Heart rate is the most effective measure of exercise and the amount of exercise. In the field of heart rate monitoring, the most accurate should be the heart rate belt, but in the current "face value" society, the cheap and accurate heart rate belt has been out, replaced by various types of bracelets and watches. The bracelet/wrist strap is relatively small and easy to wear and affordable, while sports watches often incorporate a wealth of features such as GPS, heart rate sensors, training modes, and of course the price is the most expensive of all heart rate devices. Regardless of the shape of the happiness rate monitoring, this type of electronic product is related to medicine. This article explains the principle and method of testing in the language of popular non-medical professionals. Four mature heart rate monitoring methods The PhD King of Electronic Engineering, which is engaged in the research and development of wearable medical devices, shares the current mature heart rate non-invasive measurement methods: blood oxygenation method, photoelectric volume method, ECG signal method, and arterial pressure method. (1) Blood oxygen method. If you have done a step test (a heart-forging test for heart and lung function), then you must be familiar with this heart rate test method. The heart rate tester that is attached to the tip of the index finger uses this approach. In general, a complete oximeter often has two kinds of light-emitting diodes, one wavelength of 660 nm, which is red light of visible light, and one wavelength of more than 900 nm, which is infrared light. The oxygen-carrying hemoglobin in the blood vessels and the hemoglobin not carrying oxygen have different absorption rates for the two kinds of light. As shown below. At the same time, the oxygen content in the blood vessels is consumed, and the heart pumping blood is increased, and the cycle process is consumed. This cycle is just the same as the heart rate. The advantage of the oximetry method is to provide both heart rate and oxygen saturation signals. The disadvantage is that because the transmitted light signal needs to be received at the other end, then this part of the human body must be thin enough, and the proper position of the whole body is only the fingertip and the earlobe. The wrist is too thick, the visible light cannot penetrate at all, and the range of use is limited. Therefore, many sports watches do not adopt this scheme. (2) Photoelectric volume method. This solution tracks the reflection of visible light (green light) in human tissue. Usually there are two green LEDs that emit visible light to the wrist, and then a photosensor in the middle to sense the reflected light. as follows: The skin's skin, bones, meat, fat, etc. reflect a fixed value of light, while the capillaries and arterial veins become fluctuating because they become larger and smaller as the pulse volume increases. The frequency of this fluctuation is the pulse, which is generally consistent with the heart rate. This method can only get the heart rate signal, but it is relatively resistant to the noise caused by the movement, which is very suitable for the current sports watch. As for the accuracy, in addition to the apple watch, several other Philips are using the same patented sensor. . . . . . The only flower head that can be done is nothing more than the different algorithms of the accelerometer to compensate for the motion noise. From my experience, it should be similar. As for the reason for using green light - not because the blood is red, so the green light, the real reason is that the signal drift caused by green light to the external temperature changes is the smallest. (3) ECG signal method. The sinus node rhythmically controls the systolic and diastolic heart to pump blood to the trunk. This control signal is an electrical signal (the nerve signal of the human body is expressed as an electrical signal on the nerve), which gradually spreads to the body surface and can be measured on the skin through the electrode. The principle that everyone goes to the hospital is to use this principle. This rhythm is the heart rate. In addition, the ECG signal can provide a lot of reference information for doctor diagnosis. The most accurate wearable heart rate measuring instrument on the market, the heart rate belt, is also used in this method. However, since the wavelength of the ECG signal is very long, in order to measure a signal with sufficient accuracy, the signal electrode and the reference electrode must be spaced far enough apart from the trunk space. Usually it is two points farther away from the chest, or left and right hands, or hands and feet. It is more difficult for a watch to adopt this scheme unless someone is willing to bring two watches at the same time.
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