Respiratory rate measuring device

Abstract

To provide a novel respiration rate measuring device which can measure respiration rate in a resting state in a short period of time by easy processing on the basis of waveform data containing a waveform of a motion of respiration and a motion other than respiration.SOLUTION: A respiration measuring device 10 for measuring respiration rate of a measurement target P, includes: a waveform acquiring part 32 for acquiring waveform data showing input of body motion of the measurement target P over time; a respiration waveform determining part 42 for determining a similar waveform as a respiration waveform, the similar waveform having small variation in amplitude and wavelength in a cyclic period in the waveform data acquired by the waveform acquiring part 32 and being continuous for a preset continuous sequence threshold or more; and a respiration rate calculation part 44 for calculating a respiration rate per unit time on the basis of the wavelength of the respiration waveform.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a respiratory rate measuring device that measures the respiratory rate of a measurement subject at bedtime or the like.

Background Art

[0002] Conventionally, a respiratory rate measuring device that measures the respiratory rate of a measurement subject on a bed based on body movements caused by breathing has been disclosed in, for example, Japanese Patent Application Laid-Open No. 2019-097829 (Patent Document 1). In Patent Document 1, a sheet-like detection device that detects an input due to body movement is laid on the upper surface of a bed, and the respiratory rate is measured based on the input exerted on the detection device by the body movement caused by the breathing of the measurement subject.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the respiratory rate measuring device of Patent Document 1, for example, when the measurement subject moves the body such as turning over on the bed, not only the input due to breathing but also the input based on body movements such as turning over acts on the detection device. Therefore, the input based on body movements other than breathing becomes noise, and the respiratory rate cannot be measured. Therefore, in order for the specific device of Patent Document 1 to measure the respiratory rate, it is necessary for the measurement subject to be stationary on the bed.

[0005] However, when measurements are taken over a long period of time, body movement is unavoidable, making it necessary to distinguish between waveforms caused by respiration and waveforms caused by body movements such as turning over in bed. While it is possible for the person performing the measurement to check the waveform input to the detection device, this is not practical, especially during long-term measurements. Therefore, there has been a need for a respiratory rate measuring device that can easily and quickly distinguish between waveforms caused by respiration and waveforms that include body movements other than respiration.

[0006] The problem to be solved by the present invention is to provide a novel respiratory rate measuring device that can measure the respiratory rate from a short period of resting state through simple processing based on waveform data including waveforms from respiration and waveforms from actions other than respiration. [Means for solving the problem]

[0007] The following describes preferred embodiments for understanding the present invention. However, each embodiment described below is illustrative and can be combined with others as appropriate. Furthermore, the multiple components described in each embodiment can be recognized and adopted as independently as possible, and can be combined with any component described in another embodiment as appropriate. Thus, the present invention is not limited to the embodiments described below, and various other embodiments can be realized.

[0008] The first embodiment is a respiratory rate measuring device comprising: a waveform acquisition unit that acquires waveform data showing the input due to the movement of the body of the object to be measured over time; a respiratory waveform determination unit that determines a similar waveform to be a respiratory waveform when similar waveforms with small variations in amplitude and wavelength between periods occur consecutively for a preset threshold number of times or more in the waveform data acquired by the waveform acquisition unit; and a respiratory rate calculation unit that calculates the number of breaths per unit time based on the wavelength of the respiratory waveform.

[0009] According to the respiratory rate measuring device constructed in accordance with this embodiment, based on the presence of multiple consecutive similar waveforms with small amplitude and wavelength variations in the waveform data, the respiratory waveform in a resting state, which is less affected by inputs from movements such as turning over in bed, is distinguished from other waveforms that are more heavily influenced by inputs from such movements. In this way, by a simple determination process that determines the amplitude and wavelength variations in a continuous waveform, the respiratory waveform in a resting state can be stably extracted from measurement results (waveform data) that measure inputs from body movements including movements other than breathing, and the respiratory rate per unit time can be calculated more accurately based on the wavelength of the respiratory waveform.

[0010] The threshold for the number of consecutive occurrences used to determine whether a series of similar waveforms are respiratory waveforms is not limited to a single value if there are multiple occurrences. As the value increases, waveforms heavily influenced by non-respiratory actions can be excluded with a higher probability. However, it has been confirmed that effective judgment accuracy can be achieved even when the threshold for consecutive occurrences is set to a relatively small value, such as 3 to 6. Therefore, for example, in a measurement subject with many non-respiratory actions, even if a resting state where non-respiratory actions have little effect on the waveform lasts only for a short time, it is possible to effectively obtain respiratory waveforms from the waveform data and measure the respiratory rate.

[0011] The second embodiment is the respiratory rate measuring device described in the first embodiment, wherein the consecutive count threshold is set to 3 or more.

[0012] According to the respiratory rate measuring device with a structure conforming to this embodiment, waveforms that are greatly influenced by inputs from actions other than breathing are less likely to be misidentified as respiratory waveforms, thereby improving the accuracy of respiratory waveform determination and enabling more accurate measurement of respiratory rate.

[0013] The third embodiment is a respiratory rate measuring device described in the first or second embodiment, wherein the continuous count threshold is set to 10 or less.

[0014] According to the respiratory rate measuring device with a structure conforming to this embodiment, the number of cases where respiratory waveforms cannot be obtained from waveform data is reduced, enabling stable measurement of respiratory rate.

[0015] The fourth embodiment is a respiratory rate measuring device described in any one of the first to third embodiments, wherein the threshold for the variation in the amplitude of a determination waveform, which is determined by the respiratory waveform determination unit to be similar to the waveform data, is set within a range of 50% or less of the amplitude of a reference determination waveform, and the threshold for the variation in the wavelength of the determination waveform is set within a range of 50% or less of the wavelength of a reference determination waveform.

[0016] According to the respiratory rate measuring device with a structure conforming to this embodiment, the threshold for the variation in amplitude and wavelength used to determine whether the judgment waveform is a similar waveform is set within a range of 50% or less of the reference judgment waveform, thereby enabling effective identification of respiratory waveforms from waveforms other than respiratory waveforms that are significantly influenced by factors other than respiration.

