What Is COPD? — A Balloon That Won't Empty, and the Breath That Leaves in the First Second

"It's Probably Just Getting Older"

If you walk up about two flights of stairs, you might run out of breath and have to stop. You might cough and have phlegm in your throat every morning. If you have smoked for a long time or still smoke, it is easy to brush it off, thinking, "It's probably just getting older." Shortness of breath, coughing, and phlegm are common symptoms of the disease this article will cover (PMID 32250871). However, symptoms alone cannot reliably weed out whether this disease is present, which is why diagnosis is often delayed until the disease has progressed quite a bit (PMID 25478197).

Chronic obstructive pulmonary disease is a condition where the air passages inside the lungs are damaged for a long time, leading to a state where air does not escape well when you exhale. It is also called COPD by taking the English acronym.

This article is written based on research from around the world, but for how common this disease is in Korea and how many people live without knowing it, we look at data from the Korea National Health and Nutrition Examination Survey conducted by the Korean government from 2007 to 2019. The order is what this disease changes in the lungs, what calls this disease, what the test of blowing air measures, and what changes when you quit smoking.

A Disease Where the Exhaling Path Narrows and Air Sac Walls Collapse

When you breathe out, air travels a long way from deep inside the lungs all the way out of the mouth. An airway is the tube through which air moves back and forth from the nose and mouth to deep inside the lungs.

The bronchi are tubes where the airway coming down from the throat splits into both lungs and gets narrower and narrower. At the end of these branches hang air sacs. Alveoli are tiny air sacs hanging like bunches of grapes at the ends of the airways, where oxygen and carbon dioxide are exchanged with blood.

Chronic obstructive pulmonary disease changes two places along this path. The small airways narrow and become obstructed, and the very last branches of the airways and the alveoli collapse (PMID 24692133). International guidelines define this disease as a persistent and often worsening condition of blocked airflow due to abnormalities in the airways, alveoli, or both (PMID 40633975). The main site where the disease progresses is the smallest airways (PMID 40675548).

Airflow limitation is a state where the flow of air escaping during exhalation slows down because the airway has narrowed or become blocked. The airflow limitation in this disease is not fully reversible (PMID 24692133). Airways also narrow in asthma, but the narrowing in asthma is usually reversible, which distinguishes it from this disease. How much the narrowing in asthma reverses is picked up by another part of this series, the one covering asthma.

Depending on the pattern of damage, it is sometimes divided into two sides. One side is the airway. Inflammation is a response where the body mobilizes immune cells, swells the area, and reacts against irritants such as damage, infection, or substances entering from outside the body. In the airways of this disease, inflammation and structural changes occur together (PMID 33506971). Chronic bronchitis is a condition where inflammation in the bronchi lasts for a long time, and cough and phlegm repeat for several months every year. It arises because cells in the airway produce excessive mucus and push it out, and this mucus clogs the inside of the small airways, worsening the airflow limitation (PMID 23204254).

The other side is the alveoli. Emphysema is a condition where the walls of the alveoli break down, and the tiny air sacs lose their shape. In emphysema, blood vessels in the walls between alveoli are also reported to decrease (PMID 24692133). The changes of narrowed airways and collapsed alveoli appear mixed in different proportions for each person (PMID 24692133). If chronic bronchitis and emphysema are placed at opposite ends, most people lie somewhere between them (PMID 23204254).

Comparing this damage to a balloon looks like this. When you let go of the opening of an inflated balloon, the rubber shrinks and pushes the air out. A balloon with a narrowed opening lets air out slowly, and a balloon whose rubber has stretched and lost strength has a weak pushing force. Narrowing of the airways corresponds to the opening side, and collapsing alveolar walls corresponds to the rubber side. In fact, the airflow limitation in this disease arises because resistance in the small airways increases and the lungs become prone to sagging from emphysema, making it take a long time for the lungs to empty (PMID 15325838).

Consequently, the next breath sometimes begins before the previous breath is fully exhaled. In this disease, it is common for air to remain trapped inside the lungs while they are overly inflated, which links to the blocked flow during exhalation and increases the workload on the breathing-in muscles (PMID 24692133).

Chronic obstructive pulmonary disease is a condition where the exhaling path narrows and alveolar walls collapse, making it hard for air to escape properly like a balloon that cannot empty completely, and that narrowing does not fully reverse.

What Causes This Disease?

