I||||||||||||||||||||||||||||||||||||lllll|||||||||||||||||||||||||||||||||||||||||||||||l
`
`US 200700l6086A1
`
`(19; United States
`(12) Patent Application Publication (10) Pub. No.: US 2007/0016036 A1
`Inukai et al.
`(43) Pub. Date:
`Jan. 18, 2007
`
`(54) BLOOI) PRESSURE .\/ION['l‘ORING
`API’.-\R.-KTUS
`
`(30)
`
`Foreign Application Priority Data
`
`Jun. 29, 2005
`Jun. 29. 2005
`
`(JP) .................................... .. 2005-190469
`(JP) .................................... .. 20()5-190470
`
`(75)
`
`Inventors:
`
`llidekatsu lnukai. Nagoya-511i (JP):
`.l.m_u 0ka_ lC_hilmmiya_5hi UP)
`
`.
`_
`_
`.
`_
`.
`Publlcatlml Classification
`
`C°”°5P““d""°e"‘dd’e“‘
`DRLVKER BIDDLE & REATH (DC)
`1500 K STREET,
`SUITE 110:}
`W133 I "NU-1-ON, DC 200054209 (US)
`
`(73)
`
`x\ssigr1ee:
`
`lv‘UKU!).~\ l)I~l,\'SlII ($0., I,'1‘[)_
`
`(21)
`
`‘.\pp1_Nu_:
`
`11,.r475_'93g
`
`(22)
`
`Filed:
`
`Jun. 28, 2006
`
`1 O
`
`CUFF
`
`1 2
`
`_
`
`PRESSURE
`SENSOR
`
`6001485 roorsoo
`.
`)
`
`(SI)
`
`52
`
`)
`(
`(57)
`
`Int. Cl.
`A613 5102
`(2006.01)
`U 9 (‘I
`.. .
`.
`.
`............................................
`ABSTRA(gT
`_
`_
`‘
`‘
`In !3IL1L‘Jd pressure nionrlormg appzurulrls wliielreoiitiiillously
`esuniales and monitors blood pressure by using the pulse
`wave propagation lime. blood pressure fluclualion can be
`accurately estlmzued. li both blood pressure eslnnated iron}
`the pulse wave propagation time and a wavet'or111 parameter
`obtained 1‘ro1n [he accelerated pulrye wave have abnormal
`values.
`il
`is determined lhal 1l1e blood pressure is truly
`Iluelualing. and blood pressure measurement by ;mo1l1er
`method. e.g.. blood pressure measurement using a C1111‘ is
`performed.
`
`
`
`OPERATION
`UNIT
`
`W 50
`
`:3
`—=—
`
`PRINTER
`
`60
`
`PUMP
`
`*=*——
`
`*°-
`
`DISPLAY
`
`70
`
`14
`
`2O
`
`ELECTRO-
`CAFIDIOGRAM
`ELECTRODE
`
`FINGER SENSOR
`{SF'02,
`PULSE WAVE}
`
`4°
`
`OTHER
`seusons
`
`CONTROLLER
`
`-
`
`-
`
`-
`
`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 S
`
`US 2007/0016086 A1
`
`
`
`ommEz_Emmammmma
`
`momzmm
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`
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`
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`
`002
`
`002
`
`

`
`Patent Application Publication Jan. 18, 2007 Sheet 2 of 5
`
`US 2007/0016086 A1
`
`FIG. 2
`
`PLEFHYSMOG RAPH
`
`ACCELERATED PULSE WAVE
`
`O03
`
`003
`
`

`
`Patent Application Publication Jan. 18, 2007 Sheet 3 of S
`
`US 2007/0016086 A1
`
`FIG. 3
`
`BLOOD PRESSURE
`MONITORING PROCESS
`
`
`
`START BLOOD PRESSURE
`MEASUREMENT USING
`
`CUFF, AND ACQUISITION
`OF ECG AND PULSE WAVE
`
`S101
`
`-
`
`S111
`
`S121
`
`
`
`NO
`
`CALCULATE ACCELEFIATED
`PULSE WAVE
`
`CALCULATE PULSE WAVE
`PROPAGATION TIME
`
`S113
`
`.
