Illustration depicting an elderly female patient with airflow obstruction due to asthma. During an asthma attack, the muscles around the airways tighten, and the lining inside the airways will swell, thicken, and may clog with thick mucous. The narrowed airways make it harder to move air in and out of the air sacs that make up the lungs. Enlarged view of a bronchiole during bronchospasm is also shown. Bronchospasm is defined as spasmodic contraction of the lumen (bronchial muscle) of a bronchus resulting in restricted airflow. Common triggers of asthma attacks include: allergies, infections, exercise, changes in the weather, and smoke.