Re: RC: Breeds

[CMKSAGEHIL@aol.com]

In a message dated 6/14/00 6:52:07 AM Pacific Daylight Time, 
truman.prevatt@netsrq.com writes:

<< Given that the heart is devlivering O2 and and carrying away waste 
products, in
 a volumn of blood then the faster it has to beat to deliver the necessary
 volumn implies that it is delivering less volumn per beat. Which either means
 the heart is small or inefficient. In the extreme, neither case is 
desirable. >>

You are right that stroke volume is the other aspect of cardiac output.  
However, at rest, there is no indication that the body "needs" everything 
that is being provided by the bloodstream.  The crux of the matter is when 
the heart is able to deliver O2, etc. efficiently when working--and THAT is 
determined by working pulse rates, not by resting pulse rates.  Furthermore, 
if the blood flow is sufficient to meet the body's needs, the HR will recover 
rapidly when work ceases, as there is no "backlog" in the form of waste 
products or O2 deficit.  Mike's "idle" analogy is not all THAT far off 
(although you make good points about load)--there is no indication that the 
body "needs" everything being delivered at rest (nature can be very wasteful) 
any more than an engine "needs" a slightly higher idle speed--as long as it 
is not so high as to be detrimental.  (Compare a really excessive idle speed 
to the horse on the adrenaline high, wearing itself out needlessly--but the 
horse has control of the idle set screw and can bump it up with "additives" 
when he "wants" to be screaming along on idle...)

Heidi