Asthma is a chronic disease that affects the airways and lungs. According to the World Health Organization (WHO), approximately 300 million people worldwide and 14–17 million people in the United States are affected by asthma. Asthma is the most common chronic disease in children. Severe asthma is a serious health concern that can lead to respiratory failure. Each year in the United States, as many as 470,000 people seek hospital treatment for asthma-related symptoms and the disease causes about 5000 deaths.
Signs and Symptoms
Inflammation of the bronchial airways causes them to become constricted and narrowed. Narrowing of the airways, called bronchoconstriction, produces shortness of breath, tightness in the chest, cough and wheezing.
Except in severe cases, symptoms of asthma are occasional. The duration and severity of asthma symptoms vary greatly from time to time and from patient to patient. The symptoms may be intermittent, and they can last just a few minutes or days. In severe cases, asthma symptoms may be constant and persistent.
The most reliable way to determine reversible airway obstruction is with spirometry, a test that measures the amount of air entering and leaving the lungs. This simple test can be performed in the physician’s office.
Spirometry uses a measuring device called a spirometer. The patient exhales and inhales deeply, then seals his or her lips around the mouthpiece and blows as forcefully and for as long as possible until all the air is exhaled from the lungs.
Ideally, the patient should exhale for at least 6 seconds. The spirometer measures the amount of air exhaled and the length of time it took to exhale it. To test for reversibility, the patient then inhales a bronchodilator (i.e., a drug that widens the airways in the lungs) and the spirometry is repeated. If the values of the test performed after administration of the bronchodilator are significantly better than the prebronchodilator values, the obstruction is considered reversible.
Sometimes a patient with asthma does not demonstrate reversibility after the inhalation of a bronchodilator. In this case, the patient may be treated for a few weeks with ant inflammatory medications and then returns for another spirometry test. If the posttreatment spirometry results are better than the initial results, the obstruction is considered reversible.
Peak Expiratory Flow
Because asthma symptoms vary, it is not unusual for a patient with chronic asthma to have normal spirometry. In such cases, peak expiratory flow (PEF) rate monitoring may be used to demonstrate reversible airway obstruction. A peak flow meter is a portable device that can be carried by the patient. It consists of a small tube with a gauge that measures the maximum force with which one can blow air through the tube.
The patient performs the peak flow meter test twice a day for about 2 weeks and records the results for review in a follow up appointment. The first test should be performed after waking in the morning, before taking bronchodilator medications. The patient should perform the peak expiratory flow maneuver 3 times and record the highest measurement. The second test should be done in the afternoon or early evening after taking a bronchodilator. Peak flows vary during the day and the early morning peak is lower than the evening peak. A variability greater than 20% indicates a reversible airway obstruction.
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