The resultant inhalation of air that has not been warmed and humidified by the nasal passages seems to generate increased blood flow to the linings of the bronchial tree, resulting in edema. Constriction of these small airways then follows, worsening the degree of obstruction to airflow. There is increasing evidence that the smooth muscle that lines the airways becomes progressively more sensitive to changes that occur as a result of injury to the airways from dehydration.