Asthma may present acutely or as a chronic pulmonary disease. Symptoms of acute asthma include shortness of breath, chest tightness, wheezing and cough, often productive of clear or slightly colored sputum. When present, chest pain is usually musculoskeletal in origin. Audible wheezing may not be present in mild asthma, but may be elicited by forced expiratory maneuvers. Increased diurnal variations in pulmonary function are often associated with nocturnal exacerbations. Triggers for worsening asthma include cold air exposure, exercise, viral respiratory infections, sinusitis, gastroesophageal reflux, exposure to seasonal or perennial inhalant allergens, and exposure to inhaled irritants such as cigarette smoke. Seasonal variations in asthma severity often correlate with seasonal allergen exposure. Finally, a number of medications, including P adrenergic blockers and nonsteroidal anti-inflammatory agents, as well as sulfite preservatives, may exacerbate asthma in susceptible subjects. A correlation of total suspended particles and levels of various air pollutants to exacerbation rates for asthma has been reported.
Physical signs of acute asthma include tachypnea, tachycardia, pulsus paradoxicus, hyperinflation of the chest, audible wheezing, and the use of accessory muscles of respiration. Chest roentgenogram may show flattening of the diaphragms bilaterally and increased anteroposterior dimension. Pulmonary function studies reveal an obstructive pattern which may be partially or completely reversed by the administration of (3-adrenergic agonists. Diurnal variations in peak expiratory flow rate greater than 20% are highly suggestive of asthma. Bronchopro-vocation with a variety of agents, including metha-choline and histamine, may identify subjects with BHR. However, it should be noted that the perception of asthma by an affected subject may not correlate to the degree of pulmonary dysfunction due to an impaired sensitivity to hypoxia and hypercarbia.
The differential diagnosis of asthma includes mechanical obstruction of the airway (extrathoracic and intrathoracic), laryngeal dysfunction, chronic obstructive pulmonary disease, cardiac dysfunction, pulmonary embolism, pulmonary infiltrates and eosinophilia (PIE syndrome), cough due to drugs (angiotensin-converting enzyme ACE inhibitors), and carcinoid tumors. The majority of these entities may be readily differentiated from asthma on the basis of clinical presentation, physical examination, roent-genographic studies and pulmonary function testing.
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