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Description  |
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The present invention relates generally to blood pressure evaluation
procedures and more particularly to non-invasive techniques for
determining certain information associated with blood pressure.
The most reliable ways presently known for obtaining information relating
to an individual's blood pressure require invasive procedures. Such
procedures are not carried out routinely but only under extreme
circumstances, for example during heart surgery. Under less critical
conditions, blood pressure information including specifically an
individual's systolic (maximum) and diastolic (minimum) blood pressures is
obtained non-invasively. There are two well known non-invasive techniques
presently being used today, one is commonly referred to as auscultation
and the other is based on oscillometry. Both of these non-invasive
techniques use the standard arm cuff which most people are familiar with.
However, in the auscultatory method, the systolic and diastolic pressures
are determined by listening to certain sounds (Korotkoff sounds) which
occur as a result of the cuff first being pressurized and then
depressurized whereas oscillometry actually measures changes in pressure
in the cuff as a result of changes in blood pressure as the cuff is first
pressurized and then depressurized.
As will be seen hereinafter, the various embodiments of the present
invention are based on oscillometry. In order to more fully appreciate
these embodiments, reference is made to applicant's own U.S. Pat. No.
3,903,872 (the Link patent) for obtaining blood pressure information
non-invasively. This patent which is incorporated herein by reference
describes, among other things, a way of obtaining the diastolic pressure
of an individual in accordance with a technique which will be discussed in
more detail hereinafter. In U.S. Pat. Nos. 4,009,709 and 4,074,711 (Link
et al) which are also incorporated herein by reference, non-invasive
techniques using oscillometry are disclosed for obtaining the systolic
pressure of an individual. These techniques will also be discussed
hereinafter.
While the various procedures described in the Link and Link et al patents
just recited and other patents held by applicant are satisfactory for
their intended purposes, it is an object of the present invention to
provide additional uncomplicated and yet reliable techniques for obtaining
different types of information relating to an individual's blood pressure.
SUMMARY OF THE INVENTION
A more specific object of the present invention is to provide a different
uncomplicated and yet reliable technique for generating non-invasively a
waveform closely approximating an individual's true blood pressure
waveform which, heretofore, has been obtainable by invasive means only.
Another particular object of the present invention is to provide a new way
for measuring and calculating the mean arterial pressure of an individual.
Another specific object of the present invention is to provide a new,
uncomplicated and yet reliable technique for generating a transformation
curve unique to a given patient.
Still another specific object of the present invention is to provide a
technique for successively monitoring certain parameters of a patient's
blood pressure including his systolic and diastolic pressures over closely
spaced intervals of time without having to subject the patient to cuff
pressures much greater than his diastolic pressure, other than initially
(for purposes of calibration).
Yet another specific object of the present invention is to provide a
technique for measuring a patient's diastolic and systolic blood pressures
at any given instance without ever having to subject the patient to cuff
pressures much greater than his diastolic pressure.
As will be described in more detail hereinafter, the objects just recited
are achieved by means of oscillometry. In accordance with this technique,
a suitably sized cuff, for example one which is 20 inches long and 5
inches wide, is positioned around the upper arm of an individual, a human
being specifically or a mammal in general (hereinafter referred to as the
patient) and initially pressurized to a certain minimum level. As will be
seen hereinafter in accordance with one aspect of the present invention,
this minimum level need not be much greater than the patient's diastolic
pressure to obtain certain information about the patient's blood pressure
including his diastolic and systolic pressures. However, heretofore, in
order to measure these pressure values and obtain other information, it
was necessary to subject the patient to a minimum cuff pressure greater
than the patient's systolic pressure, for example 180 Torr. It is assumed
that this latter cuff pressure will cause the patient's artery within the
sleeve to completely collapse. Thereafter, the cuff pressure is gradually
reduced toward zero during which time the cuff continuously changes in
pressure in an oscillating fashion due to the combination of (1) the
internal blood pressure changes in the patient's artery and (2) changes in
cuff pressure. The latter at any given time in the procedure is known and
oscillatory changes in cuff pressure can be readily measured, for example
with an oscilloscope. By using these two parameters in conjunction with
information which may be made available from methods disclosed in the
above-recited United States patents and the techniques of the present
invention to be described hereinafter, it is possible to achieve the
foregoing objectives in uncomplicated and reliable ways.
