about 99%. As you gain altitude, the percent of oxygen saturation of the blood drops due to a lower ambient oxygen pressure. At 5,000 ft, the percent of oxygen saturation drops to about 95%. At 10,000 ft, it drops to about 88%. At 15,000 feet, it drops to about 80%. At 20,000 ft, it drops to about 70%. On top of Everest, it drops to 58%.

I'm extrapolating these readings from charts in McArdle, Katch, and Katch's Exercise Physiology text so there may be errors.

Anyone else have this data on hand?

Miles of smiles,
Ellen

[zippetydude]

Ellen! You are definitely my hero. Okay, more questions, if you can stand 'em.

I borrowed an oximeter on Saturday to see what would happen as I ran. I went up the SB Peak trail, starting at around 6000'. My oxygen saturation, which is normally 95-96 at 3500' in Yucaipa, was at 93-94. That fits so far.

Now, for the curious part. I started to run and my oxygen saturation slowly fell to around 83-84. I held it there for over an hour, but my pulse never rose above 145. Normally, if the training is intense, my pulse will break into the 150's, but this didn't feel particularly intense and my heart didn't think it was very intense . . . but 83-84 % sounds curiously low to me. On my run back down, the saturation never rose above 88%, even though it was downhill and felt easy as pie.

I was intrigued, so when I got home I ran 3 miles on a treadmill to see what would happen. This time, my oxygen saturation dropped only to 87-88.

If lack of oxygen is the limiting factor in this sort of situation, why don't I feel out of breath? It seems like the body would either increase the pulse or increase breathing, or both. Instead, nothing much happens, but I am unable to speed up. I don't really understand the body's feedback loop, I guess.

Could you give me a course in Oxygen Saturation for Dummies?

z

[AlanK]

Z -- the device you are using -- a pulse oximeter -- is something that has intrigued my but I have never gotten around to trying one. The device is based on the difference in infrared absorption betwen oxygenated and non-oxygenated blood. There is a nice description at
http://en.wikipedia.org/wiki/Pulse_oximeter.

I know that Richard Piotrowski, moderator of http://www.mt-whitney.info/, has some experience with them. There have been discussions on that board:
http://www.mt-whitney.info/viewtopic.ph ... t=oximeter
http://www.mt-whitney.info/viewtopic.ph ... t=oximeter

[Perry]

The desire to breathe more is strongly correlated with carbon dioxide build up, more than lack of oxygen. Acclimatization increases the natural breathing rate by expelling bicarbonate and altering ph. If you consciously breath more than what you feel like, then you'll see the saturation level go up, especially with deep breaths in the diaphragm. This is assuming you are unacclimatized.

Exercise heart rates are normally lower at altitude, especially at higher intensities. In my experience, however, stroke volume increases (based on how hard my heartbeats feel, not very scientific).