Optimization of Non-invasive Diaphragm Activation Using Magnetic Phrenic Nerve Stimulation

The use of mechanical ventilation (MV) to replace spontaneous breathing has been associated with respiratory muscle dysfunction and lung injury from positive pressure. While using MV in an intensive care unit setting, the diaphragm is unloaded, potentially resulting in early development of diaphragmatic atrophy in as early as 18 hours of complete diaphragm inactivity. These changes in muscle properties result in a decrease in the force generating capability of the muscle, ultimately resulting in difficulty to restore spontaneous breathing and a subsequent prolonged weaning process or failure. A prolonged weaning period is associated with longer duration of MV, which may result in a cascade of further diaphragm dysfunction, weakness, and injury.

Stimulation of the phrenic nerves to produce diaphragm contraction and activity is a possible mechanism to reduce MV related diaphragm dysfunction. Two promising studies have shown the potential of repetitive phrenic nerve stimulation on inducing diaphragm activity in human subjects with trains of pulses via both cervical and bilateral phrenic nerve stimulation. However, neither study provided optimal stimulation settings. As such, the primary purpose of this study is to investigate the optimal settings for noninvasive phrenic nerve stimulation to induce diaphragm contraction.