"Bullwinkle" wrote in message
...
On 5/23/04 4:52 PM, in article , "Wayne
Paul" wrote:

Ah yes, you do have to be at 62K for water to boil; however, the
nitrogen in
your blood turns to gas at much lower altitude. (For most people it is
below 50K.) This phenomenon is what is commonly referred to as "your
blood
boiling."

Experiencing the "bends" is not pleasant!

Wayne
http://www.soaridaho.com/

Sorry, I normally lurk, but I can't let this one go. A newsgroup is a good
place to trade expertise. This happens to be an area in which I have
expertise, so please let me share it.

Ebullism is the phenomenon which occurs at or above Armstrong's Line,
classically 63,000 feet, in which the total barometric pressure falls
below
the partial pressure of water in the body, thus the equilibrium shifts,
and
the body begins to give up water to the environment. "Blood boiling" is
the
somewhat sensationalized term for this. People visualize exploding bodies,
and it doesn't actually happen that way. It is a very bad thing, and would
likely be fatal, although a short exposure (a few seconds) is likely
survivable.

Decompression sickness, or DCS, ("the bends") does occur in aviation, as
well as (obviously) the diving world. Classic physiology theory recognizes
a
threshold of 18,000 feet below which it should not be able to occur. It
happens when the blood and tissues of the body become supersaturated with
nitrogen. At ground level our tissues equilibrate with the atmosphere, and
as we ascend, we give up nitrogen to the atmosphere until our tissue
partial
pressures equal the partial pressure of nitrogen in the atmosphere. Thus,
climbers, ascending slowly, never experience DCS, because they stay more
or
less equilibrated to their current altitude.

Aviators, on the other hand, go quickly to altitude. Way too quickly to
reduce the amount of nitrogen in their tissues. Thus, they are
supersaturated with nitrogen and their respiratory systems are trying like
crazy to get rid of the excess. Sometimes it forms bubbles in the
bloodstream, which are cleared out by the lungs. Sometimes bubbles form in
joints causing the joint pain which originally gave DCS its nickname, the
bends. Sometimes bubbles form in the brain or nervous system, causing Type
2, neurological DCS. This can present as stroke-like symptoms.

I've treated many, many people with DCS, most from altitude chamber
training
in the military. I've also done research in which I gave volunteers
(really)
DCS, in order to track the onset and severity of VGE (the bubbles), and
the
onset and severity of DCS symptoms at various altitudes. (Then, of course,
I
brought them back to ground level and treated their DCS appropriately.)
I've
also had altitude DCS (just the joint pain type, fortunately).

You're right: it's not fun, and is a seriously under-recognized hazard in
soaring. Wave pilots should know about this, and I'm not sure they
appreciate the risk enough.

But please don't confuse ebullism with DCS. Completely different
processes,
with different physiology involved.

Thanks for reading
A concerned aerospace medicine specialist/aerospace physiologist


Very good posting Dr. Bullwinkle... Thanks for sharing this knowledge with
us.

If I can just persuade you to expand a little more on a couple of points :
1) It still isn't very clear how much of the DCS problem is related to "how
fast" we climb :.
I remember reading about the phenomenon and concluding (maybe not correctly)
that a slow climb isn't really likely to give us a problem.
So much so that I don't remember hearing much about Glider Pilots getting
"The bends" from wave soaring.
It would be a problem for the military pilots who may climb at many
thousands of feet per second.

2) out here in the American West, there are many general aviation pilots who
routinely perform long flights at +16000ft on oxygen (non-pressurized
singles and twins). I've heard their families and even some pilots complain
about certain types of pain that they thought was "the bends", but in many
cases it turns out to be just the gas we have accumulated in our intestines,
that expands to close to twice their volume at those altitudes. Best way to
avoid that kind of pain is, of course, a controlled diet avoiding
gas-generating food during those trips.