KING@KESTREL@sri-unix (11/23/82)
From: Richard M. King <KING at KESTREL>
I was doing a bit of thinking about the stuff that has wafted over the
net concerning suitless space suits. First, I offer several facts. I
apologize in advance for possible errors in memory.
1) The pressure inside a systemic vein (the lowest pressure found in
the bloodstream) is 40 mm Hg. This pressure is maintained by the various
elasticities of the parts of the bloodstream; NOT by the heart. I seem to
remember that the pressure in the pulminary vein was somewhat lower, but I
don't remember any exact figure. This would not be a problem because the
pulminary circulation is embedded in the lung, which is pressurized. This
figure is referenced to ambient. The boiling point of water at 37 deg C is
considerably less than 40 mm.
2) A rule of thumb used by divers is that a sudden reduction of
pressure by a factor of two is safe. A diver can immediately go from 10
meters to the surface, or 30 meters to ten meters. While blood pressures are
too low for this distinction to matter, I suspect that it is blood pressure
rather than external pressure that can be halved with impunity.
3) The skin is pretty impermiable when it wants to be. When I swim
vigorously (in a "fresh water" pool) I invariably need a drink of water. This
would not be the case if the skin were permiable.
We have to account for the observation that the balloonist that
dropped from 102,000 feet had a swollen hand when he landed. Consider the
following thought experiment: place a person in a box and put one of his arms
through a hole in the wall. Provide the hole with gaskets so a pressure
differential can be maintained, and increase the pressure of the room from 1
atm. to 1.5 atm. I think we would find that the victom's hand had swollen when
the experiment was finished.
So the problem was probably the pressure DIFFERENTIAL.
This means that we have to find out what differential is tolerable, and
how accurately any garment ("space leotard") has to fit the curves to avoid
excessive discomfort. I claim that this research can be done on the ground, in
comparitive safety, by working in small steps with volunteers.
Dick
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