How can smart wearable products perform the heart rate monitoring?

As the wave of smart life products hit, intelligent equipment dressing ushered in the rapid development of wrist band and smart watches, intelligent ring wearable products emerge in endlessly, the product function also became powerful, such as more and more products are standard on the function of the heart rate monitor.

Today, products with heart rate monitoring function are accepted by more and more people, even as one of the essential functions for the choice.

So, let’s talk about heart rate monitoring, and how they work with us?

Why need measure heart rate?

As one of the most vital signs of life, everyone’s heart rate varies depending on age, sex and other physiological conditions.Generally speaking, normal adults have an average of 75 beats per minute (between 60 and 100 beats per minute).The same person, when the heart rate slows during quiet or sleep, or the heart rate increases when mood or mood is agitated, the heart rate increases or slows with the influence of certain drugs or neurohumoral factors.People who do physical labor and exercise regularly have a slower heart rate.

Specifically, the factors that affect the change of heart rate are mainly three major adjustment systems, namely self-regulation, humoral regulation, and neuromodulation.

The change of heart rate can directly or indirectly reflect the health status of various aspects of the human body, which is the significance of measuring heart rate.

In the field of intelligent wearable, the measurement of heart rate is mainly manifested in three aspects.

First is sports, heart rate can reflect the real information of the body motion, if the heart rate is too high means the sport is too intense, the user’s body moisture to evaporate quickly, so this kind of movement is not a benefit to the body, but if only mild exercise and our heart rate is not high, our body also can not be burning enough calories.

Second, for the diseases, by monitoring the resting heart rate is in the normal range, monitoring of cardiac arrest in everyday activities, such as increased heart rate abnormal can play the role of timely to prevent diseases, even by ecg monitoring heart rate can also detect the rhythm of the heart.

In addition, pulse wave changes can be monitored through the finger photoelectric volume pulse wave method to analyze pulse rate, blood oxygen concentration, and microcirculation peripheral blood tube status of diabetic patients.

Finally, the mental aspect, through the monitoring of the heart rate variability, can analyze autonomic neurological function evaluation, such as stress, tension and relaxation, and sleep quality.

Smart watch SX2 02

How can heart rate monitoring be achieved?

As of the 21st century new product — smart wearable products, which have its specific usage scenarios and requirements, the application in the field of heart rate monitoring technology at present mainly include photoelectric volume pulse wave tracing, hereinafter referred to as the photoelectric method, method of ecg signal, pressure oscillation method, image categories, such as signal analysis, etc.

The photoelectric method

In simple terms, this method of measurement of heart rate is based on the principle, the material of light absorption by intelligent devices dressing green leds collocation of photosensitive photoelectric diode irradiation blood vessel for a period of time, because blood is red, it can reflect red light and green light, absorption when the heart beats, blood flow increase, with the bigger of the uptake of green;

When the heart beats, the blood flow decreases, and the green light absorbed is reduced.

Therefore, the heart rate can be monitored according to the absorbance of the blood.

Specifically, when a certain wavelengths of light ray to the skin surface, the beam will be transmitted through the way of transmission or reflection to the photoelectric receiver, in this process, due to the skin muscles and blood absorption attenuation, detector to detect the intensity of the light will be weakened.

The body’s skin, bones, meat, fat and other light reflections are fixed, while capillaries and arteriovenous veins become smaller and smaller with the pulse volume of the heart.

When the heart contracted, the peripheral blood volume was the largest and the light absorption volume was the largest, the light intensity detected was the smallest.

When the heart is diastolic, the intensity of the light detected is the largest, and the intensity of the light that the receiver receives is fluctuating. 

Most of the smart watches use the photoelectric method to monitor the heart rate, and their distinctive feature is that the sensor site is equipped with green LED lights.

There are many kinds of photoelectric sensors of this kind of measuring principle. According to the different reception positions of optical signals, the photoelectric method can be divided into two modes: transmission and reflection.

1 transmission photoelectric method

Transmittance photoelectric method refers to the generator on the smart devices (emitter) and photosensitive receiver (detector) is located in the both sides of the measured part (usually by a clamp), incident light through the skin into deeper tissue, in addition to the absorbed by skin, muscle, blood, bones and so on, the remaining portion of the light transmission is photosensitive receiver perception.According to the principle of this method for measuring part is the body sides distance short organization, such as the earlobe, fingers, toes, and a representative sample of smart apparel products are those ear clip type a heart rate monitor, fingernail type oxygen meter, etc.

