Patent Application
20190159685
The present invention relates to a technique for obtaining useful information from a measured blood pressure waveform.
Techniques are known in which changes in the internal pressure of the radial artery are measured and the shape of pressure pulses (a blood pressure waveform) is recorded. Patent Document 1 (JP 2008-61824A) discloses measuring a blood pressure waveform through tonometry and obtaining information such as AI (Augmentation Index) value, pulse wave period, baseline fluctuation rate, sharpness, ET (Ejection Time), and the like from the blood pressure waveform. Patent Document 2 (JP 2005-532111A), meanwhile, discloses measuring a blood pressure waveform using a wristwatch-type blood pressure monitor, calculating a mean arterial pressure, a mean systolic pressure, a mean diastolic pressure, a mean systolic pressure index, and a mean diastolic pressure index from the blood pressure waveform, and then outputting an alert when those values deviate from reference values.
The inventors of the present invention are undertaking diligent research toward putting into practical use blood pressure measurement devices capable of accurately measuring a blood pressure waveform for each heartbeat during free movement. Through experiments using test subjects throughout the course of this development, the inventors of the present invention discovered that many types of useful information can be extracted from blood pressure waveform data measured continuously during free movement.
AI value is one indicator expressing the load on a person's heart. To find an AI value, it has been necessary to measure a blood pressure waveform for each heartbeat, and to do so, it has thus far been necessary to take the measurement during a state of rest. In other words, it has thus far not been possible to evaluate the load placed on a user's heart by the user's activity.
The inventors of the present invention discovered that the effects of user activity appear as changes in the shape of a blood pressure waveform measured continuously during free movement, and that the load such activity places on the heart can be evaluated from those changes.
An object of the present invention is to provide a novel technique for evaluating a load placed on a heart by activity.
To achieve the above-described object, the present invention employs the following configurations.
A biological information analyzing device according to the present invention is a biological information analyzing device including: an indicator extraction unit that extracts, from blood pressure waveform data measured continuously by a sensor that is worn on a user's body and can non-invasively measure a blood pressure waveform for each of heartbeats, an indicator expressing a load placed on the user's heart by an activity; and a processing unit that outputs the indicator extracted by the indicator extraction unit, wherein the indicator extraction unit finds the indicator on the basis of a difference between a blood pressure waveform in a resting section corresponding to when the user is in a resting state and a blood pressure waveform in an active section corresponding to when the user is engaged in the activity.
Here, the resting section is a section in which the user is at rest, and the active section is a section in which the user is active. The resting section and the active section may be distinguished by being input (taught) by a person (the user him/herself or a third party). For example, the indicator extraction unit may determine the active section and the resting section on the basis of data expressing an activity start time and data expressing an activity end time for the user. In this case, the indicator extraction unit can determine that the section from the activity start time to the activity end time is the active section, and that other sections are resting sections. The resting section and the active section may be distinguished by the biological information analyzing device automatically recognizing those sections on the basis of measurement data. For example, the indicator extraction unit may determine the active section and the resting section on the basis of measurement data from a second sensor (a body movement measurement sensor, an environment measurement sensor, or the like) that detects user activity. Additionally, the indicator extraction unit may determine the resting section and the active section from the blood pressure waveform data itself.
The indicator extraction unit may obtain a time at which the effect of user activity appears as a change in the blood pressure waveform (called an “effect appearance point”), and may find an indicator on the basis of the amount of time that has passed from the start of the activity to the effect appearance point. The indicator may be the amount of time that has passed itself, or may be a value determined on the basis of the amount of time that has passed. A shorter amount of time that has passed can be said to indicate a greater load placed on the heart by the activity. The indicator extraction unit may find the first point, among ejection start points following the start of the activity, satisfying a condition in which a difference between a blood pressure value at that point in time and a representative minimum blood pressure value in the resting section is greater than or equal to a threshold, as the effect appearance point. The representative minimum blood pressure value in the resting section may be, for example, the minimum blood pressure value for one beat immediately before the active section, or the mean value of the minimum blood pressure value for a predetermined number of beats immediately before the active section.
The indicator extraction unit may calculate the indicator on the basis of a difference between a representative minimum blood pressure value in the resting section and a representative minimum blood pressure value in the active section. The indicator may be the difference itself, or may be a value determined on the basis of the difference. The representative minimum blood pressure value in the active section may, for example, be a mean minimum blood pressure value in the active section or a maximum value of the minimum blood pressure value in the active section. Alternatively, the representative minimum blood pressure value in the resting section may, for example, be a mean minimum blood pressure value from a predetermined amount of time immediately before the active section. A greater difference between these minimum blood pressure values can be said to indicate a greater load placed on the heart by the activity.
