It’s been known for decades that heart rate variability (HRV) during labor signals how a fetus is responding to stress. Lower HRV—a lower variation in heartbeats—is even a risk factor for sudden infant death syndrome. But beyond infancy, does it even matter?
Turns out it does, quite a bit. Heart rate variability is governed by the autonomic nervous system; those parasympathetic (PNS, “rest and digest”) and sympathetic (SNS, “fight or flight”) nervous system branches you’ve heard about. HRV in humans (not only fetuses and infants), is a direct response to activity in the PNS and SNS. Higher HRV—more variation in the time between heartbeats—means the PNS (or “relaxation” nervous system, which includes the vagus nerve), is more active.
In simple terms, when the parasympathetic nervous system activates, HRV increases. Our heart rate is more variable and we feel relaxed and comfortable. We’re well-regulated. If HRV lowers, we’re stressed. When chronic, this can be a risk factor or indicator of heart disease, diabetic neuropathy, stroke, and other disorders, including sudden death.
Thus, HRV is a signal of the........