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Mechanism of nocturnal hypoxia

Authoring team

Patients with COAD are already hypoxic. Thus, because of the steepness of the oxyhaemoglobin desaturation curve, any fall in PaO2 causes a large fall in oxygen saturation. A desaturation of up to 50% may occur.

There is alveolar hypoventilation due to:

  • voluntary accessory muscles are inhibited during REM sleep causing a reduction of tone of the accessory muscles of respiration
  • the breathing pattern during REM sleep is shallow which reduces alveolar ventilation in COAD
  • the reduction in muscle tone causes an increase in upper airway resistance

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