U.S. patent number 3,552,381 [Application Number 04/640,628] was granted by the patent office on 1971-01-05 for sphygmomanometric method and apparatus.
This patent grant is currently assigned to Bell Telephone Laboratories, Incorporated. Invention is credited to Gordon K. Burns, Jeofry S. Courtney-Pratt.
United States Patent |
3,552,381 |
Burns , et al. |
January 5, 1971 |
SPHYGMOMANOMETRIC METHOD AND APPARATUS
Abstract
Diastolic blood pressure measurement by arterial auscultation is
afforded by arresting flow as with a pressure cuff and then
applying increasingly negative pressure probes to the cuff
generally coincident with each phono- or electrocardiographically
ascertained minimum of the heart's pressure cycle, maintaining the
negative wave amplitude always in excess of the pulse pressure.
Cuff pressure at the onset of Korotkow sound signifies diastolic
pressure level. Apparatus is described for unattended, automatic
and continuous blood pressure monitoring using this method for
diastolic readings. Cuff pressure in one embodiment is held
constant as increasingly large negative pressure excursions are
applied; in another embodiment cuff pressure is decreased while the
negative pressure excursions are held constant in amplitude.
Inventors: |
Burns; Gordon K. (Colts Neck,
NJ), Courtney-Pratt; Jeofry S. (Springfield, NJ) |
Assignee: |
Bell Telephone Laboratories,
Incorporated (Murray Hill, Berkeley Heights, NJ)
|
Family
ID: |
24569031 |
Appl.
No.: |
04/640,628 |
Filed: |
May 23, 1967 |
Current U.S.
Class: |
600/496; 600/528;
600/586 |
Current CPC
Class: |
A61B
5/0225 (20130101); A61B 5/0002 (20130101); A61B
5/026 (20130101); A61B 5/02208 (20130101) |
Current International
Class: |
A61B
5/00 (20060101); A61B 5/026 (20060101); A61B
5/0225 (20060101); A61b 005/02 () |
Field of
Search: |
;128/2.05 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lowe; Delbert B.
Claims
We claim:
1. A method for determining diastolic blood pressure comprising the
steps of:
arresting arterial flow with applied pressure;
coincident with the occurrences of pulse pressure minima,
momentarily relieving the applied pressure by increasing amounts
until the relieved applied pressure and the pulse pressure minima
overlap sufficiently to permit spurts of arterial flow; and
concurrently with the onset of such spurts, measuring the relieved
applied pressure as representing the desired diastolic
pressure.
2. A method for determining diastolic blood pressure comprising the
steps of:
arresting flow in a selected artery;
upon the occurrence of arterial pulse wave minima points only,
progressively reducing the extent of arrest until the
recommencement of arterial flow; and
reading the arterial pressure concurrently with the onset of said
flow.
3. A method for determining diastolic blood pressure comprising the
steps of:
subjecting a selected arterial point to an applied initial pressure
above systolic;
subjecting said arterial point further to an increasingly
negative-going pressure pulse applied only at minima of the
arterial pulse wave, said negative pulse having an amplitude in
excess of the arterial pulse amplitude; and
registering the onset of arterial flow following conjunction of an
arterial pulse pressure minimum with the peak of a negative-going
pressure pulse.
4. A method for the measurement of blood pressure comprising the
steps of:
applying an initial pressure in excess of systolic to a selected
artery through an inflatable cuff;
applying to said artery through said cuff a series of narrow
negative-going pressure pulses each centered in time at one of a
plurality of successive minimum points of the arterial pulse
wave;
causing the peaks of said negative-going pulses to approach and
then intercept successive minimum points by varying the applied
cuff pressure;
detecting the onset of arterial spurts following said interception;
and, concurrently,
reading the instantaneous cuff pressure as representing a measure
of diastolic pressure.
5. A method in accordance with claim 4 wherein said negative-going
pressure pulses are substantially constant in amplitude, and
wherein the cuff pressure is varied by bleeding the cuff.
6. A method in accordance with claim 4 wherein said cuff pressure
variation is effected by progressively increasing the amplitude of
said negative-going pressure pulses while otherwise maintaining
said cuff pressure in excess of systolic.
