Airway obstruction refers to a condition in which a blockage of the airways causes a reduction of airflow to or absorption of oxygen by the lungs. This blockage may occur in any part of the complex system of passages responsible for delivering air to the lungs. Airway obstructions may be mild or severe, chronic or acute. Airway obstruction differs from airway restriction. When a person experiences airway obstruction, there is a swelling or blockage of some portion of his or her air passages. In contract, a restriction of the airways is caused when a person cannot fully expand his or her lungs to inhale.