Smart wearable products with transmission photoelectric method are usually fixed with a clamp.

The product of this monitoring method usually adopts the structure of the sealed box, which can reduce the exogenous optical interference very well, thus improving the measurement accuracy and stability.

Because of its high signal-to-noise ratio and stable signal stability, besides measuring the heart rate, it can also analyze cardiac function, blood flow and other cardiovascular physiological information through waveforms.

The disadvantage is that it is not suitable for use in wrist bands and smart watches, and the application of products in the ears, toes and other parts will have an uncomfortable feeling.

2 reflection photoelectric method

Contrary to transmit photoelectric method, reflection type photoelectric method, smart wearable devices generator (emitter) and photosensitive receiver (detector) is located in the same side of the measured parts, mainly measure the reflected light.

The advantage of this method of measuring the heart rate is very easy, the requirement of monitoring site is low, as long as the organization more smooth and subcutaneous fat little place almost all can be measured, such as forehead, wrist.

As a result, most smart wrist bands, smart watches and other smart wearable devices use this method to measure heart rate.

Moreover, the product form of smart band or smart watch also perfectly solves the double requirement of transmission photoelectric method center rate monitoring and wearing comfort.

Reflection type photoelectric method, however, although under the steady state performance is good, but when a device worn on the wrist, at the end with the user while walking or has no regulation motion like a pendulum swinging up and down, the centrifugal force will make the amount of blood appear big change;

When the systolic blood pressure interacts with the centrifugal force in the blood, it is more difficult to discern the amount of blood in the blood vessels.

Thus, the accuracy of heart rate data may be reduced.

In addition, the size of the elastic and human skin blood flow worn by wearables will also affect the monitoring accuracy.

Electrocardiogram

Electrocardiogram is the most accurate method of measuring heart rate commonly used in medical level.

Heart in each cardiac cycle, by pacemaker, atrial and ventricular excited, along with a myriad of myocardial cell action potential changes, these changes in bioelectricity are called ecg, and through the periodical change of ecg can detect the heart rate.

In addition to heart rate, electrocardiogram can also provide cardiac dysfunction, heart disease, cardiac function recovery, physical and psychological stress, etc.

For smart wearable products, equipped with sensors could measure the electrical signals to determine the user’s heart rate of myocardial contraction, principle and electrocardiogram (ecg), the accuracy of this method is very high, but the disadvantage is that circuit is more complex, of PCB space is large, vulnerable to electromagnetic interference, the sensor must be close to the skin at the same time, the place is relatively fixed, so use this way of measuring the intelligence of apparel products.

Method of pressure oscillation and image signal analysis

Pressure oscillation method is mainly used in electronic blood pressure monitor, blood pressure cuff to arm pressure, through the thin film pressure sensor to detect arterial pulse amplitude, AD conversion, thus measuring blood pressure and pulse frequency (how many pulse wave according to a certain time to calculate the heart rate).

Image signal analysis mainly USES the facial image to estimate the heart rate.

Because the color of the person’s face changes slightly when the heart beats, and there are subtle movements in the chest and shoulders, the collected images can be used to estimate the heart rate and respiration rate.

At the Massachusetts institute of technology’s Vital – Radio by router a wi-fi signals, when the signal to meet the people around you immediately begin to rebound or objects, through the special algorithm can calculate the reflection speed for each of the signal, in order to determine whether life object, if is the life, the product will record the human body heart rate and breathing rate.

The demand is higher, the two methods for users are limited to the human body is relatively static, improper methods results will be much worse, and even suffer from certain cardiovascular disease patient measurement result is not very accurate.

As a result, there are very few products that measure heart rate in the field of smart wearables.

Smart Band i9 05

How to choose smart wearable products?

For smart wearable products, it is dependent on the market positioning of the product.

If positioning as a fashion wrist band, its monitoring heart rate function a lot of time is a kind of ornament, users use most of the functions, SMS to see the time may be pushed, steps, etc., this time only need to be able to provide static heart rate function is enough.

If it is a sports smart watch, the photoelectric method wins by its convenience and wearable comfort.

Mainly applied to the direction of motion, the rate of heart rate monitoring by photoelectric method can basically meet the demand.

In addition, for the average movement monitoring requirements, sports smart watch need to accomplish dynamic heart rate function, and can monitor real-time long heart rate, and need in the movement process can be well eliminate disturbance caused by movement of the heart rate signal.

Therefore, it is better to adopt the accelerometer and other compensation algorithm.

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Post time: Oct-17-2017
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