Event duration, endotypes and hypoxic burden in obstructive sleep apnoea

Respiratory event duration is an observable phenotype of obstructive sleep apnoea (OSA) in routine polysomnographic studies and is relatively longer in Asian patients. This study examined the association of respiratory event duration with OSA severity and endotypes in Asian patients with moderate-to-severe OSA.

We recruited 1008 patients who underwent in-laboratory full-night polysomnographic studies. Event durations were averaged during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep, respectively. The associations of event duration with endotypes (including arousal threshold, loop gain, circulatory delay, upper airway collapsibility and compensation) and OSA severity (apnoea-hypopnoea index (AHI) and hypoxic burden) were examined.

Participants demonstrated a mean event duration of 25.9 s in NREM sleep. Event duration exhibited an inverse U-shaped association with AHI during NREM sleep (peaking at 26.8 s) and a negative association with AHI during REM sleep, whereas hypoxic burden consistently increased with longer event durations. After adjusting for AHI, a 1-s increase in event duration during NREM sleep was associated with a 3.46 %eupnoea (95% CI 3.20-3.73) higher arousal threshold, 1.26 %eupnoea (95% CI 1.13-1.39) greater collapsibility (V' _passive), 0.61 %eupnoea (95% CI 0.40-0.83) lower compensation, 0.07 s (95% CI 0.05-0.08) higher delay and 7.43 %·min·h^-1 (95% CI: 6.56-8.30) higher hypoxic burden. In REM sleep, event duration was positively associated with arousal threshold, loop gain and hypoxic burden, but negatively associated with V' _passive and compensation.

A high arousal threshold, a collapsible upper airway and poor compensatory function characterise long event durations in patients with OSA. AHI does not adequately reflect the disease burden associated with hypoxia caused by prolonged respiratory events.