Pulmonary Function Testing

What is Pulmonary Function Testing?

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Pulmonary function testing is not a single test, but rather, a series of maneuvers aimed at evaluating the functioning of the lungs. This testing may also be referred to as PFTs, lung function testing, spirometry, or breathing tests. Pulmonary function testing generally consists of 3 components:

  1. Spirometry- measuring how much air you exhale and how quickly, which can help evaluate for a broad range of diseases, including asthma
  2. Lung Volumes- measuring the amount of air in your lungs can help in evaluating diseases like emphysema (generally too much air) or scarring diseases like asbestosis (generally too little air)
  3. Diffusion Capacity (DLCO)- measuring how well your lungs can bring oxygen into the bloodstream can help in evaluating a number of lung diseases, including the category called interstitial lung disease

Other possible components include bronchodilator testing (generally repeating spirometry after giving you an inhaled medication to open your airways), ventilation maximums (to assess neuromuscular function), exercise stress testing (testing heart and lungs during exercise), arterial blood gases, and inhalation challenge (testing before and after administering an inhaled substance that produces an asthma-like reaction in certain conditions).

Why did my doctor order PFTs?

  • To help in the evaluation of shortness of breath or other signs or symptoms of lung disease
  • To screen those at risk for lung disease, such as smokers or ex-smokers or those exposed to certain substances
  • For disability/impairment evaluations
  • To assess prognosis and monitor disease progression
  • To determine lung condition before surgery (especially for those undergoing chest or major surgery), and assess the risk of respiratory complications during and after surgery
  • To measure the effect of a disease on lung function (including non-lung diseases)
  • To monitor the effect of medication and to evaluate treatment response

How is the testing done?

Most testing is performed in a comfortable, seated position. Testing might take up to one hour, depending upon the testing ordered. The technician will repeat tests in order to obtain your “best” results. You will have a chance to rest between test trials. You will breathe into a mouthpiece, while wearing nose clips to ensure no air passes in or out of your nose during the test.

For spirometry, you will breathe into the mouthpiece that is connected to an instrument called a spirometer. The spirometer records the amount and the rate of air that you breathe in and out over a period of time. For some of the test measurements, you will breathe normally and quietly. Other tests require forced exhalation after a deep and full breath.

Lung volume measurement can be done in two ways:

 

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  • The most accurate way is to sit in a sealed, clear box (body plethysmograph or “body box”) that looks like a telephone booth with windows, while breathing in and out or panting into a tightly sealed mouthpiece. Changes in pressure inside the box help determine the lung volumes.
  • Lung volumes 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, you breathe a harmless gas for a very short time, and then hold your breath for about 10 seconds. The concentration of the gas in the air you breathe out then is measured. The difference in the amount of gas inhaled and exhaled can help estimate how quickly gas can travel from the lungs into the blood.

Are there any risks?

This is a painless test, with little or no risk for most people. Since the test involves some forced breathing and rapid breathing, you may have some temporary shortness of breath or light-headedness. There is a very small risk of collapsed lung in people with a certain type of lung disease. The risks are greater in those who have experienced a recent (within the past month) heart attack, have certain other types of heart disease, are experiencing current heart pains, patients with severe high blood pressure, or those having undergone recent eye surgery. Abdominal pains, facial or mouth pain, confusion, or recent stroke can interfere with optimal and reliable results. Certain medications (such as beta blockers or certain asthma medicines) can also interfere with results. The physician or PFT technician should be made aware of any condition that might adversely affect the results or pose a risk to the examinee.

What can I do?

Your cooperation while performing the test is crucial in order to get accurate and reliable results. It is important to have a tight seal around the mouthpiece. If you have dentures, wearing them during the test is preferred. Wear loose, comfortable clothing. Take your regular medications, unless otherwise instructed by your doctor, and bring in a list of your medicines.

Testing subjects should preferably avoid certain activities before testing. These include:

  • smoking within one hour before the test (preferably not at all on the day of testing)
  • consuming alcohol within 4 hours of testing
  • eating a large meal within 2 hours of testing
  • performing vigorous activity within 30 minutes of testing
  • wearing constrictive clothing

How does the doctor grade the test?

Expected (or “predicted”) values are based upon your age, height, sex, and ethnicity. The predicted values may vary slightly among different laboratories.

Generally, your results will be compared to the predicted values for someone just like you. Depending upon the parameter, a value will be considered abnormal if it is less than a certain percentage of your predicted value (often 80%). Some testing provides a “lower limit of normal” and your result would be abnormal if you fall below that level.

Abnormal results may mean that you have some chest or lung disease. Talk to your doctor about the meaning of your specific test results.

Where can I find out more information?

American Lung Association
American Thoracic Society guidelines