The electroencephalographic and electrocardiographic signals and the movements of the chest and of the abdomen will be recorded with a portable polysomnograph. The electromyogram of the chin and the ELECTRO Oculogram will also be recorded. These signals will permit to identify the sleep stages. The subjects will ware a face mask connected to a pneumotachometer for the recording of the ventilatory flow. Gas will also be sampled to measure the end tidal partial pressure of CO2.