Blood pressure measure system

OPEN/CLOSE VALVE 114 OPENED

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5,261,413

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the patient feels as if he or she would be pressed by the

BLOOD PRESSURE MEASURE SYSTEM cuff endlessly because the cuff pressure is increased

continuously without any pauses in contrast to the man

BACKGROUND OF THE INVENTION ual cuff pressure increase in which the cuff pressure is

Field of the Invention 5 increased step-wise including pauses. Also, the Appli

_ ... ,, j cant has found that the reason for congestive spots to

The present invention relates to a blood pressure come om Qn ... ^ dufi tQ ^ convention^auto.

monitor or measuring device. matjc cuffpressure mcrease is that wrinkles produced m

Related Art Statement the cuff surface can not be recovered to its original

There is known a blood pressure monitor system 10 smooth «a*e because of the continuous cuffpressure

including (a) a pressing device such as a cuff for press- ,ncrease wlthout Pauses

ing a body portion of a subject, and (b) a measuring SUMMARY OF THE INVENTION

device for increasing the pressing force of the pressing .

device to a predetermined level, subsequently varying ., ",s therefore a first object of the present mvention to the pressing force, and measuring a blood pressure of provide a blood pressure monitor system which meathe subject based on Korotkoff sounds or pulse waves sures blood pressure quickly in each periodic measureobtained during the variation of the pressing force, the rnent cycle for an urgent case and which does not burmeasuring device repeating the blood pressure measure- den a patient under a stable condition or does not cause ment at a pre-set period. In the case where frequent 2Q congestive spots to come out on the patient's skin, blood pressure measurements from a patient are neces- It is a second object of the present invention to prosary, for example, during or after a surgical operation, vide a blood pressure measuring system which measures the measurement period is set at a short time on the blood pressure of a subject by effecting automatic pressmonitor system. On the other hand, for a patient under ing force increases without causing the subject to feel a stable condition, for example, in a general ward, the ^ uneasiness or pain.

measurement period is set at a long time. The above first object has been achieved according

For a patient such as during or after a surgical opera- to a first aspect of the present invention, which provides

tion, it is desirable, in addition to the use of a short a blood pressure monitor system comprising (a) pressing

measurement period, to increase the pressing force (e.g., means for pressing a body portion of a subject, (b) mea

cuff pressure) quickly so as to measure blood pressure as suring means for increasing the pressing force of the

fast as possible in each of the periodic measurement pressing means to a predetermined level, subsequently

cycles. varying the pressing force, and measuring a blood pres

On the other hand, for a patient under a stable condi- sure of the subject during the variation of the pressing

tion for whom a long measurement period is used, it is force) the measuring means repeating the blood pres

not necessary to measure blood pressure so quickly in sure measurement, (c) setting means for setting a fre

each periodic measurement cycle. Rather, it is desirable quency at which the measuring means repeats the blood

to increase the cuff pressure slowly so as to reduce ure measureme„t> and (d) changing means for

mental burden to the patient and prevent congestive cha in a rate of increase of the pressi„g force depend

spots from being produced on the patient s skin. This is j the measurement frequency set by the setting

very important, m particular, in the case where the means

blood pressure of a patient received in a general ward is 40 ^ ^ ^ ^ g ... as

monitored over a long period of time. described abo ft cha m ... ch

However, m the conventional blood pressure monitor ... . - °, ,. 6 ,

c , cc \ ■ mcrease of the pressing force dependmg upon the mea

system, the pressing force (e.g., cuff pressure) increase . , r . u ~- w

rate is not is varied that is it is kept constant for both Surem.en . fre?uetncv set \ the tf tmS means' M?re

urgent and stable cases, and therefore fails to simulta- « specifically, m the case where the measurement fre

neously satisfy the above indicated requirements for the <*uenc/.ls se/ at a «reat value, that is, the measurement

urgent and stable cases. Penod ls f at a sma11 fvalue for TMnitonng the blood

In addition, there is known a blood pressure measur- Pressurf of a Patlei"> fo5 examPle' durlnS or after a ing system including (1) a pressing device such as a cuff surSlcal operation, the changing means selects a high for pressing a body portion of a subject, and (2) a mea- 50 pressing force increase rate so as to shorten the time suring device for automatically measuring a blood pres- necessary for blood pressure measurement. Consesure of the subject based on Korotkoff sounds or pulse quently, a doctor or nurse can obtain a blood pressure waves obtained while the pressing force is decreased value verv quickly in each periodic measurement cycle after having been increased to a predetermined level. In for an urgent case. A patient who is under anesthesia this measuring system, the pressing force (e.g., cuff 55 during or after a surgical operation does not feel pain or pressure) automatically is increased, for example, with mental burden even though the pressing force is inpressurized air being supplied from an air pump. creased at a high rate.

