Electrophysiological respiratory studies in the critical care unit.

Respiratory electrophysiological studies are useful in the investigation and monitoring of respiratory failure. Phrenic nerve conduction studies and needle electromyography of the diaphragm are invaluable in establishing the diagnosis, determining the severity, and following the progression of peripheral respiratory muscle dysfunction. In addition to these established methods, repetitive phrenic nerve stimulation is of diagnostic value in patients with neuromuscular transmission defects and dyspnea. The diagnosis of impaired central respiratory drive can often be accomplished by the newly-developed techniques of transcortical magnetic stimulation of the motor cortex with recording of the diaphragm and phrenic nerve somatosensory evoked potentials. These studies are of particular value in critically ill patients where both the central and peripheral lesions may impair respiration.