Healthy and constricted bronchi. Computer artwork of a cross-section through a healthy (left) and a constricted (right) lung airway (bronchus). The healthy airway has a wide lumen (core) through which breathing can occur normally. The inflamed constricted airway has a narrowed lumen following contraction of the outer muscle layer (red) and swelling of the mucous lining, leading to congestion and impaired breathing.