(12)
`
`United States Patent
`Booth et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,440,080 B1
`Aug. 27, 2002
`
`US006440080B1
`
`(54) AUTOMATIC OSCILLOMETRIC
`APPARATUS AND METHOD FOR
`MEASURING BLOOD PRESSURE
`
`-
`_
`_
`(75) Inventors‘ John W‘ Booth’ Bruce A‘ Fnedman’
`b th f T
`FL US
`O O ampa>
`(
`)
`.
`,
`_
`(73) Ass1gnee: GE Medical Systems 'Information
`Technologies, IIlC., Milwaukee, WI
`(Us)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U-S-C- 154(1)) by 0 days-
`
`(21) Appl. No.: 09/962,380
`(22) Filed:
`Sep. 25, 2001
`
`/
`(
`)
`Int. Cl.7 ................................................ .. A61B 5 00
`51
`-
`-
`(52) US. Cl. ...................... .. 600/494, 600/495, 600/496
`(58) Field of Search ............................ .. 600/490 493—6
`’
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`9/1982 Ramsey, 111
`4,349,034 A
`4,360,029 A 11/1982 Ramsey, 111
`4,425,920 A
`1/1984 Bourland et 81.
`4,543,962 A 10/1985 Medero et al.
`4,638,810 A
`1/1987 Ramsey, III et 81.
`
`4,793,360 A * 12/1988 Miyawaki et a1. ........ .. 600/494
`4,869,261 A
`9/1989 Penal
`4,873,987 A 10/1989 Djordjevich et 211.
`4,889,133 A 12/1989 Nelson et al.
`4,949,710 A
`8/1990 Dorsett et a1.
`5 054 494 A * 10/1991 LaZZaro et a1. ........... .. 600/494
`’
`’
`5,178,154 A
`1/1993 Ackmann et a1.
`5,590,662 A
`1/1997 Hersh et al.
`5,649,543 A
`7/1997 Hosaka et a1‘
`5,785,659 A
`7/1998 Caro et aL
`5,865,755 A
`2/1999 Golub
`6,186,953 B1
`2/2001 Narimatsu
`_ d b
`_
`Cue
`y exammer
`Primary Examiner—Robert L. Nasser
`(74) Attorney, Agent, or Firm—George E. Haas; Quarles &
`Brady LLP
`(57)
`
`ABSTRACT
`
`*
`
`P
`g
`y p
`B10091 ressure of an human bein is read b a rocess that
`laces a cuff around a ortion of the human bein ’s bod .
`P
`P
`g
`y
`The Cuff is in?ated to a Prede?ned Pressure Which 0661119165
`the ?ood of blood and then the cuff is de?ated in a controlled
`manner. At a plurality of de?ation pressure levels, pressure
`pulses that occur in the cuff are integrated to produce a
`plurality of integral values. Adiastolic pressure of the human
`being is derived in response to the de?ation pressure level at
`Which occurred the integral value that is greatest in magni
`tude.
`
`20 Claims, 2 Drawing Sheets
`
`‘[16
`
`‘—__
`34
`9 V .4.
`
`‘_
`
`4
`
`207i“
`/-24
`1,
`PRESSURE
`FILTER‘
`TRANSDUCER
`25/
`
`30
`
`CONTROL
`PANEL
`AND DISPLAY
`
`CONTROLLER
`
`l
`
`E
`A
`' “29
`27
`
`l
`
`- - - K
`
`26
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`U.S. Patent
`
`Aug. 27, 2002
`
`Sheet 1 0f 2
`
`US 6,440,080 B1
`
`‘
`16
`f
`
`34
`
`2
`3
`\ CONTROL
`PANEL
`
`"8 w?” |—
`
`22 Ami], E
`
`20: L'- 30
`/'24
`PRESSURE
`TRANSDUCER
`
`FILTER
`
`‘
`
`CONTROLLER
`
`A
`"'" \
`'
`29
`50°"
`- — - K 27
`26
`
`CUFF PRESSURE
`PULSE AMPLITUDE
`
`PULSE AREA
`
`FIG.3
`
`FIG. 4
`
`FIG. 5
`
`. ii
`
`I
`
`0
`
`.
