Noninvasive blood pressure and blood oxygen measuring sensor, measuring method and wearable device

Abstract

The invention discloses a non-invasive blood pressure and blood oxygen measurement sensor, a measurement method and wearable equipment. The sensor comprises an ultrasonic array type sensor, a PPG sensor, an AD conversion module and an MCU unit. The ultrasonic array type sensor comprises a plurality of piezoelectric ceramics, and the piezoelectric ceramics are fixed on the periphery of the PPG sensor in a surrounding manner; the measurement method comprises the following steps: (1) acquiring PPG signals; (2) collecting motion artifact signals; and (3) judging whether the motion artifact signal exceeds a threshold value or not and processing the PPG signal to obtain blood pressure and blood oxygen values or directly outputting the PPG signal to obtain the blood pressure and blood oxygen values. Motion artifacts of PPG signals are detected by means of high sensitivity of the ultrasonic array, the signals serve as reference signals, the high-quality PPG signals are obtained by removing the motion artifacts, and the purposes of improving the quality of pulse wave signals and further improving the blood pressure and blood oxygen measuring precision are achieved. Therefore, blood pressure and blood oxygen measurement of a human body in a non-static state is realized.

Description

Technical Field

[0001] The present invention relates to the field of biological signal sensors, and in particular to a non-invasive blood pressure and blood oxygen measurement sensor capable of improving the quality of pulse wave signals, a wearable device including the sensor, and a non-invasive blood pressure and blood oxygen measurement method. Background Art

[0002] Wearable health monitoring technology has always played an important role in the field of medical health and is an important means of preventing a variety of chronic diseases. Among them, wearable non-invasive blood pressure and blood oxygen measurement technology is an important component, and its theoretical research and practical application are also relatively in-depth and extensive.

[0003] As far as blood pressure measurement is concerned, the existing wearable cuffless blood pressure measurement technology is mainly divided into two parts: mechanism-driven and data-driven. Mechanism-driven refers to measuring blood pressure by relying on the mapping relationship between the pulse wave itself or its changes and blood pressure. It is mainly divided into the photoelectric volume pulse wave (PPG) signal blood pressure estimation method, the skin surface pressure wave estimation blood pressure wave, the oscillometric method and the mapping relationship between the pulse wave transmission time and blood pressure. Data-driven refers to the method of relying on a large amount of pulse wave data to establish the mapping relationship between the pulse wave and blood pressure. It is divided into a machine learning method based on artificial pulse wave feature labeling and a deep learning method of automatic feature learning. However, whether it is a blood pressure measurement method based on mechanism-driven or data-driven, it is necessary to measure the pulse wave signal. Therefore, obtaining an accurate pulse wave signal is the key to improving the accuracy of blood pressure measurement. For the measurement of blood oxygen saturation, the more popular and mature method is to measure the size of blood oxygen content through transmission or reflection PPG. Based on the theory that the absorption coefficients of hemoglobin and oxyhemoglobin are different in different wavelength ranges, the blood oxygen level can be obtained by Lambert-Beer's law. Although the application of Lambert-Beer's law in transmission and reflection PPG is different, no matter which method is used to measure blood oxygen, the quality of the collected pulse wave still has a great impact on the accuracy of blood oxygen measurement.

[0004] There are many existing technologies for improving the quality of pulse waves. For example, Jian Li et al. proposed a wristband blood pressure measurement device in Thin, soft, wearable system for continuous wireless monitoring of artery blood pressure. The device uses a micro-pump to pressurize the device to obtain a better pulse wave signal; Yunghua Kao et al. optimize the distance between the photoelectric receiving tube and the LED in Design and Validation of a New PPG Module to Acquire High-Quality Physiological Signals for High-Accuracy Biomedical Sensing. The device maximizes the ratio of the pulsating (AC) and non-pulsating (DC) components in the PPG waveform to obtain a high-quality PPG signal. Both represent general methods for improving the quality of pulse wave signals, each with its own advantages, but also have certain usage defects. The former is less comfortable, while the latter can only improve the quality of the collected PPG signal, but cannot eliminate motion artifact signals in a non-calm state. In addition, removing baseline drift and motion artifacts is also an important means to improve the quality of pulse wave signals. Existing motion artifact removal methods mainly rely on accelerometers, but accelerometers reflect the overall motion state of the measured part and cannot well reflect the contact between the sensor and the skin, so the accuracy is not high. Summary of the invention

