Figure 11.

Ventilatory supply-demand dynamics. 1. At the start of an obstructive event, cumulative supply-demand difference (see Δ in Figure 10) is initially determined by the degree of upper airway obstruction (supply) and CO₂ production (demand); 2. rate of accumulation may be decreased by neuromuscular responses and increase in ventilatory efficiency as CO₂ rises; 3. when supply-demand difference meets a threshold, arousal occurs and terminates the apnea; 4. pent-up ventilatory demand is relieved due to improved upper airway patency during the arousal.