Electronic sphygmomanometer

An electronic sphygmomanometer includes a cuff, a tank that stores a prescribed amount of fluid, a pressure adjusting unit that adjusts pressurization of the cuff or the tank by supplying or discharging the fluid, a pressure detector that detects a pressure in the cuff or a pressure in the tank based on pressure information output from a pressure sensor, a blood pressure calculating unit that calculates a blood pressure value based on a change in the pressure in the cuff detected by the pressure detector, an abnormality detector, and a first channel through to the pressure adjusting unit and the pressure detector and that has one of the tank and the cuff selectively connected thereto. The abnormality detector detects whether the pressure sensor is abnormal in a state where the tank is connected to the first channel and the fluid is supplied to the tank.

TECHNICAL FIELD

This invention relates to an electronic sphygmomanometer, and more particularly to an electronic sphygmomanometer that is able to obtain high measurement accuracy.

BACKGROUND ART

Electronic sphygmomanometers that measure blood pressure using arterial pressure information detected from the upper arm, wrist or finger are in widespread use, and accurate measurement of blood pressure is desired.

Causes of fluctuation in blood pressure measurements can be roughly divided into fluctuation attributable to the person who is being measured (blood pressure fluctuation or error due to the measurement method) or fluctuation attributable to the device (abnormality of pressure sensor). The latter cause, in particular, is avoidable by periodically calibrating the device.

However, sphygmomanometers purchased for household use are generally not calibrated, except under specific circumstances such as when they malfunction. Thus, even if, for example, the output of the pressure sensor, which is vital in measuring blood pressure, is outside a stipulated tolerance range, there is no way of knowing this, and it is uncertain whether the measured blood pressure value is correct or not. Thus, in the case where there is a large difference between the measured blood pressure value and the normal blood pressure value, it is uncertain whether the blood pressure itself has fluctuated or whether the measured blood pressure value has fluctuated due to a pressure sensor error, giving the person being measured cause for concern.

Also, some sphygmomanometers for use in medical facilities are equipped with two pressure sensors, and monitor pressure based on the output of these pressure sensors. However, the functions of the two pressure sensors are used for different purposes. In other words, blood pressure is calculated with cuff pressure information obtained with one of the pressure sensors, and abnormality detection is performed based on the output of the other pressure sensor. Specifically, when the detected pressure value of the other pressure sensor greatly exceeds 300 mm Hg, for example, an abnormality is detected. In this case, safety is ensured by stopping the pump and opening the valve. This ensuring of safety is a requirement of the medical standard IEC 60601-2-30.

One example of a sphygmomanometer that is equipped with a plurality of pressure sensors and monitors operation failure of the pressure sensors is shown in the Patent Literature 1.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

With the electronic sphygmomanometer of Patent Literature 1 (JP 2-19133A), malfunction cannot be detected in the case where all of the plurality of pressure sensors mounted therein have malfunctioned. Also, mounting a plurality of pressure sensors increases the cost and size of the device, and hinders the widespread use of sphygmomanometers for household use.

Hence, one or more embodiments of the present invention provide an electronic sphygmomanometer that is able to improve the reliability of measured blood pressure values by detecting abnormality of a pressure sensor.

An electronic sphygmomanometer according to one or more embodiments of the present invention includes a cuff to be mounted on a measurement site, a tank capable of storing a prescribed amount of a fluid, a pressure adjusting unit that adjusts pressurization of the cuff or the tank by supplying or discharging the fluid, a pressure detector including a pressure sensor and for detecting a pressure in the cuff or a pressure in the tank based on pressure information output from the pressure sensor, a blood pressure calculating unit that calculates a blood pressure value based on a change in the pressure in the cuff detected by the pressure detector, an abnormality detector that detects whether the pressure sensor is abnormal, and a first channel through to the pressure adjusting unit and the pressure detector and for having one of the tank and the cuff selectively connected thereto. The abnormality detector detects whether the pressure sensor is abnormal, based on the pressure in the tank detected by the pressure detector in accordance with the pressure information output from the pressure sensor, in a state where the tank is connected to the first channel and the fluid is supplied to the connected tank.

According to one or more embodiments of the present invention, the electronic sphygmomanometer further includes a second channel through to the cuff, and a third channel through to the tank, the abnormality detector includes a channel switching unit that selectively connects one of the second channel and the third channel to the first channel, and the channel switching unit has a switching valve that connects one of the second channel and the third channel to the first channel, in accordance with a provided switching signal.

According to one or more embodiments of the present invention, the channel switching unit has a connecting portion for detachably connecting the second channel to a main body of the electronic sphygmomanometer, and a plug member for blocking off the second channel, the second channel through to the cuff integrally includes the connecting portion, and the connecting portion is a hollow cylinder, with the second channel being connected to the first channel as a result of the connecting portion being mounted on the main body such that the cylinder is inserted into the first channel and the third channel is blocked off by the inserted cylinder, and the third channel being connected to the first channel as a result of the plug member being mounted on the main body in place of the connecting portion.

According to one or more embodiments of the present invention, the pressure adjusting unit includes a pump for sending the fluid at a fixed flow rate per unit time, and supplies the prescribed amount of the fluid to the tank by driving the pump for a fixed time period.

