1182 
MONITORING 
BLOOD FLOW VELOCITY IN THE 
ASCENDING AORTA OF A HEART 
TRANSPLANT DOG. 
Figure 13. — Blood flow velocity waveform recorded with the CW Doppler flowmeter. 
we've used it for a number of years, we zero- 
cross detect with a zero-crossing detector. 
The signal-to-noise ratio was high and we il- 
luminate most of the vessel. So with these as- 
sumptions (and in fact you explain why) , I 
merely said empirically we found this to be so. 
Is that fair? I objected to your saying that you 
can't use a zero detector to derive volume flow. 
We differ in the term "derive," I guess. 
Dr. Meindl: I think what you have stated 
is fair. Under certain conditions such as a blunt 
velocity profile and insonification of the cross- 
section of the lumen, the CW Doppler flowmeter 
can provide a measurement of volume flow; 
under other conditions it may not. 
Chairman: I think we agree and I've taken 
up far too much of your time. I'm sorry. There's 
a question there. 
Dr. Landscool, Seattle : I would like to point 
out that the Pulse Doppler is extremely versa- 
tile not only as a volume flowmeter, but if used 
with a scanning arm, the percutaneous sonar ar- 
teriographic picture of an artery can be ob- 
tained, for example, the carotids or the femo- 
rals. We've also used it to determine patency 
and to make pictures of saphenous vein bypass 
graphs. This is also an additional application 
that you haven't mentioned, but an extremely 
important one, in addition to quantitative flow. 
Thank you. 
M. E. SiKORSKi, Georgia Tech, Atlanta, Ga. : 
I'm wondering what accuracy can be obtained 
as far as flow measurements are concerned. In 
certain applications, this is quite an important 
problem, especially in brain surgery. 
Dr. Meindl: To date in our work we have 
not established a reliable estimate of the ac- 
curacy of the Doppler ultrasonic flowmeter. 
My rough estimate is that its accuracy may be 
limited to ± 5% of 0. 
W. S. TOPHAM, Artificial Heart Test Facility, 
Salt Lake City: I noticed that in the recording 
that you showed of the aortic flow wave form, 
the reversal flow was notably absent. Is this be- 
cause your flowmeter is not detecting the re- 
versal of flow or is this because of the prepara- 
tion ? 
Dr. Meindl: I restricted myself here to 
talking about nondirectional flowmeters because 
they are the simplest ones and because we're 
further along in the work we're doing on them 
than we are on the bidirectional systems. 
Dr. Topham : Thank you. I wanted to make 
sure that that point was understood because the 
electromagnetic flowmeter seems to not have 
these disadvantages, and in the comparison, I 
think it's fair to make that known. 
