as) United States
`a2) Patent Application Publication (10) Pub. No.: US 2007/0016086 Al
`(43) Pub. Date: Jan. 18, 2007
`
`Inukai et al.
`
`US 20070016086A1
`
`(54) BLOOD PRESSURE MONITORING
`APPARATUS
`
`(30)
`
`Foreign Application Priority Data
`
`Ju: 29, ZOOS,
`Jun. 29, 2005
`
`CIP): scssssssscncsspescssonccctanssesvetens 2005-190469
`(IP) cc eceeeeseseeeeeaneees 2005-190470
`ek
`eyes
`a
`Fublicetion Clapaiticalion
`
`(51)
`
`Int. Cl.
`(2006.01)
`A6IB 5/02
`=
`gt
`52) UES. cscsssssteepeerssnenservsntenvenneavorneacen 600/485; 600/500
`2)
`.
`(57)
`
`ABSTRACT
`
`In blood pressure monitoring apparatus which continuously
`estimates and monitors blood pressure by using the pulse
`wave propagation time, blood pressure fluctuation can be
`accurately estimated. If both blood pressure estimated from
`the pulse wave propagation time and a waveform parameter
`obtained from the accelerated pulse wave have abnormal
`values,
`it
`is determined that
`the blood pressure is truly
`fluctuating, and blood pressure measurement by another
`method, e.g., blood pressure measurement using a cullis
`performed.
`
`OPERATION
`UNIT
`
`peo
`
`100
`
`(75)
`
`Inventors: Hidekatsu Inukai, Nagoya-shi (JP);
`Toru Oka, Ichinomiya-shi (JP)
`
`Correspondence Address:
`DRINKER BIDDLE & REATH (DC)
`1500 K STREET, N.W.
`SUITE 1100
`WASHINGTON, DC20005-1209 (US)
`
`(73) Assignee: FUKUDA DENSHI CO.,, LTD.
`
`(21) Appl. No.:
`
`11/475,938
`
`(22)
`
`Filed:
`
`Jun. 28, 2006
`
`12
`
`PRESSURE
`
`ie
`
`CUFF
`
`PUMP
`
`——
`
`i DISPLAY
`
`70
`
`14
`
`20
`
`ELECTRO-
`CARDIOGRAM
`ELECTRODE
`
`FINGER SENSOR
`(SPO2,
`PULSE WAVE)
`
`#0
`
`OTHER
`SENSORS
`
`
`
`
`CONTROLLER
`
`=|
`
`7
`
`:
`
`~ TO EXTERNAL
`APPARATUS
`
`001
`
`Apple Inc.
`APL1035
`U.S. Patent No. 8,923,941
`
`Apple Inc.
`APL1035
`U.S. Patent No. 8,923,941
`
`001
`
`

`

`Patent Application Publication
`
`Jan. 18,2007 Sheet 1 of 5
`
`US 2007/0016086 Al
`
`
`
`SYOSNAS
`
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`

`

`Patent Application Publication Jan. 18,2007 Sheet 2 of 5
`
`US 2007/0016086 Al
`
`FIG. 2
`
`PLETHYSMOGRAPH
`
`ACCELERATED PULSE WAVE
`
`003
`
`003
`
`

`

`Patent Application Publication Jan. 18,2007 Sheet 3 of 5
`
`US 2007/0016086 Al
`
`1G. 3
`
`BLOOD PRESSURE
`MONITORING PROCESS
`
`
`
`
`
`START BLOOD PRESSURE
`
`
`MEASUREMENTUSING
`CUFF, AND ACQUISITION
`OF ECG AND PULSE WAVE
`
`
`S101
`
`S111
`
`CALCULATE ACCELERATED
`PULSE WAVE
`
`$113
`
`CALCULATE WAVEFORM
`PARAMETER
`
`
`
`NO
`
`
`
`
`OUTSIDE
`IS FLUCTUATION
`AMOUNT ABNORMAL?
`NORMAL RANGE?
