Real-time synchronous pulse wave electrocardiogram monitor

Abstract

According to the design scheme, the real-time synchronous pulse wave electrocardiogram monitor comprises the steps that an electrocardiogram electrode and a pulse wave sensor are placed at the corresponding positions of a human body, and then a transmission line is connected with main equipment; switching on a bipolar power supply to supply power to each component; a sampling frequency and an acquisition mode are set by the key; the pulse wave signals and the electrocardiosignals are preprocessed through an amplifier and a filter, and the signal quality is guaranteed; finally, the dual-channel signals are input into a microcontroller, and tasks such as waveform display, heart rate calculation and synchronous communication with an upper computer are completed. According to the design scheme provided by the invention, the pulse waveform and the electrocardiogram can be quickly and accurately measured, and the cardiovascular health condition can be monitored in real time.

Description

Technical Field

[0001] This invention relates to the field of biosignal processing and medical electronic equipment, specifically to the design of a real-time synchronized pulse wave electrocardiogram monitor. Background Technology

[0002] According to the World Health Organization, cardiovascular disease has surpassed cancer as the leading cause of death worldwide, with a mortality rate reaching 31.5%. Furthermore, the number of people suffering from cardiovascular disease continues to increase annually. Currently, the incidence and prevalence of cardiovascular disease in my country continue to rise. In 2024, cardiovascular disease accounted for 47.35% of deaths in urban areas and 48.98% in rural areas. The prevalence of cardiovascular disease in China is still on the rise, with an estimated current number of patients around 430 million. Cardiovascular disease has placed an increasingly heavy burden on individual patients' health, family expenses, and society, becoming a significant public safety and social issue that cannot be ignored in contemporary society.

[0003] Cardiovascular disease is one of the leading causes of death and disability worldwide, making early screening and long-term health management crucial. Electrocardiography (ECG), the "gold standard" for detecting cardiac electrophysiological activity, is widely used in clinical diagnosis, health monitoring, and telemedicine. While ECG accurately captures cardiac electrical activity, it cannot directly reflect the effectiveness of blood flow perfusion, leading to a risk of misdiagnosis. Pulse wave (PPG), by sensing peripheral vascular pulsation, can verify the physiological effectiveness of ECG signals. The combined use of PPG and ECG constructs a two-dimensional assessment system of "cardiac electrical activity and peripheral blood flow response" for ECG monitoring, which is key to overcoming the limitations of single monitoring and enhancing clinical value. Furthermore, the combination of the two can more accurately calculate heart rate variability (HRV) and assess vascular elasticity, effectively reducing the missed diagnosis and misdiagnosis rates of single monitoring in scenarios such as arrhythmia screening and exercise ECG monitoring, providing more comprehensive and objective evidence for clinical diagnosis and physiological status assessment.

[0004] While traditional pulse wave electrocardiogram (ECG) monitoring devices play an important role in clinical diagnosis and treatment, their application limitations are becoming increasingly apparent due to constraints in their technical architecture and design concepts. Firstly, these devices are often bulky and heavy, requiring fixed clinical space, and the testing process relies on a bedridden operating mode, reducing patient convenience and making them unsuitable for diverse scenarios such as bedside emergency monitoring and community mobile screening. Secondly, the testing process heavily depends on the professional operation of medical staff, increasing labor costs and making it susceptible to human error due to electrode misalignment, parameter adjustment errors, etc., affecting data accuracy. Thirdly, data collection is primarily based on single static recordings, failing to achieve real-time dynamic monitoring and long-term trend tracking of patients' daily activities. Furthermore, data transmission largely relies on local storage, resulting in poor compatibility with telemedicine platforms and hindering the continuous management of cardiovascular chronic diseases. In addition, the high cost of equipment procurement and subsequent maintenance leads to insufficient deployment in primary healthcare institutions and difficulty in expanding to home settings, creating a gap in healthcare resource accessibility. Therefore, developing a low-cost, portable, and easy-to-operate pulse wave and electrocardiogram combined monitoring device is not only a core direction to make up for the shortcomings of traditional equipment, but also a key technical support for promoting the early screening, home management, and hierarchical diagnosis and treatment of cardiovascular diseases. Summary of the Invention

