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Spirometry with postbronchodilator response should be obtained as the primary test to establish the asthma diagnosis. Pulse oximetry measurement is desirable in all patients with acute asthma to exclude hypoxemia. The chest radiograph remains the initial imaging evaluation in most individuals with symptoms of asthma, but in most patients with asthma, chest radiography findings are normal or may indicate hyperinflation. Exercise spirometry is the standard method for assessing patients with exercise-induced bronchospasm.
Airway hyperresponsiveness or bronchial hyperreactivity in asthma is an exaggerated response to numerous exogenous and endogenous stimuli. The mechanisms involved include direct stimulation of airway smooth muscle and indirect stimulation by pharmacologically active substances from mediator-secreting cells such as mast cells or nonmyelinated sensory neurons.
The pathophysiology of asthma is complex and involves airway inflammation, intermittent airflow obstruction, and bronchial hyperresponsiveness. The mechanism of inflammation in asthma may be acute, subacute, or chronic, and the presence of airway edema and mucus secretion also contributes to airflow obstruction and bronchial reactivity. Varying degrees of mononuclear cell and eosinophil infiltration, mucus hypersecretion, desquamation of the epithelium, smooth muscle hyperplasia, and airway remodeling are present.
Asthma: Practice Essentials, Background, Anatomy