Cystic Fibrosis and Spirometry

Cystic Fibrosis (CF) affects the lungs and respiratory tract in all people living with this condition. Thick, sticky mucus can build up in the tubes leading into the lungs (airways) and affects how the air flows through them. Spirometry is a common pulmonary function test (PFT) used to track lung function over time. It is routinely done during clinic visits starting around school-age. It may also be done at home.

What are the common spirometry measurements?

  • Age and Height: These allow us to compare your test results to similar patients.

  • FVC: Total volume of air exhaled over the full breath.

  • FEV1: Volume of air exhaled in the first second of the breath.

    • This is the measurement we follow most often in clinic.

    • It is often used in clinical trials to determine the effect that the clinical trial had on lung function.

  • FEV1/FVC: The percent of breath emptied in the first second compared to the whole breath.

  • We will compare each of the above test results to your previous test results. See the chart below.

     

    • A red dot means that your results dropped at least 10% from your usual results.

    • A green dot means your results stayed about the same as usual.

What are typical spirometry results?

    •  Most people have an FVC and FEV1 of at least 80% of the normal average (also known as the predicted value).

      • Since 80% of an exhaled breath should be exhaled in the first second, a typical FEV1 to FVC ratio is at least 80%,

      • If the ratio is less than 80%, it means it is taking you longer to fully exhale.

    • Z-Score: This is a range of typical values. See the chart below. The black dot shows your test results. Think of the colors like a traffic light. If your dots are in the green zone, your results are good. If they are in the yellow zone, they are concerning. If they are in the red zone, they are signs of trouble.

Why do you track test results over time?

By comparing test results over time, we can identify any changes in your lung health, both the good and the bad. If the FEV1 or FEV1/FVC ratio goes down, that means there is obstructive lung disease.

What causes lung function to decrease?

  • Infection

  • Progression of lung disease

  • Malnutrition or weight loss

  • Cystic fibrosis related diabetes (CFRD)

  • Poor effort or technique 

Test results can be affected by how well you are able to take a deep breath in, breathe out all the air in your lungs, and the effort you use to blow the air out. 

How do my test results help my provider to plan my care?

  • Your provider will follow your results during and after an illness, CF flare or hospitalization so that they can monitor your recovery.

  • Test results can show your provider how you are responding to a new medicine or therapy.

Remember to ask your CF provider about your test results and how they compare to your past results.

Is testing safe for my child with CF?

Many parents worry that germs will be passed from patient to patient through the testing equipment. We understand this concern. Here are some things you should know:

  • Studies show that bacteria are not transmitted from pulmonary function equipment under normal circumstances.

  • The pulmonary function laboratory at Children’s Hospital of Philadelphia meets American Thoracic Society standards for all equipment. 

  • The lab uses standard precautions for all patients with CF who use our equipment. This includes:

  •  Therapists wash their hands before and after patient contact.

  • The therapist performing the PFT’s wears a gown and gloves (changing after each patient) before performing PFT’s.

  • Instructing the patient to wash their hands before doing the test.

  • Discarding the mouthpiece and nose clips after each patient use.

  • Using disposable filters with each patient to prevent bacteria from getting into the equipment.

  • Cold sterilizing the flow sensor weekly

  • Cleaning equipment after each patient with the hospital approved disinfectant

  • Patients who are colonized with Burkholderia cepacia (B. cepacia) are tested at separate times from those who are not colonized with cepacia.

These precautions protect your child very well from the transmission of bacteria through the equipment.

If you have any questions or concerns about this, please ask to speak to the Director or Medical Director of the pulmonary function laboratory.

 

Reviewed October 2024 by Ambika Shenoy MD, Clement Ren MD