A bronchodilator's a substance that the bronchi and bronchioles, decreasing airway resistance and thereby facilitating airflow. Bronchodilators may be endogenous (originating naturally within the body), or they may be medications administered for the treatment of breathing difficulties. They're most useful in obstructive lung diseases, of which asthma and chronic obstructive pulmonary disease are the most common conditions. Although this remains somewhat controversial, they might be useful in br… (More on Bronchodilator)