[0005] The present invention proposes a non-invasive blood pressure and blood oxygen measurement sensor that combines an ultrasonic array with photoelectricity, a method for removing motion artifacts, and a wearable device to solve the problem that the PPG signal is affected by motion artifacts in a non-calm state, resulting in poor signal quality and inability to perform blood pressure and blood oxygen measurement. To solve the above technical problems, the technical solution proposed by the present invention is as follows: A non-invasive blood pressure and blood oxygen measurement sensor comprises an ultrasonic array sensor, a PPG sensor, an AD conversion module and an MCU unit; the ultrasonic array sensor comprises a plurality of piezoelectric ceramics, and the piezoelectric ceramics are fixed around the periphery of the PPG sensor; the PPG signal collected by the PPG sensor is input into the MCU unit; the MCU unit transmits a voltage signal to the piezoelectric ceramics to make the piezoelectric ceramics output an ultrasonic signal, and the ultrasonic signal is reflected to cause the piezoelectric ceramics to expand and contract and generate an electrical signal, and the electrical signal is converted into a digital signal by the AD conversion module and input into the MCU unit.

[0006] The design idea of ​​the above technical solution is that the piezoelectric crystal is a material with special properties. When voltage is applied to the piezoelectric crystal, it will expand, and when the voltage is removed, it will shrink back to its original thickness. If the voltage is applied and removed quickly and repeatedly, the piezoelectric crystal will also expand and shrink rapidly, and an ultrasonic signal will be generated when the frequency exceeds 20 KHZ. In addition, the piezoelectric crystal can also receive ultrasonic waves, and the principle is the reverse process of generating ultrasonic waves. In addition, if the interface that causes the reflection of the ultrasonic wave is moving, the reflected ultrasonic signal will change in frequency due to the Doppler effect, and the piezoelectric crystal will reflect this change in the frequency of the generated voltage. In this way, a single piezoelectric crystal is a sensor that can transmit and receive dynamically changing ultrasonic waves. The ultrasonic array sensor of the present invention is composed of a number of piezoelectric ceramics (PZT). The ultrasonic emission of each piezoelectric ceramic is controlled by the MCU. The emitted ultrasonic wave bounces back to the piezoelectric ceramic on the skin surface, causing the piezoelectric ceramic to deform and generate a corresponding electrical signal. The electrical signal is then converted into a digital signal by an AD converter and transmitted to the MCU. The motion artifacts of the PPG signal are detected by relying on the high sensitivity of the ultrasonic array. The MCU determines whether the skin interface is jittering based on the difference in the frequency of the emitted and returned electromagnetic waves, and uses this signal as a reference signal to filter out the motion artifacts, thereby obtaining a high-quality PPG signal, so as to achieve the purpose of improving the quality of the pulse wave signal and thus improving the accuracy of blood pressure and blood oxygen measurement, so that the non-invasive blood pressure and blood oxygen measurement sensor can realize blood pressure and blood oxygen measurement of the human body in a non-static state, making it possible and prospective for application in wearable devices.

[0007] As a further preferred embodiment of the above technical solution, eight piezoelectric ceramics are provided, surrounding the periphery of the PPG sensor in a circular shape.

[0008] As a further preferred embodiment of the above technical solution, each of the piezoelectric ceramics is provided with a micro shielding cover, and all the shielding covers are grounded. When the piezoelectric ceramics work simultaneously, there is a crosstalk problem (noise) between each other, so a micro shielding cover is used to eliminate the interference signal between the piezoelectric ceramics to ensure the accuracy of data collection.

[0009] As a further preferred embodiment of the above technical solution, the PPG sensor includes a combined light source and a photoelectric receiver; the MCU unit inputs a voltage to the combined light source to control it to emit a light signal, and the light signal is received by the light receiver after reflection and input into the MCU unit.

[0010] As a further preferred embodiment of the above technical solution, the photoelectric receiver is a silicon photocell that can convert the received optical signal into an electrical signal; the combined light source is composed of a green LED, a red LED and an infrared LED. The PPG sensor of the reflective combined light source is used to measure the PPG signal. The combined light source is composed of green (520 nm), red (660 nm) and infrared (940 nm) LEDs. Blood pressure is estimated by the PPG signal collected by the green LED, and the algorithm principle is to use the mapping relationship between the pulse wave morphological characteristic parameters and blood pressure. Blood oxygen is calculated by calibrating the ratio of the direct-current and alternating signals of hemoglobin and oxygenated hemoglobin obtained by using the reflective red / infrared dual-color light. The principle is that the hemoglobin and oxygenated hemoglobin content reflected by the direct-current and alternating signals directly reflect the size of the blood oxygen saturation. Blood pressure and blood oxygen share a photoelectric receiver. When performing actual measurement, the light source is controlled by the PWM wave provided by the MCU unit to obtain the corresponding PPG signal.