According to one or more embodiments of the present invention, the electronic sphygmomanometer further includes a temperature detector that detects an ambient temperature of the tank, and the prescribed amount is changed in accordance with the temperature detected by the temperature detector.

According to one or more embodiments of the present invention, a result of detection by the abnormality detector is output externally.

According to one or more embodiments of the present invention, the electronic sphygmomanometer further includes a storage unit, and a result of detection by the abnormality detector is stored in the storage unit in association with data indicating the blood pressure value calculated by the blood pressure calculating unit and a time at which the blood pressure value was calculated.

According to one or more embodiments of the present invention, the abnormality detector detects whether the pressure sensor is abnormal, at a time of starting the electronic sphygmomanometer.

According to one or more embodiments of the present invention, the abnormality detector detects whether the pressure sensor is abnormal, at a time of calculating the blood pressure value by the blood pressure calculating unit.

According to one or more embodiments of the present invention, the abnormality detector detects whether the pressure sensor is abnormal, every prescribed time interval.

According to one or more embodiments of the present invention, the abnormality detector detects whether the pressure sensor is abnormal, whenever the blood pressure value calculation by the blood pressure calculating unit is performed a prescribed number of times.

According to one or more embodiments of the present invention, the abnormality detector detects whether the pressure sensor is abnormal, when an instruction is provided from outside.

According to one or more embodiments of the present invention, abnormality of a pressure sensor can be detected with only the main body of an electronic sphygmomanometer, enabling the reliability of measured blood pressure values to be improved.

DETAILED DESCRIPTION OF INVENTION

Hereinafter, embodiments of this invention are described in detail with reference to drawings. Note that in the drawings the same reference signs indicate the same or equivalent portions, and description thereof is not repeated.

In the present embodiment, an electronic sphygmomanometer that calculates blood pressure using an oscillometric method with the upper arm as the measurement site and is equipped with one pressure sensor for measuring blood pressure is described. Note that the method applied in order to calculate blood pressure is not limited to the oscillometric method. Also, the fluid used for inflating/deflating the cuff is given as air.

The external appearance of the electronic sphygmomanometer1according to one or more embodiments of the present invention is shown inFIG. 1, and the hardware configuration of the electronic sphygmomanometer is shown inFIG. 2. Referring toFIG. 1andFIG. 2, the electronic sphygmomanometer1is provided with a main body portion10and a cuff20that can be wrapped around the upper arm of a person who is being measured. The cuff20includes an air bladder21. The surface of the main body portion10has arranged thereon a display unit40constituted by liquid crystals or the like, for example, and an operation unit41consisting of a plurality of switches for receiving instructions from a user (person being measured).

The main body portion10, in addition to the display unit40and the operation unit41, includes a CPU (Central Processing Unit)100for performing centralized control of the units and various types of arithmetic operations, a processing memory42for storing data and programs for causing the CPU100to perform prescribed operations, a data storage memory43, a power supply44for supplying power to the units of the main body portion10, and a timer45that clocks the current time and outputs clocked data to the CPU100.

The operation unit41has various switches that are operated by the person being measured. That is, the operation unit41has a power switch41A operated by the person being measured in order to input a power supply ON or OFF instruction, a measurement switch41B operated in order to input a measurement start instruction, a stop switch41C operated in order to input a measurement stop instruction, a memory switch41D operated in order to input an instruction for causing information such as blood pressure data to be read out from the memory43and displayed on the display unit40, and a timer set switch41E operated in order to input an instruction for setting the timer45. The operation unit41can also include an inspection switch41F discussed later.

The main body portion10further includes a pump51, an exhaust valve (hereinafter, valve)52and a tank57that serve as a mechanism for adjusting the internal pressure (cuff pressure) of the air bladder21contained in the cuff20. The pump51and the valve52function mainly as a mechanism for adjusting the cuff pressure when measuring blood pressure, and the tank57has a fixed capacity and functions mainly as a pressure adjustment mechanism for detecting abnormality of a pressure sensor32. The main body portion10is further provided with a switching valve56for selectively connecting one of the two adjustment mechanisms to the cuff20(air bladder21) via an air tube31, and a switching valve drive circuit55for controlling the open/close operation of the switching valve56. The main body portion10is provided, in association with the tank57, with a temperature sensor571serving as a temperature detector. The temperature sensor571detects the ambient temperature of the tank57, and outputs the detected temperature to the CPU100. The CPU100, based on the input signal from the temperature sensor571, calculates a temperature coefficient that is based on the degree of expansion of air in the tank57. The CPU100calculates this temperature coefficient using a prescribed arithmetic equation. Alternatively, the CPU100decides to search a table stored in the memory42in which temperatures are associated with temperature coefficients.

The switching valve56has connected thereto an air tube31(hereinafter, first air tube31) to which the pressure sensor32, the pump51and the valve52are commonly connected, an air tube31(hereinafter, second air tube31) connected to the cuff20(air bladder21) and an air tube31(hereinafter, third air tube31) connected to the tank57. The switching valve56selectively connects one of the second air tube31and the third air tube31to the first air tube31, in accordance with a switching signal58provided by the switching valve drive circuit55. Here, “the switching valve56is switched to the cuff20side” refers to connecting the second air tube31to the first air tube31, and “the switching valve56is switched to the tank57side” refers to connecting the third air tube31to the first air tube31.