The indicator extraction unit may also calculate an indicator on the basis of a degree of similarity between the shapes of the blood pressure waveform in the resting section and the blood pressure waveform in the active section. The indicator may be the shape similarity itself, or may be a value determined on the basis of the shape similarity. The shape similarity may be found as a correlation (e.g., cross-correlation) between a representative blood pressure waveform in the resting section and a representative blood pressure waveform in the active section. The representative blood pressure waveform in the active section may, for example, be a blood pressure waveform of one beat or a mean blood pressure waveform of several beats following an effect appearance point that is a time at which an effect of the activity appears as a change in the blood pressure waveform. The representative blood pressure waveform in the resting section may, for example, be a blood pressure waveform of one beat or a mean blood pressure waveform of several beats immediately before the active section. A lower blood pressure waveform shape similarity between the resting section and the active section, i.e., a greater change in the blood pressure waveform caused by the activity, can be said to indicate a greater load placed on the heart by the activity.
Additionally, the indicator extraction unit may find a plurality of sub-indicators on the basis of a difference between the blood pressure waveform in the resting section and the blood pressure waveform in the active section, and may calculate the indicator (an overall indicator) on the basis of the plurality of sub-indicators. Here, the amount of time that has passed from the start of the activity to the effect appearance point, the difference in the representative minimum blood pressure values between the resting section and the active section, and the shape similarity of representative blood pressure waveforms in the resting section and the active section can be given as examples of the sub-indicators. The overall indicator may also be determined in light of an AI value.
Furthermore, the form in which the processing unit outputs the indicator may be selected as desired. If the overall indicator is calculated on the basis of a plurality of sub-indicators as described above, the processing unit may output the overall indicator along with the sub-indicators. At least one of a graph format and a table format can be employed as the output format. The graph may output the overall indicator with at least one of the sub-indicators serving as a coordinate axis. In the graph, the overall indicator may be plotted at a size based on the value, or may be plotted along with the value, so that the value of the overall indicator can be understood.
The processing unit may output the indicator in a format that enables the user's activity to be understood. The user's activity may be determined on the basis of data input by a person (the user him/herself or a third party), or may be determined on the basis of measurement data from a sensor that detects the user's activity. Rule-based processing, processing using a discriminator generated through machine learning, or the like can be employed when determining the activity on the basis of measurement data.
A biological information analyzing system according to the present invention is a biological information analyzing system including: a sensor, which is worn on a user's body and can non-invasively measure a blood pressure waveform for each of heartbeats; and a biological information analyzing device that analyzes biological information using data of the blood pressure waveform measured continuously by the sensor.
A program according to the present invention is a program causing a processor to function as the indicator extraction unit and the processing unit of the biological information analyzing device.
Note that the present invention can also be realized as a biological information analyzing device or system having at least some of the above configurations and functions. The present invention can also be realized as a biological information analyzing method including at least some of the above-described processes, a program that causes a computer to execute the method, or a computer-readable recording medium in which such a program is recorded in a non-transitory manner. The present invention can also be realized by combining the above-described configurations and processes as long as no technical conflicts result.
According to the present invention, a technique for evaluating a load placed on a heart by activity can be provided.
A preferred embodiment of the present invention will be described below with reference to the drawings. Note, however, that the descriptions of configurations given hereinafter should be changed as appropriate depending on the configuration of the device to which the invention is applied, various types of conditions, and so on, and the scope of the invention is not intended to be limited by the following descriptions.
Biological Information Analyzing System
The blood pressure measurement unit 20 is a unit that measures pressure pulses in the radial artery TD through tonometry. Tonometry is a non-invasive method of measuring pressure pulses using a pressure sensor, in which an artery is compressed from above the skin at an appropriate pressure to form a flat part in an artery TD, and the internal pressure and external pressure of the artery are balanced.
The body movement measurement unit 21 is a unit, including a three-axis accelerometer, that measures movement of a user's body (body movement) using the accelerometer. The body movement measurement unit 21 may include a circuit that converts the output of the three-axis accelerometer into a format that can be read by the control unit 23.
