Figure 1. Continuous sustained effort. Note presence of flow limitation on nasal cannula, -pressure transducer tracing. Note on Pes tracing a continuous increase in respiratory effort with peak end inspiratory Pes reaching always an increased negativity (approximately -15 cm H₂O) compared with -6 during nonobstructed breathing.

Figure 2. Flow limitation monitored with a pneumotachograph. The flow limitation is associated with abnormal peak end inspiratory Pes on the first 2 breaths on the left side of figure. With occurrence of an EEG arousal (underline EEG), there is an abrupt decrease in effort indicated by esophageal pressure monitoring. This pattern is called Pes reversal; it begins with the third breath from left. It is associated with a change in the EEG indicative of the EEG arousal.

Figure 3. Cyclic alternating pattern (CAP). The EEG tracing presents alternatively a burst of high-amplitude waves (phase A) and low-amplitude waves (phase B). This pattern is seen during nonrapid eye movement sleep. It indicates an instability of the state. The high-amplitude waves are formed by burst of δ waves, or a mixture of δ-α waves. The tracing also shows a nasal cannula-pressure transducer curve indicative of flow limitation.