Circuits, components, and implant site evaluations for arterial blood pressure analyses on primate

Meehan, J. P.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19690005259 2020-03-12T07:51:35+00:00Z
ntSilVMITY OF SOOTSSRN CALIMPNIA
School of Medicine
2025 Zonal Avenue
Los Angeles, California 90033
Department of Physiology
12 November 1968
NASA COMACT NO. NSR 05-018-087
QUAR'1MY PROGRESS REPUEtT:
Period covered: July 10, 1968 through October 9, 1968
1. SUMMARY
Daring this reporting period major effort was concentrated in
circuit development, acquisition of components, experimental evaluation
of implant sites and tentative scheduling. Three of the major circuits
are either in the prototype packaging or in the final breadboard stage.
The basic planning has been established based on a one year contract,
however, the change from one year to 18 months is being considered,
as shown in Table 1.
2. PLANNING
Table 1 illustrates the major flow pattern of the contract. The
essentials comprise the development of the following: Blood pressure
signal conditioning systems, blood flow signal conditioning systems,
implant cases, auxiliary circuits (such as biopotential signal condition
switches) and an integrated design and specification.
As indicated by the flow chart, the approach is to develop equipment
for each parameter, then test its operation, independent from other channels.
'When satisfactory results are obtained with each parameter, an integrated
system will be fabricated and tested.
Upon obtaining satisfactory operation of a two-channel implant
(approximately late December, 1968) several two-channel implants will be
fabricated and tested in February, 1969, In March, April and May, 1969,
a three-channel implant (blood flow, blood pressure and biopotential)
will be fabricated and tested.
Paralleling the hardware development, a system design review will
be conducted in early 1969 and circuits specifications written for sub-
contracting. It is anticipated that a proposal will be disseminated to
obtain a three-channel implant of a flight nature. These systems wo 	 b
used for further evaluation during June, 1969.	 .16111819
N'69-14591
#WOMON NWAW
	 (TRU)
ck tr	 c Erob	 o
oa	 (u	 )
s
 t
•	 t
QY TVAXWSS gas DO
NASA COCA V NO.
	 N81t 05-018-087	 -2--	 12 November 1968
TABLE	 1
TII$ IWINWAL TENTATIVB ACTIVITY STAFF
*E	 *M
July - Sept. 1968 Contract Organization 3	 2
Circuit Development
implant Site Investigation
Oct. - Dec. 1968 Circuit Development 3	 2
Preliminary Individual Circuit Testing
Development of Cases for Implanting
Preliminary Implant Tests
Jan. - March 1969 Circuit Changes, Etc. 3	 2
Specification Generation for Circuits
Integrated System Development
Major implants (Single Channel)
April -- June 1969 Circuit Modifications 3	 2
Single Channel Implants
Generation of System Specifications
Integrated System Implants
Generation of Request for Proposal
Issue Subcontract (Tentative) 3	 2
July - Sept. 1969 Modification of System 3	 2
Integrated System Implants
System Design Evaluation
Generation of Flight Experiment Plan
Oct. -Jan. 2970 Testing of Final Three-Channel Implant 3	 2
System
Circuit Specifications
* E = Engineering
* M = Medical
QUARTERLY PROGRESS REPORT
NASA CONTRACT NO. NSR 05-018-087 	 -3-	 12 November 1968
3. BLOOD PRESSURE CIRCUIT DEVELOPMENT
The primary design goals considered in the de"lopment of a blood
pressure detecting system were low power operation, small size and
reliability. The low power requirement necessitated the use of a low
bridge drive current, thus making it necessary to use a high-gain D.C.
amplifying system.
The high-gain D.C. amplifier is not commensurate with stability.
Therefore, in order to maintain stability, yet obtain low power operation,
a chopper type amplifier is required.
Figure 1 illustrates the prototype of the resulting circuit. It
consists of the basic parallel-T oscillator, a switching transistor and
an A.C. amplifier. The oscillator output drives the chopper transistor
Q1 to produce a chopped current to the resistive pressure sensor.
The differential amplifier integrates and amplifies the square wave
output from the bridge. The output of this amplifier is then subtracted
from the primary feedback through the parallel-T network by the action of
the differential operational amplifier. The result of this subtraction is
a violation of a condition for oscillation; to re-establish this condition,
the frequency of the oscillator changes. The end result is direct frequency
modulation proportional to the pressure input.
Total power requirement is low, on the order of 300 µ a at 6 volts.
Packaging can be extremely small due to the small number of components and
the use of flat pack operational amplifiers.
4. BLOOD FLOW SUMMARY
Blood flow measurement typically requires the use of rather large
power-consuming devices, thus limiting its applicability to continuous
use. Therefore any system intended for'continuous use bust bd designed to
eliminate the large power consumption.
The typical systems currently used are the electromagnetic and the
ultrasonic. The electromagnetic provides more accuracy at the expense
of large power consumption, while the ultrasonic is adaptable to low
power design but does not measure as accurately.
For our initial effort we have used the ultrasonic technique. This
system is now in the prototype breadboard stage undergoing bench testing.
The essentials of operation are as follows: An oscillator is triggered on
for approximately 1 microsecond with a free-running switch, exciting
both crystals simultaneously at the same level. After cessation of the
excitation, each crystal is affected by the energy conducted from one
crystal to the other. If there is no blood flow, each crystal has the
same voltage level and the sum is zero. However, if there is a flow,
the addition of the cross-coupled energy is enhanced in one crystal and
decreased in the other and the sum is not zero.
vIL
air ^
N ^^
he
b
> 4N Q
^^ 8
M
b
w
^
^ u
^ b
aa
a
y
Y
O
^ Y Y	 ^
wt tr
'Ins
	
