Muscular contraction of the bronchi (air passages) in the LUNG, causing narrowing. The cause is usually a stimulus, as in BRONCHITIS and ASTHMA. The result is that the patient can inhale air into the lungs but breathing out becomes difficult and requires muscular effort of the chest. Exhalation is accompanied by audible noises in the airways which can be detected with a STETHOSCOPE. Reversible obstructive airways disease can be relieved with a BRONCHODILATOR drug; if the bronchospasm cannot be relieved by drugs it is called irreversible. (See CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD).)