Respiration rate and thumps

["LYNN M. Crespo" <lynn@hpd.acast.nova.edu>]

Just had to jump in here and offer a little physiology lesson.  With
regards to the question as to whether or not a high respiration rate could
induce thumps the answer is yes.

When the respiration rate is high carbon dioxide is being eliminated from
the body.  In the blood some carbon dioxide is converted to carbonic acid.
This acid helps to balance the pH of the body.  When carbon dioxide is
quickly eliminated the body is losing its natural acid and becomes
alkaline, in other words a respiratory alkalosis has been induced.  

A key point is that when alkalosis is induced, potassium in the
bloodstream is shifted to the inside of the cells, so that even though no
total potassium is really lost from the body it is in the wrong place, and
the metabolic consequences are the same as if the horse was deficient in
potassium, in other words hypokalemic.

In addition, the change in serum pH also affects the binding of calcium in
the bloodstream also complicating the situation.  The net effect is a
respiratory induced clinical situation presenting as thumps.

When respiratory rates induce these changes in the pH of the blood, there
will be compensatory changes in how the kidneys operate to try to
normalize the situation.  Any change in pH, whether it originates in the
lungs or the kidneys will lead to other compensations.

Thumps (synchronous diaphragmatic flutter) has been induce experimentally
in animals through either making them potassium deficient, or by changing
their pH.  By the way, when horses do become potassium deficient, the loss
of electrolytes will also induce a change in pH, making them alkalotic.
It's the chicken and the egg story,  potassium deficiency leads to
alkalosis, and alkalosis leads to potassium deficiency.  In endurance
horses there are both metabolic and respiratory influences occuring
simultaneously.

To manage the situation electrolytes are an absolute necessity, and for
those horses that are rapid breathers or panters, slowing their
respiratory rate is also important. 

Lynn  


L. M. Crespo, Ph.D.
Associate Professor and Chair
Department of Pharmacology
Nova-Southeastern University

lynn@hpd.acast.nova.edu