Heidi-- I'd like to take a crack at this
question, as I have done some investigation into what the CRI shows us and
what it tells us about the condition of the horse. I will disclaim by saying I
have never discussed this personally with Dr. Ridgeway, nor am I a vet. I hope
my attempts at understanding the CRI will lead to some discussion here, maybe
by Susan G. or other vets. There are a couple of interesting
things to note about the heart. First, it is made of what is called cardiac
muscle, which is different than the skeletal muscle that moves our joints, or
the smooth muscle that lines our intestines and keep things moving along. As
such, cardiac muscle has a greater metabolic capacity than skeletal muscle,
and can keep contracting all day long basically without fatigue, unless driven
to higher levels of output through exercise or other stressors. In this case
the heart rate is actually driven upward with fatigue, as it becomes
more excitable and may pump more frequently, but more weakly.
Secondly, when the heart contracts to pump blood, the first organ in the body
to receive that blood (and the oxygen, electrolytes and nutrients it contains)
is the heart itself through the coronary blood vessels. Let's take
an example of what (I think) happens in an exercised but rested and
well-recovered horse at an endurance ride. The horse's resting pulse is taken
and determined to be 48, let's say. Then he is trotted out 125 feet and back
125 feet, and after a minute passes, his pulse is taken again. If the pulse is
at or below the initial rate before trotting out, it can serve as an indicator
that the horse is meeting or exceeding the oxygen and electrolyte demands to
the heart itself. Since the heart will likely fatigue after skeletal
muscle, the horse may be showing the effects of exercise, but able to
continue. If the post-trot heart rate goes up, it may indicate that the heart
itself is beginning to fatigue and is unable to briskly recover from further
exercise, and perhaps the horse should be pulled from competition. Like any
diagnostic tool, the vet can take these findings into account in the overall
assessment of the horse in deciding if the horse is fit to continue.
Presuming that I am even partially right in my explanation, it
serves as a tribute to Dr. Ridgeway's brilliance in figuring out such a
meaningful physiological mechanism that can reveal so effectively the
momentary cardivascular well-being of an exercised horse, and in the crude
field location of an endurance ride, to boot. All with a simple stethoscope
and a stopwatch. Go figure. Bruce
Weary
heidi larson wrote:
Ok, someone tried explaining this to me once, but I'm not sure exactly
how this works with the numbers. I remember at Renegade Ash had a
great CRI, but can't remember the numbers, this time at the Dunes, he was
40/40. Shouldn't the second number be lower and if it's not, does
that indicate something?
thanks - heidi and Ash of the 3' mane
__________________________________________________ Do You
Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
