The natural tendency for open air spaces such as the alveoli to collapse is countered by the following: Surfactant (which maintains surface tension) Continuous breathing (which keeps the alveoli open) Intermittent deep breathing (which releases surfactant into the alveoli) Periodic coughing (which clears the airways of secretions) Major consequences of atelectasis include underventilation (with hypoxia and ventilation / perfusion [V / Q] mismatch) and pneumonia.