Under the trend of multi-sign parameter monitoring and diagnostic level, wearable medical products are practicing the concept of thousand-year disease prevention

The “Huang Di Nei Jing”, which integrates ancient Chinese culture and national wisdom, is still outdated today, and even provides important guiding ideas for modern medicine. Its concept of “preventive treatment” is very powerful in the theory of health preservation and medicine today. The spirit of transcending the times. “Suwen·Four Qi Tiao Shen Dalun”: “So the sage does not cure the disease and cures the disease, and the incurable is chaotic and the treatment is not chaotic. This is also called.” Looking at it today, its scientific spirit spanning two thousand years of time and space I have to sigh. Today, people are “preventing diseases” in various ways-and the wearable meaning of 7*24 hours vital signs monitoring is here.

Wearable products are developing in the direction of multi-parameter, differentiation, and precision. Users are no longer satisfied with traditional step counting, sleep analysis, and heart rate monitoring. People are paying more and more attention to our body fat rate, mood, and continuous Blood pressure monitoring, etc., these functions are also ready to emerge. For products in the wearable market, we see two main market development trends: One is that diagnostic products in hospitals are actively seeking to go outside the hospital; traditional wearable products outside the hospital are also changing from focusing on traditional health and entertainment. The diagnostic level develops, and then they converge at the diagnostic level and out-of-hospital point. This trend can be seen from ADI’s two highly integrated AFE (analog front ends).

Signal acquisition system AFE MAX86178 supporting four vital sign test functions

In order to meet the higher performance requirements of analog/power products in the wearable market, ADI recently brought a breakthrough new product to the market-MAX86178 (formerly a product of Maxim, which has been merged into ADI). The clinical-grade analog front end integrates three complete measurement systems of optics, electrocardiogram and bioimpedance (BioZ), and supports four vital sign test functions-ECG, heart rate, blood oxygen saturation and respiration rate, meeting wearable monitoring The demand for miniaturization of the instrument can be applied to a wide range of scenarios including arrhythmia monitoring patches, new crown detection patches, disposable ECG monitors, wearable infectious disease monitoring, and wearable patient monitors.

While the three complete measurement systems are integrated with the chip, they also meet high-performance requirements: ECG (electrocardiogram) analog front-end (AFE) can achieve clinical-level ECG measurement and meet the medical standards of IEC60601-2-47, namely mobile ECG A standard for monitoring; PPG (photoplethysmogram) can achieve clinical-level blood oxygen detection, with a performance of up to 113 dB signal-to-noise ratio; BioZ (bioimpedance), which allows the design of flexible bioimpedance configurations to support multiple kinetic energy measurements , Including ICG, BIA, BIS, GSR/EDA monitoring.

For this reason, the multi-function based on MAX86178 can significantly accelerate the design of multiple vital signs detection systems. Compared with traditional discrete solutions, the size of the MAX86178 solution can be smaller, and the acquisition of signals can be achieved with optical PPG and ECG systems. Synchronize. Compared with the previous generation product MAX86176, the former is an analog front end with two-in-one PPG and ECG functions. The biggest difference from the latter is that the latter adds a new bioelectrical impedance (BioZ) measurement, which can achieve more BioZ biological Frequency range scanning of impedance, or EDA and other applications. In addition, the MAX86178 solution has certain improvements to ECG and PPG. ECG is more suitable for dry electrode applications, and PPG also has some improvements in signal-to-noise ratio.

Wearable health sensor “hub”, multi-mode sensor front end ADPD4100

ADPD4100/ADPD4101 is the “hub” of various electrical and optical sensors in wearable health and fitness equipment, suitable for heart rate and heart rate variability (HRV) monitoring, blood pressure estimation, pressure and sleep tracking, and SpO2 measurement. The multiple working modes of this new multi-parameter VSM AFE can accommodate different sensor measurements in medical and health applications, including but not limited to photoplethysmography (PPG), electrocardiogram (ECG), electrical skin activity (EDA), body composition , Respiration, temperature and ambient light measurement.

