*exerpts from an article I read.

While doctors will never advise drinking coffee as the sole treatment for asthmatic symptoms as they did hundreds of years ago. They do agree that the caffeine found in coffee is particularly beneficial in an emergency situation. Evidence shows that people have used coffee in situations where inhalers were completely unavailable, such as when on vacations and on an airplane. Coffee is particularly useful in these situations, as the patients might otherwise suffer serious consequences due to their inability to breathe properly.

Coffee has a component in it called Theobromine, which is a bronchial dilator. It's not as potent as a typical ashtmatic brochodilator, such as albuterol. It's helps if there is no inhaler nearby and one absolutely needs some help clearing the airways.