The main body portion10further has an oscillation circuit33connected to the pressure sensor32, a pump drive circuit53connected to the pump51, and a valve drive circuit54connected to the valve52. The output signal of the oscillation circuit33is provided to the CPU100.

The pump51supplies air to the air bladder21in order to increase the cuff pressure, and supplies air to the tank57in order to detect abnormality of the pressure sensor32. The valve52is opened and closed in order to discharge or enclose air in the air bladder21or the tank57. The pump drive circuit53controls the drive of the pump51based on a control signal provided by the CPU100. The pump51sends air at a fixed flow rate per unit time, in accordance with the voltage level applied by the pump drive circuit53. The valve drive circuit54opens and closes the valve52based on a control signal provided by the CPU100. The switching valve drive circuit55generates the switching signal58based on a control signal provided by the CPU100, and outputs the generated switching signal58to the switching valve56.

The pressure sensor32is a capacitance pressure sensor whose capacitance value changes according to the detected cuff pressure. The oscillation circuit33is connected to the pressure sensor32, and oscillates based on the capacitance value of the pressure sensor32. The oscillation circuit33thereby outputs a signal (hereinafter, frequency signal) having a frequency that depends on the capacitance value of the pressure sensor32to the CPU100. The CPU100detects pressure by converting the frequency signal input from the oscillation circuit33into pressure.

FIG. 3shows the functional configuration of the electronic sphygmomanometer1. InFIG. 3, only the portion of peripheral circuitry of the CPU100that directly perform input/output with the CPU100is shown.

Referring toFIG. 3, the CPU100is provided with a pressure adjusting unit111, a blood pressure calculating unit112, a sensor abnormality detector113, a recording unit114, a display processing unit115, and a switching control unit116. The switching control unit116controls the switching valve drive circuit55.

The pressure adjusting unit111adjusts the cuff pressure by controlling the pump51and the valve52via the pump drive circuit53and the valve drive circuit54, and causing air to flow into or be discharged from the air bladder21via the air tubes31. Here, the configuration including the pressure sensor32, the pump51and the valve52is called an air system.

The blood pressure calculating unit112detects pulse wave amplitude information based on the frequency signal (this frequency signal indicates a pressure information signal) input from the oscillation circuit33, and calculates systolic blood pressure and diastolic blood pressure in accordance with the oscillometric method based on the detected pulse wave amplitude information, as well as calculating the pulse rate per prescribed time period based on the detected pulse wave amplitude information. Specifically, in the process of gradually increasing (or decreasing) the cuff pressure to a prescribed value by the pressure adjusting unit111, pulse wave amplitude information is detected based on the output from the oscillation circuit33, and systolic blood pressure and diastolic blood pressure of the person being measured are calculated based on the detected pulse wave amplitude information. A conventionally known method can be applied to the blood pressure calculation and the pulse calculation performed by the blood pressure calculating unit112in accordance with the oscillometric method.

The sensor abnormality detector113detects abnormality of the pressure sensor32by inputting the frequency signal output from the oscillation circuit33and analyzing the input signal.

The recording unit114reads out data from the memory43or writes data to the memory43. Specifically, data (blood pressure measurement data) output from the blood pressure calculating unit112is input, and the input data is stored in a prescribed storage area of the memory43. Further, data (result of abnormality detection of the pressure sensor32) output from the sensor abnormality detector113is input, and the input data is stored in a prescribed storage area of the memory43. Also, the recording unit114reads out measurement data from a prescribed storage area of the memory43based on operation of the memory switch41D of the operation unit41, and outputs the read data to the display processing unit115.

The display processing unit115inputs data provided thereto, converts the input data to a displayable form, and displays the resultant data on the display unit40.

The processing procedure of blood pressure measurement according to the present embodiment is described, with reference toFIG. 4. A flowchart showing the processing procedure inFIG. 4is stored as a program in the memory42in advance, and the blood pressure measurement processing ofFIG. 4is realized by the CPU100reading out the program from the memory42and executing commands.

First, when the person being measured operates (presses) the power switch41A (step ST1), the CPU100initializes an unshown work memory (ST2).

Subsequently, a 0 mm Hg adjustment of the pressure sensor32is performed (ST3). The details of the 0 mm Hg adjustment are discussed later. Abnormality of the pressure sensor32is detected at the time of the 0 mm Hg adjustment (step ST3a). The details of this abnormal detection are discussed later.

Here, the person being measured puts on the cuff20by wrapping the cuff around the measurement site as shown inFIG. 1. When the person being measured operates (presses) the measurement switch41B after wrapping around the cuff20(step ST4), the pressure adjusting unit111outputs a control signal to the pump drive circuit53and the valve drive circuit54. The pump drive circuit53and the valve drive circuit54drive the pump51, after closing off the valve52based on the control signal. The cuff pressure is thereby gradually increased to a prescribed pressure (steps ST5, ST6). The pressure adjusting unit111detects the cuff pressure based on the frequency signal input from the oscillation circuit33, and compares the detected cuff pressure with the prescribed pressure indicated by the data read out from the memory42. Inflation is continued until it is determined that the detected cuff pressure indicates the prescribed pressure, based on the comparison result. That is, inflation (step ST5) is continued for the duration that the condition “cuff pressure<prescribed inflation value” is determined to be satisfied at step ST6.

