Method and apparatus for detecting heart rate by using photoplethysmography signal from which motion artifact has been removed

Abstract

This method for detecting a heart rate by using a photoplethysmography signal from which a motion artifact has been removed comprises steps in which a heart rate measurement device: receives a photoplethysmography signal and an acceleration signal; converts the photoplethysmography signal and the acceleration signal into a signal of a frequency domain; calculates the difference between the photoplethysmography signal and the acceleration signal in the frequency domain so as to obtain a photoplethysmography signal from which a motion artifact has been removed; and estimates a heart rate on the basis of the photoplethysmography signal from which the motion artifact has been removed.

Description

Heart rate detection method and device using photoplethysmography signal with motion artifact removed

[0001] The technique described below is a method for detecting heart rate using photoplethysmography.

[0002] Recently, various types of wearable devices (smartwatches, smart glasses, etc.) have been released. These devices are equipped with various sensors, which can measure various biosignals.

[0003] Wearable devices may be equipped with photoplethysmography (PPG) sensors. PPG is a method of detecting heart rate by detecting blood flow using light. PPG is determined by shining light (infrared or red) through a finger or earlobe, then measuring the amount of light reflected or transmitted using a light-receiving sensor. PPG is also widely used to analyze diseases such as cardiovascular disease and vascular elasticity.

[0004] [Prior Art Literature]

[0005] [Patent Document]

[0006] Publication Patent No. 10-2010-0062736

[0007] Conventional techniques for estimating heart rate using photoplethysmography (PPP) detect the R-Peak of the PPP signal, which changes with the systole of the heart, to detect the real-time changing heart rate. However, PPP measured from wearable devices contain motion artifacts. Motion artifacts are noises generated by the wearer's movements, hand tremors, etc. Since the frequency band of motion artifacts overlaps with that of PPP, it degrades the quality of the PPP signal, thereby reducing the accuracy of heart rate estimation.

[0008] The technique described below provides a method for accurately measuring heart rate by removing motion artifact from photoplethysmographic signals.

[0009] A method for detecting a heart rate using a photoplethysmogram signal from which motion artifacts have been removed includes: a step in which a heart rate measuring device receives a photoplethysmogram signal and an acceleration signal; a step in which the heart rate measuring device converts the photoplethysmogram signal and the acceleration signal into signals in a frequency domain; a step in which the heart rate measuring device calculates a difference between the photoplethysmogram signal and the acceleration signal in the frequency domain to obtain a photoplethysmogram signal from which motion artifacts have been removed; and a step in which the heart rate measuring device estimates a heart rate based on the photoplethysmogram signal from which motion artifacts have been removed.

[0010] The technology described below can be used to measure heart rate using a heart rate measurement device. The heart rate measurement device can be a wearable device. Therefore, heart rate can be measured based on the values ​​measured by the photoplethysmography sensor and acceleration sensor attached to the wearable device.

[0011] The technology described below allows for heart rate measurement using photoplethysmography signals with motion artifacts removed. This allows users to obtain more accurate heart rate measurements.

[0012] Figure 1 shows the overall process (10) of detecting a heart rate using a photoplethysmography signal from which motion artifacts have been removed by a heart rate measuring device (100).

[0013] Figure 2 is an example of a process (20) for detecting heart rate using a photoplethysmography signal from which motion artifacts have been removed.

[0014] Figure 3 is one of the embodiments (30) for detecting heart rate using a photoplethysmography signal from which motion artifacts have been removed.

[0015] Figure 4 is a configuration (40) of one embodiment of a heart rate measuring device (400).

[0016] The technology described below is susceptible to various modifications and embodiments. Specific embodiments of the technology described below may be illustrated in the drawings of the specification. However, these are intended to illustrate the technology described below and are not intended to limit the technology described below to any specific embodiments. Therefore, it should be understood that all modifications, equivalents, or alternatives that fall within the spirit and scope of the technology described below are encompassed by the technology described below.

[0017] In the terms used hereinafter, singular expressions should be understood to include plural expressions unless the context clearly dictates otherwise, and terms such as "comprises" should be understood to mean the presence of a described feature, number, step, operation, component, part, or combination thereof, but not to exclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0018] Before going into a detailed description of the drawings, it should be made clear that the division of components in this specification is merely a division based on the main function of each component. That is, two or more components described below may be combined into one component, or one component may be further divided into two or more components with more detailed functions. In addition to its own main function, each component described below may additionally perform some or all of the functions of other components, and of course, some of the main functions of each component may be exclusively performed by other components.