It has been more than 50 years since cigarette smoke was pointed out as the largest risk factor for this disease (PMID 36075255). An analysis combining population surveys from 65 countries also showed that the disease was much more common in people who smoked, along with men, low body weight, smoke from burning fuels like wood or straw, and dust and smoke in the workplace (PMID 35279265). Continued smoking is strongly linked to the disease progressing, the structure of the lungs being damaged, and the clinical course worsening (PMID 33506971).

Smoking does not finish the explanation. Roughly half of the cases of this disease worldwide are estimated to be due to non-smoking factors, and those factors vary by region (PMID 35427530). A 2009 review noted that about 3 billion people are exposed to smoke from fuels like wood, charcoal, and straw—outnumbering the 1.01 billion people who smoke—making this smoke possibly the largest risk factor globally (PMID 19716966).

An observational study is a study where researchers do not tamper with people's lives, leave them as they originally live, and watch what happens afterward. The relationships of this disease with air pollution, dust and gas in the workplace, secondhand smoke, and repeated respiratory infections in childhood come from studies like these (PMID 35427530; PMID 22845669). A correlation means they appear together, and it does not carry proof that one thing is the cause.

Korean data point in the same direction. In the Korea National Health and Nutrition Examination Survey from 2007 to 2018, about 89% of men with this disease had a history of smoking, but 86% of women with this disease had never smoked (PMID 38092558). This disease in people who have never smoked generally features milder symptoms and airflow limitation with little to no emphysema, but sudden worsening of shortness of breath can still be frequent (PMID 35427530).

The lungs while the body is growing are also on the path. The path to this disease can be divided into two. The path where lung function grows up to a normal height when young and then declines faster than usual afterward, and the path where it fails to grow to a normal height from the start. On the latter path, one can reach this disease even though the rate of decline after becoming an adult is normal or only slightly fast (PMID 33506971).

The curves drawn by lung function mostly settle before puberty. People who fell into the bottom three curves accounted for 19% of the total, but made up 55% of those whose airways were blocked at age 45. There were also exceptions, showing separate curves that went down quickly in connection with smoking after adulthood and with obesity. This is the result of measuring 865 local residents ten times from age 9 to 45 (PMID 38499347).

Childhood factors associated with which curve one goes to included childhood asthma, bronchitis, and pneumonia, parental asthma, and maternal smoking, and personal smoking and asthma persisting into adulthood magnified the influence of these factors. This is data from 2,438 people followed from age 7 to 53 in Tasmania, Australia. The authors considered these curves to be associated with early exposures that can be changed, and that factors after adulthood magnified their impact. They thus hypothesized that reducing maternal smoking and increasing vaccinations—especially if people whose parents smoked or who had low lung function in childhood smoke themselves—could reduce the risk (PMID 29628376). In a study following people born in 1946 in England, the loss of lung function left by lower airway infections and crowded homes in infancy was seen in people with a history of smoking, and was not clear in those without a smoking history (PMID 28530117). This means the starting point in childhood is not chosen by a person, and depending on what is added on top of it, adult lung function can vary.

Lung damage left behind after having tuberculosis is also linked to this disease, and Korean surveys showed the same (PMID 33506971; PMID 37038644). Tuberculosis is covered in another part of this series, the one dealing with tuberculosis. Cases where a person is born severely lacking a protein called alpha-1 antitrypsin are also a risk factor, but they are rare (PMID 17978157).

Cigarette smoke is cited as the strongest risk factor, but links with fuel smoke, workplace dust, and air pollution, as well as the starting point while the lungs are growing, are also on the path to this disease.

Pulmonary Function Testing — The Volume and Speed of Exhalation

This disease is checked by blowing air. A pulmonary function test has you inhale as deeply as possible and then exhale as hard as you can, measuring the volume and speed of the outgoing air. It is safe and straightforward, and when guided by a trained tester, most people produce reliable and repeatable results (PMID 25478197). Among the numbers that come out here, three are related to this disease.

FEV1 is the volume of air that comes out during the first 1 second when you exhale as hard as you can after inhaling as deeply as possible. It is used to grade the severity of this disease (PMID 25478197) and has been the most widely used number for tracking the course of the disease (PMID 24692133).

FVC is the total volume of air that comes out when you exhale as hard as you can to the very end in the same manner. If this value increases after using a medication that widens the airways, that is also considered evidence that the airway has widened (PMID 24692133).

