Pulmonary function testing is usually performed at a physician’s office, hospital or clinic. The physician or technician will begin by explaining the test in detail and answering any questions the patient may have.

Patient cooperation is needed to obtain the most accurate results from pulmonary function testing. The tests require patients to inhale and exhale with a specific degree of effort and at various rates and repetitions. The information obtained from these tests is only as accurate as patient participation allows.

There are many different types of pulmonary function tests, and each measures a different aspect of lung function. In many of these tests, a clip is attached to the patient’s nose to ensure that air does not escape through the nostrils. Testing usually takes between five and 30 minutes, depending on which tests are being administered.

The most common side effects of pulmonary function testing are shortness of breath, cough or dizziness from breathing in and out forcefully. Much of this discomfort is quickly alleviated by taking short rest periods between each phase of testing. Those who feel any discomfort during testing should immediately tell the test administrator. For individuals who continue to display difficulty breathing or other lung-related symptoms, a bronchodilator or other medication may be administered.

The three primary pulmonary function tests are performed as follows:

• Spirometry. Patients are asked to sit up straight or stand, place their mouths on the spirometer’s mouthpiece and form a tight seal around it while breathing normally. The spirometer records lung functions during this normal breathing pattern.
  
  Patients are then asked to inhale deeply, then exhale vigorously and quickly. Typically, this is repeated twice more, and the best reading will be recorded and compared to norms based on age, gender, race and height. A reading that falls below 80 percent of the predicted norm is considered abnormal. 
  
  

  Some physicians will perform the test once under normal circumstances, and then administer a bronchodilator to the patient before repeating the test. This allows the physician to see whether the patient’s breathing can be improved with the use of bronchodilators.  
  
  

• Lung volume measurement. Patients sit in the body plethysmograph and seal their mouths around a mouthpiece. As they breathe in and out, changes in pressure inside the box reveal the volume of gas in the lungs.
  
  An alternative to the plethysmograph involves breathing in a gas mixture for three to seven minutes before slowly exhaling completely. Calculations determine the volume of gas in the lungs.
  
  

• Diffusing capacity measurement. Patients inhale a small amount of carbon monoxide, and hold their breath for 10 seconds before exhaling into a carbon monoxide detector. The amount of carbon monoxide remaining in the exhaled air indicates how rapidly the patient is able to exchange gases from the lungs into the bloodstream.