After it is determined, based on a comparison result, that the cuff pressure has reached the prescribed pressure (condition that “cuff pressure≧prescribed inflation value” is satisfied at step ST6), the pressure adjusting unit111outputs a control signal to the pump drive circuit53and the valve drive circuit54. The pump drive circuit53and the valve drive circuit54stop the inflation by stopping the pump51based on the control signal. Thereafter, control is performed so as to gradually open the valve52. The process thereby shifts from inflation to deflation, and the cuff pressure gradually decreases (step ST7).

In this deflation process, the blood pressure calculating unit112detects pulse wave amplitude information based on the frequency signal output from the oscillation circuit33, that is, based on the cuff pressure signal detected by the pressure sensor32, and performs a prescribed arithmetic operation on the detected pulse wave amplitude information. Systolic blood pressure and diastolic blood pressure are calculated by this arithmetic operation (step ST8, ST9). Pulse wave amplitude information represents an arterial volume change component of the measurement site, and is included in the detected cuff pressure signal. Note that blood pressure measurement is not limited to the deflation process, and may be performed in the inflation process (step ST5).

Once the measured blood pressure is decided as a result of the systolic blood pressure and the diastolic blood pressure being calculated (YES at step ST9), the pressure adjusting unit111fully opens the valve52via the valve drive circuit54, and quickly exhausts the air in the cuff20(step ST10).

Data indicating the blood pressure calculated by the blood pressure calculating unit112is output to the display processing unit115and the recording unit114. The display processing unit115inputs the blood pressure data, and displays the input blood pressure data on the display unit40(step ST11). The recording unit114inputs the blood pressure data, and stores the input blood pressure data in a prescribed storage area of the memory43, in association with time data input from the timer45(step ST12).

Note that the blood pressure calculating unit112can also calculate a pulse rate based on the detected pulse wave amplitude information. The calculated pulse rate is displayed on the display unit40by the display processing unit115, and stored in the memory43by the recording unit114in association with the blood pressure data.

In the display and storage of such data, the results of abnormality detection of the pressure sensor32detected at step ST3aare also displayed, as well as being stored in memory.

Data indicating the measurement date/time, the blood pressure value (systolic blood pressure SYS, diastolic blood pressure DIA), the pulse rate, and the result of abnormality detection of the pressure sensor32are stored in association with each other in the memory43whenever blood pressure measurement is performed.

Also, exemplary storage contents of the memory43in the case where the abnormality inspection of the pressure sensor32is performed at a prescribed time interval or by a prescribed user operation rather than every blood pressure measurement are shown inFIG. 5. Referring to (A) and (B) ofFIG. 5, measurement data is stored per record. Each record includes ID (Identifier) data D1identifying the record, identification data D2of the person being measured, measurement date/time data D3, blood pressure value and pulse rate data D4, and result data D5of the abnormality detection of the pressure sensor32.

As shown in the diagram, in the case where it is judged, as a result of the current abnormality inspection, that the pressure sensor32is abnormal, a flag (“NG”) indicating that the pressure sensor32is possibly abnormal is added, as data D5, to the records of the blood pressure measurement results stored during the period from the previous inspection day to the current inspection day. Because the possibility that the pressure sensor32was abnormal at the time of measurement can thereby be presented for each piece of blood pressure measurement data in the case where measurement data is read out from the memory43and displayed on the display unit40, an index of the reliability of the data can be shown regarding the blood pressure values presented to the user at the same time.

Accordingly, the user (person being measured) can judge whether the pressure sensor32, which is the most important element for calculating blood pressure, is normal or abnormal. Hence, even in the case where a measured blood pressure value differs greatly from the normal value (e.g., value measured the previous day, value measured at a hospital, etc.), it is possible to avoid a situation where the person being measured is made to feel anxious because of not knowing whether the difference is due physiological information relating to the living body or to a malfunction of the pressure sensor32.

Here, the concept of the blood pressure calculation method using the oscillometric method in the present embodiment is described. In (A) ofFIG. 6, gradually decreasing cuff pressure is shown on the time axis clocked by the timer45. In (B) ofFIG. 6, an envelope curve600of pulse wave amplitude corresponding to abovementioned pulse wave amplitude information is shown on an identical time-axis. The envelope curve600of pulse wave amplitude is detected by extracting, in time series, the pulse wave amplitude signal superimposed on the signal (cuff pressure) from the pressure sensor32.

Referring to (A) and (B) ofFIG. 6, the blood pressure calculating unit112, on detecting the maximum amplitude value MAX on the envelope curve of pulse wave amplitude, calculates two thresholds TH_DBP and TH_SBP by multiplying the maximum value by prescribed constants (e.g., 0.7 and 0.5). The cuff pressure at the point where the threshold TH_DBP intersects the envelope curve600on the side on which the cuff pressure is lower than a cuff pressure MAP (average blood pressure) at the point in time TO at which the maximum value MAX is detected is then calculated as the diastolic blood pressure. Also, the cuff pressure at the point where the threshold TH_SBP interests the envelope curve600on the side on which the cuff pressure is higher than the cuff pressure MAP is calculated as the systolic blood pressure.

