Klarinet Archive - Posting 001075.txt from 1998/11

From: George Kidder <gkidder@-----.net>
Subj: RE: [kl] Wagner; Fiume March; Helium and Pitch
Date: Fri, 27 Nov 1998 17:43:23 -0500

In response to several posts, some physiologist's thoughts:

1) Helium at moderate pressures is not anaesthetic. At high pressures it
becomes so, apparently by inserting (dissolving) in the membrane of nerve
cells and disrupting their function, in a manner similar to that of ether.

2) Helium is used as the inert gas in deep diving, replacing nitrogen which
can cause "the bends" upon release of pressure. With helium mixtures, the
divers speak with squeaky voices, as one might expect. There can also be
problems with helium narcosis, as indicated in 1) above.

3) Unfortunately, hydrogen WAS used as a diluent for oxygen in the early
parts of the space program. The (almost) inevitable happened, and we lost a
crew of astronauts in the explosion and fire. They don't do this any more!

4) The human respiratory system does indeed respond most readily to
elevated CO2, which stimulates ventilation. (This is why medical oxygen is
almost always 5% CO2 in oxygen, to keep the respiratory center stimulated
and promote spontaneous breathing.) A single breath of helium will not
prevent the accumulation of CO2 in the blood from the respiration of
previously-inhaled oxygen. Continuous breathing of any oxygen-free gas
would be dangerous, of course. If one wanted to do long-term experiments, I
would suggest 20% oxygen in helium (the diver's gas) which I imagine would
be quite safe.

5) Just in case, don't ever do such things without someone ready to help
you out if you do get into respiratory problems. This is just common sense.

6) And finally, while there is a difference in total density between room
air and expired air (what we blow into our instruments), this is not due
only to CO2. Expired air is also a) warmer, and b) saturated with water
vapor. Both of these will also change the density and therefore the
instrument's pitch.

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