Analysis system, analysis method, program, and earphone

Abstract

This analysis system comprises a control unit that, on the basis of a first signal that is a photoplethysmographic pulse wave signal obtained from a first site of a measurement target and a second signal that is a photoplethysmographic pulse wave signal obtained from a second site different from the first site of the measurement target, obtains a difference between a waveform of the first signal and a waveform of the second signal. The control unit estimates circulatory dynamics information that is information on circulatory dynamics of the measurement target on the basis of the first signal, the second signal, and the difference.

Description

Analysis System, Analysis Method, Program, and Earphone

[0001] The present invention relates to an analysis system, an analysis method, a program, and an earphone.

[0002] There is a technology for obtaining information related to circulatory dynamics using a wearable device for health management.

[0003] International Publication No. 2022 / 116160

[0004] Liu, J. et al. Multi-wavelength photoplethysmography method for skin arterial pulse extraction. Biomed. Opt. Express 7, 4313-4326 (2016).Franklin, D. et al. Synchronized wearables for the detection of haemodynamic states via electrocardiography and multispectral photoplethysmography. Nat Biomed Eng 7, 1229-1241 (2023).Montanari, A., Ferlini, A., Balaji, A. N., Mascolo, C. & Kawsar, F. EarSet: A Multi-Modal Dataset for Studying the Impact of Head and Facial Movements on In-Ear PPG Signals. Sci Data 10, 850 (2023).Buschmann, J. P. & Huang, J New Ear Sensor for Mobile, Continuous and Long Term Pulse Oximetry, EMBS, 2010.Tigges, T. et al. In-ear photoplethysmography for central pulse waveform analysis in non-invasive hemodynamic monitoring. Current Directions in Biomedical Engineering 3, 587-590 (2017).Eid, A.-M. et al. Using the ear photoplethysmographic waveform as an early indicator of central hypovolemia in healthy volunteers utilizing LBNP induced hypovolemia model. Physiol. Meas.44, (2023).Javed, F. et al. Respiration-induced changes in ear photoplethysmography relates to relative blood volume during hemodialysis. Conf. Proc. IEEE Eng. Med. Biol. Soc. 2010, 859-862 (2010).Hickey, M., Phillips, JP & Kyriacou, PA (2015). The effect of vascular changes on the Photoplethysmographic signal at different hand elevations. Physiological Measurement, 36(3), pp. 425-440. doi: 10.1088 / 0967-3334 / 36 / 3 / 425.

[0005] However, this did not necessarily mean that highly accurate information could be obtained.

[0006] In view of the above circumstances, the present invention aims to provide a technology that enables the acquisition of more accurate information regarding circulatory dynamics.

[0007] One aspect of the present invention is an analysis system comprising a control unit that obtains the difference between the waveform of the first signal and the waveform of the second signal based on a first signal which is a photoplethysmography signal obtained from a first part of the object to be measured and a second signal which is a photoplethysmography signal obtained from a second part of the object to be measured that is different from the first part, and the control unit estimates circulatory dynamics information which is information relating to the circulatory dynamics of the object to be measured based on the first signal, the second signal and the difference.

[0008] One aspect of the present invention is an analysis method performed by an analysis system, comprising: a first signal which is a photoplethysmography signal obtained from a first part of a target to be measured; and a second signal which is a photoplethysmography signal obtained from a second part of the target to be measured that is different from the first part, and a control unit which obtains the difference between the waveform of the first signal and the waveform of the second signal, wherein the control unit estimates circulatory dynamics information which is information relating to the circulatory dynamics of the target to be measured based on the first signal, the second signal and the difference, the analysis method comprising: an acquisition step in which the control unit obtains the difference based on the first signal and the second signal; and an estimation step in which the control unit estimates the circulatory dynamics information based on the first signal, the second signal and the difference.

[0009] One aspect of the present invention is a program for causing a computer to function as the above-mentioned analysis system.

[0010] One aspect of the present invention is an earphone comprising a photoplethysmography sensor, an acceleration sensor, and a housing that accommodates the photoplethysmography sensor and the acceleration sensor.

[0011] This invention makes it possible to obtain more accurate information regarding circulatory dynamics.

[0012] An explanatory diagram illustrating the analysis system of the embodiment. A diagram showing an example of the hardware configuration of the analysis device in the embodiment. A flowchart showing an example of the processing flow performed by the analysis device in the embodiment. A diagram showing an example of an analysis system equipped with a tilt measuring instrument in a modified example. A diagram showing an example of an analysis system equipped with earphones in a modified example. A diagram showing a first example of the relationship between posture and the first and second parts in a modified example. A diagram showing a second example of the relationship between posture and the first and second parts in a modified example. A diagram showing a third example of the relationship between posture and the first and second parts in a modified example. A diagram showing an example of an equivalent circuit of blood vessels in a modified example. A diagram showing an example of the results obtained from the equivalent circuit of blood vessels in a modified example. A first diagram showing an example of experimental results in a modified example. A second diagram showing an example of experimental results in a modified example. A third diagram showing an example of experimental results in a modified example. A bird's-eye view showing a first example of an upward-facing sensor equipped in earphones in a modified example. A bird's-eye view showing a first example of a downward-facing sensor equipped in earphones in a modified example. An explanatory diagram of direction and axis in a modified example. A bird's-eye view showing a second example of an upward-facing sensor equipped in earphones in a modified example. A bird's-eye view showing a second example of a downward-facing sensor in the earphones in a modified example.

[0013] (Embodiment) Figure 1 is an explanatory diagram illustrating an analysis system 100 according to an embodiment. The analysis system 100 comprises a first sensor 101, a second sensor 102, and an analysis device 1. The analysis device 1 includes a control unit 11 which has a processor 91 such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), or NPU (Neural Network Processing Unit) connected by a bus, and a memory 92, and executes a program.

[0014] The first sensor 101 is a sensor that performs a predetermined measurement on a first part of the object 9 (an example of a measurement target) and obtains a photoplethysmography signal. Therefore, the first sensor 101 is a sensor that obtains a photoplethysmography signal (hereinafter referred to as the "first signal") obtained from the first part of the object 9. The first sensor 101 is, for example, a photoplethysmography sensor.