It should be noted at the outset that the typical 5" wide pressure cuff
entirely surrounds a corresponding 5" length of artery. The tissue of the
arm is for the most part incompressible, and therefore any change in the
volume of the artery, caused for example by pulsations of blood, results
in a corresponding change in the volume of air in the air bladder which is
within the cuff and therefore adjacent to the arm. This change in air
volume produces a small but accurately measurable pressure change in the
air. This equivalence of pressure pulsations in the cuff bladder to volume
pulsations of the artery is the essence of oscillometry.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to more fully appreciate the various techniques of the present
invention, the following more detailed information is provided in
conjunction with the drawings where:
FIG. 1 (corresponding to FIG. 6 in U.S. Pat. No. 3,903,872)
diagrammatically illustrates the shapes of successive cuff pressure versus
time pulses (cuff pulses) as the measured cuff pressure changes from 90
Torr to 80 Torr to 70 Torr, assuming the patient has a diastolic pressure
of 80 Torr.
FIG. 1A diagrammatically illustrates a full series of cuff pulses
corresponding to those in FIG. 1 from a cuff pressure of 160 Torr to a
cuff pressure of zero.
FIG. 2 diagrammatically illustrates what may be best referred to as a
"transformation" curve or a volume/pressure (V/P) curve corresponding to
the patient's arterial volume (V), that is, the volume of the patient's
artery within the cuff (as measured by cuff volume) versus wall pressure
(P.sub.w) across the artery wall within the cuff and, superimposed on this
curve, a curve which is intended to correspond to the actual blood
pressure waveform of a patient, the two curves being provided together in
order to illustrate the principles of oscillometry, as relied upon in the
above-recited patents. As will be described below, arterial volume changes
.DELTA.V produce cuff pulses P.sub.c (ac) and so FIG. 2 also represents a
curve which "transforms" blood pressure pulses into cuff pulses.
FIGS. 3 and 4 diagrammatically illustrate the transformation curve of FIG.
2 in ways which display techniques for obtaining a given patient's
systolic and diastolic blood pressures in accordance with the Link and
Link et al patents recited above.
FIG. 5 diagrammatically illustrates a curve corresponding to the compliance
of the patient's artery, that is, a curve which displays the ratio
.DELTA.V/.DELTA.P.sub.w against the arterial wall pressure P.sub.w, where
.DELTA.V is the incremental change in the arterial volume corresponding to
a preselected change in wall pressure .DELTA.P.sub.w for different cuff
pressures, this latter curve being initially determined in order to
provide the transformation curve (V/P curve) of FIG. 2 by means of
integration, as will be seen. Because arterial volume changes produce cuff
pulses, FIG. 5 also represents the relationship .sup..DELTA. P.sub.c
(ac)/.sup..DELTA. P.sub.w.
FIG. 6 diagrammatically illustrates an actual blood pressure pulse for a
given patient.
FIG. 7 diagrammatically illustrates a plotted waveform which approximates
the actual blood pressure pulse of FIG. 6 and which is generated
non-invasively in accordance with the present invention.
FIG. 8 diagrammatically illustrates a transformation curve similar to the
one illustrated in FIGS. 2-4 but exaggerated along the vertical slope with
enlarged portions of the diastolic decline forming part of an actual blood
pressure waveform superimposed thereon.
FIGS. 9(a)-(d) diagrammatically illustrate four blood pressure waveforms
having different blood pressure constants K.
FIG. 10 is a functional illustration of an arrangement for providing a
curve which closely approximates a patient's actual blood pressure
waveform and also provides the patients mean pressure and blood pressure
constant.
FIG. 11 graphically displays the peak to peak amplitude A of various cuff
pulses of FIG. 1A against cuff pressure.
FIG. 12 graphically illustrates a transformation curve corresponding to the
one illustrated in FIG. 2 but generated from the information in FIGS. 1A
and 11 only.
FIG. 13 illustrates the same curve as FIG. 21 normalized to zero volume at
negative wall pressures and having superimposed thereon its differentiated
curve.
FIG. 14 is a functional illustration of an arrangement for electronically
generating the curves of FIG. 13.
FIGS. 15a, 15b, 15c and 15d graphically illustrate how a patient is
subjected to cuff pressure with time in one down-ramp and three up-ramp
modes (hereinafter referred to as down-ramp and up-ramp pressure cycles).
FIG. 16a graphically illustrates a series of down-ramp pressure cycles with
time in which each cycle is carried out in accordance with the prior art.
FIG. 16b graphically illustrates a series of a down-ramp pressure cycles
with time in which each cycle is carried out in accordance with the prior
art.
