CERVICAL MAGNETIC STIMULATION OF THE PHRENIC NERVES IN BILATERAL DIAPHRAGM PARALYSIS

Cervical magnetic stimulation (CMS) produces a greater twitch transdia phragmatic pressure (TwPdi) than electrical stimulation. This may be b ecause CMS produces rib cage muscle activation, thus producing an insp iratory action independent of the diaphragm. Alternatively, CMS could merely stiffen the rib cage, allowing the diaphragm to act efficiently , by contracting against a stable rib cage. To examine these two hypot heses we studied five patients with isolated bilateral diaphragm paral ysis using CMS and bilateral electrical phrenic stimulation (BES). TwP di, twitch esophageal pressure (TwPes), and twitch gastric pressure (T wPgas) were measured. We also assessed maximal sniff esophageal and tr ansdiaphragmatic pressures (SnPes) (SnPdi), maximal inspiratory and ex piratory mouth pressures (MIP) (MEP), and fall in VC on moving from an upright to a supine position. Respiratory muscle strength tests were consistent with bilateral diaphragm paralysis, and the MEPs confirmed normal expiratory muscle function. The patients were able to generate a mean SnPes of -30 cm H2O, mainly because of inspiratory activity of rib cage and neck muscles. However, TwPdi and TwPes during both CMS an d BES were close to zero. We conclude that in our patients with diaphr agm paralysis caused by neuralgic amyotrophy, CMS stiffens the rib cag e but does not have an inspiratory action independent of the diaphragm .