[0011] As a further preferred embodiment of the above technical solution, the ultrasonic array sensor, PPG sensor, AD conversion module and MCU unit are encapsulated in a polydimethylsiloxane outer package. Polydimethylsiloxane (PDMS) has the advantages of being soft, non-toxic, transparent and biocompatible. As an outer package, the sensor of the present invention can be more suitable for making wearable devices for the human body.

[0012] Based on the same technical concept, the present invention also provides a wearable device, which includes the non-invasive blood pressure and blood oxygen measurement sensor described in the above technical solution.

[0013] Based on the same technical concept, the present invention also provides a non-invasive blood pressure and blood oxygen measurement method, which uses the non-invasive blood pressure and blood oxygen measurement sensor described in the above technical solution or the wearable device described in the above technical solution to achieve blood pressure and blood oxygen measurement.

[0014] As a further preferred embodiment of the above technical solution, the non-invasive blood pressure and blood oxygen measurement method comprises the following steps: (1) Collecting PPG signals through the PPG sensor and inputting them into the MCU unit; (2) The MCU transmits a voltage signal to the piezoelectric ceramic so that the piezoelectric ceramic outputs an ultrasonic signal. The piezoelectric ceramic receives the reflected ultrasonic signal and generates an electrical signal. The electrical signal is converted into a digital signal by the AD conversion module and then input into the MCU unit to obtain a motion artifact signal. (3) The MCU unit determines whether the motion artifact signal exceeds the threshold: if the motion artifact signal exceeds the threshold, the adaptive filter is turned on to process the PPG signal. If the PPG signal meets the quality requirements after processing, the PPG signal is output to obtain the blood pressure and blood oxygen value. If the PPG signal does not meet the quality requirements after processing, the measurement step is restarted; if the motion artifact signal does not exceed the threshold, the PPG signal is directly output to obtain the blood pressure and blood oxygen value.

[0015] As a further preferred embodiment of the above technical solution, after the PPG signal is collected in step (1), the PPG signal is pre-amplified, low-pass filtered, level-raised, and converted to analog-to-digital before being input into the MCU unit. In order to ensure the DC component of the PPG signal measured by blood oxygen, the present invention does not design a high-pass filter. Level raising is to raise the negative voltage signal to a positive voltage to facilitate subsequent AD conversion.

[0016] As a further optimization of the above technical solution, the cutoff frequency of the analog low-pass filter is 8 Hz, and the analog low-pass filter is completed by a second-order Sallen-Key filter. The cutoff frequencies of the analog low-pass filter and the digital low-pass filter are both 8 Hz, and the digital filter is a FIR filter, whose linear phase offset can facilitate the subsequent processing of real-time signals, and the specific filter parameters are obtained by tools in MATLAB. A second-order Sallen-Key filter is suitable for processing small signals.

[0017] As a further preferred embodiment of the above technical solution, the AD conversion module in step (2) adopts IIC communication. The AD conversion module adopts IIC communication, which facilitates the microcontroller (MCU) unit to control the ultrasonic array sensor and the reflective PPG sensor respectively in an addressing manner.

[0018] As a further preferred embodiment of the above technical solution, the adaptive filtering process in step (3) adopts a recursive least squares algorithm, and the specific content of the recursive least squares algorithm is as follows: Assume that the input signal is x(k), the output signal after filtering is y(k), and the average weighted sum of the error amplitude is , where M is the filter length; the forgetting factor is , , assuming that there is an optimal filter coefficient ,matrix And vector ,but , its gain for: ; Expected sequence and estimate The difference between for: ; Weight coefficient Updated to: ; Covariance matrix Updated to: ; in, A discrete signal representing the input; represents the output after filtering; For the recursive least squares algorithm to estimate the value, the initial value is given back, The least squares recursive operation can then begin.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The non-invasive blood pressure and blood oxygen measurement sensor and wearable device of the present invention rely on the high sensitivity of the ultrasonic array to detect the motion artifacts of the PPG signal, and use this signal as a reference signal, combined with the RLS adaptive filtering algorithm to filter it out. By removing the motion artifacts of the PPG signal, a high-quality PPG signal is obtained, so as to achieve the purpose of improving the quality of the pulse wave signal and then improving the accuracy of blood pressure and blood oxygen measurement, thereby realizing blood pressure and blood oxygen measurement in a non-static state of the human body.

