What are Lung Function Tests?
Lung function tests are also known as pulmonary function tests (PFTs) and can be completed through a variety of methods.
The purpose of the lung function test is to - obviously - test how well your lungs do their job. The tests will evaluate how well your lungs take in and hold oxygen, and remove carbon dioxide from the bloodsteam. They will examine how much air you can blow out of your lungs and how quickly, and how strong your breathing muscles are.
Lung function tests can be used to verify the presence of any difficulties, as well as track the progress of any administered treatment. They are commonly used to verify the presence of conditions such as asthma, lung tissue scarring, sarcoidosis, and chronic obstructive pulmonary disease (COPD).
What Kind of Lung Function Tests are Used?
The most common test is called spirometry. The spirometer measures how much air you can breathe in and how fast you can breathe it out. This is done by breathing into a mouthpiece attached to the spirometer. The test may be done in conjunction with walking or running on a treadmill.
Spirometry also measures:
- the amount of air you can exhale after inhaling as deeply as possible (forced vital capacity - FVC);
- the amount of air you can exhale with force in one breath (forced expiratory volume - FEV);
- the air flow mid-exhale (forced expiratory flow 25% to 75%);
- how quickly you can exhale (peak expiratory flow - PEF);
- the greatest amount of air you can inhale and exhale in 60 seconds (maximum voluntary ventilation (MVV));
- the amount of oxygen you can slowly exhale after inhaling as deeply as possible (slow vital capacity (SVC));
- the amount of air in your lungs after inhaling as deeply as possible (total lung capacity (TLC));
- the amount of air in your lungs once you've exhaled normally (functional residual capacity (FRC));
- the amount of air in your lungs after exhaling completely (residual volume (RV))Gas diffusion tests measure how well your lungs clear out carbon dioxide and oxygenate the blood. This is done through testing arterial blood gases and through inhaling of a small amount of carbon monoxide (carbon monoxide is absorbed more quickly into the bloodstream than oxygen and can provide an accurate evaluation of how the lungs are working).
Body plethysmography is done with the patient sitting in an airtight box, inhaling and exhaling through a spirometer. A shutter closes across the breathing tube and the patient will need to breathe against the shutter. This will expand and decompress the air in the lungs, which affects the pressure in the box. The difference between this volume and the original volume of the box represents the same change of volume in the lungs.
The body plethysmography test is used to measure total lung capacity and residual volume.
Inhalation challenge tests or provocation studies measure how your airways respond to substances. Amounts of a particular substance will be inhaled through a face mask or mouthpiece and spirometry readings are taken before, during, and after inhaling the substance.
Those with cystic fibrosis will be familiar with the multiple-breath washout test. With this test, air with a "tracer gas" is inhaled through a tube, then measured when exhaled.
How to Prepare for the Tests and What to Expect
Before proceeding with any of the above testing procedures, tell your doctor if you:
- have had recent chest pains or a history of heart attack
- take medication for a lung problem
- have allergies to any medications
- have had recent eye, chest, or abdominal surgery, or a collapsed lung (pneumothorax).
To prepare for the test itself:
- If you need to eat before the test, keep the meal/snack light because a full stomach can impede the full expansion of your lungs.
- Do not smoke or engage in rigorous exercise for 6 hours prior to the test.
- Wear loose clothing that will not restrict your breathing.
- Avoid food or drinks with caffeine because caffeine will relax your airways and allow in more air than usual.
- If you have dentures, be sure to wear them during the test to help form a tight seal around the mouthpiece of the spirometer.
You may experience temporary shortness of breath or lightheadedness because of the forced or rapid breathing the tests require. You will be required to wear nose clips when you breathe through the mouthpiece.
Testing may take between 5 and 30 minutes, depending on how many tests are needed to assess your situation. The accuracy of the tests depend entirely on your capability to follow preparation and intra-testing instructions. It is extremely important that you follow every instruction your doctor gives you.
Sources: www.webmd.com; www.nhlbi.nih.gov; http://health.nytimes.com; http://oac.med.jhmi.edu (John's Hopkins School of Medicine)