Beyond heart rate variability: vagal regulation of allostatic systems.

The autonomic nervous system (ANS) plays a role in a wide range of somatic and mental diseases. Whereas the role of the ANS in the regulation of the cardiovascular system seems evident, its role in the regulation of other systems associated with allostasis is less clear. Using a model of neurovisceral integration we describe how the ANS and parasympathetic tone in particular may be associated with the regulation of allostatic systems associated with glucose regulation, hypothalamic-pituitary-adrenal (HPA) axis function, and inflammatory processes. Decreased vagal function and heart rate variability (HRV) were shown to be associated with increased fasting glucose and hemoglobin A1c levels, increased overnight urinary cortisol, and increased proinflammatory cytokines and acute-phase proteins. All of these factors have been associated with increased allostatic load and poor health. Thus, vagal activity appears to play an inhibitory function in the regulation of allostatic systems. The prefrontal cortex and the amygdala are important central nervous system structures linked to the regulation of these allostatic systems via the vagus nerve. Finally, the identification of this neurovisceral regulatory system may help to illuminate the pathway via which psychosocial factors may influence health and disease.