111111
`
`1111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20070016086A l
`
`(19) United States
`(12) Patent Application Publication
`Inukai et al.
`
`{10) Pub. No.: US 2007/0016086 A1
`Jan. 18, 2007
`(43) Pub. Date:
`
`(54) BLOOD PRESSURE MONITORING
`APPARATUS
`
`(30)
`
`Foreign Application Priority Data
`
`Jun. 29, 2005
`Jun. 29, 2005
`
`(JP) ...................................... 2005- 190469
`(JP) ...................................... 2005- 190470
`
`(75)
`
`Inventors: Bidekatsu (nukai, Nagoya-shi (JP);
`Toru Oka, lchinomiya-shi (.n>)
`
`Publication C lassification
`
`Correspondence Address:
`DRINKER BIDDLE & REATH (DC)
`1500 K STREET, N.W.
`SUITE 1100
`WASHINGTO N, DC 20005-1209 (US)
`
`(73) Assignee: FUK UDA DENSHl CO., LTD.
`
`(2 1) Appl. No.:
`
`11/475,938
`
`(22) Filed:
`
`J un. 28, 2006
`
`(5 1) Lot. C l.
`A61B 5102
`(2006.01)
`(52) U.S. C l. . ........................................... 600/485; 600/500
`
`(57)
`
`.ABST RACT
`
`ln blood pressure monitoring apparatltS 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 acceler<1ted pulse wave have abnonnal
`values. it is determined that the blood pressure is tntly
`fluctuating, and blood pressure measurement by another
`method. e.g., blood pressure measurement using a cu.tJ is
`performed.
`
`10
`~
`
`CUFF
`
`12
`
`PRESSURE
`SENSOR
`
`I ,
`14~ PUMP
`
`20
`
`30
`
`ELECTRO·
`CARDIOGRAM
`ELECTRODE
`
`FINGER SENSOR
`(SP02,
`PULSE WAVE)
`
`PRINTER ~60
`
`DISPLAY ~70
`
`CONTROLLER
`
`80
`
`IIF
`
`TO EXTERNAL
`APPARATUS
`
`4
`
`0~
`
`SENSORS
`
`STORAGE UNIT
`
`90
`
`Apple Inc.
`APL1014
`U.S. Patent No. 8,942,776
`
`001
`
`

`

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`
`~70
`
`~60
`
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`
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`80
`
`DISPLAY
`
`PRINTER
`
`I
`
`I
`
`100 s
`
`r-----50
`
`OPERATION
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`UNIT
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`
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`
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`
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`
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`
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`
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`
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`
`SENSORS
`OTHER
`
`401
`
`FINGER SENSOR
`
`PULSE WAVE)
`
`(SP02,
`
`30---
`
`CONTROLLER
`
`ELECTRODE
`20~ CARDIOGRAM
`
`ELECTRO·
`
`002
`
`

`

`Patent Application Publication Jan. 18, 2007 Sheet 2 of 5
`
`US 2007/0016086 A1
`
`FIG. 2
`
`PLETHYSMOGRAPH
`
`ACCELERATED PULSE WAVE
`
`a
`+
`
`0
`
`(+)
`(-)
`
`003
`
`

`

`Patent Application Publication Jan. 18, 2007 Sheet 3 of 5
`
`US 2007/0016086 A1
`
`BLOOD PRESSURE
`MONITORING PROCESS
`
`START BLOOD PRESSURE
`MEASUREMENT USING
`CUFF, AND ACQUISITION
`OF EGG AND PULSE WAVE
`
`8101
`
`8111
`CALCULATE ACCELERATED
`PULSE WAVE
`
`8113
`CALCULATE WAVEFORM
`PARAMETER
`
`8121
`CALCULATE PULSE WAVE .
`PROPAGATION TIME
`
`8123
`CALCULATE ESTIMATED
`BLOOD PRESSURE VALUE
`
`NO
`
`BLOOD PRESSURE
`MEASUREMENT USING CUFF
`
`8140
`
`004
`
`

`

`Patent Application Publication Jan. 18, 2007 Sheet 4 of 5
`
`US 2007/0016086 A1
`
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`

`

`Patent Application Publication Jan. 18, 2007 Sheet 5 of 5
`
`US 2007/0016086 A1
`
`EXPRESSION CALIBRATING PROCESS
`
`ACQUIRE ACTUALLY MEASURED VALUE
`
`COMPARE WITH ESTIMATED BLOOD PRESSURE
`VALUE OR PAST ACTUALLY MEASURED VALUE
`
`S201
`
`S203
`
`S207
`
`NO
`
`NO
`
`~-------C_O_R_R_E_CT_C_O~E_F_FI_CI_EN_T_a ________ _J~S211
`!
