Why is it important?  

In 2011, the CDC listed respiratory diseases, specifically chronic obstructive pulmonary disease (COPD), as the third leading cause of death in the United States, claiming the lives of over 100,000 people. Pulmonary function testing is the primary method used to diagnose, stage, and monitor various respiratory diseases. In simplistic terms, respiratory diseases can be classified as either obstructive or restrictive processes. Obstructive disorders, such as emphysema and asthma, are characterized by airflow limitation and increased lung compliance, typically resulting in increased lung volumes with air trapping (known as dead space because this does not increase the functional capacity of the lungs). Conversely, restrictive disorders, such as pulmonary fibrosis or even obesity, are characterized by reduced lung volumes and an increase in overall stiffness (decreased compliance) of the lungs. Though medical treatments for these conditions continue to advance, they are still mostly limited to symptom management. Thus, it is essential to maintain a healthy respiratory system by choosing to exercise, eat right, and abstain from smoking. Early detection of abnormal values is critical in catching the disease in a state where these simple lifestyle interventions may be enough to return pulmonary function back to normal.   

How is it assessed?  

While there are a number of variables that can be measured from a standard pulmonary function test, the three most common are Forced Vital Capacity (FVC), Forced Expiratory Volume in One Second (FEV1), and the ratio between FVC and FEV1. FVC refers to the amount of air one can expire after taking the largest inspiration possible. Essentially, it describes the maximum amount of air you are capable of moving in one breath. FEV1 describes the maximum amount of air that can be expired in one second of exhaling and is an important measure of airway compliance. The interplay between FVC, FEV1, and FEV1/FVC provides a clear picture of lung function and is instrumental in the diagnosis of restrictive and obstructive diseases. FVC and FEV1 are both assessed by blowing into a tube which uses a microprocessor-driven pneumotachometer to measure air flow and then mathematically derive volume. For the FVC test, you will take the largest inspiration possible followed by the largest expiration possible. The expiratory volume will be recorded. FEV1 is measured in a similar manner, only this time you will breathe out as fast as you can and only the first second of your expiration will be recorded. The FVC to FEV1 ratio is then calculated by simple division.  

Methods of Pulmonary Physiological Testing:

1. Spirometry without bronchodilator: A spirometer is used to measure how much air a person’s lungs can hold (air volume) and the speed (air flow rate) of inhalation and exhalation during breathing. Values measured include FVC, FEV1, FEV1/FVC, FEF25-75% and PEF.

2. Spirometry with bronchodilator: Spirometry is done before and after a bronchodilator (medicine that helps open the bronchial tubes (airways) of the lungs) to show response to medication. Values measured include FVC, FEV1, FEV1/FVC, FEF25%-75% and PEF.

3. Plethysmography: Lung plethysmography is more accurate than spirometry and are based on Boyle’s Law, a scientific principle that describes the relationship between the pressure and volume of a gas. You’ll sit in a small, airtight chamber with nose clips and asked to breathe or pant against a mouthpiece when it’s both opened and closed. This will provide important measurements, including total lung capacity (TLC), functional residual capacity (FRC) and residual volume (RV).

4. DLCO: The diffusing capacity of the lungs for carbon monoxide (DLCO) is a 10-second breathe-hold measurement (single breathe method) that helps to determine the lung’s ability to transfer gas from inspired air through the bloodstream. It measures the uptake of carbon monoxide (CO) per unit time/per mm of driving pressure of CO. Since hemoglobin effects DLCO, it is adjusted for hemoglobin values. To have hemoglobin-adjusted DLCO, a hemoglobin value must be provided on the day of the study or within past 3 days via a venipuncture.

5. 6 Minute Walk Test (6MWT): This is a sub-maximal exercise test used to assess aerobic capacity and endurance. The distance covered over a time of 6 minutes is used as the outcome by which to compare changes in a performance capacity.

What to expect during the assessments:  

1. You will be asked to wear a nose clip to ensure all air movement occurs in and out of the measuring tube. It is also important to keep a tight seal with your lips around the tube throughout the measurement period.  

2. This is an effort dependent test and you will be taking several deep breaths. You will be asked to take a few "practice" breaths to get a sense of how it feels. Please be aware of repeating several of these deep breaths too quickly can lead to lightheadedness and in some rare cases, fainting. Take as much time as you need between breaths.  

Participant preparation:  

Test validity and data accuracy are greatly improved by adhering to the following guidelines prior to your assessment. Your test(s) will be given on the assumption that you have followed these recommendations:  

1. Refrain from ingesting heavy meals, alcohol, caffeine and tobacco products within 5 hours of testing  

2. You should be well rested for the test: avoid significant exertion or exercise 24 hours prior to testing and get a good night’s sleep