[0017] The amplitude and wavelength variation thresholds used by the respiratory waveform determination unit to determine similar waveforms are preferably set within a range of 10% to 50% of the amplitude and wavelength of the reference determination waveform. This allows for more effective identification of respiratory waveforms in waveforms where non-respiration influences are significant and amplitude and wavelength changes are large. Furthermore, it prevents waveforms that should be determined as respiratory waveforms but are only slightly affected by non-respiration movements from being incorrectly identified as non-respiration waveforms due to excessively low thresholds, thereby enabling more accurate extraction of respiratory waveforms from waveform data.

[0018] The fifth embodiment is a respiratory rate measuring device described in any one of the first to third embodiments, wherein the threshold for amplitude variation in the determination of whether or not the respiratory waveform is similar by the respiratory waveform determination unit is a dynamic threshold that is dynamically changed and set based on the waveform data acquired by the waveform acquisition unit.

[0019] According to the respiratory rate measuring device with a structure conforming to this embodiment, for example, the threshold for determining whether multiple waveforms are similar is dynamically changed and set based on the waveform data which is the measurement result. Compared to the case where the threshold for determining the respiratory waveform is a constant value, a threshold can be set according to the individual characteristics of the object being measured, thereby improving the accuracy of respiratory waveform determination.

[0020] The sixth aspect is a respiratory rate measuring device described in any one of the first to fifth aspects, wherein the respiratory waveform determination unit compares the amplitude and wavelength of waveforms between adjacent periods in the time series in the waveform data, and determines that the waveforms are similar waveforms if the variation in the amplitude and wavelength of those waveforms is small.

[0021] According to the respiratory rate measuring device constructed in accordance with this embodiment, the amplitude and wavelength between adjacent periods in a time series are compared to determine whether or not it is a respiratory waveform. Therefore, even in special respiratory patterns where the amplitude changes gradually, such as Cheyne-Stokes respiration, or where the wavelength changes gradually, such as in newborns, both can be determined to be similar waveforms. For this reason, even the waveforms of such special respiratory patterns can be determined to be respiratory waveforms and used to measure the respiratory rate. Furthermore, since waveforms are determined to be similar when there are no abrupt changes in amplitude and wavelength between adjacent waveforms in a time series, it is easier to determine similar waveforms, and respiratory waveforms can be obtained relatively easily even when the measurement time is short and waveform data is scarce.

[0022] The seventh embodiment is a respiratory rate measuring device described in any one of the first to fifth embodiments, wherein the respiratory waveform determination unit compares the amplitude and wavelength of a waveform of one period selected in the waveform data with the amplitude and wavelength of waveforms of other periods, and determines that the waveforms are similar waveforms if the variation in the amplitude and wavelength of those waveforms is small.

[0023] According to the respiratory rate measuring device constructed in accordance with this embodiment, by using the waveform of one selected period in the waveform data as the criterion for determining the variation in amplitude and wavelength, the process of determining similar waveforms becomes simpler and the accuracy of the determination can be improved.

[0024] The eighth aspect is the respiration rate measuring device according to any one of the first to fifth aspects, wherein the respiration waveform determination unit compares the amplitudes and wavelengths between the waveforms of a plurality of cycles selected from the waveform data, and determines that those waveforms are the similar waveforms when the variations in the amplitudes and wavelengths of those waveforms are small.

[0025] According to the respiration rate measuring device having the structure according to this aspect, for the waveforms of a plurality of cycles selected from the waveform data, by comparing the amplitudes and wavelengths in all combinations of every two cycles, whether those waveforms of the plurality of cycles are similar waveforms is determined. Therefore, it is difficult to erroneously determine that a waveform greatly affected by an operation other than respiration is a respiration waveform, and the respiration waveform can be detected with high accuracy.

[0026] The ninth aspect is the respiration rate measuring device according to any one of the first to eighth aspects, wherein the waveform acquisition unit acquires the waveform data based on the detection result of a surface pressure sensor that is laid below the measurement target and detects the acting surface pressure due to the body movement of the measurement target.

[0027] According to the respiration rate measuring device having the structure according to this aspect, the input due to body movement including respiration can be accurately detected by the surface pressure sensor laid below the measurement target. Further, there is no need to attach a sensor to the body of the measurement target, and the burden on the measurement target can be reduced.

[0028] [ The tenth aspect is the respiration rate measuring device according to the ninth aspect, wherein the surface pressure sensor has a flexible sheet shape.

[0029] According to the respiration rate measuring device having the structure according to this aspect, since the surface pressure sensor has a flexible sheet shape, there is little discomfort even if the measurement target touches the surface pressure sensor directly or indirectly. For example, even if the surface pressure sensor is laid on a mattress of a bed, it is difficult to affect the comfort of lying.

[0030] The eleventh embodiment is a respiratory rate measuring device described in any one of the first to tenth embodiments, which is further equipped with an infant apnea determination unit that determines that the infant is in an apneic state when the respiratory rate per unit time calculated by the respiratory rate calculation unit falls below a preset lower limit.

[0031] According to the respiratory rate measuring device constructed in accordance with this embodiment, it is possible to more accurately identify and respond quickly to an infant's apnea state by understanding the number of breaths per unit time. [Effects of the Invention]

[0032] According to the present invention, the respiratory rate can be measured from a short period of resting state by simple processing based on waveform data that includes waveforms from respiration and waveforms from actions other than respiration. [Brief explanation of the drawing]

[0033] [Figure 1] Plan view showing a respiratory rate measuring device as the first embodiment of the present invention in use. [Figure 2] Block diagram of the respiratory rate measurement device shown in Figure 1. [Figure 3] Perspective view of the detection device that constitutes the respiratory rate measurement device shown in Figure 1. [Figure 4] This figure shows an enlarged cross-section of the sensor sheet constituting the detection device shown in Figure 3, and corresponds to the cross-section IV-IV in Figure 2. [Figure 5] An example of waveform data acquired by the respiratory rate measurement device shown in Figure 1. [Figure 6] Figure 1 is a model diagram illustrating the determination of respiratory waveforms in a respiratory rate measurement device. [Figure 7] The table below shows the respiratory rate measurement results from the respiratory rate measurement device shown in Figure 1, classified by the number of consecutive occurrences of similar waveforms. [Figure 8] A flowchart explaining the process when using dynamic thresholds to determine the respiratory waveform shown in Figure 6. [Figure 9]Figure 8 shows a graph illustrating the change in the dynamic threshold over time when determining the respiratory waveform using the dynamic threshold. [Figure 10] Table showing respiration measurement results for both fixed threshold and dynamic threshold methods. [Modes for carrying out the invention]

[0034] Embodiments of the present invention will be described below with reference to the drawings.

