Klarinet Archive - Posting 001163.txt from 1998/11

From: "Diane Karius, Ph.D." <dikarius@-----.edu>
Subj: Re: [kl] burping, helium and pitch
Date: Tue, 1 Dec 1998 00:55:05 -0500

Tony Pay wrote (after a snip):
> Clearly there is a process of absorbtion of oxygen and emission of CO2
> in the lungs that takes a little time. What in fact is the timescale
> for the interchange?
Any given red blood cell will spend about 750 msec (.75 sec) in a
capillary at the alveoli. However, it only takes about 250 msec (.25
sec) in order for the oxygen to equilibrate. CO2 has also come to
equilibrium in about the same amount of time (it is much more
soluble, but the pressure gradient is considerably less).

> I seem to remember that the effective surface area
> of the inside of the lung is extraordinarly large.
Yes - there are about 300 million alveoli in the lungs, giving a
surface area of 85 square meters (roughly the size of a tennis court,
if we were to take the lungs and spread them out in a single layer).

> Perhaps there is also a diffusion effect, so the CO2 diffuses into
> the mouth and upper portions of the trachaea, even though it's
> denser?
There will some exchange of CO2/O2 at the mucosa of the mouth and
pharynx (areas traditionally considered anatomic dead space) because
there is a fairly high number of capillaries coming in reasonable
contact with the gas, but it will be much less than in the lungs
because of the surface area. I can't give you exact numbers right
now, but I'm planning on going downstairs where I have my handy CO2
monitor (us respiratory neurophysiologists have some of the neatest
toys... and the most amazing collection of totally irrelevant
trivia) to check my supposition about how much, but I suspect that
the CO2 concentration will be considerably lower than that found in
end-tidal (alveolar) air, even allowing for the extra time. As
previously noted, the air is also being humidified and warmed here-
this process is believed to be complete by the time the room
temeperature air gets to the larynx so I don't know that holding
one's breath for a few seconds would change things that terribly
much.

Diane R. Karius, Ph.D.
Department of Physiology
University of Health Sciences
1750 Independence Ave.
Kansas City, MO 641o6-1453
email: dikarius@-----.EDU

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