Fig. 1.

An example of periodic breathing induced by proportional assist ventilation in a female patient with obstructive sleep apnea [apnea-hypopnea index (AHI) = 23 events/h]. The patient had stable breathing at 100% assist with volume assist = 16 cmH₂O/l and flow assist = 4 cmH₂O·l^–1·s^–1 for 3 min before tidal volume (Vt) amplification factor was measured by dropping the %assist to 0% for 1 breath (solid arrow). After this disturbance to ventilation, sustained periodic breathing developed. There was no sign of electroencephalogram (EEG) arousal during cyclical breathing, as indicated by inset. Pmask, mask pressure.