[0015] The second sensor 102 is a sensor that performs a predetermined measurement on a second part of the object 9 and obtains a photoplethysmography signal. Therefore, the second sensor 102 is a sensor that obtains a photoplethysmography signal (hereinafter referred to as the "second signal") obtained from the second part of the object 9. The second sensor 102 is, for example, a photoplethysmography sensor. The second part is different from the first part.

[0016] In the example in Figure 1, subject 9 is a person. However, subject 9 is not necessarily limited to a person; it could be an animal other than a person, such as a dog, cat, bird, or fish.

[0017] Furthermore, the first and second parts may be located opposite each other, for example. The first part may be, for example, the tragus. As mentioned above, the first and second parts may be located opposite each other, so if the first part is the tragus, the second part may be, for example, the antitragus.

[0018] The control unit 11 performs, for example, a waveform difference acquisition process. The waveform difference acquisition process is a process to obtain the difference between the waveform of the first signal and the waveform of the second signal (hereinafter referred to as "waveform difference"). This waveform difference is information about peripheral blood vessels. The control unit 11 also performs, for example, an estimation process. The estimation process is a process to estimate circulatory dynamics information, which is information about the circulatory dynamics of the target 9, based on the first signal, the second signal, and the waveform difference.

[0019] The process of obtaining circulatory dynamics information based on waveform differences may be estimated using, for example, the technology disclosed in Patent Document 1. Alternatively, it may be estimated using, for example, a trained mathematical model that estimates circulatory dynamics information based on waveform differences. A trained mathematical model refers to a mathematical model that has been trained using machine learning techniques until predetermined conditions for the termination of training are met. The predetermined conditions for the termination of training can be any conditions for the termination of training, but for example, it may be a condition that the change in the mathematical model due to loss-based updates is smaller than a predetermined change, or it may be a condition that a predetermined number of training sessions have been performed.

[0020] Hemodynamic information may include, for example, the blood pressure of subject 9, the peripheral vascular compliance of subject 9, or the peripheral vascular resistance of subject 9.

[0021] Figure 1 shows image G101. In image G101, the horizontal axis represents time, and the vertical axis represents the signal strength of the photoplethysmography (PSL) wave. The zero point on the horizontal axis is defined as the end of the pulse wave expansion. Image G101 shows two graphs, one of which is an example of the first signal, and the other is an example of the second signal. The control unit 11 performs waveform difference acquisition processing to acquire the difference between, for example, the waveform of the first signal shown in image G101 and the waveform of the second signal shown in image G101. The control unit 11 then performs estimation based on the obtained difference (i.e., waveform difference).

[0022] <Effects of Estimation Processing> The effects of estimation processing will be explained. Photoplethysmography is a technique that measures blood volume by irradiating with light and measuring its absorption, reflection, or transmission. Therefore, the amount of blood at the location where light is irradiated, such as the first or second site, will affect the measurement result.

[0023] As is well known, gravity acts on animals living on Earth. Therefore, considering this, the measurement results may change depending on the positional relationship of the measurement site with respect to gravity. For example, the measurement results for each site may differ depending on whether the line connecting the first and second sites is perpendicular to gravity or parallel to gravity.

[0024] If the line connecting the first and second parts is parallel to gravity, the difference in hydrostatic pressure will result in a difference in the amount of blood stored in, for example, capillaries and venules. This difference will manifest, for example, as a difference in peripheral vascular compliance or peripheral vascular resistance between the first and second parts. For example, if both the first and second parts are parts of a finger and the line connecting them is parallel to gravity, a difference in hydrostatic pressure of approximately 1.2 mmHg will occur between the first and second parts. Also, for example, if both the first and second parts are parts of the external auditory canal and the line connecting them is parallel to gravity, a pressure difference of approximately 0.6 mmHg will occur between the first and second parts.

[0025] These differences manifest as differences between the waveforms of the photoplethysmography (PPS) signals obtained from the first site and those obtained from the second site, as shown in image G101 of Figure 1. This is also demonstrated in the experimental results shown in Figures X1 and X2, which will be described later in the modified examples. Therefore, the estimation process that performs estimation based on waveform differences takes the effect of gravity into consideration. Consequently, the execution of the estimation process yields more accurate information on circulatory dynamics than estimations that do not rely on waveform differences.

[0026] Furthermore, the technologies disclosed in Non-Patent Documents 1-8 and Patent Document 9 did not take the effect of gravity into consideration. In other words, estimation based on waveform differences was not performed. The reason for this is that in the field of research on technologies for inferring circulatory dynamics information based on photoplethysmography signals, the idea that gravity should affect the measurement simply did not exist.

[0027] <Example of Hardware Configuration of Analysis Device 1> Figure 2 shows an example of the hardware configuration of analysis device 1 in the embodiment. Analysis device 1 includes a control unit 11 that executes a program, and functions as a device comprising the control unit 11, an interface unit 12, and a storage unit 13 through the execution of the program.

[0028] More specifically, the processor 91 reads the program stored in the storage unit 13 and stores the read program in the memory 92. By executing the program stored in the memory 92, the processor 91 functions as a device comprising a control unit 11, an interface unit 12, and a storage unit 13.

[0029] The control unit 11 controls the operation of each functional unit of the analysis device 1. As described above, the control unit 11 performs, for example, waveform difference acquisition processing. As described above, the control unit 11 performs, for example, estimation processing. The control unit 11 acquires, for example, information stored in the memory unit 13. Specifically, the process of acquiring information stored in the memory unit 13 is reading.

[0030] The interface unit 12 includes a communication interface for connecting the analysis device 1 to an external device. The interface unit 12 communicates with the external device via wired or wireless connection.

[0031] The external device may be, for example, a first sensor 101. In this case, the control unit 11 acquires the first signal through communication via the interface unit 12. The external device may be, for example, a second sensor 102. In this case, the control unit 11 acquires the second signal through communication via the interface unit 12.

