Pulmonary function tests are a group of tests that measure how well the lungs take in and release air and how well they move gases such as oxygen from the atmosphere into the body’s circulation. Since the test involves some forced breathing and rapid breathing, patients may have some temporary shortness of breath or lightheadedness. Patients breathe through a tight-fitting mouthpiece, and patients will have nose clips.

Pulmonary function tests are done to:

• Diagnose certain types of lung disease (such as cardiac asthma, CHF, asthma, bronchitis, and emphysema)
• Find the cause of shortness of breath
• Measure whether exposure to chemicals at work affects lung function
• Check lung function before someone has surgery

It also can be done to:

• Assess the effect of medication
• Measure progress in disease treatment

For some of the test measurements, patients can breathe normally and quietly. Other tests require forced inhalation or exhalation after a deep breath. Sometimes patients will be asked to inhale the substance or a medicine to see how it changes your test results.

Lung volume measurement can be done in two ways:

• The most accurate way is to sit in a sealed, clear box that looks like a telephone booth (body plethysmograph) while breathing in and out into a mouthpiece. Changes in pressure inside the box help determine the lung volume.
• Lung volume can also be measured when you breathe nitrogen or helium gas through a tube for a certain period of time. The concentration of the gas in a chamber attached to the tube is measured to estimate the lung volume.

To measure diffusion capacity, patients will breathe a harmless gas, called a tracer gas, for a very short time, often for only one breath. The concentration of the gas in the air you breathe out is measured. The difference in the amount of gas inhaled and exhaled measures how effectively gas travels from the lungs into the blood. This test allows the doctor to estimate how well the lungs move oxygen from the air into the bloodstream.