The environment measurement unit 22 is a unit that measures environment information that can affect the user's physical/mental state (and blood pressure in particular). The environment measurement unit 22 can include a temperature sensor, a humidity sensor, an illuminance sensor, an altitude sensor, a location sensor, and the like, for example. The environment measurement unit 22 may include a circuit that converts the output of these sensors into a format that can be read by the control unit 23.
The control unit 23 is a unit that handles a variety of processes, such as controlling the various parts of the biological information analyzing system 10, acquiring data from the measurement unit 2, storing the acquired data in the storage unit 27, processing/analyzing the data, inputting/outputting the data, and so on. The control unit 23 includes a hardware processor (called a CPU hereinafter), ROM (Read-Only Memory), RAM (Random Access Memory), and the like. The processing carried out by the control unit 23, which will be described later, is realized by the CPU reading programs stored in the ROM or the storage unit 27 and executing those programs. The RAM functions as a work memory when the control unit 23 carries out various types of processes. Although the present embodiment describes a configuration in which the control unit 23 acquires the data from the measurement unit 2 and stores the data in the storage unit 27, the configuration may be such that the data is stored (written) directly from the measurement unit 2 into the storage unit 27.
The constituent elements of the embodiment, e.g., the measurement units, an indicator extraction unit, a processing unit, a determination unit, a risk database, the input unit, the output unit, a case database, and the like may be provided as hardware in the biological information analyzing system 10. The indicator extraction unit, the processing unit, and the determination unit may receive executable programs stored in the storage unit 27 and execute those programs. The indicator extraction unit, the processing unit, and the determination unit may receive data from the blood pressure measurement unit 20, the body movement measurement unit 21, the environment measurement unit 22, the input unit 24, the output unit 25, the communication unit 26, the storage unit 27, and so on as necessary. Databases such as the risk database and the case database may be provided in the storage unit 27 or the like, and may store information arranged so that the data can be searched and accumulated with ease. The structure, operations, and the like of the biological information analyzing system 10 are disclosed in JP 2016-082069, for example. The content thereof is incorporated into this specification by reference. The structure, operations, and the like of the blood pressure measurement unit are disclosed in JP 2016-087003A. The content thereof is incorporated into this specification by reference.
The input unit 24 is a unit that provides an operation interface to the user. For example, operation buttons, switches, a touch panel, or the like can be used.
The output unit 25 is a unit that provides, to the user, an interface that outputs information. For example, a display device that outputs information as images (a liquid crystal display or the like), an audio output device or a buzzer that outputs information as audio, an LED that outputs information by emitting or extinguishing light, a vibration device that outputs information as vibrations, or the like can be used.
The communication unit 26 is a unit that carries out data communication with other devices. Any system, including wireless LAN, Bluetooth (registered trademark), or the like, may be used as the data communication system.
The storage unit 27 is a storage medium in which data can be stored and from which data can be read out, and stores programs executed by the control unit 23, measurement data obtained from the measurement units, various types of data obtained by processing the measurement data, and so on. The storage unit 27 is a medium that electrically, magnetically, optically, mechanically, or chemically stores the information to be stored. Flash memory can be used, for example. The storage unit 27 may be a portable type such as a memory card, or may be built into the biological information analyzing system 10.
Some or all of the body movement measurement unit 21, the environment measurement unit 22, the control unit 23, the input unit 24, the output unit 25, and the storage unit 27 may be configured as devices separate from the main unit 11. In other words, as long as the main unit 11 including the blood pressure measurement unit 20 and a circuit that controls the blood pressure measurement unit 20 can be worn on a wrist, the structures of other units can be designed as desired. In this case, the main unit 11 is linked to the other units via the communication unit 26. A variety of configurations are conceivable, such as implementing the functions of the control unit 23, the input unit 24, the output unit 25, and so on as a smartphone app, or obtaining necessary data from an activity meter having the functions of the body movement measurement unit 21, the environment measurement unit 22, and so on. Sensors that measure biological information aside from blood pressure may be provided as well. For example, a sleep sensor, a pulse oximeter (SpO2 sensor), a breathing sensor (flow sensor), a blood sugar level sensor, and so on may be combined as well.
Although the present embodiment describes providing a sensor that measures blood pressure (the blood pressure measurement unit 20) and a configuration that carries out analysis processes on blood pressure waveform data (the control unit 23 and the like) in a single device, these elements may be configured as separate entities. In the present embodiment, a configuration that carries out analysis processes on biological information (the control unit 23 and the like) is called a “biological information analyzing device”, and a device configured by combining a measurement unit and the biological information analyzing device is called a “biological information analyzing system”. However, these names are used for the sake of simplicity, and the measurement unit and the configuration that carries out analysis processes on biological information may as a whole be called a “biological information analyzing device”, or other names may be used instead.
