Circuitry for blood flow and pressure probe

Meehan, J. P.

English

NASA Technical Reports Server

UNIVERSITY OF SOUTHEXN CALIFQRWI 
School of Ltledicine 
2025 Zonal awnst? 
m s  Angeles, California 90033 
Department of Physiology 
27 Hay 1969 
NASA COTPERACT NO. NSR 05-018-087 
PROGRESS REPORT: 
Period covered: O c t o b e r  10, 1968 through April 9, 1969 
During th i s  report ing period the major efforts were concentrated i n  
continued development of implant c i r c u i t r y  such as blood f l o w ,  blood pressure, 
and the development of a data t ransfer  system, 
2. 
3, 
BLOOD PRESSURE CIRCUIT DEWELOPMEMT 
The development of the blood pressure detect ing c i r c u i t  has continued 
in a fashion s imilar  to that previously described i n  the report dated 12 
November 1968. Some refinements have been included and one un i t  packaged 
using large components since some of the  miniature components are awaiting 
Figure 1. 
Figure 2, 
Figure 3. 
Figure 3% 
Figure 4. 
Figure 5 .  
Figure 6. 
Figure 7. 
Figure 8 .  
Figure 9. 
Figure 10, 
Figure 11. 
Figure 12. 
Figure 13. 
Figure 14. 
Figure 15. 
delivery. 
BLOOD FJLOV? SIGhTAL CONDITIONER 
The s ignal  conditioner cons is t s  of the following c i rcu i t s :  
A free-running multivibrator 
A pulsed 5 Plc o s c i l l a t o r  
A delayed plus and minus p o w e r  supply switch 
A delayed plus and minus power supply switch 
A 5 Plc swining amplifier 
A 5 NC peaking amplifier 
A peak detector 
A blood flow probe implant X10 mag. 
Renal a r t e ry  blood f low 
Arterial blood pressure s igna l  conditioner 
Venous blood pressure s igna l  conditioner 
Engineering data, circuit i n  Figrare 10 
Engineering &ita, c i r c i u t  i n  Figure 10 
Simplified venous pressure signal conditioner 
Engineering data from Ffguxe 13 
Engineering data from Figure 13 
3.1 Free Running m l t i v i b r a t o r  
The free-running multivibrator (Fig. 1) consis ts  of a s i l icone  
controlled switch (SCS) which is allowed to  repe t i t ive ly  gate itself 
through an RC charging network, 
reaches 4 . 8 ~  w i t h  respect t o  ground, the SCS gates. When the SCS gates, 
when the voltage on the cathode gate 
https://ntrs.nasa.gov/search.jsp?R=19690019271 2020-03-12T03:16:20+00:00Z
PROGRESS REPORT 
NASA CONTRACT NO. NSR 05-018-087 
-2 - 
27 Hay 1969 
3.2 
3.3 
3 *4 
the voltage at  the cathode w i l l  be applied voltage minus the drop 
across the SCS itself. 
the RC network consisting of the 18K, and the 2200 pf capacitor w i l l  
charge through the diode posit ively,  
the base of the FT709 approaches -5.7v, the t rans is tor  w i l l  begin t o  
conduct. A s  it conducts harder, it draws the SCS cathode gate towards 
-6v and eventually shorts  out the cathode t o  cathode gate voltage 
cut t ing the SCS off.  
the voltage on i51e..o$F capacitor below the necessary gating voltage, 
denying the SCS gating u n t i l  a complete recharging cycle has occurred, 
The RC combination of the 9 1 s  and theL05vf capacitor controls the off 
period of the SCS, and the combination or‘ the 18 K and the 2200 pf ‘ 
capacitor controls the pulse w i d t h  l +  secj-’)( 200.cC sec +n. 
W i t h  the +5.5 vol t s  appearing on the 2Knload,  
When the voltage appearing on 
During the FT709 conduction, the t rans is tor  drops 
Five Nc Osci l la tor  
The 5 Mc esc i l l a to r  (Fig. 2) is a conventional Colpi t ts  o sc i l l a to r  
w i t h  the exception that it is pulsed on by the SCS multivibrator 
described i n  Para. 3.1. Also, the col lector  load has been designed 
as the primary of a toroidal  transformer which t ransfers  the %IC pulse 
t o  the crystals of the flow probe. 
Delayed Power Switches 
The delayed power supply switch (Fig. 3) consis ts  mainly of a 