`
`.
`
`.
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`U.S. Patent
`
`Aug. 27, 2002
`
`Sheet 2 0f 2
`
`US 6,440,080 B1
`
`FIG.‘ 2
`
`(555? K40
`[SET STEP COUNT = 0]
`
`42
`
`IINFLATE CUFF TO OCCLUDE PRESSURE]
`
`'
`
`(SET MEASUREMENT COUNT = 0|
`2
`'0
`/
`FMEAsuRE AND sToRE CUFF PRESSUREJ
`/" 48
`IINCREMENT MEASUREMENT COUNU
`
`46
`
`X
`MEASUREMENTS
`TAKEN?
`
`K- 54
`iv NO
`COMPUTE AND STORE
`OSCILLATION AMPLITUDE FOR STEP
`
`| INCREMENT STEP COUNT K’ 56
`
`IDEFLATE CUFF ONE STEP 1/’ 58
`
`64
`/
`T
`FIND STEP WITH GREATEST PEAK TO PEAK OSCILLATION]
`
`| FIND SYSTOLIC PRESSURE I/' 66
`I
`K68
`FIND STEP WITH LARGEST OSCILLATION AREA
`AND SET DIASTOLIC PRESSURE TO STEP PRESSURE
`(E
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`US 6,440,080 B1
`
`1
`AUTOMATIC OSCILLOMETRIC
`APPARATUS AND METHOD FOR
`MEASURING BLOOD PRESSURE
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`Not applicable.
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH OR DEVELOPMENT
`
`Not applicable.
`
`BACKGROUND OF THE INVENTION
`
`2
`cease and the pressure is again noted, Which pressure is
`referred to as diastolic pressure and is taken as an estimate
`of the true intra-arterial diastolic pressure. The difference
`betWeen the diastolic pressure and systolic pressure is
`termed pulse pressure. Previously the constriction pressure
`has been derived from an in?atable cuff connected to a
`mercury column manometer or to an aneroid type gauge
`having a dial scale calibrated in millimeters of mercury. It is
`also knoWn that the auscultatory estimate of diastolic pres
`sure can at times be inaccurate; auscultation can be very
`technique dependent and varies, for example, due to the
`hearing ability of the clinician taking the reading.
`Furthermore, auscultation can, in some cases, be quite
`confusing When determining diastolic estimates because the
`Korotkoff sounds may never disappear as the cuff pressure
`is loWered.
`A previous automatic indirect blood pressure reading
`apparatus employed the oscillometric method in Which an
`arm cuff is in?ated to a pressure at Which blood ?oW is
`occluded. The cuff then is de?ated at predetermined pressure
`increments in a step-Wise manner. At each step, the pressure
`in the cuff is measured repeatedly using a suitably short
`sampling period in order to detect pressure ?uctuations. The
`instantaneous pressure in the cuff is due to the in?ation
`pressure and the force exerted by the pressure pulsations in
`the patient’s blood vessels during each heartbeat. The beat
`ing heart causes the pressure in the cuff to oscillate at each
`step of de?ation. The apparatus continues in this fashion
`until a complete envelope of oscillation amplitude versus
`cuff pressure is obtained. The cuff pressure at Which the
`maximum amplitude oscillations are obtained is indicative
`of the mean arterial pressure. The systolic and diastolic
`pressure estimates are also determined from prede?ned
`functions of the envelope data. The oscillometrically deter
`mined systolic, MAP, and diastolic are considered estimates
`of the true intra-arterial pressure values. HoWever, it is also
`knoWn that arterial compliance plays a major role in the
`estimating functions; arterial compliance can change in
`complicated and unpredictable Ways as physiological cir
`cumstances change.