[0032] The interface unit 12 may include input devices such as a mouse, keyboard, or touch panel. The interface unit 12 may also be configured as an interface connecting these input devices to the analysis device 1. In this way, the input devices of the interface unit 12 receive various types of information to the analysis device 1 via wired or wireless connections. Note that the information does not necessarily have to be input to the communication interface of the interface unit 12; it may also be input to the input devices of the interface unit 12.

[0033] The interface unit 12 outputs various types of information, for example. The interface unit 12 includes, for example, a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, or an organic EL (Electro-Luminescence) display, as well as a speaker. The interface unit 12 may be configured as an interface for connecting these display devices or speakers to the analysis device 1. Therefore, the interface unit 12 may output information input to its input device as an image or sound, for example.

[0034] The storage unit 13 is configured using a computer-readable storage medium (non-transitory computer-readable recording medium) such as a magnetic hard disk drive or a semiconductor storage device. The storage unit 13 stores various information related to the analysis device 1. The storage unit 13 stores various information generated by the operation of the control unit 11, for example. The storage unit 13 may reside, for example, on the cloud.

[0035] Figure 3 is a flowchart showing an example of the processing flow performed by the analysis device 1 in the embodiment. The control unit 11 performs waveform difference acquisition processing (step S101). Next, the control unit 11 performs estimation processing (step S102).

[0036] The analysis device 1, configured in this way, performs estimation processing. As a result, the analysis device 1 can obtain more accurate information regarding circulatory dynamics, as described in <Effects of Estimation Processing>.

[0037] Furthermore, the analysis system 100 configured in this way includes an analysis device 1. Therefore, the analysis system 100 can acquire information on circulatory dynamics with higher accuracy.

[0038] (Variation) In addition, the estimation process may also estimate the circulatory dynamics information based on the tilt information. The tilt information is information that shows the tilt of object 9 with respect to gravity.

[0039] Figure 4 shows an example of the analysis system 100a in a modified example. The analysis system 100a differs from the analysis system 100 in that it further includes a tilt measuring instrument 201.

[0040] The tilt measuring device 201 measures the tilt of object 9 with respect to gravity. Therefore, the tilt measuring device 201 acquires tilt information. The tilt measuring device 201 is, for example, a gyroscope. The tilt measuring device 201 may also be, for example, an accelerometer. The accelerometer may be, for example, a 3-axis accelerometer, a 6-axis accelerometer, or a 9-axis accelerometer. The tilt measuring device 201 may also be, for example, an inertial measurement unit or a tilt sensor.

[0041] In the analysis system 100a, the control unit 11 estimates circulatory dynamics information based on the tilt information obtained from the tilt measuring device 201 during the estimation process. The control unit 11 obtains the tilt information from the tilt measuring device 201 wirelessly or via a wired connection, for example, through the interface unit 12.

[0042] Furthermore, the analysis system 100 or analysis system 100a does not necessarily need to have only two sensors for obtaining photoplethysmography signals. The analysis system 100 or analysis system 100a may have three or more sensors for obtaining photoplethysmography signals. These sensors measure different parts of the body. Each sensor that obtains a photoplethysmography signal outputs a photoplethysmography signal. The control unit 11 then receives these signals. Therefore, it can be said that the control unit 11 obtains photoplethysmography signals obtained from N (where N is three or more) different parts of the object being measured.

[0043] In an analysis system 100a equipped with three or more sensors for obtaining photoplethysmography signals, the control unit 11 may, for example, perform a decision process. The decision process is a process of determining, based on slope information, which two differences to obtain from each photoplethysmography signal obtained from N different locations on the object to be measured. In the waveform difference acquisition process, the control unit 11 that performs the decision process takes one of the photoplethysmography signals determined in the decision process as the first signal and the other as the second signal, and obtains the difference between the waveform of the first signal and the waveform of the second signal.

[0044] In the determination process, for example, it is a process of obtaining the difference in waveforms of the photoplethysmogram signals obtained from two locations through which each straight line passing through two out of N locations has the highest parallelism with respect to the direction of gravity.

[0045] The determination process does not necessarily have to be executed. For example, in the waveform difference acquisition process, the control unit 11 obtains the difference in waveforms between the p-th signal and the q-th signal, including the difference between the waveform of the first signal and the waveform of the second signal, and estimates the circulatory dynamic information based on all or some of the obtained differences including the difference between the waveform of the first signal and the waveform of the second signal. Since all the obtained differences include the difference between the waveform of the first signal and the waveform of the second signal, estimating the circulatory dynamic information based on all or some of the obtained differences including the difference between the waveform of the first signal and the waveform of the second signal is an example of the estimation process.

[0046] Note that the p-th signal is a photoplethysmogram signal obtained from the p-th site. The p-th site is the p-th site among the N sites according to a predetermined rule. The q-th signal is a photoplethysmogram signal obtained from the q-th site different from the p-th site. The q-th site is the q-th site among the N sites according to a predetermined rule and is different from the p-th site. Here, p is an integer from 1 to N, and q is an integer different from p and from 1 to N. [[ID=B]]

[0047] Estimating the circulatory dynamic information based on all or some of the obtained differences including the difference between the waveform of the first signal and the waveform of the second signal may be, for example, an estimation using a learned mathematical model obtained in advance by a machine learning technique, and the mathematical model estimates the circulatory dynamic information based on all or some of the above differences including the difference between the waveform of the first signal and the waveform of the second signal.

[0048] FIG. 5 is a diagram showing an example of the analysis system 100b in a modified example. The analysis system 100b is different from the analysis system 100 in that it includes the earphone 301. The earphone 301 is an earphone including a housing 300, a first sensor 101, and a second sensor 102. The housing 300 is the housing of the earphone 301 and houses at least the first sensor 101 and the second sensor 102.

[0049] In the example shown in Figure 5, the earphone 301 is equipped with two sensors, a first sensor 101 and a second sensor 102. However, the earphone 301 is not necessarily limited to these two sensors; it may be equipped with N sensors. The earphone 301 may also be equipped with a tilt measuring device 201. The analysis system 100b may be a smart ring. Figures 14 to 17, described later, show an example of a bird's-eye view of the first sensor 101 and the second sensor 102 equipped in the earphone 301.

