JAMES D. MEINDL 
1177 
ANTENNA 
AUDIO INPUT 
100 MHz FM TRANSMITTER AND AUDIO AMPLIFIER 
Figure 8. — Schematic diagram of audio amplifier FM transmitter circuit. 
PERFORMANCE 
The instantaneous blood flow velocity in the 
ascending- aorta of a post-operative heart trans- 
plant dog is illustrated in Figure 13. The signal 
was telemetered with a totally implanted CW 
velocity flowmeter. The transducer was designed 
as described in Figure 2 to respond to blood 
velocity at the center of the lumen. Referring 
to (4), no calibration was necessary since the 
frequency (fj) and the sonic angle of attack (6) 
j were fixed in the design. An accurate flow zero 
j was obtained by setting f,i equal to zero. Drift 
in the scale factor was negligible since the ex- 
citation frequency (fj) was stable to within 
±1%. 
' Figure 14 illustrates the blood flow velocity 
waveform at the center of the lumen and an 
eight channel display of the instantaneous 
blood velocity profile in the descending aorta 
I of an anesthetized dog as recorded with a pulsed 
' Doppler flowmeter. 
Although initial tests of the two implantable 
flowmeters described in this paper have been 
reasonably encouraging, a substantial eflfort by 
a variety of users is needed in order to fully 
develop the potential of these new instruments. 
SUMMARY 
Accurate measurement of pulsatile blood flow 
can be achieved on a chronic basis in research 
animals through the use of implantable ultra- 
sonic flowmeters. The use of a CW flowmeter to 
measure flow velocity at a particular location 
and a pulsed flowmeter to measure velocity pro- 
file or volume flow is particularly attractive. 
Both instruments can be electronically precali- 
brated and exhibit virtually no baseline or scale 
factor changes during chronic experiments. 
Silicon integrated circuits offer significant ad- 
vantages in reduced size and power drain as 
well as improved reliability in these instru- 
ments. Additional effort is needed to evaluate 