[0005] To address the aforementioned needs, this invention designs a dual-channel pulse wave electrocardiogram (ECG) monitor. Users only need to wear standard limb-lead ECG electrodes and a transmissive pulse wave sensor to acquire both ECG and pulse wave signals. After amplification and filtering, the device can stably and accurately extract pulse wave and ECG signals, converting the signals into waveforms and displaying them intuitively on an OLED screen in the form of an electrocardiogram.

[0006] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0007] A real-time synchronized pulse wave electrocardiogram monitor includes the following steps:

[0008] Step 1: Place the ECG electrodes and pulse wave sensor on the human body surface and connect the leads to the acquisition device. First, connect the ECG electrodes by attaching silver chloride bioelectrode pads to the left and right subclavian fossa and the lower edge of the left rib cage. The electrode pads should be used with conductive gel or ointment to improve skin contact and reduce impedance. Next, connect the yellow electrode of the standard limb lead ECG electrode line to the left subclavian fossa electrode pad, the red electrode to the right subclavian fossa electrode pad, and the green electrode to the lower edge of the left rib cage electrode pad. Then, connect the pulse wave sensor by inserting the pad of the index finger into the finger clip-on pulse wave sensor. Finally, insert the ECG transmission line and pulse wave transmission line into the dual-channel 3.5mm TRS interface of the hardware acquisition device.

[0009] Step two involves connecting the bipolar power supply circuit to provide the necessary power to the various electronic components of the acquisition device, ensuring stable system operation. Unlike the unipolar power supply used in conventional electrical equipment, this device uses a ±5V bipolar power supply. Its advantages are: 1. The bipolar power supply provides both positive and negative voltage rails, accommodating the positive and negative fluctuations of ECG and pulse wave signals (such as the positive peak of the QRS complex and the negative trough of the T wave in ECG signals), reducing amplitude distortion caused by the voltage limitation of the unipolar power supply, and improving the integrity of signal acquisition. 2. The baseline of ECG and pulse wave signals is easily affected by respiratory and electromyographic interference, causing fluctuations. The bipolar power supply, through symmetrical voltage bias, can stabilize the signal baseline near the power supply midpoint, eliminating the need for additional complex circuit compensation, simplifying the design while improving signal stability. 3. The circuit powered by the bipolar power supply has a more stable signal ground and power ground potential, effectively suppressing common-mode interference and 50Hz power frequency interference, reducing the impact of external electromagnetic noise on weak ECG and pulse wave signals, and ensuring the accuracy of monitoring data.

[0010] Step 3: Configure the mode and begin collecting pulse wave and ECG signals. This monitor is equipped with a 0.96-inch OLED screen as the user interface. Users can set the sampling rate to 100Hz, 200Hz, 500Hz, and 1000Hz via the button menu. Once configured, pulse wave and ECG monitoring can begin. Additionally, users can access the device's heart rate acquisition mode through this interface. The built-in algorithm accurately calculates the number of heartbeats per minute by counting the peaks and troughs of the pulse wave per unit time.

[0011] Step four involves amplifying and filtering the synchronously acquired pulse wave and electrocardiogram (ECG) signals. For the ECG signal, firstly, it is amplified by a pre-amplifier with a gain of 7. Then, it passes through a 108Hz low-pass filter and a 0.1Hz high-pass filter; this frequency band is typical for ECG signals, effectively removing high-frequency electromyography interference and low-frequency baseline drift. Next, a dual-T notch filter precisely suppresses 50Hz power frequency and harmonic interference, improving the signal-to-noise ratio, enhancing characteristic waveform recognition, and ensuring the accuracy and stability of the ECG signal. Finally, the signal is amplified 50 times by an inverting amplifier and 5 times by an inverting adder. For the pulse wave signal, it is first amplified 4 times by an inverting amplifier, and then the voltage is boosted to 1.65V by a voltage follower.