[0050] Furthermore, the ear tissue is thin, allowing light to pass through. Therefore, if the measurement site of the sensor that obtains the photoplethysmography signal is a part of the ear, the measurement results will be strongly influenced by ambient light. Also, since light is absorbed or reflected when it hits cartilage, the measurement results will be strongly influenced by cartilage. Normally, a sensor that obtains the photoplethysmography signal positioned downward relative to gravity will measure tissue containing more blood, and therefore the light emitted from the sensor will be absorbed more strongly. Here, "normally" is defined as the skin tissue at all measurement sites being uniform and having sufficient thickness relative to the penetration depth of the light source. Incidentally, the sensor that obtains the photoplethysmography signal may be a photoplethysmography sensor.

[0051] Furthermore, when comparing a sensor that obtains a photoplethysmography signal positioned downward relative to gravity (hereinafter referred to as the "downward sensor") with a sensor that obtains a photoplethysmography signal positioned upward relative to gravity (hereinafter referred to as the "upward sensor"), the measurement site of the downward sensor is positioned more downward relative to gravity than the measurement site of the upward sensor.

[0052] Based on the above, when the sensor that obtains the photoplethysmography signal is a photoplethysmography sensor, the measurement accuracy is improved if the condition that the light source of the downward-facing sensor emits light with a wavelength greater than or equal to the wavelength of light emitted by the light source of the upward-facing sensor (hereinafter referred to as the "wavelength condition") is met. Furthermore, when the sensor that obtains the photoplethysmography signal is a photoplethysmography sensor, the measurement accuracy is improved if the condition that the distance between the light source of the downward-facing sensor and the detector of the downward-facing sensor is greater than or equal to the distance between the light source of the upward-facing sensor and the detector of the upward-facing sensor (hereinafter referred to as the "distance condition") is met.

[0053] The upward-facing sensor is either the first sensor 101 or the second sensor 102, and the downward-facing sensor is the other of the first sensor 101 or the second sensor 102. Therefore, when the wavelength condition is met, one of the first sensor 101 or the second sensor 102 is positioned downward relative to gravity, and the other is positioned upward relative to gravity. The light source of the downward-facing sensor, which is positioned downward relative to gravity, outputs light with a wavelength greater than or equal to the wavelength of the light output by the light source of the upward-facing sensor, which is positioned upward relative to gravity.

[0054] Furthermore, if the distance condition is met, one of the first sensor 101 or the second sensor 102 is positioned downward with respect to gravity, and the other is positioned upward with respect to gravity, and the distance between the light source and detector of the downward-facing sensor (the one positioned downward with respect to gravity) is greater than or equal to the distance between the light source and detector of the upward-facing sensor (the other one positioned upward with respect to gravity).

[0055] For example, if the light source for the upward-facing sensor is a light source with a wavelength of 515 nm to 530 nm, the light source for the downward-facing sensor may be a light source that outputs light with a wavelength of 515 nm or greater. Therefore, in this case, the light source for the downward-facing sensor may be a light source that outputs light with a wavelength of 570 nm to 620 nm. The distance between the light source and the detector may be approximately 2.5 mm to 4.5 mm for the downward-facing sensor, for example, if the distance for the upward-facing sensor is approximately 1 mm to approximately 3 mm.

[0056] Furthermore, if the measurement site of the sensor that obtains the photoplethysmography signal is a part of the ear, the measurement site may be a location that is appropriate for the degree of vascular concentration, tissue thickness, cartilage, etc.

[0057] In the example shown in Figure 5, the earphone 301 was described as being equipped with a first sensor 101 and a second sensor 102. However, the first sensor 101 and the second sensor 102 do not necessarily have to be provided in the earphone. The first sensor 101 and the second sensor 102 may be provided in, for example, the smart ring described above. The first sensor 101 and the second sensor 102 may be provided in, for example, the smart watch described above. The first sensor 101 and the second sensor 102 may be provided in, for example, the smart glasses described above. Furthermore, the first sensor 101 and the second sensor 102 may be provided in, for example, the smart wear described above.

[0058] When the first sensor 101 and the second sensor 102 are provided in something other than earphones, the light output by the light source of the upward-facing sensor or downward-facing sensor may be, for example, green (around 520 nm), red (around 660 nm), near-infrared (around 880-940 nm), or infrared. When the first sensor 101 and the second sensor 102 are provided in something other than earphones, the distance between the light source and the detector may be longer than when the first sensor 101 and the second sensor 102 are provided in earphones. For example, if the light output by the light source is red or infrared, the longer distance may be, for example, approximately 12 mm.

[0059] Furthermore, the earphone 301 in Figure 5 may also include a tilt measuring device 201 in addition to the housing 300, the first sensor 101, and the second sensor 102. In this case, the housing 300 may also house the tilt measuring device 201 in addition to the first sensor 101 and the second sensor 102. That is, the earphone 301 may include a photoplethysmography sensor, an acceleration sensor, and a housing that houses the photoplethysmography sensor and the acceleration sensor.

[0060] <Relationship between posture and measurement site> The first and second measurement sites may be in positions corresponding to the posture of the subject 9. Figures 6 to 8 show examples of the relationship between posture and the first and second measurement sites.

[0061] Figure 6 shows a first example of the relationship between posture and the first and second body parts in a modified example. More specifically, Figure 6 shows the relationship between posture and the first and second body parts when the posture of subject 9 is supine. An example of the first body part is indicated by arrow K1 in Figure 6, specifically pointing to the tragus or its vicinity. An example of the second body part is indicated by arrow K2 in Figure 6, specifically pointing to the antitragus or its vicinity.

[0062] Figure 7 shows a second example of the relationship between posture and the first and second parts in a modified example. More specifically, Figure 7 shows the relationship between posture and the first and second parts when the posture of subject 9 is semi-sitting. An example of the first part is indicated by arrow K3 in Figure 7, which specifically points slightly above or near the tragus. An example of the second part is indicated by arrow K4 in Figure 7, which specifically points slightly below the antitragus (between the intertragal notch and the antitragus) or near there.