`
`BRIEF SUMMARY OF THE INVENTION
`The oscillometric blood pressure is determined indirectly
`from a cuff that is placed around a portion of the body, such
`as an upper arm, of the human being Whose blood pressure
`is desired. The cuff is in?ated to a predetermined pressure,
`preferably great enough to occlude the ?oW of blood in the
`limb of the patient. Then the cuff is de?ated in a controlled
`manner to produce a de?ation pressure in the cuff that
`decreases With time. In the preferred embodiment, the cuff
`is de?ated in regular pressure increments thereby producing
`a plurality of discrete de?ation pressure levels.
`During each of a plurality of heartbeats, the pressure
`oscillations that occur at the discrete de?ation pressure
`levels are measured and stored in the apparatus. The com
`plete data set of the amplitude of the oscillations versus the
`discrete pressure levels is knoWn as the oscillometric enve
`lope. The oscillometric estimate of the mean arterial pres
`sure is determined from this envelope data. For example, the
`estimate of the mean arterial pressure (MAP) is the de?ation
`pressure level that occurs When the oscillation measure
`ments have the greatest amplitude. Similarly, the systolic
`pressure can be estimated from the envelope data by ?nding
`the discrete pressure level Which occurred When the oscil
`lation amplitude is a predetermined fraction of the maximum
`oscillation siZe at cuff pressures above MAP. Note that
`interpolating betWeen discrete de?ation pressure levels may
`produce a more accurate estimate of systolic pressure.
`
`The invention generally relates to oscillometric blood
`pressure determining techniques, and more particularly to
`determining the diastolic pressure using that technique.
`Knowing the pressures exerted by blood on the blood
`vessel Walls of patients is of great value to those engaged in
`medical practice. In the case of humans, the pressure in the
`vascular system is measured for many reasons, including
`diagnosis, ascertainment of the progress of therapy, the
`physiological state When under anesthesia, etc. As an
`example, the determination of arterial blood pressure is an
`essential element in the diagnosis of a patient suspected of
`cardiac disease. Normal human arterial blood pressure
`ranges betWeen 80—120 millimeters of mercury, Whereas
`elevations of arterial blood pressure above that range are
`found in cases of congestive heart failure, renal artery
`disease, coarctation of the aorta, etc. Additionally, untreated
`hypertension is knoWn to be associated With an increased
`risk of stroke, coronary artery disease, and aneurysms.
`During the cycle of the heartbeat, Which normally occurs
`approximately once per second, the arterial blood pressure
`oscillates. When the heart muscle contracts, knoWn as
`systole, blood is pushed into the arteries. This increases the
`arterial pressure. When the heart muscle relaxes, knoWn as
`diastole, the arterial blood pressure falls. The maximum of
`the arterial pressure oscillation during the heartbeat is
`knoWn as systolic pressure; the minimum is knoWn as
`diastolic pressure. The arterial pressure versus time Wave
`form can also be used to calculate What is knoWn as mean
`arterial pressure. The mean arterial pressure (MAP) is cal
`culated by integrating the arterial pressure Waveform for one
`cycle and then dividing that quantity by the cycle period.
`The indirect techniques of oscillometry and auscultation are
`used in practice to estimate the systolic, mean, and diastolic
`pressures non-invasively. HoWever, it is knoWn that under
`certain rare conditions the diastolic estimate Which oscil
`lometry produces is inaccurate, yet the systolic and MAP
`estimates are good. It is the purpose of this invention to
`improve the diastolic estimate using easily obtained, but
`previously ignored oscillometric information.
`The auscultatory method is commonly used by medical
`personnel to indirectly measure arterial blood pressure. In
`this technique, constrictive pressure is gradually applied
`about the limb of the patient until the ?oW of blood through
`the limb vessel has been arrested, as determined by listening
`to a stethoscope applied over the vessel at a point distal the
`point of constriction. Then upon gradual release of the
`constriction pressure, the beginning of the ?oW through the
`vessel can be heard and the constriction pressure is noted on
`a gauge reading in millimeters of mercury. This pressure is
`referred to as systolic pressure and is taken as an estimate of
`the true intra-arterial systolic pressure. The pressure then is
`gradually released further until the sounds of the ?oW again
`
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`3
`Diastolic pressure can be estimated from the envelope
`data by ?nding the discrete pressure level Which occurred
`When the oscillation amplitude is a predetermined fraction of
`the maximum oscillation siZe at cuff pressures beloW MAP.
