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Fiaure 15. Puff amplifier circuit diagram.

16


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Fieure 6. Recording of alternating diastolic and systolic blood pressure measurements.

10


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Fieuse 20. And circuit diagram.


A DEVICE AND METHOD FOR RAPID INDIRECT MEASUREMENT OF
HUMAN SYSTOLIC AND DIASTOLIC BLOOD PRESSURES

I. Introduction.

Aeromedical research studies often require the
assessment of blood pressure as a reflection of
physiological reactivity. In many such studies,
measurements of the dynamic blood pressure
transients are desirable. Although arterial
catheterization provides a direct access to the
dynamic measurement of human blood pressure,
this procedure carries inherent medical risks
which are not warranted for our useTM*. A device
and method for rapid indirect measurement of
blood pressure were therefore sought from com-
mercial sources. Since they were neither avail-
able nor forthcoming, it became necessary to de-
velop them ourselves. The complete rationale
and evaluation of this device and method have
been reported previously *. This report will deal
mainly with the method of measurement and the
components, construction and technical operation
of the device.

II. Device and Method.

Figure 1 shows the control panel of the ap-
paratus. In general, it consists of two identical
units, each serving one of the two brachial cuffs
shown. Each unit is capable of measuring either
systolic or diastolic pressure continuously or both
pressures alternately, by invoking a manual
switchover control. The aneroid gauges shown
may be used optionally to calibrate the pressure
transducer in each unit or to monitor visually
the respective pressures during each measurement
eycle. Figure 2 shows an overall view of the
internal assemblage. The individual circuit
boards were mounted vertically for compactness
of design and easy service accessibility. For
later reference, note the plastic, low pressure
reservoir and, below it, the battery modules for
powering field experiments. The remainder of
this section will deal mainly with the details of
the measurement cycles and their regulation.

The measurement cycles can be described best
by viewing a single, rapid tracing of one systolic
and one diastolic measurement, as shown in
Figure 3. Point A in each tracing marks the
initiation of cuff inflation by manual switch
activation of each unit. Appropriate valving
thereby is opened to provide a constant 6-psi
source of compressed air to each cuff via a plastic,
low pressure reservoir. Point B in each tracing
marks the end of the rapid, cuff inflation portion
of each cycle. At this point, a pressure limit
switch, which can be set at any desired pressure,
activates a relay for the initiation of the next
portion of the cycle. For the systolic cycle, this
next portion consists of a slow deflation bleed
and, for the diastolic cycle, a slow inflation bleed.
The bleed rates occurring between Points B and
C in each tracing can be set at any desired value
commensurate with the measurement accuracy
and measurement rate requirements of the par-
ticular experiment being conducted at the time.
The slow bleed in each tracing is the pressure-
seeking portion of the cycle.

Each unit is provided with two sensors to detect
the systolic or diastolic pressure in each cycle.
A microphone located in each cuff, is positioned
over the brachial artery. Its amplifier circuit
allows frequencies of 20 to 180 Hz only to be
detected. Via this sensor, the standard ausculta-
tive criteria of systolic and diastolic pressure
levels are utilized’. The filtering of all other
frequencies offers some protection against en-
vironmental and/or body movement noises. A
delicate thermistor bead, housed in a rigid metal
container in each unit, is able to detect very
sensitively in each cuff the “puff” of pressure
that occurs with each passing arterial pulsation.
As shown in Figure 4, both sensors must be
activated simultaneously in order to denote either
the systolic or diastolic pressure. Simultaneous
activation of both sensors is necessary to trigger
the relay for rapid deflation of each cuff.



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AC-106 +12V

SOLID STATE SWITCH

Fieure 19. Solid state switch circuit diagram.

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19


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hyperventilation.

Recording of the physiological effects of a 45 second bout of voluntary

Fiovure 11.

14


Ficure 1. Control panel of the automatic blood pressure device.


systolic and diastolic pressures via this two cuff
system versus the standard single cuff methods
of 20- to 30-second duration should be obvious.

Individual measurements obtained by this
system would still be more physiologically desir-
able in the hypothetical case of the availability
of only one arm. This might occur in the case
of a one armed person or in operating, and re-
covery room situations, in which only one arm is
available for pressure monitoring because the
other arm is being utilized for a simultaneous
intravenous infusion. As shown in Figure 6,
alternate cycles of systolic and diastolic measure-
ments are readily attainable using only one unit
and one brachial cuff. In this example, the
alternate cycle was invoked by a manual switch-
over procedure. The internal circuitry of each
unit was designed to accept the optional addition
of a switching circuit that provides fully auto-
matic alteration of individual systolic and di-
astolic cycles. If this circuit is added, automatic
alteration is triggered by the cuff deflation relay.
As shown in Figure 6, the total time for both
cycles is approximately ten seconds. This dura-
tion can be halved by procedures described pre-
viously in this paper. However, even at 10
seconds per pair of pressure determinations, this
far exceeds the measurement rates available via
the standard, single cuff methods and does so
with more comfort and significantly less brachial
circulatory impedance.

