DIAPHRAGM PACING - CLINICAL AND EXPERIMENTAL RESULTS

Over the last 26 years diaphragm pacing has been used in over 400 adul ts and 70 children to support ventilation and oxygenation. Diaphragm p acing can be useful for conditions in which the brain stem respiratory centers provide little or no stimulation to the respiratory muscles, i.e. central hypoventilation syndrome, Amold-Chiari malformation/brain stem dysfunction, and high quadriplegia. Because the pacing systems a re so portable, the greatest advantages accrue to those patients who r equire ventilatory support both while awake and asleep. Infants and ch ildren require tracheostomy to avoid upper airway obstruction and bila teral pacing to meet higher metabolic demands. The stimulus parameters most appropriate for pediatric patients have been characterized as lo w stimulus frequency, short inspiratory time, and moderate respiratory rate. Use of similar stimulus parameters in an immature animal model has resulted in preservation of diaphragmatic structure and function b ut transformation of the diaphragm from a mixed muscle to one with a u niform population of type 1, fatigue-resistant fibers (physiologic, hi stochemical, myosin isoform, and ultrastructural evidence). In 33 pedi atric patients, representing 96 patient-years of use, there were 26 fa ilures of the pacing systems requiring removal and/or replacement of t he internal components. Mean time to failure was 56 months. Of our 36 patients who had diaphragm pacing systems implanted, 26 are alive and 22 are currently using the pacing systems. Two recent advances may fur ther improve the long-term outcome of patients using diaphragm pacing. Smaller, better encapsulated receivers may improve system longevity a nd a new stimulus electrode may reduce the risk of diaphragmatic damag e.