Continuous non-invasive blood pressure measurement solution, say goodbye to the era of "rolling up your sleeves"

According to statistics, there are more than 270 million patients with hypertension in my country, and 40% of them do not know that they have hypertension. In order to effectively control hypertension, my country promulgated the "National Primary Hypertension Prevention and Control Management Guidelines" in 2017, and tried to control the prevalence of hypertension through early prevention. Some experts suggest that normal adults should measure their blood pressure at least once every two years, people at high risk of hypertension should measure their blood pressure every six months, and patients with hypertension should measure their blood pressure at least once a week...

October 8 is my country's "National Hypertension Day", and this year's publicity theme is "Know Your Blood Pressure". According to statistics, there are more than 270 million hypertensive patients in my country, and 40% of them do not know that they have hypertension. In order to effectively control hypertension, my country promulgated the "National Primary Hypertension Prevention and Control Management Guidelines" in 2017, and tried to control the prevalence of hypertension through early prevention. Some experts suggest that normal adults should measure their blood pressure at least once every two years, people at high risk of hypertension should measure their blood pressure every six months, and hypertensive patients should measure their blood pressure at least once a week.

Should you roll up your sleeves before measuring your blood pressure?

Currently, we use traditional cuff non-invasive blood pressure devices to measure blood pressure, which uses the Korotkoff method to monitor the vibration of blood and obtain systolic and diastolic blood pressure at fixed or longer time intervals (usually more than 15 minutes). Although the measurement effect is very good, the user experience is not very good.

Why is the user experience of using a cuff non-invasive blood pressure device not very good? First of all, it cannot be measured continuously. Generally, the blood pressure value needs to be measured 1 to 2 times, and the average value is taken as the true blood pressure value of the subject. Secondly, the width of the cuff and the tightness of the measurement site will have a certain impact on the measurement results. Finally, when measuring blood pressure, the sphygmomanometer cuff and stethoscope should be kept as close to the skin as possible, so that the blood pressure measurement can be as accurate as possible. This means that when we use a cuff non-invasive blood pressure device, we must first "undress or roll up our sleeves", especially in winter. The correct way to measure blood pressure is to take off clothes so that the upper limb on the side where the blood pressure is measured is completely exposed. However, a study published in the Chinese Journal of Hypertension stated that taking off clothes will cause a significant increase in blood pressure, and the more clothes you take off, the more obvious it is.

Continuous, comfortable, and wearable blood pressure measurement solution

Continuous non-invasive blood pressure measurement is a technology that monitors the systolic and diastolic blood pressure of the human body in real time or at short intervals. Unlike traditional cuff non-invasive blood pressure device measurement, continuous non-invasive blood pressure provides a continuous and comfortable blood pressure measurement method, and more importantly, it can be easily integrated into existing wearable device platforms such as wristbands and watches.

Simply put, the continuous non-invasive measurement method is to measure blood pressure continuously and non-invasively over a period of time. It can detect beat-to-beat blood pressure and continuous arterial pressure waveform, providing a more sufficient basis for clinical diagnosis and treatment, especially in clinical monitoring and observing continuous changes in blood pressure under special circumstances. It has incomparable advantages over invasive blood pressure and traditional cuff blood pressure measurement.

ADI's continuous non-invasive blood pressure solution achieves ultra-high measurement accuracy

Analog Devices offers a broad range of highly integrated PPG AFEs, ECG AFEs, low power MCUs, power management solutions, and flexible discrete components to optimize product quality and reliability for wearable, continuous, non-invasive blood pressure applications.

The pulse transit time (PTT) method is a research hotspot in the application of continuous non-invasive blood pressure. Its principle is to identify the key characteristic nodes of the plethysmograph (PPG) waveform and calculate the time delay between the current PPG signal and other reference signals such as plethysmograph (PPG), electrocardiogram (ECG) and ballistocardiogram (BCG). Therefore, several combinations of single PPG, multiple PPGs, PPG+ECG and PPG+BCG can be used. Here, the combination of PPG+PPG and PPG+ECG is taken as an example, as shown in Figure 1 below.

Figure 1. Blood pressure measurement using different sensor combinations

The left side of Figure 1 shows multiple PPG solutions suitable for continuous non-invasive blood pressure applications. The blood pressure value can be calculated by the time delay between multiple PPG signal feature points, which need to be pre-processed and identified by software. The location of the PPG sensor is not fixed, but it is necessary to obtain a sufficiently long delay time as much as possible. The greater the distance along the arterial blood vessel, the greater the delay. Therefore, if the sensors of compact wearable devices are placed very compactly, it must be possible to obtain data faster. In addition, the obtained PTT is independent of the absolute time delay, and the final blood pressure needs to be obtained through an algorithm.

The right side of Figure 1 shows a combination of PPG and ECG for a continuous non-invasive blood pressure solution. In this case, the PPG signal is acquired on the wrist or finger of one hand, while the ECG signal is acquired on both hands. The signals must be synchronized and tracked in the time domain to facilitate subsequent data and algorithm processing, as shown in Figure 2 after the synchronization of the PPG and ECG signals.

Figure 2. Synchronized PPG and ECG signals

The figure below shows the multi-sensor fusion diagram of ADI's continuous non-invasive blood pressure integrated discrete component solution. It is easy to expand more sensors using analog MUX switches. These sensors are synchronized through analog MUX switches and ADC scanning, and sensor data is collected one by one. The sampling time interval depends on the ADC sampling rate and the number of channels, and is fixed.

Figure 3. Multi-sensor fusion with integrated discrete component solution

According to Figure 3, some discrete components can be replaced by the latest highly integrated analog front end (AFE). Some AFEs or modules already include the above discrete components, analog MUX switches, and ADCs, so you only need to select one AFE as the host and get the data of all other sensors. Figure 4 shows the multi-sensor fusion of the integrated AFE solution, where PPG is selected as the host sensor to acquire PPG and ECG signals simultaneously. In addition, the host sensor data can be read through the SPI or I 2 C interface.

Figure 4. Multi-sensor fusion with integrated analog front-end solution

From the perspective of the signal chain, ADI provides data communication technologies ranging from sensors and signal conditioning to power and energy collection, signal processing, and cloud-connected data. It combines ADI's own or third-party software algorithm support, and strengthens its power technology advantages through the acquisition of Linear to achieve ultra-low power standby and energy collection functions that are very important for wearable devices. It can be said that ADI provides a complete solution covering the entire signal chain.

Conclusion

Wang Sheng, marketing director of the Asia Pacific region of ADI's healthcare division, believes that whether it is wearable or other market segments, the hope of driving industry and industry development through the combination of "healthcare" is inseparable from the following two points: First, the continuous enrichment and improvement of health care functions, including the collection and processing of basic motion and vital signs signals, and even the monitoring of environmental related data; second, intelligence, as an access window for artificial intelligence, or even a direct hardware device for artificial intelligence end users, through the fusion processing of big data to achieve intelligent deep information mining, thereby solving user pain points and improving the user experience. ADI's continuous non-invasive blood pressure solution is based on these perspectives to provide customers with a complete high-performance solution.

In addition to focusing on high-performance products and system-level solutions, ADI has also established a strong software algorithm team and a professional local technical support team to provide customers with in-depth technical services. This not only reflects ADI's commitment to helping customers meet the market opportunities of medical artificial intelligence, but also provides a glimpse of ADI's strategic pace in the field of medical electronics in China.