[0035] Figure 1 shows a respiratory rate measuring device 10 as a first embodiment of the present invention in use. As also shown in Figure 2, the respiratory rate measuring device 10 includes a piezoelectric surface pressure sensor 12 that receives body movement (vibration) of the subject P and outputs a detection signal corresponding to the body movement, and a processing device 14 that analyzes and processes the detection signal output from the surface pressure sensor 12. In the following description, as a general rule, the vertical direction refers to the vertical vertical direction in Figure 1, which is the thickness direction of the sensor sheet 16 in use.

[0036] As shown in Figure 3, the surface pressure sensor 12 includes a sensor sheet 16. The sensor sheet 16 is a flexible, substantially rectangular sheet, and in this embodiment, it is in the shape of an elongated strip. As shown in Figure 4, the sensor sheet 16 includes a piezoelectric layer 18, a pair of electrode layers 20a and 20b arranged in an overlapping state on both sides of the piezoelectric layer 18 in the pressure-sensitive direction, and a pair of protective layers 22a and 22b.

[0037] The piezoelectric layer 18 can be made of materials such as ceramics, synthetic resins, or rubber elastic materials (including elastomers). However, in this embodiment, it is made of a rubber elastic material, which has a relatively smaller volume resistivity ρv than ceramics or synthetic resins. If the volume resistivity is small, the cutoff frequency will be higher than, for example, the lower limit frequency of vibration frequencies caused by breathing, and will be on the lower frequency side of the vibration frequency band caused by breathing, which may hinder the detection of the primary frequency component of the breathing signal. For this reason, it is desirable to increase the resistance value of the rubber elastic material so that the cutoff frequency is lower than, for example, the lower limit frequency of vibration frequencies caused by breathing. Specifically, the volume resistivity ρv of the piezoelectric layer 18 is 10 9 It is preferable that it be Ω·cm or more, and 10 10 It is more preferable that the value be Ω·cm or greater.

[0038] The rubber elastic material used as the piezoelectric layer 18 is not limited, but it is preferable to use one or more selected from crosslinked rubber and thermoplastic elastomers, for example, urethane rubber, silicone rubber, nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), acrylic rubber, natural rubber, isoprene rubber, ethylene-propylene-diene rubber (EPDM), ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-acrylic acid ester copolymer, butyl rubber, styrene-butadiene rubber, fluororubber, epichlorohydrin rubber, etc. Alternatively, a modified elastomer with introduced functional groups may be used. As a modified elastomer, hydrogenated nitrile rubber having one or more selected from carboxyl groups, hydroxyl groups, and amino groups is preferred.

[0039] Furthermore, the piezoelectric layer 18 contains piezoelectric particles. The piezoelectric particles are particles of a piezoelectric compound. As piezoelectric compounds, ferroelectrics having a perovskite-type crystal structure are known, and one or more of the following can be suitably used: barium titanate, strontium titanate, potassium niobate, sodium niobate, lithium niobate, potassium sodium niobate, potassium sodium lithium niobate, lead zirconate titanate (PZT), barium strontium titanate (BST), bismuth lanthanum titanate (BLT), and bismuth strontium tantalate (SBT).

[0040] The electrode layers 20a and 20b preferably have flexibility that allows them to deform in accordance with the piezoelectric layer 18. Such electrode layers 20a and 20b can be formed from, for example, a conductive material with a conductive material compounded into a binder, conductive fibers, etc. As the binder, the same material as the crosslinked rubber and thermoplastic elastomer that constitute the piezoelectric layer 18 can be used.

[0041] Furthermore, the conductive material incorporated into the electrode layers 20a and 20b is not limited, but can be appropriately selected from, for example, metal particles made of silver, gold, copper, nickel, rhodium, palladium, chromium, titanium, platinum, iron, and alloys thereof; metal oxide particles made of zinc oxide, titanium oxide, etc.; metal carbide particles made of titanium carbonate, etc.; metal nanowires made of silver, gold, copper, platinum, and nickel, etc.; carbon black, carbon nanotubes, graphite, thin-layer graphite, graphene, and other conductive carbon materials.

[0042] The protective layers 22a and 22b are not limited to any particular material, but it is desirable that they possess electrical insulation, durability, and biocompatibility in addition to flexibility.

[0043] In this embodiment, the piezoelectric layer 18, electrode layers 20a and 20b, and protective layers 22a and 22b are all in the shape of thin rectangular plates. The electrode layers 20a and 20b are fixed to both sides of the piezoelectric layer 18 in the thickness direction, and the protective layers 22a and 22b are fixed to both sides of the piezoelectric layer 18 and electrode layers 20a and 20b in the thickness direction. As a result, the piezoelectric layer 18 and electrode layers 20a and 20b are embedded inside the protective layers 22a and 22b without being exposed to the outside. With this structure, the sensor sheet 16 is formed as a thin, substantially rectangular sheet.

[0044] Furthermore, in the central part of the sensor sheet 16 in the width direction, the region where the piezoelectric layer 18 and the electrode layers 20a and 20b overlap in the thickness direction is defined as the pressure-sensitive area 24, and an electric charge is generated when a load is applied to the pressure-sensitive area 24. The pressure-sensitive area 24 may be a single structure throughout, or it may be a cell structure divided into multiple pressure-sensitive areas in the planar direction.

[0045] The control device 26 includes a housing 28 attached to one end of the sensor sheet 16 in the longitudinal direction. As shown in Figure 2, the control device 26 includes a measurement circuit 30, a waveform data generation circuit 32 as a waveform acquisition unit, a filter 34, and a power supply circuit 36. The measurement circuit 30, the waveform data generation circuit 32, the filter 34, and the power supply circuit 36 ​​are composed of, for example, chips mounted on an electronic circuit board, and the electronic circuit board is housed in the housing 28.