7. Apparatus for measuring blood pressure comprising:
a pressure member for the application of controlled constricting
force to an artery;
a pressure monitor for registering the pressure applied by said
member to said artery;
means for registering the occurrence of successive minima points of
the arterial pulse pressure wave;
means for applying to said member an initial pressure in excess of
systolic to fully constrict said artery;
means for further applying to said member a succession of narrow,
increasingly negative-going pressure pulses, each centered in time
at successive ones of said arterial pulse wave minimum points, in
response to said registration thereof;
means for detecting the onset of arterial flow following the abrupt
momentary penetration of one of said negative-going pulses through
a minimum point of said arterial pulse wave; and
means responsive to said arterial flow onset detection for
recording the instantaneous pressure registered by said pressure
monitor, said recording being a measure of the diastolic
pressure.
8. Apparatus for determining diastolic blood pressure
comprising:
first means for applying pressure to a selected artery sufficient
to arrest flow;
second means for registering the occurence of minimum points of the
arterial pulse pressure wave;
third means responsive to each successive said registration for
reducing the pressure applied by said first means, said reduction
being in increasingly greater amounts causing said arresting
pressure to approach, and finally to equal, the value of said
diastolic pressure as indicated by the onset of arterial spurts;
and
fourth means for indicating the arterial pressure concurrently with
the onset of said spurts.
9. Apparatus in accordance with claim 8 wherein said second means
comprises:
means for monitoring the cardiac cycle events and for deriving
therefrom a recurrent timing pulse in rhythm with the arterial
pulse;
means for synchronizing the occurrence of said timing pulses with
successive minima of the arterial pulse; and
means for transmitting said timing pulses to said third means.
10. Apparatus in accordance with claim 9 wherein said first means
comprises an inflatable arm cuff and wherein said fourth means
comprises a pressure-indicating device connected thereto.
Description
This invention relates in general to sphygmomanometry; and more
particularly to a new method for determining the systolic and
diastolic blood pressure by the auscultatory technique.
BACKGROUND OF THE INVENTION
Blood pressure dynamics provide invaluable medical insights in the
detection and diagnosis of circulatory and cardiac disorders.
Pressure determination is particularly useful, for example, in
ascertaining the contractibility of the heart muscle and the
distensibility of the ventricles, arteries and veins. As a further
example, with continuous monitoring of blood pressure after a major
cardiac failure, the oncoming of relapse often can be detected in
time for corrective medical action.
Compared with blood flow and blood volume--the other two principal
circulatory attributes--blood pressure is the most easily
determined and recorded. Yet its accurate measurement by means
other than direct catheter insertion into an artery is nonetheless
a difficult and exacting task. As the direct method is neither
convenient nor altogether safe, its employment is reserved usually
for exigent human cardiopulmonary diagnostic work; and hence the
various indirect blood pressure measurement methods predominate by
far in most practice.
Of these, the auscultatory method is most commonly employed
clinically. The basic elements for manual practice of this method
are the familiar inflatable rubber arm cuff connected to a pump and
to a manometer, and a stethoscope. The method relies on detection
of the Korotkow sounds observable during relief of constriction of
an artery subjected to a varying pressure applied from without, and
their correct interpretation as criteria for the systolic and the
diastolic pressure points. Normal arterial blood flow is
essentially inaudible; but if an artery is completely constricted
as by an inflated cuff and then relieved enough to allow slight
reopening of the arterial lumen, a distinct rhythmic tapping sound
commences. The onset of these tapping sounds, as heard through the
stethoscope, for example, signifies the point of systolic pressure
which is then read from the manometer. As cuff pressure is further
reduced, the sound alters markedly in both quality and intensity.
Finally, just prior to disappearing, the arterial sound is faint
and muffled. The manometer pressure at the time of complete
disappearance of this muffled sound reflects the diastolic
pressure.
Although the initial arterial sounds corresponding to the systolic
pressure point usually are readily detectable either by a human
listener stethoscopically or through numerous electromechanical
arrangements, it is extremely difficult to detect accurately the
point at which the muffled sounds corresponding to the diastolic
pressure level disappear. This is particularly so with respect to
automated sphygmomanometric schemes, a wide variety of which are
found in the prior art.
