Spirometry measures lung function by testing the patient’s ability to inhale and exhale. The test is the most common of the three pulmonary function tests used to assess the health of the patient’s lungs and airways. Spirometry tests are usually carried out in children over 5 years of age, because of the testing requirements involved, but can be done on cooperative younger children. Although there is a lack of “normal” testing values for younger children, physicians can still obtain important information from the test. The ability to complete spirometry tests is often dependent on the individual.

The spirometry test uses a device called a spirometer to evaluate three pulmonary functions. The spirometer uses the data acquired during the test to fill in certain values. These values include:

• Maximum volume ventilation (MVV). Measures the complete volume an individual exhales in a 15-second period. This number is multiplied by four to find the value for one minute.
  
  
• Forced vital capacity (FVC). Measures the volume of air exhaled over a continuous six-second period. This helps provide an indication of how much air the lungs can hold.
  
  
• Forced expiratory capacity (FEV1). Measures the speed of air exhaled in one second.

The recordings of the information obtained from the test are known as spirograms. The information provides a good evaluation of the health of an individual’s respiratory system. Spirometry is also useful for the diagnosis of several types of respiratory conditions. These include:

• Reactive airway diseases (e.g., asthma)

• Chronic obstructive pulmonary disease (COPD, including chronic bronchitis and emphysema)
  
  
• Respiratory diseases (e.g., cystic fibrosis)
  
  
• Abnormal blood flow to the lungs (e.g., pulmonary hypertension)

Besides diagnosis, spirometry is useful for comparing the progression of respiratory conditions. Many types of conditions (e.g., asthma, COPD) are characterized by steadily deteriorating lung function. Spirometry can be used to gauge how quickly and severely a patient’s airways are becoming obstructed. Spirometry measurements repeated over several years can determine the development and extent of airway obstruction.

Spirometry can also be used to determine the effectiveness of therapy. A patient who achieves better spirometry numbers after using a bronchodilator, for instance, has a respiratory condition that is responsive to drug treatments. Conversely, the failure of a patient to respond to bronchodilators may suggest permanent respiratory damage. In addition, a physician may use spirometry to monitor the effectiveness of therapy. For instance, a physician may increase or decrease a patient’s medication dosage after reviewing their spirometry results. Spirometry also can be used to evaluate the risk of operations for a patient.