[0046] The measurement circuit 30 is electrically connected to the electrode layers 20a and 20b of the sensor sheet 16. When a compressive force is applied to the sensor sheet 16 in the thickness direction, the charge (voltage) generated in the piezoelectric layer 18 is transmitted to the measurement circuit 30 by the electrode layers 20a and 20b, and the magnitude of the voltage corresponding to this charge is measured by the measurement circuit 30. The measurement circuit 30 includes a charge amplifier that converts the charge generated in the sensor sheet 16 into a voltage, and an A / D converter that converts the voltage output converted by the charge amplifier into a digital signal. The measurement circuit 30 also includes a signal amplification unit, which can appropriately amplify, for example, the charge generated in the sensor sheet 16, the voltage converted by the charge amplifier, and the digital signal converted by the A / D converter.

[0047] The waveform data generation circuit 32 calculates the magnitude of the input to the sensor sheet 16 based on the magnitude of the voltage measured by the measurement circuit 30, and generates waveform data showing the change in the input over time. The waveform data obtained by the waveform data generation circuit 32 is filtered by the filter 34 to become waveform data used for measuring respiratory rate, as illustrated in Figure 5. The filter 34 is a digital filter, and may be, for example, a low-pass filter or high-pass filter that removes high-frequency or low-frequency components from the waveform data, or a band-pass filter that extracts specific frequency components.

[0048] The measurement circuit 30, the waveform data generation circuit 32, and the filter 34 operate by being powered by the power supply circuit 36. The power supply circuit 36 ​​appropriately controls the power supplied from an external source to supply operating power to the measurement circuit 30, the waveform data generation circuit 32, and the filter 34. The power supply circuit 36 ​​is connected to an external power supply device 40 via a processing device 14, which will be described later.

[0049] The control device 26 is connected to the processing unit 14 by external wiring 38. The processing unit 14 is, for example, a desktop or laptop computer and has a hardware configuration that includes a central processing unit (CPU), RAM, ROM, a display unit (46) such as a display, and an input device such as a keyboard. The processing unit 14 is electrically connected to the control device 26 by wired or wireless communication and is capable of receiving waveform data from the control device 26. The processing unit 14 is also connected to a power supply unit 40 and, in this embodiment, supplies power from the power supply unit 40 to the power supply circuit 36 ​​of the control device 26. The processing unit 14 includes a respiratory waveform determination unit 42, a respiratory rate calculation unit 44, and a display unit 46.

[0050] The respiratory waveform determination unit 42 performs a respiratory waveform determination process to extract respiratory waveforms that are less affected by actions other than breathing from the waveform data received from the waveform data generation circuit 32 of the control device 26.

[0051] In other words, the waveform of body movement caused by breathing is stable with little change over time, and there are few rapid changes in amplitude and wavelength. On the other hand, the waveform of body movement including movements other than breathing, such as turning over in bed, changes relatively large over time, and rapid changes in amplitude and wavelength are likely to occur. Therefore, the breathing waveform determination unit 42 of this embodiment determines that a waveform (similar waveform) is a breathing waveform when, in the waveform data, waveforms with amplitude and wavelength variation smaller than a threshold (similar waveforms) continue for a number of cycles equal to or greater than a preset threshold number, as shown in Figure 6. Through this breathing waveform determination process, the breathing waveform determination unit 42 can distinguish between breathing waveforms, which are less affected by movements other than breathing, and waveforms, which are more affected by movements other than breathing, in the body movement waveform data, and extract only the breathing waveforms. The breathing waveform determination unit 42 then extracts and stores the breathing waveforms from the waveform data and transmits the extracted breathing waveform data to the breathing rate calculation unit 44, which will be described later.

[0052] In the respiratory waveform determination unit 42, the determination threshold for the amplitude variation of the determination waveform to be determined as similar is set within a range of 50% or less of the amplitude of the reference determination waveform, and the determination threshold for the wavelength variation of the determination waveform is set within a range of 50% or less of the wavelength of the reference determination waveform. In this embodiment, in the respiratory waveform determination unit 42, the determination threshold for the amplitude variation of the determination waveform is set to 20% of the amplitude of the reference determination waveform, and the determination threshold for the wavelength variation of the determination waveform is set to 20% of the wavelength of the reference determination waveform. Therefore, the respiratory waveform determination unit 42 determines that the determination waveform is a similar waveform when the amplitude variation (difference in amplitude) of the determination waveform is 20% or less of the amplitude of the reference determination waveform, and the wavelength variation (difference in wavelength) of the determination waveform is 20% or less of the amplitude of the reference determination waveform.

[0053] More specifically, for example, the respiratory waveform determination unit 42 of this embodiment determines that the first to third waveforms 50, 52, and 54 constituting the determination waveform 48 are similar waveforms if, in the determination waveform 48 consisting of three consecutive periodic waveforms as shown in Figure 6, the difference between the amplitude A1 of the first waveform 50 and the amplitude A2 of the second waveform 52, and the difference between the amplitude A2 of the second waveform 52 and the amplitude A3 of the third waveform 54 are both 20% or less of the amplitude of the reference determination waveform 48 (for example, the amplitude A1 of the first waveform 50), and the difference between the wavelength λ1 of the first waveform 50 and the wavelength λ2 of the second waveform 52, and the difference between the wavelength λ2 of the second waveform 52 and the wavelength λ3 of the third waveform 54 are both 20% or less of the wavelength of the reference determination waveform 48 (for example, the wavelength λ1 of the first waveform 50). In this embodiment, the first waveform 50, the second waveform 52, and the third waveform 54 have boundaries at the intersection points when the reference line L, shown as a dashed line in Figure 6, crosses from bottom to top in the figure. Therefore, the maximum and minimum values ​​of the input are clear in all cases, making it easy to grasp the amplitude.

[0054] However, the respiratory waveform determination unit 42 does not necessarily determine the respiratory waveform based on the variation in amplitude and wavelength of the determination waveform, but rather does not necessarily have to be done solely by comparing two waveforms that are consecutive in time series. For example, the respiratory waveform determination unit 42 may determine the first to third waveforms 50, 52, and 54 to be similar waveforms if the difference between the amplitude A1 and wavelength λ1 of the first waveform 50 and the amplitude A2 and wavelength λ2 of the second waveform 52, and the difference between the amplitude A1 and wavelength λ1 of the first waveform 50 and the amplitude A3 and wavelength λ3 of the third waveform 54 are all 20% or less of the amplitude and wavelength of the reference determination waveform 48. This allows for a relatively small tolerance range for the variation in amplitude and wavelength in the determination waveform, thereby more reliably excluding waveforms that are heavily influenced by actions other than breathing. Note that the waveform used as the criterion for determining the variation in amplitude and wavelength is not necessarily limited to the first waveform in the time series, but may be, for example, an intermediate waveform or the last waveform. Criteria for determining amplitude and wavelength variation can include, for example, specifying the time-series position of the judgment waveform (e.g., the first, last, or nth instance) to set a reference waveform, or using frequently occurring values, average values, or intermediate values ​​excluding the maximum and minimum as criteria.

