JAMES D. MEINDL 
1183 
20- 
VELOCITY ~ 
(cm/sec) 10 — 
(o) 
VELOCITY 
(cm/sec) 
(b) 
I 
0 5 10 15 
RANGE (mm) 
Figure 14. — Blood flow velocity waveform and velocity profile recorded with the pulsed Doppler flowmeter. 
Dr. Meindl: May I ask a question? You 
said "disadvantages"; could you define them? 
I think people would be interested in them. 
Dr. Topham : One of the criteria that you 
suggested was that you be able to use precali- 
brated probes and that you also have a standard 
electrical zero. 
Dr. Meindl : That's correct. 
Dr. Topham : Well, the electromagnetic flow- 
meter gives us these same capabilities now with- 
out the problem of having to worry about 
the non-reversal of flow or the reversal of 
flow; they're precalibrated probes. Admittedly, 
they're not electronically precalibrated, they 
have to go through some sort of calibrating pro- 
cedure. But they're guaranteed within plus or 
minus 5 per cent accuracy that you stated and 
electrical zero which I showed in my paper is 
very good. It's very reliable now in many of 
the flowmeters that are available. 
Dr. Meindl: I would like to make it clear 
that although the ultrasonic flowmeters I de- 
scribed in my paper are nondirectional, there 
is no inherent reason why an ultrasonic flow- 
meter cannot measure bidirectional flow. In 
fact, we are quite actively engaged in designing 
bidirectional ultrasonic flowmeters using both 
the CW and pulsed modes of operation. These 
systems can be precalibrated. 
Dr. Topham : I have not seen a bidirectional 
flowmeter, and I know that's my ignorance. I 
hear them discussed but I've never seen one. 
Dr. Meindl : The reason we're working on it 
is because there aren't any available. 
Chairman : One moment here, I might make 
a comment again as Chairman and as having 
worked with the Doppler flowmeter and also 
having worked with the electromagnetic flow- 
meter and with a number of other flowmeters. 
I'll say without regard to anybody else, I've yet 
to see a flowmeter that I've convinced is accurate 
to plus or minus 5 per cent, and it will be some 
time, I believe, before a manufacturer can stand 
behind that. I'll be very happy to see it and I'll 
probably use the thing if I can possibly find one. 
Questioner (Unidentified) : What do you 