`Interpolating betWeen discrete de?ation pressure levels may
`produce a more accurate estimate of diastolic pressure. This
`method can lead to errors in the determination of diastolic
`pressure under some circumstances.
`In the preferred embodiment, the diastolic pressure is
`determined by measuring the area of the oscillation com
`plexes. The diastolic pressure is determined by ?nding the
`de?ation pressure beloW MAP that produces the largest
`oscillation area.
`If for a given measurement, the measured amplitude under
`the oscillation pulse is greatest at MAP, then the diastolic
`pressure Will be determined from the de?ation pressure
`Where the oscillation amplitude is a predetermined fraction
`of the maximum amplitude.
`In an alternative embodiment, the diastolic pressure is
`determined by ?nding a ?rst de?ation pressure at Which the
`maximum oscillation area occurs and a second de?ation
`pressure at Which the predetermined amplitude ratio occurs.
`The diastolic pressure is calculated as the average of the ?rst
`and second de?ation pressures.
`
`DESCRIPTION OF THE OF THE DRAWINGS
`
`FIG. 1 is a block diagram of an indirect noninvasive
`apparatus for measuring blood pressure;
`FIG. 2 is ?oWchart of the operation of the apparatus;
`FIG. 3 is a graph of pressure in a cuff of the apparatus;
`FIG. 4 is a graph of the amplitude of the oscillation pulses
`of the cuff pressure; and
`FIG. 5 is a graph of the area of the oscillation pulses.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`With reference to FIG. 1, an automatic blood pressure
`measuring apparatus 10 employs an in?atable cuff 12 shoWn
`Wrapped around an arm 14 of a human medical patient. The
`in?atable cuff 12 is connected to a pump 16 by a ?exible ?rst
`tube 18. The ?rst tube also connects to an electrically
`operated de?ation valve 20 and to a protective over pressure
`sWitch 34 Which responds to excessive pressure being
`applied to the cuff 12. A?exible second tube 22 couples the
`cuff 12 to a pressure transducer 24 Which produces an
`electrical signal at output that indicates the pressure Within
`the cuff.
`The output of the pressure transducer 24 is connected
`directly to one input of a multiplexer 27. The pressure
`transducer output also is coupled to a band pass ?lter 25
`Which in turn is connected to an ampli?er 26 Which has an
`output connected to another input of the multiplexer 27. The
`?lter 25 and ampli?er 26 are designed to reject the dc.
`component of pressure signal produced by the transducer 24
`and yet amplify the blood pressure oscillations, as Will be
`described. Speci?cally, the ?lter 25 passes those signals
`having frequency components in an approximate range of
`one to ten HertZ and strongly rejects other frequency com
`ponents. The ampli?er 26 magni?es loW level signals from
`the ?lter 25. The output signal from the ampli?er 26
`corresponds to the oscillations, or the ac. component, of the
`pressure in the cuff 12. These components have been used in
`previous blood pressure sensors and are Well knoWn to those
`skilled in the art. Alternatively, the un?ltered cuff pressure
`signal could be used if it has enough analog to digital
`conversion resolution.
`
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`4
`The multiplexer 27 selects one of the tWo pressure signals
`and couples the selected signal to an analog input 29 of a
`controller 28. The controller 28 is a computeriZed device
`Which includes a conventional microprocessor, a memory
`for storing a program that controls operation of the apparatus
`10 and data used in the execution of that program, and input
`and output circuits to interface the controller to other com
`ponents of the apparatus. For example, the output of the
`multiplexer 27 is connected to an input of an internal analog
`to digital converter of the controller 28. A control panel and
`display 32 provides a user interface to the blood pressure
`measuring apparatus. The controller 28 has an output con
`nected to control the pump 16.
