Pulmonary Function Tests in COPD Progression Monitoring

By Dr. Liji Thomas, MDReviewed by Danielle Ellis, B.Sc.

What are pulmonary function tests? 
Why are pulmonary function tests crucial in COPD management?
Types of pulmonary function tests used in COPD monitoring
Interpreting pulmonary function test results: What do the numbers mean?
How often should COPD patients undergo pulmonary function tests?
Improving COPD outcomes through regular pulmonary function testing
References
Further reading

What are pulmonary function tests? 

Pulmonary function tests (PFTs) are tests of lung function. They are intended to evaluate and monitor chronic obstructive pulmonary disease (COPD).

COPD is characterized by emphysema, the lung being overstretched with fixed airway obstruction. The lungs in COPD have lost their elastic recoil, while the airways are unable to stay open due to the loss of their elastic wall fibers. This causes static and dynamic hyperinflation at rest and with increased breathing during exercise, leading to dyspnea. ^1,2,3

Various types of PFT are used to diagnose and manage COPD. These include spirometry (tests based on blowing out the breath as hard as possible after the deepest possible inhalation), lung volume measurement by techniques like plethysmography and helium diffusion, and total lung diffusion capacity for carbon monoxide (DLCO) to assess gas exchange at alveolar level.³

Why are pulmonary function tests crucial in COPD management?

Spirometry is the gold standard in the diagnosis of COPD. Without it, COPD may be missed in some and wrongly diagnosed in others. The former do not receive the treatment they need, while the latter may suffer adverse effects of treatment while not being treated for their true illness.³

Spirometry, along with symptoms and exacerbation frequency, also determines changes in therapy in these patients. Thirdly, it offers an objective measure of disease progression and can help assess the prognosis.³

A recent study estimated that only 5% of COPD patients were diagnosed as such.⁸ According to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines (2024), spirometry is used to determine the severity of COPD both initially and during the course of treatment. COPD staging is based on the FEV1 after bronchodilator use, from stage I (mild COPD, FEV1/FVC ratio of 0.7 with the FEV1 >80% of predicted value), to stage IV (FEV1 below 30% of predicted value).³

However, spirometry alone cannot reveal the complexity of COPD, especially since the FEV1 does not always correlate with symptoms or health status. Experts opine, “Incorporating additional pulmonary function tests (PFTs) in the everyday clinical evaluation of COPD patients may prove essential in tailoring medical management to meet the needs of such a heterogeneous patient population.”⁴

Types of pulmonary function tests used in COPD monitoring

PFTs are of three basic types: spirometry, lung volumes, and lung diffusion capacity for carbon monoxide (DLCO).³

Spirometry measures the airflow and lung capacity. Three measurements are used: forced vital capacity (FVC), post-bronchodilator forced expiratory volume in one second (FEV1), and FEV1/FVC ratio. The FVC refers to the total volume of air blown out as fast as possible after the deepest possible inhalation and reflects the amount of air held in the lungs.³

The FEV1 is the air blown out in the first second and reflects the ease of airflow. It decreases with narrowing or inflammation of the airways, as in COPD. The FEV1/FVC ratio shows whether airflow is disproportionately reduced relative to lung capacity and is characteristically low in COPD.

Plethysmography (the gold standard in COPD), helium dilution, and nitrogen washout are used to assess lung volumes. Plethysmography measures pressure-volume changes of the chest cavity, and therefore the lung, in a closed system, adding information on total lung capacity (TLC), residual volume (RV), and functional residual capacity (FRC) as well as airway resistance.^3,

The TLC refers to the air in the lung after inhaling as deeply as possible. After exhaling as much as possible, what is left is the RV, while the FRC refers to the air left after a normal exhalation.³

DLCO measures how easily CO diffuses from the lungs to the red blood cells, thus indicating ease of gas exchange.³

Interpreting pulmonary function test results: What do the numbers mean?

The FVC shows how much air the lungs can hold. The FEV1 measures how much air can be exhaled in one breath after inhaling as deeply as possible and mirrors airflow. A post-bronchodilator FEV1/FVC ratio below 0.70 is typically diagnostic of COPD. ³

In particular, a concave flow-volume spirometric curve betokens small airway obstruction before symptoms set in.

