Keywords: Adrenergic beta-Agonists - diagnostic use, Albuterol - diagnostic use, Respiratory System - drug effects, Administration, Inhalation, Adrenergic beta-Agonists - diagnostic use, Adult, Albuterol - diagnostic use, Forced Expiratory Flow Rates, Humans, Male, Methacholine Chloride - diagnostic use, Middle Aged, Respiratory System - physiopathology, Smoking - physiopathology