Figure 3: 5-min epoch of polysomnography with patient–ventilator asynchrony. Ineffective efforts (arrows) and arterial oxygen saturation oscillations related to patient–ventilator asynchrony. SpO2: arterial oxygen saturation measured by pulse oximetry; Tho: thoracic movements; Abd: abdominal movements; PTT: pulse transit time; Flow: flow signal; Pre: pressure. Reproduced with permission of the European Respiratory Society©. Eur Respir Mon November 2008 41:350-366.