[0019] Additionally, in performing a method or method of operation, each process constituting the method may occur in a different order than the stated order, unless the context clearly indicates a specific order. That is, each process may occur in the same order as the stated order, may be performed substantially simultaneously, or may be performed in the opposite order.

[0020] Below, we examine the overall process of performing a heart rate detection method using a photoplethysmography signal with motion artifact removed by a heart rate measurement device.

[0021] Figure 1 shows the overall process (10) of detecting a heart rate using a photoplethysmography signal from which motion artifacts have been removed by a heart rate measuring device (100).

[0022] The heart rate measuring device (100) can receive a photoplethysmography signal and an acceleration signal. The heart rate measuring device (100) can convert the photoplethysmography signal and the acceleration signal into signals in the frequency domain. The heart rate measuring device (100) can obtain a photoplethysmography signal from which motion artifacts have been removed by calculating the difference between the photoplethysmography signal and the acceleration signal in the frequency domain. The heart rate measuring device (100) can estimate a heart rate based on the photoplethysmography signal from which motion artifacts have been removed.

[0023] Below, a method for detecting heart rate using a photoplethysmography signal from which motion artifacts have been removed is described in detail.

[0024] Figure 2 is an example of a process (20) for detecting heart rate using a photoplethysmography signal from which motion artifacts have been removed.

[0025] The heart rate measuring device can receive photoplethysmography signals and acceleration signals (200).

[0026] Photoplethysmography (PPG) signals can be a biosignal obtained by measuring the light reflected or transmitted from skin tissue after a light source is excited subcutaneously. PPG can be used to determine cardiac activity by measuring blood flow through blood vessels.

[0027] Motion artifacts can be present in photoplethysmography signals. Motion artifacts can refer to noise caused by movement, such as hand tremors, during photoplethysmography measurements. The presence of motion artifacts can alter the photoplethysmography signal. Motion artifacts can also be caused by changes in acceleration. Information about motion artifacts can be obtained from the acceleration signal.

[0028] Acceleration signals can represent information measuring a user's movements. They can be used to determine the degree to which a user is tilted or moving. Acceleration signals can be acceleration signals along three axes (X, Y, and Z).

[0029] The photoplethysmography and acceleration signals may be signals measured from sensors attached to a wearable device of the subject. In one embodiment, the photoplethysmography and acceleration signals may be signals measured from sensors attached to a smartwatch worn by the subject.

[0030] The heart rate measuring device can also remove (Detrend) the oscillations that are changed by breathing and the heart among the signals included in the input photoplethysmographic signal.

[0031] The heart rate measurement device may also calculate the RMS (Root Mean Square) for the three-axis acceleration signal components to calculate the quantitative magnitude of the movement contained in the input acceleration signal.

[0032] The heart rate measurement device can also synchronize the input photoplethysmography signal and acceleration signal. This may be to ensure that the photoplethysmography signal and acceleration signal are measured simultaneously, allowing for comparison using the same number of samples.

[0033] The heart rate measuring device can convert photoplethysmography signals and acceleration signals into signals in the frequency domain (210).

[0034] Heart rate monitoring devices can utilize the Fourier transform to convert signals into frequency domain signals. This allows the device to calculate the periodogram of photoplethysmography and acceleration signals, thereby calculating the frequency magnitude of each signal component.

[0035] Heart rate monitoring devices can normalize photoplethysmography and acceleration signals. This allows the heart rate monitoring device to unify the units of photoplethysmography and acceleration signals. For example, the units of photoplethysmography (mV) and acceleration (m / s2) differ, making it difficult to compare the two signals. To address this issue, both signals can be normalized.

[0036] A heart rate monitoring device can assign different weights to the photoplethysmography signal and acceleration signal depending on the user's level of movement. In one embodiment, the heart rate monitoring device can weight the acceleration signal in the frequency domain based on the user's speed. This can minimize loss of components of the photoplethysmography signal during signal restoration.