Many such schemes, for example, convert the Korotkow sounds heard
as the cuff deflates into a varying electrical signal which is
amplified and then interpreted. Insofar as diastolic pressure
detection is concerned, however, this approach involves an
inherently uncertain distinguishing of assumed background noise
from the desired end-point muffled arterial sounds which connote
the diastolic pressure point. Other methods rely on the detection
of apparently characteristic sounds lying in a low-frequency band
and occurring during the arterial pulse pressure interval to
provide indices of the systolic and diastolic pressures. Another
attempted remedy of the detection problem involves extremely
sensitive pickup devices for converting the arterial pulse into an
electrical signal.
These and other known prior art schemes do not overcome, however,
the basic problem of detecting with certainty against a background
of noise and perturbations the critical diastolic pressure
signified by the disappearance of all arterial sound.
Accordingly, one object of the invention is to improve the
capability of sphygmomanometers to correctly detect the Korotkow
sound corresponding to the diastolic blood pressure.
A further object of the invention is to reduce the need for human
attending of a convalescing cardiac patient.
A further object of the invention is to make possible a preferred
system for automatic and continuous monitoring of the systolic and
diastolic pressures of a patient and for their transmission to a
remote monitoring point.
SUMMARY OF THE INVENTIVE CONCEPT
The basic principle of the invention, broadly, may be practiced by
subjecting a selected artery to an applied initial pressure
substantially above systolic and then effecting thereupon a gradual
applied pressure decrease coupled with the application of a brief,
constant, negative-going pressure peak at each minimum of the
heart's pressure cycle, this peak having an amplitude in excess of
the pulse pressure.
In one exemplary embodiment illustrating the practice of the
invention, the heart's pulse repetition frequency is monitored and
supplied to a cyclic pump connected to an arm cuff. The pump cycle
time is governed by this input. The pump thus applies the mentioned
negative-going pressure peak to the cuff coincidentally with the
occurrence of successive minima of the heart's pressure cycle. The
cuff is deflated, but with its maximum pressure maintained higher
than the systolic blood pressure. The cuff's negative-going
pressure excursions imparted through the cyclic pump action
approach the diastolic arterial pressure, but because of their
timing do not interact with the systolic level at all. Hence, a
stethoscopic monitoring of the arterial sounds at this point will
detect no Korotkow sounds. However, when cuff pressure at the
instant of the negative-going excursion is low enough to allow
opening of the arterial lumen, Korotkow sounds signifying the
diastolic pressure level are detected and the desired manometric
reading of the cuff is taken.
Thus, audio detection of an initial blood flow surge in the artery
occasioned by the coincidence of the diastolic arterial pressure
and the peak of the negative-going pressure excursion in the cuff
is readily afforded without the presence of ambiguous background
noises so characteristic of the methods which rely instead on
detection of the disappearance of sounds.
The invention and other objects, features and advantages thereof
will be readily apprehended from a reading of the detailed
description to follow of an illustrative embodiment thereof.
DESCRIPTION OF THE DRAWING
FIGS. 1A--1D are graphs depicting certain events in the cardiac
cycle;
FIG. 2 is a graph showing conventional detection of systolic
pressure;
FIGS. 3A and 3B are graphs illustrating the present detection
scheme for diastolic pressure;
FIG. 4 is a schematic block diagram broadly illustrating an
exemplary method for practice of the invention; and
FIG. 5 is a more detailed schematic diagram illustrative of the
practice of the invention.
GENERAL DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
An insight into the inventive concept may be gained more readily
with an appreciation of the basic cardiac cycle, particularly the
time-pressure event sequences occurring in the heart and their
relationship to the arterial blood pressure fluctuations.
FIG. 1 traces the cardiac events and the resulting pressure in the
left ventricle. On the same time scale, the brachial arterial
pressure resulting from the cardiac events is traced. Although the
left ventricle pressure is shown, the aorta pressure follows
similar traces timewise. The vertical time lines a through g
denote, respectively: a. onset of ventricular contraction; b. end
of ventricular contraction and opening of semilunar valves; c. end
of ventricular ejection and ventricular systole; d. closure of
semilunar valves and onset of ventricular relaxation; e. opening of
the arteriovenous valves and onset of ventricular filling; and f.
and g. continued but slower ventricular filling or diastasis,
ending with atrial contraction.