[0063] Figure 8 shows a third example of the relationship between posture and the first and second parts in a modified example. More specifically, Figure 8 shows the relationship between posture and the first and second parts when the posture of subject 9 is sitting or standing. An example of the first part is indicated by arrow K5 in Figure 8, specifically pointing to the area above the ear canal. An example of the second part is indicated by arrow K6 in Figure 8, specifically pointing to the area below the ear canal (intertragal notch).

[0064] Furthermore, as shown in Figure 8, it is easier to position the sensors in an ideal location (vertical direction of the body) when the user is sitting or standing compared to when they are lying down.

[0065] <Equivalent Circuit> To deepen understanding, Figures 9 and 10 illustrate the equivalent circuit of a blood vessel that explains the relationship between blood accumulation and pulse wave waveform, and provide an example of the results obtained from that equivalent circuit.

[0066] Figure 9 shows an example of an equivalent circuit of blood vessels in a modified example. In Figure 9, Q(t) is defined as the blood volume in the aortic arch at time t. In Figure 9, P(t) is defined as the blood pressure in the aortic arch at time t. In Figure 9, resistance Zc represents the resistance to blood flow in the aortic valve and arteries. In Figure 9, capacitor C represents peripheral vascular compliance. In Figure 9, resistance R represents peripheral vascular resistance. Note that the “sensor” in Figure 9 refers to a photoplethysmography sensor.

[0067] Figure 10 shows an example of the results obtained from the equivalent circuit of a blood vessel in a modified example. In Figure 10, φ is the phase angle of the combined impedance due to peripheral vascular resistance and peripheral vascular compliance. C in Figure 10 Ｍ The definition is peripheral vascular compliance. As can be seen from the symbol indicating resistance R in Figure 10, J101 is part of the circuit, but here it represents peripheral vascular resistance. J102 in Figure 10 is capacitor C Ｍ As can be seen from the symbols indicating it, it is part of the circuit, but here it shows peripheral vascular compliance. J103 in Figure 10 shows the vector of the combined impedance.

[0068] The results in Figure 10 show that a change in the phase angle of the secondary impedance in Figure 9 causes a change in the shape of the pulse wave waveform. Furthermore, the results in Figure 10 show that the phase angle of the secondary impedance in Figure 9 is relatively determined by changes in peripheral vascular resistance and peripheral vascular compliance. Therefore, the results in Figure 10 show that blood accumulation in capillaries and venules affects the shape of the pulse wave waveform if it changes either or both of the peripheral vascular resistance and / or peripheral vascular compliance.

[0069] <Experimental Results> To deepen our understanding of analysis systems 100, 100a, and 100b, examples of experimental results related to analysis systems 100, 100a, and 100b are shown.

[0070] Figure 11 is the first figure showing an example of experimental results in a modified example. Figure 11 shows an example of the conversion of a photoplethysmography signal obtained from a finger, where the object 9 changes the orientation of its own palm. In Figure 11, the horizontal axis d1 represents time, and the vertical axis d2 represents the count. The count here is defined as the output voltage value of the detector, which has been converted to a digital value by an AD converter. More specifically, the count here is the value that has been amplified by an amplifier, etc., and then discretized by an AD converter.

[0071] Graph G201 in Figure 11 is a graph obtained from the graph in image G102. In the graph in image G102, the horizontal axis represents time, and the vertical axis represents the signal strength of the photoplethysmography (PSL) wave. The zero point on the horizontal axis of the graph in image G102 is defined as the start time of measurement. Image G102 shows two graphs; one is an example of the first signal, and the other is an example of the second signal.

[0072] Graph G201 shows that when the palm is facing downwards, blood accumulates and the measurement site of the sensor facing downwards relative to gravity becomes darker. Darkening means that the amount of light detected by the photodetector decreases. Graph G201 shows that when the palm is facing upwards, blood decreases and the area becomes brighter. Brightening means that the amount of light detected by the photodetector increases. Note that at the point when the value of the horizontal axis d1 has elapsed 20 seconds after the start of measurement, subject 9 changed the orientation of its palm from downwards to upwards. Figure 11 shows that the amplitude, DC component, and waveform shape of the photoplethysmography signal changed due to the effect of gravity. Figure 11 also shows that there is almost no change in blood pressure due to the change in the orientation of the palm.

[0073] Furthermore, image G102 in Figure 11 shows that the systolic peak is delayed in the waveform measured by the downward-facing sensor compared to the waveform measured by the upward-facing sensor. Also, compared to the waveform measured by the upward-facing sensor, the waveform measured by the downward-facing sensor shows a phase delay, indicating that a waveform change on the integration side has occurred. The definition of a waveform change on the integration side is an increase in the integration ratio as described in Patent Document 1.

[0074] Figure 12 is a second figure showing an example of experimental results in a modified example. Figure 12 shows an example of the change in the photoplethysmography signal obtained from the antitragus when subject 9 changes position from prone to supine. In Figure 12, the horizontal axis d3 represents time, and the vertical axis d4 represents counts. The definition of count here is the output voltage value of the detector, which has been converted to a digital value by the AD converter. Graph G202 in Figure 12 is a graph obtained from the graph of image G101, which is also shown in Figure 1. Image G101 in Figure 12 shows that, compared to the supine position, a delay in the systolic peak occurs in the supine position, and a change in the waveform on the integral side occurs.

[0075] Graph G202 shows that when the patient is in a prone position facing upward, the blood volume decreases and the graph becomes brighter. Brighter and darker means that the amount of light detected by the photodetector increases. Note that subject 9 changed position from prone to supine when the value on the horizontal axis d3 was 20 seconds after the start of measurement. Figure 12 shows that the amplitude, DC component, and waveform shape of the photoplethysmography signal changed due to the change in body position.

[0076] Figure 13 is a third figure showing an example of experimental results in a modified example. Figure 13 shows an example of the change in the photoplethysmography signal obtained from the tragus when subject 9 changes its position from prone to supine. In Figure 13, the horizontal axis d5 indicates time, and the vertical axis d6 indicates the count. The definition of the count here is the output voltage value of the detector, which has been converted to a digital value by the AD converter.