`
`
`
`
`
`
`YES
`
`YES
`
`NO
`
`
`
`
`
`$130
`
`HAVE
`TWO CONDITIONS
`
`BEEN CONTINUOUSLY MET
`
`FOR PREDETERMINED PERIOD,
`
`
`OR HAS PREDETERMINEDTIME
`ELAPSED SINCE LAST
`
`
`MEASUREMENT
`
`9
`
`[YES
`
`NO
`
`BLOOD PRESSURE
`MEASUREMENTUSING CUFF
`
`S140
`
`004
`
`004
`
`

`

`Patent Application Publication
`
`Jan. 18,2007 Sheet 4 of 5
`
`US 2007/0016086 Al
`
`TWWYON bold
`
`Y3AO0Vdd
`
`Y3MOT
`
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`
`(98S)Ow]
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`Y3AOVdd——
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`Y3A0Wdd——
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`Wadell-"=
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`

`

`Patent Application Publication Jan. 18,2007 Sheet 5 of 5
`
`US 2007/0016086 Al
`
`FIG. 5
`
`ACQUIRE ACTUALLY MEASURED VALUE
`
`$201
`
`COMPAREWITH ESTIMATED BLOOD PRESSURE
`VALUE OR PAST ACTUALLY MEASURED VALUE
`
`S203
`
`me
`
`i
`
`$205
`IS CALIBRATION NECESSARY?
`
`YES
`
`V
`
`CALIBRATE COEFFICIENT &
`
`S207
`
`1
`
`IS WAVEFORM PARAMETER
`FLUCTUATION LARGE?
`
`$209
`
`
`
`CORRECT COEFFICIENT o
`
`i)
`
`S211
`
`$213
`
`S215
`
`CALIBRATE COEFFICIENT B
`
`STORE EXPRESSION
`
`END
`
`006
`
`006
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`BLOOD PRESSURE MONITORING APPARATUS
`
`CLAIM OF PRIORITY
`
`(0001] This application claims priority from Japanese
`Patent Application Nos. 2005-190496 and 2005-190470,
`both filed on Jun. 29, 2005, which are hereby incorporated
`by reference herein.
`
`FIELD OF THE INVENTION
`
`[0002] The present invention relates to blood pressure
`monitoring apparatus for noninvasively and continuously
`monitoring blood pressure.
`
`BACKGROUNDOF THE INVENTION
`
`In an operating room, ICU, orthelike, it is some-
`[0003]
`times necessary to continuously monitor the blood pressure
`of a patient. As a conventional technique of noninvasively
`and continuously monitoring the blood pressure, blood
`pressure estimation based on the pulse wave propagation
`time is known,
`
`[0004] This technique uses the fact that the time (pulse
`wave propagation time) required for a pulse wave to propa-
`gate between two points in a living body or the pulse wave
`propagation velocity obtained by dividing the blood vessel
`length between the twopoints by the pulse wave propaga-
`tion time has a correlation with the blood pressure. For
`example, the pulse wave propagation time is continuously
`measured and applied to an expression having a precali-
`brated coefficient,
`thereby continuously calculating and
`monitoring an estimated blood pressure (e.g., Japanese
`Patent Laid-Open No. 10-66681).
`
`To measure the pulse wave propagation time, how-
`[0005]
`ever, pulse waves must be measured in different locations, so
`the measurement requires a long time. Also,it is sometimes
`difficult to attach sensors or cuffs for measuring pulse waves
`to two locations. As described in Japanese Patent Laid-Open
`No. 10-66681, therefore, a general approachis to calculate
`the pulse wave propagation time by using an electrocardio-
`gram (ECG) normally measured by a biological information
`monitoring apparatus and a pulse wave measured in one
`predetermined location (e.g., a fingertip) of a living body.
`
`[0006] Unfortunately, the use of an ECG inthe calculation
`of the pulse wave propagation time has a problem of the
`measurement accuracy. That is, an ECG is a signal which
`represents not a pulse wavebutthe electrical state change of
`the heart. There is a time difference (preejection period)
`between the timing at which the electrical state change
`occurs and the timing at which the heart actually contracts
`to generate a pulse wave. Accordingly,
`the pulse wave
`propagation time calculated by using the observation timing
`ofthe feature point of an ECGas a starting point contains an
`error caused by the preejection period.