`
`.
`
`S123
`
`CALCULATE WAVEFORM
`PARAMETER
`
`CALCULATE ESTIMATED
`BLOOD PRESSURE VALUE
`
`
`
`
`
`
`
`
`S115
`S125
`
`IS FLUCTUATION
`OUTSIDE
`AMOUNT ABNORMAL?
`NORMAL RANGE?
`
`
`
`YES
`YES
`
`
`
`
`
`
`
`
`
`
`S130
`
`
`
`
`NO
`
`
`
`
`HAVE
`TWO CONDITIONS
`BEEN CONTINUOUSLY MET
`FOR PREDETERMINED PERIOD,
`OR HAS PREDETERMINED TIME
`ELAPSED SINCE LAST
`MEASUREMENT
`9
`
`
`
`T
`
`YES
`
`BLOOD PRESSURE
`MEASUREMENT USING CUFF
`
`S1 40
`
`O04
`
`
`
`NO
`
`004
`
`

`
`Patent Application Publication Jan. 18, 2007 Sheet 4 of 5
`
`w0nu2SU
`
`M(D80m
`
`mmn_n_3.I.I
`
`E29:....
`
`96I
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`mm_>o-.&m.||.
`
`
`
`¢m_>o.<%ull
`
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`
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`
`q.0_n_
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`
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`oom
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`
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`
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`
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`
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`
`m$5
`$032.3«$9mi?8%
`
`
`
`63.mE_._
`
`005
`
`

`
`Patent Application Publication Jan. 18, 2007 Sheet 5 of S
`
`US 2007/0016086 A1
`
`FHG. 5
`
`EXPRESSION CALIBRATING PROCESS
`
`ACQUIRE ACTUALLY MEASURED VALUE
`
`S201
`
`commas wnm ESTIMATED BLOOD PRESSURE
`VALUE on PAST ACTUALLY MEASURED VALUE
`
`S203
`
`"0
`
`IS CALIBRATION NECESSARY?
`
`'
`
`S205
`
`YES
`
`CALIBRATE COEFFICIENT 0t
`
`8207
`
`S209
` IS WAVEFORM PARAMETER
`
`FLUCTUATION LARGE?
`
`YES
`
`D
`
`O06
`
`
`
`006
`
`

`
`US 200790016086 A1
`
`Jan. 18, 200'?
`
`BLOOD PRESSURE M0.\"ITORING APPARATUS
`
`CLAJM 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.
`
`FIFJJ) OF TI-Iii lNV'Ii£N'I‘l()N
`
`[0002] The present invention relates to blood pressure
`monitoring apparatus for noninvasively and continuously
`monitoring blood pressure.
`
`BACKGROUND OF THE INVENTION
`
`In an operating room. ICU. or the like. it is sortie-
`[0003]
`times necessary to continuously monitor the blood pressure
`ofa patient. As a conventional technique of noninvasively
`and continuously monitoring I11e 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 titne) 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 two points 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—0pen 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 cutfs for measuring pulse waves
`to two locations. As described in Japanese Patent Laid-Open
`No. 10-66681. therefore. a general approach is to calculate
`the pulse wave propagation time by using an electrocardio-
`gram (ECG) normally measured by a biological infonnation
`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 in the 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 wave but the electrical state change of
`the heart. There is a time dilierence (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 ECG as 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 tnonitoring apparatus normally per-
`forms control such that
`if blood pressure continuously
`measured on the basis of the pulse wave propagation time is
`
`is
`abnormal, more accurate blood pressure measurement
`performed by using a cuff or the like. and an alarm is output
`if an abnonnal value is detected by this measurement.
`
`[0009] Blood pressure measurement using a cuif is 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 euil blood pressure measure-
`ment is important not only to perform an appropriate therapy
`but also to reduce the load on a patient.