Blood Pressure Waveform Measurement
When the biological information analyzing system 10 is secured to the wrist and started, the control unit 23 controls the compression mechanism 31 of the blood pressure measurement unit 20 to keep the compressive force of the pressure sensor 30 in an appropriate state (a tonometry state). Pressure signals detected by the pressure sensor 30 are then acquired sequentially by the control unit 23. The pressure signals obtained by the pressure sensor 30 are generated by taking analog physical amounts (e.g., voltage values) outputted by the pressure detection elements 300 and digitizing those physical amounts through an A/D conversion circuit or the like that employs a known technique. Suitable analog values such as current values, resistance values, or the like may be employed as the analog physical amounts, depending on the types of the pressure detection elements 300. The signal processing such as A/D conversion may be carried out by providing a predetermined circuit in the blood pressure measurement unit 20, or may be carried out by another unit (not shown) provided between the blood pressure measurement unit 20 and the control unit 23. The pressure signals acquired by the control unit 23 correspond to instantaneous values of the internal pressure of the radial artery TD. Accordingly, time series data of a blood pressure waveform can be obtained by acquiring a pressure signal at a time granularity and continuity that enable the blood pressure waveform of a single heartbeat to be obtained. The control unit 23 stores the pressure signals sequentially obtained from the pressure sensor 30 in the storage unit 27 along with information of the measurement times of the signals. The control unit 23 may store the acquired pressure signals as-is in the storage unit 27, or may store the pressure signals in the storage unit 27 after applying necessary signal processing to the pressure signals. The “necessary signal processing” may include processing for correcting the pressure signals so that the amplitude of the pressure signals matches a blood pressure value (e.g., an upper arm blood pressure), processing for reducing or removing noise from the pressure signals, or the like, for example.
The blood pressure measurement unit 20 according to the present embodiment has advantages such as those described below.
A blood pressure waveform can be measured for each heartbeat. Thus for example, a variety of indicators related to blood pressure, heart condition, cardiovascular risk, and so on can be obtained on the basis of the shape characteristics of the blood pressure waveform. Additionally, the instantaneous value of the blood pressure can be monitored, which makes it possible to immediately detect blood pressure surges (sudden rises in blood pressure value), reliably detect blood pressure fluctuations and disturbances in the blood pressure waveform appearing only over extremely short amounts of time (one to several heartbeats), and so on.
Blood pressure monitors that are secured to the wrist or upper arm and measure blood pressure through the oscillometric method are in practical use as portable blood pressure monitors. However, a conventional portable blood pressure monitor can only measure a mean blood pressure value from fluctuations in the internal pressure of a cuff over several heartbeats, spanning several seconds to several tens of seconds, and thus cannot obtain time series data of a blood pressure waveform for each heartbeat, as is the case with the blood pressure measurement unit 20 according to the present embodiment.
The blood pressure waveform time series data can be recorded. When the blood pressure waveform time series data is acquired, a variety of indicators pertaining to blood pressure, heart condition, cardiovascular risk, and the like can be obtained by finding characteristics pertaining to changes in the blood pressure waveform over time, analyzing the frequency of the time series data and extracting specific frequency components, and so on, for example.
Because the device is configured as a portable (wearable) device, measurements place little burden on the user, and it is relatively easy to take continuous measurements for long periods of time, monitor blood pressure throughout the entire day, and so on. Furthermore, the portable form makes it possible not only to measure resting blood pressure, but also to measure changes in blood pressure during free movement (e.g., during daily activities, exercise, and so on). This in turn makes it possible to understand the effects of daily activities (sleeping, meals, commuting, work, taking medicine, and so on), exercise, and so on on blood pressure, for example.
Conventional products are devices of a type in which a blood pressure measurement unit is secured to the arm or wrist and the measurement is taken in a state of rest, and changes in blood pressure during daily activities, exercise, and so on cannot be measured, as with the biological information analyzing system 10 according to the present embodiment.
It is easy to link or combine the system with other sensors. For example, causal relationship evaluations or compound evaluations can be made using information obtained from other sensors (body movement, environment information such as temperature, other biological information such as SpO2 or breathing, and the like).