[0012] Step five involves inputting the amplified and filtered dual-channel pulse wave signal and ECG signal into the STM32 microcontroller unit for tasks such as AD conversion, waveform plotting, and heart rate calculation. The system is based on clock synchronization, using an external crystal oscillator to generate a stable reference clock and a timer to output synchronous trigger pulses, ensuring that the dual-channel 12-bit ADC starts sampling simultaneously and avoiding phase shift between the two signals. The core of waveform plotting focuses on the stable and synchronized display of the two waveforms. Key details are divided into three parts: 1. Dual-channel independent baseline correction and QRS complex detection: For the characteristics of ECG and pulse wave signals, a moving average algorithm is used to correct baseline drift caused by respiration and electromyography in real time, fixing the baselines of the two waveforms at the vertical midpoints of the upper and lower halves of the OLED screen respectively, preventing one-way offset from obscuring the other. 2. Partition coordinate mapping: The display area is planned according to the screen resolution to ensure complete synchronization of the two waveforms in the time dimension. 3. Parallel refresh control: The microcontroller receives two digital signals and processes them in parallel, allocating an independent buffer for each signal. Each time a set of synchronized data (one point each for ECG and pulse wave) is acquired, the corresponding buffer is updated. When a column is full, a partial refresh is initiated, updating only the upper and lower halves of the waveform area to avoid full-screen flicker and ensure clear visual visibility. Furthermore, the device is equipped with a USART serial communication interface, allowing monitoring data to be synchronized to a host computer.

[0013] Compared with the prior art, the advantages of the present invention are as follows:

[0014] This invention designs a real-time synchronous pulse wave electrocardiogram (ECG) monitor. First, standard lead ECG electrodes are placed in the left and right subclavian fossa and the lower edge of the left rib cage, respectively. Then, the fingertip is placed in a finger clip-on pulse wave sensor. Next, the metal ends of the two signal lines are connected to a dual-channel 3.5mm TRS interface, completing the connection between the main device and the body. Then, the power is turned on, and the device begins acquiring pulse wave and ECG signals in configuration mode. The initial signals are amplified and filtered before being input to the microcontroller for AD conversion, waveform plotting, and heart rate calculation. Finally, two high-quality pulse wave and ECG waveforms are displayed on an OLED screen.

[0015] This invention employs a clock-synchronized triggering STM32's built-in 12-bit dual-channel ADC, supporting sampling rate adjustment from 100 to 1000Hz to ensure no phase shift between ECG and pulse wave signals. Combined with a ±5V bipolar power supply, the signal distortion rate is <1%, and the signal-to-noise ratio is ≥120dB, resolving the issues of unipolar power supply clipping and common-mode interference, achieving high-precision synchronous acquisition of two weak physiological signals. Regarding the display solution, a partitioned display is designed based on a 0.96-inch OLED screen, with the upper and lower sections simultaneously displaying the two waveforms. Through independent moving average baseline correction and local refresh technology (refresh delay <10ms), waveform obstruction and flicker are avoided, resulting in significantly better observation intuitiveness and data readability compared to traditional single-channel display solutions. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the acquisition principle of a real-time synchronous pulse wave electrocardiogram monitor.

[0017] Figure 2 This is a system hardware block diagram.

[0018] Figure 3 This is a flowchart of the user interface.

[0019] Figure 4 This is a schematic diagram of a pulse wave electrocardiogram filtering and amplification circuit.

[0020] Figure 5 This is a schematic diagram of a microcontroller circuit. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this is not intended to limit the invention.

