How Does the Smart Watch Perform Heart Rate Monitoring?

How Does the Smart Watch Perform Heart Rate Monitoring?


By reading this article, you can learn in detail the specific methods for smartwatches to monitor heart rate, so that you can use this smart wearable device.

the specific benefits of having a smartwatch

As one of the most important vital signs of the human body, everyone's heart rate varies with age, gender, and other physiological conditions. Generally speaking, the average heart rate of a normal adult at rest is about 75 beats per minute (between 60 and 100 beats per minute).

In the same person, the heart rate slows down during quiet or sleep, and the heart rate increases during exercise or emotional excitement. Under the influence of certain drugs or neurohumoral factors, the heart rate will increase or decrease. People who do physical labor and physical exercise often have a slower heart rate.

Specifically, the main factors affecting heart rate changes are the three major regulatory systems, namely self-regulation, humoral regulation, and neuroregulation. The change of heart rate can directly or indirectly reflect the health of the human body in many aspects, which is the meaning of measuring heart rate. In the field of smart wear, the significance of measuring heart rate is mainly manifested in three aspects.

First of all, in terms of exercise, the heart rate can reflect the real information of the user's body during exercise. If the heart rate is too high and the exercise is too vigorous, and the user's body water evaporates too fast, then this kind of exercise is not beneficial to the body. If the heart rate is not high enough for light exercise, the user It is also impossible to burn enough calories.

Secondly, in terms of disease, monitoring whether the resting heart rate is in the normal range, monitoring cardiac arrest and abnormal heart rate during daily activities can play a role in preventing diseases in time, and even monitoring the heart rate through ECG can detect whether the heart rhythm is abnormal. In addition, fingertip photoplethysmography can also monitor pulse wave changes to analyze pulse rate, blood oxygen concentration, and the state of microcirculation and peripheral blood vessels in diabetic patients.

Finally, the mental aspect. Through the monitored heart rate variability, the autonomic nerve function assessment can be analyzed, such as mental stress, tension and relaxation, and sleep quality.

With the arrival of the intelligent wave, smartwatches have ushered in a period of rapid development, and the functions of the products are constantly improving. For example, more and more smartwatches are equipped with a heart rate monitoring function that can feedback the health of the human body in real-time. We understand the following heart rate monitoring methods to clarify the specific methods for smartwatches to monitor heart rate.

Photoelectric method

Simply put, this method of measuring heart rate is based on the principle of light absorption by substances. The green LED lamp of the smart wearable device is matched with the photosensitive photodiode to illuminate the blood vessel for a period of time. Since the blood is red, it can reflect the red light and absorb it.

With a green light, when the heart beats, the blood flow increases, and the amount of green light absorbed will increase accordingly; when the heart beats the gap, the blood flow will decrease, and the absorbed green light will also decrease. Therefore, the heart rate can be measured based on the absorbance of blood.

Specifically, when a light beam of a certain wavelength irradiates the skin surface, the light beam will be transmitted to the photoelectric receiver through transmission or reflection. In this process, due to the attenuation effect of skin muscle and blood absorption, the detector monitors the intensity of the light Will weaken. The body's skin, bones, meat, fat, etc. reflect light at a fixed value, while capillaries and arteries, and veins are constantly increasing and decreasing 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 the largest, and the detected light intensity is the smallest; when the heart is diastolic, the opposite is true, the detected light intensity is the largest, and the light intensity received by the light receiver follows. Shows pulsating changes.

Most smartwatches use the photoelectric method to monitor heart rate. Their obvious feature is that the sensor part is equipped with a green LED light.

There are many types of photoelectric sensors for this measurement principle. According to the different receiving positions of the light signal, the photoelectric method can be divided into two modes: transmission and reflection.

(1) Transmissive photoelectric method

The transmission photoelectric method refers to the fact that the generator and photosensitive receiver on the wearable device are located on both sides of the measured part (usually fixed by a clip). The incident light passes through the skin and enters deep tissues, except for skin, muscle, blood, Outside of the absorption by bones, the remaining part of the light transmission is sensed by the photosensitive receiver.

