Lung function tests

Lung (also called pulmonary) function tests evaluate how well the lungs work. The most common test is spirometry. This quantifies the amount and speed at which air can be moved out of the lungs. The test is painless. The patient breathes into a mouthpiece attached to a spirometer (recording device). A chart, called a spirogram is generated by the machine.

Spirometry can measure:

• Forced vital capacity (FVC).
• Forced expiratory volume (FEV).
• Forced expiratory flow 25% to 75%.
• Peak expiratory flow (PEF).
• Maximum voluntary ventilation (MVV).
• Slow vital capacity (SVC).
• Total lung capacity (TLC).
• Functional residual capacity (FRC).
• Residual volume (RV).
• Expiratory reserve volume (ERV).

After this is done, sometimes the series is repeated after the patient inhales a drug (usually albuterol) to expand the airways of the lung. Afterwards, test results are compared to 'predicted results' that are calculated on the basis of age, height, weight and gender.

Further lung testing may include gas diffusion, body plethysomgraphy, residual volume, exercise stress tests, and arterial blood gases. Lung function tests help in evaluating asthma and chronic obstructive pulmonary disease (COPD, includes emphysema and chronic bronchitis). An electrocardiogram (EKG) may also be done and, if results are abnormal, follow-up may include a dobutamine echo or stress thallium test.

Lung function tests are used to help determine the cause of breathing problems and to diagnose certain lung diseases. They can help to differentiate between different forms of respiratory disease, such as obstructive conditions like asthma or problems caused by infections such as PCP. Lung function tests are also useful for monitoring treatment efficacy.