The arterial pressure fluctuations are synchronous with the heart
beats. Further, since the rate of propagation of the ventricular
pulse wave in the heart is from 3 to 4 meters per second and in the
limb arteries is approximately 7 to 14 meters per second, for
purposes of the present invention the time lag between a cardiac
event and its arterial effects may often be neglected. FIG. 1B
illustrates the foregoing, showing the occurrence of the systolic
arterial pressure concurrently with the contraction or systole of
the ventricle. The trough or region of minimum arterial pressure
substantially coincides with the end of the resting phase or
diastole of the cardiac cycle, and is the diastolic pressure.
Certain of the events occuring in the cardiac cycle are represented
in the electrocardiogram trace of FIG. 1C; and in the
phonocardiographic trace of FIG. 1D. The possible use of these
cardiac traces in the practice of the present invention is
explained below.
The basic inventive concept may be illustrated readily with the aid
of FIGS. 2, 3A and 3B. FIG. 2 depicts the fluctuating pressure in
an artery as running from a diastolic of about 80 to a systolic of
about 120 mm Hg. As is well known, these pressures as well as their
difference (pulse pressure) will vary considerably from case to
case, depending upon age, individual health, and other factors.
Measurement of systolic pressure is achieved in conventional
fashion by completely constricting arterial flow, as with a cuff,
and then slowly bleeding the cuff while stethoscopically probing
for the onset of Korotkow sounds. Typically, as is illustrated in
FIG. 2, no sound is heard at the pulses denoted 1-- 6; but at pulse
7 the slowly falling cuff pressure briefly coincides with the
maximum arterial pressure. A sound connoting blood flow is heard
and a concurrent reading of the cuff manometer yields the systolic
pressure.
Now the diastolic pressure measurement is taken, in accordance with
the practice of the inventive concept, by inflating the cuff to a
point in excess of systolic pressure and then gradually reducing
cuff pressure while concurrently superimposing upon the cuff
pressure a negative-going narrow pressure pulse or wave, in this
case having a substantially constant amplitude which is larger than
the maximum likely arterial pulse pressure. The negative "probe" is
applied to the cuff so as to coincide in time with the minimum
points of the arterial pulse as determined, for example, by
reference to cardiac cycle events monitored
electrocardiographically (FIG. 1C), phonocardiographically (FIG.
1D), or otherwise. The resulting sequence is depicted in FIG. 3A.
The onset of arterial flow again is detected stethoscopically when
cuff pressure coincides with arterial pressure at the diastolic
floor between the fifth and sixth positive heart pulses.
Alternatively, rather than reducing cuff pressure and applying a
constant negative-going probe, it may be desirable to maintain the
cuff pressure at a constant level in excess of systolic and apply a
succession of increasingly negative pulse probes as depicted in
FIG. 3B. The result in either case is the same.
FIG. 4 illustrates a system suitable for practice of the present
invention. A conventional arm cuff 10 is applied to a patient whose
blood pressure is to be measured by the present inventive method.
Associated with cuff 10 is a cuff pump 20, pneumatic in the
illustration but hydraulic if desired, for elevating cuff pressure
to a controlled point above the maximum arterial pressure. Also
associated with cuff 10 is a variable or cyclic pump 30 that when
suitably synchronized with the repetition rate of the heart imparts
to cuff 10 brief negative pressure surges having an amplitude
materially larger, for example, 60 mm Hg., than the pulse pressure.
The duration of the negative-going surge produced by pump 30
typically is from 50-- 100 milliseconds depending upon the duration
of the patient's ventricular relaxation.
The duration as well as the correct timing of these surges is
determined by a heart pulse detector 40 which monitors the cardiac
cycle. Detector 40 may comprise, for example, a phonocardiograph
which utilizes a low-frequency sensitive transducer 41 applied to
the patient's chest, and suitable amplifying and filtering
circuitry to produce an enhanced electrical analogue of the heart
sounds. Those sounds occurring at the onset of ventricular
contraction--time a of FIG. 1D--are prominent, readily detectable
and hence suitable as recurrent pulses which are applied to cyclic
pump 30 for timing of the negative-going excursions. Other cardiac
cycle events, or other event-monitoring methods including
electrocardiography, apexcardiography, etc., may of course be
employed alternatively to generate the desired indication of the
heart's pulses. For example, a sphygmograph could be used to detect
the pulsating in an unconstricted artery and this used as a source
of timing pulses.