[0022] To more clearly illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 The following is an implementation process of the present invention, including the following steps:

[0024] 1) Sensor and electrode connection. Attach silver chloride electrode pads to the left and right subclavian fossa and the lower edge of the left rib, and connect the standard limb lead wires accordingly. Then, place the pad of your index finger into the finger clip-on pulse wave sensor, and insert the two transmission lines into the dual-channel 3.5 mm TRS interface of the acquisition device.

[0025] 2) Connect a ±5V bipolar power supply to power the equipment and ensure stable system operation. This power supply can accommodate positive and negative fluctuations in pulse wave and ECG signals, reducing amplitude distortion. Furthermore, it keeps the signal baseline near the power supply midpoint, improving signal stability.

[0026] 3) Mode Configuration and Data Acquisition. Using the 0.96-inch OLED screen, select a sampling rate of 100 / 200 / 500 / 1000Hz to start pulse wave ECG monitoring. You can also switch to heart rate mode to calculate heart rate per minute based on the number of pulse wave peaks and troughs.

[0027] 4) The two signals are preprocessed using amplifiers and filters to ensure high-quality signals. The ECG signal is first amplified by an instrumentation amplifier with a gain of 7. Then, a 0.1Hz high-pass filter removes low-frequency baseline drift, a 108Hz low-pass filter removes high-frequency electromyography interference, and a 50Hz notch filter removes power frequency interference. Finally, it is amplified 50 times by an inverting amplifier and further amplified 5 times by an inverting adder. The pulse wave signal is first amplified 4 times by an inverting amplifier, then boosted to 1.65V by a voltage follower to meet the requirements of subsequent AD conversion.

[0028] 5) The microcontroller processes the two signals. The signals are input to the STM32 main control chip, and an external crystal oscillator synchronously triggers dual-channel 12-bit ADC sampling to avoid phase shift. Dual independent moving averages correct the baseline, and the signals are mapped to the OLED screen in separate zones for display. Parallel buffering and partial refresh ensure synchronized and clear waveforms. Furthermore, data transmission can be achieved through communication with the host computer via the USART serial port.

[0029] Figure 2 The diagram shown is a system hardware block diagram of the present invention. The hardware architecture of the pulse wave electrocardiogram synchronous measurement device is designed to achieve high-precision capture and processing of cardiac mechanical and electrophysiological activities. The core components of the device are as follows: a contact electrode serves as the signal acquisition front end, capturing weak bioelectrical signals generated by the fingertip and heart region through the skin interface; a medical-grade lead wire serves as the signal transmission medium; and the signal conditioning unit includes a three-stage amplification circuit to effectively suppress environmental electromagnetic interference and motion artifacts. The STM32 microcontroller, equipped with a real-time operating system, not only completes 12-bit ADC sampling and data buffering but also implements tasks such as QRS complex detection and heart rate calculation through embedded algorithms. A USART serial port module is used as the communication interface to ensure that monitoring data can be synchronized to the host computer in real time. The power management system provides a ±5V bipolar power supply to ensure that the voltage amplitude meets the monitoring requirements.

[0030] Figure 3The diagram shows the user interface flowchart of this invention. In this system, the user interface plays a central role, undertaking a series of key functions such as controlling hardware components, processing acquired data, analyzing signals, and providing user interaction. The core objective of the user interface design is to achieve efficient interaction with the operator. To this end, it integrates multiple practical functions to meet the user's needs in different scenarios. First, users can configure the device through the interface, flexibly adjusting the device's operating mode and parameters to adapt to different measurement requirements. Second, the user interface clearly displays measurement data, including intuitively presenting pulse waves and electrocardiogram waveforms, allowing users to observe signal changes in real time. Furthermore, the user interface can display heart rate values ​​in real time, providing users with immediate physiological status feedback. To meet more precise measurement needs, users can also adjust the sampling rate through the interface to optimize the accuracy and efficiency of data acquisition. Simultaneously, the user interface supports serial port functionality, enabling waveform display and heart rate data printing via the serial port, facilitating remote monitoring or data interaction with other devices. The integration of these functions not only enhances the user experience but also strengthens the practicality and flexibility of the pulse wave electrocardiogram measurement device.