`~-------C_AL_IB_M __ TE_C~O_E_FF_IC_IE_N_T_~ ______ __J~S213
`l
`~---------S_TO_R_E_E_X~PR_E_S_SI_O_N ________ ~~S215
`~
`END
`
`(
`
`)
`
`006
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`BLOOD PRESSURE MONITORING APPARATUS
`
`CLAIM OF PRJORITY
`
`(0001] Tb.is 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 TNVENTION
`
`(0002] The present invention relates to blood pressure
`monitoring apparatus for noninvasively and continuously
`monitoring blood pressure.
`
`BACKGROUND OF TI-l E INVEN110N
`
`In an operating room, ICU, or the like, it is some(cid:173)
`(0003]
`times necessary to continuously monitor the blood pressure
`of a patient. As a conventional technique of noninvasively
`and continuously m011itoring the blood pressure, blood
`pressure estimation based on the pulse wave propagation
`time is known.
`
`[0004] This technique uses the fact that the ti me (pulse
`wave propagation time) required for a pulse wave to propa(cid:173)
`gate between two points in a living body or the pulse wave
`propagation velocity obtained by dividing the blood vessel
`length between the two points by the pulse wave propaga(cid:173)
`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(cid:173)
`brated coefficient, thereby continuously calculating and
`monitoring an estimated blood pressure (e.g., Japanese
`Patent Laid-Open No. 10-66681).
`
`(0005] To measure the pulse wave propagation time, how(cid:173)
`ever, pulse waves must be measured in differen t 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 descdbed in Japanese Patent Laid-Open
`No. I 0-66681. therefore, a general approach is to calcttlate
`the pulse wave propagation time by using an electrocardio(cid:173)
`gram (ECG) normally measured by a biological infom1ation
`monitoring apparat11s and a pulse wave measured in one
`predetermined location (e.g., a fingertip) of a living body.
`
`[0006] Unfort1mately. tbe use of an ECG in the calculation
`of the pulse wave propagation time has a problem of the
`measurement accuracy. That is, an ECG is a signal wb.ich
`represents not a pulse wave but the electrical state change of
`the heart. There is a time d ilference (preejection period)
`between the timing at which the electrical state change
`occurs and the tinting at wb.ich the heart acl1tally contracts
`to generate a pulse wave. Accordingly, the p ulse wave
`propagation time calculated by using the observation timing
`of the feat11re point of an ECG as a starting point contains an
`error caused by the preejection period.
`
`(0007] If the preelection period is constant, tb.is error is
`easy to correct. However, tbe 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 apparat11s normally per(cid:173)
`forms control such that if blood pressure continuously
`meas ured on the basis of the pulse wave propagation time is
`
`abnonnal, more accurate blood pressure measurement is
`performed by using a cuff or tbe like. and an alarm is output
`if an abnonnal value is detected by tllis measurement.
`
`(0009] Blood pressure measurement using a cuff is estab(cid:173)
`lished as a method of noninvasively measuring the blood
`pressure, and effective to automatically obtain a well reliable
`blood pressure. [-Jowever, tllis method requires avascular(cid:173)
`ization. so the frequent use of tbe method is undesirable
`because the load on a patient increases. Therefore. accurate
`determination of the need lor cuff blood pressure measure(cid:173)
`ment is in1portant not only to perform an appropriate therapy
`but also to reduce the load on a patient.
`
`the determination accuracy as
`increase
`[0010] To
`described above, it is also important to increase the accuracy
`of the estimated blood pressure based on the pulse wave
`propagation time 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(cid:173)
`ation of the problems of 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 appamtus which
`continuously estimates blood pressure on the basis of the
`pulse wave propagation time, and performs more accurate
`blood pressure measurement where necessary.
`
`[0012] Jt is another object of the present invention to
`increase the accuracy of an estimated blood pressure in
`blood pressure monitoring apparatus wb.ich continuously
`estimates blood pressure on the basis of the pulse wave
`propagation time.