A flow detector 50 including a low-frequency sensitive pressure
transducer 51 placed over the brachial artery just below the arm
cuff 10 monitors the artery and detects those sounds signifying the
onset of arterial flow. In addition, a cuff pressure monitor 60
associated with cuff 10 continuously monitors the latter's pressure
and supplies the pressure readings corresponding to the blood
systolic and diastolic pressures to any one of several possible
output devices. The latter may include, for example, the onsite
recording oscillograph designated 80 for recording at the patient's
bedside or elsewhere in the hospital the pressure information; the
data interface 90 which converts the pressure readings to a form
suitable for transmission through the telephone switching network;
or a central monitoring position 100 which includes visual displays
101, 102 of the diastolic and systolic pressures received from a
selected one of a plurality of cuff pressure monitors servicing
different patients.
The basic operation of the scheme shown in FIG. 4 advantageously
may be automated with the addition of a control unit 110,
hereinafter called "CU". The general functional operation of such a
system then is as follows, when implementing the approach
illustrated in FIG. 3A.
With the patient recumbent to minimize the effects of hydrostatic
pressure and with the arm cuff 10 and transducers 41, 51 in place,
CU 110 is activated and turns on cuff pump 20. Pneumatic or
hydraulic pressure is supplied from pump 20 to cuff 10 via a
flexible nondistensible line 21 which may be of rubber,
polyethylene plastic or the like. As cuff pressure increases and
the brachial lumen is constricted, arterial sounds are detected by
transducer 51. When blood flow is completely arrested, these sounds
disappear which occasions a signal to be sent from flow detector 50
to CU 110. On receipt of this signal CU 110 turns off cuff pump 20
and operates a bleeder valve 22 associated with flexible line 21.
Bleeder valve 22 operation allows the cuff pressure to decrease
substantially along the upper curve of FIG. 2, for example, until
it drops to a point at which it just balances the peak portion of
the arterial pressure.
At this point flow detector 50 registers the initial arterial
sounds, signaling the opening of the heretofore fully constricted
brachial lumen and thus the measuring point for systolic pressure.
Accordingly, flow detector 50 signals the occurrence of this event
to the control unit which promptly directs cuff pressure monitor 60
to read the instantaneous cuff pressure and to supply this reading
to user units 80, 90, 100.
When the systolic pressure reading is completed, CU 110 directs
cuff pump 20 to reinflate cuff 10, and concurrently signals bleeder
valve 22 to close. As before, cuff 10 is inflated and flow detector
50 supplies an indication of when arterial flow is completely
arrested. CU 110 receives this indication from flow detector 50,
and this time allows the pump 20 to continue inflating cuff 10
until pressure monitor 60 reads approximately 20 to 30 mm Hg. above
the pressure at which arterial flow was fully arrested. At this
point CU 110 turns cuff pump 20 off, reopens bleeder valve 22 and
actuates cyclic pump 30, the latter supplying negative-going
pressure excursions to cuff 10. During the time of ventricular
relaxation, as determined by heart pulse detector 40, and as cuff
10 is slowly deflated, the cyclic negative excursions finally
intercept the valley or minimum points of arterial pressure denoted
in FIG. 3. At such time flow detector 50 again registers the onset
of Korotkow sounds, signifying opening of the arterial lumen, but,
significantly, this time at the diastolic pressure level.
CU 110 receives a signal indicative of diastolic flow from detector
50, and instructs cuff pressure monitor 60 to read the
instantaneous cuff pressure and to supply this reading to the user
units 80, 90, 100.
Implementation of the procedures illustrated graphically in FIG. 3B
follows the foregoing, except that once constant cuff pressure is
established, relief valve 20 is kept closed and the increasingly
negative pulse probes are generated by pump 30.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
FIG. 5 depicts in somewhat more detail the illustrative embodiment
of the invention described with respect to FIG. 4, and in which
like numerical designations denote like component parts. The heart
pulse detector 40 comprises a pressure transducer 41 applied
tightly to the chest. Transducer 41 may be of the type employing a
rubber sheet contact portion hydraulically connected to a movable
piston. Generally suitable alternatives to a pressure transducer
include strain gages, piezoelectric crystals, capacitance
transducers, light and photocell arrangements, and others.
