On 5/23/04 9:52 PM, in article
, "Arnie"
wrote:

[SNIPPAGE]

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.


Arnie,

1) Rates of ascent above, say, 100 fpm is way too fast to equilibrate. Thus
you are building a supersaturation (increased body burden of nitrogen). By
comparison, climbing is much slower, and you're exercising the whole time
(thus moving blood around and clearing tissue compartments more efficiently
than sedentary pilots). The recent record setting climb of Everest from base
camp to summit in 8 hours, works out to about 24 fpm.
Rate of ascent is not particularly predictive or protective, above a certain
threshold. Exercising and prebreathing are better than adjusting rates of
ascent.

2) Trapped gas problems, like bowel gas, or gas in the middle ears, or gas
under a new dental filling, are not DCS. They are certainly aeromedical
issues of which pilots and others should be aware, but not DCS. In military
altitude chambers, trainees are told not to try to hold their gas out of
politeness, rather to let 'er rip.


nafod40 (Mike) also asked:
Does breathing 100% O2 from chocks to chocks help lower the N2 in the
body? In other words, is there a secondary benefit to breathing 100% O2
other than that you don't pass out?

Answer: In the studies I did, my test subjects pre-breathed 100% oxygen at
ground level for a full hour before going to altitude. They kept breathing
100% oxygen the whole time they were there (at 25, 30 or 40 thousand feet)
and they STILL got DCS.

Even my inside observers, who prebreathed for two full hours before ascent,
occasionally got DCS. They got it at a lower rate, though. My most severe
cases of DCS came from this group, though (a case of chokes: resolved
quickly in a hyperbaric chamber).

Short answer: prebreathing is good, but not perfect.

Thanks again.