[0037] Mathematical formula 1 is used to normalize the acceleration signal and then assign weights according to the user's speed.

[0038]

[0039] f' in Equation 1 acccan be an acceleration signal in the frequency domain where the normalization process and weighting process have been performed. In Equation 1, W acc may be a weight given to the acceleration signal. In Equation 1, f acc can be an acceleration signal in the frequency domain. In Equation 1, f min acc may be the minimum frequency of the photoplethysmographic signal in the frequency domain. In Equation 1, f max pgg may be the maximum frequency of the photoplethysmographic signal in the frequency domain.

[0040] The heart rate measuring device can obtain a photoplethysmogram signal with motion artifact removed by calculating the difference between the photoplethysmogram signal and the acceleration signal in the frequency domain (220).

[0041] In one embodiment, a heart rate measurement device can calculate the difference between the photoplethysmogram signal and the acceleration signal by subtracting the acceleration signal from the photoplethysmogram signal in the frequency domain. This allows the photoplethysmogram signal to be obtained from which motion artifacts are removed by removing the acceleration signal included in the photoplethysmogram signal.

[0042] Mathematical equation 2 is an example of a difference equation used to calculate the difference between two signals.

[0043]

[0044] f' in Equation 2 ppg can be a photoplethysmographic signal with the noise removed in the frequency domain. In mathematical expression 2, f ppg can be a photoplethysmographic signal in the frequency domain. In Equation 2, f' acc is the acceleration signal in the frequency domain. Specifically, f' acc It can be an acceleration signal in the frequency domain in which the normalization process and weighting process in mathematical expression 1 have been performed.

[0045] The heart rate measuring device can estimate the heart rate based on the photoplethysmography signal from which the motion artifact in the frequency domain has been removed (230).

[0046] In one embodiment, the heart rate measuring device can estimate the heart rate by selecting the frequency value with the strongest magnitude among the photoplethysmogram signals from which the acceleration signal has been removed in the frequency domain, and then multiplying the frequency by a preset value. For example, if the frequency with the strongest signal in the periodogram of the photoplethysmogram from which the acceleration signal has been removed is 1 Hz, the current heart rate can be estimated as 60 by multiplying 1 Hz by the preset value of 60 (BPM).

[0047] The heart rate measuring device can determine the final heart rate by comparing the estimated heart rate with the heart rate calculated through another heart rate estimation algorithm (240).

[0048] In one embodiment, the heart rate measurement device may utilize an R-peak based heart rate estimation algorithm as another algorithm. Specifically, the heart rate measurement device may calculate a heart rate from an input photoplethysmography signal based on the R-peak based heart rate estimation algorithm. The R-peak based heart rate estimation algorithm is one of the methods for detecting a heart rate based on the R-Peak of a photoplethysmography signal that changes due to the systole of the heart.

[0049] In one embodiment, the heart rate measuring device may calculate the difference between the estimated heart rate and the heart rate calculated through another heart rate estimation algorithm, and then determine the final heart rate based on whether the difference is less than or equal to a threshold value. For example, if the difference between the estimated heart rate and the heart rate calculated through another heart rate estimation algorithm is less than or equal to the threshold value, the estimated heart rate may be determined as the final heart rate. Alternatively, if the difference between the estimated heart rate and the heart rate calculated through another heart rate estimation algorithm is greater than or equal to the threshold value, the heart rate calculated through the other heart rate estimation algorithm may be determined as the final heart rate.

[0050] Fig. 3 is one embodiment (30) of detecting heart rate using a photoplethysmography signal from which motion artifacts have been removed. Fig. 3 is one embodiment of using a smartwatch as a heart rate measuring device.

[0051] The smartwatch can receive photoplethysmography signals and 3-axis acceleration signals measured by the sensor (300). The 3-axis acceleration signal can include acceleration signals for the x-axis, y-axis, and z-axis.

[0052] The smartwatch can save the input photoplethysmography signal and 3-axis acceleration signal (310).

[0053] The smartwatch can synchronize (resample) the photoplethysmography signal and the 3-axis acceleration signal (320). That is, the photoplethysmography signal and the 3-axis acceleration signal are signals measured simultaneously from the wearable device, and synchronization (320) can be performed so that the same number of samples is made to equalize the size of the frequency domain.