The heart beat pulses received by transducer 41 are converted to an
anolog electrical signal that is applied to an amplifier 44. The
latter may, for example, be a direct-coupled transistor amplifier
especially sensitive to frequencies of 2-- 100 c.p.s., and operated
Class C. The enhanced heart-pulse signal from amplifier 44 is
supplied to a filter 45. Advantageously, filter 45 is designed to
pass only heart sounds--particularly the sounds of ventricular
contraction, which as explained below are here relied upon for
timing pulses--while otherwise blocking spurious body noise and any
electrical ambient disturbance.
The output of filter 45 is a recurring brief pulse, essentially as
shown in FIG. 1D. In the instant embodiment, as the pulse output of
filter 45 happens not to coincide with the occurrence of the
ventricular relaxation period of interest, it is necessary to
insert a time delay through a timer 46. The delay must be
sufficient to shift the pulse backwards in time so that it will
occur substantially in the middle of the period between the
vertical lines f and g in FIG. 1 which essentially bracket the
ventricular relaxation period. Timer 46 may be any of numerous
conventional delay circuits including, for example, a gate-opening
"one-shot" triggered by the leading edge of the ventricular
contraction pulse, an RC network, or others.
The output of timer 46 is a pulse applied to a motor control unit
31 associated with cyclic pump 30. Unit 31 is adapted to vary the
cycling time of pump 30 so as to effect the coincidence of the
pump's negative excursion with the receipt of the timing pulse from
timer 46. This cycling time variation can be effected, for example,
by varying the speed of pump 30, or by various other well-known
control methods.
Pump 30 itself must be constructed so as to produce a
negative-pressure pulse with a selected constant amplitude in
excess of the usual approximately 40 mm Hg. pulse pressure, say, in
the vicinity of -60 mm Hg. The pump pulse time width must be less
than the period of ventricular relaxation, which of course varies
with individuals and specific health. As a median, however, this
period of ventricular relaxation may be taken as being of
approximately a 200 to 300 milliseconds duration; and hence the
duration of the negative pulse produced by pump 30 should be about
one-quarter to one-half of that, or 75-- 150 milliseconds. With
these rather rapid pressure rise and fall times, care must be taken
in a pneumatic system design to insure its rapid response in these
short times without introducing pressure transients that may
interfere with system operation.
The flow detector 50 depicted in FIG. 5 consists of a pressure
transducer 51 similar to transducer 41 and suitable for intimate
contact with the human skin surface directly above an artery. As
only the Korotkow sounds corresponding to onset of arterial flow
following complete arterial constriction must be detected in the
practice of the instant invention, transducer 51 should be selected
for its sensitivity to the characteristics of these sounds only and
not to extraneous bodily and other ambient noise. The output of
transducer 51 is supplied to an amplifier 52. The output of
amplifier 52 is suitably filtered in filter 53 to further attenuate
extraneous arterial and bodily sounds and to pass only those sounds
corresponding to the onset of arterial blood flow following the
equilibrium between blood pressure and cuff pressure.
In the operation of the embodiment described, it is useful for
detector 50 to be able to distinguish among (1) disappearance of
arterial sounds with increasing cuff pressure; (2) the onset of
arterial sounds in the absence of negative excursions; and (3) the
onset of arterial sounds in the presence of negative excursions.
This recognition may be supplied by a suitable logic unit 54,
having as inputs the amplified and filtered arterial sound detected
by transducer 51 and an indication of cuff pressure from monitor
60. Logic unit 54 may be a pulse memory circuit, for example, which
recognizes the coincidence of a disappearing arterial sound with
increasing (80 mm Hg. or more) cuff pressure as a sign that cuff
pressure has increased beyond the systolic arterial pressure.
Similarly, the onset of arterial sound with decreasing cuff
pressure in the absence of negative cuff pressure excursions is
recognized by logic unit 54 as the point at which systolic pressure
is to be measured. Finally, the onset of arterial sounds with a
decreasing cuff pressure in the presence of negative cuff pressure
excursions is recognized by logic unit 54 as signifying the time at
which measurement of the diastolic pressure must occur. The
recognition of each of the above states is transmitted by detector
50 to CU 110.
Cuff 10 is a strong, inelastic inflatable cloth band connected by
indistensible air or hydraulic lines 21, 32, 23 to pump 20, pump 30
and cuff pressure monitor 60, respectively. As seen in FIG. 5,
monitor 60 comprises advantageously a conventional pressure
oscillograph 61 or other suitable direct-reading pressure gauge
located at the site of the patient's bed. Connected to manometer
61, and responding to the pressure variations therein registered,
is a suitable transducer 62 for converting the oscillograph
pressure variations into a varying electric signal, as for example
a voltage, so that each discrete voltage level of the transducer
relates to a specific pressure. Transducer 62 may be replaced by
other suitable devices as, for example, a digital voltmeter.