p
Y
IL
N
on
v4
M 11► 	 N Q
O
V
Yp O
rl
Y
CO sin
Y
O h
r
O Q' a 4 ^
a ^ cQ
i
Y
O
Q
to
Y
Tv^
N
QUM1TERLY PROGRESS REPORT
NASA CONTRACT NO. NSR 05-018.087 	 12 November 1968
-4-
It is necessary, however, to control the timing of the events
since it takes several microseconds to transmit the energy from one
crystal to the other. The reflected uignal requires approximately
6 to 8 microseconds to appear on the cross crystal, therefore, the
amplifier is gated approximately 6 microseconds after the crystal is
excited and remains on for approximately 1 microsecond. The effect
of the blood flow, then, is to amplitude modulate the input to an
amplifier. After suitable amplification, the amplitude modulation is
peak detected to recover an analog signal of blood flow.
4.1 BIAOD FLOW BLOCK DIAGRAM
Figure 2 illustrates the block diagram of the blood flow
signal conditioner.
Switch Sl
 activates the 5 megahertz oscillator for 1 microsecond
each 200 microseconds. The activation of the 5 megahertz oscillator
excites both crystals with a 12-volt peak-to-peak sine wave signal for
a period of 1 microsecond. The excitation sends a burst of energy from
one crystal to the other within approximately 6 microseconds. The
relative phase of this energy is modified by the blood flow during
transit and, therefore, the voltage measured from point A to B varies
in amplitude proportional to the phase difference.
Assuming there is no blood flow, the energy reflected from crystal
A requires 6 microseconds to reach crystal B, and that from crystal B
requires 6 microseconds to reach crystal A. Therefore the amplifiers
Kl and K2 are gated at 6 microseconds after the oscillator is gated.
The amplifiers are gated off after 7 microseconds to avoid detecting
and amplifying the second reflected signals from the crystals. Amplifier
K3 peak detects the amplitude modulation signal and produces an analog
signal of the blood flow.
S. IMPLANTED TRANSMITTER POWER COMMOLLER
Since it is unwise to design low-current circuits when stability
is of major importance, an alternate method must be found to conserve
power.
Controlling the transmission time to approximately 5 % is one
technique to alleviate the problem. Continuous transmission is not
generally beneficial in a space application since the ability to recover
data continuously is absent. Analyzing this much data is also a rather
formidable task.
A 5% duty cycle will allow data capture of 4 1t minutes for each
orbit, which is the typical available data capture time. Thus an
efficient operation would be to activate the implanted transmitter by
command upon the spacecraft's entry into the data capture zone, and
to design the switch to automatically deactivate at the end of 5 minutes.
Transmission could be activated upon the craft's entry into any data
capture zone; thus spot checking the animals woule be possible if necessary.
N
V'j
N
m
YIW
IQv^
^iwv
?^I
OW
v? Z
O^
>o►. J
OtW
z
QUARTEMY PROGRESS REPORT
NASA CONTRACT NO. NOR 05-018-087
	