As previously mentioned, both the cuff pres-
sure “puff” detector and microphone auscultative
detector must be activated simultaneously in
order to trigger the systolic and diastolic pres-
sure readings during the slow bleed portion of
each cycle. This is clearly shown in Figure 5,
where the activation of both sensors at point C
in each cycle triggers the appropriate pressure
delineating, cuff deflating relay. The simul-
taneous activation of both sensors can occur only
during the slow bleed portion (B-C) of each
cycle due to an “enabling” circuit that is turned
on by the relay at point B and turned off by the
relay at point C. During the slow inflation por-
tion (B-C) of the diastolic cycle only, one or
more “puffs” may be detected prior to the dual
sensor, relay triggering that occurs at point C,
because of the uninterrupted, pulsatile, brachial
blood flow. By the simultaneous use of a stand-
ard stethoscope, whose bell is positioned just
distal to the cuff microphone, the correct systolic

OO

and diastolic microphone gain settings are em-
pirically adjusted during automatic cycling to
agree with the accepted standards of auscultative
blood pressure criteria’.

By adjusting the rapid inflation pressure Iimit,
the bleed rate, and the recycling low pressure
limit, maximum measurement rates approaching
those available via an intra-arterial catheter can
be achieved. Because of the resulting significant
circulatory impedance, this approach should be
utilized only for short duration assessment of
physiological phenomena during which maximum
changes in blood pressure are expected. An
example of maximum measurement rate is shown
in Figure 7. In the 1 minute delineated in this
recording, 33 diastolic and 31 systolic measure-
ments were obtained simultaneously. Since the
manually determined pulse rate at this time was
90 beats per minute, approximately one pair of
determinations per 3 beats was achieved. The
physiological desirability of this relatively be-
nign approach versus the more hazardous intra-
arterial catheter method for the assessment of
human blood pressure transients should be ob-
vious.

Regarding the pressure sensing element used
in this apparatus, most of the commercially
available transducers are satisfactory. Pressure
calibration is greatly simplified by the linear
core type transducer. Furthermore, this linearity
will greatly simplify on line, digital printout
accessibility in those instances in which data
reduction of large numbers of maximum meas-
urement rate records is necessary.

III. Recordings of Physiological Transients.

To achieve a more integrated assessment of
subjects undergoing experimental physiological
procedures, other parameters may be recorded
with the blood pressure. One example of this is
shown in Figure 8, where the blood pressure,
respiration, electrocardiogram, and instantaneous
heart rate were recorded during a single Mueller
maneuver (a sustained negative intrapulmonic
pressure with glottis closed). Here we can see
the classic response of decreases in both the
systolic and diastolic pressures and the biphasic
heart rate response of an initial slowing followed
by a sustained increase. There was very little
body movement during the thoracic muscular
strain of this maneuver. This strain was suffi-
cient to produce some noise artifact in the heart


The delineation of the systolic and diastolic
pressures, and the rapid cuff deflation toward
zero cuff pressure occur at point C in both
tracings.

The next cycle may be initiated by manual
switch activation when single measurements only
are desired. When fully automatic, maximum
rate cycling is desired, the next cycle can be
initiated during the deflation portion of the cycle
by either of two optional procedures. One option
is a low-pressure-limit switch, which can be set
at any desired pressure value below that which
occurs at point C. Since the cycling rate can be
increased by elevating the setting of the low-
pressure-limit switch and since the brachial cir-
culatory impedance varies directly as the cycling
rate, the use of this option to obtain a maximum
measurement rate is desirable only for assessing
very short duration physiological transients dur-
ing which maximum blood pressure changes are
expected. Such transients, for instance, might
include a 60-second cold pressor exposure, a
respiratory “Mueller” maneuver, a 30- to 45-
second rapid decompression exposure, or a short
duration bout of hyperventilation. The systolic
measurement is of prime concern in this regard,
since the brachial circulation is cut off completely
during some portion of its measuring cycle. As
an empirical example of maximum measuring
rate, with the low-pressure-limit switch set at
10 mm Hg, we are routinely capable of obtaining
20 to 25 measurements each of systolic and di-
astolic pressure per minute. Under these condi-
tions, the earliest onset of ischemic “tingling”
occurs in the systolic arm only in about 4 minutes.
This is more than enough time in which to
measure any of the previously mentioned phys-
iological pressure transients. When repeated as-
sessments of these types of transients are neces-
sary in one individual, ample circulatory rest
time between assessments should be invoked for
maximum subject comfort. When automatic
cycling at lesser measurement rates is desired,
the second control option can be invoked. This
consists of an inter-cycle, automatic time delay,
which can be set for any duration up to 20 sec-
onds. The initiation of this delay is triggered
by the same relay that initiates cuff deflation at
point C of the cycle. Under resting subject con-
ditions, measurement rates of approximately 10
systolic and diastolic pressures each per minute
for several hours of continuous measurement

have been tolerated without overt ischemic sen-
sation or discomfort.