[0054] The smartwatch can detrend the AC component from the photoplethysmography signal (330). The smartwatch can quantitatively determine movement by calculating the RMS (Root Mean Square) of the three-axis acceleration signal (331).

[0055] Smartwatches can detect photoplethysmography signals in the frequency domain and determine the periodogram of the photoplethysmography signal. Smartwatches can detect acceleration signals in the frequency domain and determine the periodogram of the acceleration signal.

[0056] The smartwatch can normalize the acceleration signal in the frequency domain and then calculate and assign a weight (340). That is, the smartwatch can normalize the acceleration signal in the frequency domain using the aforementioned mathematical expression 1 and then assign a weight.

[0057] The smartwatch can obtain a photoplethysmogram signal with the noise frequency removed by subtracting the acceleration signal from the photoplethysmogram signal (350). For this purpose, the smartwatch can use the difference equation of Equation 2.

[0058] The smartwatch can estimate the heart rate by selecting the frequency with the strongest signal among the photoplethysmogram signals from which the noise frequency in the frequency domain has been removed and then multiplying it by a preset value (360). In other words, the smartwatch can estimate the current heart rate to be 60 by selecting 1 Hz, the frequency with the strongest signal, and then multiplying it by a preset value of 60 (BPM).

[0059] The smartwatch can calculate the heart rate ((HRRR)) using the R Peak-based heart rate algorithm, which is a heart rate estimation algorithm, based on the input photoplethysmography signal (310) (370).

[0060] The smartwatch can compare the estimated heart rate with the heart rate calculated through the R Peak-based heart rate algorithm described above (380). That is, the estimated heart rate (HR f ) and heart rate (HR) calculated using R peak-based algorithm RR ) is the threshold value (Th HR ) can be calculated as being above or below.

[0061] The smartwatch calculates the estimated heart rate (HR) if the difference value is below a threshold. f ) can be output as the final heart rate. Conversely, if the difference value is greater than the threshold, the smartwatch calculates the heart rate through the R peak-based algorithm as the final heart rate (HR). RR ) can be output (390).

[0062] The following describes the heart rate measuring device.

[0063] Figure 4 is a configuration (40) of one embodiment of a heart rate measuring device (400).

[0064] The heart rate measuring device (400) may correspond to the heart rate measuring device (100) described in Fig. 1. The heart rate measuring device (400) may be a device that performs a heart rate detection method using a photoplethysmography signal from which the aforementioned motion artifact has been removed.

[0065] The heart rate measuring device (400) can be physically implemented in various forms. For example, the heart rate measuring device (400) may take the form of a PC, laptop, server, or data processing chipset. Alternatively, the heart rate measuring device (400) may take the form of a wearable device (smart watch, smart glasses, smart ring), etc.

[0066] The heart rate measuring device (400) may include an input device (410), a storage device (420), a calculation device (430), an output device (440), an interface device (450), and a communication device (460).

[0067] The input device (410) may include an interface device (keyboard, mouse, touch screen, etc.) that receives a certain command or data. The input device (410) may also include a configuration that receives information through a separate storage device (USB, CD, hard disk, etc.). The input device (410) may receive the input data through a separate measuring device or a separate database. The input device (410) may receive data through wired or wireless communication. The input device (410) may be connected to a sensor and receive data measured by the sensor.

[0068] The input device (410) can receive biosignals, information, models, etc. necessary for performing a heart rate detection method using a photoplethysmography signal from which motion artifacts have been removed. The input device (410) can receive a photoplethysmography signal. The input device (410) can receive an acceleration signal.

[0069] The storage device (420) can store information input through the input device (410). The storage device (420) can store information generated during the calculation process of the calculation device (430). That is, the storage device (420) can include a memory. The storage device (420) can store the results calculated by the calculation device (430).

[0070] The storage device (420) can store biosignals, information, models, etc. necessary for performing the heart rate detection method using the photoplethysmography signal from which the aforementioned noise has been removed. The storage device (420) can store the photoplethysmography signal. The storage device (420) can store an acceleration signal.

[0071] The computing device (430) may be a device such as a processor, AP, or chip embedded with a program that processes data and performs certain operations. The computing device (430) may generate a control signal that controls the heart rate measuring device.

