FRANKLIN, VATNER, HIGGINS, PATRICK, KEMPER AND VAN CITTERS 
1133 
S. Cassin, University of Florida, Gainesville : 
i You had a measure of velocity on the organs 
that you were measuring flow in. You also meas- 
ured or had a measurement for flow in one of 
the channels. It isn't quite clear to me how you 
go from velocity to flow without a measure of 
diameter? Were you measuring flow with an- 
other flowmeter, other than a Doppler? 
Dr. Vatner: No, we measure flow through 
j the flowmeter and there are a number of ways in 
which you can convert to volume flow, as long 
as, in a chronic situation as these are, the ves- 
sel size within the transducer remains con- 
strained. And we do this by assessing the in- 
ternal vessel area, the external area, at surgery 
and the internal area at sacrifice of the animal. 
Also, we calibrate a certain percentage of these 
flow probes in vivo and vitro at the conclusion 
I or at sacrifice of the animal. So in these situa- 
tions, we have foun^ the Doppler flowmeter to 
reliably indicate volume flow as well as velocity. 
In the acute situation, however, this may not be 
entirely true. 
Dr. Cassin : You're assuming then, that the 
vessel size that you measure at the time of im- 
plantation is constant, because you have meas- 
urements of flow during the experiment and ob- 
viously you hadn't done the surgery at the end ? 
Dr. Vatner : Yes. That's right. The assump- 
tion is during the experiment, the vessel size 
remains constant. What we do during these vol- 
ume calibrations is alter pressure over a wide 
range, alter flow rates over a wide range and 
conduct calibrations at these levels. When it's 
found that the flowmeter still measures volume 
flow, no matter whether the pressure is altered 
or the flow rates are altered, then we can as- 
sume during the experiment, which was at a 
time very close to this, that it measured volume 
flow as well. 
Chairman : An additional comment. Dr. Vat- 
ner also conducted comparisons with the elec- 
tromagnetic flowmeter under these same condi- 
tions in a small number of cases and has found 
them to be identical. But I don't think we'll 
solve whether the Doppler flowmeter measures 
volume flow or not this afternoon. I think it does 
under these conditions. 
Questioner (unidentified) : I had one other 
question concerning the decrease in renal blood 
flow that occurred under certain conditions. I 
presume that you had in mind that it decreased 
simply because of the decrease in oxygen supply 
to the tissues. Have you any data concerning 
the A-V differences or the oxygen consumption 
of the kidney under those conditions? 
Dr. Vatner : No. 
Questioner : Then you don't really know that 
in fact it does have a decrease in oxygen sup- 
ply? 
Dr. Vatner: All we know is that cardiac 
output must have been severely limited during 
exercise. 
Questioner : Right. But the A-V differences 
are usually so small that I question whether or 
not there really is a decrease. 
Dr. Vatner : It's not the oxygen availability 
to the kidney that we were worried about. It's 
the oxygen available during exercise to the pe- 
ripheral muscles and coronary beds that's im- 
portant, and this is why the compensatory mech- 
anism of diversion of viscera flow was utilized. 