`Another output of the controller 28 is coupled to a ?rst
`input of an AND gate 30. The AND gate 30 has a second
`input connected to the over pressure sWitch 34 and an output
`that connects to control the de?ation valve 20. In the event
`of an excessive pressure in the cuff 12, the over pressure
`sWitch 34 opens Which results in the output of the AND gate
`opening the de?ation valve 20 to relieve that excessive
`pressure in the cuff 12. Additional devices can be provided
`to alert the attending personnel to abnormal pressure or
`functional conditions.
`In operation, the cuff 12 is Wrapped around the arm 14 of
`a patient Whose blood pressure is to be measured. The
`attendant then activates a sWitch on the control panel 32
`Which commences the measurement operation. Speci?cally,
`the controller 28 responds to the electrical signal produced
`When that sWitch is operated by commencing execution of a
`control program Which performs a measurement cycle.
`With reference to FIG. 2, the control program commences
`at step 40 With the controller 28 initialiZing a step count to
`a value of Zero. At step 42, the controller produces output
`signals Which close the de?ation valve 20 and activatea the
`pump 16 to in?ate the cuff 12. As the cuff is being in?ated,
`the controller 28 monitors the electrical signal from the
`pressure transducer 24 Which indicates the pressure Within
`the cuff 12. The cuff is in?ated to a prede?ned pressure
`Which is knoWn to occlude the ?oW of blood Within the
`blood vessels of the arm 14. For example, if previous
`pressure measurements have been taken from this patient,
`the occlude pressure may be a prede?ned amount (eg 60
`mm of mercury) greater than the previous systolic pressure.
`Once this occlude pressure has been obtained, the controller
`28 terminates operation of the pump 16 While maintaining
`the de?ation valve 20 in a closed state.
`The controller 28 then begins a controlled de?ation of the
`cuff 12 While periodically measuring the pressure therein. In
`the preferred embodiment of the present invention, the
`controller gradually de?ates the cuff in a series of steps as
`shoWn in FIG. 3 and the nominal pressure at each step is
`referred to herein as the “de?ation pressure” or the “de?a
`tion step pressure”. For example, each step may be a
`decrease in pressure of eight millimeters of mercury. As
`noted previously the instantaneous pressure at each step is
`not alWays constant, but oscillates slightly due to the force
`exerted on the cuff 12 by the blood pulsing through the
`patient’s blood vessels. A plurality of pressure measure
`ments are taken at each step to measure those pressure
`oscillations. As Will be described, the systolic and diastolic
`pressures are derived from an analysis of the pressure
`?uctuations at the different pressure steps. Alternatively, the
`pressure Within the cuff can be de?ated in a continuous,
`preferably linear, manner While continuously measuring the
`pressure ?uctuations Within the cuff 12. As a further
`alternative, the cuff pressure measurements used to estimate
`the patient’s blood pressure can be acquired While the cuff
`is being in?ated.
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`5
`The pressure measuring begins at step 44 Where the
`controller 28 sets a measurement count to Zero. The execu
`tion of the software program then enters a loop at Which a
`plurality of measurements of the pressure Within the cuff 12
`are taken. At step 46, the signal from the pressure transducer
`24 is read by the controller 28 and stored in memory. The
`signal produced by the pressure transducer 24 can be read
`directly to sense the de?ation step pressure and then the
`pressure signal processes by the band pass ?lter 25 and
`ampli?er 26 can be read to obtain a measurement of the
`amplitude of the blood pressure oscillation Waveform. Spe
`ci?cally the ?lter and ampli?er remove the baseband or do
`offset of the pressure measurement that is due to the de?a
`tion step pressure leaving only the ac. component repre
`senting the oscillation Waveform. Then, the measurement
`count is incremented at step 48 before the program advances
`to step 50 Where a determination is made Whether the
`requisite number of measurements, designated by the vari
`able X, has been taken at this pressure step. If not, the
`program execution loops back to step 46 to acquire another
`measurement.