`
`If the preelection period is constant, this error is
`[0007]
`easy to correct. However, the preejection period changes
`from one person to another, and can change occasionally
`even in the same person. Therefore, an improvement of the
`accuracy by correction is limited.
`
`[0008] Blood pressure monitoring apparatus normally per-
`forms control such that
`if blood pressure continuously
`measured on the basis of the pulse wave propagation timeis
`
`is
`abnormal, more accurate blood pressure measurement
`performed by using a cuff or the like, and an alarmis output
`if an abnormal value is detected by this measurement.
`
`[0009] Blood pressure measurement using a cuffis estab-
`lished as a method of noninvasively measuring the blood
`pressure, and effective to automatically obtain a well reliable
`blood pressure. However, this method requires avascular-
`ization, so the frequent use of the method is undesirable
`because the load on a patient increases. Therefore, accurate
`determination of the need for culf blood pressure measure-
`ment is important not only to perform an appropriate therapy
`but also to reduce the load ona patient.
`
`as
`accuracy
`determination
`the
`increase
`[0010] To
`described above,it is also importantto increase the accuracy
`of the estimated blood pressure based on the pulse wave
`propagationtime calculated from an ECG and a pulse wave
`observed at one point.
`
`SUMMARY OF THE INVENTION
`
`[0011] The present invention has been made in consider-
`ation of the problemsof the prior art as described above, and
`has as its object to make it possible to more accurately
`determine the necessity of high-accuracy blood pressure
`measurement, in blood pressure monitoring apparatus which
`continuously estimates blood pressure on the basis ofthe
`pulse wave propagation time, and performs more accurate
`blood pressure measurement where necessary.
`
`invention to
`is another object of the present
`It
`[0012]
`increase the accuracy of an estimated blood pressure in
`blood pressure monitoring apparatus which continuously
`estimates blood pressure on the basis of the pulse wave
`propagation time.
`
`[0013] According to one aspect ofthe present invention,
`there is provided a blood pressure monitoring apparatus
`comprising: blood pressure measuring unit adapted to mea-
`sure blood pressure in response to blood pressure measure-
`ment designation; pulse wave acquiring unit adapted to
`acquire a pulse wavein a predetermined locationof a living
`body; pulse wave propagationtime calculating unit adapted
`to calculate a pulse wave propagation time from the pulse
`wave, and one of an electrocardiogram and a pulse wave
`acquired from a location different from the predetermined
`location; estimated blood pressure calculating unit adapted
`to calculate an estimated blood pressure on the basis ofthe
`pulse wave propagation time: accelerated pulse wave cal-
`culating unit adapted to calculate an accelerated pulse wave
`from the pulse wave; waveform parameter calculating unit
`adapted to calculate a predetermined waveform parameter
`from a waveform contained in the accelerated pulse wave:
`and control unit adapted to provide the blood pressure
`measurement designation to the blood pressure measuring
`unit to cause the blood pressure measuring unit to measure
`blood pressure, if both the estimated blood pressure and the
`predetermined waveform parameter are abnormal.
`
`[0014] According to another aspect of the present inven-
`tion, there is provided a blood pressure monitoring apparatus
`comprising: blood pressure measuring unit adapted to mea-
`sure blood pressure by a predetermined method; pulse wave
`acquiring unit adapted to acquire a pulse wave in a prede-
`termined locationof a living body; pulse wave propagation
`time calculating unit adapted to calculate a pulse wave
`
`007
`
`007
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`FIG. 5 is a flowchart explaining the operation of
`[0023]
`calibrating an expression for calculating an estimated blood
`pressure, in the biological information monitoring apparatus
`according to the embodiment of the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`propagation time from the pulse wave, and one of an
`electrocardiogram and a pulse wave acquired froma loca-
`tion different from the predetermined location; estimated
`blood pressure calculating unit adapted to calculate an
`estimated blood pressure by applying the pulse wave propa-
`gationtime to a predetermined expression; accelerated pulse
`wave calculating unit adapted to calculate an accelerated
`pulse wave from the pulse wave; waveform parameter
`calculating unit adapted to calculate a predetermined wave-
`form parameter from a waveform contained in the acceler-
`ated pulse wave;and calibrating unit adapted to calibrate the
`[0025] FIG.1is a block diagram showing an example of
`
`expression by using a value measured by the blood pressure
`the functional arrangement of a biological
`information
`measuring unit, wherein if a fluctuation amount of the
`monitoring apparatus as blood pressure monitoring appara-
`waveform parameter exceeds a predetermined amount, the
`tus according to the embodimentof the present invention.
