Low power blood flow transmitter to determine cardiovascular response to weightlessnes

Casados, L.

Henriksen, J.

Meehan, J. P.

Rader, R.

English

NASA Technical Reports Server

UNIVERSITY OF SOUTIBRN CALIFORNIA 
N. 
I School of Medicine 
' - ' 1 2025 Zonal Avenue - N A g  CR109872 
I Los Angeles, Cal i fornia  90033 
Department of Physiology 
NASA CONTRACT NO. NSR 05-018-087 
fi June 1970 
PWGRESS REPORT 
Period Covered: March 1, 1970 t o  May 31, 1970 
SUMMARY 
During t h i s  reporting period the  major e f f o r t s  were directed toward 
evaluating and testing blood flow c i rcu i t ry .  A dog was implanted t o  
evaluate the flow probe and c i rcu i t ry .  An implantable u n i t  fo r  use on a 
large primate w a s  fabricated and readied f o r  implant. A complete analysis 
of the approach w a s  conducted and prepared fo r  publication. An abs t rac t  
on implantable biological  instrumentation was presented a t  the 1970 
National Telemetry Conference held i n  Los Angeles April 27-30. 
Dog Implant 
On April 15, 1970, a small Beagle dog was implanted with a 5 m flow probe 
on the terminal aorta. The flow probe leads were exposed on April  26, and 
connected t o  external  blood flow electronics.  Data were recorded periodically 
u n t i l  April 30. On May 1, the flow probe leads were placed subcutaneously. 
The system was again tes ted on June 1, and found t o  be qu i te  operable. The 
dog w i l l  be maintained fo r  several  months i n  order to evaluate the a b i l i t y  
of the probe t o  susta in  long term implant. 
https://ntrs.nasa.gov/search.jsp?R=19700024754 2020-03-11T23:11:57+00:00Z
15 June 1970 
PROGRESS REPORT 
NASA CONTRACT NO. NSR 05-018-087 
-2 - 
Preparation of Publication 
It is f e l t  tha t  thin technique of acquiring flow data is suff icient ly 
unique t o  m e r i t  publication. Accordingly a paper is being prepared which 
describes the merits of t h i s  approach. A copy of the f i r s t  d ra f t  of t h i s  
paper is attached. 
In April an abstract on implantable biological instrunentation was 
presented a t  the National T e l e a t r y  Conference. A copy of t h i s  abstract 
I is also attached. 
John P. Meehan, M.D. 
Principal Investigator 
A LOW POWER BLOOD FLOW TBANSMI'lTER 
by 
Rader, R., Henriksen, J., and Meehan, J. 
Department of Physiology 
University of Southern Cal i fornia  
School of Medic h e  
INmDUCTION 
Until the  maturation of biotelemetry techniques, acquisi t ion of chronic 
physiological information from unrestrained test subjects  was severely limited. 
The umbilical connection between the  test subject  and a recording device 
precluded many types of experiments. In  many cases biotelemetry techniques 
have not produced acceptable experimental conditions. The presence of bulky 
equipment on the subject  and the need t o  protect  the  equipment from the subject  
has r e s t r i c t ed  its application.  The des i re  t o  el iminate these problems and 
produce improved experimental conditions has prompted the  development of an 
extremely l o w  power, s m a l l  s i z e ,  t o t a l l y  implantable blood flow telemetry system. 
For this e f f o r t  an ul t rasonic  technique was selected because of several  
cleaxly iden t i f i ab le  advantages. As contrasted with the  electromagnetic 
techniques, the ul t rasonic  flow sensing probes a re  l i gh t e r ,  power requirements 
a re  l ess ,  zero s t a b i l i t y  is be t t e r  and the s igna l  l eve l  is higher. 
now CONCEPT 
The block diagram i n  Figure 1 i l l u s t r a t e s  the  system operation. Piezoelectr ic  
I crys ta l s  resonant a t  5 MHz a re  r i g id ly  positioned diagonally across a flow s e c t i m .  
c rys ta l s  are e l ec t r i ca l l y  pulsed simultaneously i n  phase opposition fo r  
I 
v- 
