Research on heart rate variability (HRV), cardiac vagal tone, and their relationship to anxiety
is reviewed in the context of the autonomic flexibility and neurovisceral integration models of
adaptive functioning. These perspectives address the qualities of response flexibility and
inhibition across multiple levels, incorporating central and autonomic nervous system
mechanisms of environmental engagement, as well as principles derived from non-linear
dynamics. These models predict reduced HRV and vagal tone in anxiety, and the literature�…