Re: Heartrate Threshold

[Tivers <Tivers@aol.com>]

In a message dated 98-05-18 11:31:03 EDT, fmechelh@c-s-k.de writes:

<< refill time of the heart itself. I remember reading an article of
Engelhard. He
 said that if HR goes up, the length of working phase (pressing blood) stays
constant
 at one point, because there is no way to save time anymore. However, the
refill
 phase (which is also the relaxing phase of the heart muscle itself) is
shortened
 more and more. Up to some 1/1000 sec. where the time is too short to refill
the
 heart again. I think this is what Tom mentioned as fibrillation.
 
 Thats also interesting with the HRmax. of ponies (maybe small Arabians also).
I
 suggest they should be higher (?)
 
 regards
 Frank >>


Here's something interesting: heart size tracks with body weight and with
cardiac output, but not with contractile fraction (how completely the left
ventricle contracts) in horses at rest. This may mean, in gifted horses, that
there is a reserve cardiac output in horse that have big hearts but don't have
to use their capacity when at rest.

ti