Nowadays, the heart rate monitoring function of intelligent wearable products represented by smart bracelets and smart watches is being accepted by more and more people, and even some people have already regarded it as one of the necessary functions for selecting products. So how does smart wearables monitor heart rate? Today, let’s talk about heart rate monitoring. As one of the most important vital signs of the human body, each person's heart rate will vary according to age, gender and other physiological conditions. In general, the average heart rate of a normal adult is about 75 beats / min (60 to 100 beats / min). In the same person, when the heart rate is slow or sleep, the heart rate is slowed down, and the heart rate is accelerated during exercise or emotional excitement. Under the influence of certain drugs or neurohumoral factors, the heart rate may be accelerated or slowed down. People who often perform physical labor and physical exercise usually have a slow heart rate. Specifically, the factors affecting heart rate changes are mainly three major regulatory systems, namely, self-regulation, fluid regulation, and neuromodulation. Changes in heart rate can directly or indirectly reflect the various aspects of the body's health, which is the significance of measuring heart rate. In the field of smart wear, the significance of measuring heart rate is mainly reflected in three aspects. The first is sports. The heart rate can reflect the real information of the user during exercise. If the heart rate is too high, the exercise is too intense, and the user's body water evaporates too quickly. This kind of exercise is not good for the body. If the heart rate is only low, the user is not high enough. It is impossible to burn enough calories. Secondly, in terms of diseases, monitoring the resting heart rate in the normal range, monitoring cardiac arrest during daily activities, abnormally increased heart rate, etc. can play a role in preventing diseases in a timely manner, and even detecting heart rate through ECG can detect abnormal heart rhythm. In addition, pulse wave changes can be monitored by fingertip photoplethysmography to analyze pulse rate, blood oxygen concentration, microcirculatory peripheral vascular status in diabetic patients, and the like. Finally, the mental aspect, through the monitoring of heart rate variability, can analyze autonomic function assessment, such as mental stress, tension and relaxation, and sleep quality. As an emerging product of the 21st century, smart wearable products, due to its specific use scenarios and wearing requirements, the heart rate monitoring technology applied in this field currently mainly has photoplethysmography, which is called photoelectric method, ECG signal method, pressure oscillation. Law, image signal analysis and other categories. Photoelectric method Simply put, this method of measuring heart rate is based on the principle of absorption of light by matter. The green LED lamp of the smart wearable device is used to illuminate the blood vessel with the photodiode for a period of time. Since the blood is red, it can reflect the red light. In green light, when the heart beats, the blood flow increases, and the absorption of green light will increase. When the heart beats, the blood flow will decrease and the absorbed green light will decrease. Therefore, the heart rate can be measured based on the absorbance of blood. Specifically, when a beam of a certain wavelength is irradiated onto the surface of the skin, the beam will be transmitted to the photoreceiver by transmission or reflection. In the process, the detector monitors the intensity of the light due to the attenuation of skin muscle and blood absorption. Will be weakened. The skin, bones, meat, fat, etc. of the human body reflect the light at a fixed value, while the capillaries and arteries and veins become larger and smaller with the pulse volume under the action of the heart. When the heart contracts, the peripheral blood volume is the largest, the light absorption is also the largest, and the detected light intensity is the smallest. When the heart is dilated, on the contrary, the detected light intensity is the largest, so that the light intensity received by the light receiver is followed. A pulsating change. Most smart watches use photoelectric methods to monitor heart rate. Their distinctive feature is that the sensor is equipped with green LED lights. There are many kinds of photoelectric sensors for this measurement principle. According to the different receiving positions of optical signals, the photoelectric method can be divided into two modes of transmission and reflection. 1 transmission photoelectric method Transmissive photoelectric method refers to the fact that the emitter and the photosensitive detector on the wearable device are located on both sides of the measured part (usually fixed by a clip), and the incident light passes through the skin into the deep tissue, except Except for absorption by skin, muscle, blood, bones, etc., the remaining portion of the light transmission is perceived by the photosensitive receiver. According to its principle, the measuring part suitable for this method is a tissue with a relatively short distance between the two sides of the human body, such as earlobe, fingers, toes, etc., and representative smart wearable products are ear clip type heart rate monitors and nail oximeters. Wait. Smart wearable products using transmissive optoelectronic methods are usually secured with a clip. The product of this monitoring method usually adopts a structure of sealing the cassette in shape, which can well reduce external light interference, thereby improving measurement accuracy and stability. Because of its high signal-to-noise ratio and stable signal, in addition to measuring heart rate, it can analyze many cardiovascular physiological information such as heartbeat function and blood flow through waveform. The disadvantage is that it is not suitable for use on smart wristbands and smart watches, and products applied to earlobes, toes and the like have a feeling of uncomfortable wearing. 