According to its principle, this method is suitable for measuring parts of the human body with a relatively short distance between the two sides of the body, such as earlobes, fingers, toes, etc., and representative smart wearable products are those ear clip heart rate monitors and nail oximeters.

The product of this monitoring method usually adopts the structure of a sealed cassette in appearance, which can well reduce the external light interference, thereby improving the measurement accuracy and stability.

Due to its high signal-to-noise ratio and stable signal, in addition to measuring heart rate, it can also analyze heartbeat function, blood flow, and many other cardiovascular physiological information through waveforms. The disadvantage is that it is not suitable for use on smart bracelets and smartwatches, and products used on earlobes, toes, and other parts will feel uncomfortable to wear.

(2) Reflective photoelectric method

Contrary to the transmissive photoelectric method, in the reflective photoelectric method, the generator and the photosensitive receiver on the wearable device are located on the same side of the measured part, and the reflected light is mainly measured.

The advantage of this method for measuring heart rate is that it is very simple and has low requirements for the measurement site. As long as the tissue is relatively smooth and there is less subcutaneous fat, it can almost be measured, such as the forehead and wrist.

Therefore, most wearable devices such as smart bracelets and smartwatches adopt this method to measure heart rate. Moreover, the appearance of smart bracelets or smartwatches in the form of products also perfectly solves the dual requirements of transmission-type photoelectric method center rate monitoring and wearing comfort.

However, although the reflective photoelectric method performs well in a stable state when the device is worn on 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; The interaction of systolic pressure and centrifugal force in the blood makes it more difficult to distinguish the amount of blood in the blood vessels.

Therefore, the accuracy of the heart rate data may be reduced. In addition, the tightness of the wearable device and the blood flow of the human skin will also affect the accuracy of the monitoring.

ECG method

The ECG signal method is actually the most accurate method of measuring heart rate commonly used at the medical level. In each cardiac cycle, the heart is excited by the pace point, atrium, and ventricle one after another, accompanied by countless changes in the action potential of myocardial cells.

These changes in bioelectricity are called electrocardiograms and can be detected by the periodic changes of the electrocardiogram. Heart rate. In addition to heart rate, ECG can also provide information including heart dysfunction, heart disease, and recovery of heart function, the patient's physical and psychological stress, etc.

For smartwatches, the equipped sensor can judge the user's heart rate by measuring the electrical signal of myocardial contraction. The principle is similar to that of the electrocardiogram.

This method has high accuracy, but the disadvantage is that the circuit is more complicated and takes up more PCB space. Susceptible to electromagnetic interference, and the sensor must be close to the skin, and the placement position is relatively fixed, so smart wearable products using this measurement method are rare.

Pressure oscillation method and image signal analysis method

The pressure oscillation method is mainly used in electronic sphygmomanometers. The cuff of the sphygmomanometer pressurizes the arm, and the pulsation amplitude of the arteries is detected by the membrane pressure sensor for AD conversion, thereby measuring blood pressure and pulse rate (according to how many pulse waves there are in a certain period of time).

The image signal analysis method mainly uses facial images to estimate heart rate. Because the color of the human face changes slightly when the heartbeats, and there are subtle movements of the chest and shoulders, the heart rate and respiratory rate can be estimated from the collected images.

These two methods have higher requirements for users and are limited to the situation where the human body is relatively static. The results of improper methods will be 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.

The smartwatch designed and manufactured by ProSelect is equipped with a sensitive heart rate sensor, which can monitor and feedback our body's heart rate health in real-time. When used with training equipment, it can also achieve a better heart rate training effect.

We are a high-quality wearable device manufacturer with many years of experience. We always focus on product quality and customer needs. In order to control the quality of our products, we are equipped with a professional quality inspection system and a comprehensive management team. We can also provide a thoughtful one-stop shopping service according to the diverse needs of users. If you want to buy our smartwatches, please contact us immediately!