[0072] The calculation device (430) can perform the calculations necessary to perform a heart rate detection method using a photoplethysmography signal from which motion artifacts have been removed.

[0073] The computing device (430) can convert the photoplethysmography signal and the acceleration signal into signals in the frequency domain. The computing device (430) can obtain a photoplethysmography signal from which motion artifacts have been removed by calculating the difference between the photoplethysmography signal and the acceleration signal in the frequency domain. The computing device (430) can estimate the heart rate based on the photoplethysmography signal from which motion artifacts have been removed.

[0074] The output device (440) may be a device that outputs certain information. The output device (440) may output interfaces required for data processing, input data, analysis results, etc. The output device (440) may be physically implemented in various forms, such as a display, a device that outputs documents, etc.

[0075] The output device (440) can output the heart rate estimated by the calculation device (430). For example, the output device (440) can be a display device of a smart watch, and can output the heart rate estimated by the calculation device (430) to the display device.

[0076] The interface device (450) may be a device that receives certain commands and data from an external source. The interface device (450) may receive information necessary for performing a heart rate detection method using a photoplethysmography signal from which motion artifacts have been removed from a physically connected input device or an external storage device. The interface device (450) may receive a control signal for controlling the heart rate measuring device (400). The interface device (450) may output the results analyzed by the heart rate measuring device (400).

[0077] The communication device (460) may refer to a configuration that receives and transmits certain information via a wired or wireless network. The communication device (460) may receive a control signal necessary to control the heart rate measuring device (400). The communication device (460) may transmit the results analyzed by the heart rate measuring device (400).

[0078] The method for detecting heart rate using the photoplethysmography signal from which the aforementioned noise has been removed can be implemented as a program (or application) including an executable algorithm that can be executed on a computer.

[0079] The above program may be provided stored on a non-transitory computer readable medium.

[0080] A non-transitory readable medium refers to a medium that stores data semi-permanently and can be read by a device, rather than a medium that stores data for a short period of time, such as a register, cache, or memory. Specifically, the various applications or programs described above may be stored and provided on a non-transitory readable medium, such as a CD, DVD, hard disk, Blu-ray disk, USB, memory card, ROM (read-only memory), PROM (programmable read only memory), EPROM (Erasable PROM, EPROM), EEPROM (Electrically EPROM), or flash memory.

[0081] Temporarily readable media refers to various types of RAM, such as Static RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), Synchronous DRAM (Synclink DRAM, SLDRAM), and Direct Rambus RAM (DRRAM).

[0082] The present embodiment and the drawings attached to the present specification only clearly illustrate a part of the technical idea included in the above-described technology, and it will be obvious that all modified examples and specific embodiments that can be easily inferred by a person skilled in the art within the scope of the technical idea included in the specification and drawings of the above-described technology are included in the scope of the rights of the above-described technology.

Claims

1. A step in which a heart rate measuring device receives a photoplethysmographic signal and an acceleration signal; A step of converting the photoplethysmography signal and the acceleration signal into signals in the frequency domain by the heart rate measuring device; The step of the heart rate measuring device calculating the difference between the photoplethysmography signal and the acceleration signal in the frequency domain to obtain a photoplethysmography signal with motion artifact removed; and A heart rate detection method using a photoplethysmography signal from which motion artifacts have been removed, comprising: a step of estimating a heart rate based on the photoplethysmography signal from which motion artifacts have been removed by the heart rate measuring device.

2. In paragraph 1, A heart rate detection method using a photoplethysmography signal with noise removed, wherein the acceleration signal includes acceleration signals for each of the X-axis, Y-axis, and Z-axis directions.

3. In paragraph 1, A heart rate detection method using a photoplethysmography signal from which motion artifacts have been removed, further comprising a step of removing oscillations caused by respiration and heart rate from signals included in the input photoplethysmography signal by the heart rate measuring device.

4. In paragraph 1, A heart rate detection method using a photoplethysmography signal from which motion artifacts have been removed, further comprising a step of normalizing an acceleration signal converted into a signal in the frequency domain by the heart rate measuring device to unify the unit with the photoplethysmography signal in the frequency domain.

