Vagal tone and the inflammatory reflex.

Inhibition of sympathoexcitatory circuits is influenced by cerebral structures and mediated via vagal mechanisms. Studies of pharmacologic blockade of the prefrontal cortex together with neuroimaging studies support the role of the right hemisphere in parasympathetic control of the heart via its connection with the right vagus nerve. Neural mechanisms also regulate inflammation; vagus nerve activity inhibits macrophage activation and the synthesis of tumor necrosis factor in the reticuloendothelial system through the release of acetylcholine. Data suggest an association between heart rate variability and inflammation that may support the concept of a cholinergic anti-inflammatory pathway.