Pacing of the diaphragm is not a novel technique. In the early 1990s, physicians often experimented with using phrenic nerve stimulation to produce contraction of the diaphragm. In the 1950s, phrenic nerve stimulation was used to treat patients with polio, with little success. [1, 2, 3, 4] At that time, surgery for diaphragm pacing was still crude; a more sophisticated approach was not developed until the late 1980s.
The father of modern diaphragm pacing was Dr William W L Glenn from Yale University, who showed that the technique was not only practical but could be used clinically for the treatment for several medical disorders. Currently, several renowned clinical centers now offer diaphragm pacing for selected patients. 
At present, diaphragmatic pacing systems are still cumbersome, though work is being done on more portable miniature systems. All currently available systems involve an external transmitter and an implanted receiver. Fully implantable diaphragmatic pacing systems are being developed. The improved pacing systems now being used are more affordable and much easier to implant than the earlier systems were. 
See the images below.
Clinical trials will be required to determine whether diaphragm pacing is worth the expense and in which patient populations it is most useful. Given the increasing number of patients with sleep apnea and severe chronic obstructive pulmonary disease (COPD), diaphragm pacing may have a significant role to play in managing these conditions, at least during the night.
Indications and Contraindications
Diaphragm pacing is performed to provide ventilatory support in 2 main clinical scenarios, as follows:
Central alveolar ventilation, or what is better known as sleep apnea
High spinal cord paralysis in which the drive for respiration is still present but the injury to the spinal cord prevents stimulation from the phrenic nerves
Another, albeit rare, use of diaphragm pacing is to treat patients with intractable hiccups. The remaining group of patients in whom diaphragm pacing has been used consists of those with severe COPD. In these individuals, the hypoxic stimulation is diminished by administration of any amount of oxygen.
Diaphragm pacing is contraindicated for patients in whom the phrenic nerve is not functional. Such patients include those with severe traumatic injury to the nerve, those with nerve tumors, and most of those with neuropathies. In addition, diaphragm pacing is contraindicated for patients with conditions in which the diaphragm itself is not functional. Such conditions include myasthenia gravis, muscular dystrophy and advanced parenchymal lung disease.
Compared with positive-pressure ventilation, diaphragm pacing has a number of advantages. A major advantage is that it allows a greater degree of independence. With diaphragm pacing, the patient is no longer isolated in a room, attached to a mechanical ventilator with an uncomfortable tube down the upper airways. Patients with central hypoventilation may be able to ambulate, go to work, travel, and perform most daily living activities. Portable diaphragmatic pacemakers are available that can be used for ambulatory monitoring of heart rate and rhythm.
Another major advantage is that diaphragm pacing affords the patient the ability to speak, which is impossible with an endotracheal tube in place. Once diaphragm pacing has been performed, the tracheostomy stoma can be plugged and speech resumed. For patients who are quadriplegic and on a ventilator, the speech capability made possible by diaphragm pacing is immensely desirable. [11, 12, 13, 14]
Moreover, diaphragm pacing, unlike endotracheal intubation, does not result in tracheal injury, tracheomalacia, tracheal stenosis, subglottic stenosis, tracheoesophageal fistula, or tracheitis. These problems are not trivial and can be life-threatening.
Furthermore, the extremely irritating copious secretions seen during mechanical ventilation are avoided. Patients on a ventilator are always at risk for death. The tubing may become kinked, coiled, obstructed, or even disconnected. The tracheostomy site may become plugged, or the ventilator may malfunction. All of these problems are avoided in patients undergoing diaphragm pacing. Patients who are quadriplegic have almost no way of correcting any of these problems if no attendant is available.
Whereas it is clear that diaphragm pacing can improve quality of life in patients for whom it is indicated, there is, as yet, little evidence to indicate that it improves survival in these patients. 
Since the early studies on diaphragm pacing in the 1970s, data have been accumulated to show that the technique is effective and does help support ventilation in certain patient populations.
In the early days, the system utilized alternate-side pacing because bilateral high-frequency ventilation often caused rapid diaphragmatic fatigue. By the 1980s, however, continuous bilateral low-frequency stimulation of the preconditioned diaphragm for complete respiratory support was possible. [16, 17] Today, selected patients have the option for this surgery and are able to live a life of better quality.