extended periods (hours) of respirator-free pacing. If the utility of the device is confirmed in additional individuals, diaphragm pacing with intramuscular electrodes placed by laparoscopic surgery may provide a less invasive and less costly alternative to conventional phrenic nerve pacing.
The objective of some lower-extremity FES systems is to enable individuals with paraplegia to stand and transfer themselves. The functional goals associated with standing include reaching for high objects, having face-to-face interactions with other people, and transferring between surfaces independently or with minimal assistance. At present there are no commercial or FDA-approved systems for FES-aided standing; however, one implantable system has reached the multicenter clinical trial stage of development (Davis et al., 2001).
The only FDA-approved FES system for ambulation available is a surface stimulation system (Parastep). Individuals with paraplegia wear a microprocessor-stimulator unit at the waist and use a walker with controls built into the handles. This system allows these individuals to stand and walk with a reciprocal gait for limited distances. Use of the system has additional medical benefits, such as providing increased blood flow to the lower extremities, a lower heart rate at subpeak work intensities, increased muscle mass, and reduced spasticity and also has psychological benefits (Klose et al., 1997; Graupe and Kohn, 1998).
FES devices can also be used to maintain an individual’s muscle fitness and potentially encourage the recovery of function. Decreased muscle mass is a secondary condition that, if left untreated, can diminish the potential for complete recovery. A common cause of muscle atrophy is the loss of motor neurons in the spinal cord that drive muscle contraction. Other, usually less severe but more widespread atrophy occurs over time because of the disuse of paralyzed but still innervated muscles. FES can help reverse disuse atrophy by stimulating muscle activity, but it relies on intact nerve-muscle connections and cannot easily be used to stimulate denervated muscles.
FES devices have received a mixed reception from both clinicians and individuals with spinal cord injuries. Originally, the controllers and stimulating electrodes were large and cumbersome and did not provide very fine control; however, technological advances are leading to reductions in the sizes of these devices and reductions in the numbers of surgical procedures required for implementation. In addition, the implanted electrodes have improved reliabilities and longevities. Some individuals with spinal cord injuries and their clinicians are dissuaded from using FES devices because of the surgical procedures required to implant the systems and, in the case of Vocare, the additional damage to the nervous system that results from the requirement to transect some of the sensory nerves that enter the spinal cord (Creasey et al., 2001). However, the potential benefit to an individual’s