[0077] Graph G203 in Figure 13 is a graph obtained from the graph in image G103. In the graph in image G103, the horizontal axis represents time, and the vertical axis represents the signal strength of the photoplethysmography (PPS) wave. The zero point on the horizontal axis of the graph in image G103 is defined as the end of the pulse wave expansion. Image G103 shows two graphs; one is an example of the first signal, and the other is an example of the second signal.

[0078] Image G103 in Figure 13 shows that a delay occurs in the systolic peak and that the waveform changes on the integrated side. Note that subject 9 changed position from prone to supine when the value of d5 on the horizontal axis was 20 seconds after the start of measurement. Figure 13 shows that the change in the DC component of the photoplethysmography signal and the change in the waveform may not coincide due to the change in body position.

[0079] Therefore, the experimental results show the following. First, regarding waveform deformation, the experimental results show that there is no discrepancy with the state of peripheral blood accumulation induced by changes in posture. Next, we will explain the DC component of the photoplethysmography signal, which is generally considered to represent peripheral blood accumulation. The experimental results show that there is a discrepancy between the relationship between blood accumulation due to posture changes and the change in the DC component. This indicates that focusing on waveform changes can more accurately capture the phenomenon of changes in peripheral blood volume. The reason why the DC component is generally considered to represent peripheral blood accumulation is that when there is little blood, the absorbance is low, and therefore the DC component decreases, and when there is a lot of blood, the absorbance is high, and therefore the DC component increases.

[0080] The waveform differences may be represented, for example, by amplitude or DC component. The waveform differences may be represented, for example, by the difference or ratio of the value obtained by dividing the amplitude by the DC component, or by the amount of change in the onset at the end of expansion or the peak position of the systolic phase (local PTT) of the waveform.

[0081] Furthermore, waveform differences may be represented, for example, by differences in the integration ratio described above. Alternatively, waveform differences may be represented by Dynamic Time Warping, as described in Reference 1 below. Furthermore, waveform differences may be represented by a predetermined index used in a given machine learning technique.

[0082] Reference 1: P. Senin. “Dynamic time warping algorithm review”, CSDL Technical report, 2009.

[0083] <Example of earphone 301> Let's explain earphone 301 in more detail.

[0084] In the earphone 301, the housing 300 has a shape that is suitable for a person's right or left ear. More specifically, in the earphone 301, the housing 300 has a shape that can be fitted into a person's right or left ear. That is, in the earphone 301, the housing 300 has a shape that can be fitted into a person's ear.

[0085] Such an earphone 301 may, when fitted into either the right or left ear of a person in a standing or sitting position, have at least two photoplethysmography sensors positioned such that they are tilted towards the head and tail directions relative to the dorsoventral direction of the person. More specifically, such an earphone 301 may, when fitted into either the right or left ear of a person in a standing or sitting position, have at least two photoplethysmography sensors positioned such that they are tilted towards the head and tail directions relative to the dorsoventral direction of the person. In other words, such an earphone 301 may, when fitted into the ear of a person in a standing or sitting position, have at least two photoplethysmography sensors positioned such that they are tilted towards the head and tail directions relative to the dorsoventral direction of the person. Such an earphone 301 may further include a housing 300 that houses a tilt measuring device 201 in addition to the first sensor 101 and the second sensor 102.

[0086] In the earphone 301, the housing 300 has a shape that is suitable for a person's right or left ear. More specifically, in the earphone 301, the housing 300 has a shape that can be fitted into a person's right or left ear. That is, in the earphone 301, the housing 300 has a shape that can be fitted into a person's ear.

[0087] Such an earphone 301 may, when fitted into either the right or left ear of a person in a supine position, have at least two photoplethysmography sensors positioned such that they are tilted ventrally and dorsally relative to the head-to-tail direction of the person. More specifically, such an earphone 301 may, when fitted into either the right or left ear of a person in a supine position, have at least two photoplethysmography sensors positioned such that they are tilted ventrally and dorsally relative to the head-to-tail direction of the person. That is, such an earphone 301 may, when fitted into the ear of a person in a supine position, have at least two photoplethysmography sensors positioned such that they are tilted ventrally and dorsally relative to the head-to-tail direction of the person. Such an earphone 301 may further include a housing 300 that houses a tilt measuring device 201 in addition to the first sensor 101 and the second sensor 102.

[0088] Let's now explain a more specific example of the earphone 301. An example of the upward and downward sensors provided by the earphone 301 is shown using Figures 14 to 18. As mentioned above, the upward sensor is either the first sensor 101 or the second sensor 102, and the downward sensor is the other of the first sensor 101 or the second sensor 102. For the sake of simplicity, Figures 14 to 18 will explain using the example where the upward sensor is the first sensor 101 and the downward sensor is the second sensor 102.

[0089] Figure 14 is a bird's-eye view showing a first example of an upward-facing sensor provided in the earphone 301 in a modified example. Figure 15 is a bird's-eye view showing a first example of a downward-facing sensor provided in the earphone 301 in a modified example. More specifically, the upward-facing sensor in Figure 14 and the downward-facing sensor in Figure 15 are examples of an upward-facing sensor and a downward-facing sensor that can be attached to the ear of a person sitting or standing.

[0090] The upward-facing sensor in Figure 14 comprises a light source 111 and a detector 112. The upward-facing sensor in Figure 14 is a photoplethysmography sensor, the light source 111 is the light source provided by the photoplethysmography sensor, and the detector 112 is the detector provided by the photoplethysmography sensor. The downward-facing sensor in Figure 15 comprises a light source 121 and a detector 122. The downward-facing sensor in Figure 15 is a photoplethysmography sensor, the light source 121 is the light source provided by the photoplethysmography sensor, and the detector 122 is the detector provided by the photoplethysmography sensor.

[0091] Vector K7 is a vector perpendicular to the plane of the upward-facing sensor in Figure 14 that faces inward when the upward-facing sensor is attached to the ear. Vector K8 is a vector perpendicular to the plane of the upward-facing sensor in Figure 14 that faces outward when the upward-facing sensor is attached to the ear. Vector K9 is a vector perpendicular to the plane of the downward-facing sensor in Figure 15 that faces inward when the downward-facing sensor is attached to the ear. Vector K10 is a vector perpendicular to the plane of the downward-facing sensor in Figure 15 that faces outward when the downward-facing sensor is attached to the ear.

