Blood pressure measuring device and control method for the blood pressure measuring device

Abstract

Blood pressure measuring device (1), which has: a cuff (40) which, when worn on a blood pressure measuring area, pressurizes an artery in the measuring area at the pressure of a fluid in the cuff (40); a piezoelectric pump (31) which increases the pressure within the cuff (40); an air outlet unit (32) which reduces the pressure within the cuff (40); a pressure detection unit (33) which detects the cuff pressure, which is the pressure content of the cuff (40); and a control unit (20) wherein the control unit (20) includes: a determining device which determines a control amplitude and determining a control frequency of a voltage applied to the piezoelectric pump (31) (step S111 to step S114, step S131 to step S134); an applied voltage control means which carries out the control so that a voltage at the control amplitude and control frequency determined by the determining means is applied to the piezoelectric pump (31) (step S121, step S122); and a blood pressure measuring device which calculates a blood pressure value based on the cuff pressure detected by the pressure detecting unit during inflation when the cuff pressure is increased by the piezoelectric pump (31) (step S123), and wherein the applied voltage control means can control the amplitude of the voltage in predetermined steps and, in a predetermined order, applies a voltage having an amplitude which is a value above the control amplitude by at least one step and a voltage having an amplitude which is a value below the control amplitude by at least one step, so that the discharge of the piezoelectric pump (31) is approximately the same as when a voltage at the control amplitude determined by the determining means is applied (step S111, step S112, step S121, step S122, step S131 to step S133).

Description

Technical area

[0001] The invention relates to blood pressure measuring devices and control methods for blood pressure measuring devices, and more particularly, it relates to blood pressure measuring devices suitable for measuring a blood pressure during inflation of a cuff and to control methods for such blood pressure measuring devices. Background of the state of the art

[0002] An electronic sphygmomanometer that uses oscillometric technology is known as a typical electronic sphygmomanometer. In an electronic sphygmomanometer that uses oscillometric technology, a cuff containing an air bladder is wrapped around a part of a body, and changes in the volume of an arterial vessel pressurized by inflation / deflation of the air bladder are obtained as changes in the amplitude of the pressure in the air bladder (a cuff pressure), which are then used to calculate a blood pressure. To accurately measure blood pressure during cuff inflation, it is necessary to appropriately control the rate at which the pressure inside the cuff is increased. For example, it is necessary to inflate the cuff at a constant rate.

[0003] JP 2009-74418A (hereinafter "Patent Literature 1") proposes a piezoelectric micropump driven by using a piezoelectric element, and discusses the application of such a pump to an electronic blood pressure monitor. Meanwhile, JP 2010-255447A (hereinafter "Patent Literature 2"), JP 2010-162487A (hereinafter "Patent Literature 3"), and so on propose setting a drive frequency according to the material of a piezoelectric element and a diaphragm, and performing control near the drive frequency.

[0004] Although conventional blood pressure monitor pumps control the pump discharge via pulse width modulation (PWM) control, piezoelectric pump discharge control is generally considered to be performed by driving the pump at the drive frequency and controlling the discharge via voltage control. Citation listPatent literature Patent Literature 1: JP 2009-74418A Patent Literature 2: JP 2010-255447A Patent Literature 3: JP 2010-162487A

[0005] JP H08-187288A describes a blood pressure monitoring device that monitors the blood pressure of a living being by varying the pressure of a cuff wrapped around a body part. It includes means for controlling the cuff pressure, calculating the amplitude of pulse waves, and determining the minimum blood pressure value based on the amplitude of the pulse waves. Summary of the inventionTechnical problem

[0006] However, such piezoelectric pumps have had the following problems: (1) the precision of voltage control corresponds to the precision of pump discharge, and thus, it is necessary to increase the precision of voltage control to control the inflation rate at a proper speed; (2) attempting to increase the precision of voltage control results in an increase in the number of components and the like to adjust the resolution, resulting in an increase in the cost of the circuitry; and (3) although increasing the resolution by adding AM modulation to the voltage control can be considered, such a system is affected by pulsations, ambient noise, and the like when installed in a blood pressure monitor.

[0007] Having become aware of the aforementioned problems, it is an object of this invention to provide a blood pressure measuring device and a control method for such a blood pressure measuring device which, when inflation is controlled by using a piezoelectric pump during inflation for blood pressure measurement, are capable of increasing the precision of blood pressure measurement by suppressing the occurrence of noise, reducing the influence of pulsations, and controlling inflation at a high degree of precision. Solution to the problem

[0008] To achieve the aforementioned object, a blood pressure measuring device according to one aspect of the invention includes a cuff which, when worn on a blood pressure measuring area, pressurizes an artery in the measuring area at the pressure of a fluid in the cuff, a piezoelectric pump which increases the pressure inside the cuff, an air outlet unit which reduces the pressure inside the cuff, a pressure detecting unit which detects the cuff pressure, which is the pressure inside the cuff, and a control unit.

[0009] The control unit includes a determination unit that determines a control amplitude and a control frequency of a voltage applied to the piezoelectric pump, an applied voltage control unit that performs control so that a voltage at the control amplitude and at the control frequency determined by the determination unit is applied to the piezoelectric pump, and a blood pressure measurement unit that calculates a blood pressure value based on the cuff pressure detected by the pressure detection unit during inflation when the cuff pressure is increased by the piezoelectric pump.The applied voltage control unit can control the amplitude of the voltage in predetermined steps and applies, in a predetermined order, a voltage having an amplitude which is a value above the control amplitude by at least one step and a voltage having an amplitude which is a value below the control amplitude by at least one step, so that the output of the piezoelectric pump is approximately the same as when a voltage at the control amplitude determined by the determining unit is applied.