`
`as
`accuracy
`determination
`the
`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 Ol’ Tllli lNVl3N'l‘l(JN
`
`[0011] The present invention has been made in consider-
`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 higll-accuracy blood pressure
`rueasurernent. in blood Pressure monitoring apparatus which
`continuously estitnates blood pressure on the basis of the
`pulse wave propagation time. and performs tnore 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 of the 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 wave itt a predeterlnincd location ofa living
`body: pulse wave propagation time calculating unit adapted
`to calculate a pulse wave propagation time frotn the pulse
`wave. and one of an eleetrocandiogratn 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 of the
`pulse wave propagation time; accelerated pulse wave cal-
`culating unit adapted to calculate an accelerated pulse wave
`front the pulse wave; waveform parameter calculating urtit
`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 un.it 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 providcd 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 location of a living body: pulse wave propagation
`time calculating tuiit adapted to calculate a pulse wave
`
`007
`
`007
`
`

`
`US 2007f0016086 A1
`
`Jan. 18, 200'?
`
`propagation time from the pulse wave. and one of an
`electrocardiogram and a pulse wave acquired frotn a loca-
`tion diflerent from the predetermined location; estimated
`blood pressure calculating unit adapted to calculate an
`estimated blood pressure by applying tl1e pulse wave propa-
`gation time to a predetennined 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
`expression by using a value measured by the blood pressure
`measuring unit". wherein if a fluctuation amount of the
`waveform parameter exceeds a predetennined amount. the
`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.
`
`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 and reflecting 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
`propagation time calculated from an ECG and a pulse wave
`observed at one point. Tltcrefore. 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 of the continuous
`
`estimated blood pressure based on the pulse wave propaga-
`tion time calculated from an IECG 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 apparent from the following description taken in
`conjunction with the accompanying drawings. in which like
`reference characters designate the same or similar parts
`Lh.r0Ltghot.tt the figures thereof.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0018] The accompanying drawings. which are incorpo-
`rated in and constitute a pan of the specification. illustrate
`embodintents of the invention and.
`together with the
`description. serve to explain the principles of the invention.
`
`FIG. 1 is a block diagram showing an example of
`[0019]
`the arrangement of a biological
`infonnation monitoring
`apparatus as blood pressure monitoring apparatus according
`to an embodiment of the present invention;
`
`FIG. 2 is a graph showing examples of an original
`[0020]
`waveform and its accelerated pulse wave;
`
`FIG. 3 is a flowchart explaining the blood pressure
`[0021]
`monitoring operation of the biological information monitor-
`ing apparatus according to the embodiment of the 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
`
`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
`
`[0024] A preferred embodiment of the present invention
`will now be described in detail
`in accordance with the
`
`accompanying drawings.
`
`FIG. 1 is a block diagram showing an example of
`[0025]
`the functional arrangement of a biological
`information
`monitoring apparatus as blood pressure monitoring appara-
`tus according to the embodiment of the present invention.
`
`[0026] Referring to FIG. 1. a cuff 10 has a band-like form.
`and incorporates a rubber pouch which expands and cort-
`tracts by pumping of a pump 14. The cuif 10 is normally
`attached to one of Ll'lE‘.‘ limbs. typically the upper arm of a
`patient. A pressure sensor 12 senses a change in pressure
`applied to the gas filled in the internal rubber pouch ofthe
`cufl'l0. converts the pressure signal into an electrical signal,
`and outputs the electrical signal to a controller 100.
`
`[0027] An clectrocardiograrn (l.iC(i] 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 wavefonn as an ECG signal to the controller 100.
`A linger 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 wavelength of light. On the
`basis of these facts, the finger sensor 30 generally measures
`the oxygen saturation degree by using two wavelengths. i.e..
`red light and infrared light. Also. since the AC component of
`transmitted light or reflected light changes in accordance
`with the blood [low volume. this AC component is detected
`as a photoplethysmograph (PTG}.
`
`[0028] Other sensors 4!} 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.
`
`[0029] An operation unit 50 is a man-machine interface by
`which the user (measurcr) inputs various settings and infor-
`mation concerning a patient and provides instructions to the
`biological information 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 ofthe apparatus.