`calibrating unit performs the calibration after correcting a
`calibration amount which is applied when the fluctuation
`amount of the waveform parameter does not exceed the
`predetermined amount.
`
`[0024] A preferred embodiment ofthe present invention
`will now be described in detail
`in accordance with the
`
`accompanying drawings.
`
`[0026] Referring to FIG. 1, a cuff 10 has a band-like form,
`and incorporates a rubber pouch which expands and con-
`tracts by pumping of a pump 14. The cuff 10 is normally
`attached to one of the limbs, typically the upper arm ofa
`patient. A pressure sensor 12 senses a change in pressure
`applied to the gas filled in the internal rubber pouch ofthe
`cuff 10, converts the pressure signal into an electrical signal,
`and outputs the electrical signal to a controller 100.
`
`[0027] An electrocardiogram (ECG) electrode 20 com-
`prising a plurality of electrodes is attached to a predeter-
`mined position of the chest of a patient, and outputs an
`induced waveform as an ECGsignal to the controller 100.
`A finger sensor 30 is a so-called pulse oximeter which
`optically senses and outputs an oxygen saturation degree
`(SPO2) and plethysmograph to the controller 100. The
`absorbance of hemoglobin changes in accordance with
`whether hemoglobin combines with oxygen, and also
`changes in accordance with the wavelengthoflight. On the
`basis of these facts, the finger sensor 30 generally measures
`the oxygen saturation degree by using two wavelengths,1.e.,
`red light and infrared light. Also, since theAC component of
`transmitted light or reflected light changes in accordance
`with the blood flow volume, thisAC component is detected
`as a photoplethysmograph (PTG).
`
`[0028] Other sensors 40 sense other biological informa-
`tion such as the respiration and body temperature of a
`patient, and one or more sensors are connected to the
`controller 100 as needed. The other sensors 40 are not
`
`directly related to the blood pressure monitoring operation
`of this embodiment, so no further explanation thereof will be
`made.
`
`In the present invention having the above arrange-
`[0015]
`the necessity of blood pressure measurement by
`ments,
`another method is determined by considering: the waveform
`parameter, which is obtained from the accelerated pulse
`wave andreflecting the functional state of the blood vessel,
`is taken into consideration as well as the continuous esti-
`mated blood pressure, which is based on the pulse wave
`propagationtime calculated from an ECG and a pulse wave
`observed at one point. Therefore, the determination accuracy
`can be increased.
`
`[0016] Also, according to the present invention, the wave-
`form parameter obtained from the accelerated pulse wave is
`taken into consideration in the calculation ofthe continuous
`estimated blood pressure based on the pulse wave propaga-
`tion time calculated from an ECG and a pulse wave mea-
`sured at one point. Accordingly, the accuracy of the esti-
`mated blood pressure can be increased.
`
`[0017] Other features and advantages of the present inven-
`tion will be apparentfromthe following description takenin
`conjunction with the accompanying drawings, in whichlike
`reference characters designate the same or similar parts
`throughout the figures thereof.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0018] The accompanying drawings, which are incorpo-
`rated in and constitute a part of the specification, illustrate
`embodiments of the invention and,
`together with the
`description, serve to explain the principles of the invention.
`
`[0029] An operationunit 50 is a man-machineinterface by
`[0019] FIG.1is a block diagram showing an example of
`
`which the user (measurer) inputs various settings and infor-
`the arrangement of a biological
`information monitoring
`mation concerning a patient and provides instructions to the
`apparatus as blood pressure monitoring apparatus according
`biological information monitoring apparatus. The operation
`to an embodimentofthe present invention;
`unit 50 is generally constructed by appropriately combining
`a keyboard, a mouse, buttons, switches, dials, a touch panel,
`and thelike.
