Respirology/ ICU

Mechanism of a Mixed Apnea

Mixed apneas are characterized by absent respiratory effort and airflow in the first section of the event and respiratory effort without airflow in the later portion [1].

Proposed Mechanism:

An initial obstructive apnea is followed by a post-apnea hyperpnea/hyperventilation once the upper airway opens. Carbon dioxide is blown off (hypocapnia), and CO2 levels drop below the apneic threshold at the termination of the obstructive apnea.

The subsequent apneic event starts as central apnea until the CO2 level rises, reaching the apneic threshold, and respiratory effort resumes [2].


  1. Simon Herkenrath, Katja Pavsic, Marcel Treml, Lars Hagmeyer, Winfried Randerath. Mixed apnea metrics during diagnostic polysomnographies in obstructive sleep apnea patients with/without treatment-emergent central sleep apnea. European Respiratory Journal 2019 54: PA824; DOI: 10.1183/13993003.congress-2019.PA824
  2. Iber C, Davies SF, Chapman RC, Mahowald MM. A possible mechanism for mixed apnea in obstructive sleep apnea. Chest. 1986 Jun;89(6):800-5. doi: 10.1378/chest.89.6.800. PMID: 3086045.
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Dr. C Humphreys

Internal Medicine

Published by
Dr. C Humphreys

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