[0092] In the upward-facing sensor of Figure 14, the positions of the light source 111 and the detector 112 do not necessarily have to be in the same relative position as in Figure 14. For example, the positions of the light source 111 and the detector 112 may be reversed compared to the example in Figure 14. Similarly, in the downward-facing sensor of Figure 15, the positions of the light source 121 and the detector 122 do not necessarily have to be in the same relative position as in Figure 15. For example, the positions of the light source 121 and the detector 122 may be reversed compared to the example in Figure 15.

[0093] Furthermore, when upward and downward sensors are provided in the ear of a person in a seated or standing position, the axis perpendicular to the elliptical hole may be parallel to the external auditory canal. Also, when upward and downward sensors are provided in the ear of a person in a seated or standing position, the upward and downward sensors are positioned at an angle toward the cranial and craudal directions, respectively, rather than the dorsal-ventral direction of a human. Note that "sensor tilted" means that the direction of the optical axis of the sensor is directed toward the cranial or craudal direction, relative to the state where the direction of the sensor's optical axis is in the dorsal-ventral direction. In other words, when a sensor is tilted, with respect to rotation around the parallel axis (lateral axis), and considering counterclockwise rotation as viewed from the left side of a human as positive, and the dorsal direction as 0°, the direction of the optical axes of the upward and downward sensors is not 0° and 180°, respectively. Here, the definition of the cranial-caudal-dorsal-ventral direction of a human is as shown in Figure 16. This method creates an effect of accumulation due to altitude differences between measurement sites, making it possible to measure circulatory dynamics.

[0094] In this case, the upward-facing sensor may be tilted at +45° to +135° when viewed from the left side of a person, with respect to rotation around the parallel axis (Lateral axis) in Figure 16, where counterclockwise rotation is considered positive and the back direction is 0°. The downward-facing sensor may be tilted at +225° to +315°. That is, the tilt angle θ may be, for example, +45 ≤ θ ≤ +135. By doing so, a large difference in altitude is created between the upward-facing and downward-facing sensors during measurement, and the effect of accumulation is increased, thereby improving the accuracy of circulatory dynamics measurement.

[0095] Figure 16 is an explanatory diagram of the directions and axes in a modified example. The XZ plane in the figure is the sagittal plane. The YZ plane in the figure is the coronal plane. The XY plane in the figure is the transverse plane. The person in Figure 16 is standing, and the perpendicular from the top of the head to the floor is parallel to the Z axis. In Figure 16, the axis from ventral to dorsal is parallel to the X axis. In Figure 16, the axis from medial to lateral is parallel to the Y axis. In Figure 16, the axis from cranial to caudal is parallel to the Z axis.

[0096] The lateral axis mentioned above is the axis that runs from medial (inside) to lateral (outside). Also, the dorsal-ventral direction in humans is the direction that runs from ventral to dosal.

[0097] Figure 17 is a bird's-eye view showing a second example of an upward-facing sensor provided in the earphone 301 in a modified example. Figure 18 is a bird's-eye view showing a second example of a downward-facing sensor provided in the earphone 301 in a modified example. More specifically, the upward-facing sensor in Figure 17 and the downward-facing sensor in Figure 18 are examples of an upward-facing sensor and a downward-facing sensor that can be attached to the ear of a person in a seated, supine, or semi-seated position. Hereafter, components having the same function as the upward-facing sensor described in Figure 14 and the downward-facing sensor described in Figure 15 will be denoted by the same reference numerals as in Figure 14 or Figure 15, and their explanation will be omitted.

[0098] Vector K11 is a vector perpendicular to the plane of the upward-facing sensor in Figure 17 that faces inward when the upward-facing sensor is attached to the ear. Vector K12 is a vector perpendicular to the plane of the upward-facing sensor in Figure 17 that faces outward when the upward-facing sensor is attached to the ear. Vector K13 is a vector perpendicular to the plane of the downward-facing sensor in Figure 18 that faces inward when the downward-facing sensor is attached to the ear. Vector K14 is a vector perpendicular to the plane of the downward-facing sensor in Figure 18 that faces outward when the downward-facing sensor is attached to the ear.

[0099] Furthermore, when upward and downward sensors are provided in the ears of a person in a supine or semi-sitting position, the axis perpendicular to the elliptical hole may be parallel to the external auditory canal, as in the examples in Figures 14 and 15. Also, when upward and downward sensors are provided in the ears of a person in a seated supine or semi-sitting position, the upward and downward sensors are positioned at an angle ventral and dorsal, respectively, relative to the cranial-craudal direction of a human. Note that "tilted" means that the direction of the optical axis of the sensor is ventral or dorsal, relative to the state where the direction of the sensor's optical axis is in the cranial-craudal direction. This creates the effect of accumulation due to the difference in altitude between measurement sites, making it possible to measure hemodynamics. However, compared to the examples in Figures 14 and 15, the position is more anterior + lateral / posterior + medial. For example, the solid angle may be 15 to 90 degrees. Note that the cranial-craudal direction is the direction from cranial to craudal.

[0100] In this case, the upward-facing sensor may be tilted at +135° to +225° when viewed from the left side of a person, with respect to rotation around the parallel axis (Lateral axis) in Figure 16, where counterclockwise rotation is considered positive when viewed from the left side of a person, and the back direction is 0°. The downward-facing sensor may be tilted at -45° to +45°. That is, the tilt angle θ may be, for example, -45 ≤ θ ≤ +45. By doing so, a large difference in altitude is created between the upward-facing and downward-facing sensors during measurement, and the effect of accumulation is increased, thereby improving the accuracy of circulatory dynamics measurement.

[0101] Note that the upward-facing sensor in Figure 16 may be tilted outwards, and the downward-facing sensor in Figure 17 may be tilted inwards by up to 45 degrees.

[0102] Furthermore, the distance between the light source and the detector may be a predetermined distance based on signal strength, regardless of orientation.