`
`FIG. 2 is a graph showing examples ofanoriginal
`[0020]
`waveform and its accelerated pulse wave;
`
`FIG. 3 is a flowchart explaining the blood pressure
`[0021]
`monitoring operation ofthe biological information monitor-
`ing apparatus according to the embodiment ofthe present
`invention:
`
`FIG. 4 is a graph showing actual examples of blood
`[0022]
`pressure calculated by the biological information monitoring
`apparatus according to the embodiment, a direct blood
`pressure measured invasively, and waveform parameters:
`and
`
`[0030] A printer 60 and display 70 are representative
`output devices, and visually output thestate ofthe apparatus,
`measurement results, and the like. An external interface (I/F)
`80 is typically a network interface, serial interface (e.g., a
`USBor IEEE1394), modem, or the like, and communicates
`with an external apparatus which is connected invasively or
`across a network.
`
`[0031] Astorage unit 90 is typically a hard disk drive, and
`records programs for controlling the operation of the bio-
`
`008
`
`008
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`information monitoring apparatus, various data,
`logical
`measurement results, personal information of patients, and
`the like. The storage unit 90 may also include at least one
`other type of storage device, e.g., a device which reads and
`writes a writable removable medium such as a memory card
`or an optical disk.
`
`telesystolic component obtained when the blood pressure
`was measured last time by using a cuff is used as the other
`condition described above. That is,
`it is possible to deter-
`minethat the possibility that the blood pressure has actually
`fluctuated is higher when a changeis found in the center or
`periphery in addition to the change in estimated blood
`pressure,
`than when only the estimated blood pressure
`fluctuates or only the change in the center or periphery is
`found.
`
`[0032] The controller 100 controls the operation of the
`whole biological
`information monitoring apparatus. The
`controller 100 has, e.g., a CPU and RAM,and controls the
`individual units by loading the control programs stored in
`[0039] Note that in this embodiment, a wave height ratio
`the storage unit 90 into the RAM and executing the loaded
`b/a of b-waveto a-waveis used as a parameterindicating the
`programs by the CPU,
`thereby implementing processes
`state of the center, and a wave heightratio d/a of d-wave to
`including the blood pressure monitoring operation (to be
`a-wave is used as a parameter indicating the state of the
`described later) of the biological
`information monitoring
`periphery. The ratios to the wave height of a-waveare herein
`apparatus. Note that not all the processes need be executed
`used in order to compare the parameters obtained from an
`using software by the CPU. For example, signal processing
`accelerated pulse wave whennocalibration exists inastrict
`sense, and this is a kind of normalization.
`such as A/D conversionand filtering of signals input from
`the various sensors may also be assigned to a DSP or
`dedicated hardware,
`thereby appropriately using another
`arrangement.
`
`[0033] The blood pressure monitoring operation by the
`biological information monitoring apparatus of this embodi-
`ment will be explained below.
`
`[0034] The biological information monitoring apparatus
`ofthis embodimentis similar to the prior art in that the pulse
`wave propagation velocity is continuously calculated by
`using an ECGand plethysmograph, and an estimated blood
`pressure is continuously calculated by using an expression
`having a precalibrated coeflicient, and that the necessity of
`blood pressure measurement using a culf is determined by
`using the estimated blood pressure.
`
`In this embodiment, however, it is determined that
`[0035]
`blood pressure measurement using a cuffis necessary only
`whenanother condition is met in addition to the estimated
`blood pressure, thereby increasing the abnormality detection
`accuracy in continuous blood pressure monitoring. This
`embodimentis characterizedin that the value ofa parameter
`obtained from an accelerated pulse wave is used as the other
`condition.
`
`[0036] The accelerated pulse wave is obtained by calcu-
`lating second-ordertime differential of a pulse wave, and has
`characteristic waves from a-wave to e-wave as shownin
`FIG. 2. A-wave and b-wave represent presystolic compo-
`nents, c-wave and d-wave represent telesystolic compo-
`nents, and e-wave represents a diastolic component(e.g.,
`Iketani et al., “Plethysmograph (Accelerated Pulse Wave)
`for Evaluating Degree of Arteriosclerosis by Hypertension”,
`vol. 10, no. 6, 2003, pp. 54-60).