[0031] Figure 4 The diagram shows the circuit schematic of the pulse wave ECG amplification and filtering section in this invention. For the ECG signal, the weak signal is first amplified by an instrumentation amplifier with a gain of 7. Then, a 0.1Hz high-pass filter removes low-frequency baseline drift, and a 108Hz low-pass filter removes high-frequency electromyography interference. Subsequently, a 50Hz notch filter precisely suppresses power frequency interference. Finally, the signal is amplified 50 times by an inverting amplifier and 5 times by an inverting adder to achieve a secondary gain to meet the acquisition requirements. For the pulse wave signal, it is first amplified 4 times by an inverting amplifier, and then boosted by a voltage follower to 1.65V to adapt to the subsequent ADC input range. Both design paths ensure signal purity and compatibility.

[0032] The specific calculation process for the ECG amplifier circuit is as follows:

[0033]

[0034] In the formula, For output voltage, Input voltage, and For comparison resistors.

[0035] The ECG amplifier circuit can gradually amplify weak ECG signals at the millivolt level to an amplitude suitable for the AD converter, providing a signal foundation that meets the accuracy requirements for subsequent filtering and digital processing.

[0036] The specific calculation process for the pulse wave amplifier circuit is as follows:

[0037]

[0038] In the formula, For output voltage, Input voltage, and For comparison resistors.

[0039] Similar to electrocardiogram (ECG) amplifier circuits, pulse wave amplifier circuits amplify weak pulse wave signals from the human body to the range of the ADC (Amplifier-Digital Converter) for further processing by the microcontroller.

[0040] Figure 5 The diagram shown illustrates the circuit schematic of the main control chip in this invention. For the synchronous acquisition of pulse wave and ECG signals, a clock-triggered, synchronous sampling, and real-time transmission control strategy is employed to ensure no phase shift between the two signals. Using a microcontroller as the core, an external crystal oscillator provides a stable reference clock. A timer generates a synchronous trigger pulse, driving a dual-channel 12-bit ADC to start simultaneously. The ADC acquires pre-processed pulse wave and ECG signals adapted to its input range, respectively. The data is temporarily stored for subsequent processing, ensuring timing consistency between the two signals. This acquisition method, with its temporary data storage, does not consume CPU resources, ensuring efficient subsequent signal processing.

Claims

1. A real-time synchronized pulse wave electrocardiogram monitor, characterized in that, Includes the following steps: (1) Attach the ECG electrodes (left / right infraclavicular fossa, lower edge of left rib), insert the finger clip pulse sensor into the pad of your index finger, and then connect the acquisition device interface; (2) Connect the positive and negative 5V bipolar power supply to power the equipment components; (3) Set the sampling rate through the buttons on the OLED screen, select the pulse wave ECG waveform monitoring mode or the heart rate calculation mode, and then start the data collection; (4) The signal is preprocessed by amplifier and filter. The electrocardiogram signal is amplified, bandwidth filtered, and power frequency notch filtered before being amplified again. The pulse wave signal is amplified and the voltage is increased. (5) The microcontroller drives the dual-channel ADC to synchronously acquire signals and simultaneously completes tasks such as AD conversion, waveform drawing, and USART serial communication.

2. The real-time synchronized pulse wave electrocardiogram monitor according to claim 1, characterized in that... In step (1), the specific method for placing the ECG electrodes on the surface of the human body and inserting the fingertip of the index finger into the finger clip pulse wave sensor is as follows: First, connect the ECG electrodes: Take the silver chloride bioelectrode pads and apply conductive gel or ointment to their conductive surfaces to improve skin contact and reduce impedance. Attach them to the corresponding left / right infraclavicular fossa and the lower edge of the left rib cage. Then, connect the yellow electrode of the standard limb lead ECG electrode cable to the left infraclavicular fossa electrode pad, the red electrode to the right infraclavicular fossa electrode pad, and the green electrode to the lower edge of the left rib cage electrode pad. Next, connect the pulse wave sensor: Dry your index finger and place it inside the finger clip-on pulse wave sensor. Finally, insert the ECG transmission line and pulse wave transmission line into the dual-channel 3.5mm TRS interface of the hardware acquisition device.