However, a patient whose upper arm is subject to On the other hand, in the case where the measureautomatic cuff pressure increase by the above measur- rnent period is set at a long time for a patient under a ing system, may feel such uneasiness or pain as he or she 60 stable condition, the changing means selects a low would not feel when undergoing manual cuff pressure pressing force increase rate so as to relieve the patient of increase. This may badly affect the accuracy of blood the mental burden or the congestive spots on the papressure measurement. In addition, the conventional tient's skin. In addition, in the case where the low pressautomatic cuff pressure increase may cause congestive ing force increase rate is established with an air pump spots to come out on the patient's skin. 65 being operated at a low rotational speed, noise pro

The Applicant has recognized that the reason for a duced from the pump is accordingly reduced, which

patient to feel uneasiness or pain when being subject to allows the other patients in a general ward to sleep at

the conventional automatic cuff pressure increase is that nights without being disturbed by such noise.

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According to a feature of the first aspect of the inven- sure in the reservoir with the pressurized air from the

tion, the changing means judges whether or not the pump, to an upper limit of a predetermined pressure

measurement frequency is greater than a reference range, and subsequently maintaining the reservoir pres

value, and selects a first pressing force increase rate if sure within the pressure range.

the judgement is negative and a second pressing force 5 According to yet another feature of the second aspect increase rate higher than the first increase rate if the of the invention, the regulating means effects the stepjudgement is affirmative. wise pressing force increase after having continuously According to another feature of the first aspect of the increased the pressing force to a predetermined low invention, the pressing means comprises an inflatable level.

cuff, the measuring means comprises an air pump which 10 According to a further feature of the second aspect of

supplies the cuff with pressurized air, and the changing the invention, the regulating means utilizes constant

means comprises a pump drive/regulate circuit which values as the first and second periods, respectively,

changes a rotational speed of the air pump in two steps In a preferred embodiment according to the second

depending upon the selected first or second increase aspect of the invention, the regulating means increases

rate. 15 the pressing force by a predetermined value in the each

According to yet another feature of the first aspect of first period, the invention, the setting means is manually operated to In another embodiment according to the second asset a measurement period as the measurement fre- pect of the invention, the measuring means periodically quency, the setting means generating to the changing measures the blood pressure at predetermined intervals means an electrical signal representing the measurement 20 of time.

^Se above second object has been achieved accord- BRIEF DESCRIPTION OF THE DRAWINGS

ing to a second aspect of the present invention, which The above and optional objects, features and advan

provides a blood pressure measuring system comprising tages of the present invention will be better understood

(1) pressing means for pressing a body portion of a 25 by reading the following detailed description of the

subject, (2) automatic regulating means for step-wise presently preferred embodiments of the invention when

increasing the pressing force of the pressing means to a considered in conjunction with the accompanying

predetermined level, the step-wise increase of the press- drawings, in which:

ing force including alternate first and second periods, FIG. 1 is a diagrammatic view of a blood pressure

the pressing force being increased in each of the first 30 monitor system embodying the present invention;

periods and maintained in each of the second periods, FIG. 2 is a flow chart for illustrating the operation of

and (c) measuring means for measuring a blood pressure the monitor system of FIG. 1;

of the subject while the pressing force is decreased after FIG. 3 is a diagrammatic view of a blood pressure

the step-wise increase. measure system embodying the present invention;

In the blood pressure measuring system constructed 35 FIG, 4 is a flow chart for illustrating the operation of

as described above, the automatic regulating means the measure system of FIG. 3; and

step-wise increases the pressing force of the pressing FIG. 5 is a graph of a stepped curve representing an

means to a predetermined level, such that the step-wise automatic cuff pressure increase effected by the mea

pressing force increase includes alternate first and sec- sure system of FIG. 3.

ond periods, the pressing force being increased in each 40 ___.„ r.t,C/-DTd-tt^xt ^ -rue

of the first periods and maintained in each of the second ^prefirred Sbotsmfnts

periods. Thus, the present measure system is free from PREFERRED EMBODIMENTS

the problem that a subject may feel as if he or she would Referring first to FIG. 1, there is shown the circuit

be pressed endlessly when undergoing automatic con- diagram of a blood pressure monitor system embodying

tinuous pressing force (e.g. cuff pressure) increase, 45 the present invention.