`
`[0013] According to one aspect of the present invention,
`there is provided a blood pressure monitoring apparatus
`comprising: blood pressure measuring Lmit adap ted to mea(cid:173)
`sure blood pressure in response to blood pressure measure(cid:173)
`ment designation; pulse wave acquiring unit adapted to
`acqui re a pulse wave in a predetermined location o f a living
`body: pulse wave propagation time calculating tulit 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 unjt adapted
`to calculate an estimated blood pressure on the basis of the
`pulse wave propagation time; accelerated pulse wave cal(cid:173)
`culating unit adapted to calculate an accelerated pulse wave
`from tbe pulse wave; waveform parameter calculating unit
`adap ted to calculate a predetermined wavefom1 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 wavefom1 parameter are abnormal.
`
`(0014] According to another aspect of the present inven(cid:173)
`tion, there is provided a blood pressure monitoring apparatus
`comprising: blood pressure measuring unit adapted to mea(cid:173)
`sure blood pressure by a predetermined method; pulse wave
`acquiring unit adapted to acqui re a pulse wave in a prede(cid:173)
`tennined location of a living body: pulse wave propagation
`time calculating tmit adap ted to calculate a pu lse wave
`
`007
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`2
`
`propagation time from the pulse wave, and one of an
`electrocardiogram and a pulse wave acquired from a loca(cid:173)
`tion different from the predetermined location: estimated
`blood pressure calculating unit adapted to calculate au
`estimated blood pressure by ap plying the pulse wave propa(cid:173)
`gation time to a predetermined expression; accelerated pulse
`wave calculating unit adapted to calculate an accelerated
`pulse wave from the pulse wave: waveform parameter
`caJculating unit adapted to calculate a predetermined wave(cid:173)
`form parameter from a waveform contained in the acceler(cid:173)
`ated pulse wave; and calibrating tmit adapted to calibrate the
`expression by using a value measured by the blood pressure
`measuring tmit, wherein if a fluctuation amount of the
`waveform parameter exceeds a predetermined amount. the
`calibrating unit performs the calibration after correcting a
`caJ ibration amount which is applied when the fluct11ation
`amOLmt of the wavefom1 parameter does not exceed the
`predetermined amou nt.
`In the present invention having the above arrange(cid:173)
`[0015]
`ments, the necessity of blood pressure measurement by
`another method is detenuined by considering: the wavefonu
`parameter. which is obtained from the accelerated pulse
`wave and reflecting the functional state of the blood vessel,
`is ta ken into consideration as well as the cont inuous esti(cid:173)
`mated blood pressure, which is based on the pulse wave
`propagation time 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(cid:173)
`form parameter obtained from the accelerated pulse wave is
`taken into consideration in tl1e calculation of the continuous
`estimated blood pressure based o n the pulse wave propaga(cid:173)
`tion time calculated from an ECG and a pulse wave mea(cid:173)
`sured at one point. Accordingly, the accuracy of the esti(cid:173)
`mated blood pressure can be increased.
`
`[0017) Other feat11res and advantages ofthe present inven(cid:173)
`tion will be apparent from the following description taken in
`conjtmction with the accompanying drawings, in which like
`reference characters designate the same or sinlilar parts
`throughout the figures thereof.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`[0018) Tbe accompanying drawings, which are incorpo(cid:173)
`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.
`
`[0019) FIG. 1 is a block diagram showing an example of
`the arrangement of a biological information monitoring
`apparatus as blood pressure monitoring apparat11s according
`to an embodiment of the present invention;
`
`[0020] FIG. 2 is a graph showing examples of an original
`waveform and its accelerated pulse wave;
`
`[0021] FIG. 3 is a flowchart explaining the blood pressure
`monitoring operation of the biologicaJ information monitor(cid:173)
`ing apparatus according to the embodiment of the present
`invent ion:
`
`[0022] FIG. 4 is a graph showing acn1al examples of blood
`pressure calculated by the biological information monitoring
`apparatus according to the embodiment, a direct blood
`pressure measured invasively, and waveform parameters:
`and
`
`[0023) FIG. 5 is a flowchart explaining the operation of
`calibrating an expression for calculating an estimated blood
`pressure, in the biologica l information monitoring apparatus
`according to the embodiment of the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`[0024) A preferred embodiment of the present invention
`will now be described in detail in accordance with the
`accompanying drawings.