FIG. 17 graphically illustrates a patient's transformation curve
(corresponding to any of the transformation curves discussed previously)
and a particular cuff pulse curve of the patient superimposed thereon.
FIG. 18 graphically illustrates a curve (corresponding to the curve of FIG.
5 in Link U.S. Pat. No. 3,903,872) for obtaining the diastolic pressure of
the patient.
FIGS. 19a, 19b and 19c graphically illustrate three cuff pulses unique to
the patient at respective cuff pressures of 50, 60 and 70 Torr.
FIG. 20 graphically illustrates the results of a stat mode of monitoring a
particular patient's systolic, diastolic and mean pressures over an
extended period of time in accordance with the present invention by taking
successive measurements at closely spaced intervals but without having to
subject the patient to cuff pressures above the systolic level each time.
FIG. 21a functionally illustrates an apparatus for monitoring a patient's
systolic, diastolic and mean pressures over an extended period of time by
taking successive measurements without having to subject the patient to
cuff pressures as high as the patient's systolic pressure each time.
FIG. 21b illustrates a block diagram of an actual working embodiment of the
apparatus of FIG. 21a (as well as the arrangements of FIGS. 10, 14 and
25).
FIG. 22 graphically illustrates two curves corresponding to the curve
described in FIG. 5 of Link U.S. Pat. No. 3,903,872 at two different time
intervals and over an applied cuff pressure range which includes a maximum
cuff pressure which, at all times, is less than the patient's anticipated
systolic pressure.
FIG. 23 graphically illustrates a patient's transformation curve which is
the integration of the curve of FIG. 22 and which thereby corresponds to
the patient's transformation curve over the cuff pressure range utilized
to generate the curve of FIG. 23, and superimposed thereon is the
patient's cuff pulse generated at a cuff pressure of 60 Torr.
FIG. 25 functionally illustrates an apparatus for determining certain blood
pressure parameters of a given patient including his systolic and
diastolic pressures without having to subject the patient to cuff
pressures as high as the patient's anticipated systolic pressure.
FIGS. 26-28A, B are flow diagrams corresponding to the techniques disclosed
with respect to FIGS. 10, 14, 21a and 25.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning first to FIG. 1, this figure diagrammatically illustrates three
successive cuff pressure waveforms 10h, 10i and 10j which correspond to
the change in arterial volume in a pressurized cuff, as described above,
at three different cuff pressures, specifically cuff pressures of 90 Torr,
80 Torr and 70 Torr respectively. In actual practice, a greater number of
cuff pressure waveforms (hereinafter referred to as cuff pulses) are
generated starting at a high cuff pressure such as 160 Torr and ending at
a cuff pressure of zero, as will be seen in FIG. 1A.
By generating these waveforms at known cuff pressures, both the diastolic
and systolic pressures of a patient can be determined in accordance with
the above-recited patents. While this will be explained in more detail
below, it is important to note initially that each wave form has what may
be referred to as a systolic rise S.sub.r at one end of the waveform, a
diastolic decline D.sub.d at the opposite end and a maximum amplitude A.
Moreover, for purposes of graphical illustration, because each applied
cuff pressure to which the patient is subjected is a fixed value or at
least a slowly changing value, it will sometimes be referred to
hereinafter a P.sub.c (dc). At the same time, because the cuff pulses
themselves are the result of a fluctuation in cuff pressure with time (due
to the change in the patient's blood pressure), they will sometimes be
referred to herein as P.sub.c (ac). Note also that P.sub.c (dc) may assume
values from 0 to 250 Torr whereas the cuff pulses P.sub.c (ac) usually
have peak to peak values less than 10 Torr.
The systolic rise S.sub.r, the diastolic decline D.sub.d and the amplitude
A vary from pulse to pulse for reasons to be explained hereinafter. It is
because of these variations that the techniques disclosed in the Link and
Link et al patents recited above can be used to determine the diastolic
and systolic pressures. Specifically, as will be seen, when the diastolic
pressure of a patient is equal to the applied cuff pressure P.sub.c (dc),
the cuff pulse P.sub.c (ac) generated has a final diastolic decline which
is greater in slope than the diastolic decline of any of the other cuff
pulses. Thus, assuming that the final diastolic decline has a maximum
slope at the cuff pulse 10i illustrated in FIG. 1, the patient providing
these waveforms would have a diastolic pressure of 80 Torr. At the same
time, this patient's systolic pressure can be determined by first finding
which of the cuff pulses displays a maximum amplitude A and then, moving
up in cuff pressure, finding the cuff pulse having half that amplitude.