`The requisite number of measurements determines the
`length of time that the apparatus remains at each pressure
`step of the de?ation process. The requisite number X is large
`enough to ensure that the pressure Will be measured over at
`least one cardiac cycle. When that number of measurements
`has been taken, the program execution advances to step 52
`at Which the measurements for the current step are analyZed
`to determine Whether they contain artifacts Which Will
`interfere With accurate blood pressure determination. As is
`Well knoWn, artifacts can be produced by arm movement
`during the sensing or by an attendant bumping against the
`cuff. Various processes exist for detecting these artifacts,
`such as described in Us. Pat. No. 4,349,034, the description
`of Which is incorporated by reference. If a signi?cant artifact
`is found, the program execution returns to step 44 to acquire
`another set of measurements at the present de?ation step.
`This loop continues until satisfactory measurements are
`taken or until a determination is made by the controller 28
`that accurate measurement is not possible.
`Once a valid set of pressure measurements has been
`acquired for a given pressure step, the program execution
`advances to step 54 Where the maximum oscillation ampli
`tude for that step is computed. As the pressure Within the cuff
`is released, the force exerted on the cuff by the arterial blood
`?oW produce greater oscillations of the cuff pressure. In
`other Words, When the pressure in the cuff is relatively high,
`only the pressure peaks of each pulse of blood in the
`patient’s arm exceed the de?ation cuff pressure so as to vary
`the total cuff pressure. As the cuff 12 is de?ated further, a
`greater portion of each blood pressure pulse exceeds the
`de?ation cuff pressure, thereby producing pressure oscilla
`tions With larger amplitudes as depicted in FIG. 4. Therefore,
`at step 54, the controller 28 calculates the difference betWeen
`the greatest pressure measured during the step and the
`de?ation pressure of that step. That difference is stored in
`memory as the pulse or oscillation amplitude for the asso
`ciated de?ation pressure step.
`The operation of the measurement apparatus then pro
`ceeds to step 56 Where the de?ation step count is incre
`mented. Next at step 58, the controller opens the de?ation
`valve 20 to release a given amount of pressure Within the
`cuff 12. The controller 28 directly monitors the signal from
`the pressure transducer 24 until the pressure has decreased
`by the desired amount, for example eight millimeters of
`mercury. Then a determination is made at step 60 Whether
`the requisite number of pressure steps has been completed
`
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`for the measurement cycle. The measurement cycle may be
`de?ned in terms of a given number of steps, or dynamically
`by observing the oscillation amplitudes measured for each
`step, the measurement cycle can terminate When those
`amplitudes are not longer changing.
`Upon completion of the measurement cycle, the controller
`28 opens the de?ation valve 20 at step 62 to release any
`remaining pressure Within the cuff 12. Then at step 64, the
`controller examines the oscillation amplitudes stored in
`memory for each of the de?ation steps. Speci?cally, the
`stored value representing the greatest oscillation amplitude
`is located, as occurred for example at time T2 in FIG. 4, and
`the de?ation step pressure at that time is identi?ed. That step
`
`pressure corresponds to the mean arterial pressure At step 66 the systolic pressure is derived by ?rst calculating
`
`a reference peak oscillation amplitude that is given fraction
`(e.g. 0.5) of the greatest oscillation amplitude. The de?ation
`step pressure at the time T1 When that reference peak
`oscillation amplitude ?rst occurred is found. The de?ation
`pressure at that step then corresponds to the systolic pres
`sure. The peak oscillation amplitude of any de?ation step
`may not correspond exactly to the calculated reference peak
`oscillation amplitude. In Which case the reference peak
`oscillation amplitude falls betWeen the peak oscillation
`amplitudes of tWo adjacent de?ation steps. When that
`occurs, the systolic pressure is derived by interpolating the
`de?ation pressures for those steps.