[0010] Preferably, the applied voltage control unit applies voltages having two amplitude values ​​in an alternating manner. The two values ​​are a value a predetermined step above and a value a predetermined step below the control amplitude determined by the determining unit, respectively. The control unit further includes an application ratio determining unit that, based on the control amplitude determined by the determining unit and the two values, determines a time ratio for which the voltages at the two values ​​are applied in an alternating manner, such that the output of the piezoelectric pump is substantially the same as in the case where a voltage at the control amplitude is applied.The applied voltage control unit applies the voltages having two amplitude values ​​according to the time ratio determined by the application ratio determining unit.

[0011] In addition, the applied voltage control unit further applies the voltages so that a difference between the two values ​​is a minimum.

[0012] Preferably, the applied voltage control unit applies the voltages having two amplitude values ​​determined by the determining unit in an alternating manner at the same time ratio. The control unit further includes an applied voltage determining unit that, based on the control amplitude determined by the determining unit, determines the value of a step above the control amplitude and the value of a step below the control amplitude such that the output of the piezoelectric pump is substantially the same as in the case where a voltage at the control amplitude is applied. The applied voltage control unit applies the voltages having two amplitude values ​​determined by the applied voltage determining unit in an alternating manner.

[0013] Further preferably, the applied voltage determining unit determines the two values ​​such that a difference between the two values ​​is a minimum.

[0014] Preferably, the determining unit determines an optimal frequency for the value of the amplitude of the voltage applied by the applied voltage control unit as the control frequency.

[0015] A control method of a blood pressure measuring device according to another aspect of the invention is a control method of a blood pressure measuring device including a cuff which, when worn on a blood pressure measuring region, pressurizes an artery in the measuring region at the pressure of a fluid in the cuff, a piezoelectric pump which increases the pressure inside the cuff, an air outlet unit which reduces the pressure inside the cuff, a pressure detecting unit which detects the cuff pressure, which is the pressure inside the cuff, and a control unit.

[0016] The control method includes the steps of the control unit determining a control amplitude and a control frequency of a voltage applied to the piezoelectric pump, executing control so that a voltage at the control amplitude and the control frequency determined by the determining unit is applied to the piezoelectric pump, and calculating a blood pressure value based on the cuff pressure detected by the pressure detecting unit during inflation when the cuff pressure is increased by the piezoelectric pump.The step of performing the control may control the amplitude of the voltage in predetermined steps and includes a step of applying, in a predetermined order, a voltage having an amplitude which is a value above the control amplitude by at least one step and a voltage having an amplitude which is a value below the control amplitude by at least one step, such that the control is substantially the same as when a voltage is applied at the predetermined control amplitude. Advantageous effects of the invention

[0017] According to this invention, a control amplitude and a control frequency of a voltage applied to the piezoelectric pump are determined, control is performed so that a voltage at the predetermined control amplitude and control frequency is applied to the piezoelectric pump, and a blood pressure value is calculated based on the cuff pressure detected by the pressure detecting unit during inflation when the cuff pressure is increased by the piezoelectric pump.In controlling the piezoelectric pump, the amplitude of the voltage may be controlled in predetermined steps, and a voltage having an amplitude which is a value above the control amplitude by at least one step and a voltage having an amplitude which is a value below the control amplitude by at least one step are applied in a predetermined order such that the control is substantially the same as when a voltage at the predetermined control amplitude is applied.

[0018] By amplitude modulating the applied voltage, the piezoelectric pump can be controlled in substantially the same manner as in the case where the target voltage is applied. However, according to the invention, the occurrence of amplitude modulation frequency noise can be suppressed compared to the case where control is performed by amplitude modulation. Furthermore, where, for example, pulsations occur when increasing the cuff pressure in the case where control is performed by amplitude modulation, the influence of the pulsations can be reduced according to the invention. Furthermore, according to the invention, the same high-precision inflation control can be achieved as in the case where control is performed by amplitude modulation.

[0019] As a result, it is possible to provide a blood pressure measuring device and a control method for such a blood pressure measuring device which, when inflation is controlled by using the piezoelectric pump during inflation for blood pressure measurement, can increase the precision of blood pressure measurement by suppressing the occurrence of noise, reducing the influence of pulsations, and controlling inflation at a high degree of precision. Short description of the drawings Fig. 1 is a perspective view of the exterior of a measuring device according to an embodiment of the invention. Fig. 2 is a block diagram showing the overall configuration of the blood pressure monitor according to the embodiment. Fig. Figure 3 is a graph showing a flow rate required for constant speed inflation. Fig. Figure 4 is a graph illustrating changes in cuff pressure in the case where a piezoelectric pump control voltage is modulated with AM. Fig. 5 is a diagram illustrating the concept of the piezoelectric pump voltage control according to the invention. Fig. 6 is a graph illustrating a control result in the case where a piezoelectric pump is subjected to voltage control according to an embodiment of the invention. Fig. 7 is a flowchart illustrating the flow of a blood pressure measurement process executed by the blood pressure meter according to the first embodiment. Fig. 8 is a flowchart illustrating the flow of a blood pressure measurement process executed by the blood pressure meter according to the second embodiment. Description of the embodiments

[0020] Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. Note that identical or corresponding elements in the drawings are given the same reference numerals, and descriptions thereof will not be repeated. First embodiments

[0021] In the following, a piezoelectric pump drive controller will be described when performing inflation-based measurement using an oscillometric blood pressure monitor that performs measurements during inflation as an embodiment of the invention.