The output of transducer 62 is twofold: first, to logic unit 54 for
reasons above indicated; and secondly, to one or more user units,
examples of which are recorder 80, data interface 90 and central
monitor position 100 shown in FIGS. 4 and 5. It may be desirable in
some instances to provide an analog-to-digital converter 63 between
the transducer 62 and the various outputs, depending on the
requirements to be met. Additionally, a gate 64 disposed between
transducer 62 and the various user units 80, 90, 100 and under the
control of CU 110 allows the output readings of transducer 62 to be
selectively supplied to these user units if desired.
CU 110 advantageously includes a cycler 111 and a cycle control 112
which directs the sequence of operations performed by cycler 111 in
accordance with inputs received from selected points in the
system.
OPERATION
Practice of the inventive concept by the system shown in FIG. 5
follows in general the procedures earlier described for the
operation of the system depicted in negative-going 4. The
below-described operations may be achieved through numerous circuit
arrangements. Hence, in FIG. 5, functional lines only are set
out.
Initially, cycle control 112 is activated and directs cycler 111 to
the position indicated as 1. In this position, control unit 110
supplies power to cuff pump 20 to inflate the cuff 10 through
now-closed valve 22. Arterial sound is monitored and processed in
flow detector 50 as described. Shortly logic unit 54 detects that
arterial blood flow is completely arrested, and supplies this
information to cycle control 112. On receipt of this, cycle control
112 allows cuff pressure to increase another 20-- 30 mm and
thereafter shifts cycler 111 to position 2. In this position, power
to the cuff pump is cut off and cuff bleeder valve 22, heretofore
closed, is opened. Cuff pressure drops, and when it balances with
the peak portion of the arterial pressure, arterial sound is
detected by transducer 51 and registered in logic unit 54. Together
with its input from transducer 62, logic unit 54 recognizes this
state as the systolic pressure point and notifies cycle control
112. In response, cycle control 112 instructs cycler 111 to shift
to position 3. In position 3, bleeder valve 22 is closed and a
signal is sent to gate 64 to pass the reading of transducer 62 on
to the user units 80, 90, 100.
Immediately thereafter cycle control 112 shifts the cycler to
position 4 wherein cuff pump 20 is reenergized for repeated
inflation of cuff 10. Again, cuff pressure increases sufficiently
to cause full arterial constriction and hence complete
disappearance of arterial sound. Logic unit 54 recognizes this and
informs cycle control 112 which now allows pump 20 to continue
inflating cuff 10 to an additional 50-- 70 mm Hg. This point
reached, cycle control 112 directs the cycler to position 5.
In this position, bleeder valve 22 is reopened and cyclic pump 30
is turned on through motor control 31. Motor control 31, once
activated, energizes and times motor 30 in the manner already
described. Cuff pressure again decreases and the timed cyclic
negative excursions finally intercept the minimum arterial
pressure. Arterial sounds are detected by transducer 51, processed
and supplied to logic unit 54 which together with the input from
transducer 62 recognizes this as the point for diastolic pressure
measurement and informs cycle control 112. In response, cycle
control 112 advances cycler 111 to position 6. In this position,
bleeder valve 22 is quickly closed and cyclic pump 30 deenergized;
and gate 64 is opened instantaneously to pass the diastolic
pressure reading.
A seventh position is included in control unit 110 as a no-pressure
rest position which starts a timing interval within cycle control
112 at the end of which cycler 111 is returned to position 1 and
the entire cycle is repeated.
In summary, the method of the present invention avoids the drawback
inherent in known prior art diastolic measurement relying on
identifying the point at which arterial flow returns to being
completely unrestricted. As noted, this point is far more difficult
to detect. The present invention avoids this problem altogether
while enabling essentially the same detection scheme to be
practiced for measuring the diastolic pressure as for measuring
systolic pressure. Considerably more accurate readings are obtained
with actually less complex detecting equipment than heretofore
used.
It is to be understood that the embodiments described herein are
merely illustrative of the principles of the invention. Various
modifications may be made thereto by persons skilled in the
art.
* * * * *