Biological Information Analyzing Device
The indicator extraction unit 50 obtains, from the storage unit 27, the blood pressure waveform time series data measured continuously by the blood pressure measurement unit 20. The indicator extraction unit 50 extracts an indicator pertaining to characteristics of the blood pressure waveform, from the obtained blood pressure waveform time series data. Here, “characteristics of the blood pressure waveform” include shape characteristics of the blood pressure waveform for a single heartbeat, changes in the blood pressure waveform over time, a frequency component of the blood pressure waveform, and so on. The blood pressure waveform characteristics are not limited thereto, however. The extracted indicator is output to the processing unit 51. Because there are a variety of blood pressure waveform characteristics and indicators, the characteristics and indicators to be extracted can be designed and selected as appropriate in accordance with the purpose of the processing by the processing unit 51. The characteristics and indicators that can be extracted from the blood pressure waveform measurement data in the present embodiment will be described later.
When finding the indicator, the indicator extraction unit 50 can use the measurement data from the body movement measurement unit 21 and/or the measurement data from the environment measurement unit 22 in addition to the blood pressure waveform measurement data. Although not illustrated, measurement data from a sleep sensor, an SpO2 sensor, a breathing sensor (flow sensor), a blood sugar level sensor, or the like may be combined as well. Carrying out a compound analysis on multiple types of measurement data obtained from multiple types of sensors enables a higher level of information analysis to be carried out on the blood pressure waveform. For example, the blood pressure waveform data can be classified into user states, such as resting and active, times of high and low temperature, and so on. Alternatively, causal relationships, correlations, and so on among the measurement data can be evaluated, by extracting the effects of body movement, activity amounts and activity intensity, changes in temperature, and so on on blood pressure.
The processing unit 51 receives the indicator extracted by the indicator extraction unit 50. The processing unit 51 carries out processing on the basis of the received indicator. A variety of processes are conceivable as the processes based on the indicator. For example, values of or changes in the extracted indicator may be provided to the user, a doctor, a nurse, or the like and used for health management, treatment, health guidance, and so on. Alternatively, circulatory system risk may be predicted, guidelines for maintaining one's health or reducing risks may be provided, or the like, on the basis of the extracted indicator. Furthermore, if a rise in cardiovascular risk has been detected or predicted on the basis of the indicator, the user or an attending doctor may be notified, control may be carried out to prevent activity that will place an excessive burden on the user's heart or prevent the occurrence of the circulatory system event, and so on.
Information Obtained from Blood Pressure Waveform
The blood pressure waveform is a compound wave including an “ejection wave” produced when the heart contracts to expel blood and a “reflected wave” produced when the ejection wave is reflected by peripheral vessels, arterial branches, and so on. Examples of characteristic points that can be extracted from a blood pressure waveform corresponding to a single heartbeat are listed below.
The indicator extraction unit 50 may use any algorithm to detect the characteristic points. For example, the indicator extraction unit 50 may extract a characteristic point (inflection point) of the blood pressure waveform by operating so as to find a nth-order differential waveforms of the blood pressure waveform and detect a zero crossing point thereof (for points F1, F2, F4, F5, and F6, this can be detected from a first-order differential waveform, and for point F3, from a second-order or fourth-order waveform). Alternatively, the indicator extraction unit 50 may identify the positions of the characteristic points by reading out a waveform pattern, in which characteristic points have been arranged in advance, from the storage unit 27, and fitting the blood pressure waveform in question to the waveform pattern.
By operating on the basis of the times t and the pressures BP of the above characteristic points F1 to F6, the indicator extraction unit 50 can obtain a variety of information (values, feature amounts, indicators, and the like) from the blood pressure waveform of a single heartbeat. The following provides representative examples of information that can be obtained from the blood pressure waveform. Note that tx and BPx represent the time and blood pressure, respectively, of a characteristic point Fx.
pulse wave interval (heartbeat period) TA=t6−t1
heart rate PR=1/TA
pulse wave rise time UT=t2−t1
systole TS=t4−t1
diastole TD=t6−t4
reflected wave delay time=t3−t1
maximum blood pressure (systolic blood pressure) SBP=BP2
minimum blood pressure (diastolic blood pressure) DBP=BP1
mean blood pressure MAP=area of blood pressure waveform from t1 to t6/heartbeat period TA
systolic mean blood pressure=area of blood pressure waveform from t1 to t4/systole TS
diastolic mean blood pressure=area of blood pressure waveform from t4 to t6/diastole TD
pulse pressure PP=maximum blood pressure SBP−minimum blood pressure DBP
late systolic pressure SBP2=BP3
AI (Augmentation Index)=(late systolic pressure SBP2−minimum blood pressure DBP)/pulse pressure PP
Basic statistical amounts of this information (values, feature amounts, indicators) can also be used as indicators. The basic statistical amounts include representative values (mean values, median values, mode values, maximum values, minimum values, and the like) and dispersion (variance, standard deviation, coefficient of variation, and the like), for example. Changes over time in this information (values, characteristic values, indicators) can also be used as indicators.