[0055] Furthermore, for example, the respiratory waveform determination unit 42 may determine the first to third waveforms 50, 52, and 54 as similar waveforms if the difference between the amplitude A1 and wavelength λ1 of the first waveform 50 and the amplitude A2 and wavelength λ2 of the second waveform 52, the difference between the amplitude A1 and wavelength λ1 of the first waveform 50 and the amplitude A3 and wavelength λ3 of the third waveform 54, and the difference between the amplitude A2 and wavelength λ2 of the second waveform 52 and the amplitude A3 and wavelength λ3 of the third waveform 54 are all 20% or less of the amplitude and wavelength of the reference determination waveform 48. In short, it is also possible to refer to the variation in amplitude and wavelength among all the waveforms that constitute the determination waveform. According to this, since a waveform is determined to be a respiratory waveform when the variation in amplitude and wavelength of the first to third waveforms 50, 52, and 54 is smaller, waveforms that are greatly influenced by actions other than breathing can be more reliably excluded.

[0056] The respiratory waveform determination unit 42 determines that a determination waveform is a respiratory waveform based on the amplitude and wavelength variation determination threshold (amplitude and wavelength respiratory determination threshold). This threshold is preferably set within a range of 10-50%, and more preferably within a range of 10-30%, of the amplitude and wavelength of the reference determination waveform. A smaller amplitude and wavelength respiratory determination threshold results in smaller amplitude and wavelength variation between determination waveforms, making it easier to exclude waveforms that are heavily influenced by actions other than breathing. On the other hand, setting a larger amplitude and wavelength respiratory determination threshold makes it easier to acquire respiratory waveforms even when the number of waveform data is small during short-term measurements.

[0057] In this embodiment, the respiratory waveform determination unit 42 has a consecutive count threshold set to 3. When the respiratory waveform determination unit 42 determines that waveforms with three or more consecutive cycles in the waveform data are similar waveforms, it determines those similar waveforms to be respiratory waveforms. In the respiratory waveform determination process of the respiratory waveform determination unit 42, the consecutive count threshold for similar waveforms to be determined to be respiratory waveforms is not particularly limited as long as it is 2 or more, but it is desirable to set it to 3 or more. Furthermore, it is desirable to set the consecutive count threshold for similar waveforms to be determined to be respiratory waveforms to 10 or less, and more preferably to 6 or less. For example, in the waveform data shown in Figure 5, there are two waveforms determined to be respiratory waveforms during the measurement time.

[0058] The respiratory waveform determination process performed by the respiratory waveform determination unit 42 is executed repeatedly while advancing the time in the waveform data. This allows the respiratory waveform determination process to be performed over the entire time series of the waveform data, and also allows for obtaining four or more consecutive respiratory waveforms. The respiratory waveform determination unit 42 may perform the respiratory waveform determination process in real time in response to input to the sensor sheet 16, or it may perform the respiratory waveform determination process on the accumulated waveform data after accumulating the waveform data over a predetermined measurement time.

[0059] Figure 7 is a table showing the results of a similar waveform determination process performed on waveform data obtained by actual measurement, where the difference in amplitude and wavelength between adjacent waveforms in a time series is considered to be within a ±20% threshold. The results are classified by the number of consecutive similar waveforms (number of consecutive periods). According to Figure 7, the number of waveforms that were determined to be similar waveforms for three or more consecutive periods, which are determined to be respiratory waveforms, was 466 out of a total of 1013 waveforms measured. 547 waveforms were determined not to be respiratory waveforms (the number of consecutive similar waveforms was 1 or 2). Thus, by setting the amplitude and wavelength determination thresholds to 20% of the reference determination waveform, and determining a waveform as a respiratory waveform when similar waveforms with amplitude and wavelength variations (changes) below the determination threshold are consecutive for three or more periods, it has been confirmed by actual measurement that it is possible to stably acquire respiratory waveforms while sufficiently excluding waveforms that are heavily influenced by actions other than breathing.

[0060] The respiratory waveform data extracted from the waveform data by the respiratory waveform determination unit 42 is transmitted to the respiratory rate calculation unit 44. The respiratory rate calculation unit 44 calculates the number of breaths per unit time based on the wavelength of the respiratory waveform, which indicates the time required for one breath. Specifically, for example, if one wavelength of the respiratory waveform is 2 seconds, the number of breaths per minute is estimated to be 30.

[0061] The processing unit 14 of this embodiment includes a display unit 46, such as a display. The display unit 46 is capable of displaying a graph of the waveform data generated by the waveform data generation circuit 32, the determination result of the respiratory waveform determination unit 42, the respiratory rate calculated by the respiratory rate calculation unit 44, and so on.

[0062] The processing device 14 of this embodiment includes an infant apnea determination unit 56. When the respiratory rate measuring device 10 measures the respiratory rate of an infant, the infant apnea determination unit 56 determines that the infant is in an apneic state if the respiratory rate per unit time calculated by the respiratory rate calculation unit 44 falls below a preset lower limit. Specifically, for example, when measuring the respiratory rate of an infant, if the respiratory rate per minute calculated by the respiratory rate calculation unit 44 is less than 20, the infant apnea determination unit 56 determines that the infant P being measured is in an apneic state.

[0063] The infant apnea detection unit 56 controls the alert unit 58 of the processing unit 14 to perform notification means such as emitting a warning sound, illuminating a warning light, or sending a notification email to medical personnel if the infant's apnea state continues for a predetermined period of time. The type of alarm issued by the alert unit 58 is not particularly limited as long as it conveys to people nearby or medical personnel at a distance that the infant is experiencing apnea. In addition, as a means of warning about the infant's apnea state, the infant apnea detection unit 56 can also, for example, transmit a control signal to the display unit 46 to display a warning on the display unit 46.

[0064] The processing unit 14 includes not only a computing device (CPU, etc.) that performs processing such as determining the respiratory waveform and calculating the respiratory rate, but also a storage device (hard disk, etc.) that stores received data, the results of determination and calculation, etc. The respiratory waveform determination unit 42, the respiratory rate calculation unit 44, and the infant apnea determination unit 56 can be configured by a combination of these computing devices and storage devices.

