Figure 2.

Raw data examples showing a transient reduction in CPAP (Pmask) that induced a respiratory-related (A) inspiratory arousal and (B) expiratory arousal. Raw genioglossus (GG) and tensor palatini (TP) EMG (EMGgg and EMGtp) were rectified, moving-time-averaged (100 ms window) and expressed as a %maximum for each participant [4, 23], i.e. GG MTA and TP MTA. Some of the key study parameters quantified are shown, including respiratory arousal threshold, the nadir epiglottic pressure (Pepi), or NadirPepi, immediately preceding arousal [2, 4]; ∆NadirPepi/∆tDrop, rate of change of NadirPepi during the CPAP drop, measured from the first breath following each CPAP reduction to the breath immediately prior to arousal; ∆Pepi/∆tPreArB, rate of change of Pepi during the breath immediately preceding arousal, measured from the breath start to NadirPepi within that breath; time to arousal; and NadirSpO₂, the minimum blood arterial oxygen saturation (SpO₂) caused by the reduction in CPAP. Respiratory and pharyngeal muscle parameters were quantified for the two breaths following each CPAP reduction (breaths 1 and 2) and where available for three breaths prior to arousal (breaths −3 to −1), including (not all indicated on Figure): PIF = peak inspiratory flow; tidal volume and minute ventilation; Ti = inspiratory time; Te = expiratory time; Ttot = Ti + Te; Ti/Ttot = duty cycle; RR = respiratory rate; EMGgg Peak and Tonic muscle activity; EMGtp Peak and Tonic muscle activity. Note the greater increase in tensor palatini muscle activity and flow prior to the expiratory arousal (B) compared with inspiratory arousal (A).