[Arousals from sleep in patients with obstructive disordered breathing: a comparison study for mechanisms].

OBJECTIVE: To explore the stimuli triggering respiratory arousal.

METHODS: Twenty-five patients with excessive daytime sleepiness (EDS) were monitored by nocturnal polysomonography (PSG) and respiratory inductive plethysmography. Patients with obstructive apnea/hypopnea index (AHI) >/= 5/h were diagnosed as obstructive sleep apnea syndrome (OSAS). Patients with Epworth Sleepiness Score >/= 12, frequent inspiratory flow limitation related arousal during sleep and AHI < 5/h were diagnosed as upper airway resistance syndrome (UARS). Seven normal subjects were recruited as controls.

RESULTS: Patients with OSAS: AHI (32.8 +/- 19.1)/h, percentage of time spend when oxygen saturation lower than 90% (SLT90%) (11.3 +/- 16.5)%, arousal index (ArI) (35 +/- 17)/h, n = 15. Patients with UARS: AHI (2.5 +/- 1.4)/h, SLT90% (0.1 +/- 0.1)%, ArI (30 +/- 16)/h, n = 10. Normal subjects: AHI (5.9 +/- 4.4)/h, SLT90% (0.2 +/- 0.4)%, ArI (13 +/- 5)/h, n = 7. Though the levels of AHI and SLT90% in patients with UARS were similar to those in normal subjects (H = 2.92, P = 0.87 or H = 0.086, P = 0.77), much lower than those in OSAS patients (H = 12.3, P = 0.000 5 and H = 6.64, P = 0.01), ArI in UARS was just as high as that in OSAS (H = 0.49, P = 0.48).

CONCLUSION: Arousals from sleep in patients with obstructive sleep disordered breathing might be mainly caused by inspiratory flow limitation rather than by episodic apnea or desaturation.