[0022] First, a configuration of a blood pressure monitor 1 according to this embodiment will be described. Fig. 1 is a perspective view of the exterior of the blood pressure monitor 1 according to this embodiment of the invention. As shown in Fig. As shown in FIG. 1, the blood pressure monitor 1 according to this embodiment includes a main body 10, a cuff 40, and an air tube 50. The main body 10 includes a box-shaped casing, and a display unit 21 and an operation unit 23 are provided on the upper surface thereof. During measurement, the main body 10 is used by placing it on a support surface such as a table or the like.

[0023] The cuff 40 primarily includes a band-shaped and air-bellows-shaped outer cover 41 and a pressurizing air bladder 42 contained within the outer cover 41, serving as a pressurizing fluid bladder. The cuff 40 has an overall annular shape. During measurement, the cuff 40 is used by wrapping it around and wearing it on the upper arm of a subject. The air hose 50 connects the main body 10 and the cuff 40, which are configured as separate units.

[0024] Fig. Fig. 2 is a block diagram showing the overall configuration of the blood pressure monitor 1 according to this embodiment. As shown in Fig. 2, in addition to the aforementioned display unit 21 and the operation unit 23, the main body 10 includes a control unit 20, a storage unit 22, a power supply unit 24, a piezoelectric pump 31, a discharge valve 32, a pressure sensor 33, a DC-DC amplifier circuit 61, a voltage control circuit 62, a driving control circuit 63, an amplifier 71, and an A / D converter 72. The piezoelectric pump 31 and the discharge valve 32 correspond to an inflation / deflation mechanism for increasing / decreasing the internal pressure of the pressurizing air bladder 42.

[0025] The pressure-applying air bladder 42 supplies pressure to the upper arm when worn thereon and has an internal space therein. The pressure-applying air bladder 42 is connected to the aforementioned piezoelectric pump 31, the exhaust valve 32, and the pressure sensor 33, respectively, via the aforementioned air hose 50. As a result, the pressure-applying air bladder 42 is inflated and expanded under the drive of the piezoelectric pump 31; the internal pressure is maintained, the pressure-applying air bladder 42 is deflated and contracts, and so on, by controlling the drive of the exhaust valve 32.

[0026] The control unit 20 is configured of, for example, a CPU (central processing unit) and is a unit for controlling the blood pressure monitor 1 as a whole.

[0027] The display unit 21 is configured of, for example, an LCD (liquid crystal display) and is a unit for displaying the measurement results and the like.

[0028] The storage unit 22 is configured of, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), or the like, and stores programs for causing the control unit 20 and the like to execute the processes for measuring a blood pressure value, storing the measurement results, and so on.

[0029] The operation unit 23 is a unit for accepting operations performed by a measuring person or the like and inputting such external commands to the control unit 20, the power supply unit 24, and the like.

[0030] The power supply unit 24 is a unit for supplying power to the various units of the blood pressure monitor 1, such as the control unit 20 and the piezoelectric pump 31, and is a battery in this embodiment. However, the power supply unit 24 is not limited to this and may receive power supplied from an external power source, such as an AC outlet.

[0031] The control unit 20 inputs control signals for driving the piezoelectric pump 31 and the discharge valve 32 to the voltage control circuit 62 and the driving control circuit 63, respectively, and inputs the blood pressure values ​​serving as measurement results to the display unit 21 and the storage unit 22. The control unit 20 also includes a blood pressure information obtaining unit (not shown) that obtains a blood pressure value of a measured subject based on a pressure value detected by the pressure sensor 33 via the amplifier 71 and the A / D converter 72. The blood pressure value obtained by the blood pressure information obtaining unit is input to the aforementioned display unit 21 and the storage unit 22 as a measurement result.

[0032] Note that the blood pressure monitor 1 may also include a separate output unit that outputs a blood pressure value to an external device such as a PC (personal computer), a printer, or the like as the measurement result. For example, a serial communication line, a device that writes to various types of recording media, or the like may be used as the output unit.

[0033] The DC-DC boosting circuit 61 is a circuit that boosts the voltage of the battery serving as the power supply unit 24 to a voltage suitable for driving the piezoelectric pump 31.

[0034] The voltage control circuit 62 controls the voltage supplied to the piezoelectric pump 31 based on a voltage value indicated by a control signal input from the control unit 20.

[0035] The driving control circuit 63 controls the piezoelectric pump 31 and the exhaust valve 32 based on a control signal input from the control unit 20. Specifically, the driving control circuit 63 controls the frequency of a current supplied to the piezoelectric pump 31 based on a control frequency indicated by the control signal input from the control unit 20. In addition, the driving control circuit 63 controls the exhaust valve 32 to open and close based on the control signal input from the control unit 20.

[0036] The piezoelectric pump 31 is a unit for increasing the internal pressure of the pressurizing air bladder 42 (also referred to hereinafter as "cuff pressure") by supplying air to the interior of the pressurizing air bladder 42, and its operations are controlled by the aforementioned driving control circuit 63. The piezoelectric pump 31 discharges air at a predetermined flow rate by applying an AC current of a predetermined amplitude V0 at a predetermined driving frequency f0. Note that a sine-wave AC current may be applied, a square-wave AC current may be applied, and so on. Hereinafter, the value of a peak-to-peak potential difference Vp-p may be used when discussing the value of a voltage applied to the piezoelectric pump 31. The amplitude is half the value of Vpp.Relative to Vp-p, the value of the voltage changes in a range of values ​​from, for example, -Vp-p / 2 to Vp-p / 2.