delay circuit and 2 SCS switches, one i n  the posi t ive and the other 
i n  the negative supply leads. The delay c i r c u i t  operates as follows: 
When the SCS switch (Fig. 1) generates a pulse, it is channeled 
through the diode and is deposited on the 3300 pf capacitor. 
charge is held after the input pulse is gone by the diode being backward- 
biased. 
supplying charging current t o  the gating c i r c u i t  of the posit ive supply 
switch. 
voltage across the SCS load i n i t i a t e s  three d i f fe ren t  things,  One, it 
gates the negative supply switch a l m o s t  ins tant ly  (Pig. 31, ‘(two) it 
supplies posit ive power t o  the amplifiers; and (three), it supplies 
charging current t o  the base c i r c u i t  of the  FT709 connected-across-the- 
storage capacitor (3300 p f ) .  
The 
Now the 3300 pf capacitor is essent ia l ly  a +5.5v battery 
Once the posit ive supply switch has gated, then the posit ive 
With the posit ive supply switch on, there is no longer any need fo r  
the voltage stored on the 3300 pf capacitor. If the voltage w a s  allowed 
t o  remain on the capacitor, then the SCS would continue t o  gate itself 
and this would introduce undesirable data on the output of the s ignal  
conditioner. Therefore, tlie t rans is tor  connected-across-the-storage 
capacitor is biased on through the diode and a 2.2 
the charge on the capacitor. 
pulse on the input. 
k r e s i s to r  depleting 
Now the delay c i r c u i t  is ready fo r  another 
Five r k  Summing Amplifier 
The first amplifier consis ts  of an RCA 3016 integrated c i r c u i t  
(Fig, 4 ) .  The amplifier connected i n  the configuration of a noninverting 
high gain amplifier works very nicely as a summing amplifier for  the 
5 II4c simals a m a r i n a  a t  each crystal. The a m D l i f i e r  is sated on bv the 
pROC333SS REPORT 
NASA COJTJXUiCT NO. NSR 05-018-087 27 lalay 1969 
4. 
5. 
3.5 
3.6  
power supply SCS switches. 
on only during that ins t an t  when the  5 PSc return appears a t  the 
summing input of the  amplifier. The reasons fo r  this is (1) t o  
prevent amplifier saturat ion,  and (2)  f o r  ultimate s ignal  definit ion: 
and (3)  to  conserve power. 
It is desirable t o  gate the amplifier 
Five PIC Peaking Amplifier 
The peaking amplifier c0nsiss;S of an RCA 3016 integrated circuit 
(Fig. 5). 
zer0-crnao.i-y detector, and being gated on only during the 5 Ilc signal  
= turn ,  the amplifier w i l l  de tec t  the  phase-shifting cycle and produce 
a pulse varying i n  amplitude d i r e c t l y  proportional t o  d i f f e r e n t i a l  
blood flow. 
tJith the amplifier connected i n  the configuration of a 
Peak Detector 
The last stage of the s igna l  conditioner cons is t s  also of an 
W-3016 (Fig.6). As the  output s igna l  of the second amplifier 
consis ts  of a Wain of pulses approximately . 2 ~  sec wide and having 
an in te rva l  of 
amplifier connected i n  the configuration of a noninverting peak 
detector.  
s ignal  d i r e c t l y  proportional to the blood flow being measured. 
200 p sec, it is necessary to  use an operational 
The t r a i n  of output pulses are now conver.tsed t o  an analog 
S-ry 
With the exci ta t ion osc i l l a to r  and the  s tages  of amplification and 
detection being gated on for  only a 
consumption is qu i t e  low compared to conventional methods of blood flow 
detection. 
.5% duty cycle, the  total power 
BLOOD FLOW C3XCUIT PFSLD'IZNARY TEST 
To tes t  the c i r c u i t  described i n  Para. 3 ,  a dog was  implanted with a 
modified commercially-available blood flow probe. 
around the rena l  a r t e ry  of a large dog as i l l u s t r a t e d  i n  Figure 7. A 
sample of the resu l t ing  da ta  is displayed i n  Figure 8 .  