`measurement results. and the like. An extemal interface (IEF)
`80 is typically a network interface. serial interface [e.g.. a
`USB or IEEEl394]. modem. or the like. and communicates
`with an external apparatus which is connected invasively or
`across a network.
`
`[0031] A storage ttnit 90 is typically a hard disk drive. and
`records programs for controlling the operation of the bio-
`
`O08
`
`008
`
`

`
`US 200700016086 A1
`
`Jan. 18, 200'?
`
`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.
`
`[0032] The controller 100 controls the operation of the
`whole biological
`inlortnatiott monitoring apparatus. The
`controller 100 has. e.g.. a (‘PU and RAM. and controls the
`individual tutits 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
`information monitoring
`apparatus. Note that not all the processes need be executed
`using software by the CPU. For example. signal processing
`such as NI.) conversion and Filtering o l‘ 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 infonnation monitoring apparatus
`ofthis embodiment is similar to the prior art in that the pulse
`wave propagation velocity is continuously calculated by
`using an l.<)CG and plethysmograph. and art estimated blood
`pressure is continuously calculated by ttsing an expression
`having a precalibrated eoetiicient. and that the necessity of
`blood pressure measurement using a cull‘ is determined by
`using the estimated blood pressure.
`
`I11 this etnbodiment, however, it is determined that
`[0035]
`blood pressure measurement using at cufl'is necessary only
`when another condition is met in addition to the estimated
`blood pressure. thereby increasing the abnormality detection
`accuracy in continuous blood pressure monitoring. This
`embodiment is characterized in that the value ol‘a parameter
`obtained from an accelerated pulse wave is used as the other
`condition.
`
`[0036] The accelerated pulse wave is obtained by calcu-
`lating second-order time dilferential of a pulse wave. and has
`characteristic waves from a-wave to e—wave as shown in
`
`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.. “Pletltysmograplt [Accelerated Pulse Wave)
`for [Evaluating Degree of Artcriosclcrosis by I-Iypertension".
`vol.
`it). no. 6. 2003. pp. 54-60).
`
`[0037] According to lketani 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 vvlten
`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 condition that at
`[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
`
`telesystolic component obtained when the blood pressure
`was measured last time by using a cufl" is used as the other
`condition described above. That is.
`it is possible to deter-
`mine that the possibility Lhat the blood pressure has actually
`lluctuated is higher wlten a cltangc is found in the center or
`periphery in addition to the change in estimated blood
`pressure.
`than when only the estimated blood pressure
`lluctuates or only the change itt the center or periphery is
`found.
`
`[0039] Note that in this emboditnent. a wave height ratio
`bfa of b—wave to a—wave is used as a parameter indicating the
`state of the center, and a wave height ratio dfa of d-wave to
`a-wave is used as a parameter indicating the state of the
`periphery. The ratios to the wave height ofa-wave are herein
`used in order to compare the parameters obtained from an
`accelerated pulse wave when no calibration exists in a strict
`sense, and this is a kind of l1t‘)t't11flllI(.€ltlUl't.
`
`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 shown in FIG. 3.
`
`First. in step $101. the acquisition ol'an F,(.‘G and
`[004]]
`pulse wave is started. Also. as ittitiali’/.atiI:Itt.
`initial blood
`pressure measurement using a culf 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] of the accelerated pulse
`wave and the process (steps 5121 to $125) of estimating the
`blood pressure on the basis ol‘ the pulse wave propagation
`velocity are perfonned in parallel.
`
`the controller 100 calculates the
`In step S111.
`[0042]
`accelerated pulse wave frotn the photoelectric pletl1yst11o-
`graph from the linger sensor 30. In step S113. on the basis
`ol'a-wave to d-wave contained in one pulse of the acceler-
`ated pulse wave. parameters conceming the presystolic
`component and telesystolic component, i.e., the wave height
`ratios bfa and dfa in this entbodilncnt. are obtained.
