Pulmonary Function Testing
Your pulmonary function (ability to breathe) should be checked annually while you are still able to walk, and every six months after ambulation (walking ability) is lost. Starting these tests as early as possible will can also allow you to become familiar with the equipment.
Close observation of your respiratory function will help your doctor determine your progress and evaluate whether you need assistance with breathing and coughing.
Video: What to Expect at Your Pulmonary Visit
What is a Pulmonary Function Test?
There are several different types of Pulmonary Function Tests (PFTs). Spirometry is the most common type, and is important for patients with Duchenne.
Spirometry focus on two aspects of your breathing:
- Measures volume, or how much air can be moved in and out of the lungs. This allows your doctor to measure your vital capacity – the total volume that can be exhaled after inhaling maximally.
- Measures flow, or how fast the air moves out of the lungs. This allows your doctor to measure how open your airways are and whether you have asthma.
Other tests may be done to evaluate pressures (how strongly you can suck air in and blow air out) and the strength of your cough.
What to expect
It is important to start breathing tests early so that you can become familiar with the equipment. Know that the test does not hurt and that it must be done to find out how to make your breathing better.
- Before the test, your height and/or lengths will be measured because your lung size is related to your height. If you are non-ambulatory, it is important to measure lengths, such as ulnar (forearm) length or arm span.
- You may become tired or frustrated during the test. You may need to a rest period in between blowing into the machine.
- You will be asked to wear a nose clip to keep from breathing through your nose.
- You will be asked to take a deep breath and blow the air out into a mouthpiece.
- You will repeat the test several times to get your best, most consistent result.
What is your doctor or respiratory therapist looking for?
There are several measurements taken when you are having a PFT. These measurements may decrease as your breathing muscles weaken. It is important for your breathing to be evaluated at least yearly so that these measurements can be tracked.
Forced vital capacity (FVC)
To measure forced vital capacity (FVC), you will inhale and fill your lungs as deeply as possible, then exhale as much air out as you can. The total volume of air breathed out is the “forced vital capacity.” You may need to complete this test in different positions (standing, sitting, etc.). Decreased FVC may indicate the need for assistance with breathing using assistive devices (such as BiPAP). Assistive devices make it easier to breathe in.
Cough Peak Flow (CPF)
To measure CPF, you will take a deep breath in, and then cough into a mouthpiece as hard as you can. This will show how hard your child is able to cough. Decreased CPF may indicate the need for help with coughing, for example, using manual assistance or mechanical assistance (such as a Cough Assist machine).
Measuring Pressures
Maximal Inspiratory Pressure (MIP)
To measure MIP, you will exhale completely, then inhale against a closed mouthpiece. The harder you can suck air in, the stronger your inspiratory muscles are. This helps measure how strong your respiratory muscles are when you take a deep breath.
Maximal Expiratory Pressure (MEP)
To measure MEP, you will take a deep breath in, then blow as hard as you can against a closed mouthpiece. The harder you can blow air out, the stronger your respiratory muscles are when you exhale. This is most important for testing the muscles used to cough.
Peak Cough Flow (PCF)
Coughing is very important. If your cough is weak, you may not be able to clear your airway. If you cannot clear your airway, secretions may go into your lungs and cause pneumonia. The PCF test will show how strong your cough is and whether you might need assistance coughing when you are well and/or sick. If you do need assistance coughing, your pulmonologist and respiratory therapist will help show you different ways to assist your cough.