`
`[0025] FIG. 1 is a block diagram showing an example of
`the functional arrangement of a biological information
`monitoring ap parat11s as blood pressure monitoring appara(cid:173)
`tlJS according to the embodiment of the present invention.
`
`[0026] Referring to FIG. 1, a cufrtO has a band-like form,
`and incorporates a wbber pouch which expands and con(cid:173)
`tracts by plllllping of a plllllp 14. The cufl:' 10 is normally
`attached to one of tl1e limbs, typically tl1e upper ann of a
`patient. A pressure sensor 12 senses a change in pressure
`appJjed to the gas filled in the internal rubber pouch of the
`cu:fflO. converts the pressure signal into an electrical signal,
`and outputs the electrical signal to a controller 100.
`
`[0027) An electrocardiogran1 (ECG) electrode 20 com(cid:173)
`prising a plurality of electrodes is attached to a predeter(cid:173)
`mined position of the chest of a patient, and outputs an
`induced wavefonn as au ECG signal to the controller 100.
`A finger sensor 30 is a so-called pulse oximeter which
`optically senses and outputs an oxygen saturation degree
`(SP02) and plethysmograpl1 to the controller 100. The
`absorbance of hemoglobin changes in accordance with
`whether hemoglobin combines with oxygen, and aJso
`changes in accordance with the wavelength of light. On the
`basis of these facts, the finger sensor 30 general ly measures
`the oxygen saturation degree by using two wavelengths, i.e.,
`red light and infrared light. Also, since theAC componem of
`transo:litted light or reflected light changes in accordance
`with the blood How volume, this AC component is detected
`as a photoplethysmograph (PTG).
`
`[0028) Other sensors 40 sense other biological informa(cid:173)
`tion such as the respiration and body temperatl!fe of a
`patient. and one or more sensors are connected to the
`controlle r 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.
`
`[0029] An operation unit 50 is a man-machine interface by
`wl:lich the user (measurer) inputs various settings and infor(cid:173)
`mation conceming a patient and provides instructions to the
`biological infonnation monitoring apparatus. The operation
`unit 50 is generally constructed by appropriately combining
`a keyboard, a mouse, buttons. switches, dials, a touch panel,
`and the like.
`
`[0030] A printer 60 and display 70 are representative
`output devices, and visually output the state of the apparatus.
`measurement results, and tbe like. An external interface (l/F)
`80 is typically a network interface. seria l interface (e.g., a
`USB or IEEE 1394). modem, or the like. and communicates
`with an external apparatus which is COllllected invasively or
`across a network.
`
`[0031] A storage tmit 90 is typically a hard disk drive. and
`records programs for controlling the operation of the bio-
`
`008
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`3
`
`logical information monitoring apparatus, various data,
`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 a nd
`writes a writable removable mediwn such as a memory card
`or an optical disk.
`
`(0032] The controller 100 controls the operation of the
`whole biological information monitoriJlg apparatus. The
`controller 100 has, e.g., a CPU and RAM, and controls the
`individual tmits by loading the control programs stored in
`the storage unit 90 into the RAM and executing the loaded
`programs by the CPU, thereby implementing processes
`including the blood pressure monitoring operation (to be
`described later) of the biological inlormation monitoring
`apparat11s. Note that not all the processes need be executed
`using software by U1e CPU. For example, signal processing
`sucl1 as NO conversion and filtering of signals input from
`the various sensors may also be assigned to a DSP or
`dedicated hardware, thereby appropriately using another
`arrru1gement.
`
`[0033) The blood pressure monitoring operation by the
`biological information monitori.ng apparatus of this embodi(cid:173)
`ment will be explained below.
`
`[0034) The biological information monitoring apparams
`of this embodin.lent is similar to the prior art in that the pulse
`wave propagation velocity is continuously calculatt-'Cl by
`using an ECG and plethysmograph. aJ1d an estimated blood
`pressure is continuously calculated by using an expression
`having a precalibrated coefficieni. and that tbe necessity of
`blood pressure measurement using a cuff is determined by
`using the estimated blood pressure.