Acquisition of Condition Data for Pressure Sensor Abnormality Detection

In the present embodiment, prescribed condition data for abnormality detection of the pressure sensor32is acquired in advance such as at the time of factory shipment of the electronic sphygmomanometer1, and the acquired prescribed condition data is stored in the memory42. The procedure for acquiring this prescribed condition data is described.

A flowchart of schematic processing for prescribed condition acquisition at the time of factory shipment is shown inFIG. 7. First, processing for adjusting the pressure sensor32is performed (step STA1). Prescribed condition data for 0 mm Hg correction is detected by the adjustment processing. Subsequently, prescribed condition data for abnormality detection of the pressure sensor32is detected (step STA2).

The pressure sensor adjustment processing (step STA1) shown inFIG. 7is described, with reference toFIG. 8. Note that a pressurization device is connected to the electronic sphygmomanometer1instead of the cuff20.

First, an operator operates the power switch41A (step STB1). Subsequently, the switching control unit116controls the switching valve drive circuit55. The switching valve drive circuit55outputs the switching signal58in response to the control, and switches the switching valve56to the cuff20side (step STB2). Air thereby flows, via the air tubes31, between the air system and the pressurization device which is connected instead of the cuff20.

Subsequently, the pressure adjusting unit111controls the valve drive circuit54so as to close off the valve52. The valve52is closed off in response to this control (step STB3).

The output of the pressure sensor32when prescribed pressure values (0 mm Hg, 300 mm Hg) are applied by the connected pressurization device (in the present embodiment, this refers to frequencies M0 and M300 of the output signal of the oscillation circuit33) is measured, and the measured values are stored in a prescribed storage area of the memory43(steps STB4to STB7). The prescribed pressure values (0 mm Hg, 300 mm Hg) are dependent on the electronic sphygmomanometer1being designed to be able to measure blood pressures from 0-299 mm Hg. These measured values are not rewritable in the memory43, and will not be erased. The prescribed condition data for 0 mm Hg correction at the time of blood pressure measurement is thereby acquired. A linear equation of characteristics L1inFIG. 10discussed later can thereby be detected.

Thereafter, the valve drive circuit54opens the valve52, and the air enclosed in the air system is quickly exhausted (step STB8).

Next, the prescribed condition data detection processing (step STA2ofFIG. 7) for abnormality detection of the pressure sensor32is described with reference toFIG. 9.

Referring toFIG. 9, first the switching control unit116controls the switching valve drive circuit55. As a result of this control, the switching valve drive circuit55switches the switching valve56to the cuff20side (step STC0). At this time, the valve52is open, and stays in an open state until step STC5discussed later.

Subsequently, 0 mm Hg correction processing on the pressure sensor32is performed (step STC1).

Thereafter, the switching control unit116controls the switching valve drive circuit55. The switching valve drive circuit55, in response to the control, outputs the switching signal58, and switches the switching valve56from the cuff20side to the tank57side (step STC2). Subsequently, the sensor abnormality detector113detects whether the cuff pressure, that is, the internal pressure of the tank57, indicates 0 mm Hg, based on the output signal of the oscillation circuit33(step ST3). When it is detected that the cuff pressure indicates 0 mm Hg (YES at step STC3), the CPU100stores the frequency signal output by the oscillation circuit33in the memory43as a sensor output F0(step STC4). Next, the pressure adjusting unit111controls the valve drive circuit54. In response to this control, the valve drive circuit54closes the open valve52(step STC5).

Subsequently, the pressure adjusting unit111controls the pump drive circuit53. The pump drive circuit53, in response to the control, supplies an arbitrary fixed voltage Vp to the pump51, and operates the pump51. Because the number of rotations of the pump51is decided by the supplied voltage, the pump rotates for a number of times that depends on the fixed voltage Vp, and supplies air to the tank57(step STC6).

Subsequently, the pressure adjusting unit111clocks the elapsed time from the drive start of the pump51as a drive time period Tp using the timer45(step STC7). The pump is continually driven and time is continually clocked until it is detected that the frequency signal output by the oscillation circuit33indicates a prescribed pressure (e.g., internal pressure of the tank57is 70 mm Hg) (YES at step STC8).

When it is determined that the internal pressure of the tank57indicates 70 mm Hg (YES at step STC8), the pressure adjusting unit111controls the pump drive circuit53. In response to this control, the pump drive circuit53stops voltage supply to the pump51, and causes rotation of the pump51to stop (step STC9). Supply of air to the tank57is thereby stopped.

Thereafter, data indicating an output F70(frequency signal output by the oscillation circuit33) of the pressure sensor32, the drive time period Tp of the pump51, and the fixed voltage Vp are stored in the memory43via the recording unit114(step STC10).

Thereafter, the pressure adjusting unit111controls the valve drive circuit54. In response to the control, the valve drive circuit54opens the closed valve52(step STC11). The air in the tank57is thereby quickly exhausted.

Thereafter, the switching control unit116controls the switching valve drive circuit55. The switching valve drive circuit55thereby switches the switching valve56from the tank57side to the cuff20side (step STC12). An air channel between the air system and the cuff20is thereby established.

