616 
PHYSIOLOGY 
DISCUSSION 
J. W. Clayton, University of Wisconsin, 
Madison: Today there is a great deal of con- 
cern about the use of aerosol products which in 
some cases are propelled by a class of materials 
known as the fluorocarbons. These are fluoro- 
alkanes, and in some cases the dog is used to 
evaluate the effects of cardiac rhythm from 
inhalation of these materials. Would you com- 
ment on that please ? 
Dr. Hamlin : Yes, I think a dog is a partic- 
ularly bad model to test the arrythmogenicity 
of any compound. Dr. Harris, why may be here 
in the audience, might care to comment about 
it. He has shown that if one stimulates the stel- 
late ganglia of a dog that has been anesthetized 
with halothane, one will not produce an arryth- 
mia. Whereas, if one stimulates that of a cat or, 
probably man, horrendous ventricular arhyth- 
mias may occur. So it appears that the dog, at 
least, might not be a very good model at all to 
study the sensitivity of a myocardium, partic- 
ularly if that sensitivity is enhanced by auto- 
nomic efferent drive. 
Dr. Clayton : How about the monkey then ? 
Dr. Hamlin : I can't say about the monkey. 
J. W. Buchanan, University of Pennsyl- 
vania, Philadelphia, Pa. : Dr. Hamlin, you might 
review for this audience some of the aspects of 
sinus arrythmia in the dog and how to account 
for it in studies. 
Dr. Hamlin : It is very interesting when one 
analyzes the normal electrocardiogram of some 
of the species. One sees rather striking varia- 
tions. And I think when one looks at what is 
considered normal for these animals, and might 
be considered abnormal for man, there probably 
is an interesting story. Sinus arrythmia is 
probably as pronounced in the dog as in any 
other species, possibly with the exception of 
some birds. The mechanism of it was of interest 
to us, as I'm certain it is to Dr. Levy, who is 
quite expert in the determination of sinus rate 
as a balance between autonomic nerves. We 
found that there are changes in RR intervals of 
the dog's electrocardiogram, varying between 
300 and 1200 milliseconds. This waxing and 
waning of heart rate in the dog appears to be 
a function of vagal efferent activity. In the 
bird, on the other hand, it's been proposed that 
the fluctuations in heart rate are a sequel to 
fluctuations in sympathetic efferent activity, 
so when one studies the effects of blood pres- 
sure on the reduction or increase of heart rate, 
there might be some large species' differences. 
Dr. Buchanan: Another question. Would 
you comment on how to standardize limb posi- 
tioning for dogs in repeat studies so that they 
don't encounter this variation in the electro- 
cardiogram you mentioned with the limb posi- 
tion? 
Dr. Hamlin : Surely. This is a very important 
problem and I think that there are two ways 
of getting electrocardiograms. One is where the 
trace jumps all over the place and the animal 
is unanesthetized and unrestrained and you 
try to look for gross changes. The other is where 
the animal is properly restrained — even if medi- 
cally restrained. One can obtain certain stand- 
ardizations if the limb leads and the neck are 
placed in the proper position. Dr. Hill at the 
University of Pennsylvania did an excellent 
study in which he showed that the thoracic 
limbs should come out at about right angles to 
the torso, that the position of the pelvic limbs 
was less important than that of the cranial 
limbs, and that the neck should be placed so 
that the Y-axis of the animal is fairly straight. 
That the limbs be placed in a consistent position 
is extremely important, as Dr. Buchanan sug- 
gests, in interpreting the electrocardiogram of 
any quadruped. 
W. C. Van Arsdel, Food & Drug Administra- 
tion, Washington, D.C. : The electrical axes of 
the QRS&T in some species are a little different. 
Have you gone into that? 
Dr. Hamlin: The next parameter we were 
going to add to our characterization of these 
animals is the T-wave. Unfortunately, the 
T-wave, as Dr. Lepeschkin knows, is like a 
chameleon in many of these animals. It's very 
labile and in some of the species, not only is it 
labile, but it's multiphasic. For example, the 
horse has a polyphasic T-wave ; and because of 
its liability, it's pretty hard to characterize it 
accurately. Although one can get a consensus, 
I really wouldn't care to talk about it now be- 
cause it's something on which we have so little 
information. 
