This research investigates respiratory control in normal subjects and in patients with respiratory system abnormalities by examining aspects of respiratory muscle function under various states and with several respiratory stimuli. In the first of three phases of the study segmental muscle reflexes are examined using electromyographic responses of important respiratory muscles to sudden respiratory loads and their release. The second phase combines the techniques of sleep research and respiratory physiology to investigate the relationships between states of sleep and respiratory control. Using both EMG's of respiratory muscles and magnetometer measurements of thoracoabdominal motion, patterns of breathing, reflex responses to loading and responses to hypercapnia will be assessed in normals, respiratory disease patients and patients with sleep apnea syndromes while awake and in both quiet and R.E.M. sleep. The third phase addresses the problem of respiratory muscle fatigue and its relationship to respiratory disability and failure. Two indicators of respiratory muscle fatigue, respiratory muscle incoordination and frequency shifts in respiratory muscle electromyograms, will be evaluated as early indices of fatigue and failure. Studies will be done in three subject groups, normal subjects, high (Cl-2) quadriplegics with electrophrenic pacers and patients in actual, impending or recovering respiratory failure.