`
`[0037] According to Iketani et al., the presystolic compo-
`nent reflects-a driving pressure wave generated by ejection
`of the blood when the heart contracts, and the telesystolic
`component is a re-elevated pressure wave generated when
`the driving pressure wave propagates to the periphery, and
`the returned reflected wave overlaps the driving pressure
`wave. Accordingly, it can be presumed that the presystolic
`component represents the state of the heart (center), and the
`telesystolic component represents the state of the periphery.
`
`In this embodiment, therefore, the conditionthatat
`[0038]
`least one of the presystolic component or telesystolic com-
`ponent fluctuates by an amount exceeding a predetermined
`amount from the value of the presystolic component or
`
`the blood
`[0040] On the basis of the above description,
`pressure monitoring operation of the biological information
`monitoring apparatus according to this embodiment will be
`explained with reference to a flowchart shownin FIG, 3.
`
`First, in step S101, the acquisition of an ECGand
`(0041]
`pulse wave is started. Also, as initialization,
`initial blood
`pressure measurement using a cuff is performed, and the
`initial values of an accelerated pulse wave parameter and
`estimated blood pressure are calculated by a method to be
`explained below, and stored in the storage unit 90. After that,
`the processing (steps S111 to S115) ofthe accelerated pulse
`wave and the process (steps S121 to S125) of estimating the
`blood pressure on the basis of the pulse wave propagation
`velocity are performed inparallel.
`
`the controller 100 calculates the
`In step S111,
`(0042]
`accelerated pulse wave from the photoelectric plethysmo-
`graph from the finger sensor 30. In step $113, on the basis
`of a-wave to d-wave contained in one pulse of the acceler-
`ated pulse wave, parameters concerning the presystolic
`component and telesystolic component, i.e., the wave height
`ratios b/a and d/a in this embodiment, are obtained.
`
`In step $115, the controller 100 calculates fluctua-
`[0043]
`from the obtained parameter values and values
`tions
`obtained in the last cuff blood pressure measurement, and
`determines whether
`the fluctuations are abnormal. For
`example, the controller 100 sets
`D1(%)=1-{b/a(current) }/{b/a(ref)}x100
`D2(%)=1-{d/a(current)}/{d/a(ref}}x100
`
`The controller 100 can check the presence/absence ofabnor-
`mality by determining whether one, both, or a predetermined
`one of
`
`|Dl/>Thh
`|D2/>Thd
`
`(la)
`(15)
`
`is satisfied. Since, however,b/a is a parameter indicating the
`state ofthe center, it is desirable to take account of at least
`the value ofb/a. In step S115, the parameters as objects of
`abnormality determination, the expressions for abnormality
`determination, and the threshold values used are predeter-
`mined. However, these values and expressions need not be
`fixed but can be changed any time.
`
`[0044] Note that in the above equations, (current) indi-
`cates a present calculated value, and (ref) indicates a refer-
`
`009
`
`009
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`ence calculated value obtained in the last cuff blood pressure
`measurement. Note also that the threshold values Thb and
`
`Thd indicating normal ranges can be either equal or indi-
`vidually set. In addition, the fluctuation need not be absolute
`values, and it is also possible to individually set the thresh-
`old value (upper limit) on the increasing side and the
`threshold value (lower limit) on the decreasing side. Prac-
`tical values of the threshold values can be appropriately
`determined. For example, Thb=Thd=20(%) can be set in
`inequalities (1a) and (1b).
`
`It is also possible to dynamically changethe thresh-
`[0045]
`old values in accordance with the results ofperiodical blood
`pressure measurements using a cull. For example, if the
`result of culf blood pressure measurement is smaller than a
`predetermined value,
`it
`is possible to make the threshold
`value on the decreasing side stricter (make the threshold
`value easier to exceed) than when the measurementresult is
`not smaller than the predetermined value, thereby monitor-
`ing the decrease in blood pressure more strictly. More
`specifically, when the normal range is defined by the upper
`and lower limits, the lower limit is set to be high. In this
`case,
`the lower limit becomes easier to exceed, so the
`decrease in blood pressure canbe strictly monitored. On the
`contrary, if the cuff measurementresult is large,it is possible
`to make the threshold value on the increasing side stricter
`(make the upper limit of the normal range smaller).