The FEV1/FVC ratio is the share of the total volume exhaled to the very end that came out in the first 1 second. The diagnostic criteria for this disease hinge on this ratio, and its severity hinges on FEV1 (PMID 25478197).

One medication steps into the test. A bronchodilator is a drug that relaxes the muscles surrounding the bronchi to widen narrowed airways. It is measured first without the medication, and if blockage is seen, it is measured again after inhaling this drug (PMID 39638416).

The Global Initiative for Chronic Obstructive Lung Disease (GOLD) report recommends suspecting this disease in people with long-lasting respiratory symptoms or exposure to risk factors, and sets an FEV1/FVC ratio below 0.7 after using a bronchodilator as the condition to confirm the diagnosis. The same document notes that results coming out near the cutoff line must be re-measured to make an accurate diagnosis (PMID 39638416). A diagnosis is not determined by a single number. A review summarizes that diagnosis requires symptoms, a blockage that persists even after using medication, and a history of significant exposure to risk factors together (PMID 30838057).

Where to draw the line is not settled as a single standard. One review suggests that rather than using a fixed 0.7, using the lower limit of the normal range determined by values from baseline healthy people is better for avoiding overdiagnosing or missing diagnoses (PMID 36794439). Depending on which line is used, the 2019 prevalence estimates for people aged 30 to 79 worldwide split between 10.3% and 7.6% (PMID 35279265).

This test does not catch all changes. Small airway disease is already widespread before it shows up in ordinary numbers (PMID 25478197). A 2022 international panel report criticized that this test is sluggish to detect early changes, underused, frequently misread, and fails to predict symptoms (PMID 36075255).

A pulmonary function test measures the breath coming out in the first 1 second and the breath coming out to the very end, looking at the blockage through their ratio. The diagnostic line is drawn by guidelines, and where to place that line is still debated.

While Blowing as Hard as You Can

In the examination room, you bite into a tube, inhale as deeply as possible, and exhale all the way out with maximum force on cue. The machine measures the volume and speed of that breath as it leaves. The volume that comes out in the first second is FEV1, and the volume that comes out all the way to the end is FVC.

Returning to the balloon, a balloon with a narrowed opening and a tired rubber wall lets out very little wind in a rush at the start. In the actual lungs as well, changes that block the airways and changes where the air sacs collapse form the basis of airflow limitation, and that blockage is recorded as a lowered FEV1/FVC ratio (PMID 24692133). The reason the first second matters is that through a blocked pathway, breath pours out much less from the very beginning.

When the test is over, graphs come out along with the numbers. Spirometry shows the volume and speed of the breath both as numbers and as graphs that draw the shape of the breath going out (PMID 34752275). One review recommends reading the result not from the numbers alone but together with two graphs: one that plots exhaled volume over time, and one that plots speed against exhaled volume (PMID 35130676). On the first graph, the height read at the 1-second mark is FEV1, and the height where the curve stops rising and levels off is FVC. The second graph plots the speed of the air during a full breath in and out against the volume of air in the lungs, so when the breath in is drawn too, it forms a loop (PMID 35130676). In this disease, a descending side of this graph that is scooped inward is counted as a characteristic feature (PMID 31511572).

Still, the scooped shape alone is not used to pick out this disease. In a study that followed 852 people aged 45 in Tasmania, Australia, for 8 years, the degree of scooping was associated with later developing wheeze and breathlessness on exertion, but the post-bronchodilator FEV1/FVC ratio was more accurate at picking out who would newly develop this disease (PMID 41532089). Other shapes on the report, and how the verdict can split depending on where the line for normal is drawn, are traced in "Reading a Spirometry Report — One Point Among Your Peers, Two Graphs Drawn by a Breath".

Next, you inhale a bronchodilator and blow again. The narrowing in this disease does not reverse completely, so we check whether the ratio remains low even after using the medication (PMID 21079536). The direction set by the GOLD Science Committee in GOLD 2025 is to use the pre-bronchodilator value to help rule out this disease, and the post-bronchodilator value to help confirm the diagnosis (PMID 39638416).

This scene does not end with a single number. A ratio that stays low even after using medication is merely one of the conditions needed for diagnosis, and symptoms and a history of exposure must be present alongside it (PMID 30838057). Results that come out close to the cutoff line are retested (PMID 39638416), very early changes may not yet show up in these numbers (PMID 25478197), and where to draw the line differs across guidelines and review articles (PMID 36794439). The symptoms of this disease resemble those of asthma or heart disease, making it easy to misdiagnose, and the pulmonary function test is ranked as the best method to separate the three (PMID 21079536). Gathering the symptoms, exposure history, and distinction from other conditions to read what an individual's numbers mean is the doctor's task.

