Heart Rate Variability refers to the natural pattern of your pulse being faster when you breathe in and slower when you breath out, because the parasympathetic nervous system acts like a brake during your out breaths.
High Resting Heart Rate Variability signals that your system is getting good input from both the parasympathetic and sympathetic branches of your nervous system, and your parasympathetic nervous system helps you in situations requiring willpower.
Transient increases in Heart Rate Variability can be thought of as reflecting self-regulatory effort and are like withdrawals from your willpower bank account.
Smart phone apps you can use to measure your stress from a heart rate perspective are beginning to come to market. I’ve been experimenting with this one – free iphone heart rate variability app Stress Check Pro by Azumio. I can’t 100% vouch for the algorithm they use since I don’t know the details, but I’ve been experimenting with using it and it’s producing logical results for me. It measures heart rate and heart rate variability using the iphone camera to detect small changes in your finger pulse (I’ve been testing it using the iphone 4). You use it by putting your finger tip over the iphone camera and it detects changes in blood flow in your finger (i.e., your pulse). The app learns from your data so you can’t share the app with others if you share your phone.
Azumio also make a free pulse app, and the results from that match the results I get when I take my pulse by hand.
You can use these apps to learn when your stress is affecting you physiologically, and can do something to reduce your stress (for example, slow breathing). (Keep in mind that elevations sometimes reflect good stress, such as the initial stages of falling in love, check out the neurobiology of falling in love).
We have long known that people whose heart rates are lower (during discussions of conflict topics and also just at baseline), tend to have better relationship satisfaction when followed up years later (study).
One of the ways to use the above apps is that if your arousal climbs sharply while you’re having a conflict discussion, take a break from conflict discussion and only return to it when your arousal is lower (you can’t communicate well while you are having a fight/flight/freeze reaction). You can also use the apps to see what affect it’s having on YOUR body when you yell at / meanly criticize your partner. It might help motivate you to not do it.
There is also some emerging research on Heart Rate Variability and Couple Relationships (e.g., this study and this study).