2 reflective photoelectric method Contrary to the transmissive photoelectric method, in the reflective photoelectric method, an emitter and a photodetector on the wearable device are located on the same side of the measured portion, and mainly measure the reflected light. The advantage of measuring heart rate in this way is very simple, and the requirements on the measurement site are also very low. As long as the tissue is smooth and the amount of subcutaneous fat is small, it can be measured, such as forehead and wrist. Therefore, most smart phones, smart watches and other wearable devices use this method to measure heart rate. Moreover, the appearance of a smart bracelet or smart watch product also perfectly solves the dual requirements of transmissive photoelectric center rate monitoring and wearing comfort. However, although the reflective photoelectric method performs well under steady state, when the device is worn at the end of the wrist, it will swing up and down like a pendulum as the user walks or moves irregularly. The centrifugal force will cause a large change in blood volume; Systolic pressure and centrifugal force interact in the blood, making it harder to distinguish the blood volume in the blood vessels. It is therefore possible to reduce the accuracy of the heart rate data. In addition, the tightness of wearable devices and the amount of blood flow to the human skin can also affect monitoring accuracy. ECG signal method The ECG signal method is actually the most accurate method for measuring heart rate commonly used at the medical level. During each cardiac cycle, the heart is excited by the pacemaker, the atria, and the ventricle. With the changes in the action potentials of countless cardiomyocytes, these changes in bioelectricity are called ECG, and can be detected by periodic changes in ECG. Heart rate. In addition to heart rate, the ECG can also provide cardiac dysfunction, heart disease, and recovery of cardiac function, physical and psychological stress of the patient. For smart wearable devices, the sensor can determine the heart rate of the user by measuring the electrical signal of myocardial contraction. The principle is similar to that of the electrocardiogram. The accuracy of this method is very high, but the disadvantage is that the circuit is more complicated and takes up PCB space. It is relatively large and susceptible to electromagnetic interference. At the same time, the sensor must be close to the skin and placed at a relatively fixed position. Therefore, smart wearable products using this measurement method are rare. ECG lead system. Pressure oscillation method and image signal analysis The pressure oscillation method is mainly applied to the electronic sphygmomanometer. The sphygmomanometer cuff is pressed to the arm, and the pulse amplitude of the arterial blood vessel is detected by the membrane pressure sensor to perform AD conversion, thereby measuring the blood pressure and the pulse rate (how many pulse waves are available according to a certain period of time) Calculate the heart rate). Image signal analysis mainly uses the facial image to estimate the heart rate. Because the color of the face changes slightly when the heart beats, and the chest and shoulders also have subtle movements, the collected image can be estimated heart rate and respiratory rate. The Vital-Radio launched by the Massachusetts Institute of Technology is a Wi-Fi signal sent by the router. When the signal encounters people or objects around it, it will rebound immediately. The special algorithm can calculate the reflection speed of each signal. In order to judge whether there is a living object, if it is a living body, this product will record the human heart rate and respiratory rate. These two methods are more demanding for the user, and are limited to the relatively static situation of the human body. The improper results of the method are also much worse, and even the measurement results of patients with certain cardiovascular diseases are not accurate. Therefore, there are very few products in the field of smart wearable devices that use these two methods to measure heart rate. After reading the heart rate monitoring methods described above, which smart wearable device should consumers choose? For smart wearable device manufacturers, this depends on the market positioning of the product. If you are positioned as a fashion bracelet, its ability to monitor your heart rate is often just an embellishment. Most of the functions that users use may be time watching, SMS push, step counting, etc. At this time, you only need to provide static heart rate function. enough. If it is a sports watch, the photoelectric method wins with its convenience and wearing comfort; mainly used in the direction of motion, then the heart rate accuracy rate monitored by photoelectric method can basically meet the demand. In addition, for ordinary sports monitoring needs, sports watches need to achieve dynamic heart rate function, and can monitor heart rate for a long time in real time, and need to better eliminate heart rate signal interference caused by exercise during exercise. Therefore, using a compensation algorithm such as an accelerometer is a better choice. A foreign study comparing Apple Watch with professional heart rate monitor Mio Alpha showed that Apple Watch heart rate monitoring is comparable to Mio Alpha. For the average consumer, the heart rate monitoring function of most smart wearable products in the world is more accurate, and it is more than enough as a tool for ordinary people's sports and fitness monitoring. Therefore, you only need to choose according to your own estimated price, personal preference and other characteristics. However, for relatively professional athletes, it is recommended to wear a heart rate chest strap that measures ECG signals because these products are more accurate and can provide more health indicators by monitoring athletes' heart rate variability. Pure Sine Wave,Single Phase Hybrid Inverter,3 Phase Hybrid Inverter,Split Phase Hybrid Inveter Easun Power Technology Corp Limited , https://www.epinverter.com
