Fig. 3.
Example polysomnographic tracings of an obstructive sleep apnoea event induced by reducing continuous positive airway pressure (from therapeutic to 2cmH2O) in a 52 yr old male patient with severe OSA (apnoea/hypopnea index= 34.5 events per hour). EMGgg= Electromyogram of the genioglossus muscle (intramuscular), EEG= electroencephalogram (C3-A2), Pepi= pressure at the level of the epiglottis, Pmask= pressure measured via nasal mask, Vt = tidal volume and flow measured via nasal mask and pneumotachograph. There was increased EMGgg activity during the apnoeic event, though it was not significant enough to restore flow without arousal. The arousal threshold is characterized using Pepi, and after arousal there is a large ventilatory response.