Spirometry Testing For Asthma


You may have shortness of breath, chest tightness, or coughing spasms when you exert yourself in cold weather, or you may hear wheezing sounds from your chest during colds. Perhaps your mother, father, or sister had asthma. Does this mean you have asthma? To make the diagnosis, your physician can provide simple, painless breathing tests during an office visit, using a device called a spirometer.

Historical Perspective

Spirometers were first used over 150 years ago by British physicians treating patients with consumption (tuberculosis of the lung). Spirometers then measured only the amount of air that a patient could blow out, called the “vital capacity,” meaning the ability to live. A healthy young woman has a vital capacity of about 4 liters (one gallon of air), while a patient with severe tuberculosis has a vital capacity of only 2 liters. The ability to measure how fast a person can blow out their air was added to spirometers during the 1950s. These old water-filled spirometers weighed more than 70 pounds, and it took the nurse 20 minutes to calculate the results from the paper tracings. Only hospital laboratories had spirometers until the 1980s.

Modern Hand-Held Devices

Today, modern office spirometers are hand-held, fully automated, and accurate within 3 percent, and they can store and print the results and record trends. Most physicians purchase them to test patients during an office visit for asthma and smoking-related lung diseases (chronic bronchitis and emphysema). Disposable mouthpieces eliminate the chance of infection.

In asthma, airways throughout the bronchial tree are narrowed, due to inflammation and contraction of the smooth muscle that surrounds the airway walls. Narrowed areas of the airways turn into whistles, creating a wheezing sound during breathing that can be heard by a physician using a stethoscope. You also may be able to hear faint wheezes more clearly by using your fingers to plug your ears while exhaling rapidly. However, since several other types of lung diseases cause noisy breathing and wheezing, the diagnosis of asthma requires an objective test, such as spirometry.

Measuring Airway Narrowing

Spirometry testing can determine the degree of airway narrowing. You simply take as deep a breath as possible and then blast out the air as fast as possible into a spirometer. The spirometer measures the speed with which air was exhaled during the first second (FEV1) and the total amount (volume) of air exhaled (FVC). Typically, you won’t be able to move air quickly through narrowed airways if you have asthma, so the amount of air exhaled in the first second is reduced compared to symptom-free periods.

If symptoms are present, it is usually easy to make the diagnosis of asthma using a spirometer. Asthma is indicated when a low FEV1/FVC ratio confirms airway obstruction and 15 minutes after inhalation of an asthma medication, such as albuterol, the FEV1 increases more than 12 percent and your symptoms resolve. However, asthma is characterized by rapid changes in airway narrowing, which sometimes makes a physician’s diagnosis more difficult. The wheezing may have cleared up by the time you visit the physician, and the spirometry test then may be normal. In such cases, the National Asthma Education Panel recommends either home monitoring of the peak flow several times a day for two weeks, or a challenge test in a hospital pulmonary function laboratory detoxic kaina. Asthma is confirmed by home monitoring when the peak flow decreases by more than 20 percent during the morning.

Tracking Improvement

Once your physician diagnosis asthma, spirometry is used to measure the improvement resulting from treatment. With successful treatment, the speed with which you can exhale air in the first second improves until it remains in the normal range all day, every day. Inhaled corticosteroids and other anti-inflammatory drugs often take several days or weeks to show maximal benefit. While undergoing treatment, spirometry tests performed during return visits to your physician will show this improvement or indicate the need for a change in treatment.

Asthma may now be objectively diagnosed and monitored using a quick, easy, and inexpensive spirometry test in your primary-care physician’s office. Treating asthma without measuring the FEV1 is like treating hypertension without measuring the blood pressure.

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