People Who Live Without Knowing It

This disease is not uncommon in Korea either. Among the 15,613 people who underwent a pulmonary function test in the 2015–2019 National Health and Nutrition Examination Survey, 12.9% met the diagnostic criteria for this disease, and among participants aged 70 and older, nearly 1 in 3 did (PMID 37038644). As we saw earlier, such proportions vary depending on where you draw the line for diagnosis. In the 2010–2012 survey, 13.7% of 8,969 people aged 40 and older met the criteria (PMID 26019762).

The global picture is similar. In regional population surveys across the Americas, Europe, Australia, and Asia, 10% to 12% of adults aged 40 and older showed persistent airflow limitation on pulmonary function tests, but only 20% to 30% of them had been diagnosed. This means that around 70% of this disease worldwide may remain undiagnosed (PMID 29979608).

There is also an error in the opposite direction. The same review cited studies showing that 30% to 60% of people already diagnosed with this disease did not actually have it (PMID 29979608). When researchers re-examined people recorded as having this disease in primary care after using a bronchodilator, 50% to 75% had airflow limitation. The authors considered that some of these cases might have involved reversible narrowing like asthma or other conditions being treated as this disease, and added that the data were inconsistent and of ordinary quality (PMID 37130651). In both directions, not performing a pulmonary function test is cited as the strongest predictor of misdiagnosis (PMID 30838057).

The subsequent outcomes of people who lived without knowing their condition were also tracked. In a general population survey in Copenhagen, Denmark, among 32,518 high-risk individuals aged 40 and older who had a smoking history of 10 pack-years or more and no history of asthma, 3,699 (11%) met the criteria for this disease, and 78% of them were undiagnosed (PMID 28389225). Following them for a median of 6.1 years, people who had symptoms but were undiagnosed experienced more sudden worsening of shortness of breath, pneumonia, respiratory-cause deaths, and all-cause deaths than those without this disease. Even those without symptoms experienced more sudden worsening of shortness of breath, pneumonia, and all-cause deaths, with no clear difference only in respiratory-cause deaths (PMID 28389225). Diagnosing early makes it possible to address risk factors like smoking sooner (PMID 25478197).

Many people live with this disease undiagnosed, whereas conversely, some people who do not have it are treated for it, with the failure to perform a pulmonary function test cited as the biggest reason in both directions.

A Sudden Turn for the Worse — Exacerbation

A few days into a cold, you find yourself much more short of breath than usual, and your phlegm increases. A COPD exacerbation is when shortness of breath, coughing, and phlegm suddenly worsen beyond your usual day-to-day fluctuations, requiring treatment to be added or changed. By some definitions, the criteria are worsened shortness of breath and an increase in the amount or pus-like appearance of phlegm (PMID 33893708).

Most are triggered by a viral or bacterial infection in the airways (PMID 24507843), and air pollution or the weather are also listed as triggers (PMID 27028990). Colds, the flu, and pneumonia themselves are covered in another installment of this series, the one on colds, the flu, and pneumonia.

Exacerbations leave a large, lasting impact on your health status and also adversely affect lung function (PMID 26937187). One review summarizes that exacerbations erode lung function, increase the risk of subsequent exacerbations and heart and blood vessel events, and can lead to early death (PMID 38664329). A significant number of exacerbations go unrecognized and untreated, and such untreated exacerbations have a worse course than treated ones (PMID 26937187).

In severe exacerbations, respiratory failure—where the body fails to adequately supply oxygen and remove carbon dioxide—can occur, making hospitalization necessary (PMID 27028990; PMID 15351196), and mechanical breathing support treatments are sometimes used (PMID 28298398). Shortness of breath that makes it difficult to finish a sentence, bluish lips, confusion, or breathlessness that does not subside with your usual medications are warning signs that medical guidelines list as reasons to seek care promptly. A physician determines what caused the worsening and how severe it is by combining a physical examination with pulse oximetry, sputum tests, chest X-rays, and blood tests (PMID 27028990).

Preventing exacerbations is one of the core goals of treating this disease, and non-drug methods are used alongside various medications (PMID 24507843). One review on exacerbations listed influenza and pneumococcal vaccinations as recommended measures (PMID 29540496).