[0065] In a respiratory rate measuring device 10 with such a structure, for example as shown in Figure 1, the sensor sheet 16 of the surface pressure sensor 12 is placed on top of the mattress of the bed 60, and the sensor sheet 16 is laid under the subject P lying on the bed 60, and the respiratory rate of the subject P is measured is measured. The longitudinally shaped sensor sheet 16 is preferably arranged to extend laterally across the bed 60 and positioned near the chest of the subject P. This makes it easier to detect the movement of the subject P's chest due to breathing. For example, a belt with adjustable length may be provided on the surface pressure sensor 12, and the belt may be wrapped around the mattress of the bed 60 to fix the surface pressure sensor 12 to the bed 60 (mattress) and position the sensor sheet 16 on the mattress.

[0066] Since the sensor sheet 16 is a flexible sheet, it deforms to conform to the unevenness of the body surface of the object being measured P, making it less likely to cause pain or discomfort to the object being measured P. Furthermore, because it is laid beneath the object being measured P, discomfort to the object being measured P is reduced compared to when it is attached to the object being measured P. Alternatively, a sheet may be placed over the mattress on which the sensor sheet 16 is stacked to prevent the object being measured P from directly contacting the sensor sheet 16.

[0067] Then, the subject P, lying on the bed 60 to which the sensor sheet 16 is attached, inputs a compressive force in the thickness direction to the sensor sheet 16 through body movements, including breathing. The sensor sheet receives input from a combination of body movements, including not only those caused by breathing but also those caused by actions such as turning over in bed. The respiratory rate measuring device 10 according to this embodiment focuses on the fact that the amplitude and wavelength of the waveform caused by breathing do not change significantly and remain stable in the waveform data, which is the result of detection by the surface pressure sensor 12 of the input due to body movement. When similar waveforms with similar amplitude and wavelength appear consecutively for a period exceeding a preset threshold number of consecutive occurrences, it determines that it is a respiratory waveform. As a result, in waveform data where various body movements are acting in combination, respiratory waveforms that are less affected by movements other than breathing can be accurately extracted, and the respiratory rate can be calculated with higher reliability based on the respiratory waveform.

[0068] The respiratory waveform determination unit 42 of this embodiment determines a waveform to be a respiratory waveform when similar waveforms with small variations in amplitude and wavelength appear consecutively three or more times. This makes it less likely that waveforms caused by actions other than breathing, whose amplitude and wavelength happen to be similar, will be mistakenly identified as respiratory waveforms, thereby improving the accuracy of respiratory waveform determination.

[0069] Furthermore, it is desirable to set the threshold for the number of consecutive similar waveforms used in the respiratory waveform determination process of the respiratory waveform determination unit 42 to 10 or less. This makes it less likely that waveforms with little influence from actions other than breathing will be mistakenly determined not to be respiratory waveforms, and respiratory waveforms can be effectively obtained from waveform data. In particular, in this embodiment, since the threshold for the number of consecutive similar waveforms is set to 3, it is possible to acquire respiratory waveforms in a short resting state of a few seconds to more than ten seconds while sufficiently excluding waveforms with a large influence from actions other than breathing from the respiratory waveform. Therefore, the respiratory rate of not only adult humans but also infants and toddlers with short resting times and many actions other than breathing, or non-human mammals such as dogs, can be effectively measured.

[0070] The number of consecutive similar waveforms that the respiratory waveform determination unit 42 determines to be a respiratory waveform is set appropriately, taking into consideration the required accuracy and ease of measurement, as a larger number of similar waveforms makes it easier to eliminate the influence of actions other than the required breathing, while a smaller number allows for obtaining a respiratory waveform in a shorter time. Preferably, the number of consecutive similar waveforms is set within the range of 3 to 10 times, as described above, and more preferably within the range of 3 to 6 times.

[0071] Incidentally, in addition to pre-setting specific numerical values ​​as described above, the amplitude and wavelength respiration thresholds can also be dynamically set based on the measurement results of the waveform data. Specifically, for example, respiration detection processing can be performed using dynamic respiration thresholds, as shown in the flowchart in Figure 8.

[0072] In other words, in the respiration determination process shown in Figure 8, after measuring at least three waveforms, in step (hereinafter S) 1, the natural number m is set to 1, and then in S2, the difference between the amplitude and wavelength of the m-th waveform (the m-th waveform) and the (m+1)th waveform (the m+1 waveform) is calculated, and it is determined whether the difference in amplitude is 50% or less of the amplitude of the reference waveform (e.g., the m-th waveform) and whether the difference in wavelength is 50% or less of the wavelength of the reference waveform (e.g., the m-th waveform).

[0073] In S2, if at least one of the difference in amplitude and wavelength between the m-th waveform and the (m+1)-th waveform is greater than 50% of the amplitude and wavelength of the reference waveform (S2 is No), then in S3, 1 is added to m before executing the processes from S2 onward.

[0074] In S2, if the difference in amplitude and wavelength between the m-th waveform and the (m+1)-th waveform are both 50% or less of the amplitude and wavelength of the reference waveform (S2 is Yes), then in S4, the difference between the amplitude and wavelength of the (m+1)-th waveform (the (m+1)-th waveform) and the amplitude and wavelength of the (m+2)-th waveform (the (m+2)-th waveform) is calculated, and it is determined whether the difference in amplitude is 50% or less of the amplitude of the reference waveform (e.g., the (m+1)-th waveform) and whether the difference in wavelength is 50% or less of the wavelength of the reference waveform (e.g., the (m+1)-th waveform).

[0075] In S4, if at least one of the difference in amplitude and wavelength between the (m+1)th waveform and the (m+2)th waveform is greater than 50% of the amplitude and wavelength of the reference waveform (S4 is No), then in S3, 1 is added to m before executing the processes from S2 onward.

[0076] In S4, if the difference in amplitude and wavelength between the m+1th waveform and the m+2nd waveform is 50% or less of the amplitude and wavelength of the reference waveform (S4 is Yes), then in S5, the determination waveform consisting of the mth to m+2th waveforms is stored as a calculation target waveform where similar waveforms continue for 3 periods. Then, in S6, a determination is made as to whether a predetermined data storage time has elapsed. If it is determined in S6 that the predetermined data storage time has not elapsed (S6 is No), then 1 is added to m in S3 and the processing from S2 onwards is executed.