5. In paragraph 1, A heart rate detection method using a photoplethysmography signal from which motion artifacts have been removed, further comprising a step of weighting an acceleration signal converted into a signal in the frequency domain by the heart rate measuring device according to the user's speed.

6. In paragraph 1, A method for detecting a heart rate using a photoplethysmogram signal from which motion artifacts have been removed, wherein the step of estimating the heart rate includes the step of selecting a frequency value having the strongest magnitude among the photoplethysmogram signals from which the acceleration signal has been removed in the frequency domain, and then estimating the heart rate by multiplying the selected frequency by a preset value.

7. In paragraph 1, A heart rate detection method using a photoplethysmography signal with motion artifact removed, further comprising a step of determining a final heart rate by comparing the estimated heart rate with a heart rate calculated through another heart rate estimation algorithm by the heart rate measuring device.

8. In paragraph 7, The above heart rate estimation algorithm is a heart rate detection method using a photoplethysmography signal with motion artifact removed, including an algorithm for estimating a heart rate based on the R-Peak of a photoplethysmography signal that changes due to the systole of the heart.

9. In paragraph 7, The steps to determine the final heart rate are A step of calculating the difference between the estimated heart rate and the heart rate calculated through the other heart rate estimation algorithm; and A method for detecting a heart rate using a photoplethysmography signal with motion artifact removed, comprising: a step of determining the estimated heart rate as the final heart rate if the calculated difference value is less than or equal to a preset threshold value, and determining the heart rate calculated through another heart rate estimation algorithm as the final heart rate if the calculated difference value is greater than or equal to the preset threshold value; 10. Input device for receiving photoplethysmography signals and acceleration signals; A computing device that converts the photoplethysmography signal and the acceleration signal into signals in the frequency domain, calculates the difference between the photoplethysmography signal and the acceleration signal in the frequency domain to obtain a photoplethysmography signal from which motion artifacts have been removed, and estimates a heart rate based on the photoplethysmography signal from which motion artifacts have been removed; and A heart rate detection device using a photoplethysmography signal from which motion artifacts have been removed, comprising a storage device storing the photoplethysmography signal and acceleration signal.

11. In paragraph 10, A heart rate detection device using a photoplethysmography signal with noise removed, wherein the above acceleration signal includes acceleration signals for each of the X-axis, Y-axis, and Z-axis directions.

12. In paragraph 10, The above-mentioned calculating device is a heart rate detection device using a photoplethysmography signal with motion artifacts removed, which removes oscillations that are changed by breathing and the heart among the signals included in the input photoplethysmography signal.

13. In paragraph 10, The above-mentioned calculation device is a heart rate detection device using a photoplethysmography signal with noise removed, which normalizes the acceleration signal converted into a signal in the frequency domain to unify the unit with the photoplethysmography signal in the frequency domain.

14. In paragraph 10, The above-mentioned calculating device is a heart rate detection device using a photoplethysmography signal with motion artifacts removed, which weights the acceleration signal converted into a signal in the frequency domain according to the user's speed.

15. In paragraph 10, The above-mentioned calculation device estimates the heart rate by selecting a frequency value having the strongest magnitude among the photoplethysmogram signals from which the acceleration signal has been removed in the frequency domain, and then multiplying the selected frequency by a preset value to estimate the heart rate. A heart rate detection device using a photoplethysmogram signal from which motion artifacts have been removed.

16. In paragraph 10, A heart rate detection device using a photoplethysmography signal with motion artifact removed, wherein the above-mentioned calculating device determines a final heart rate by comparing the estimated heart rate with a heart rate calculated through another heart rate estimation algorithm.

17. In paragraph 16, The above heart rate estimation algorithm is a heart rate detection device using a photoplethysmography signal with motion artifact removed, including an algorithm for estimating a heart rate based on the R-Peak of the photoplethysmography signal that changes due to the systole of the heart.

18. In paragraph 16, The above calculation device determines the final heart rate. A heart rate detection device using a photoplethysmography signal with motion artifact removed, wherein the difference between the estimated heart rate and the heart rate calculated through the other heart rate estimation algorithm is calculated, and if the calculated difference value is less than or equal to a preset threshold, the estimated heart rate is determined as the final heart rate, and if it is greater than or equal to the preset threshold, the heart rate calculated through the other heart rate estimation algorithm is determined as the final heart rate.

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