Exacerbations are highly related with airway inflammation. An increased airway inflammation is the key factor of the pathogenesis of exacerbations. Any stimulation which increases airway inflammation could result in bronchial wall edema and increased mucus production. Increased mucus production is considered as an important phenotype of many acute episodes of COPD, which would cause increased sputum production. The increased sputum production in the airways would reduce the airway diameter and this effect would be enhanced if the viscosity of the sputum also
