Re: RC: Re: Long holds, Heart Rate, tying up, electrolytes

[David LeBlanc <dleblanc@mindspring.com>]

At 06:24 PM 12/21/99 EST, Tivers@aol.com wrote:
>In a message dated 12/21/99 2:13:45 PM Pacific Standard Time, step@fsr.com 
>writes:

> Why HR/CRI can be normal, when something 'not normal'
> is obviously going on in the horse. The heart isn't
> working harder than 'normal' - this indicates that the
> tissues are being adequately fueled (substrate, 
> hydration). Is there some overiding factor?
> CNS, automonic response? Any answers? - any guesses?

>I don't think we understand all the factors that move heartrate around. In 
>the past, we've supposed that we know, but we don't. and HR recoveries are 
>far trickier than orking HRs to understand.

This is what I did my research on while in my first bout of graduate
school.  You can model heart rate as being part of a non-linear feedback
system.  If you take a Fourier transform of the beat to beat heart 'rate'
(r-wave to r-wave), and sort out the component frequencies, what you find
is that underlying the base heart rate, there are slower waves that follow
the respiratory rate, oscillations in blood pressure, p02 waves, and body
temperature.  Mammals use their heart rate to regulate all of the above,
and in the case of respiratory rate, it tends to drive heart rate.  This is
why you can bring your heart rate down after strenuous work by consciously
lowering your respiration rate.  Unfortunately, blood pressure, oxygen
level, and body temperature don't tell the whole story.  There's a lot of
other systems involved, too.

So the bottom line is that heart rate is an extremely complex, non-linear
system.  Non-linear (for the many non-mathematicians here) means that for
the same set of inputs, you can obtain more than one set of results.  This
makes things extremely hard to analyze, and most physicians (whether
working on humans or animals) don't have the engineering training to
properly analyze the systems involved.  Even with an engineering
background, and lots of data, there are still a large number of cases that
aren't fully explained with even the best of data - and I'm talking what
can be obtained in a hospital, not what can be pulled in the field.  This
makes research on horses a lot more difficult.

When confronted with a non-linear system where you're not sure that you
even have all the causal parameters, and some of your inputs appear to be
stochastic in nature (random), even the best scientists are likely to
resort to empirical methods.  For example, we design aircraft that way -
even though aerospace engineering is much more of a science than horses
are, there's still quite a bit of it that is just based on testing and
seeing what works.  Same sort of thing happens a lot in things like
wastewater treatment - we use bacteria, and a monoculture under ideal lab
conditions can be modeled quite precisely.  But  a real treatment reactor
with varied input streams doesn't model all that well, and even a PhD does
well to listen to the plant operator.  The operator may not understand the
Monod equation, or have studied microbiology, but he does know how to make
the plant work.

In fact, the very idea that anything more than a trivial system can be
explained using deterministic methods is considered outdated.

Although I think the sport could seriously benefit from some dedicated,
scholarly research, unless we're all willing to stop riding until the
scientists do have a better handle on what's going on, we're stuck just
doing the best we can with what we can determine in the field.  Heart rate
is a good surrogate for a lot of parameters, and will tell you a lot of the
time whether an animal is exhausted (we're talking mammals here).  The
problem is that there are many other cases that heart rate won't explain,
and too many times that animals surprise us with what they do.

The problem isn't limited to horses.  Bicyclists have been known to win
races, fall off their bikes and die of exhaustion.  You can probably find
examples in other sports where long-term exertion occurs.  Why one person
dies when the one right behind them doesn't is a mystery.

So what it all comes down to in the end is that we've only got some pieces
of the puzzle, and we have no better alternative than to rely on people's
intuition - this often works better than science does when you have a lot
of unknowns.  Exhaustion is going to be a function of the individual, heart
rate, hydration, several enzyme levels, diet, and even attitude.  I'm all
for giving vets better tools to do their jobs with, but dismissing years of
real-world experience just isn't realistic.


David LeBlanc
dleblanc@mindspring.com


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Ridecamp is a service of Endurance Net, http://www.endurance.net.    
Information, Policy, Disclaimer: http://www.endurance.net/RideCamp   
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=