Message-ID: <003001c1b24a$bbc294a0$6401a8c0@cfl.rr.com>
From: "Ted Noel" <tednoel@cfl.rr.com>
To: <lancair.list@olsusa.com>
Subject: Oxygen
Date: Sun, 10 Feb 2002 10:50:58 -0500
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Fred Moreno points out another cause of hypoxia which I did not cover in my
last post. Please allow me to explain it a bit more technically than he did.

The problem Fred mentioned is lack of hypoxic drive. To explain, your body
has two chemoreceptor (chemical control) mechanisms for breathing. The
stronger one is the hypercarbic drive. To demonstrate this, simply hold your
breath. Your blood level of carbon dioxide will rise, and hypercarbia (high
CO2) will make your blood a bit acid compared to normal. This will stimulate
you to breathe to eliminate CO2 and bring your blood acidity down.

The second chemoreceptor is for oxygen. And in about 10% of the population,
it doesn't work very well. For non-pilots, this results in Altitude-Mountain
Sickness (AMS). Skiers run into this. When my wife and I went skiing at
Copper Mountain Colorado, (base elevation 9,700 MSL) she got AMS. She
doesn't get the normal drive to increase breathing when her oxygen level
gets low. So when we ski, Nancy takes a drug called Diamox (Acetazolamide)
for 5 days. This drug makes her blood a bit acid, and tricks the CO2
chemoreceptor into making her breathe faster. Now she doesn't get AMS. Of
course, carbonated beverages taste awful...

Many pilots may be subject to AMS when at high cabin pressure altitudes.
They may get hypoxic, sleepy, disoriented, and so on. The cure is oxygen and
lower altitude. This cause of hypoxia CAN be overcome with oxygen, unlike
shunting. It just takes a bit more, since the CO2 level in the lungs is
higher, taking up more of the space for oxygen.

The precaution? An oximeter is again an excellent idea. Diamox is a lousy
idea, since you must start the day before, and if you fly frequently you run
into a host of drug issues that are beyond this posting.
Ted Noel MD

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