[0037] The outlet valve 32 is a unit for maintaining the internal pressure in the pressurizing air bladder 42, opening the internal space of the pressurizing air bladder 42 to the outside, and reducing the cuff pressure, and so on, and the operations thereof are controlled by the aforementioned driving control circuit 63.

[0038] The pressure sensor 33 detects the internal pressure of the pressurizing air bladder 42 and inputs an output signal based on the detected pressure to the amplifier 71. The amplifier 71 amplifies the level of the signal input from the pressure sensor 33. The A / D converter 72 converts the signal amplified by the amplifier 71 into a digital signal and inputs the generated digital signal to the control unit 20.

[0039] Fig. Figure 3 is a graph showing the flow rate required for constant speed inflation. As shown in Fig. 3, in the case where the piezoelectric pump 31 is controlled at a set voltage and the peak-to-peak potential difference of the voltage of 15 Vp-p, the flow rate of the air discharged from the piezoelectric pump 31 is about 50 ml / min when the cuff pressure is about 0 mmHg, about 25 ml / min when the cuff pressure is 50 mmHg, and about 0 ml / min when the cuff pressure is 110 mmHg.

[0040] Similarly, when the peak-to-peak potential difference of the voltage is 20 Vp-p, the outlet flow rate of the piezoelectric pump 31 drops from about 100 ml / min to about 70 ml / min, to about 30 ml / min, to about 10 ml / min, to about 0 ml / min, as the cuff pressure increases from about 0 mmHg to 50 mmHg, to 100 mmHg, to 150 mmHg, and to 170 mmHg.

[0041] Furthermore, in cases where the peak-to-peak potential difference of the voltage applied to the piezoelectric pump 31 is 25 Vp-p, 30 Vp-p, 35 Vp-p and also 40 Vp-p, the outlet flow rate of the piezoelectric pump 31 falls as the cuff pressure increases.

[0042] Meanwhile, in the case where the circumference of a wrist, which is a range on which the cuff 40 is to be worn, is a minimum length that the cuff 40 can cope with, the flow rate required by the piezoelectric pump 31 when the cuff 50 is inflated at a constant speed increases from about 30 ml / min to about 35 ml / min, while the cuff pressure increases from 40 mmHg to 250 mmHg.

[0043] On the other hand, in the case where the wrist circumference is a maximum length that the cuff 40 can handle, the flow rate required for inflation at a constant speed is about 145 ml / min when the cuff pressure is 30 mmHg, but drops as the cuff pressure increases, and becomes about 80 ml / min when the cuff pressure is 100 mmHg, about 75 ml / min when the cuff pressure is 150 mmHg, and about 75 ml / min when the cuff pressure is 250 mmHg.

[0044] In the case where the wrist circumference is between the minimum length and the maximum length that can be handled by the cuff 40, the cuff 40 can be inflated at a constant speed by controlling the flow rate relative to the cuff pressure according to a constant speed inflation control range indicated by the hatched diagonal lines in the graph in Fig. 3 is displayed.

[0045] Accordingly, in the case where the wrist circumference is the minimum, it is necessary to control the flow rate to change in the aforementioned manner as the pressure increases, so that in the case where the cuff 40 is inflated at a constant speed, the peak-to-peak potential difference of the voltage applied to the piezoelectric pump 31 is increased from about 14 Vp-p as the cuff pressure increases, and reaches about 33 Vp-p when the cuff pressure reaches 250 mmHg.

[0046] Similarly, in the case where the wrist circumference is the maximum, it is necessary to control the flow rate to change in the aforementioned manner as the cuff pressure increases, so that in the case where the cuff 40 is inflated at a constant speed, the peak-to-peak potential difference of the voltage applied to the piezoelectric pump 31 is reduced from about 26 Vp-p to about 23 Vp-p at the time the cuff pressure reaches about 60 mmHg, is increased again thereafter and reaches about 37 Vp-p when the cuff pressure reaches 250 mmHg.

[0047] In this way, in order to inflate the cuff 40 at a constant speed, it is necessary to control the voltage applied to the piezoelectric pump 31 within a given voltage amplitude range (here, a range in which the peak-to-peak potential difference is approximately 12 Vp-p to 40 Vp-p, or, in other words, an amplitude range from 6 V to 20 V). Since this is a digital control, it is also necessary to increase the resolution of the control voltage to increase the precision of control during constant speed inflation. However, this approach requires the use of an expensive control circuit, which will result in an increase in the manufacturing cost of the sphygmomanometer 1.

[0048] Fig. Figure 4 is a graph illustrating the changes in cuff pressure in the case where the voltage for controlling the piezoelectric pump 31 is amplitude modulated. As in Fig. As shown in Figure 4, AM modulating the control voltage can be considered as a way to increase the resolution of the control voltage.

[0049] However, doing so causes pulsations to occur with increasing cuff pressure, as indicated by the graph. Such pulsations have a negative impact on the blood pressure measurement performed by the blood pressure monitor 1 (e.g., deteriorating measurement accuracy). Furthermore, noise will be generated if the pulsations have a frequency in the audible range. The volume of the noise will increase as the amplitude of the pulsations increases.

[0050] Fig. Fig. 5 is a diagram illustrating the concept of voltage control for the piezoelectric pump 31 according to this invention. As in Fig. As shown in Fig. 5, in the blood pressure monitor 1 according to this embodiment, the value of the amplitude of the voltage that can be controlled is changed in steps to realize digital control of the voltage applied to the piezoelectric pump 31, etc. For example, in the case where a control step is equal to 1 V, and the amplitude V0 of a target voltage is 20.3 V, 20 V, 21 V, or the like can be applied to the piezoelectric pump 31, but 20.3 V cannot be applied to the piezoelectric pump 31.

