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DISCUSSION 
CHAIRMAN HAWTHORNE : That's a very excel- 
lent paper, Dr. Amend. I'd like to ask you a 
question. If, as you showed, the stroke volume 
and mean pressure were increased and the 
heart rate unchanged in your hypertensive pon- 
ies, why wasn't the peripheral resistance 
changed? 
Dr. Amend: Because as the flow increased 
the pressure increased proportionally. 
Dr. Hawthorne: I don't see how you could 
calculate a peripheral resistance which was not 
increased. But it's still an interesting point. 
John T. Reeves, University of Kentucky, 
Lexington, Ky. : I think in most people with hy- 
pertension, the cardiac output is not increased. 
I can't cite a reference, but there is a group 
with increased output that are known to have 
"hyperkinetic circulation." They tend to have 
tachycardia in addition to the high output, and, 
in general, the syndrome seems to be reversed 
by beta blocking drugs. Have you used beta 
blocking drugs in the equine species and what, 
if any, effects ? 
Dr. Amend : There's only been one report of 
the application of beta blocking drugs in equine 
species. It was the report of Tavernor and Lees 
in the horse. Their report was simply a general 
evaluation of the effects of propranolol in the 
horse. I wanted to try beta blocking agents in 
these hypertensive ponies and never had an op- 
portunity so I really can't speak more about it. 
We did match our groups in terms of heart rate 
specifically for the purpose of matching systolic 
time intervals. Therefore, we lost the opportun- 
ity to see whether or not the ponies in fact had 
increased heart rate. As I recall, over the total 
normal group, they were not particularly 
changed, even though heart rates were not 
matched. 