The cuff pressure responsible for producing this half amplitude pulse will
approximately equal the patient's systolic blood pressure. In order to
more fully understand these capabilities, reference is made to FIGS. 2-5
in conjunction with the above-recited Link and Link et al patents.
Turning now to FIG. 2, attention is directed to the curves illustrated
there in order to explain why the cuff pulses of FIG. 1 result from
changes in cuff pressure. The generally S-shaped transformation curve 12
illustrated is shown within a horizontal/vertical coordinate system where
the horizontal axis is the transmural pressure or the wall pressure
P.sub.w across the artery wall of a given patient, within the confines of
the applied cuff. The vertical axis corresponds to the arterial volume V
of the artery within the cuff, as measured by the internal volume of the
cuff itself. In actuality, the transformation curve transforms applied
blood pressure waveforms (which directly effect P.sub.w on the horizontal
axis) to cuff pulses P.sub.c (ac) (which are dependent on arterial volume
V within the cuff on the vertical axis). It will be appreciated that since
the cuff pulses P.sub.c (ac) are caused by and are proportional to
arterial volume changes .DELTA.V, the vertical axis of the S-shaped curve
of FIG. 2 may be labelled by V or P.sub.c (ac) interchangeably depending
on the phenomena being described. The proportionality of P.sub.c (ac) to V
is valid over the central regions of the S-shaped curve of FIG. 2 but may
be less valid for very small cuff pressures P.sub.c (dc). In order to
fully understand this transformation curve (hereinafter also referred to
as an arterial or a cuff curve), it is important to keep in mind the
definition of P.sub.w. The wall pressure P.sub.w of the artery of the
patient at any given time is equal to the blood pressure P.sub.b of the
patient within the artery at that time less the applied pressure of the
cuff P.sub.c (dc). Thus:
P.sub.w =P.sub.b -P.sub.c (dc) (1)
For purposes of the present discussion, it will be assumed that pressure is
measured in Torr (mmHg) and that the section of the horizontal axis to the
right of the vertical axis represents positive wall pressures while the
section of the axis to the left of the vertical axis represents negative
wall pressures. As a result, when no pressure is applied to the cuff (e.g.
P.sub.c =0), P.sub.w at any given point in time is equal to the blood
pressure of the patient at that time. As the cuff is pressurized, P.sub.w
decreases (moves to the left along the horizontal axis). When the cuff
pressure P.sub.c is equal to the blood pressure P.sub.b at any given point
in time, P.sub.w at that moment is equal to zero (e.g. at the vertical
axis). As the cuff pressure is increased beyond the blood pressure at any
point in time, P.sub.w at that time becomes more negative (moves further
to the left on the horizontal axis).
With the definitions of the vertical axis P.sub.c (ac) or V and the
horizontal axis P.sub.w in mind, attention is now directed to an
interpretation of the generally S-shaped cuff curve 12 within this
coordinate system. For the moment, it is being assumed that this curve is
characteristic of the particular patient being evaluated. That is, it is
being assumed that the patient's artery within the cuff and therefore the
cuff itself will change in volume along the S-shaped curve and only along
the curve with changes in P.sub.W. Hereinafter, with regard to FIG. 3, it
will be shown that the transformation curve 12 of a given patient can be
generated from his cuff pulses 10 and corresponding applied cuff pressures
P.sub.c (dc). Thus, for the time being, it will be assumed that the
transformation curve illustrated in FIG. 2 corresponds to that of the
given patient.
With the foregoing in mind, the transformation curve of FIG. 2 will now be
examined. Let it first be assumed that no pressure is applied to the
patient's cuff so that P.sub.c (dc) equals zero. As a result, P.sub.w
equals the blood pressure P.sub.b of the patient. In this regard, it is
important to note that P.sub.b varies with time between the patient's
diastolic blood pressure P.sub.b (D) and his systolic blood pressure
P.sub.b (S). For purposes of this discussion, let it be assumed that these
values are known and that specifically the patient's diastolic blood
pressure is 80 Torr and his systolic blood pressure is 120 Torr. thus,
with no pressure in the cuff P.sub.w (the wall pressure or transmural
pressure) oscillates back and forth with time between P.sub.b (D) and
P.sub.b (S), that is, between 80 Torr and 120 Torr. This 40 Torr measuring
band is illustrated by dotted lines in FIG. 2 at 14 and actually
represents the patient's pulse pressure which is equal to 40 Torr in this
case; pulse pressure=P.sub.b (S)-P.sub.b (D)=120-80=40 Torr.