Of further interest in Figure 3 are the time
segments of the measurement cycle. Segment
A-B in each tracing represents the rapid, cuff
inflation portion of each cycle. This amounted
to 0.7 second for the diastolic cycle and 1.5 sec-
onds for the systolic cycle. In this example,
brachial circulation in the systolic arm only was
completely cut off (A’-C) for 1.9 seconds. Bra-
chial circulation, of course, is never completely
cut off in the diastolic arm. The 1.9-second
circulatory cutoff in the systolic arm is much
more physiologically desirable than that which
occurs during manual, or automatic, single cuff
methods of measurement. The circulatory cut-
off, as measured from the cycles shown in Figure
5, is approximately 7 seconds in duration. A
more detailed analysis of circulatory cutoff dur-
ing systolic measurement has been reported pre-
viously’. The slow bleed portion (B-C), as
shown in Figure 3, amounted to 2.5 seconds for
the diastolic cycle and 1.7 seconds for the systolic
cycle. This time segment in both tracings, as
well as the total circulatory cutoff segment
(A?-C) in the systolic tracing, can be shortened
markedly by increasing the bleed rate or increas-
ing the pressure setting of point B in the diastolic
cycle and decreasing the pressure setting of point
B in the systolic cycle. Resetting point B is
more preferable ordinarily, since increasing the
bleed rate tends to decrease measurement accu-
racy. In this example (Figure 3), cuff deflation
to 10 mm Hg amounted to 1.7 seconds for the
diastolic cycle and 1.8 seconds for the systolic
cycle. The relatively short time durations of
segments A-B and C-D are somewhat surprising,
since the length of the 4.5-mm ID polyvinyl
tubing from the compressed air source to the
plastic, low pressure reservoir is 8.5 ft and from
the reservoir to each cuff is an additional 8.5 ft.
These time segments could also be shortened
presumably by decreasing the length of this tub-
ing. In this example, the total cycle time (A-D)
is 4.9 seconds for the diastolic measurement and
5.0 seconds for the systolic measurement. As
shown in Figure 3, when both cycles are initiated
simultaneously, both are completed within 5.0
seconds. Under special conditions, it is possible
to reduce this cycle time to approximately 2
seconds. The total physiological desirability of
obtaining repeated, single determinations of


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BLOCK DIAGRAM DIASTOLIC SYSTEM
Figure 12. Block diagram, diastolic system.
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Figure 13. Block diagram, systolic system.

15


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REFERENCES

. Stevens, P. M., “Cardiovascular Dynamics During

Orthostasis and the Influence of Intravascular In-
strumentation,” Am. J. Cardiol. 17:211, 1966.

. Nagle, F. G., J. Naughton, and B. Balke, “Comparison

of Simultaneous Measurements of Intraaortic and
Ausculatory Blood Pressures with Pressure-Flow
Dynamics During Rest and Exercise,” OAM Report
No, 66-36, October 1966.

Zuidema, G. D., R. Edelberg, and E. W. Salzman,
“A Device for the Indirect Recording of Blood Pres-
sure,” WADC Report No. 55-427, 1955.

Levin, H. S., J. V. Messer, and J. Pines, “Repeated
Venous and Arterial Catheterization in Man—An
Analysis of Complications,” Am. Heart J. 73 :475, 1967.

5. Lategola, M. T., and J. Naughton, “The Restoration
of Cardiovascular Integrity in Postmyocardially-
Infarcted Aviation Personnel,” J. Aerospace Med.
88 :1067, 1967.

6, Lategola, M. T. and H. F. Harrison, “Rapid and
Frequent Measurement of Human Systolic and Di-
astolic Blood Pressures,” [.8.4. Trans, 7:11, 1968.

7. Bordley, J., C. A. R. Connor, W. F. Hamilton, W. J.
Kerr, and C. J. Wiggers, “Recommendations for Blood
Pressure Determinations by Sphygmomanometers,”
Circulation 4 :503, 1951.



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H.F. HARRISON
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PULSE CIRCUIT
Figure 21. Pulse circuit diagram.
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H.F. HARRISON
AC-106

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POWER SUPPLY

Fieure 22. Power supply circuit diagram.