0 mm Hg Correction of Pressure Sensor

The blood pressure calculating unit112, when measuring blood pressure, compares the measured values of the calibrated output of the pressure sensor acquired at the time of manufacture (frequency signal data M0 and M300) with the measured value of the output of the pressure sensor at the time of initialization, and performs 0 mm Hg correction of the pressure sensor32at the current point in time based on the comparison result.

Specifically, the blood pressure calculating unit112calculates a pressure value P (mm Hg) in accordance with Equation 1, where “M0” and “M300” represent the measured values of the output of the pressure sensor32when calibrated for 0 mm Hg and 300 mm Hg at the time of manufacture, “U0” represents the measured value of the output at the time of initialization of the pressure sensor32at step ST3, and “f” represents the frequency of the signal currently output from the oscillation circuit33. The calculated pressure value P is equivalent to the cuff pressure in (A) ofFIG. 6.
Pressure valueP={(f−U0)/(M300−M0)}×300  (Eq. 1)

Calculation of the pressure value P in accordance with the above-mentioned Equation 1 is further described, with reference to the graph ofFIG. 10showing the characteristics of the pressure sensor32. In the graph ofFIG. 10, pressure (mm Hg) indicating cuff pressure is shown on the horizontal axis, and frequency (Hz) of the output signal of the oscillation circuit33is shown on the vertical axis. The characteristics L1of the pressure sensor32at the time of manufacture of the electronic sphygmomanometer1and the current characteristics L2of the pressure sensor32are shown inFIG. 10.

If the characteristics L1of the pressure sensor32at the time of manufacture and the current characteristics L2of the pressure sensor are the same, pressure value P=(f−M0)/(M300−M0)×300 (Eq. 2) is satisfied, but in reality the characteristics of the pressure sensor32cannot maintain the characteristics L1at the time of manufacture due to various factors such as usage, and the characteristics L1change to the current characteristics L2, for example. The output U0 at the time of initialization of the pressure sensor32arises with this change in characteristics. Accordingly, using the output U0 at the time of initialization of the pressure sensor32enables Equation 2 to be rewritten as Equation 1.

The procedure by which the output U0 is thus detected to derive Equation 1 is called 0 mm Hg correction.

Pressure Sensor Initialization at the Time of Blood Pressure Measurement

The procedure for initializing the pressure sensor3(step ST3) which includes abnormality detection of the pressure sensor32(step ST3a) is described, with reference to the flowchart ofFIG. 11. Processing in accordance with this flowchart is carried out in the aforementioned step ST3. Note that it is assumed that air in the tank57has been sufficiently exhausted and the internal pressure is 0 mm Hg.

In this processing, the output value of the pressure sensor32when a prescribed amount of air has been sent to the tank57is compared with the values of prescribed condition data detected in advance, and abnormality of the pressure sensor32is detected, based on the comparison result.

At the time of initialization of the pressure sensor32, the switching control unit116first outputs a control signal to the switching valve drive circuit55. The switching valve drive circuit55outputs the switching signal58based on the control signal. The switching valve56is switched from the tank57side to the cuff20side in accordance with the switching signal58(step ST110). Accordingly, the first air tube31and the second air tube31are connected via the switching valve56, and an air channel is constituted by both tubes. 0 mm Hg correction of the pressure sensor32is performed in this state (step ST111). In other words, data f0(equivalent to data U0 inFIG. 10) of the frequency signal of the oscillation circuit33when the air in the air bladder21of the cuff20has been sufficiently exhausted to achieve a zero cuff pressure is detected and temporarily stored in the memory43.

Thereafter, the switching control unit116outputs a control signal to the switching valve drive circuit55. The switching valve drive circuit55switches the switching valve56to the tank57side, based on the control signal. Accordingly, the air tube connected to the first air tube31via the switching valve56is switched from the second air tube31to the third air tube31. Air flows in the direction of the tank57side as a result of the switching valve56(step ST121).

Next, the CPU100reads out prescribed condition data (voltage Vp, time period Tp) from the memory43(step ST123). The valve52is then closed off by the valve drive circuit54, and the prescribed voltage Vp is applied to the pump51for the read fixed time period Tp by the pump drive circuit53. The pump51thereby rotates and air is sent to the tank57(steps ST131to ST151). The pressure sensor abnormality detector113detects the output value of the pressure sensor32(data f70of the frequency signal of the oscillation circuit33) when the fixed time period Tp has elapsed (step ST161), and temporarily stores the detected data f70in the memory43.

The CPU100then reads out data f0and data F0from the memory43, and calculates a difference MD of both pieces of read data. The difference MD serves as the aforementioned 0 mm Hg correction amount. Also, data f70and data F70are read out from the memory43, and a difference Δf70of both pieces of read data is calculated. A difference Δf of the difference Δf70and the difference MD is then compared with a prescribed value (e.g., frequency value equivalent to 3 mm Hg), and abnormality of the pressure sensor32is detected based on the comparison result (step ST171).

Specifically, when it is detected, based on the comparison result, that the difference Δf is less than or equal to a prescribed value, it is judged that the pressure sensor32is normal (YES at step ST171), whereas when it is detected that the difference Δf is greater than the prescribed value (NO at step ST171), it is judged that the pressure sensor32is abnormal (step ST181). In the case where abnormality of the pressure sensor32is detected, this information is displayed on the display unit40.