`
`In this embodiment, however. it is dctem1ined that
`[0035]
`blood pressure measurement using a cuff is necessary only
`when another condition is met in addition to the estimated
`blood pressure. thereby increasing the abnormality detection
`accuracy in contin.uous blood pressure monitoring. Tb.is
`embodiment is characterized in that the value of a parameter
`obtained f:rom an accelerated pulse wave is used as the other
`condition.
`
`[0036] 111e accelerated pulse wave is obtained by calcu(cid:173)
`lating second-order time differential of a pulse wave, and has
`characteristic waves from a-wave io e-wave as shown in
`FIG. 2. A-wave and b-wave represent presystolic compo(cid:173)
`nents, c-wave and d-wave represent telesystolic compo(cid:173)
`nents, and e-wave represents a diastolic component (e.g.,
`Jketani et al., "Plethysmograph (Accelerated Pulse Wave)
`lor Evaluating Degree of Arteriosclerosis by Hypertension'·,
`vol. 10, no. 6, 2003. pp. 54-60).
`
`(0037] According to Iketani et a!., d1e presystolic compo(cid:173)
`nent reflects-a driving pressure wave generated by ejection
`of the blood when the heart contracts, and the telesystolic
`component is a re-elevatcd pressltfe wave generated when
`the driving pressure wave propagates to the periphery. and
`the rett1rned reflected wave overlaps the driving pressure
`wave. Accordingly, it can be presumed thai the presystolic
`component represents the state of the heart (center), and the
`telesystol.ic component represents d1e state of the periphery.
`In this embodiment, therefore, the condition that at
`[0038]
`least one of the presystolic component or telesystolic com(cid:173)
`ponent fluctuates by an runount exceeding a predetermined
`amount from the value of d1e presystolic component or
`
`telesystolic component obtained when the blood pressure
`was measured last time by using a cuff is used as d1e other
`condition described above. Ibat is. it is possible to deter(cid:173)
`mine that the possibility that the blood pressure has acmally
`fluctuated is higher when a change is lound in the center or
`periphery in addition to the change in estimated blood
`pressure, than when only the estimated blood pressure
`fluct11ates or only the change in the center or periphery is
`found.
`
`[0039) Note that in this embodiment, a wave height ratio
`b/a ofb-wave to a-wave is used as a parameter indicating the
`state of the center, and a wave height ratio d/a of d-wave to
`a-wave is used as a parameter indicating the state of the
`periphery. The ratios to the wave height of a-wave are herein
`used in order to compare the par3llleters obtained from an
`accelerated pulse wave when no calibration exists in a strict
`sense, and tbis is a kind of normalization.
`
`[0040] On d1e basis of the above description, the blood
`pressure monitoring operation of the biological infonnation
`monitoring apparat11s according to this embodiment will be
`explained with reJerence to a flowchart shown in FIG. 3.
`
`[0041) First, in step Sl 01, the acquisition of an ECG and
`pulse wave is s tartt.'Cl. 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 SU S) of the accclera1ed pulse
`wave and the process (steps S121 to Sl25) of estimating the
`blood pressure on the bas is of the pulse wave propagation
`velocity are performed in parallel.
`
`In step S111, the controller 100 calculates the
`[0042)
`accelerated pulse wave from the photoelectric pledlysmo(cid:173)
`graph from the finger sensor 30. In step S113. on the basis
`of a-wave to d-wave contained in one pulse of the acceler(cid:173)
`ated pulse wave. par3Jlleters concerning the presystolic
`component and telesystolic component, i.e., the wave height
`ratios b/a and d/a in d1is embodiment, are obtained.
`In step SUS, the controller 100 calculates fluctua (cid:173)
`[0043)
`tions from
`the obtained paraJneter values and values
`obtained in the last cuff blood pressure measurement, and
`determines whether the fl uctuations are abnormal. For
`example, the controller 100 sets
`
`Dl (%)=! - { b/a(current) }I{ b/a(ref) }x 100
`D2(%)al-{ d/a(current) }/ { d/a(ref) }x 100
`111e controller 100 can check the presence/absence of abnor(cid:173)
`mality by determining whether one, both, or a predetermined
`one of
`iDt/>nlb
`ID2f>n!d
`( ib)
`is satisfied. Since, however, b/a is a parameter indicating the
`state of the center, it is desirable to take account of at least
`the value of b/a. ln step sns, the par3llleters as objects of
`abnormality determination, the expressions for abnormality
`determination, and the threshold values used are predeter(cid:173)
`mined. 1-lowever, these values and expressions need not be
`fixed but can be changed any time.