[0077] If it is determined in S6 that a predetermined data storage time has elapsed (S6 is Yes), then in S7, the amplitude standard deviation σ1 and the wavelength standard deviation σ2 are calculated for the waveform to be calculated that was stored in S5. Next, in S8, σ1 × 100 is set as the amplitude breathing threshold T1, and σ2 × 100 is set as the wavelength breathing threshold T2.

[0078] Next, in S9 and S11, a respiration waveform determination process is performed on the nth waveform (wavelength n), the (n+1)th waveform (wavelength n+1), and the (n+2)th waveform (wavelength n+2). Specifically, in S9, it is determined whether the difference in amplitude between the nth waveform and the (n+1)th waveform is less than or equal to T1% of the amplitude of the reference waveform (e.g., the nth waveform), and whether the difference in wavelength between the nth waveform and the (n+1)th waveform is less than or equal to T2% of the wavelength of the reference waveform. Note that n is any natural number; for example, if the minimum value of n is set to 1, respiration determination can be performed on the entire measured waveform. Also, for example, if the minimum value of n is the maximum value of m at the end of processing up to S8 plus 1, respiration determination can be performed only on the waveform data after the initial dynamic threshold setting is complete, without including the waveform data used in the process of setting the initial dynamic threshold up to S8.

[0079] In S9, if at least one of the following is true (S9 is No): the difference in amplitude between the nth waveform and the (n+1th)th waveform is greater than T1% of the amplitude of the reference waveform, or the difference in wavelength between the nth waveform and the (n+1th)th waveform is greater than T2% of the wavelength of the reference waveform, then in S10, 1 is added to n and the processing from S9 onward is executed.

[0080] In S9, if the difference in amplitude between the nth waveform and the (n+1)th waveform is less than or equal to T1% of the amplitude of the reference waveform, and the difference in wavelength between the nth waveform and the (n+1)th waveform is less than or equal to T2% of the wavelength of the reference waveform (S9 is Yes), then in S11, it is determined whether the difference in amplitude between the (n+1)th waveform and the (n+2)th waveform is less than or equal to T1% of the amplitude of the reference waveform (e.g., the (n+1)th waveform), and whether the difference in wavelength between the (n+1)th waveform and the (n+2)th waveform is less than or equal to T2% of the wavelength of the reference waveform (e.g., the (n+1)th waveform).

[0081] In S11, if at least one of the following is true (S11 is No): the difference in amplitude between the (n+1)th waveform and the (n+2)th waveform is greater than T1% of the amplitude of the reference waveform, or the difference in wavelength between the (n+1)th waveform and the (n+2)th waveform is greater than T2% of the wavelength of the reference waveform, then in S10, 1 is added to n and the processes from S9 onward are executed.

[0082] In S11, if the difference in amplitude between the (n+1)th waveform and the (n+2)th waveform is less than or equal to T1% of the amplitude of the reference waveform, and the difference in wavelength between the (n+1)th waveform and the (n+2)th waveform is less than or equal to T2% of the wavelength of the reference waveform (S11 is Yes), then the variation in the three consecutive waveforms in time series (waveforms n to n+2) is small, and in S12, the judgment waveform consisting of waveforms n to n+2 is stored as a respiratory waveform with three consecutive similar waveforms.

[0083] Next, in S13, it is determined whether or not the pre-set measurement time has elapsed. If it is determined in S13 that the measurement time has elapsed (S13 is Yes), the respiratory waveform determination process is terminated.

[0084] If it is determined in S13 that the measurement time has not elapsed (S13 is No), then in S14, the amplitude standard deviation σ1' and the wavelength standard deviation σ2' are calculated for the calculation target waveform stored in S5 and the respiratory waveform stored in S12, respectively. Next, in S15, σ1' × 100 is set as the amplitude respiratory judgment threshold T1, and σ2' × 100 is set as the wavelength respiratory judgment threshold T2.

[0085] After setting the respiratory thresholds T1 and T2 in S15, 1 is added to n in S10 before executing the processes from S9 onwards.

[0086] Through the above processing, the resting respiratory waveform, which is less affected by movements other than breathing, can be identified and extracted from the body movement waveform data detected by the sensor sheet 16 based on a dynamic respiratory judgment threshold.

[0087] As shown in Figure 9, the dynamic respiratory threshold fluctuates significantly in the initial stages of measurement, but stabilizes at a convergence value of approximately 20% as the measurement time increases and the number of waveform data increases. Specifically, by performing the processing shown in Figure 8 for approximately 30 minutes, the dynamic threshold stabilizes at approximately 20%. Therefore, for example, by extracting respiratory waveforms only from waveform data after a predetermined time (e.g., 30 minutes) has elapsed since the start of processing from S9 onwards, respiratory waveforms less affected by non-respiratory movements can be extracted with greater accuracy. Furthermore, it has been confirmed from actual measurement results that the convergence value of the dynamic respiratory threshold is around 20%, and if the respiratory threshold is set to a fixed value of around 20%, the respiratory rate can be measured with greater accuracy. In Figure 9, (a) shows the trend of the dynamic respiratory threshold when the measurement target P is a newborn, and (b) shows the trend of the dynamic respiratory threshold when the measurement target P is an adult.

[0088] Furthermore, as shown in Figure 10, there is no significant difference in the average respiratory time or its standard deviation between cases where the respiratory detection threshold is fixed (20%) and cases where the respiratory detection threshold is dynamically set. This suggests that it is possible to effectively measure the respiratory rate in both cases. In addition, when the measurement time is long and the number of waveforms to be measured is large, further improvement in measurement accuracy can be expected by adopting a dynamic respiratory detection threshold.

[0089] Although embodiments of the present invention have been described in detail above, the present invention is not limited by its specific description. For example, the sensor for acquiring waveform data due to body movement is not limited to a sheet-shaped surface pressure sensor. Furthermore, when a sheet-shaped surface pressure sensor is used, it is not necessarily limited to a longitudinal strip shape, but may be a sheet shape such as a square or a circle.

