Printed in UK- all rights reserved Copyright ©ERS Journals Ltd 1998 European Respiratory Journal

Patients with obstructive sleep apnoea/hypopnoea syn-drome (SAHS) experience repeated episodes of increased upper airway resistance leading to profound disturbances in sleep architecture and arterial blood gases [1, 2]. Re-peated inspiratory efforts occur during an obstructive sleep apnoea until arousal ensues and airway patency is restor-ed [3]. The increased upper airway resistance in patients with SAHS can be assessed indirectly by the analysis of different signals, such as the time profile of the inspiratory flow signal, the noise of snoring, the use of strain gauges or inductance plethysmographs [4–7]. However, as the recent description of the upper airway resistance syndrome has pointed out [8], the classical noninvasive techniques previously described are unable to detect the full range of respiratory-related flow events that occur throughout th