`
`( Ia)
`
`[0044) Note that i.n the above equations. (current) indi(cid:173)
`cates a present calculated value, and (reJ) indicates a refer-
`
`009
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`4
`
`ence calculated value obtained in the last cuff blood pressure
`measurement. Note also tbat tbe threshold values Thb and
`Thd indicating normal ranges can be either equal or indi(cid:173)
`vidually set. In addition, the fl uctuation need not be absolute
`values, and it is also possible to individually set the thresh(cid:173)
`old value (upper limit) on tbe increasing side and tbe
`threshold value (lower limit) on tbe decreasing side. Prac(cid:173)
`tical values of tbe threshold values can be appropriately
`determined. For example, Thb~Thd~20(%) can be set in
`inequalities ( l a) and ( lb).
`
`It is also possible to dynamically change the thresh(cid:173)
`[004S]
`old values in accordance with tbe results of periodical blood
`pressure measurements using a cu fi For example. if the
`result of cuff blood pressure measurement is smaller than a
`predetermined value, it is possible to make the threshold
`value on the decreasin g side stricter (make the threshold
`value easier to exceed) than when the measurement result is
`not smaller than the predetermined value, thereby monitor(cid:173)
`ing tbe decrease in blood pressure more strictly. More
`specifically, when the normal range is defined by the upper
`and lower limits, tbe lower limit is set to be high. In this
`case, the lower limit becomes easier to exceed, so the
`decrease io blood pressure can be strictly monitored. On the
`contrary, if the cuff measurement result is large, it is possible
`to make the threshold value on the increasing side stricter
`(make tbe upper limit of tbe normal range smaller).
`
`[0046] The fluctuation amount need not be a ratio (per(cid:173)
`centage). but may also be a difference.
`
`If the fluctuation anlotmt is Jound to be abnormal i.n
`[0047)
`step SUS, the flow advances to step S130. If the fluctuatiou
`amomll is found to be normal in step SUS, the flow remrns
`to step Slll to continue the processing for the next heart
`beat.
`
`l11 steps S121 to Sl2S. the same blood pressure
`[0048)
`estimating process as tbe conventioual method is executed.
`In step S l21, tbe pulse wave propagation time is
`[0049]
`calculated on the basis of an ECG detected by the electro(cid:173)
`cardiogram electrode 20 and a plethysmograph seused by
`tbe ringer sensor 30. Mo re specifically, the contro ller 100
`performs sig nal processing su ch as noise removal and wave(cid:173)
`fonu shaping norn1ally performed on an ECG and plethys(cid:173)
`mograph, and calcula tes the time difference between feat11re
`points in the heart beats of the ECG and plethysmograph as
`tbe pulse wave propagation velocity. In this case, the feature
`point of tbe ECG can be, e.g .. the peak position of the R
`wave, and the feature point of the plethysmograph can be the
`leading edge of the waveform. Also, as described above,
`tbere is a time difference (preelection period) betweeu the
`appearance of the R wave to the generatiou of the act11al
`pulse wave. Therefore, correction can be perforn1ed by
`subtracting a time corresponding to a preejection period
`statistically calculated beforehand from the time difference
`between the feat11re points.
`In step S123, an estimated blood pressure is
`[0050)
`obtained from the calculated pulse wave propagation time.
`
`(OOSl] That is, an estimated blood pressure is calculated
`by applying the pulse wave propagation time to
`
`Eslirnated blood pressure=ax(pulse wave propag.~tion
`time [ nlSec ])+13
`(2)
`(a. and ~ arc coefficients, a<O, ~>0) as disclosed in. e.g ..
`Japanese Patent Laid-Open No. 10-66681.
`
`[0052) Note that the coefficients a. aud B need only be
`determined in advance. That is, this equation is a linear
`equation with two unknowns. so the values of the coeffi(cid:173)
`cients a and ~ can be detennined by using at least two
`actually measured blood pressures and the correspond ing
`pulse wave propagatiou times.
`
`(OOS3) Each coefficient need not be fixed but may also be
`updated to an optimum value by using an actually measured
`value obtained by another method (cuff measurement or
`direct measurement) and tbe pulse wave propagation time at
`the correspouding timing.