The probe was connected 
BLOOD PRESSUTRF: CIX?JITS 
Two low power blood pressure s ignal  conditioning circuits are nearing 
a f i n a l  stage of development. 
miniature low power operational amplifiers have been ordered f o r  use i n  a 
f i n a l  packaging. The use of the newly designed osc i l l a to r  w i t h  minia ture  
components w i l l  r e s u l t  i n  a s igna l  conditioner approximately the s i z e  of a 
1/3 inch cube. 
biopotential  amplifiers of nearly the same physical s ize .  
channel telemetry system tiill  thus occupy approximately 1/2 of a cubic inch 
not including power supplies. The current  drain w i l l  be approximately - +200pper channel for a t o t a l  d ra in  of - + 1200p a for  a six channel system. 
Prototype uni t s  have been packaged and 
S l igh t  modifications t o  the basic osc i l l a to r  can produce 
A typical  s i x  
PKoGReSS REPORT 
NASA CONTRACT NO. NSR 05-018-076 27 Hay 1969 
-4 - 
5.1 Arterial ~ l o o d  Pressure System 
Due to  higher pressure i n  the arterial systemf higher leve l  s ignals  
can be obtained from the pressure sensors than can be obtained from the 
venous system. 
less gain i n  the amplifying system and r e s u l t s  i n  p o w e r  and s i z e  
savings. Figure 9 i l l u s t r a t e s  a signal  condition c i r c u i t  diagram f o r  
f o r  a recently developed arterial pressure signal conditioner. 
Temperature and voltage s t a b i l i t y  is qui te  good due t o  the small number 
of components and the use of the high qua l i ty  operational amplifier, 
Some work remains t o  be completed on t h i s  u n i t  before f i n a l  use is 
possible. 
This fortunate condition renders it possible to employ 
5.2 Venous Signal Conditioner 
The c i r c u i t  fo r  one type of venous pressure system is depicted i n  
Figure 10, 
pressure conditioners due to  the decrease sensor output. 
data on th i s  system is presented i n  Figures 11 and 12 ,  
of th i s  amplifier is also qu i t e  good. 
of the same o s c i l l a t o r  is presented i n  Figure 13. 
been removed, resu l t ing  i n  fewer c i r c u i t  components. Engineering data 
f o r  t h i s  c i r c u i t  is presented i n  Figures 14 and 15, 
that both systems have been cal ibrated fo r  a fu l l s ca l e  output fo r  
300 mmHg, To obtain s e n s i t i v i t y  for venous fu l l s ca l e  f o r  50 InmI-Ig, 
gain of the amplifier is increased by approximately 5 .  
supply f o r  both systems is good. A one v o l t  supply voltage produces a 
frequent change on the order of 2% of fu l l sca le .  
Additional c i r c u i t r y  is required r e l a t ive  t o  the arterial 
Engineering 
The s t a b i l i t y  
A somewhat simplified -vefs ion 
The t r ans i s to r  has 
It can be noted 
voltage s t a b i l i t y  
6. F U T W  EFFrnTS 
The effort during the next f e w  months w i l l  be directed mainly toward 
t e s t ing  the c i r c u i t r y  described by performing animal tests, 
Principal Investigator 
BLOOD F L O W  
F R E E  RUNNING MULTIVIBRAJOR 
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BLOOD FLOW 
PULSED 5 M C  O S C I L L A T O  - R 
vc C “0 roRRolo CORE 
B L O O D  FLOW 2 
D E L A Y E O t 6 V  SWITCH 0 
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- 22K 
B L O O D  FLOW 
S L A V E D  Vee S W I T C H  
3460 
2.2 
C O M M O N  
B L O O D  F L O W  
FIRST A M P t l F I E  R 
B L O O D  F L O W  
SECOND AMPLIFIER 
(+--#-- 
FROM ZED 
M P i i  FIE R 
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4 7  K 
Ve e 
B L O O D  F L O W  
PEAK D E T E C T O R  
4 
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Department of physiology Progress report, 10 Oct. 1968 - 9 Apr. 1969

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