Males have a higher apnoeic threshold than women. This predisposes to central sleep apnoeas during NREM sleep-stage transitions. The hyperventilation related to arousal at the end of sleep apnoeas lowers the Pco2 and if this falls below the apnoeic threshold it will lead to a central sleep apnoea. The upper airway tends to occlude during the prolonged expiration of a central sleep apnoea, particularly if the Pco2 is low.
This difference in apnoeic threshold is probably hormone related. Administration of testosterone to women raises it to the male level and anti-androgens in men shift it to the female level.
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