Asthma is a chronic lung disease that affects more than 25 million people in the United States.  Asthma interferes with breathing by inflaming, thereby narrowing the airways.  Asthma is typically characterized by episodes of breathlessness and wheezing.  When these episodes are more serious, they are known as asthma attacks.  Because the trouble starts from chronic inflammation in the airways that carry air to the lungs, it is good to know how these airways work.