Respiratory abnormalities are complex in Myotonic dystrophy type 1. Some patients presented with isolated alveolar hypoventilation and breathe rhythm irregularity. Nocturnal ventilation is usually proposed but usual modes of ventilation can't provide enough respiratory assistance for patients especially during REM sleep or too much respiratory assistance increasing the risk of asynchrony. The goal of this study is to evaluate the effect of the mode AVAPS (a mode permitting a pressure support with guaranteed volume and offering advantage of volume and pressure support with Bipap A30 Phillips Respironics) compared to bilevel pressure support.