More on Altitude changes... And all that fizz...

["Patricia E. Peters" <patpeters1@juno.com>]

On Thu, 07 Sep 2000 <robandcarla@hotmail.com says...

One of my mares experienced ... depression ..was told it may have been
climate, altitude change. .
...I remeber something maybe Steph and Krusty was in France about a week
or two? correct me if I am wrong here. I know that the plane ride was no
picnic for a horse.  

SO KIRSTEN SAYS... (re: what about higher altitude changes? would that
not effect the horses oxygen?)  Humans take time to adjust because it
takes time for the body to ramp up its RBC production rate.  Horses OTOH,
store RBCs and therefore have an extra supply readily available. 
Therefore, unless the elevation gain is extreme (say Sea Level to 11,000
feet), a horse should have sufficient RBCs on hand to accommodate the
reduced concentration of oxygen.    
 
THEN TOM SAYS... (re:  How can you get past the slower recovery times
since the oxygen would be somewhat thinner than what they are used to?)  
 You can�t That takes time. And an exercise challenge or two. Weeks.
ti 
  
SO PAT THROWS ALL CAUTION TO THE WIND AND SAYS...

No doubt I am stretching my neck out WAY too far,  and I will probably
vaporize in the resulting flame-fest, but what the heck� I might like the
abuse� so go ahead and flame me, spank me, make me write tearful
retractions� gosh�I like it already�

Please allow me to add another possible factor for your
consideration�Inert gas in solution in the blood and body tissues, and
Henry�s Law. (The basic idea says that the solubility of any gas in a
given liquid is almost directly proportional to the partial pressure that
that gas exerts on the liquid).

Pilots and scuba divers know that there has been a lot of research done
on pigs, sheep, humans, dogs, cats and monkeys as to the effect of
pressure changes on dissolved inert gasses in the body.  Given the solid
principles of physics that govern these effects, I cannot see why horses
would be significantly different.  

Let me explain what I mean�

We all know that the atmospheric pressure at sea level is about 14.7psi,
and this pressure drops as we ascend to altitude.  We also know that,
except for some trace elements, the air that you and your horse breathes
is comprised of roughly 20% O2 and about 80% N2 (Nitrogen), so the
partial pressure of N2 in this mixture at sea level is .80 x 14.7psi.  Of
course, when you ascend to altitude, the percentages stay the same, but
the partial pressure exerted by the gas drops along with the total
ambient pressure. 

Now this next part might surprise you.  You already know that you have O2
in solution (in liquid form) traveling around your body right now; it got
there through your lungs, and your body is metabolizing it (using it to
help fuel your body).  But did you also realize that you and your horse
have N2 in solution in your blood and body tissues right now?  Its not
doing anything (inert gas); its just there because as the blood passes
through the lungs, the tension of N2 in the air in your lungs causes that
N2 to either flow into the blood or out of the blood until the gas
tensions on both sides (air in lungs vs. in blood) are equal.

So, then, When you go up to the mountains (or up in a partly-pressurized
airplane cabin or cargo bay), and you start breathing air at a lesser
pressure, the N2 wants to flow out of your body tissues and out of your
blood, and into your lungs.  You then start to exhale more N2 than you
inhale, until the partial pressures are again equal on both sides. 

This would not present a problem were it not for two things.  The first
problem is that it takes over 12 hours for the body to get even CLOSE to
eliminating enough of the excess N2 to bring itself back into balance. 
The second problem then, is Henry�s law (governing the solubility of the
gas under changing pressures).  Because the gas cannot stay in solution
as well at the lesser pressure, some of the N2 actually starts to come
out of solution right in the blood�.  

It makes microscopic BUBBLES�.  It FIZZES� you know, like soda pop.  No
joke.  A lot of solid research has been done on a variety of animals and
on humans to study this.  Your body can tolerate a small amount of this
fizzing.  Way too much causes a clinical case of decompression sickness�
scuba divers know it as the bends.   

But few laymen fully appreciate the scope of physiological challenges
presented by even a little bit of fizzing. Most notably is the cascade of
chemical reactions that occur as these inter-vascular bubbles bounce off
of the platelets in the blood, and stimulate them to coagulate, while
causing the tissue cells that make up the vessel walls to take on a shape
that invites plasma to leak out of the blood vessels and into the
tissues.   

So, the blood kind of gets like sludge, some body tissues swell with
edema, and the immune system spends some of its resources on trying to
fight fizz. Of course, fatigue is a very common symptom, and the overall
efficiency of the circulatory system is somewhat compromised for a while,
but the biggest challenge to the system overall is DEHYDRATION.  Big time
challenge to hydration status here, and that challenge can continue to
one extent or another for a few days while the body is busy washing out
the used platelets and other such battle waste.  

To me, it seems reasonable to hypothesize that any area of the body that
has less than optimal circulation will suffer a bit more, and be more
prone to injury during this time.  The horses legs come to mind, as do
any sites of prior injuries anywhere in the body.  I do not know how long
it takes for the horse�s body to fully recover from this, but humans,
pigs and sheep can take up to 72 hours (although most of the challenge
happens within the first day or two).  

As far as I know, the only do-able way to mitigate this effect (beyond
hydration of course) is to breathe pure O2 for as long as practicable,
which for obvious reasons results in a much faster rate of elimination of
N2 from the blood into the lungs, and in so doing, significantly reduces
the volume of fizzing in the blood.  

So what do you think?  Substance or stretch?