`
`[0046] The fluctuation amount need not be a ratio (per-
`centage), but may also be a difference.
`
`Ifthe fluctuation amountis found to be abnormal in
`(0047]
`step S115, the flow advances to step S130. If the fluctuation
`amount is found to be normalin step 5115, the flow returns
`to step S111 to continue the processing for the next heart
`beat.
`
`In steps S121 to S125, the same blood pressure
`[0048]
`estimating process as the conventional method is executed.
`[0049]
`In step S121, the pulse wave propagationtime is
`calculated on the basis of an ECG detected by the electro-
`cardiogram electrode 20 and a plethysmograph sensed by
`the finger sensor 30. More specifically, the controller 100
`performssignal processing such as noise removal and wave-
`form shaping normally performed on an ECG and plethys-
`mograph, and calculates the time difference between feature
`points in the heart beats of the ECGand plethysmographas
`the pulse wave propagationvelocity. In this case, the feature
`point of the ECG canbe, e.g.. the peak position of the R
`wave,and the feature point of the plethysmographcan be the
`leading edge of the waveform. Also, as described above,
`there is a time difference (preelection period) between the
`appearance of the R wave to the generation ofthe actual
`pulse wave. Therefore, correction can be performed by
`subtracting a time corresponding to a preejection period
`statistically calculated beforehand from the time difference
`between the feature points.
`
`In step $123, an estimated blood pressure is
`[0050]
`obtained from the calculated pulse wave propagation time.
`[0051] That is, an estimated blood pressure is calculated
`by applying the pulse wave propagation time to
`Estimated blood pressure=cax(pulse wave propagation
`time [msec])+B
`
`(2)
`
`[0052] Note that the coefficients @ and fp need only be
`determined in advance. That is, this equation is a linear
`equation with two unknowns, so the values of the coefli-
`cients a and f can be determined by using at least two
`actually measured blood pressures and the corresponding
`pulse wave propagation times.
`
`[0053] Each coefficient need not be fixed but may also be
`updated to an optimumvalue by using an actually measured
`value obtained by another method (cuff measurement or
`direct measurement) and the pulse wave propagationtimeat
`the corresponding timing.
`
`In step $125, whether the estimated blood pressure
`[0054]
`is an abnormal value is determined. This determination can
`be performed by determining whether the estimated blood
`pressure is larger than the upper limit or smaller than the
`lowerlimit of a predetermined normal range, or determining
`whetherthe estimated blood pressure fluctuates more than a
`predetermined amount (which can be either a fluctuation
`ratio or difference) from the value of the last cuff blood
`pressure measurement.
`
`[0055] Like the threshold values of the waveform param-
`eters, these upper limit, lower limit, and fluctuation amount
`can be either fixed with respect to the value of cuff blood
`pressure measurement, or dynamically changed in accor-
`dance with practical measured values.
`
`If the estimated blood pressure is found to be
`[0056]
`abnormal in step $125, the flow advances to step $130. Ifthe
`estimated blood pressure is found to be normal in step S125,
`the flow returns to step 8121 to continue the processing for
`the next heart beat.
`
`In step $130, whether the conditions for executing
`[0057]
`cull blood pressure measurementaresatisfied is determined.
`That is, whether one of the following conditions is met is
`determined.
`
`(1) Both the pulse wave parameter and estimated
`(0058]
`blood pressure are continuously found to be abnormal for
`a predetermined period.
`[0059]
`(2) A predetermined time has elapsed sincethelast
`cuff blood pressure measurement.