[0103] Thus, when the part of the earphone that contacts the upper surface of the ear canal (of a typical human) is defined as surface 1, and the part of the earphone that contacts the lower surface of the ear canal is defined as surface 2, the sensors can be placed directly on surface 1 and surface 2 in the standing and sitting positions. Furthermore, in the supine and semi-sitting positions, a surface 3 that faces inward towards the head and contacts the concha, and a surface 4 that contacts the tragus are defined, and sensors can be placed on surface 3 and surface 4, or the upper sensor can be placed in a position that contacts a blood-rich area between surface 1 and surface 4, and the lower sensor can be placed in a position that contacts a blood-rich area between surface 2 and surface 3.

[0104] The analysis device 1 may be implemented using multiple information processing devices connected to each other via a network. In this case, each process executed by the control unit 11 may be performed by multiple information processing devices in a distributed manner.

[0105] Furthermore, all or part of the functions of analysis system 100, analysis system 100a, analysis system 100b, and analysis device 1 may be implemented using hardware such as ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Computer-readable recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may also be transmitted via a telecommunications line.

[0106] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0107] 100, 100a, 100b... Analysis system, 101... First sensor, 102... Second sensor, 1... Analysis device, 11... Control unit, 12... Interface unit, 13... Memory unit, 201... Tilt measuring instrument, 300... Housing, 301... Earphone, 111... Light source, 112... Detector, 121... Light source, 122... Detector, 91... Processor, 92... Memory

Claims

1. An analysis system comprising: a control unit that obtains the difference between the waveform of the first signal and the waveform of the second signal based on a first signal which is a photoplethysmography signal obtained from a first part of the object to be measured and a second signal which is a photoplethysmography signal obtained from a second part of the object to be measured that is different from the first part, wherein the control unit estimates circulatory dynamics information which is information relating to the circulatory dynamics of the object to be measured based on the first signal, the second signal and the difference.

2. The analysis system according to claim 1, wherein the control unit further estimates the circulatory dynamics information based on tilt information, which is information indicating the tilt of the object to be measured with respect to gravity.

3. The analysis system according to claim 1, wherein the first part and the second part are located opposite each other.

4. The analysis system according to claim 1, wherein the circulatory dynamics information indicates the blood pressure of the subject being measured.

5. The analysis system according to claim 1, wherein the hemodynamic information indicates the peripheral vascular compliance of the subject of measurement.

6. The analysis system according to claim 1, wherein the hemodynamic information indicates the peripheral vascular resistance of the subject to measurement.

7. The analysis system according to claim 1, wherein the first part is the tragus and the second part is the antitragus.

8. The analysis system according to claim 1, further comprising: a first sensor which is a photoplethysmography sensor for acquiring the first signal; and a second sensor which is a photoplethysmography sensor for acquiring the second signal.

9. The analysis system according to claim 1, further comprising: an earphone, which is a first sensor that is a photoplethysmography sensor for acquiring the first signal; and a second sensor that is a photoplethysmography sensor for acquiring the second signal.

10. The analysis system according to claim 9, wherein one of the first sensor or the second sensor is positioned downward with respect to gravity, and the other is positioned upward with respect to gravity, and the light source of the downward sensor, which is positioned downward with respect to gravity, outputs light with a wavelength greater than or equal to the wavelength of light output by the light source of the upward sensor, which is positioned upward with respect to gravity.

11. The analysis system according to claim 9, wherein one of the first sensor or the second sensor is positioned downward with respect to gravity, and the other is positioned upward with respect to gravity, and the distance between the light source and detector of the downward-facing sensor (the one positioned downward with respect to gravity) is greater than or equal to the distance between the light source and detector of the upward-facing sensor (the other one positioned upward with respect to gravity).

12. The control unit obtains the difference between the waveform of the p signal and the waveform of the q signal (where p is an integer between 1 and N, and q is an integer between 1 and N that is different from p), which includes the difference between the waveform of the first signal and the waveform of the second signal, from among the photoplethysmography signals obtained from N different locations (N is 3 or more) of the object to be measured, and estimates the circulatory dynamics information based on all or some of the obtained differences, including the difference between the waveform of the first signal and the waveform of the second signal, wherein the p signal is a photoplethysmography signal obtained from the p location, which is the p-th location among the N locations according to a predetermined rule, and the q signal is a photoplethysmography signal obtained from the q location, which is the q-th location among the N locations according to the rule, and is different from the p location, the analysis system according to claim 1.

13. The control unit determines which two differences to obtain from each photoplethysmography signal obtained from N different locations (N is 3 or more) of the object to be measured, based on tilt information which is information indicating the tilt of the object to be measured with respect to gravity, and obtains the difference between the waveform of the first signal and the waveform of the second signal, with one of the determined photoplethysmography signals being the first signal and the other being the second signal.

14. An analysis method performed by an analysis system, comprising: a first signal which is a photoplethysmography signal obtained from a first part of the object to be measured, and a second signal which is a photoplethysmography signal obtained from a second part of the object to be measured different from the first part, wherein the control unit obtains the difference between the waveform of the first signal and the waveform of the second signal, and the control unit estimates circulatory dynamics information which is information relating to the circulatory dynamics of the object to be measured based on the first signal, the second signal and the difference, the analysis method comprising: an acquisition step in which the control unit obtains the difference based on the first signal and the second signal; and an estimation step in which the control unit estimates the circulatory dynamics information based on the first signal, the second signal and the difference.

15. A program for causing a computer to function as an analysis system according to any one of claims 1 to 13.

16. An earphone comprising a photoplethysmography sensor, an accelerometer, and a housing for housing the photoplethysmography sensor and the accelerometer.

17. The earphone according to claim 16, wherein the housing has a shape that can be fitted into a human ear, and when fitted into the ear, at least two of the photoplethysmography sensors are positioned at an angle toward the head and tail direction relative to the dorsoventricular direction of the person, respectively.

18. The earphone according to claim 16, wherein the housing has a shape that can be fitted into a human ear, and when fitted into the ear, at least two of the photoplethysmography sensors are positioned at an angle to the ventral and dorsal directions relative to the head-to-tail direction of the person.

Images