[0051] Note that in the case where the control resolution is 10 bits from 10 V to 40 V, the control can be carried out in control steps of about 30 mV, whereas in the case where the control resolution is 5 bits, the control can be carried out in control steps of about 1 V.

[0052] According to the invention, in such a case, a period corresponding to a ratio D1 of a given cycle 1 / f am is driven at a driving voltage having an amplitude V1 and an optimal frequency f1 for this driving voltage having an amplitude V1, and a period corresponding to a ratio D2 is driven at a driving voltage having an amplitude V2 and an optimal frequency f2 for this driving voltage having an amplitude V2; this controls the piezoelectric pump 31 so that the air is discharged at a flow rate equivalent to the case of driving at the target voltage having an amplitude V0.

[0053] In this embodiment, the amplitudes V1 and V2 of the driving voltage and the duty cycles D1 and D2 are determined such that V0 = V1 × D1 + V2 × D2 (where V2 ≤ V0 ≤ V1) and D1 + D2 = 1.

[0054] Note that f_am is a frequency which is approximately the same as the frequency of AM modulation (amplitude modulation), as described with reference to Fig. 4, and is a value of, for example, about 30 Hz to about 200 Hz; since the pulse wave component of a blood pressure is included in the frequencies below 30 Hz, it is necessary for f_am to be a frequency greater than 30 Hz, but it may be another frequency as long as it is a frequency lower than the driving frequency of the piezoelectric pump (for example, a value close to 20 kHz).

[0055] Although the controller becomes more responsive as the value of f_am increases, this also increases the processing load on the control unit 20, and thus the value of f_am is determined based on the processing speed of the control unit 20.

[0056] In addition, the noise caused by the pulsations can be suppressed, the amount of such noise can be reduced, and so on, by ensuring the smallest possible difference between V1 and V2.

[0057] For example, in the case where the target voltage amplitude V0 = 20.3 V, V1 = 21 V and V2 = 20 V, V0 = V1 × D1 + V2 × D2 and D1 + D2 = 1, and thus the duty cycles D1 and D2 can be calculated as 0.3 and 0.7, respectively.

[0058] Similarly, in the case where the target voltage amplitude V0 = 20.5 V and the duty cycles D1 and D2 are each set at 0.5, V0 = V1 × D1 + V1 × D2 and D1 + D2 = 1, and thus V1 + V2 = 41. In this case, V1 and V2 can take a variety of combinations; for example, V1 may be 29 V and V2 may be 12 V, V1 may be 22 V and V2 may be 19 V, and so on. However, since it is preferable that the difference between V1 and V2 be as small as possible, as mentioned above, the latter combination is desirable.

[0059] Fig. Fig. 6 is a graph illustrating a control result in the case where the piezoelectric pump 31 is subjected to voltage control according to this embodiment of the invention. As shown in Fig. 6, the dot-dash line graph and the broken line graph show changes in the discharge flow rate of the piezoelectric pump 31 during inflation in the case where the piezoelectric pump 31 is driven at 20 V and 21 V, respectively.

[0060] Meanwhile, the solid line graph indicates changes in the discharge flow rate of the piezoelectric pump 31 during inflation in the case where the target voltage is 20.5 V and the piezoelectric pump 31 is driven while switching the duty ratio of 50% between 20 V and 21 V. It can be seen that in the case where the target voltage is 20.5 V and control is performed while switching between 20 V and 21 V in this way, a discharge flow rate exactly between that obtained by 20 V driving and that obtained by 21 V driving is achieved.

[0061] Fig. Fig. 7 is a flowchart illustrating the flow of a blood pressure measurement process performed by the blood pressure meter 1 according to the first embodiment. As shown in Fig. 7, the control unit 20 determines in step S111 the amplitude V of the target voltage for the piezoelectric pump 31 based on data previously stored in the storage unit 22 and indicated by the graphs shown in Fig. 3, a winding state of the cuff 40 (the wrist circumference, regardless of whether the cuff 40 is wrapped tightly or loosely), the current cuff pressure and the flow rate required for inflation at a constant speed.

[0062] Next, in step S112, the control unit 20 calculates V1 and V2 and the duty ratios D1 and D2 in the case where the control is carried out during switching between the driving voltages V1 and V2 to discharge the air at the same flow rate as for the target voltage V0, in a cycle 1 / f_am, a predetermined AM modulation frequency f_am, according to the method described in Fig. 5 is shown.

[0063] In step S113, the control unit 20 determines whether or not V1 and V2 calculated in step S112 satisfy the relationship |V1-V2| ≤ Limit, or in other words, whether the difference between V1 and V2 is less than or equal to a limit. In the case where it is determined that the difference is not less than or equal to the limit (that is, in the case where a determination of NO is made in step S113), the control unit 20 returns the processing being executed to the process in step S112.

[0064] On the other hand, in the case where it is determined that the relationship |V1-V2| ≤ Limit is satisfied (that is, in the case where a determination of YES is made in step S113), in step S114, the control unit 20 determines the optimal frequencies f1 and f2 for V1 and V2, respectively, calculated in step S112, based on characteristic data of the piezoelectric pump 31 previously stored in the storage unit 22. Here, although the optimal frequencies are frequencies that allow the air to be discharged at a maximum flow rate, the optimal frequencies may be frequencies that allow maximum pump efficiency to be achieved.

[0065] Next, in step S121, a signal indicative of a voltage value is sent to the voltage control circuit 62, and a signal indicative of a driving frequency is sent to the driving control circuit 63 so as to drive the piezoelectric pump 31 at the driving voltage V1 calculated in step S112 and at the driving frequency f1 calculated in step S114 for a time D1 / f_am.

