A 23-year-old woman has had several episodes of severe wheezing over the past 3 years. She is a nonsmoker and feels well in between episodes. She has no personal or family history of atopy. The wheezing episodes are most likely to occur in spring. Which of the following is the most likely mechanism of wheezing in this woman?

There is a constant state of hyperreactivity of the bronchi, during which exposure to an irritant precipitates an asthmatic attack. A following subacute phase has been described that can lead to late complications. The presence of inflammation in the airways has resulted in increased usage of inhaled corticosteroids for maintenance therapy. Many cases of asthma have no discernible allergic component.