Eighty percent of the fibers of the vagus nerve are afferent (sensory) fibers, which means that they bring information back from the body to the brain, while only 20 percent are efferent (motor) fibers that carry instructions from the brain to the body. Some of the afferent fibers from parts of CN IX and CN X monitor the amount of oxygen and carbon dioxide in the blood. By improving our pattern of breathing with these exercises, we tell the brain (via the afferent nerves) that we are safe and that our visceral organs are functioning properly. This in turn facilitates ventral vagal activity.