The patient's actual blood pressure waveform 15 is superimposed on the
V/P.sub.w coordinate system in FIG. 2 within the pulse pressure band 14.
As seen there, this waveform is made up of a series of actual blood
pressure pulses 16 (pressure versus time), each of which corresponds to a
single beat of the patient's heart. Note that each pulse starts at a
minimum pressure (the diastolic pressure of the patient) at a given time
t.sub.o and sharply increases along its leading edge which is the systolic
rise S.sub.r until it reaches a maximum (the patient's systolic blood
pressure), at which time it drops back down along a trailing edge which
includes a dichrotic notch and a diastolic decline D.sub.d to the minimum
pressure again at a second time t.sub.o. At those points in time when the
patient's blood pressure is at a minimum (that is, at the diastolic ends
of pulses 16), the volume of the patient's artery and therefore the volume
of the cuff is fixed by the arterial curve at the value indicated at
V.sub.1 (P.sub.w =80). This corresponds to the minimum pressure level for
the patient's cuff pulse P.sub.c (ac) at an applied cuff pressure P.sub.c
(dc) of zero. On the other hand, whenever the patient's blood pressure is
maximum (at the systolic end of each blood pressure pulse 16), the
arterial curve fixed arterial and therefore cuff volume at the slightly
higher value indicated at V.sub.w (P.sub.w =120). This corresponds to the
maximum pressure level for the patient's cuff pulse P.sub.c (ac) at an
applied cuff pressure P.sub.c (dc) of zero. Therefore, it should be
apparent that for each heart beat (e.g., the time increment from t.sub.o
to t.sub.o), assuming a cuff pressure P.sub.c (dc) of zero, the volume V
(the cuff volume) moves between the values V.sub.1 and V.sub.2, thereby
generating a cuff pulse 10q for each heart beat corresponding to those
illustrated in FIG. 1 but at a cuff pressure P.sub.c (dc)=0, as shown in
FIG. 1A. Thus, as the patient's blood pressure rises from a minimum to a
maximum, the volume of the artery rises from V.sub.1 to V.sub.2 in a
generally corresponding manner (and so does the cuff pulse 10q) and as the
patient's blood pressure drops back down to a minimum, the arterial volume
falls from V.sub.2 to V.sub.1 in a generally corresponding manner (and so
does the cuff pulse 10q). Thus, each of the cuff pulses 10 in FIG. 2 has a
systolic rise S.sub.r and a diastolic decline D.sub.d corresponding to the
systolic rise and diastolic decline of each blood pressure pulse 16.
Having shown how the cuff pulses 10q are dependent upon the transformation
curve at an applied cuff pressure of zero, we will now describe how the
transformation curve causes these cuff pulses to change with applied cuff
pressure. Let us assume now an applied cuff pressure P.sub.c (dc) of 50
Torr. Under these conditions, P.sub.w oscillates back and forth between 30
Torr and 70 Torr. The 30 Torr value is determined by subtracting the cuff
pressure P.sub.c (dc) of 50 Torr from the diastolic blood pressure P.sub.b
(D) of 80 Torr and the 70 Torr value is determined by subtracting the same
P.sub.c (dc) of 50 Torr from the systolic blood pressure P.sub.b (D) of
120 Torr. Thus, the entire 40 Torr band has merely been shifted to the
left an amount equal to 50 Torr as indicated by the bank 14'. Under these
circumstances, P.sub.w oscillates back and forth along a steeper segment
of the arterial or transformation curve so as to cause the volume of the
patient's artery and therefore the volume of the cuff to oscillate between
the values V.sub.3 and V.sub.4. This results in the production of cuff
pulses 10l at a P.sub.c (dc) of 50 Torr. Note that the amplitude of each
cuff pulse 10l is greater than the amplitude of each cuff pulse 10q. This
is because the 40 Torr band 14' at an applied cuff pressure of 50 Torr is
on a steeper part of the volume curve than the band 14 at an applied cuff
pressure of zero. Indeed, as we increase the cuff pressure P.sub.c (dc)
(which decreases P.sub.w) and therefore move the pressure band to the left
on the horizontal axis, we first continue to move along steeper sections
of the arterial curve and thereafter less steep sections. Therefore, the
amplitude (see FIGS. 1 and 1A) of the corresponding cuff pulses 10q, 10l
and so on will first increase to a maximum and then decrease again. At a
cuff pressure P.sub.c (dc) of 100 Torr, the entire 40 Torr pressure band
is shifted to the left so as to uniformly straddle opposite sides of the
vertical zero axis, as indicated at 14". This results in a corresponding
cuff pulse 10g having approximately a maximum amplitude (.sup..DELTA. Vmax
in FIG. 2).
