How to analyze HRV and how to measure HRV through smart watches

Why check heart rate variability?

HRV is an interesting and non-invasive method to identify these ANS imbalances. If a person’s system is more in battle or flight mode, the difference between subsequent heartbeats is small. If a person is in a more relaxed state, the variation between beats is large. In other words, the healthier the ANS, the faster the shift speed and the more flexibility and flexibility it exhibits. In the past few decades, research has shown a relationship between low HRV and worsening depression or anxiety. Low HRV is even associated with increased risk of death and cardiovascular disease.

People with high HRV may have better cardiovascular health and be more resilient to stress. HRV can also provide personal feedback on lifestyle and help motivate those who are considering steps towards a healthier life. It is interesting to see how HRV changes when more mindfulness, meditation, sleep, and especially physical activities are incorporated into life. For those who like data and numbers, this may be a good way to track how the nervous system not only responds to the environment, but also to emotions, thoughts, and feelings.

Heart rate variability is not only related to the condition of our nervous system and heart, but also a response to our daily habits and conditions. We can measure HRV through Veepoo Watch RIG.

How is heart rate variability analyzed?

Heart rate variability analysis is most commonly used to calculate the R wave in the electrocardiogram. By measuring the time interval between RRs, it becomes a series of numbers, and then further calculation and analysis. The mode can be analyzed in time domain (or time domain) and frequency domain (or frequency domain). Heart rate variability analysis usually excludes cases with obvious abnormal rhythms such as arrhythmia, but studies the slight heart rate differences under normal rhythm.

Time domain analysis

Usually, the continuously measured ECG waveform is used to directly calculate and analyze the discrete degree of the corresponding heartbeat interval, for example:

SDNN (Standard deviation of NN intervals), usually calculates the standard deviation of the 24-hour normal heartbeat interval; the unit is milliseconds

SDANN (Standard deviation of the average NN intervals), usually divided into five-minute continuous intervals, first calculate the average of the heartbeat interval every five minutes, and then calculate the standard deviation of the average interval; the unit is milliseconds.

NN50 (Number of pairs of successive NNs that differ by more than 50 ms), the number of intervals between each pair of adjacent normal heartbeats in the ECG, the difference exceeds 50 ms.

pNN50 (Proportion of NN50 divided by total number of NNs), the number of NN50 divided by the total number of normal heartbeat intervals in the measured electrocardiogram.

Frequency domain analysis (Frequency domain)

The discrete Fourier transform is used to convert the time series of the heartbeat interval into the frequency domain, which is expressed in the form of power spectral density or spectral distribution. Generally, the spectrum analysis of heart rate variability signals uses 200 to 500 continuous heartbeat intervals to stably record performance, so the recording takes several minutes. The frequency of the general heartbeat interval spectrum appears below 1 Hz, and several peaks can be found in the range of 0 to 0.4 Hz. Mainly high frequency area (0.15-0.40 Hz) and low frequency area (0.04-0.15 Hz). The high frequency area usually reflects the activity of the parasympathetic nerve, and the low frequency area is regulated by both the sympathetic and parasympathetic nervous system.

How to check heart rate variability?

In the past, the monitoring of HRV was mainly through medical devices. At this time, we have to go to the hospital to perform HRV monitoring. This is a very cumbersome and tiring process. However, since smart watches use the HRV function on it, HRV monitoring has become more convenient. Especially since 2020, manufacturers such as Huawei, Apple, Samsung, OPPO, Xiaomi, Huami, Veepoo 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. The ECG signal sampling frequency can reach 512HZ. And in 2021, OnePlus and Meizu also joined the smart watch market. When using Watch RIG for HRV monitoring, it only takes 30 seconds to get the result. Now the standard of HRV monitoring has reached the medical level. In the future, the application of HRV in smart watches will be more accurate.

Let us look forward to HRV technology in smart watches.