Heart diameter is derived from measured transit time of 2.25 MHz ultrasonic pulse between two piezoelectric crystals attached to diametrically opposite heart surfaces. Miniature instrument implanted in chest telemeters information to external receiver-converter. System permits continual dimensional data recording taken from awake animals during long-term experiments

Lee, R. D.

English

NASA Technical Reports Server

June 1971	
.	 Brief 71-10163 
NASA TECH BRIEF
	
A 
Aines Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the, Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Miniature Implantable Instrument Measures and Transmits Heart Function Data 
The problem: 
Measure heart dimensions and dimension changes 
during the cardiac cycle in order to characterize 
the hydraulic and/or muscle function for an intact 
ventricle.
	
-1	 Sonomicrometer Electronics 
	
I	 I
_________ 
Switch  
	
Electronicsi	 Pulse	 RF	
_
 
L1
Figure 1. Block Diagram of Sonomicrometer 
at low voltage and power in conjunction with a 
telemetry link at 88 to 108 MHz (FM). An actua-
tor, which radiates an impulse at 700 kHz, 
is used to energize an implanted electronic switch 
that activates the battery (2.7 to 4.05 V) feeding cur-
metry 
lsnhltter 
- - - - -j 
The solution: 
The heart diameter is derived from the measured 
transit time of a 2.25 MHz ultrasonic pulse be-
tween two piezoelectric crystals attached to diametric-
ally opposite surfaces of the heart. A miniature instru-
ment implanted within the chest cavity telemeters 
information to an external receiver-converter. The en-
tire system permits the continual recording of di-
mensional data taken from awake, undisturbed 
animals during long-term experiments, without the 
complications of externally mounted instrumentation. 
How it's done: 
The sonomicrometer, a miniature implantable 
ultrasonic system. (Figure 1), was designed to operate
rent into the circuitry of the ultrasonic measuring 
system and the telemetry transmitter. The pulse gen-
erator of the ultrasonic system supplies electrical 
pulses at a repetition rate of 450 Hz to the ultra-
sonic projector. The projector converts the electrical 
pulses to 2.25 MHz ultrasonic pulses that traverse 
the biomedia and impinge on the ultrasonic sensor. 
The sensor converts the ultrasonic pulses to electrical 
pulses that are subsequently amplified and used to 
amplitude-modulate the FM telemetry signal so that 
it can be transmitted to a remote telemetry re-
ceiver. Output signals from the receiver are fed 
to a gated pulse converter which provides an analog 
voltage signal suitable for recording. Heart dimen-
sional information is obtained from the elapsed time 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free frbm privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000162 2020-03-17T02:25:05+00:00Z
Pulse	 Ultrasonic	 TeImetry 
Generator	 Transducers	 Amplifier	 Transmitter 
RFC
V.. ' 
-	 Figure 2.	 Circuit Diagram of Sonomicrometer 
between	 the projector impulse and the sensor im- electronic components
	 mounted	 in	 a	 plastic	 billet. 
pulse, and is based on a sonic velocity of 1540 m/sec. The circuit components are hermetically sealed in a 
The	 repetition	 rate	 of	 the	 relaxation	 oscillator metal	 container,	 with	 the	 loop	 antenna connected 
formed	 by	 transistors	 Ql	 and	 Q2	 of	 the	 pulse through a two-pin glass header; the ultrasonic trans-
generator (Figure 2) is determined by the time con- ducers and the battery are connected to a four-pin 
stant of resistor RI and capacitor C2. The energy header at the other end. The electronic switch is also 
stored in C2 is rapidly discharged through Q2 when hermetically sealed within a metal container, which 
the	 forward	 bias on	 the base of Q1	 is exceeded; has a four-pin	 header	 for the	 antenna	 and	 other 
and,	 since	 the	 current	 path	 includes	 the	 primary connections. A high-melting-point wax is used to en-
winding	 of	 transformer	 TI,	 positive	 and	 negative case and support the antenna and header connec-
output spikes are generated in the secondary wind- tions.	 A	 single	 coat	 of	 a commercial	 vinyl	 com-
ing.	 A	 fast	 diode,	 CR1,	 allows	 only	 the	 negative pound is used over the wax to improve the adhesion 
current spike to be passed into the resonant circuit of a commercial elastomeric meterial which is applied 
formed by inductor Ll and the capacitance of the as a final coating. 
ultrasonic projector crystal Xl. The results are a 2.25 The	 battery package	 for the	 system consists of 
MHz ultrasonic impulse, which travels through the two or three 1.35 V pacemaker mercury cells con-
biomedia	 at	 a	 slow	 speed,	 and	 a	 burst	 of	 rf nected in series ano encapsulated in a silicone rub-
power to the input winding of transformer T2. The ber, coated with a vinyl compound for protection 
direct-coupled, voltage impulse, which represents the against	 body	 fluids.	 The	 ultrasonic	 transducers	 (a 
ultrasonic projector burst and the impulse derived pair of 1-cm diameter piezoelectric crystals) are sealed 
from the sensor after it has traversed the biomedia, in the vinyl compound and mounted in an expanded, 
is amplified by two tuned transformer-coupled transis- cellular polystyrene unit coated with the vinyl corn-
tor amplifier stages,	 Q3	 and	 Q4,	 to	 a level	 suffi- pound. 
cient to amplitude-modulate the telemetry transistor Reference: Q5. This transistor and associated components serve Lee,	 R.D.; and Sandier H.: Miniature Implantable 
as	 the	 rf oscillator and	 telemetry transmitter. 	 The 
- Sonomicrometer System. J. App!.	 Phi sw!., 28(1), 
circuit is a modified version of the Colpitts oscillator, 
where	 inductor	 L2	 also	 serves	 as the	 loop	 trans- 110	 1970 
mitting antenna. Notes: 
The miniature, implantable, telemetry-actuated elec- 1. The sonomicrometer circuitry can tolerate supply 
tronic	 switch,	 developed	 for	 use	 with	 the	 sono- voltage variations in the range of 2.0 to 4.0 V. 
micrometer, is fully controllable by single-frequency 2. Requests for further information may be directed 
telemetry pulses and has zero power dissipation when to: 
off. To activate the implanted switch, the actuator Technology Utilization Officer 
antenna	 is	 positioned	 near	 the	 switch	 antenna; Ames Research Center 
when the actuator is operated, a 700-kHz rf signal Moffett Field, California 94035 
is radiated. The tuned, implanted antenna picks up Reference: TSP71-10163 
the radiated signal which then actuates the switch, Patent status 
energizing the implanted soriomicrometer. The sono- No patent action is contemplated by NASA. 
micrometer can be turned off by a succeeding 700 
kHz rf signal. Source: Robert D. Lee 
The sonomicrometer and the electronic switch are Ames Research Center 
packaged in a cordwood-type configuration, with the (ARC-10201) 
Brief 7 1-10163 Category 02,05 
C2	 •	 R6 I C3 IC 12 
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Miniature implantable instrument measures and transmits heart function data

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