Diaphragmatic Pacemaker

The diaphragm is a major respiratory muscle and plays an integral part in normal respiration. It is supplied by the phrenic nerve, which originates mainly from the fourth cervical nerve, but also receives contribution from the third and fifth cervical nerves. The phrenic nerve contains sensory, motor, and sympathetic nerve fibers, and it supplies motor supply to the diaphragm and sensory supply to the central tendon. Both phrenic nerves runs along the scalene anterior muscle deep to the carotid sheath. The right phrenic nerve passes over the brachiocephalic artery and posterior to the subclavian vein and over the right atrium. It enters the diaphragm at the level of T8th verbetrae. The left phrenic nerve also runs posterior to the left subclavian vein and passes over the pericardium of the left ventricle and penetrates the left hemidiaphragm separately. The diaphragm, on the other hand, is an elliptical cylindroid structure that is capped by the fibrous dome. The central tendon, which is the highest part of the diaphragm, consists of interwoven collagenous fibers; whereas, the cylindrical portion of the diaphragm consists of a continuous muscle fiber band, the majority of which is directly in contact with the inner surface of the lower ribs. Injury to the central nervous system, phrenic nerve, or diaphragm can lead to an impairment of diaphragm function and lead to respiratory impairment, resulting in a decrease in tidal volume, minute ventilation, and abnormal gas exchange. Injuries to the nerve can be of various types, as described in Table 1 [1, 2]. Diaphragmatic pacing (phrenic nerve pacing) can lead to significant improvements in quality of life and decrease complications along with the savings in a mechanical ventilator dependent patients. In the current chapter of this book we will discuss the role of a diaphragmatic pacemaker (Phrenic nerve stimulator).