Can sleep-disordered breathing increase sympathetic activity and disrupt cortisol regulation?

Sleep-disordered breathing (SDB), primarily characterized by obstructive sleep apnea, triggers a cascade of physiological stressors that disrupt autonomic and endocrine homeostasis.

Clinical and physiological evidence

• Airway obstruction and sleep fragmentation: Repetitive upper airway collapse leads to severe gas-exchange disturbances, characterized by cycles of oxygen desaturation and reoxygenation (intermittent hypoxia). This hypoxia, combined with escalating negative intrathoracic pressure, activates carotid and central medullary chemoreceptors, triggering cortical microarousals to restore airway patency but severely fragmenting sleep architecture.

Mechanistic pathways of autonomic and HPA-axis disruption

• Sympathoexcitation: Intermittent hypoxia induces sensory plasticity and long-term facilitation in the carotid body via an angiotensin II–AT1–NADPH oxidase–reactive oxygen species (ROS) axis and hypoxia-inducible factor-1 (HIF-1) signaling. This sensory plasticity increases baseline sensory discharge, driving sustained elevations in muscle sympathetic nerve activity (MSNA). Concurrently, cortical microarousals independently trigger acute central sympathetic surges and transient spikes in heart rate and blood pressure.
• HPA-axis dysregulation: Elevated nocturnal sympathetic activity and sleep fragmentation stimulate hypothalamic corticotropin-releasing hormone (CRH) release. This chronically drives adrenocorticotropic hormone (ACTH) and cortisol secretion, resulting in disrupted diurnal cortisol regulation. This disruption is characterized by higher 24-hour cortisol levels, elevated evening or nocturnal cortisol, and a blunted cortisol awakening response (CAR).

Bottom line

• Strong clinical and scientific evidence confirms that SDB-induced intermittent hypoxia and microarousals drive systemic sympathoexcitation and HPA-axis dysfunction, a pathological state that can be successfully mitigated and partially or fully normalized through compliant continuous positive airway pressure (CPAP) therapy.