Photoplethysmography. PPG measurement can detect changes in the blood volume of the tissue microvascular bed associated with each cardiac cycle. The total absorption of light is correlated with changes in blood volume caused by systolic and diastolic events, producing a PPG signal. The PPG measurement is carried out as follows: LED light pulses are injected into human tissue, and then the reflected/transmitted light is collected by a photodiode, and the light is converted into a photocurrent. ADPD4100 processes and measures the photocurrent, and generates a digital PPG signal. For different PPG measurement situations, the AFE can be flexibly configured to one of four working modes without any changes to the hardware connection: continuous connection mode, multiple integration mode, floating mode and digital integration mode.

Pulse oximetry. Pulse oximetry uses red light (usually 660 nm wavelength) and infrared (IR) LEDs (usually 940 nm wavelength). Deoxyhemoglobin mainly absorbs light with a wavelength of 660 nm, while oxyhemoglobin mainly absorbs light with a wavelength of 940 nm. The photodiode senses the unabsorbed light, and then divides the sensed signal into a DC component and an AC component. The direct current component represents light absorption caused by tissue, venous blood, and non-pulsatile arterial blood. The AC component represents pulsatile arterial blood. Any two time slots of the ADPD4100 can be configured to measure the response to red light and IR LEDs to measure SpO2. The remaining time slots can be configured to measure PPG from LEDs of different wavelengths, and can also support ECG measurement, lead-off detection, respiration measurement, and other sensor measurements.

Heart rate monitoring. For heart rate monitoring, a green LED with a wavelength of about 540 nm is generally preferred. Its modulation index is higher than that of red or IR LEDs, so it can produce the best PPG signal. It also provides a good CTR level, so the power consumption is not too high. AC SNR is a parameter related to signal quality, which can be calculated by multiplying DC SNR by the modulation index. For example, when the modulation index is 1%, 95 dB DC SNR is equivalent to 55 dB AC SNR.

ECG measurement. ECG measurement has been incorporated into wearable devices, such as watches for spot checks and chest stickers for continuous monitoring. Such devices usually use electrodes made of metal and other conductive materials. These electrodes are polarized electrodes and are called dry electrodes. The main challenge of using dry electrodes for ECG measurement is that the electrode-skin contact impedance is very high and the overpotential is relatively high.

When applied to ECG measurement, the ADPD4100 uses a novel method that uses a passive resistor-capacitor (RC) circuit to track the differential voltage on a pair of electrodes. The passive RC circuit can be as simple as only three components, namely two resistors RS and one capacitor CS, as shown in Figure 3a. Each sampling process of ECG data is divided into two steps.

Respiration measurement based on impedance. When the ADPD4100 is used to measure respiration, it detects the changes in the bioimpedance of the lungs during the inhalation and expiration cycles. When the patient breathes, the volume of the lung expands and contracts, causing changes in the impedance of the chest. This impedance change can be measured by injecting current into the chest path and measuring the pressure drop.

Summary of this article:

The past decade has witnessed tremendous progress in the fields of mobile phones, wearable devices and digital health. Especially with the continuous development of Electronic technology and new breakthroughs in technologies such as cloud computing, artificial intelligence, Internet of Things and 5G, digital healthcare has been rapidly expanded and adopted. The increasing awareness of people’s health has led to the need for small but high-precision equipment that should be able to measure various vital signs and health indicators, such as body temperature, heart rate, respiratory rate, blood oxygen saturation, blood pressure, and body composition. It is a challenge to add multiple detection functions to such a small device because it requires a smaller form factor, lower power consumption, and a multi-parameter function with significantly improved performance. However, these challenges can now be met with a single analog front end (AFE) solution. New AFEs like ADPD4100 and MAX86178 can be used as multi-parameter vital signs monitoring centers to support simultaneous measurements. It has the characteristics of low noise, high signal-to-noise ratio, small size and low power consumption, which can significantly improve medical equipment, especially wearable technology.

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