Diaphragmatic muscle conditioning to allow for bilateral simultaneous pacing 

A. cannot be effectively accomplished in infants. 
B. should start immediately after implantation of the first electrode. 
C. should start immediately after implantation of the second electrode.
D. usually requires four to six months in adults. 

Answer D

Since the diaphragm is composed of skeletal muscle, a single electrical stimulus will not produce effective contraction. Diaphragmatic pacing requires conditioning of the muscle so that a train of electrical stimuli will cause a summated contraction. In addition, conditioning is necessary to convert the muscle fibers to the exclusively slow fibers which will allow for sustained mechanical work. This process usually requires four to six months in adults and older children. 

Infants and young children can undergo bilateral diaphragmatic pacing. However, pacing parameters differ from adults and full-time bilateral pacing is not feasible. Conditioning can usually be started two weeks after implantation of the second electrode. During the conditioning, length of pacing time, frequency of electrical stimulation and respiratory rate are gradually increased. Until the diaphragms are fully conditioned, the patient must continue to be supported by mechanical ventilation, and a tracheostomy is necessary. During daytime pacing, a tracheal button can be worn. The conditioning process should not be hurried, since this can cause nerve and muscle damage.