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Hey y'all, are we talking about an at-home resting heart rate, or at-ride?  My
Arab/RMH has an at-home RHR of 28 but at a ride it's 36-40.  So I'm just
curious.
-Sharon L. in Maine



Quoting Bruce Weary <bweary@xxxxxxxxxxxx>:

>    In light of recent ideas put forth about heart rates and fitness, I
> would like to make a few comments. Now, I'm no cardiac expert, but I did
> have my heart broken in 4th grade. By Barb Remigio, and, no, I don't
> want to talk about it.
>     Beverly was wondering about the usefulness of a low resting heart
> rate in an unconditioned endurance candidate. Heart rate in people is
> determined by, among other things, the strength of contraction, stroke
> volume, elasticity of peripheral vessels and the health, age and
> physical condition of the person.
>   In people, exercise affects all of these things  (except age) and has
> additional benefits, as well. There is increased vascular supply to the
> periphery and the heart itself. Sweating efficiency and heat tolerance
> may increase. There are some other interesting effects that occur in the
> nervous system, as well, that are worth noting. The Vagus nerve
> increases it's output in fit individuals, and this increased "vagal
> tone" actually slows the heart rate, and stimulates gut function. In
> tests involving fit individuals vs. less fit individuals, the fitter
> people tested had higher vagal tone, and thus lower resting rates. These
> fitter individuals also have less sensitivity of the baroreceptors
> (pressure receptors) in the upper aorta, and this makes the heart less
> reactive to blood pressure, so the heart rate is less during exercise
> in  conditioned individuals. This vagal tone is also what's largely
> responsible for our lowered heart rates during sleep.
>    Low blood pressure is rare, and not  directly a function of
> bradycardia. It is usually from the effects of myocardial infarct,
> blockage, or the effects of medications, (beta blockers, digoxin)
> dehydration, blood loss or other medical condition. The term
> "pathological bradycardia" applies to these situations. Fainting from
> "physiological bradycardia" (slow heart rate from fitness) is rare
> enough that other causes should be suspected first.
>    So, since the horse is a mammal, too, it's reasonable to assume that
> many of these principles apply to the horse, as well. The lower resting
> heart rate in an unfit horse may mean that he is able to meet his oxygen
> demands more easily from the genetic get-go, and exercise will only
> increase his advantage. His "fit" rate may or may not change, (it
> frequently does in people) but he will presumably be more efficient at
> distributing blood and retiring his oxygen debt with fewer contractions,
> and probably meet ride criteria that much quicker. Horses do vary, though.
>     As far as a horse recovering to a "pathologically low" heart rate,
> this is unlikely, unless the horse's sympathetic nervous system is
> completely inoperable. There are other criteria that will keep the
> healthy horse's heart rate at a sufficient level until he stablizes,
> such as oxygen debt, internal heat, dehydration, electrolyte loss,
> fatigue, pain, and other factors that stimulate the sympathetics, which
> tell the heart rate to stay up. When the sympathetic influence
> decreases, the parasympathetic system slows the heart rate. There are a
> series of "checks and balances" that drive all this. Horses that crash
> may have criteria that overwhelm these mechanisms and the horse is in
> trouble before he can right himself, and thus he needs veterinary
> attention. So, good recoveries are indeed, all other things being equal,
> a good indicator of fitness and exercise tolerance. Every sanctioned
> endurance in the country has, as its core recovery criteria, an
> acceptable heart rate. Good or bad, finishing criteria doesn't demand
> that normal gut sounds, capillary refill, jugular refill, skin tenting
> or anal tone be present for a completion, as important as they are. This
> might be something worth looking at. And, Dr. Ridgeway's CRI is based
> entirely on the heart rate recovery, due to all the other physiological
> factors acting on the heart rate, which helps give an overall view of
> how the horse is tolerating his work, not just how he's retiring his
> oxygen debt.
>     As far as Barb Remigio is concerned, I sent her love and moved on to
> 5th grade. I was 16, and it was time to get on with my life.   Dr Q,
> world renowned heart throb.
>
>
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