`
`I11 step S115, the controller 100 calculates fluctua-
`[0043]
`tions from the obtained panuneter values and values
`obtained in the last cuff blood pressure measurement. and
`determines whether
`the Fluctuations are abnormal. For
`
`example. the controller 100 sets
`D1(%l=l—{ fr.-tcurrentl}-"{bfa'tref't}:¢I00
`D2(°/alel-{a’a’rttcurrent)}."{d;‘atrefl}xt0tIt
`
`The controller 100 can check the presencefabsence ofabnor-
`mality by determining whether one. both. ora predetermined
`one of
`
`IJ'J1l.">i'}'r:‘J-
`|D2f:v Hid
`
`tlal
`t 1 by
`
`is satisfied. Since. however. bra is a parameter indicating the
`state of the center. it is desirable to take account of at least
`the value of bfa. In step S115. the parameters as objects ol‘
`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 itt the above equations. (current) indi-
`cates a present calculated vaiue, and (ref) indicates a refer-
`
`O09
`
`009
`
`

`
`US 2007f0016086 A1
`
`Jan. 18, 200'?
`
`euce calculated value obtained in tile last cutfblood pressure
`measurenient. 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 tl1e thresh-
`old value (upper limit) on the increasing side and the
`threshold value [lower litnit) on the decreasing side. Prac-
`tical values of the threshold values can be appropriately
`determined. For example, Thb='l'hd=20(%) can be set in
`inequalities (la) and (lb).
`
`It is also possible to dynamically change the thresh-
`[0045]
`old values in accordance with the results ofperiodical blood
`pressure measurements using a cufl". For example. if the
`result of cull blood pressure measurement is smaller than a
`predetermined value.
`it
`is possible to make tl1e threshold
`value on the decreasing side stricter (make the threshold
`value easier to exceed) than when the measurement result is
`not smaller than the predetenuined 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 can be strictly monitored. On the
`contrary. if the cuif measurement result 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 fiuctuation amount need not be a ratio [per-
`centage). but may also be a difierettce.
`
`if the lluctuation amount is found to be abnormal in
`[0047]
`step $115. the flow advances to step $130. If the liuctuation
`a111ount is found to be normal in step S115, the flow returns
`to step S11] to oontinue 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.
`
`In step S12], the pulse wave propagation time is
`[0049]
`calculated on the basis of an ECG detected by the electro-
`cardiogram electrode 20 and a plethysmograph sensed by
`l.l1e linger sensor 30. More specifically.
`l.l1e controller 100
`performs signal processing such as noise removal and wave-
`form shaping normally performed ou an ECG and plethys-
`mograph. and calculates the time difference between feature
`points in the heart beats of the ECG and plethysmograpli as
`the pulse wave propagation velocity. In this case. the feature
`point of the ECG can be. e.g.. the peak position of the R
`wave. and tile feature point of the plethysmograph can be the
`leading edge of the waveform. Also. as described above.
`there is a time ditference (preeiection period) between the
`appearance of the R wave to the generation of the actual
`pulse wave. Therefore. correction can be performed by
`subtracting a time corresponding to a preejection period
`statistically calculated beforehand irom the time diflerence
`between the feature points.
`
`In step S123. 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
`Eslintiltetl blood p1'K.‘SEs'llTl‘==t'_‘(X[]'J1:|lSl.’. wave‘ propagation
`time [m.sec]t+[.'u
`
`{2}
`
`[0052] Note that the coefiicients 0. and [3 need only be
`deterntined in advance. That is. this equation is a linear
`equation with two unknowns. so the values of the coefl:'t—
`cients 0‘. and B can be determined by using at least two
`actually measured blood pressures and the corresponding
`pulse wave propagation times.
`
`[0053] Each coeflicient need not be fixed bttt may also be
`updated to an optimum value by using an actually measured
`value obtained by another method {cuff measurement or
`direct measurement) and the pulse wave propagation time at
`the corresponding timing.
`
`in step S125. whether the estimated blood pressure
`[0054]
`is an abnormal value is determined. This detennination can
`
`be perfonned by determining whether the estimated blood
`pressure is larger than the upper limit or smaller than the
`lower limit of a predetermined normal range. or detennining
`whether the estimated blood pressure lluctuates more than a
`predetermined amottnt (which can be either a fluctuation
`ratio or dilierence) front the value of the last cull blood
`pressure measurement.
