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<< Lancair Builders' Mail List >>
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After reading the various pieces about oxygen use at altitude I felt
compelled to pass along some information I have gathered over the years.
There have been several articles published in the Internet aviation
networks on oxygen that discussed in depth the effects of oxygen and its
use for aviators. I found their descriptions to accurately reflect my
testing. Briefly, and working from memory, here are the highlights.
The breathing mechanism is triggered first by rising carbon dioxide
levels in the blood, and then by low oxygen levels as the "emergency
backup." (Not necessarily true in heavy smokers, as I recall.) At
altitude, your body loses carbon dioxide comparatively quickly, and the
breathing response is delayed until the oxygen level falls. Then you
start breathing again. The body will adjust after a while, but not in a
few hours typical of a flight. The net result, confirmed by oximeter
use (including my own experience) is that you measure your blood oxygen
level, and it goes up and down over a period of minutes while flying as
you go into and out of periods of very mild oxygen deprivation. I found
my blood oxygen saturation level to be as low as 87% (97% is normal) as
low as 8000 feet in the initial portion of the flight. A drop of 10% is
enough to trigger effects of mild oxygen deprivation.
What this means is that for the user to get the full effect of oxygen at
altitude, you have to breathe! If you consciously breath at a normal
rate while using oxygen, you will find the blood oxygen level quickly
restores to normal. If you fail to pay attention, your body will stop
the automatic breathing process because of the rapid rate of carbon
dioxide loss at altitude until oxygen levels fall. So conscious
breathing exercises are called for to obtain the full benefits of
oxygen. Avoiding these periods of low oxygen level also eliminates the
headaches that you can sometimes experience even when using oxygen.
I spoke to John Forker who flew his Lancair IV to California from New
Zealand. John had an oximeter aboard and did a lot of testing to
relieve the boredom of long over water flight. He found that by more
rapid, "manually controlled" breathing at a more rapid rate, he could
hold his blood oxygen levels in the 90's even at higher altitudes (in
the teens, as I recall) without oxygen. But it required continuous
effort and monitoring of the oximeter. The tendency is to relax, and
then to stop breathing, and then hypoxia sets in.
So the message is:
1) Using oxygen does not guarantee fully saturated blood oxygen levels
all the time.
2) To get the full effects of oxygen, you should consciously watch your
breathing patterns, and breath a bit more often than your internal body
signals suggest. Don't over do it. Just be aware that your body can be
fooled, and you can stop breathing for many tens of seconds while your
body waits for the carbon dioxide levels to build up. In the mean time
your oxygen levels are falling.
If a medical specialist can shed additional light or correct any errors
in my reporting, please speak up.
Fred Moreno
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