[0020] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 This is a schematic diagram of the structure of the non-invasive blood pressure and blood oxygen measurement sensor of Example 1 when viewed from the side; Figure 2 This is a schematic diagram of the structure of the non-invasive blood pressure and blood oxygen measurement sensor of Example 1 when viewed from above; Figure 3 It is a schematic structural diagram of the piezoelectric ceramic and its outer shielding cover of Example 1; Figure 4 The non-invasive blood pressure and blood oxygen measurement sensor of Example 1 is used in a wearable device (health monitoring watch); Figure 5 Schematic diagram of the process of the non-invasive blood pressure and blood oxygen measurement method of Example 1.

[0022] Legend: 1. Polydimethylsiloxane outer packaging; 2. Circuit board; 3. Silicon photocell; 4. Black fence structure; 5. Combined LED light source; 6. Outer packaging of ultrasonic array sensor; 7. Ultrasonic array sensor; 8. Skin and tissue; 9. Blood; 13 is green LED; 14 is red LED; 15 is infrared LED; 20 is outer shielding cover; 21 is piezoelectric ceramic; 22. Wearable device; 23. Real-time display interface on mobile terminal. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0024] Embodiment 1: like Figure 1 and Figure 2 As shown, the non-invasive blood pressure and blood oxygen measurement sensor of this embodiment includes an ultrasonic array sensor, a PPG sensor with a reflective combined light source, an AD conversion module and an MCU unit.

[0025] Among them, the PPG sensor of the reflective combined light source is used to measure the PPG signal. The combined light source is composed of green light (520 nm), red light (660 nm) and infrared light (940 nm) LEDs. The photoelectric receiver is a silicon photocell, which can convert the received optical signal into an electrical signal. The collected PPG signal is input into the MCU for subsequent digital signal processing and physiological parameter calculation after pre-amplification, analog low-pass filtering (in order to ensure the DC component of the PPG signal measured by blood oxygen, a high-pass filter is not designed in this embodiment), level lifting and analog-to-digital conversion. The cutoff frequency of the analog low-pass filter and the digital low-pass filter is 8HZ, the digital filter is a FIR filter, and the specific filter parameters are obtained by the tool in MATLAB. The analog filter is a second-order Sallen-Key filter.

[0026] Among them, AD conversion module, MCU unit, filter and other components are integrated on the circuit board.

[0027] The ultrasonic array sensor includes 8 piezoelectric ceramics, which are surrounded by a circle on the periphery of the PPG sensor. A micro shielding cover is provided outside each piezoelectric ceramic, and all shielding covers are grounded. The MCU unit transmits a voltage signal to the piezoelectric ceramic through the input and output interface of the piezoelectric ceramic, so that the piezoelectric ceramic outputs an ultrasonic signal. The ultrasonic signal is reflected to cause the piezoelectric ceramic to expand and contract and generate an electrical signal. The electrical signal is converted into a digital signal by the AD conversion module and input into the MCU unit.

[0028] like Figure 4As shown, the non-invasive blood pressure and blood oxygen measurement sensor of this embodiment can be used in smart watch wearable devices. Before starting the measurement, the subject must first fix the present invention on the measured part. There are two ways to start the measurement: one is to directly press the button on the wearable measurement platform, and the other is to control it through the mobile phone connected to the platform Bluetooth. By controlling the measurement platform with a mobile phone, more operations can be performed and more information can be viewed.

[0029] like Figure 5 As shown, the non-invasive blood pressure and blood oxygen measurement method of this embodiment includes the following steps: The specific contents of the recursive least squares algorithm are as follows: Assume that the input signal is x(k), the output signal after filtering is y(k), and the average weighted sum of the error amplitude is , where M is the filter length; the forgetting factor is , , assuming that there is an optimal filter coefficient ,matrix And vector ,but , its gain for: ; Expected sequence and estimate The difference between for: ; Weight coefficient Updated to: ; Covariance matrix Updated to: ; in, A discrete signal representing the input; represents the output after filtering; For the recursive least squares algorithm to estimate the value, the initial value is given back, The least squares recursive operation can then begin.

