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Is HRV only related to the heart?


The relationship between HRV and the nervous system


HRV is regulated by the autonomic nervous system (ANS) and its sympathetic and parasympathetic branches. It is widely regarded as a non-invasive marker of autonomic nervous system activity. The sympathetic branch of the ANS is the pressure or fight or flight system that prepares us to act, react, and perform.

The parasympathetic nerve is characterized by rest and the digestive system, which allows the body to shut down and recover “after the fight is over.” The sympathetic nerve branch activates the production of stress hormones and increases the contraction rate and strength of the heart and reduces the heart rate variability, which is necessary in cases of sports and mental or physical stress. Conversely, the branch of the parasympathetic nerve slows the heart rate and increases the HRV to restore homeostasis after the stress has passed. This natural interaction between the two systems allows the heart to respond quickly to different situations and needs.

The importance of heart rate variability

Under normal and healthy conditions, HRV should increase during relaxation activities, when the parasympathetic nervous system should be dominant (see Figure 2 for an example). On the other hand, HRV naturally decreases during periods of stress, when sympathetic nerve activity increases to help the body keep up with demand. Therefore, when the heart beats slowly, the HRV is usually higher, and when the heart starts to beat faster, such as during stress or exercise, the HRV decreases.

HRV levels change naturally every day, depending on the level of activity and the degree of work-related stress, but if a person is in a state of physical or mental stress or overload for a long time, the natural interaction between these two systems can be disrupted , The body will fall into a state of sympathetic innervation. Even at rest, HRV is very low and stress hormone level is very high. This is very exhausting to the body and may cause various mental and physical health problems.

The graph above reflects a person’s HRV graph (RMSSD in milliseconds) within 24 hours, showing how HRV dropped to almost zero during exercise (stopping of parasympathetic nerve activity) and increased significantly during meditation and sleep.

Genetic factors explain approximately 30% of overall HRV levels, but a person can improve their personal HRV by improving their health, fitness, stress management, and recovery skills. High HRV is generally considered an indicator of heart health. Many studies have found that higher HRV is associated with lower morbidity and mortality, as well as improved mental health and quality of life. We have to accept what genes give us, even if there are some general reference values, it is meaningless to compare with other people’s HRV values. The good news is that lifestyle has a great influence on HRV. We can take active measures to improve our lifestyle, actively exercise and strive to achieve a better balance in our lives, and in the process, our HRV may also improve.

How is HRV used in smart watches?

The HRV function is not only used in traditional medical devices, but also in smart watches that have been booming in recent years. Moreover, the accuracy of the data monitored on the smart watch is not worse than that of traditional medical devices. This is mainly due to the high-precision sensor on the back of the smart watch. Starting in 2020, Huawei, Apple, Samsung, OPPO, Xiaomi, Huami, Veepoo and other manufacturers have developed the HRV function to the extreme and put it into use on their products, especially the newly developed product Watch RIG of Veepoo, and its ECG signal The sampling frequency can reach 512HZ. The standard has reached the medical level. In the future, the application of HRV in smart watches will be more accurate.

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