`The present inventor has found that the diastolic pressure
`occurs at the highest de?ation pressure at Which the oscil
`lations have the greatest area. In other Words, the diastolic
`pressure of the patient can be derived by integrating pressure
`measurements for each de?ation step and ?nding de?ation
`cuff pressure of the de?ation step at Which the greatest
`integral occurred. This is accomplished at step 68 by sum
`ming the pressure measurements during each de?ation step
`and identifying the ?rst de?ation step to occur that is
`associated With the largest sum. The de?ation pressure for
`that step corresponds to the diastolic pressure.
`Therefore, the present apparatus determines the systolic
`pressure based on a fraction of the mean pressure during the
`measurement cycle, and determines the diastolic pressure
`based on an integral of the pressure oscillations Which occur
`during each step; and speci?cally, based on the de?ation
`pressure Which occurs at a step that has the greatest integral.
`As a variation of the method by Which the diastolic
`pressure value is determined, the integration procedure
`described above is used to produce a ?rst estimate of the
`diastolic pressure. Then a second estimate of the diastolic
`pressure is derived by ?rst calculating a reference value that
`is given fraction of the greatest oscillation amplitude. The
`de?ation step that occurred after the occurrence of the
`greatest oscillation amplitude are inspected to ?nd the step
`having a peak oscillation amplitude that is closest arithmeti
`cally to the reference value. The de?ation pressure at that
`step then is de?ned as the second estimate of the diastolic
`pressure. That second estimate also can be derived by
`interpolating the de?ation pressures for adjacent de?ation
`steps betWeen Which the reference value is located. The a
`diastolic pressure value then is determined by averaging the
`?rst and second estimates of the diastolic pressure, although
`other arithmetic functions can be employed to derive the
`diastolic pressure value from those estimates.
`The foregoing description Was primarily directed to a
`preferred embodiment of the invention. Although some
`attention Was given to various alternatives Within the scope
`of the invention, it is anticipated that one skilled in the art
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`US 6,440,080 B1
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`7
`Will likely realize additional alternatives that are noW appar
`ent from disclosure of embodiments of the invention.
`Accordingly, the scope of the invention should be deter
`mined from the following claims and not limited by the
`above disclosure.
`What is claimed is:
`1. A method for indirectly measuring blood pressure
`comprising:
`placing a cuff around a portion of a human being;
`varying pressure Within the cuff to produce a plurality of
`cuff pressure levels;
`While at a given cuff pressure level, measuring and storing
`the given cuff pressure level and a plurality of pressure
`oscillation amplitude values to produce a pressure
`oscillation Waveform, thereby producing a plurality of
`measurements;
`integrating a plurality of pressure oscillations of the
`pressure oscillation Waveform to produce a plurality of
`integral values; and
`deriving a ?rst estimate of diastolic pressure for the
`human being in response to the cuff pressure level
`Which occurred coincident With the pressure oscillation
`Which produced the integral value that is greatest in
`magnitude.
`2. The method as recited in claim 1 Wherein the integrat
`ing comprises individually summing pressure oscillation
`amplitude values Which correspond to each of the plurality
`of pressure oscillations.
`3. The method as recited in claim 1 Wherein varying
`pressure Within the cuff comprises in?ating the cuff.
`4. The method as recited in claim 1 Wherein varying
`pressure Within the cuff comprises in?ating the cuff to a
`predetermined pressure, and thereafter de?ating the cuff to
`produce the plurality of pressure levels Which decrease With
`time.
`5. The method as recited in claim 1 further comprising:
`determining a peak value for each pressure oscillation;
`identifying a peak value of greatest magnitude;
`deriving a second estimate of diastolic pressure Which
`corresponds to the cuff pressure level Which occurred
`coincident With the pressure oscillation that has the
`peak value of greatest magnitude; and
`calculating a diastolic, pressure value as a function of the
`?rst estimate of diastolic pressure and the second
`estimate of diastolic pressure.