`[0060]
`Ifone of these conditions is met, the controller 100
`controls the pump 14 to raise the pressure of the cuff 10,
`monitors the input signal from the pressure sensor 12 while
`gradually exhausting the air after avascularization, and cal-
`culates the highest blood pressure, average blood pressure,
`and lowest blood pressure on the basis of the well-known
`oscillometric method. The controller 100 also stores, in the
`storage unit 90,
`the waveform parameters and estimated
`blood pressure obtained immediately before the blood pres-
`sure measurement using the cuff 10, and uses them in
`calibration of the coefficients a and ( contained in the
`equation for calculating the estimated blood pressure and in
`processing after that. Note that during the cuff blood pres-
`sure measurement, the waveform parameter calculation and
`determination process in steps S111 to S115 and the esti-
`mated blood pressure calculation process in steps $121 to
`$125are interrupted, or the results are ignored.
`
`(0061] After that, the above processing is repeated until
`the termination of monitoring is designated.
`
`(a and f are coefficients, a<0, p>0) as disclosed in, e.g.,
`Japanese Patent Laid-Open No. 10-66681.
`
`FIG. 4 is a graph showing therelationship between
`[0062]
`an estimated blood pressure continuously calculated by the
`
`010
`
`010
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`blood pressure measuring apparatus of this embodiment, a
`direct blood pressure measured invasively, and waveform
`parameters.
`[0063] Referring to FIG. 4, ESYSindicates the estimated
`blood pressure calculated on the basis of the pulse wave
`propagation time, and ISYS indicates the direct blood pres-
`sure measured invasively. The straight lines drawn above
`and below these blood pressures indicate values which are
`+20% and -20%, respectively, from cul? measurement val-
`ues when cuff measurementis performed at times t0, tl, and
`t2.
`
`is, FIG. 4 shows the direct blood pressure
`[0064] That
`measured invasively in order to show the relationship
`between the estimated blood pressure and the actual blood
`pressure, but no invasive measurement is performed by the
`actual blood pressure monitoring apparatus (if direct mea-
`surement is performed, blood pressure estimationitself has
`no meaning). In practice, cuff measurement is periodically
`performed, and, during a period in which no cuff blood
`pressure measurement
`is performed, monitoring is per-
`formed using the estimated blood pressure based on the
`pulse wave propagation time. FIG. 4 shows the case in
`which the last culf blood pressure measurement values
`+20% are used as the threshold values for determining
`whether the estimated blood pressure can be regarded as a
`normal value.
`
`FIG. 4 also shows whether the waveform param-
`[0065]
`eters b/a and d/a have exceeded the threshold values by
`BPA, OVER and DPA, , OVER,respectively.
`[0066]
`In FIG. 4, between times t0 and t1, the waveform
`parameter (b/a) sometimes indicates an abnormal value.
`However, no cuff activation is performed because the esti-
`mated blood pressure falls within the normal range, and
`periodic cuff blood pressure measurement is performed at
`time tl after a predetermined time has elapsed since time t0.
`[0067] After time t1, the estimated blood pressure exceeds
`the lower limit and upperlimit in some periods, but both the
`two waveform parameters have normal values, so no cull
`activation is performed either. After that, however, both the
`estimated blood pressure and the waveform parameter(b/a)
`show abnormal values, so cuff blood pressure measurement
`is executed at time 12. Since (t1-t0)>(t2-11), the cuffacti-
`vation at time t2 is shorter than the periodic interval.
`[0068] After time 12, the waveform parameter shows an
`abnormal value fora while, but the estimated blood pressure
`falls within the normal range, so no culf activation is
`performed.
`[0069] As shownin FIG. 4, the blood pressure monitoring
`apparatus of this embodiment determines the presence/
`absenceofthe true fluctuation in blood pressure by using the
`values of the parameters obtained fromthe accelerated pulse
`wave andindicating the state of the blood vessel, in addition
`to the estimated blood pressure calculated onthe basis of the
`pulse wave propagation time obtained from an ECG and
`pulse wave. Accordingly, the necessity of cuff blood pres-
`sure measurement can be determined more accurately than
`the conventional methods.
`
`(Equation Calibrating Process)
`[0070] The process of calibrating the equation for calcu-
`lating the estimated blood pressure in the blood pressure
`monitoring apparatus ofthis embodiment will be explained
`below.
`
`[0071] As described above, when the result o