Air Damage
by Alex Vasauskas

Copyright 2003

all rights reserved

The human body responds differently in hyperbaric
environments, like scuba diving, than it does at normal
atmospheric pressure. Oxygen becomes toxic at increased
partial pressures. Nitrogen is also no longer benign. In
addition to narcosis, it apparently also causes problems
with microcirculation.

George Irvine, Project Director of the Woodville Karst Plain
Project (www.wkpp.org), asserts that high partial pressure
of nitrogen in breathing-air or gas causes red blood cells
to become rigid. According to him, this rigidity can block
microcirculation through capillaries, and the effect is
similar to sickle cell anemia. But, replacing nitrogen with
helium, as in trimix or heliox, seems to decrease this
effect:

”Red blood cells are biconcave disks that fold when needed
to pass through the smallest capillaries, many of which
supply the "fastest" tissues (the best perfused). Nitrogen
under pressure causes a surface tension effect on the red
cells which makes them rigid, and they then either will not
pass or they trigger the stretch receptors in the
capillaries and thus a whole litany of immune system
reactions, which then effectively shunt the blood away from
or around these areas and results in dcs and dcs-like
symptoms, often referred to as "flu like symptoms" which are
actually far more insidious.

”Helium in sufficient amounts seems to ameliorate this
effect. The stronger the mix, the less the effect.

”Deep air diving is like giving yourself a case of [Sickle]
Cell Anemia - that is what happens when cells "sickle" and
explains the pain that its victims feel, as well as the loss
of capacity associated therewith.”

According to Mr. Irvine, a minimum of 30% helium is
necessary to begin counteracting red cell rigidity
attributable to nitrogen, and it is recommended at all
depths.

Unfortunately, Mr. Irvine indicates that his information
comes from proprietary commercial diving resources, and is
not available to be reviewed.

However, the Undersea & Hyperbaric Medical Society
(www.uhms.org) has published a study that provides some
corroboration for Mr. Irvine: Taylor WF, Chen S, Barshtein
G, Hyde DE, Yedgar S. "Enhanced aggregability of human red
blood cells by diving." Undersea Hyper Med 1998;
25(3)167-170. This study concluded that increased ambient
pressure during diving increases the aggregability of red
blood cells, which could block microcirculation.

Interestingly, although the scientists performing the study
did not make the connection, the study’s results also
suggest that increased nitrogen pressure is the culprit for
the red cell aggregation, and that replacing nitrogen with
helium stops the progression of the aggregation.

The study found a "dramatic" increase of aggregability of
red blood cells from the surface down to 66 fsw. From 66
fsw to 300 fsw there was a "relatively small additional
effect". What appears significant here is that the
experimenters maintained a constant pressure of nitrogen
from 66 fsw on down by starting to add helium at this depth.
But, surprisingly, they did not correlate the change in red
blood cell aggregability with the fact that the pressure of
nitrogen was no longer being increased:

”If the increase in RBC aggregation is in part caused by an
increase in partial pressure of inert gas, one would expect
a proportional increase of RBC aggregation at 300 fsw. That
was not observed. Together with the in vitro experiment,
these results suggest that the elevation of RBC
aggregability is due to hydrostatic rather than to partial
gas pressure, but this remains to be confirmed.”

Unfortunately, there appear to be no follow-up studies
involving either increasing nitrogen pressure below 66 fsw,
or using heliox from the surface.

Microcirculation being blocked is bad, whether it is due to
clumped, groups of cells and/or Mr. Irvine’s rigid cells.
What this study suggests is that adding He and reducing N2
may be important at all depths to protect one's
microcirculation, in addition to maintaining alertness.

If anyone wants a copy of the article, contact me at
surlyc@alaska.net.