Can residual respiratory events and arousals during CPAP fragment sleep and worsen daytime functioning?

Residual sleep disruption remains clinically relevant in CPAP-treated obstructive sleep apnea, particularly when symptoms persist despite an apparently acceptable device-reported AHI. The overall claim is plausible with moderate confidence: arousals clearly fragment sleep and reduce its restorative quality; residual respiratory events can contribute when they trigger such arousals, but they are not the only explanation for sleepiness or cognitive symptoms.

Sleep continuity and restorative sleep

• Recurrent EEG-defined arousals/awakenings are established sleep fragmentation. CPAP titration explicitly targets respiratory-effort–related arousals, and one CPAP study reported respiratory arousals falling from 40.9 to 1.9/hour with treatment.
• Reduced event and micro-arousal burden has occurred alongside improved sleep efficiency and REM sleep, supporting the clinical importance of sleep continuity and architecture.
• Residual events are associated with higher arousal burden—for example, treatment-emergent central sleep apnea was associated with higher AHI and arousal index—but an independent causal contribution of residual events during ongoing CPAP is not established.

Daytime sleepiness and cognition

• An arousal index >25/hour was associated with subjective residual sleepiness in a CPAP-treated cohort. Nonetheless, residual AHI/oxygen-desaturation measures have not consistently correlated with Epworth Sleepiness Scale scores; residual sleepiness affects an estimated 10–28% of treated patients.
• Better sustained attention over six months has accompanied lower AHI and arousal burden, but low residual AHI alone did not predict worse vigilance in a recent clinic cohort.
• Memory mechanisms are biologically credible: CPAP-associated word-pair-memory improvement accompanied more N3 sleep and increased frontal slow-spindle activity. Yet a small selective slow-wave-sleep disruption experiment did not significantly impair spatial-maze memory.

Clinical implications

• Persistent symptoms merit review of PSG-level event–arousal timing, sleep stages, oxygenation, leak, pressure adequacy, adherence, and treatment-emergent central apnea—not device AHI alone. Insufficient sleep, sedating medications, depression, comorbidity, and other sleep disorders also warrant assessment.

Bottom line

• Residual respiratory events and especially their associated arousals can plausibly sustain fragmented, less restorative sleep and contribute to sleepiness, attentional difficulty, and impaired memory consolidation, but these outcomes are multifactorial and should not be attributed to residual AHI alone.