The most frequent symptoms of asthma, wheezing, coughing, chest tightness, and breathlessness occur differently among patients and are common symptoms for other diseases, such as rhinitis, sinusitis, obstructive airway diseases, gastroesophageal reflux (GERD) or drug-related cough.9 Asthma often has some distinguishing features that assist in diagnosis, such as recurrence, reversibility, daily variation and response to triggers.10
Asthma is considered persistent when symptoms occur more than two days per week or more than two nights per month. It is considered intermittent when symptoms occur less often.11 Asthma symptoms may be mild, moderate or severe and the symptoms may vary over time.
When asthma is diagnosed in children, approximately 70-90% of patients have coexisting allergies. The remaining 10-30% of pediatric patients have non-allergic asthma. Pediatric asthma frequently occurs by five years of age.11
When asthma is diagnosed in adults, it can be due to allergic and/or non-allergic factors and frequently complicated by other existing diseases and treatments.12
Physical changes result when allergic triggers initiate an inflammatory response that may cause asthma symptoms such as coughing, wheezing, chest tightness and shortness of breath. Inflammation affects respiratory hyper-responsiveness and airflow reduction.13 Inflammation may continue through several phases, including an acute phase, a late phase and a chronic phase. Inflammatory cells are recruited to the respiratory tract in the acute phase. During the late phase, the inflammatory cells and locally occurring cells are activated. During the chronic phase, which can last for days and weeks, persistent cell damage and repair continue to occur.14 Lung function can fluctuate and slowly deteriorate.
Once sensitization to an allergen occurs, the inflammatory process may be initiated on subsequent exposures. During the acute phase, mast cells are activated and produce inflammatory mediators.15 These mediators include histamine and leukotrienes. The resulting inflammation process causes mucus production and tissue swelling. During the late phase, eosinophils and T cells cause increased inflammation, airway epithelium destruction, loss of cell protection, airway swelling and increased thick mucus production.16 Along with these changes the asthmatic airways experience muscle tightening, increased wall thickening, airway narrowing and abnormal mucus overproduction. Some changes lead to irreversible airway remodeling, including mucus plugs, wall thickening and lumen narrowing.
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