`
`[0055] Like the threshold values of the wavefonu param-
`eters. these upper litnit. lower limit. and t‘luctuation amount
`can be either fixed with respect to the value of cu ff blood
`pressure measurement, or dynamically changed in accor-
`dance with practical measured values.
`
`lf the estimated blood pressure is found to be
`[0056]
`abnormal in step S125, the flow advances to step S130. lfthe
`estimated blood pressure is found to be nonnal in step S125.
`the flow returns to step S121 to continue the processing for
`the next heart beat.
`
`in step S130. whether the conditions for executing
`[0057]
`cull" blood pressure measurement are satisfied 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.
`
`(2) A predetemtined time has elapsed since the last
`[0059]
`cufi" blood pressure measurenient.
`[0060]
`If one of these conditions is met. the controller 100
`controls the pump 14 to raise the pressure of the cut? 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 wavefomi parameters and estimated
`blood pressure obtained immediately before the blood pres-
`sure measurement using the call 10. and uses them in
`calibration of the coeflicients o. and [3 contained in the
`equation for calculating the estimated blood pressure and in
`processing after that. Note that during the cufl' 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 3121 to
`S125 are interrupted. or the results are ignored.
`
`[006]] After that, the above processing is repeated tuttil
`the termination of monitoring is designated.
`
`|3>0) as disclosed in. e.g..
`(or. and fl are coeflicients. 0‘.-:0.
`Japanese Patent Laid-Open No. 10-66681.
`
`1'' 1G. 4 is a graph showing the relationship between
`[0062]
`an estimated blood pressure continuously calculated by the
`
`010
`
`010
`
`

`
`US 2007f0016086 A1
`
`Jan. 18, 200'?
`
`blood pressure measuring apparatus of this embodiment. a
`direct blood pressure measured invasively. and waveform
`parameters.
`
`[0063] Referring to FIG. 4. ESYS indicates the estimated
`blood pnessttrc calculated on t.l1e basis of t.he pulse wave
`propagation time, and ISYS indicates the direct biood pres-
`sure measured invasively. The straight lines drawn above
`and below these blood pressures indicate values which are
`+20% and -20%, respectively. froin cull" measurement val-
`ues when cufl' measurement is performed at times t0. t1. 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 estimation itselfhas
`no meaning). In practice, cufl" measurement is periodically
`performed. and. during a period in which no cuff blood
`pressure measurement
`is performed. monitoring is per-
`fomied using the estimated blood pressure based on the
`pulse wave propagation time. FIG. 4 shows the case in
`which the last cull‘ blood pressure measurement values
`320% 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 bfa and dial have exceeded the tlueshold values by
`BPAH OVER and DPA13 OVER, respectively.
`[0066]
`In FIG. 4. between times t0 and t1. the waveform
`parameter (bin) sometimes indicates an abnonnal value.
`1' Inwever. no cuff activation is performed because the esti-
`mated blood pressure falls within the normal range. and
`periodic cuEl' blood pressure measurement is performed at
`time tl alter a predetermined time has elapsed since time t0.
`[0067] After time t1. the estimated blood pressure exceeds
`the lower limit and upper limit in some periods. but both the
`two waveform parameters have normal values. so no cufl'
`activation is performed either. After that. however. both the
`estimated blood pressure and the wavcfomt parameter {bfa]
`show abnormal values. so cufl" blood pressure measurement
`is executed at time 12. Since (tl—t0]>(t2—tl), the cufl‘ acti-
`vation at time t2 is shorter than the periodic interval.
`[0068] After time t2. the wavefonn parameter shows an
`abnormal value fora while. but the estimated blood pressure
`falls within the nonnal range. so no culf activation is
`performed.
`[0069] As shown in FIG. 4. the blood pressure monitoring
`apparatus of this embodiment detemiines the presence!’
`absence of the true fluctuation in blood pressure by using the
`values of the parameters obtained front the accelerated pulse
`wav