By computing a plurality of pieces of beat information, the indicator extraction unit 50 can obtain an indicator called BRS (baroreflex sensitivity). This is an indicator expressing the capacity of blood pressure to regulate to a constant value. The spontaneous sequence method is an example of the calculation method. This is a method in which only a sequence in which the maximum blood pressure SBP and the pulse wave interval TA rise or fall in synchronization for three or more consecutive beats is extracted, the maximum blood pressure SBP and the pulse wave interval TA are plotted on a two-dimensional plane, and a slope obtained when a regression line is found through the least-squares method is defined as the BRS.
As described thus far, using the biological information analyzing system 10 according to the present embodiment makes it possible to obtain a variety of information from the blood pressure waveform data. However, the biological information analyzing system 10 need not include functions for obtaining all of the above-described information. It is acceptable to provide only the functions for obtaining the necessary information, in accordance with the configuration, user, purpose of usage, location of usage, and so on of the biological information analyzing system 10. Additionally, the configuration may be such that the functions are provided as program modules (application software), and functions can be added by installing the required program modules in the biological information analyzing system 10.
The following Examples describe specific examples of the application of the biological information analyzing system 10.
The AI (Augmented Index) value is one indicator expressing the load on the heart, artery hardness, and so on. The AI value is found as an amplitude ratio between an ejection wave (drive pressure wave) produced by the ejection of blood from the left ventricle, and a reflected wave (reflected pressure wave) in which the ejection wave propagates through the circulatory system, is reflected by branches in the blood vessels, and returns. In other words,
AI value=(late systolic pressure SBP2−diastolic blood pressure DBP)/(systolic blood pressure SBP-diastolic blood pressure DBP)
The higher the AI value is, the greater the afterload on the left ventricle is. It is thus thought that if the AI value can be measured while the user is active, the load placed on the left ventricle by that activity can be evaluated.
However, blood pressure waveform measurement devices according to conventional techniques can only measure blood pressure waveforms when the user is at rest (when seated, laying face-up, or the like). In other words, with blood pressure measurement devices according to conventional techniques, it is not possible to measure the AI value during activity and evaluate the load placed on the left ventricle by that activity.
In addition to when the user is resting, the above-described biological information analyzing system 10 can measure the blood pressure waveform during free movement as well. Indicators aside from the AI value can also be obtained. As such, this Example provides a biological information analyzing device capable of evaluating the load placed on the user's left ventricle by activity (exercise), on the basis of blood pressure waveform data obtained when the user is performing such activity.
Blood Pressure Waveform during Activity
As illustrated in
Indicators
Accordingly, in this Example, the effects of activity on the user's left ventricle are evaluated in light of the following indicators, in addition to the AI value.
1. Effect Appearance Time T
The first indicator is the time T from the start of user activity to when the effect appears in the blood pressure waveform (an effect appearance time).
This will be described in detail with reference to
2. Minimum Blood Pressure Value Change Amount V
The second indicator is a minimum blood pressure value change amount V produced by user activity. In this Example, the change amount V is found as a difference between the blood pressure value at the effect appearance point 1501 and the resting mean minimum blood pressure value 1502. However, the change amount V is not limited to the difference between the blood pressure value at the effect appearance point 1501 and the resting mean minimum blood pressure value 1502, and may instead be found as a difference between a representative minimum blood pressure value in the resting section and a representative minimum blood pressure value in the active section. For example, the maximum value of the minimum blood pressure value in 1403 in the active section may be used as the representative minimum blood pressure value in the active section. It is thought that a greater change amount V indicates a greater load on the left ventricle by the activity.
3. Waveform Similarity S
The third indicator is a shape similarity S for the blood pressure waveform of a representative single beat at rest and during activity. The waveform similarity S can be found as a cross-correlation function between two representative waveforms, when at rest and during activity, normalized with respect to the time direction.
