Hypoxia and Sleep-disordered Breathing: Friend or Foe?

Hypoxia is a hallmark feature of respiratory disease and has multiple effects on the central nervous system. For example, experimentally induced acute sustained isocapnic hypoxia (oxygen saturation as measured by pulse oximetry [SpO2], 80–85%) blunts respiratory sensation and symptom perception in asthma and suppresses cough reflex sensitivity and arousal responses to airway closure during sleep in healthy individuals. The effects of repetitive intermittent hypoxia, as occurs nightly in sleep-disordered breathing, are generally considered deleterious for the cardiovascular system. For instance, 2–4 weeks of nightly intermittent hypoxia increases daytime blood pressure and sympathetic nerve activity in healthy individuals, potentially via renin-angiotensin mechanisms. In addition, the overnight sleep apnea–related hypoxic burden metric, which includes both hypoxemia frequency and magnitude components, predicts cardiovascular mortality...