80 percent in those with symptomatic asthma. In many cases, however, the constriction, even during or after strenuous exercise, is not clinically significant except in cases of severe to moderate emphysema. In May 2013, the American Thoracic Society issued the first treatment guidelines for EIB. Allergen-induced bronchoconstriction While a different cause, this has very similar symptoms, namely the immunological reaction involving release of inflammatory mediators. Inhalation of allergens in sensitized subjects develops into bronchoconstriction within 10 minutes, reaches a maximum within 30 minutes, and usually resolves itself within one to three hours. In some subjects, the constriction does not return to normal, and recurs after three to four hours, which may last up to a day or more. The first is named the early asthmatic response, and the latter the late asthmatic response. Bronchioconstriction can occur as a result of anaphylaxis, even when the allergen is not inhaled. Physiology Bronchoconstriction is defined as the narrowing of the airways in the lungs (bronchi and bronchioles). Air flow in air passages can get restricted in three ways: a spasmodic state of the smooth muscles in bronchi and bronchioles an inflammation in the middle layers of the bronchi and bronchioles excessive production of mucus. The bronchial spasm is due to the activation of parasympathetic nervous system. Postganglionic parasympathetic fibers will release acetylcholine causing the constriction of the smooth muscle layer surrounding the bronchi. These smooth muscle cells have muscarinic M3 receptors on their membrane. The activation of these receptors by acetylcholine will activate an intracellular G protein, that in turn will activate the phospholipase C pathway, that will end in an increase of intracellular calcium concentrations and therefore contraction of the smooth muscle cell. The muscle contraction will cause the diameter of the bronchus to decrease, therefore increasing its resistance to airflow. Bronchoconstriction is common in people with respiratory problems, such as asthma, COPD, and cystic fibrosis. Management Medical management of transient bronchoconstriction or chronic bronchitis depends on the severity and etiology of the underlying disease and can be treated with combinations of the following medications: B-receptor agonists: Medications that stimulate the β2 receptor subtype on pulmonary smooth muscle will result in smooth muscle relaxation, bronchodilation, and increased airflow into the lungs during inhalation. These medications include short-acting beta agonists (SABAs) such as albuterol which typically last 4–6 hours, and long-acting beta agonists (LABAs) such as salmeterol which lasts 12 hours. For example,