The blood pressure waveform of one beat immediately before the start of activity can be used as the representative waveform during rest. Alternatively, a mean blood pressure waveform of several beats immediately before the start of activity can be used as the representative waveform during rest. The blood pressure waveform of one beat starting from the effect appearance point 1501 can be used as the representative waveform during activity. Alternatively, a mean blood pressure waveform of several beats during the active section (e.g., a predetermined number of beats following the effect appearance point, all beats in which it is determined that the effect of activity is present, and so on) can be used as the representative waveform during activity.
A lower waveform similarity S indicates a greater change in the waveform due to activity, which is thought to indicate a greater load on the left ventricle by the activity.
Overall Indicator
In this Example, the indicator extraction unit 50 calculates an overall indicator E as follows, using the AI value and the above-described three indicators T, V, and S (all of which have been normalized).
E=AI+(1−S)×{0.1×(1−T)+0.2V}
Note that “AI” is the mean value of the AI values in the active section.
The definition of the overall indicator E given here is one example, and the overall indicator E may be defined so that the overall indicator E increases as the AI value increases, as the effect appearance time T decreases, as the change amount V increases, or as the waveform similarity S decreases. Additionally, not all of these indicators need be used.
The flow of processing according to this Example will be described with reference to the flowchart in
In step S104, the measurement of the user's continuous blood pressure waveform data by the biological information analyzing system 10 ends. The user's continuous blood pressure waveform data from between step S101 and S104 is stored in the storage unit 27 of the biological information analyzing system 10, as described above.
Note that it is not necessary for the user to exercise only once, and the exercise may be carried out several times by repeating the processing from steps S102 to S103. At this time, the type of exercise may vary. Additionally, the instructor may input the type of exercise instructed to the user into the biological information analyzing system 10 or the other system as data.
In step S105, the indicator extraction unit 50 acquires the blood pressure waveform time series data from the storage unit 27 and divides the data into units corresponding to beats. This division can be carried out by finding the ejection start point (point F1 in
In step S106, the indicator extraction unit 50 finds a mean minimum blood pressure value during rest. Specifically, the indicator extraction unit 50 extracts the blood pressure waveform data from the resting section, obtains the minimum blood pressure value in each beat, and obtains the mean value of the obtained minimum blood pressure values. The resting section and the active section can be distinguished from each other on the basis of the data of the exercise start time and the exercise end time obtained from the storage unit 27 or another device. Beats present in both the resting section and the active section are excluded from the calculation of the mean minimum blood pressure value. Note that the indicator extraction unit 50 need not find the mean of the minimum blood pressure values for all of the beats in the resting section, and may instead find the minimum blood pressure values of a predetermined number of beats immediately before the activity is started (that is, the end of the resting section). The indicator extraction unit 50 stores the resting mean minimum blood pressure value that has been found in the storage unit 27.
In step S107, the indicator extraction unit 50 detects the effect appearance point after the start of exercise. As described above, the effect appearance point can be found as the start point of the first beat where the minimum blood pressure value is greater than the resting mean minimum blood pressure value by the threshold Th or more. Once the effect appearance point has been found, in step S108, the indicator extraction unit 50 finds the indicators T, V, S, and E using the effect appearance point.
The indicator T corresponds to the amount of time from the start of activity until the effect of activity appears in the blood pressure waveform, and thus the indicator extraction unit 50 can find the indicator T as the amount of time from the exercise start time (the start time of the active section) to the effect appearance point.
The indicator V is an amount of change in the minimum blood pressure value due to activity, and thus the indicator extraction unit 50 can find the indicator V as a difference between the resting mean minimum blood pressure value calculated in step S106 and the minimum blood pressure value in the beat at the effect appearance point. Note that the maximum value of the minimum blood pressure value in the active section, or the mean value of the minimum blood pressure values in a predetermined number of beats in the active section, may be used as the minimum blood pressure value during exercise.
The indicator S is the waveform similarity of the blood pressure waveforms in a single beat between during rest and during activity. The indicator extraction unit 50 first determines representative blood pressure waveforms during rest and during activity from the measurement data stored in the storage unit 27. A mean blood pressure waveform of several beats immediately before the start of activity can be used as the representative waveform during rest. The mean of the blood pressure waveform of one beat or a plurality of blood pressure waveforms starting from the effect appearance point can be used as the representative waveform during activity. The process for finding the mean of the blood pressure waveforms can be carried out by first carrying out a normalizing process for unifying the number of data included in a single beat, and then finding the mean of the blood pressure values at each point in time. Next, the indicator extraction unit 50 determines the correlation between the representative blood pressure waveforms during rest and during activity using a cross-correlation function. Note that the indicator extraction unit 50 carries out the normalizing process for unifying the number of data included in the representative blood pressure waveforms during rest and during activity before calculating the correlation.
