Asthma

Clinical Manifestations

The presentation of asthma can vary, but some of the more common symptoms include wheezing (often recurrent), cough, recurrent chest tightness or shortness of breath, and increased sputum production. Symptoms of asthma are often sporadic and become worse at night. Symptoms typically occur or worsen with exercise, viral infections, exposure to allergens or irritants, weather changes (cold air increases symptoms), gastroesophageal reflux, laughing, and crying. The variations of presentation and triggers make an accurate history one of the most important tools in diagnosing asthma.

The physical exam may or may not demonstrate cough or wheezing. Wheezing typically occurs in the expiratory phase, but it can occur during inspiration as well. Other physical exam findings may be signs of allergic rhinitis (see the entry Allergies) and atopic rashes such as eczema.

Diagnostic Testing

Chest X-rays are helpful because they can exclude other causes of wheezing that mimic asthma, such as bronchitis, pneumonia, congestive heart failure, or foreign body aspiration. A typical chest X-ray finding in asthma is lung hyperinflation with a flattened diaphragm. A pulse oximetry reading can also be helpful.

Pulmonary function tests (PFTs) are the gold standard in helping diagnose and manage asthma. Spirometry can be done in the ambulatory or emergency setting and is an objective measure of lung function. Spirometry measures the expiratory flow rates, comparing baseline values based on the patient's age, race, and height. A decrease in forced expiratory volume in the first second after full inspiration (FEV1) is characteristic in obstructive lung diseases, including asthma and chronic obstructive pulmonary disease. The hallmark of spirometry in asthma, though, is an increase in FEV1 of >200 ml and of >12% from baseline after use of a bronchodilator. It is recommended to perform spirometry at the initial assessment in order to establish a baseline, after treatment has been initiated and symptoms have stabilized, during periods of prolonged loss of asthma control and at least every 1 to 2 years if the patient is stable.

If spirometry is normal and asthma is still suspected, a methacholine challenge can be done. This is done by having patients breathe increasing concentrations of methacholine and measuring FEV1 and subjective symptoms after each dose. Testing stops if the methacholine concentration reaches 8 mg/ml without any significant change in lung function. This has a high specificity, meaning that a negative test essentially excludes asthma. A decrease in FEV1 of greater than 20% from baseline is a positive test.

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