AMA #31: Heart rate variability (HRV), alcohol, sleep, and more

It turns out, when the sympathetic system is revved up, HRV goes down. And when the parasympathetic system is in control, HRV goes up ... As the heart rate speeds up, which is what's happening under sympathetic tone, there's less variability between the beats; when the heart rate slows down, when the body is relaxing, there's more variability between beats.

HRV stands for heart rate variability, and that's a pretty descriptive term because what it measures is the variation in time between heart beats, and that's measured in milliseconds.

The parasympathetic system, the way we would always learn to remember this in medical school was this was the rest and digest system. So, this is the down-regulating system. It conserves energy, it aids in digestion, it slows heart rate.