The indicator extraction unit 50 calculates the AI value for each beat in the active section, and also averages those values to calculate the average AI value for the active section. Likewise, the indicator extraction unit 50 calculates the AI value for each beat in the resting section, and also averages those values to calculate the average AI value for the resting section. The AI value calculation is a known technique and will therefore not be described here.
In step S109, the indicator extraction unit 50 calculates the overall indicator E on the basis of the indicators T, V, S, and AI. The indicator extraction unit 50 stores the calculated overall indicator E in the storage unit 27 in association with the indicators T, V, S, and AI on which the calculation is based. As described above, the overall indicator E can be calculated as E=AI+(1·S)×{0.1×(1−T)+0.2V}, but this is merely an example. The following definitions may be given: E increases as the AI value increases; E increases as the effect appearance time T decreases; E increases as the change amount V increases; and E increases as the waveform similarity S decreases.
In step S110, the processing unit 51 obtains the indicators E, T, V, S, and AI stored in the storage unit 27, and generates display screen data for making displays such as those illustrated in
According to the present embodiment, the load placed on a heart by activity can be evaluated using continuous blood pressure waveform data obtained during free movement. Additionally, a plurality of indicators (sub-indicators) are calculated from different viewpoints with respect to the load on the heart, and an overall indicator that consolidates the sub-indicators is calculated as well, and thus the load on the heart can be evaluated from a variety of viewpoints. Furthermore, the sub-indicators and the overall indicator can be output in a consolidated format, which makes it possible for the user, a doctor, or the like to understand the load on the heart easily and precisely.
Variation
Instead of a doctor inputting the exercise start time and end time, the exercise start time and end time, the active section, and the resting section can be detected on the basis of data measured by the body movement measurement unit 21. Furthermore, the type of exercise can also be determined on the basis of data measured by the body movement measurement unit 21. This makes it possible to evaluate the load on the left ventricle by activity, even in the absence of an assistant such as a doctor.
The configurations in the above-described embodiment and Example are merely specific examples of the present invention, and are not intended to limit the scope of the present invention. The present invention can employ a variety of specific configurations without departing from the technical spirit thereof.
The technical spirit disclosed in the present specification can be specified as inventions such as those described below.
Addendum 1
A biological information analyzing device comprising:
a hardware processor; and
memory storing a program,
wherein through the program, the hardware processor:
obtains blood pressure waveform data measured continuously by a sensor, which is worn on a user's body and can non-invasively measure a blood pressure waveform for each of heartbeats;
extracts an indicator expressing a load placed on the user's heart by an activity on the basis of a difference between a blood pressure waveform in a resting section corresponding to when the user is in a resting state and a blood pressure waveform in an active section corresponding to when the user is engaged in the activity; and outputs the extracted indicator.
Addendum 2
A biological information analyzing system comprising:
a sensor, which is worn on a user's body and can non-invasively measure a blood pressure waveform for each of heartbeats;
a hardware processor; and
memory storing a program,
wherein through the program, the hardware processor:
obtains blood pressure waveform data continuously measured by the sensor;
extracts an indicator expressing a load placed on the user's heart by an activity on the basis of a difference between a blood pressure waveform in a resting section corresponding to when the user is in a resting state and a blood pressure waveform in an active section corresponding to when the user is engaged in the activity; and outputs the extracted indicator.
Addendum 3
A biological information analyzing method comprising:
a step of at least one hardware processor acquiring, from blood pressure waveform data measured continuously by a sensor worn on a user's body and capable of non-invasively measuring a blood pressure waveform for each of heartbeats, a blood pressure waveform in a resting section corresponding to when the user is in a resting state and a blood pressure waveform in an active section corresponding to when the user is engaged in an activity;
a step of at least one hardware processor extracting an indicator expressing a load placed on the user's heart by the activity on the basis of a difference between the blood pressure waveform in the resting section corresponding to when the user is in a resting state and the blood pressure waveform in the active section corresponding to when the user is engaged in the activity; and
a step of at least one hardware processor outputting the extracted indicator.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-082463 | Apr 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/015276 | 4/14/2017 | WO | 00 |