thereby relieving the subject of such uneasiness or pain In FIG. 1, reference numeral 10 designates a rubber

as he or she might feel due to the conventional monoto- bag or cuff adapted to be set around an upper arm or the

nous cuff pressure increase. This results in preventing like of a living subject. An air pump 16 is connected to

the accuracy of blood pressure measurement from being the cuff 10 via piping 14. The rotational speed of the air

deteriorated because of that uneasiness or pain. In addi- 50 pump 16 is regulated by a pump drive/regulate circuit

tion, wrinkles produced by cuff pressurization are re- 12. The pump circuit 12 is responsive to a drive signal

stored to their original smooth state during each of the supplied from an output interface 42 (described later),

second periods in which the pressing force is main- to step-wise change the rotational speed of the air pump

tained. This contributes to preventing congestive spots 16, more specifically, in the present embodiment, in two

from being produced on subject's skin. 55 steps, so that air pressure in the cuff 10 (hereinafter,

According to a feature of the second aspect of the referred to as the "cuff pressure") is increased at a low

invention, the pressing means comprises an inflatable or a high rate by being supplied with pressurized air

cuff, and the regulating means comprises an open/close from the pump 16. Consequently, the upper arm of the

valve, an air reservoir, and an air pump which supplies subject is pressed by the inflated cuff 10. In the present

the reservoir with pressurized air, the open/close valve 60 embodiment, the cuff 10 serves as pressing means,

being opened during the each first period so as to allow A pressure sensor 18, a rapid-deflation valve 20, and

the pressurized air stored in the reservoir to be supplied a slow-deflation valve 22 are associated with the piping

to the cuff and thereby increase a pressure in the cuff, 14 in a parallel relationship with each other. The pres

the open/close valve being closed during the each sec- sure sensor 18 detects the cuff pressure and generates a

ond period so as to maintain the pressure in the cuff. 65 pressure signal SP representing the detected cuff pres

According to another feature of the second aspect of sure, to a filter circuit 24. The filter circuit 24 includes

the invention, the measuring system further comprises a a low-pass filter which transmits only a component

means for, in the each second period, increasing a pres- representing a static pressure out of the cuff pressure 5,261,413

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(hereinafter, the component is referred to as the "cuff cuit 12 cooperate with each other to serve as pressure

pressure signal SK"). The cuff pressure signal SK is increase rate changing means.

supplied to a central processing unit (CPU) 28 via a first Step S6 is followed by Step S7 in which a timer (not

analog to digital (A/D) converter 26. shown) starts to count for measuring a time lapse from

A microphone 30 is associated with the cuff 10. The 5 the commencement of the cuff pressure increase. Subse

microphone 30 detects arterial sounds (i.e., Korotkoff quently, the control of the CPU 32 goes to Step S8 to

sounds) produced from an artery running in the upper identify whether or not the cuff pressure has exceeded

arm of the subject, and generates a sound signal SO a reference pressure level (e.g., 180 mmHg) which is

representing the detected Korotkoff sounds, to a band- estimated to be greater than the systolic blood pressure

pass filter 32. The band-pass filter 32 transmits only a 10 of the subject. If a negative judgement is made in Step

component having a frequency of about 30 to 80 Hz. S8, the control of the CPU 32 repeats Step S8 until an

The sound signal SO is supplied to the CPU 28 via a affirmative judgement is made. If the cuff pressure has

second A/D converter 34. exceeded the reference pressure level and an affirmative

A setting device 35 is connected to the CPU 28. Be- judgement is made in Step S8, the control goes to Step

fore starting a blood pressure monitoring, an operator 15 S9 in which the rotation of the air pump 16 is stopped

such as a doctor or nurse manually operates the setting and the slow-deflation valve 22 is opened. Conse

device 35 for setting a period (or frequency) of blood quently, the cuff pressure starts to be decreased slowly,

pressure measurements. The setting device 35 generates Step S9 is followed by Step S10 to identify whether

to the CPU 28 a period signal ST representing the set or not a Korotkoff sound has been detected, by utilizing

period. 20 the sound signal SO. In the case where a negative judge

The CPU 28 is connected via data bus to a read only ment is made in Step S10, the control waits for an affir

memory 36, a random access memory 38, a display 40, mative judgement. When an affirmative result is pro

and the output interface 42. The CPU 28 processes vided, a magnitude of the signal SO corresponding to

input signals by utilizing control programs pre-stored in the Korotkoff sound, and a magnitude of the cuff pres

the ROM 36 and temporary-storage function of the 25 sure signal SK at the time of detection of the Korotkoff