The TLC, and later the RV, are elevated in COPD due to emphysematous hyperinflation of the lungs. The DLCO is proportional to the severity of COPD due to the loss of lung alveoli, the units of gas diffusion. With the DLCO below 55%, oxygen may be required during exercise, as determined by exercise oximetry.³

Alternative tests like slow vital capacity (SVC) and forced expiratory volume in six seconds (FEV6) have been suggested for those who cannot perform the forced breathing maneuvers required for conventional spirometry.³

How often should COPD patients undergo pulmonary function tests?

Depending on disease severity, COPD patients should be followed up at intervals of two weeks (recently discharged from hospital, severe frequent COPD exacerbations) to six months (for mild stable COPD).

The GOLD guidelines recommend doing PFTs once a year, at least, to pick up signs of rapid progression. These include FEV1 and timed walking test for FRC. The earlier COPD and its exacerbations are diagnosed, the faster treatment can be begun.

“The potential importance of detecting early fixed airway obstruction for prevention of lung cancer and non-respiratory end-organ disease also needs to be better highlighted in public health campaigns.”⁷

Improving COPD outcomes through regular pulmonary function testing

Pulmonary function testing can help identify patients with COPD. As many patients testify, “It was a relief to know there was a reason for the chest infections and shortness of breath and that there was treatment available, even if it wasn’t a cure.” (Meredith Lores, Australia).⁹

The PFT results help to determine the best type of therapy to start on, and help monitor response to therapy. Regular PFTs can pick up early signs of deterioration and exacerbations, thus preventing major desaturation episodes or picking out the right time for additional interventions such as oxygen inhalation. Older guidelines did recommend repeating PFTs for this purpose, but this has been revised in the latest GOLD guidelines.

References

1. Wood, K. L., (2024). Overview of Tests of Pulmonary Function. MSD Manual. Available at https://www.msdmanuals.com/professional/pulmonary-disorders/tests-of-pulmonary-function-pft/overview-of-tests-of-pulmonary-function. Accessed on October 10, 2024.
2. Pulmonary Function Tests (2024). Available at https://www.lung.org/lung-health-diseases/lung-procedures-and-tests/lung-function-tests. Accessed on October 10, 2024.
3. Bailey, K. L. (2014). The Importance of the Assessment of Pulmonary Function in COPD. Medicine Clinics of North America. doi: https://doi.org/10.1016%2Fj.mcna.2012.04.011. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3998207/. Accessed on October 10, 2024.
4. Kakavas, S., Kotsiou, O. S., Perlikos, F., (2021). Pulmonary function testing in COPD: looking beyond the curtain of FEV1. NPJ Primary Care Respiratory Medicine. doi: https://doi.org/10.1038/s41533-021-00236-w. Available at https://pubmed.ncbi.nlm.nih.gov/33963190/. Accessed on October 10, 2024.
5. Criee, C. P., Sorichter, S., Smith, H. J., et al. (2011). Body plethysmography e Its principles and clinical use. Respiratory Medicine. doi: http://dx.doi.org/10.1016/j.rmed.2011.02.006. Available at https://www.resmedjournal.com/article/S0954-6111(11)00055-2/pdf. Accessed on October 15, 2024.
6. Chronic Obstructive Pulmonary Disease (COPD). BMJ Best Practice. Available at https://bestpractice.bmj.com/topics/en-us/7/monitoring#referencePop1. Accessed on October 15, 2024.
7. Johns, D. P., Walters, J. A. E., and Walters, E. H. (2014). Diagnosis and early detection of COPD using spirometry. Journal of Thoracic Disease. doi: https://doi.org/10.3978%2Fj.issn.2072-1439.2014.08.18. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4255165/. Accessed on October 16, 2024.
8. Park, M., Lee, T. S., Lee, J., et al. (2023). Most patients with COPD are unaware of their health threats and are not diagnosed: a national-level study using pulmonary function test. Scientific Reports. doi: https://doi.org/10.1038/s41598-023-32485-9. Available at https://pubmed.ncbi.nlm.nih.gov/37041257/. Accessed on October 16, 2024.
9. Meredith’s story: COPD (2024). Available at https://lungfoundation.com.au/stories/merediths-story/. Accessed on October 16, 2024.

Further Reading

• All Chronic Obstructive Pulmonary Disease Content
• What is Chronic Obstructive Pulmonary Disease?
• Chronic Obstructive Pulmonary Disease Causes
• Chronic Obstructive Pulmonary Disease Process
• Chronic Obstructive Pulmonary Disease Management