w approximately one microsecond. Acoustical energy gene>a-d at each crys ta l -  
f 1 Iinterfi is directed toward the  o ~ p o  ite ( 
I - .  k 
the energy t o  cross from each c rys t a l  t o  the < t ) r c  
stal. The time required fo r  
is proportional t o  the * 
distance between c rys t a l s  and the mayni t lde and d i rec t ion  of the flow velocity.  b 
If the flow is zero the time i red  for , accoustical  energy t o  a r r ive  at k- - 
7 t h e ~ r . ~ ~ - - -  remains i n  phase opposi t i k . 2  I 
not zero and directed t o  the r i gh t ,  the  energy from X1 t o  X2 a r r ive s  i n  advance 
of t h a t  from X2 to  X1, r esu l t ing  i n  a phase s h i f t  and non-cancellation of the 
c rys t a l  voltages. Specif ical ly ,  i f  the c r y s t a l  exci ta t ion voltages are: 
Vxtr = VMAX COS cu f 
V x z ~ = - V m ~ x  Cosw f 
then the resonant c r y s t a l  pickup voltages are: 
where is the angle i n  radians a t t r i bu t ab l e  t o  the flow veloci ty  and Y 
a constant angle a t t r i bu t ed  t o  the probe geometry. The constant K is 
- - 
related t o  at tenuation proper t ies  of the mediam, t o  distance,between 
and t o  the Q of the crysta ls .  
I f  the  two pickup s igna ls  are added as i l l u s t r a t e d  i n  Figure 1, the r e s u l t  is 
where Ao is the amplifier  gain. The magnitude of the  s ignal  voltage is thus 
a function of Sin 0 , The value of and y can be derived by consideration 
of the geometry and the  flow velocity,  In  par t i cu la r  the t i m e  required f o r  
energy t o  rad ia te  from XI to X2 i ~ ;  
Where C is the  veloci ty  of the accoustical  energy i n  the mediamd is the angle 
between the flow veloci ty  and the energy direct ion,  is the veloci ty  of blood flw 
and D the perpendicular distance bet-sn c rys t a l  faces. Division or 
By the valid assumption that V CO S < / C  <4 I 
the higher power terms can be neglected to give 
The tota l  phase s h i f t  between crystal  X2 pickup signal and a continuous wave 
signal allowed to continue on the same time axis  is: 
theref ore : 
and thus: 
The output voltage then becomes: 
For convenience l e t :  I 
A o Z k V ~ d g  ~ / ; v  &dtr r o s s  - sle 
The fac tor  w g a constant phase re la ted t o  probe dimensions and exci ta t ion 
C 
frequency,contributes no useful  information. 
The function w d ~  C O S ~ ( / C %  
contains the useful infonnation and produces amplitude modulation of the s ignal  
proportional to the s i n  of the function. For a low value of veloci ty  the phase 
s h i f t  produced is small allowing s i n  0 t o  be replaced with 0 ,  
The s igna l  l eve l  then becanes: 
L 
For typ ica l  probes and prac t ica l  probe exci ta t ion voltages the value of K Vmax 
has been found to be approximately 0.5 vol t .  The value of K1 thus becomes 
approximately 0.3 x 10'~. The s igna l  is then: 
e For flow measurement on a 1 cm diameter vessel ,  a 30 mv s ignal  can be realized.  This can be contrasted with an electromagnetic level  of 0.3 mv f o r  the  same posi t ion and a pickup s ignal  on the order of 1 0 y V  f o r  the  back sca t t e r  u l t rasonic  technique, The select ion of the 180 degree quiescent phase 
difference between the pickup voltage r e s u l t s  i n  the  maximum sens i t iv i ty .  
I f  the flow veloci ty  exceeds the value which make 8 s  77,/2 the flow 
veloci ty  becomes indeterminate. I n  pract ice ,  the flow velocity is qui te  low, 
producing a maxihum phase s h i f t  of less than 0.1 radians. 
' I w  
Negative flow can he de 
4 placed i n  para l le  1 w 
zted by proper c i r c u i t  manipulatic A capacitor T* ler a summing resis-EiEr' o r  'a-urrent lmi t in 'q  resistox 
i n  the probe dr ive  c i r c u i t  produces a phase &if$ ?$ z s o  =ow2 Ts. produces 
---- - a mla- 
