Surface abdominal and rib cage motion reflect diaphragmatic and intercostal contributions to breathing, but the relationship of these indexes to diaphragm and intercostal function is more complex. In neuromuscular diseases, the mechanical coupling between muscle activation and rib cage motion may be further distorted. Although the abdominal contribution gives only an indirect index of diaphragm function, more direct measurements such as transdiaphragmatic pressure were avoided in this study to minimize instrumentation of these subjects. Despite these limitations, however, the mean abdominal contributions of our subjects in wakefulness and sleep were well below normal and their relationship in these patients to oxygen desaturation in REM sleep underlines the importance of diaphragm dysfunction in their vulnerability to sleep desaturation. The similarity between the fall in bilateral diaphragm paralysis in dogs lends further support to this view. there
In summary we have found that patients with global muscle weakness due to Duchenne MD can maintain a normal Ve when awake, but when confronted with the additional mechanical and neurophysiologic adaptations of sleep, they cannot defend their Ve as well as normal subjects. Diaphragm dysfunction reflected by abdominal paradox developed in several patients and the extent of the abnormal diaphragm function in NREM sleep appears predictive of the development of oxygen desaturation during REM periods. Whether this reflects an abnormal increase in upper airway resistance, diaphragmatic weakness, or a combination of the two is unclear. However, the presence of a normal Ve when awake does not preclude significant nocturnal hypoventilation in these patients. Oxygen treatment may prolong individual episodes of hypo-pnea but its effect on overall ventilation and breathing pattern were not significant and should prove a safe way of alleviating episodic nocturnal hypoventilation.