`6. The method as recited in claim 5 Wherein calculating a
`diastolic pressure value averages the ?rst estimate of dias
`tolic pressure and the second estimate of diastolic pressure.
`7. The method as recited in claim 1 further comprising
`determining an estimated mean arterial pressure for the
`human being from the plurality of measurements.
`8. The method as recited in claim 1 further comprising
`determining an estimated systolic pressure for the human
`being from the plurality of measurements.
`9. A method for indirectly measuring blood pressure
`comprising the steps of:
`(a) placing a cuff around a portion of a human being’s
`body;
`(b) in?ating the cuff to a predetermined pressure;
`(c) periodically measuring pressure in the cuff thereby
`producing an oscillation pressure Waveform;
`(d) de?ating the cuff by a predetermined increment of
`pressure, Which results in a de?ation pressure in the
`cuff;
`(e) repeating the steps (c) and (d) for a plurality of times
`thereby producing a plurality of oscillation pressure
`Waveforms;
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`(f) utiliZing an oscillometric technique to estimate a
`systolic pressure and a mean arterial pressure for the
`human being from a plurality of oscillation amplitudes
`derived from the oscillation pressure Waveforms;
`(g) integrating the plurality of measurements taken during
`each different de?ation pressure to derive an integral
`value for each different de?ation pressure; and
`(h) deriving a ?rst estimate of diastolic pressure of the
`human being from the de?ation pressure associated
`With the greatest integral value.
`10. The method as recited in claim 9 further comprising:
`identifying a separate peak value for each of the plurality
`of oscillation pressure Waveforms;
`identifying a peak value of greatest magnitude;
`deriving a second estimate of diastolic pressure Which
`corresponds to the de?ation pressure Which occurred
`coincident With the oscillation pressure Waveform that
`has the peak value of greatest magnitude; and
`calculating a diastolic pressure value as a function of the
`?rst estimate of diastolic pressure and the second
`estimate of diastolic pressure.
`11. The method as recited in claim 10 Wherein calculating
`a diastolic pressure value averages the ?rst estimate of
`diastolic pressure and the second estimate of diastolic pres
`sure.
`12. The method as recited in claim 9 Wherein the step of
`integrating the plurality of measurements comprising sepa
`rately summing a plurality of measurements.
`13. The method as recited in claim 9 Wherein the step of
`in?ating the cuff to a predetermined pressure comprising
`activating an electrically operated pump.
`14. The method as recited in claim 9 Wherein the step of
`de?ating the cuff comprises opening an electrically con
`trolled valve for a period of time.
`15. The method as recited in claim 9 Wherein de?ating the
`cuff comprises opening an electrically controlled valve,
`measuring pressure in the cuff, and closing the electrically
`controlled valve When the pressure in the cuff has decreased
`by the predetermined increment.
`16. An apparatus for producing information indicative of
`blood pressure of an human being through indirect mea
`surement comprising:
`an in?atable cuff;
`a pump connected to the cuff, for in?ating the cuff to a
`pressure above systolic pressure of the human being;
`a de?ating valve connected to the cuff to release ?uid
`from Within the cuff thereby varying pressure Within
`the cuff;
`a transducer that measures pressure oscillations in the cuff
`caused by heartbeats of the human being; and
`a controller responsive to the transducer for initially
`energiZing the pump to in?ate the cuff and subse
`quently energiZing the de?ating valve incrementally to
`de?ate the cuff at predetermined pressure increments,
`Wherein the controller integrates the pressure oscilla
`tions occasioned by successive heartbeats to produce a
`plurality of integral values and identi?es as a diastolic
`pressure, the pressure Which occurs in the cuff When the
`pressure oscillations have an integral value of greatest
`magnitude.
`17. The apparatus as recited in claim 16 Wherein the
`controller integrates the pressure oscillations by summing a
`plurality of measurements of pressure in the cuff acquired
`from the transd