an output s igna l  a t  zero flow which increases w i t h  poelt ive flow and decreases m 
with reverse o r  negative flow. 
Flow C h c u i t  
The c i r c u i t  required t o  perform the operation i l lus t ra ted  i n  Figure 1 is 
shown i n  Figure 2. The output of a subcarrier osci l lator  is connected t o  the 
cathode gate of SCSl. When the gate voltage rises above 0.7 v o l t  SCSl turns 
on and forward biases the 5 mc oscilLator t ransis tor  Q2 and the 5 mc power 
amplifier t ransis tor  Q1. Coincidental with the SCSl turn on capacitors, I.
C7 starts to  charge through R12. When Q3 is suff icient ly forward biased, 
SCSl turns off leaving a change on C9 which bleeds through R1 5 turning on 
SCS2. This turns on the amplifier t ransis tor  QB, 97, QQ, and Qg, just  prior 
t o  th@ arr iva l  of the incident acoustical energy a t  each crystal. The on 
time of the amplifiers is controlled by the time constant determined by It20 
and C l q .  The RC network connected t o  the emitter of Qg r ec t i f i e s  and f i l t e r s  
the amplified RF signal producing a D.C. signal proportional to flow velocity. 
The output is then connected to the subcarrier osci l lator  t o  produce frequency 
modulation proportional to flow velocity. The output of the subcarrier osci l lator  
is also connected t o  a car r ier  osc i l la tor  operating a t  230 mr: t o  ef fec t  
transmission of the flow velocity signal. Due t o  the nature of the response 
there is an inabil i ty  t o  different iate  the direction of flow by observing the 
output. For an ideal case where the crystals  are w e l l  matched and the slmrming 
resistances are equal, the response curve w i l l  be as i l lus t ra ted  a t  the top 
i n  Figure 3. ~y paralleling ~1 w i t h  a small capacitor the pickup signal on 
X2 leads the pickup signal on X 1  and thus for  zero f l o w  there appears t o  be a 
flow from XI toward X2. The response curve for  this condition is i l lustrated 
at the bottom of Figure 3. A t  zero flow there is a positive voltage getting 
more positive for positive flow and less  positive for reverse f l w .  Since 
GO acquire 
legative flow is quite small, only a s l ight  adjusbnent is required 
reverse flow. . 
The pulsed operation which is necessary far proper functioning a l so  
minimizef3 current consmption. For the c i r c u i t  i l l u s t r a t ed ,  the current  
cansumption is approximately 4 0 0 . ~  a. A prototype c i r c u i t  package is  shown 
i n  Figure 4. In this package an 18 v o l t  supply with a 12 v o l t  regulator has 
been emplupd. 'Phh flow probes employed have been ccmmercially available 
un i t s  modified f o r  our par t icu la r  use. The recordings i n  Figure 5 i l lustrate 
the r e s u l t s  of the i n s t rmen t  application on a small beagle dog. The flow 
probe was implanted on the terminal aorta and allowed to  heal f o r  several  
days then the  connector was exposed and connected t o  an external  instrunent 
package which was contained i n  a small  jacket. 
(This work is supported by NASA CONTRACT NO. NSR 05-018-087) 
2 
- 81 RIN ,Rf - ~t (e l tea 
* 7 RIN PULSE 
GENERATOR 
4 RECTIFIER 9 AND 3 
eo AND m 5MHo FILTER € 0  OSCILLATOR --u, = 
A 
- 
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- GATE PULSE 
- - 
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2 
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FLOW 
4 
1 K 8 . a  
2 CRYSTAL XI 
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CRYSTAL Xt  
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4 ,  OUTPUT 
BLOOD FLOh BLOCK DIAGRAM 
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FLOW VELOCITY (0)  0 FLOW VELOCITY It) 
FLOW VELOCITY  ( -  ' 0  FLOW VELOCITY (+) 
x *  - X I  X I  - x 2  
F
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4.
 
