Selective Vagus Nerve Stimulation in Human

Introduction:

The use of nerve stimulation for treating and controlling a variety of medical, psychiatric, and neurological disorders has seen significant growth over the last several decades. In particular, vagal nerve stimulation (VNS) has been the subject of considerable research.

The vagus nerve extensively innervates the thoracic and abdominal viscera (afferent 80% of fibres) and is an important route of information into the central nervous system (efferent 20% of fibres). One of the vagus main functions is to monitor and control the activity of the internal organs and glands such as the heart, lung, stomach, bladder and pancreas.

Activation of the parasympathetic pathway leads to negative chronotropic, negative dromotropic, and negative inotropic changes in the heart. 11 The postganglionic neurons in the vagus nerve project to the sinoatrial (SA) and atrioventricular (AV) nodes, as well as to the atrial and ventricular musculature. In the adult, the right vagus nerve innervates predominantly the SA node, the atrial muscle and, to a much lesser degree, the AV node. On the other hand, the left vagus nerve innervates the SA node and atrial muscle to a lesser degree than it innervates the AV node. However, there can be significant overlap in the anatomical distribution.

Stimulation of the right vagus slows the rate of discharge of the pacemaker cells in the SA node thus slows the SA node rate and thereby reduces the HR. Stimulation of the left vagus nerve produces some slowing of the SA node, prolongation of AV conduction and partial or total AV block. Detailed human data of the vagus nerve stimulation and its effects on heart rate are not available.