Respiration during sleep in neuromuscular and thoracic cage disorders.

Many of the neuromuscular and thoracic cage disorders are associated with disorders of breathing during sleep. The abnormal mechanics of the chest wall impairs respiratory muscle function and this is compounded if there is underlying muscle weakness. Respiratory abnormalities appear during REM sleep before NREM or wakefulness. Central sleep apnoeas are characteristic, but obstructive apnoeas are also occur because of loss of tone in the upper airway dilator muscles. Arousals from sleep return the blood gases towards normal, but cause fragmentation of sleep, leading to daytime sleepiness. Ventilatory failure occurs particularly if the vital capacity is less than 1.0-1.5 litres or if the maximal inspiratory mouth pressure is less than 20-25cmH2O. Non invasive ventilation effectively prevents both central and obstructive apnoeas and improves the sleep architecture and daytime blood gases.