`In step Sl2S. whether tbe estimated blood pressure
`[OOS4)
`is an abnorn1al vah.1e is det·ermined. This detem1ination can
`be perforn1ed by determining whether the estimated blood
`pressure is larger than the upper limit or smaller tban the
`lower limit of a predeternlined normal range, or detennining
`whether the estimated blood pressure fluctuates more than. a
`predetermined amou nt (which can be e ither a fluct uation
`ratio or difterence) from the value of the last cull' blood
`pressure measurement.
`
`[005S) Like the threshold values of the wavefom1 param(cid:173)
`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(cid:173)
`dance witb practical measured values.
`
`If the estimated blood pressure is found to be
`[OOS6)
`abnorn1al in step Sl2S, the flow advances to step S130.1fthe
`estimated blood press me is found to be norn1al in step S12S,
`the flow returns to step S121 to continue tbe processing for
`the next heart beat.
`
`In step S130. whether the conditions for executiug
`[OOS7)
`cuJfblood pressure measurement arc satisfied is determined.
`That is, whether one of the following conditions is met is
`del en:niued.
`[OOS8)
`(1) Botb the pulse wave parameter and estimated
`blood pressure are continuously found to be ab normal for
`a predetermined period.
`[0059)
`(2) A pr<.-detem1ined time has elapsed since the last
`cuJf blood pressure measurement.
`[0060)
`If one of these conditions is met, the controller 100
`controls the pump 14 to raise the pressure of the cuff 10,
`monitors the input signal lrorn the pressure sensor 12 while
`gradually exhausting the a ir after avascularization. and cal(cid:173)
`culates the highest blood pressure. average blood pressure,
`and lowest blood pressure on the basis of tbe well-kuowu
`oscillometric method. The cont roller 100 also stores, in the
`storage unit 90. tbe wavefonn parameters and estimated
`blood pressure obtained illllllediately before the blood pres(cid:173)
`sure measurement using the cuiJ 10. and uses them in
`calibration of the coefficients a. and B contained in the
`equat.ion for calculating the estimated blood pressure and in
`processing after that. Note that during the cuff blood pres(cid:173)
`sure measurement, tbe wavelorm parameter calculation and
`determination process in steps Slll to SlJS a nd the esti(cid:173)
`mated blood pressure calculation process in steps S121 to
`Sl25 are interrupted, or U1e results are ignored.
`
`[0061] After tbat, the above processing is repeated tm til
`the termination of monitoring is designated.
`
`[0062] FIG. 4 is a graph showing tbe relationship between
`an estimated blood pressure continuously calculated by the
`
`010
`
`

`

`US 2007/0016086 Al
`
`Jan. 18, 2007
`
`5
`
`blood pressure measuring apparatus of this embodiment, a
`direct blood pressure measured invasively, and wavefonn
`parameters.
`(0063] Referring to FIG. 4. ESYS indicates the estimated
`blood pressure calculated on tl1e basis of the pulse wave
`propagation time, <md JSYS ind.icates the direct blood pres(cid:173)
`sure measured invasively. The straight lines drawn above
`and below these blood pressures indicate values which are
`+20% and -200/o, respectively, from culr measurement val(cid:173)
`ues when cuff measurement is performed at times tO. tl. and
`t2.
`(0064] That is. FIG. 4 shows the direct blood pressure
`measured invasively in order to show ilie relationship
`between the estimated blood pressure and the acll1al blood
`pressure, but no invasive measurement is performed by ilie
`actual blood pressure monitoring apparatus (if direct mea(cid:173)
`surement is performed, blood pressure estimation itself has
`no meaning). In practice, cuff measmement is periodically
`performed. and. during a period in which no cuff blood
`pressure measurement is perfonned, monitoring is per(cid:173)
`formed using the estimated blood pressure based on the
`pulse wave propagation time. FIG. 4 shows ilie case in
`which the last culf blood pressure measurement values
`±20% are used as the threshold values for detem1iruug
`whether the estimated blood pressure can be regarded as a
`normal value.
`(0065] FIG. 4 also shows whether the waveform param(cid:173)
`eters b/a and d/a have exceeded ilie threshold values by
`BPA
`OVER and DPA13 OVER, respectively.