[0066] Next, in step S122, a signal indicative of a voltage value is sent to the voltage control circuit 62, and a signal indicative of a driving frequency is sent to the driving control circuit 63 so as to drive the piezoelectric pump 31 at the driving voltage V2 calculated in step S112 and at the driving frequency f2 calculated in step S114 for a time D2 / f_am.

[0067] Next, in step S123, the control unit 20 calculates a blood pressure value according to a conventional method based on changes in cuff pressure detected by the pressure sensor 33 and indicated by a signal input to the control unit 20 via the amplifier 71 and the A / D converter 72.

[0068] Then, in step S124, the control unit 20 determines whether the blood pressure measurement is completed. If it is determined that the blood pressure measurement is not completed (that is, if a determination of NO is made in step S124), the control unit 20 returns the processing being executed to the process in step S111.

[0069] On the other hand, in the case where it is determined that the blood pressure measurement is completed (that is, in the case where a determination of YES is made in step S124), the control unit 20 controls the voltage control circuit 62 and the driving control circuit 63 to stop the driving of the piezoelectric pump 31 in step S125.

[0070] Next, in step S126, the control unit 20 controls the display unit 21 to display the blood pressure measurement result. After step S126, the control unit 20 terminates the blood pressure measurement process. Second embodiment

[0071] Fig. Fig. 8 is a flowchart illustrating the flow of a blood pressure measurement process performed by the blood pressure meter 1 according to the second embodiment. As shown in Fig. 8, in step S131, the same process as that shown in step S111 in Fig. 7, and described in the first embodiment, and thus redundant descriptions will not be repeated.

[0072] Next, in step S132, the control unit 20 determines a voltage V1 one step higher and a voltage V2 one step lower than the target voltage V0 calculated in step S131, according to the controllable resolution. For example, in the case where the resolution can be controlled in 1 V increments, the target voltage V0 = 20.3 V, V1 = 21 V, and V2 = 20 V.

[0073] Next, in step S133, the control unit 20 calculates the duty ratios D1 and D2 in the case where the control is executed while switching between the driving voltages V1 and V2 determined in step S132 to eject the air at the same flow rate as for the target voltage V0, in a cycle 1 / f_am, of a predetermined AM modulation frequency f_am according to the method described in Fig. 5 is shown.

[0074] Then, in step S134, the control unit 20 determines the optimal frequencies f1 and f2 for V1 and V2, respectively, calculated in step S132, based on the characteristic data of the piezoelectric pump 31 previously stored in the storage unit 22.

[0075] The processes from step S121 to step S126 are the same as the corresponding processes described in Fig. 7, and therefore redundant descriptions thereof will not be repeated.

[0076] The blood pressure monitor 1 according to the embodiments described above achieves effects such as those described below. (1) The blood pressure monitor 1 includes the cuff 40 which, when worn on a blood pressure measuring area, pressurizes an artery in the measuring area at the pressure of a fluid therein, the piezoelectric pump 31 which increases the pressure inside the cuff 40, the outlet valve 32 which reduces the pressure inside the cuff 40, the pressure sensor 33 which detects the cuff pressure, which is the pressure inside the cuff 40, and the control unit 20.

[0077] The control unit 20 determines a control amplitude and a control frequency of the voltage applied to the piezoelectric pump 31 as described in step S111 to step S114 of the Fig. 7 and in step S131 to step S134 in Fig. 8; it carries out the control so that the voltages at the previously determined control amplitudes V1 and V2 and the control frequencies f1 and f2 are applied to the piezoelectric pump 31, as shown in step S121 and step S122 in Fig. 7 and Fig. 8; and calculates a blood pressure value based on the cuff pressure detected by the pressure sensor 33 during inflation when the cuff pressure is increased by the piezoelectric pump 31, as shown in step S123 in Fig. 7 and Fig. 8. In addition, the control unit 200 can control the amplitude of the voltage in predetermined steps and applies, in a predetermined sequence, a voltage having an amplitude which is a value V1 above the control amplitude by at least one step, and a voltage having an amplitude which is a value V2 below the control amplitude by substantially one step, so that the discharge of the piezoelectric pump 31 is approximately the same as when a voltage at the predetermined control amplitude V0 is applied, as in step S111 and step S112 in Fig. 7, in step S131 to step S133 in Fig. 8 and in step S121 and step S122 in Fig. 7 and Fig. 8 is displayed.

[0078] By AM modulating the applied voltage, the piezoelectric pump 31 can be controlled so that the outlet flow rate is substantially the same as in the case where the target voltage is applied. However, in the sphygmomanometer 1 according to the embodiments, the occurrence of AM modulation frequency noise can be suppressed compared to a case where control is performed by AM modulation. Furthermore, whereas pulsations occur when increasing the cuff pressure in the case where control is performed via AM modulation, the influence of pulsations can be reduced in the sphygmomanometer 1 according to the embodiments. Furthermore, in the sphygmomanometer 1 according to these embodiments, the same high-precision inflation control can be achieved as in the case where control is performed by AM modulation.

[0079] As a result, when the inflation is controlled using the electric pump 31 during inflation for blood pressure measurement, the precision of blood pressure measurement can be increased by suppressing the occurrence of noise, the influence of pulsations can be reduced, and the inflation is controlled at a high degree of precision.