3. The real-time synchronized pulse wave electrocardiogram monitor according to claim 1, characterized in that... In step (2), the specific advantages of using a bipolar power supply are: Bipolar power supplies, with their positive and negative voltage rails, can more completely absorb the positive and negative fluctuations of ECG and pulse wave signals (such as the positive peak of the QRS complex and the negative trough of the T wave in an ECG signal), avoiding signal amplitude distortion caused by the voltage limitation of unipolar power supplies and effectively improving the integrity of signal acquisition. Furthermore, the baseline of ECG and pulse wave signals is susceptible to fluctuations caused by respiratory and electromyographic interference. Bipolar power supplies, through symmetrical voltage biasing, can stabilize the signal baseline near the power supply midpoint, eliminating the need for additional complex circuit compensation, simplifying the design process and significantly improving signal stability. Finally, circuits powered by bipolar power supplies have more stable signal ground and power ground potentials, effectively suppressing common-mode interference and 50Hz power frequency interference, reducing the impact of external electromagnetic noise on weak ECG and pulse wave signals, and ensuring the accuracy of monitoring data.

4. A real-time synchronized pulse wave electrocardiogram monitor according to claim 1, characterized in that... In step (3), the specific advantages of adjustable sampling rate are: The dynamic sampling rate can flexibly adapt to different monitoring needs. For routine health monitoring, selecting 100 or 200Hz can reduce data volume, lower device power consumption, and meet long-term use requirements. When detailed analysis of ECG QRS wave details or pulse wave characteristics is needed, adjusting to 500 or 1000Hz can completely capture minute signal fluctuations and avoid the loss of critical information.

5. A real-time synchronized pulse wave electrocardiogram monitor according to claim 1, characterized in that... In step (4), the amplifier combined with the filter in the ECG processing circuit can both filter out potential noise interference in the ECG signal and further amplify the ECG signal. The specific method for amplifying the ECG signal using the amplifier circuit is as follows: Electrocardiogram (ECG) signals, being a typical type of weak signal, need to be amplified to an amplitude range that a microcontroller can process to ensure the accuracy of the obtained signal results. The calculation formula for the in-phase amplifier circuit is as follows: In the formula, For output voltage, Input voltage, and For comparison resistors.

6. A real-time synchronized pulse wave electrocardiogram monitor according to claim 1, characterized in that... In step (4), the amplifier combined with the filter in the ECG processing circuit can both filter out potential noise interference in the ECG signal and further amplify the ECG signal. Specifically, the method for amplifying the pulse wave signal using the amplifier circuit is as follows: As a physiological signal with a low voltage amplitude at the millivolt level, the pulse wave signal also needs to be amplified by a certain factor for effective monitoring. The calculation formula for the amplification circuit is as follows: In the formula, For output voltage, Input voltage, and For comparison resistors.

7. A real-time synchronized pulse wave electrocardiogram monitor according to claim 1, characterized in that... Step (5) includes: To achieve synchronous acquisition of pulse wave and electrocardiogram signal, a control strategy of clock triggering, synchronous sampling and real-time transmission is adopted to ensure that there is no phase shift between the two signals. The system is centered around a microcontroller, with an external crystal oscillator providing a stable reference clock. A timer generates synchronous trigger pulses to drive dual-channel 12-bit ADCs to start simultaneously, acquiring pre-processed pulse waves and ECG signals adapted to the ADC input range. The acquired data is temporarily stored for subsequent processing, effectively ensuring the timing consistency of the two signals. In this acquisition method, data storage does not consume CPU resources, ensuring efficient subsequent signal processing.

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