21


AM 70-21

A DEVICE AND METHOD FOR RAPID INDIRECT
MEASUREMENT OF HUMAN SYSTOLIC AND
DIASTOLIC BLOOD PRESSURES

Michael T. Lategola, Ph. D. and Hiley F. Harrison

Approved by Released by
J. Ropert Dire, M.D. P. V. Smcen, M.D.
Cuter, Civ, AEROMEDICAL Fepera Arr Surceon
Instirure

December 1970

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine


Fievre 3. Simultaneous recording of one diastolic and one systolic blood pressure measurement.


Figure 2. Internal view of the automatic blood pressure device.


rate recording but none appeared in the blood
pressure recordings. The diastolic measurement
rate during this Mueller maneuver was 34 per
minute. .

In Figure 9, a dynamic recording of the effects
of a 1-minute tilt to 60° feet downward is shown.
Here we can see that the tilt produced some small
biphasic changes in the systolic pressure, an ini-
tial decrease in the diastolic pressure followed
by a typical sustained compensatory vasocon-
strictor rise, an increased respiratory amplitude,
and a typical sustained compensatory rise in the
heart rate. As in the Mueller maneuver, there
is little or no body movement during this pro-
cedure other than an increased postural tonicity
in the leg muscles during the tilt. Some noise
appeared in the heart rate recording but, again,
none appeared in the blood pressure tracings.

Figure 10 shows a recording of the effects of
a rather painful immersion of one bare foot into
a bucket of ice and water. Here we can see an
initial drop of about 10 mm Hg in the diastolic
pressure followed by a marked, sustained rise of
approximately 20 mm Hg above control levels,
a small sustained rise in the systolic pressure,
low-amplitude gasping-type respiration, and a
sustained rise in the heart: rate of about 15 beats
per minute. Following the removal of the foot
from the ice and water, the return to preimmer-
sion control values was somewhat delayed due
to the slow disappearance of the pain of immer-
sion. The value of dynamic recording of this
type should be obvious. As in the two previous
procedures, body movement was at a minimum,

Figure 11 shows a recording of the effects of
a 45-second bout of hyperventilation. Here we
can see the large sustained changes of a decrease
in diastolic pressure, an increase in systolic pres-
sure, and an increase in the heart rate. The
increased heart rate and widening pulse pressure
are most likely related to the invoked exercise
level of the hyperventilation. The thoracic
movement during this maneuver was quite severe
as reflected by the noise in the heart rate record-
ing. With the exception of the short noise arti-
fact in the systolic tracing only, which was

BO

caused by a violent double cough, the blood
pressure recordings seem to have been well pro-
tected against hyperventilation body-movement
artifact.

IV. Conclusions.

The feasibility of the described device for dy-
namic recording of physiological blood pressure
transients in humans under minor body movement
conditions has been established. The measure-
ment rates attainable certainly approxmiate those
available via the more hazardous intra-arterial
methods. The use of digital printout equipment
should keep data reduction within a reasonable
processing time. For “steady-state” single meas-
urements the 5-second maximum for one pair of
pressure determinations seems to be more physio-
logically desirable than the 30-second measure-
ment of the standard single cuff methods. Meas-
urement accuracy is at least equal to standard
auscultatory methods.

Besides all the obvious possible experimental
uses of this system as it now exists several others
may be noteworthy in passing. Field studies with
this apparatus are quite feasible using smaller
capacity compressed-air tanks or motor driven
compressors, an already included 2-hour capacity
rechargeable battery pack, and a battery-powered,
electromagnetic tape recorder. Our projected
studies of inflight fatigue assessment of pilots fall
in this category. In medical centers, critical blood
pressure monitoring with maximum patient com-
fort during surgical procedures in the operating
room, in the post-surgical recovery room, in inten-
sive care wards, and in cardiac and general emer-
gency wards is feasible. The use of this apparatus
to measure blood pressure along with adjunct
parameters during physiological and pharma-
cological laboratory demonstrations in medical
school teaching activities is also feasible. Finally,
the capability for rapid, single determinations and
short duration bursts of maximum rate measure-
ments should be of imense value to the physio-
logical assessment of astronauts in space flight ex-
periments.



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Fieure 17. Squaring amplifier circuit diagram.

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H.F. HARRISON
TIMING CIRCUIT AC-106

Ficure 18. Timing circuit diagram.

18






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Recording of maximum measurement rate of diastolic and systolic blood pressures.

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Fiovre 9. Recording of the physiological effects of a feet downward 60° tilt for a duration of one minute.

Fieure 10. Recording of the physiological effects of a one minute, barefoot immersion in ice and water.

18


ACKNOWLEDGMENT

The authors gratefully acknowledge the invaluable assistance of Mrs.
Peggy Lyne for testing and recording procedures.




Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center. ‘The general public may purchase from National ‘Technical Information Service,
U.S. Dept. of Commerce, Springfield, Va. 22151.


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Ficure 4. Recording of the dual-sensor triggering of diastolic and systolic blood pressure measurements.


Ficure 8. Recording of the physiological effects of a single “Mueller” maneuver.

12