12 November 4968
-5-
it might be of further benefit to design the control device with
two modes of operation, i.e., (1) command activation with automatic
deactivation (2) command activation with command deactivation. The
two-mode operation would be beneficial in ground testing where a 4h
minute interval is inac:eruate to completes the experiment and, on occasion,
it might be required for obtaining more than a 5 minute continuity of
data during flight. Such a possibility might occur if there was an on-
board recorder and it was desired to obtain data on the recorder during
certain tests. Such a switch would require three commands:
(1) Command ON -- automatic OPP
72) Command ON -- continuously
(3) Command OFF
Currently the control being designed and used is of the two-command
variety, i.e., command ON continuously and command Ott'. The ON command
is initiated by a 250 =-conducted signal and the command OFF by a
500 IOC-conducted signal. Investigation of a three-command control will
also be considered.
5.1 SWITCHING TECHNIOUE
Since it is difficult to radiate energy to a subject at any
distance from the command source, it is suggests* that under certain
circumstances the command frequencies actually be applied directly to the
animal,.
A possible technique would be to condition the unrestrained animal
to grasp the electrodes which would inject the command signal directly
into the subject. The command signal's presence on the electrode would
be established by ground command and the animal could be cued by an
audio or visual signal slaved to the 99bund command.
This me*liod hays the disadvantage of disturbing the animal before
each recording session during an unrestrained type of experiment.
Consequently, a technique for transmitting high energy signals to the
animal must be established when it is necessary not to edsturb the
animal. For a restrained experiment a permanent electrode could be
positioned to be in contact with the animal at all times.
QUARTERLY PROGRESS REPORT
NASA CONTRACT NO. NSR 05-018-007 	 12 November 1968
-6-
5.2 SWITCH OPERATION
The circuit is centered around a device (3N84) which is
basically a four layer semiconductor that operates on an avalanche
principle (Figure 3). This type of device is highly desirable for
power switching due to its low output impedance and very fast rise and
fall times. The only problems encountered in the configuration of a
power switch is that of gating the device off. When the device is on,
the impedance looking into the gate is approximately 100 n using about
a 1 K n, load at 6 V DC. This necessitates the use of a high gain
amplifier in the off gate situation. In the on gate situation the gate
input impedance is very high and only requires about 10 p a for gating.
Once the gating requirements have been met DC wise, then the timed
circuits for the ON gate and OFF gate were easy to design. The timed
circuits in either case are r---rely a LC tank circuit turad to two
separate frequencies far enough apart to avoid accidental gating.
Coupling to the ON and OFF gate amplifiers was accomplished with
AC coupling and clamping.
6. RESULTS
The results of the first three monthh I s effort has been mainly
the design and development of the blood pressure and blood flow signal
conditioning systems. This work is of paramount importance since
simultaneous application of these two measurements permits determination
of the peripheral resistance component of the cardiovascular system.
The ability to obtain these two parameters continuously by using implanted
equipment is nearing realization. Instantaneous low power operation linked
with a 5% duty cycle of transmission theoretically will allow several months
of data acquisition.
7. FUTURE EFFORTS
During the next three months work will continue on the
development of blood pressure and blood flow signal conditioning systems.
original Copy Signed
Ik AMD P. Mahrn, M.D.
John P. Meehan, M.D.
Principal Investigator
C4
IL .^
V
h
w
O
e^ w
^^ 3
O M Id
^j
i4iWZb	 71
2
ZO
On^
to
N
^	 Z
1^	 N
d
rI
P4
so
N
u	 ^
i
2k
^O
J	 J	 O N
t^
t/
t
r


Observation of arterial blood pressure of the primate AAP-Bio-A-1 Quarterly progress report, 10 Jul. - 9 Oct. 1968

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server