[0080] (2) In the second embodiment, the control unit 20 applies voltages having two amplitude values ​​in an alternating manner as shown by step S121 and step S122 in Fig. 8. The two values ​​are respectively a value V1, a predetermined step above, and a value V2, a predetermined step below the determined control amplitude V0 (where the “predetermined step” is 1 in the second embodiment). Meanwhile, based on the determined control amplitude V0 and the two values ​​V1 and V2, the control unit 20 determines the ratios of the time D1 and Dt2 for which the voltages at the two values ​​V1 and V2 are applied in an alternating manner, so that the ejection of the piezoelectric pump 31 is substantially the same as in the case where a voltage at the control amplitude V0 is applied, as shown in step S133 of the Fig. 8. The control unit 20 then applies the voltages having two amplitude values ​​V1 and V2, corresponding to the predetermined ratios of the time D1 and S2, as shown in step S121 and step S122 of the Fig. 8 is displayed.

[0081] By doing so, the values ​​V1 and V2, which are the same predetermined number above and below, are determined, and thus the amplitude of the applied voltages can be determined more easily than in the case where the values ​​are determined at different steps above and below.

[0082] (3) In addition, the control unit 20 applies the voltages so that a difference between the two values ​​V1 and V2 is a minimum, as described in step S132, step S121 and step S122 of the Fig. 8 is displayed.

[0083] This can suppress the noise caused by the pulsations, reduce the volume of such noise, and so on.

[0084] (4) The control unit 20 may apply the voltages having the determined two amplitude values ​​V1 and V2 in an alternating manner, at the same time ratio, namely D1 = D2 = 0.5, as shown in Fig. 5 and described in the first embodiment. Here, based on the determined control amplitude V0, the control unit 20 determines the value V1, one step above the control amplitude V0, and the value V2, one step below the control amplitude V0, so that the output of the piezoelectric pump 31 is substantially the same as in the case where a voltage at the control amplitude V0 is applied, as in step S112 of the Fig. 7. Then, the control unit 20 applies the determined voltages having two amplitude values ​​V1 and V2 in an alternating manner as shown in step S121 and step S122 in Fig. 7 is shown.

[0085] (5) In step S113 of the Fig. 7, the control unit 20 determines whether the difference between the two values ​​V1 and V2 is less than or equal to a predetermined limit, and if the difference is not less than or equal to the limit, it redetermines the two values ​​V1 and V2 so that the difference between the two values ​​V1 and V2 is less than or equal to the limit. Furthermore, the control unit 20 may determine the two values ​​such that a difference between the two values ​​is a minimum.

[0086] The noise generated by the pulsations can be suppressed, the volume of such noise can be reduced, and so on, in both the cases where the difference between the two values ​​V1 and V2 is less than or equal to the limit and in the case where the difference is set to a minimum.

[0087] (6) The control unit 20 determines the optimal frequencies f1 and f2 for the values ​​V1 and V2 of the amplitude of the applied voltages as the control frequency, as described in step S114 of the Fig. 7 and in step S134 of the Fig. 8 is displayed.

[0088] This allows the optimal frequencies for the respective voltages to be applied, even when the voltage is applied while switching within a variety of amplitudes. Accordingly, the piezoelectric pump 31 can be controlled in an optimal manner regardless of the timing.

[0089] Next, variations of the aforementioned embodiments will be described. (1) The aforementioned embodiments list air as the fluid supplied to the cuff 40 by the piezoelectric pump 31. However, the fluid supplied to the cuff 40 by the piezoelectric pump 31 is not limited thereto, and other fluids, such as liquid or gel, may also be used. The invention is also not limited to a fluid and may instead use uniform particles, such as microspheres or the like. (2) Although the aforementioned embodiments describe the measurement area dimension as corresponding to the wrist circumference, the invention is not limited to this, and different dimensions may be applied to different measurement areas. For example, in the case where the measurement area is the arm, the dimension is the circumference of the arm. (3) As in Fig. 7 and Fig. 8, in the aforementioned embodiments, the cycles in which the control amplitude V0 is determined and the control parameters such as V1, V2, f1, and f2 are updated, and the cycle in which the blood pressure value is calculated to be D1 / f_am + D2 / f_am = 1 / f_am at each cycle, or in other words, at each single cycle of the power-on control are described. However, the invention is not limited to this, and the cycle of updating the control parameters and calculating the blood pressure value can be set for a plurality of power-on control cycles. (4) In the aforementioned first embodiment, in step S112 of the Fig. 7 the voltage amplitudes V1 and V2 are first determined, and the duty cycles D1 and D2 can then be calculated for the amplitudes V1 and V2, or the duty cycles D1 and D2 can first be determined, and the voltage amplitudes V1 and V2 can then be calculated for the duty cycles D1 and D2. (5) The aforementioned embodiments describe a case where control is performed while switching between the two voltage amplitudes V1 and V2. However, the invention is not limited to this, and control may be performed while switching between three or more voltage amplitudes. For example, control may be performed while switching between four voltage amplitudes, namely 19 V, 20 V, 21 V, and 22 V, at a duty ratio of 0.25, so that the fluid can be ejected at the same flow rate as when the target voltage has an amplitude of 20.5 V. (6) In the aforementioned second embodiment, as in step S132 of the Fig.As described in Figure 8, the voltage V1, one step above the controllable resolution, and the voltage V2, one step below the controllable resolution, are determined relative to the target voltage V0. This allows the voltage to be applied such that the difference between V1 and V2 is a minimum. However, the invention is not limited to this, and the voltages may be determined two or more steps above and below the controllable resolution relative to the target voltage V0, respectively. For example, a voltage V1 of 25 V and a voltage V2 of 16 V are determined five steps above and five steps below, respectively, in the controllable resolution, resulting in a target voltage V0 of 20.3 V. The noise caused by the pulsations will not deteriorate as long as the difference between V1 and V2 is less than or equal to the aforementioned limit. (7) In the aforementioned embodiments, the blood pressure monitor 1 is described as a device of the invention. However, the invention is not limited thereto and can also be adopted as a control method of the blood pressure monitor 1. The invention can also be adopted as a control program for the blood pressure monitor 1.