[0030] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application. The above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and changes obtained without departing from the technical concept of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A non-invasive blood pressure and blood oxygen measurement sensor, characterized in that: It includes an ultrasonic array sensor, a PPG sensor, an AD conversion module and an MCU unit; the ultrasonic array sensor includes a plurality of piezoelectric ceramics, which are fixed around the periphery of the PPG sensor; the PPG signal collected by the PPG sensor is input into the MCU unit; the MCU unit transmits a voltage signal to the piezoelectric ceramics to make the piezoelectric ceramics output an ultrasonic signal, and the ultrasonic signal is reflected to cause the piezoelectric ceramics to expand and contract and generate an electrical signal, which is converted into a digital signal by the AD conversion module and input into the MCU unit.

2. The non-invasive blood pressure and blood oxygen measurement sensor according to claim 1, characterized in that: A micro shielding cover is arranged outside each of the piezoelectric ceramics, and all the shielding covers are grounded.

3. The non-invasive blood pressure and blood oxygen measurement sensor according to claim 1, characterized in that: The PPG sensor includes a combined light source and a photoelectric receiver; the MCU unit inputs a voltage to the combined light source to control it to emit a light signal, and the light signal is received by the light receiver after reflection and input into the MCU unit.

4. The non-invasive blood pressure and blood oxygen measurement sensor according to claim 3, characterized in that: The photoelectric receiver is a silicon photocell which can convert the received optical signal into an electrical signal; the combined light source is composed of a green light LED, a red light LED and an infrared light LED.

5. The non-invasive blood pressure and blood oxygen measurement sensor according to any one of claims 1 to 4, characterized in that: The ultrasonic array sensor, PPG sensor, AD conversion module and MCU unit are packaged in a polydimethylsiloxane outer package.

6. A wearable device, characterized in that: The wearable device comprises the non-invasive blood pressure and blood oxygen measurement sensor according to any one of claims 1 to 5.

7. A non-invasive blood pressure and blood oxygen measurement method, characterized in that: The non-invasive blood pressure and blood oxygen measurement sensor described in any one of claims 1 to 5 or the wearable device described in claim 6 is used to measure blood pressure and blood oxygen.

8. The non-invasive blood pressure and blood oxygen measurement method according to claim 7, characterized in that: The following steps are involved: (1) Collecting PPG signals through the PPG sensor and inputting them into the MCU unit; (2) The MCU transmits a voltage signal to the piezoelectric ceramic so that the piezoelectric ceramic outputs an ultrasonic signal. The piezoelectric ceramic receives the reflected ultrasonic signal and generates an electrical signal. The electrical signal is converted into a digital signal by the AD conversion module and then input into the MCU unit to obtain a motion artifact signal. (3) The MCU unit determines whether the motion artifact signal exceeds the threshold: if the motion artifact signal exceeds the threshold, the adaptive filter is turned on to process the PPG signal. If the PPG signal meets the quality requirements after processing, the PPG signal is output to obtain the blood pressure and blood oxygen value. If the PPG signal does not meet the quality requirements after processing, the measurement step is restarted; if the motion artifact signal does not exceed the threshold, the PPG signal is directly output to obtain the blood pressure and blood oxygen value.

9. The non-invasive blood pressure and blood oxygen measurement method according to claim 8, characterized in that: After the PPG signal is collected in step (1), the PPG signal is pre-amplified, analog low-pass filtered, level-raised and analog-to-digital converted before being input into the MCU unit; the cutoff frequency of the analog low-pass filter is 8 Hz, and the analog low-pass filter is completed using a second-order Sallen-Key filter; the AD conversion module in step (2) uses IIC communication.

10. The non-invasive blood pressure and blood oxygen measurement method according to claim 8, characterized in that: The adaptive filtering process in step (3) adopts a recursive least squares algorithm, and the specific content of the recursive least squares algorithm is as follows: Assume that the input signal is x(k), the output signal after filtering is y(k), and the average weighted sum of the error amplitude is , where M is the filter length; the forgetting factor is , , assuming that there is an optimal filter coefficient ,matrix And vector ,but , its gain for: ； Expected sequence and estimate The difference between for: ； Weight coefficient Updated to: ； Covariance matrix Updated to: ； in, A discrete signal representing the input; represents the output after filtering; For the recursive least squares algorithm to estimate the value, the initial value is given back, The least squares recursive operation can then begin.

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