Pulmonary Function Tests (PFTs) are a way of testing lung health. It helps your CF Team get a better picture of how you or your child is doing. It is important to remember, however, that it is only one piece of the picture; other pieces include your medical history (the description of any symptoms and any illnesses you may have had recently), your physical examination, and other tests (such as cultures, x-rays, or labs). Depending upon how you or your child is doing, the history, physical examination, PFTs, or other tests may carry different levels of importance. This section will help you understand how your CF team looks at you or your child's PFTs.

First, there are the testing techniques. For any PFT to be useful, the person with CF must be able to perform the test properly. The testing is usually done with coaching by RTs (Respiratory Therapists), and by looking at the tests, they can tell if it was done right. Not only does the test need to be done correctly, but also the person doing the test should be able to do the test the same way again, and again.

The most common PFT is called 'spirometry', and we usually start asking children with CF to attempt the test around 5 years of age. Some might be able to do it younger; many are still learning how to do it properly for two or three more years. All breathing tests are done through a tube. The RT will ask the person with CF to hold the tube in their mouth, with their lips around the tube. The RT coach you or your child in how to breathe. The key to doing spirometry testing is to take as big a breath in as you can, and then to breathe it out 'explosively', as hard and fast as possible, AND keeping exhaling until you can't breathe out any more; until there's no more air left inside anymore; then you take as big a breath in as you can, and you're done your first test. As mentioned above, we need to be sure that the testing is consistent, so you or your child will be asked to do the test at least 3 times to be sure there is little variation. The computer compares the value of these tests done by the person with CF, with similarly aged persons of the same size (one reason you are weighed and measured) and gender without CF, and gives the 'percent predicted value'. Thus if you are normal, you would get 100%, if you were 10% better you would get 110%, and if you were 10% worse, you would be 90%.

Spirometry testing has several components to it. FVC or Forced Vital Capacity is the size of the biggest breath someone can blow out. FEV1 is the Forced Expired Volume after 1 second of blowing out. FEF25-75 is the Forced Expiratory Flow between the 25th to 75th percent of your breathing out. FVC and FEV1 (as well as their ratio, FEV1/FVC) mostly reflect a person's larger airways. Forced expiratory flows (FEFs) are usually thought to be more related to smaller airways. FEFs often are more 'sensitive', changing up or down more easily, but are less specific, meaning when they change it may not necessarily reflect anything significant. There has to be a bigger drop in FEFs before we say they are abnormal.

  Measured Test 
  Normal      Mild 
    Moderate    Severe 
  FVC  More than 80%    60 - 80%     40 - 60%   Less than 40%
  FEV1  More than 80%    60 - 80%     35 - 60%   Less than 35%
  FEF25-75  More than 65%    50 - 65%     30 - 50%   Less than 30%

One of the most important things about PFTs is that we can look at how a PFT changes over time, between two clinic visits, or over any period of time, revealing in some ways how a person's CF is changing. PFTs can only be compared, however, if the person doing the PFT is able to do them correctly. If the person's technique varies, the results vary, and we are not able to compare. Assuming we can compare tests, what constitutes something important? It is common for a person, with or without CF to have some minor changes, up or down, in their PFTs. If a person's FEV1 goes up or down 5%, is that significant? The American Thoracic Society has established certain changes as being "clinically" significant, meaning a person might feel a change in their breathing (e.g. some degree of one or more of the following: less tolerance of exercise, more tired, shortness of breath, cough, wheeze, chest tightness, or other symptoms). We also use these numbers to determine whether a person has a significant response to a breathing treatment or other medications.

Measured Test   % Change to be Significant
 FVC  10% or greater
 FEV1  10% or greater
 FEF25-75  30% or greater

Although the above is true, because of the progressive nature of pulmonary decline in CF, CF care providers often use a lower threshold to decide if something is significant. For example, in the research studies that looked at inhaled TOBI average FEV1 improved 10%, with Pulmozyme average FEV1 increased 7%, with chronic azithromycin it was 7%, and hypertonic saline showed 5% improvement. Additionally, at the Central CT CF Center, we are very concerned with a 10% decrease, but also worry if PFTs drop 5%. We want to stop any decline early.

Although spirometry (FVC, FEV1, and FEFs) are the most common PFT done, there are other testing techniques. These include lung volumes that look at total lung capacity (TLC) and residual volume (RV). These are more complex tests that actually measure air within the lung that a person cannot exhaled no matter how hard they try. They can show whether a person has restriction due to scarring, or gas trapping. Newer PFT techniques are being developed so that we may assess children younger than 5 or 6, but who are somewhat cooperative with instructions. Finally, you may be aware or have read about 'infant pulmonary function tests'. Infant PFTs require very specialized equipment, and are generally done as part of research studies, rather than for routine care.