[0090] It should be understood that the above-disclosed embodiments are exemplary in every way and not limiting in any way. The scope of the present invention is defined not by the aforementioned descriptions, but by the scope of the appended claims, and all changes that substantially fall within the same spirit as the scope of the claims are intended to be embraced therein as well. List of reference symbols 1 blood pressure monitor 10 Main part 20 Control unit 21 Display unit 22 storage unit 23 Control unit 24 Power supply unit 31 piezoelectric pump 32 exhaust valve 33 Pressure sensor 40 cuff 41 outer cover 42 pressurizing air bellows 50 air hose 61 DC-DC amplifier circuit 62 Voltage control unit 63 driving control unit 71 amplifiers 72 converters

Claims

[1] Blood pressure measuring device (1), which comprises: a cuff (40) which, when worn on a blood pressure measuring area, pressurizes an artery in the measuring area at the pressure of a fluid in the cuff (40); a piezoelectric pump (31) which increases the pressure within the cuff (40); an air outlet unit (32) which reduces the pressure within the cuff (40); a pressure detection unit (33) which detects the cuff pressure, which is the pressure content of the cuff (40); and a control unit (20) wherein the control unit (20) includes: a determining device which determines a control amplitude and determining a control frequency of a voltage applied to the piezoelectric pump (31) (step S111 to step S114, step S131 to step S134); an applied voltage control means which carries out the control so that a voltage at the control amplitude and control frequency determined by the determining means is applied to the piezoelectric pump (31) (step S121, step S122); and a blood pressure measuring device which calculates a blood pressure value based on the cuff pressure detected by the pressure detecting unit during inflation when the cuff pressure is increased by the piezoelectric pump (31) (step S123), and wherein the applied voltage control means can control the amplitude of the voltage in predetermined steps, and, in a predetermined order, applies a voltage having an amplitude which is a value above the control amplitude by at least one step and a voltage having an amplitude which is a value below the control amplitude by at least one step, so that the discharge of the piezoelectric pump (31) is approximately the same as when a voltage at the control amplitude determined by the determining means is applied (step S111, step S112, step S121, step S122, step S131 to step S133). [2] Blood pressure measuring device according to claim 1, wherein the applied voltage control means applies voltages having two amplitude values in an alternating manner (step S121, step S122); the two values are a value of a predetermined step above and a value of a predetermined step below the control amplitude, each of which is determined by the determining device; the control unit (20) further includes an application ratio determining means which, based on the control amplitude determined by the determining means and the two values, determines a time ratio for which the voltages at the two values are applied in an alternating manner, so that the output of the piezoelectric pump (31) is substantially the same as in the case where a voltage at the control amplitude is applied (step S133); and the applied voltage control means applies the voltages having two amplitude values according to the time ratio determined by the application ratio determining means (step S121, step S122). [3] The blood pressure measuring device according to claim 2, wherein the applied voltage control means applies the voltages so that a difference between the two values is a minimum (step S132, step S121, step S122). [4] Blood pressure measuring device according to claim 1, wherein the applied voltage control means applies the voltages having two amplitude values determined by the determining means in an alternating manner at the same time ratio; the control unit (20) further includes an applied voltage control means which, based on the control amplitude determined by the determining means, determines the value of a step above the control amplitude and the value of a step below the control amplitude, so that the output of the piezoelectric pump (31) is substantially the same in the case where a voltage is applied at the control amplitude (step S112); and the applied voltage control means applies the voltages having two amplitude values determined by the applied voltage control means in an alternating manner (step S121, step S122). [5] A blood pressure measuring device according to claim 4, wherein the applied voltage control means determines two values such that a difference between the two values is a minimum. [6] The blood pressure measuring device according to claim 1, wherein the determining means determines an optimal frequency for the value of the amplitude of the voltage applied by the applied voltage control means as the control frequency (step S114, step S134). [7] Control method for a blood pressure measuring device (1), wherein the blood pressure measuring device (1) includes: a cuff (40) which, when worn on a blood pressure measuring area, pressurizes an artery in the measuring area at the pressure of a fluid in the cuff (40); a piezoelectric pump (31) which increases the pressure within the cuff; an air outlet unit (32) which reduces the pressure within the; a pressure detection unit (33) which detects the cuff pressure, which is the pressure within the cuff; and a control unit (20), and wherein the control method comprises the steps of the control unit (20) has: Determining a control amplitude and a control frequency of a voltage applied to the piezoelectric pump (31) (step S111 to step S114, step S131 to step S134); Carrying out the control so that a voltage at the control amplitude and the control frequency determined by the determining unit is applied to the piezoelectric pump (31) (step S121, step S122); and Calculating a blood pressure value based on the cuff pressure detected by the pressure detecting unit (33) during inflation when the cuff pressure is increased by the piezoelectric pump (31) (step S123), wherein the step of performing the control can control the amplitude of the voltage in predetermined steps, and a step of applying, in a predetermined sequence, a voltage having an amplitude which is a value above the control amplitude by at least one step, and a voltage having an amplitude which is a value below the control amplitude by at least one step, so that the output of the piezoelectric pump (31) is approximately the same, such as when a voltage at the predetermined control amplitude is applied (step S111, step S112, step S121, step S122, step S131 to step S133).

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