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Figure 8. Brief 2 minute) polysomnographic recording in REM sleep in a patient with chronic myopathy. The signals are as follows: SaO2, airflow (V), posteroanterior motion of rib cage (RCPA) and abdomen (ABPA), electro-oculogram (EOG), and integrated surface electromyo-grams from inspiratory intercostals (EMGint) and diaphragm (EMGdi) (the ECG is superimposed on EMG signals). A-D, Periods of REM sleep. During periods A and C, marked irregular eye movements ("phasic" REM) are accompanied by reduced EMG activity and consequently reduced motion and flow with subsequent desaturation; rib cage and abdominal motion remain in phase, indicating central hypopneas. During periods B and D, eye movements are relatively quiescent and EMG activity increases with consequent increased motion and flow and subsequent recovery of SaO2 (increasing SaO2 during period C reflects the increased ventilation in period B). Reprinted by permission from Reference 24.

Sleep studies should be performed in all patients for whom nocturnal ventilatory support is being considered. On occasion, the finding of frequent hypopneas and/or apneas that are predominantly obstructive will suggest a trial of treatment with nasal continuous positive airway pressure. More frequently, however, in patients with respiratory muscle weakness, bilevel pressure support or another method of noninvasive intermittent positive pressure ventilation will be the treatment of choice. Because there is no evidence that treatment of abnormalities of gas exchange per se during sleep is beneficial, currently there is no indication for widespread application of polysomnography in the absence of relevant symptoms.

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