I've been using the mobile device made by Heartmath lately — https://store.heartmath.com/tech/. It looks at HRV (heart rate variability) and gives you a realtime plot, thereby offering visual feedback about how my breathing is affecting how steady the time between heartbeats is. Hearthmath calls low HRV "coherence" and getting into a lower HRV state (i.e. via regular, smooth breathing; maybe 1 in/out breath each ~10 seconds) is strongly associated with enhanced levels of calm and clarity — and I would strongly suspect (though can't know for sure) that similar effects would be seen as in the paper w.r.t. the immune system. I've found it exceptionally helpful.
I am on and off a long-term meditator (for about a year I was meditating as much as 2 hours a day). Some people don't achieve deeper states of calm and contentedness, in spite of meditating often (I've encountered this among serious practitioners of zen, for example; this happens to me sometimes, too) and I strongly suspect that lowering HRV would help.
I think you have it backwards, you want a higher HRV, not lower. A higher HRV is healthier. Being in a calm state will have higher HRV, being stressed will result in a lower HRV. Higher HRV is associated with reduced morbidity and mortality, and improved psychological well-being and quality of life.
Interesting. I have an EEG headband (Muse) that tracks a single composite measure of “calmness” while meditating. When I use it, the graph looks like a random walk—it barely registers what subjectively feels like a deep state of calm. I just assumed it didn’t work and stopped using it.
Then I gave it to my dad, who has been an ER doctor for 40 years but has no knowledge of or experience with meditation. Within seconds, his calmness graph plummeted to the minimum value (lower = better) and flatlined. There was a brief spike in attention when the dishwasher changed cycles in the other room, then it cratered again. He just nonchalantly explained that he can control his heart rate to calm himself down, which sounds like a superpower to me.
I am on and off a long-term meditator (for about a year I was meditating as much as 2 hours a day). Some people don't achieve deeper states of calm and contentedness, in spite of meditating often (I've encountered this among serious practitioners of zen, for example; this happens to me sometimes, too) and I strongly suspect that lowering HRV would help.