Figure Number 5 a 
Subject Name & Descript;ion ltFlo't Canine 
Date & Time 
Recording Speed 
Recording Condition 
H e a r t  Rate 
Resting Night 
F ~ O W  Level (Relative) 
, 8 ,  
i l l  
: i i !  I : (  
- 
-- 
Figure Number 
Subject Name & Description 
Date & T h  
8 .. 
'i d L I . Recording Speed 
Recording Condition 
Heart Rate 
"Flow Canine 
Resting Day 
 low Level (Relative) 
5 c Figure Nlzaber 
Subject Name & Description "Flo" canine 
Date & T h e  6-2-70 1115 
Recording Speed 2 d s e c  
Recording Condition motional Arousal 
Heart Rate 210 BPM 
Flow Level (Relative) 
Figure Number 
Subject Name 6r Description "Flow Canine 
D a t e  & Time 
Retcording Speed 
Recording Condition 
Heart  ate 
Feeding 
Flow Level (Relative) 
Figure Number 
Subject Name & Description 
D a t e  & Time 
Recording Speed 
Recording Condition 
mart Rate 
Flow Level (Relative) 
Canine 
, . I .  
Figure Nlnaber 5 f 
Subject Name & Description "Flo" Canine 
Date & T h  6-2-70 1422 
Recording Speed 10 d s e c  
Recording Condition post Treadmill Training 
Heart R a t e  237 BPM 
Flow Level (Relative) 2 0 
Figure 6: Svstem Calibration 
,r 
-* 
An approximate caliaratlon was pgrronaea ~y expeulng mown 
volmes from a syringe in a period of one second. The results 
.. .! 
are shown in the tracing. The sensitivity is approximately 
2 ml/div. SENSITIVITY = 0.1 volt per divisjon, 
L- -J.i 
TRANSMISSION OF CARDIOVASCULAR RESPONSE TO WETGXTLESSNESS 
Rader , R. , Meehan , J .P . , ~ e n r i k s e n  ,J . , Casados .L. 
Department of physiology, University of Southern ~ a l i f o r n i a  
815 W. 37th Stregt, Los Angeles, California 90007 
Pressures, flowr and dimensions chsracterize cardiovascular dynamics. 
An implantable systbm senaing these three parameters has been designed fo r  use 
on the apollo application@ program t o  determine cardiwascular  reeponses of 
sub-human primates t o  l m g  term weightlessness. The use of a 160 ma hour 
battery with an average current of 500 U a  per data channel and a duty cycle of 
2%, r e su l t s  i n  an operating l i f e  of 250 days. 
Blood pressure is detected by a miniature implantable sensor which is 
driven by a sine wave osc i l l a tor .  The output of the sensor is connected t o  a 
d i f fe ren t ia tor  to achieve amplification and a 90 degree phase sh i f t .  The 
di f fe ren t ia tor  output is s\rmmed with the primary feedback t o  prodwe frequency 
modulation proportional to  pressure. Blood f l w  is detected by an ,u l t r amnic  
technique. Two crya ta l s  placed diagonally across a blood v e s m l  are driven 
180 degrees out  of phase by a pulsed 5 mHz osc i l la tor .  Uhder conditions of no 
flow, the sum of the c rys t a l  voltages is zero because the t r a n s i t  time from one 
to the other c rys t a l  is equal and no phase difference ex is t s .  When there is flow, 
the s ignal  on the c rys t a l s  d i f f e r s  i n  phase due t o  unequal t r a n s i t  times and the 
suxmed s ignal  is not zero. The amplitude modulated s ignal  is  r ec t i f i ed  t o  yield 
a voltage analog of blood velocity. Knowledge of the probe diameter is su f f i c i en t  
t o  yield blood flow. Vascular dimensions are  a l so  deterutined by ul t rasonic  
techniques. One crys ta l ,  placeQ on the vascular s t ructure ,  i s  excited with a 5 
mHt pulsed osc i l l a tor  and the t r a n s i t  time of the energy t o  the second c rys ta l  on 
the same s t ructure  is measured. The knowledge of velocity of ultrasonic energy 
i n  t i s sue  and body f lu ids  is su f f i c i en t  t o  obtain dimensions. 
I 
(This work was supported by NASA CONTRACT NO. NSR 05-018-087) 


A low power blood flow transmitter. Transmission of cardiovascular response to weightlessness Progress report, 1 Mar. - 31 May 1970

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