mechanism of nocturnal hypoxia
Last reviewed 01/2018
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