RAM 38, and generates drive signals via the output sound, are stored in the RAM 38, in Step S10. Step S10

interface 42 to the pump drive/regulate circuit 2 and is followed by Step Sll, namely, blood pressure deter

drive circuits (not shown) for the rapid- and slow-defla- mine routine.

tion valves 20, 22, so as to regulate the air pump 16 and In Step Sll, a well-known blood pressure determine the two valves 20, 22, respectively. In addition, the 30 algorithm is implemented to determine, as systolic and CPU 28 operates for determining a blood pressure of diastolic blood pressures, the cuff pressures at the time the subject by utilizing the sound signal SO and cuff of appearance and disappearance of the Korotkoff pressure signal SK, and commands the display 40 to sounds, respectively. Step Sll is followed by Step S12 indicate the determined blood pressure. to identify whether or not the blood pressure measureHereinafter, there will be described the operation of 35 ment has been completed. If the measurement has not the blood pressure monitor system constructed as de- ended and therefore a negative judgement is made in scribed above, by reference to the flow chart of FIG. 2. Step S12, the control goes back to repeat Step S10 Upon application of electric power to the monitor through Step S12. On the other hand, if the measuresystem, the CPU 32 effects initialization operations, and ment has been completed and an affirmative judgement subsequently the control of the CPU 32 proceeds with 40 is made in Step S12, the control goes to Step S13 to Step SI to identify whether or not a start switch (not indicate the measured blood pressures on the display 40. shown) has been turned ON. If a negative judgement is In addition, the rapid-deflation valve 20 is opened, made in Step SI, the control of the CPU 32 repeats Step Step S13 is followed by Step S14 to judge whether or SI until an affirmative judgement is made. On the other not a value, T, counted by the previously-described hand, if an affirmative result is provided in Step SI, the 45 timer has exceeded the set period Tm. If a negative control goes to Step S2 to identify whether or not the judgement is made in Step S14, the control of the CPU period signal ST representing a set period, Tm, is pres- 32 repeats this step until an affirmative judgement is ent at the CPU 32. In the case where a negative result is made. Meanwhile, if the value T has exceeded the perprovided in Step S2, the control repeats Step S2 and iod Tm and accordingly an affirmative judgement is waits for an affirmative judgement. In the case where an 50 made in Step S14, the control goes to Step S15 to reset affirmative judgement is made in Step S2, the control of the timer count T to zero. Step S15 is followed by Step the CPU 32 goes to Step S3 to judge whether or not the S16 to judge whether or not the previously-described set period Tm is not smaller than a reference value, in start switch has been turned OFF. In the case where an the present embodiment, 10 minutes. If an affirmative affirmative judgement is made in Step S16, the control judgement is made in Step S3, the control goes to Step 55 of the CPU 32 quits this program. On the other hand, if S4 to select a first pressure increase rate so that the cuff a negative judgement is made in Step S16, the control pressure is increased at a low rate, and then proceeds to goes back to Steps S2 and the following steps for carryStep S6. On the other hand, if a negative judgement is ing out another blood pressure measurement. Thus, made in Step S3, the control goes to Step S5 to select a blood pressure measurements successively are carried second pressure increase rate higher than the first pres- 60 out at the period Tm (that is, at a frequency correspondsure increase rate so that the cuff pressure is increased at ing to the period Tm), and the measured blood pressures a high rate, and then proceeds to Step S6. are indicated on the display 40 for each of the periodic

In Step S6, both the rapid- and slow-deflation valves measurement cycles.

20, 22 are closed, and the air pump 16 is driven or ro- As is apparent from the foregoing description, the

tated by the drive/regulate circuit 12 at the low or high 65 present blood pressure monitor system operates in such

rate selected in Step S4 or Step S5. Thus, the cuff pres- a way that, in the case where the measurement period

sure starts to be increased. In the present embodiment, Tm is set at less than 10 minutes in an urgent situation

Steps S3 through S5 and the pump drive/regulate cir- such as during or after a surgical operation, the previ