Moving still further to the left, at for example, an applied cuff pressure
P.sub.c (dc) of 160 Torr, the entire 40 Torr band is moved a substantial
distance to the left of the vertical axis, as indicated at 14"' such that
the resultant change in volume (amplitude of the corresponding cuff pulse
10a) is quite small. By increasing the cuff pressure to even a greater
amount, the band is moved still further to the left, eventually producing
very small changes in volume V. From a physical standpoint, this
represents a collapsed artery. In other words, sufficient cuff pressure
P.sub.c (dc) is being applied over and above the internal blood pressure
P.sub.b to cause the wall of the artery to collapse. At the other extreme,
that is, when the cuff pressure P.sub.c (dc) is zero, there are no
external constraints placed on the artery and the latter is free to
fluctuate back and forth based on its internal pressure P.sub.b only.
Between these extremes, the amplitude of cuff pulse 10 (e.g. .DELTA.V)
will increase to a maximum and then decrease again, as stated. It is this
latter characteristic which is used to determine the patient's systolic
pressure in accordance with the previously recited Link et al patents, as
will be described with regard to FIGS. 3 and 4.
As previously mentioned, it should be noted that a blood pressure increase
causes an arterial volume increase. This arterial volume increase causes a
cuff bladder air volume decrease which in turn causes a cuff bladder
air-pressure increase. Therefore, at a given applied cuff pressure P.sub.c
(dc), a blood pressure increase results in a cuff air pressure increase.
This is emphasized as follows:
______________________________________
blood arterial cuff air cuff air
pressure volume volume pressure
increase increase decrease increase
Thus:
blood cuff air
pressure pressure
increase increase
or .sup..DELTA. P.sub.b
.sup..DELTA. P.sub.c (ac)
______________________________________
The converse to the above is also true, that is, a decrease in blood
pressure results in a decrease in cuff air pressure. Therefore, at a given
applied cuff pressure P.sub.c (dc), the amplitude P.sub.c (ac) or Pac of a
Patient's cuff pulse varies directly with the patient's blood pressure
pulse.
Referring to FIG. 3, the same transformation curve 12 illustrated in FIG. 2
is again shown but with a single superimposed pressure band 14"" at a cuff
pressure Pc of 120 Torr. Assume again that the diastolic pressure of the
patient is 80 Torr and his systolic pressure is 120 which means that
P.sub.c (dc) is equal to the patient's systolic pressure for band 14"".
Under these circumstances, P.sub.w oscillates back and forth within band
14"" between wall pressures of -40 Torr and zero, as shown. This results
in a change in arterial volume .DELTA.V (e.g., the amplitude A of a
corresponding cuff pulse) which is approximately equal to one-half of the
maximum change in arterial volume (e.g., max cuff pulse amplitude). It may
be recalled that a maximum change in volume .DELTA.V max (and therefore a
maximum cuff pulse amplitude) results from an applied cuff pressure
P.sub.c (dc) of about 100 Torr (e.g. the pressure band 14" in FIG. 2).
Thus, when the cuff pressure Pc is equal to the patient's systolic blood
pressure P.sub.b (S), the amplitude A of the resultant cuff pulse 10 is
about one-half of the amplitude of the cuff pulse having a maximum
amplitude. Therefore, a patient's systolic blood pressure can be
determined by first generating a series of cuff pulses across the cuff
pressure spectrum, as in FIG. 1A. From these pulses, the one having
maximum amplitude Amax is determined and then the cuff pulse having half
that amplitude (at a greater cuff pressure) is found. Once that pulse is
found, its associated cuff pressure is assumed to be equal to the
patient's systolic pressure. This is discussed in more detail in Link et
al U.S. Pat. Nos. 4,009,709 and 4,074,711 and means are provided in these
latter patents for electronically making these evaluations.
Returning to FIG. 2, it should be noted that the actual blood pressure
waveform 15 is shown having a uniform repetition rate, for example 60
pulses/minute, and that each blood pressure 16 making up this waveform is
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