Once abnormality detection of the pressure sensor32has ended, the valve52is opened by the valve drive circuit54, and all the air in the tank57is exhausted (ST191). Thereafter, the switching control unit116outputs a control signal to the switching valve drive circuit55. The switching valve drive circuit55switches the switching valve56to the cuff20side, based on the control signal. Accordingly, the air tube connected to the first air tube31via the switching valve56is switched from the third air tube31to the second air tube31. Air thereby flows in the direction of the cuff20side (step ST201). Initialization of the pressure sensor32(step ST3) is thereby ended.

Because the required volume (capacity) of the tank57need only be the capacity required for the inspection (i.e., amount of air supplied to the tank57in the time period Tp during which the pump51has the voltage Vp applied thereto and rotates), being a comparatively small volume such as 70 mm Hg, for example, device miniaturization is not inhibited even when the tank57is used in order to detect abnormality of the pressure sensor32.

Note that although the internal pressure of the tank57is fixed at 70 mm Hg, and the supply flow rate to the tank57by the pump51is fixed by the product of the applied voltage Vp and the time period Tp, these values may be changed according to the environmental conditions around the electronic sphygmomanometer1, or more specifically, around the tank57.

For example, the fluid densities in the tank57differ even at the same pressure when the ambient temperatures at the time of manufacture and at the time of blood pressure measurement differ, making it necessary to change the amount of air allowed to flow into the tank57by adjusting the drive time period and/or drive voltage of the pump51depending on the temperature. In other words, the drive time period and/or drive voltage of the pump51may be changed by summing the temperature coefficients that are based on the degree of expansion of air which is dependent on the temperature detected by the temperature sensor571.

Exemplary Display

FIG. 12shows exemplary display of a result of abnormality detection of the pressure sensor32on the display unit40. InFIG. 12, the display processing unit115turns off the characters “NG” and only turns on the characters “OK” if the pressure sensor32is normal. If abnormal, the characters “OK” are turned off and the characters “NG” are turned on. On this display, measurement time data402clocked by the timer45and systolic blood pressure data403, diastolic blood pressure data404and pulse rate data405that result from the blood pressure measurement are displayed together with the “NG”/“OK” display.

The recorded data D3to D5are also read out and displayed on the display ofFIG. 12, in the case where the memory switch41D of the operation unit41is operated and measurement data in the memory43is read out and displayed.

The person being measured is able to obtain the timing at which the manufacturer will be requested to calibrate the pressure sensor32, by checking such a display. Accordingly, performing blood pressure measurement without realizing that the pressure sensor32is abnormal can be avoided, and the reliability of measured blood pressure values can be improved.

Manual Switching of Air Tubes31

As described above, switching is performed automatically so as to connect one of the third air tube31on the tank57side and the second air tube31on the cuff20side to the first air tube31using the switching valve56, but switching may be performed manually as shown inFIG. 13andFIG. 14. InFIG. 13andFIG. 14, the thick arrow indicates the direction in which air flows.

In order to perform manual switching, an inspection plug312and a measurement plug311that are detachable from the main body portion10are used in place of the switching valve56, the switching valve drive circuit55and the switching control unit116. Referring toFIG. 1, the cuff20is detachably connected to the main body portion10, as a result of the air tube31connected to the cuff20being detachably inserted into an insertion opening10A preformed in a lateral face of the casing of the main body portion10.

FIG. 13shows a state in which the state of switching to the cuff20side by the aforementioned switching valve56is realized by alternatively using the measurement plug311. Referring toFIG. 13, the air tube31joined to the cuff20(equivalent to the second air tube31) is inserted into an opening of the measurement plug311, which is a hollow cylindrical member, at one end in the longitudinal direction, thereby integrally connecting both parts. By inserting the other opening side of the measurement plug311externally into the insertion opening10A preformed in the lateral face of the casing of the main body portion10, the air tube31(first air tube31) joined to the internal air system is inserted into the other opening. In this state, the channel of the third air tube31joined to the tank57is positioned orthogonally to the lateral face extending in the longitudinal direction of the measurement plug311by the measurement plug311being inserted, causing the channel of the third air tube31to be plugged and blocked off by the measurement plug311. As a result, the second air tube31is connectable to the first air tube31.

FIG. 14shows a state in which the state of switching to the tank57side by the aforementioned switching valve56is alternatively realized by the inspection plug312. Referring toFIG. 14, the insertion opening10A is completely blocked off, as a result of the inspection plug312being inserted externally into the insertion opening10A preformed in the lateral face of the casing of the main body portion10. In this state, the inspection plug312functions as a plug member for blocking off the second air tube31, and acts so as to establish an air channel linking the third air tube31connected to the tank57and the first air tube31connected to the air system, in order to inspect for abnormality of the pressure sensor32.

FIG. 15shows the procedure of pressure sensor initialization processing (step ST3) using the plugs shown inFIG. 13andFIG. 14. The other procedures of blood pressure measurement processing apart from the pressure sensor initialization processing are the same as those shown inFIG. 4, and description thereof is omitted. Here, because a trigger for starting inspection needs to be input in the case of using the inspection plug312, an inspection switch41F is additionally provided in the operation unit41. The trigger for starting inspection is input by the person being measured pressing the inspection switch41F. Alternatively to the inspection switch41F, the connection of the inspection plug312may be detected by a sensor or the like, and a trigger for starting inspection may be input based on the detection signal from the sensor or the like.