[0090] In the above embodiment, an example was shown in which the respiratory rate of the subject P lying on the bed 60 was measured. However, the subject P does not necessarily have to be in a supine position during measurement; it may be in a sitting or standing position, or any other posture. For example, the surface pressure sensor 12 can be placed on the seat of a chair to measure the respiratory rate of the subject P in a sitting position. As mentioned above, the subject P is not limited to an adult human being as illustrated in Figure 1, but may also be an infant or toddler, including a newborn, or a mammal other than a human, such as a dog or cat.

[0091] In the above embodiment, an example was shown in which a processing unit 14 connected to the surface pressure sensor 12 performs respiratory waveform determination processing and respiratory rate calculation calculations separately from the control unit 26 of the surface pressure sensor 12. However, the control unit 26 of the surface pressure sensor 12 can also be equipped with the functions to perform these determination and calculation processes. Furthermore, the information display function by the display unit 46, the infant apnea determination function by the infant apnea determination unit 56, and the notification function by the alert unit 58, which were provided by the processing unit 14, can all be set in the control unit 26 of the surface pressure sensor 12. In the above embodiment, a structure was illustrated in which power is indirectly supplied from the power supply unit 40 to the control unit 26 via the processing unit 14. However, for example, the control unit 26 may be directly connected to the power supply unit 40 by external wiring 38.

[0092] In the above embodiment, a laptop or desktop computer was given as an example of the processing unit 14, but a mobile device such as a smartphone or tablet terminal can also be used as the processing unit. [Explanation of Symbols]

[0093] 10 Respiratory rate measuring device (first embodiment) 12 Surface pressure sensors 14 Processing Unit 16 Sensor Sheet 18 Piezoelectric layer 20a,20b electrode layer 22a,22b Protective layer 24 Pressure-sensitive section 26 Control device 28 Housing 30 Measurement Circuit 32. Waveform data generation circuit (waveform acquisition unit) 34 Filters 36 Power circuit 38 External wiring 40 Power supply 42 Respiratory waveform determination section 44 Breathing rate calculator 46 Display section 48 Judgment waveform 50 1st waveform 52 2nd waveform 54 3rd waveform 56 Infant apnea detection unit 58 Alert Section 60 beds P measurement target

Claims

1. A waveform acquisition unit acquires waveform data that shows the input due to the movement of the object being measured over time, A respiratory waveform determination unit determines that a similar waveform is a respiratory waveform if, in the waveform data acquired by the waveform acquisition unit, similar waveforms with small variations in amplitude and wavelength between periods occur consecutively for a preset threshold number of times or more. A respiratory rate calculation unit that calculates the number of breaths per unit time based on the wavelength of the respiratory waveform. Equipped with, The respiratory waveform determination unit is As the judgment waveform values ​​used as the judgment criteria, the amplitude and wavelength of any one period waveform selected in the waveform data, or the amplitude and wavelength obtained as the most frequent value, average value, or median value from multiple periods of waveforms in the waveform data, are adopted, and A respiratory rate measuring device that determines waveforms to be similar waveforms if the difference in amplitude and wavelength obtained by comparing the amplitude and wavelength of waveforms between adjacent periods in the time series in the waveform data is smaller than each determination threshold set within a range of 50% or less of the amplitude and wavelength of the determination waveform value.

2. A waveform acquisition unit acquires waveform data that shows the input due to the movement of the object being measured over time, A respiratory waveform determination unit determines that a similar waveform is a respiratory waveform if, in the waveform data acquired by the waveform acquisition unit, similar waveforms with small variations in amplitude and wavelength between periods occur consecutively for a preset threshold number of times or more. A respiratory rate calculation unit that calculates the number of breaths per unit time based on the wavelength of the respiratory waveform. Equipped with, The respiratory waveform determination unit is As the judgment waveform values ​​used as the judgment criteria, the amplitude and wavelength of any one period waveform selected in the waveform data, or the amplitude and wavelength obtained as the most frequent value, average value, or median value from multiple periods of waveforms in the waveform data, are adopted, and A respiratory rate measuring device that determines waveforms to be similar waveforms if the difference in amplitude and wavelength obtained by comparing the amplitude and wavelength of a selected waveform of one period in the waveform data with the amplitude and wavelength of a waveform of another period is smaller than each determination threshold set within a range of 50% or less of the amplitude and wavelength of the determination waveform value.

3. A waveform acquisition unit acquires waveform data that shows the input due to the movement of the object being measured over time, A respiratory waveform determination unit determines that a similar waveform is a respiratory waveform if, in the waveform data acquired by the waveform acquisition unit, similar waveforms with small variations in amplitude and wavelength between periods occur consecutively for a preset threshold number of times or more. A respiratory rate calculation unit that calculates the number of breaths per unit time based on the wavelength of the respiratory waveform. Equipped with, The respiratory waveform determination unit is As the judgment waveform values ​​used as the judgment criteria, the amplitude and wavelength of any one period waveform selected in the waveform data, or the amplitude and wavelength obtained as the most frequent value, average value, or median value from multiple periods of waveforms in the waveform data, are adopted, and A respiratory rate measuring device that determines waveforms to be similar waveforms by comparing the amplitude and wavelength between multiple selected waveforms in the waveform data, and finding that the difference in amplitude and wavelength obtained is smaller than each determination threshold set within a range of 50% or less of the amplitude and wavelength of the determination waveform value.

4. The respiratory rate measuring device according to any one of claims 1 to 3, wherein the threshold for consecutive counts is set to 3 or more.

5. The respiratory rate measuring device according to any one of claims 1 to 3, wherein the threshold for consecutive counts is set to be 2 or more and 10 or less.

6. The respiratory rate measuring device according to any one of claims 1 to 3, wherein each determination threshold used by the respiratory waveform determination unit to determine whether or not the waveforms are similar is a dynamic threshold that is dynamically changed and set based on the waveform data acquired by the waveform acquisition unit.

7. The respiratory rate measuring device according to any one of claims 1 to 3, wherein the waveform acquisition unit acquires the waveform data based on the detection result of a surface pressure sensor which is placed below the object to be measured and detects the surface pressure acting on the object due to its movement.

8. The respiratory rate measuring device according to claim 7, wherein the surface pressure sensor is in the form of a flexible sheet.

9. A respiratory rate measuring device according to any one of claims 1 to 3, further comprising an infant apnea determination unit that determines that an infant is in an apneic state when the respiratory rate per unit time of the infant calculated by the respiratory rate calculation unit falls below a preset lower limit.

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