1204 
MONITORING 
from smaller implanted units and retransmit the 
received signals for long distances. Lastly, im- 
plantable units have potential applications di- 
rectly for use in man. Examples of such applica- 
tions would be electromographic transducers to 
control artificial arms or legs, blood vessel 
clamps, controllers for an artificial heart and 
ECG and intravascular pressure sensors. 
SUMMARY 
Single and multichannel implantable teleme- 
try systems have been developed and tested in 
various animals. 
Such units have remained operational v^^ith 
continuous or intermittent data transmission 
for periods in excess of one year. 
Systems have recently been developed v^^hich 
allovi' for measurement of flow and dimensions 
as well as ECG and pressure. 
Although implanted systems may add com- 
plexity to many experiments, they are proving 
to be invaluable for situations requiring long- 
term monitoring of multiple parameters or 
when uncooperative animal subjects are in- 
volved. 
REFERENCES 
1. Fryer, T. B., Debor, G., and Winget, C. M. Min- 
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Appl. Physiol. 21:295-298, 1966. 
2. Collins, G. C. Miniature passive pressure tran- 
sensor for implanting in the eye. IEEE Trans. 
Biomed. Eng. BME 14, pp. 77-83, 1967. 
3. Sandler, H., Fryer, T. B., and Datnow, B. 
Single channel pressure telemetry unit. J. Appl. 
Physiol. 26:235-238, 1969. 
4. Deboo, G. J., and Fryer, T. B. Miniature biopo- 
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4:138-142, 1965. 
5. Fryer, T. B. Implantable biotelemetry system de- 
velopments at Ames Research Center. NASA 
Technical Report SP 5094, 1971. 
6. Sandler, H., Fryer, T. B., Westbrook, R. M. 
and Konigsberg, E. Miniature Implantable Accel- 
erometers. In : Implanted Cardiovascular Instru- 
mentation. E. p. McCutcheon, Ed. Academic 
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7. Kolnek, S. a., and Hursen, T. F. A reliable nu- 
clear battery for cardiac pacemaking. Proc. Conf. 
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8. Lee, R. D., and Sandler, H. Miniature implant- 
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9. Cook, G. R., and Sandler, H. An implantable ul- 
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10. Fryer, T. B., Sandler, H., and Datnow, B. A 
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DISCUSSION 
Chairman Franklin: I might comment 
that we're sufficiently impressed with Tom's 
success in use of the electromagnetic flowmeter, 
particularly at the ascending aorta, that we're 
building one as well. This simple CW Doppler 
flowmeter is more subject to error and I must 
say I'm looking forward to finishing that up. 
We're using Tom's circuitry. 
P. Stein, University of Oklahoma, Okla- 
homa City: How do you establish zero with 
your flow transducers when they're located at 
sites other than the ascending aorta? 
Dr. Fryer : The results with the square wave 
have been very good, although this always is a 
problem using any type of flowmeter. In our 
laboratory where individual flows were meas- 
ured and compared, for the ascending aorta 
and the three main branches arising from the 
aorta we were able to obtain good results. We 
have no unique method for determining zero. 
To get a zero many people have used various 
flow occluding or blocking techniques. They are 
difficult to apply in awake animals. Recent 
studies where we have tested vasoactive drugs 
or performed ventricular pacing have resulted 
in episodes of several skipped beats or periods 
of aseptole on withdrawal of the drug or pacing. 