First, a user inserts the measurement plug311into the insertion opening10A, as shown inFIG. 13(step STI0). In this state, 0 mm Hg correction processing of the pressure sensor32is performed (step STI1). This 0 mm Hg correction processing is similar to step ST111.

Thereafter, the person being measured removes the measurement plug311from the insertion opening10A, and inserts the inspection plug312instead (step STI2). The electronic sphygmomanometer will thereby be in the state shown inFIG. 14. In this state, the person being measured operates the inspection switch41F (step STI3). The mode ofFIG. 14is thereby achieved, and the configuration for inspecting for abnormality of the pressure sensor32is adopted.

The processing of the subsequent steps STI4to STI11is the same as the processing of steps ST121to ST191inFIG. 11, and description thereof is omitted.

When abnormality detection of the pressure sensor32is completed by the above procedure, in step STI12the person being measured removes the inspection plug312from the insertion opening10A and inserts the measurement plug311instead, in order to measure the blood pressure value. The electronic sphygmomanometer1will thereby be in the state shown inFIG. 13.

The procedure for abnormality detection of the pressure sensor32using the inspection plug312is thereby ended.

External Connection of Tank to Main Body Portion10

In the above description, the tank57used for abnormality detection of the pressure sensor32was provided in the main body portion10, but the tank57may be connected externally to the main body portion10.

A main body portion10X of an electronic sphygmomanometer1A is shown inFIG. 16andFIG. 17. InFIG. 16andFIG. 17, the switching valve56, the switching valve drive circuit55and the switching control unit116are not required as a result of the tank57being provided externally to the main body portion. The remaining configuration of the electronic sphygmomanometer1A is similar to that shown inFIG. 2.

Referring toFIG. 16, the cuff20is detachably connected to the main body portion10X, as a result of the air tube31connected to the cuff20being detachably inserted into the insertion opening10A preformed in the lateral face of the casing of the main body portion10X. In the present embodiment, the tank57is inserted into the insertion opening10A instead of the cuff20in the abnormality inspection of the pressure sensor32(seeFIG. 17), whereas the cuff20is inserted into the insertion opening10A in place of the tank57when the inspection has ended or when measuring blood pressure.

FIG. 18shows the procedure of pressure sensor initialization processing according to the configuration ofFIG. 16andFIG. 17. This procedure is equivalent to the processing of step ST3inFIG. 4. The other procedures of blood pressure measurement processing apart from the pressure sensor initialization processing are the same as those shown inFIG. 4, and description thereof is omitted.

Here, because a trigger for starting abnormality inspection needs to be input in the case of using the external tank57, the inspection switch41F is added to the operation unit41. The trigger for starting inspection is input by the person being measured pressing the inspection switch41F. Alternatively to the inspection switch41F, the detection signal of a sensor or the like may be used. In other words, external connection of the tank57may be detected by a sensor or the like, and a trigger for starting inspection may be input based on the detection signal from the sensor.

First, the user connects the cuff20to the insertion opening10A (step STJ0). In this state, 0 mm Hg correction processing on the pressure sensor32is performed (step STJ1). The 0 mm Hg correction processing is similar to step ST111.

Thereafter, the person being measured removes the cuff20from the insertion opening10A, and connects the tank57instead (step STJ2). In this state, the person being measured operates the inspection switch41F (step STJ3). The electronic sphygmomanometer1A thereby adopts the configuration for inspecting for abnormality of the pressure sensor32, as shown inFIG. 17.

The processing of the subsequent steps STJ4to STJ11is the same as the processing of steps ST121to ST191inFIG. 11, and description thereof is omitted. Once abnormality detection of the pressure sensor32is completed by the above procedure, in step STJ12the person being measured removes the tank57from the insertion opening10A, and connects the cuff20instead, in order to measure the blood pressure value.

The procedure for abnormality detection of the pressure sensor32using the external tank57is thereby ended.

Other Embodiments

In the abovementioned embodiment, the electronic sphygmomanometer1is a floor standing sphygmomanometer configured such that the cuff20is wrapped around an upper arm portion, but, as shown inFIG. 19, one or more embodiments of the present invention can be similarly applied to a wrist-type electronic sphygmomanometer in which the cuff20and the main body portion10are integrally constituted, and the cuff20is wrapped around the wrist.

In the abovementioned embodiment, processing for initializing the pressure sensor32including processing for detecting abnormality of the pressure sensor32may be carried out directly after operation of the power switch41A is detected (step ST1) and before the initialization processing (step ST2). Alternatively, the initialization may be carried out directly after the measurement switch41B is operated (step ST4).

Although the data in (A) and (B) ofFIG. 5is assumed to be stored in the internal memory43, this data may be stored in an unshown external memory.

The processing for detecting abnormality of the pressure sensor32may be performed at a prescribed time interval, or may be performed whenever blood pressure measurement is performed a prescribed number of times. Alternatively, a configuration may be adopted in which abnormality detection is performed when the person being measured inputs an inspection instruction from outside, without determining the interval.

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