The HRV measurement system is similar to the heart rate measurement system of common fitness equipment. There are two common techniques for measuring heart rate: one is based on electrocardiogram (EKG) and the other is based on optical pulse pickup (as in pulse oximeter system). EKG is the most commonly used technology because it can provide reliable performance for the wearer in any case, and it will not be affected no matter what state the user is in (e.g. shaking or resting). This system requires electrodes to be connected to the user’s chest or arm. EKG is easy to develop and can work continuously, mainly because the amplitude of EKG signal is usually 1 mV. With the help of new low-cost electronic devices, the operation of the process has become quite simple. In the current EKG heart rate measuring equipment, the chest strap sports watch is a good example.
In short, heart rate variability analysis is to record heart rate and calculate its change trend over time. For individuals, HRV is almost or completely absent when the body is completely relaxed. Experts point out that low heart rate and no HRV means that the human body is in the best relaxed state.
A reference design of EKG heart rate measurement system using msp430g2452.
The circuit can be easily extended to perform HRV measurement. Another way to calculate HRV is to measure heart rate using techniques often used with pulse oximeters. Fig. 4 is an optical pulse pickup system based on pulse oximeter technology.