An exacerbation is a time when breathing suddenly worsens due to triggers like infection, and because it can erode lung function even after it passes, treatment for this disease focuses heavily on reducing exacerbations.

What Changes When You Quit Smoking

The question "My lungs are already damaged, so what difference does it make if I quit now?" is common. The airflow limitation of this disease cannot be completely reversed, but the slope at which lung function declines changes.

There is a randomized trial that followed 5,887 smokers aged 35 to 60 with mild airflow limitation across 10 hospitals in the US and Canada for 5 years. The group assigned to a smoking cessation program had a smaller decrease in FEV1 than the group that received no intervention, with most of that difference occurring in the first year and being greatest for those who quit all the way through (PMID 7966841). A report summarizing the results of this trial noted that for those who quit at a mild stage, lung function improved slightly at first and thereafter the rate of annual decline became close to normal (PMID 8637302).

A 2015 review gathering studies from early or mild stages also concludes that the earlier one quits, the greater the effect on lung function (PMID 25363328). A 2004 review noted that other than quitting smoking, there is no method or drug that alters the rate of lung function decline and the progression of the disease (PMID 15351196). This means that while you cannot replace the balloon with a new one, you can slow down the rate at which the force of pushing air out weakens.

Survival and exacerbations change as well. When participants of the same trial were followed for up to 14.5 years, the group assigned to the smoking cessation program had fewer total deaths than the group that received usual care (8.83 vs. 10.38 per 1,000 person-years). This was true even though only 21.7% of people in the program group had actually quit smoking at the 5-year mark, and the authors noted that this result applies to people with blocked airways (PMID 15710956). Reviews also conclude that quitting smoking increases survival for people with this disease (PMID 20854053) and is key to preventing future exacerbations (PMID 29540496). According to a review summarizing the 2026 GOLD report, this report lists smoking cessation, along with vaccinations and other measures, as a core method that changes the course of the disease (PMID 41806208). The direction these evidences point to is the future rather than the past years.

There are helpful ways to go about quitting. About 70% of people who smoke want to quit, but it takes an average of about six attempts to stay quit long-term (PMID 35133411). Behavioral support such as counseling and medications to aid smoking cessation each increased smoking cessation, and mild or minor side effects were reported with some medications (PMID 38997788). The 6-month cessation rate for the group that used both together was 15.2%, which was higher than the 8.6% of the group that received brief advice or usual care (PMID 35133411).

E-cigarettes entered the market without evidence on their risks, long-term safety, or usefulness for quitting smoking. While clinical trials where they were used alongside counseling show results suggesting they may help reduce conventional cigarettes (though nicotine dependence did not decrease), analyses pooling observational studies have not linked them to smoking cessation, and although lung function did not change in most trials, there are reports that bodily markers suggesting lung disease increased; thus, the conclusion of a 2022 review is that large, long-term studies are needed to understand the risks of long-term use. The same review notes that medical staff should discourage use by non-smokers and adolescents, and should also discourage smoking them concurrently without reducing or quitting conventional cigarettes (PMID 35041473).

The narrowing of this disease cannot be completely reversed, but quitting smoking slows the rate at which lung function declines, and the earlier you quit, the greater that difference is.

Medicines That Widen the Airway, and Practice Moving Again

Inhalers are medications breathed in through the mouth so they reach the airway directly. Most drug treatment for this disease takes this form, with the bronchodilators seen earlier at its center. Inhaled bronchodilators have been cited as the most effective way to ease the effort of breathing and reduce breathlessness (PMID 19650945).

According to a review summarizing the 2026 GOLD report, the report places airway-widening drugs at the starting point, describes adding drugs like anti-inflammatory inhalers for some individuals whose symptoms persist or whose flare-ups continue, and notes that limits remain regarding the effectiveness, cost, and generalization of new treatments (PMID 41806208). Learning how to use an inhaler and receiving steady check-ups afterward are also cited as part of the treatment (PMID 21079536). Although a 2015 review noted that evidence has accumulated showing long-acting bronchodilators can slow the rate of lung function decline even in mild stages, the same review noted that many unanswered questions remain regarding the best treatment for mild stages (PMID 25363328).

When breathing is difficult, people move less, and moving less leads to muscle loss and a further drop in exercise capacity, creating a vicious cycle (PMID 31223602). Medications relieve breathlessness, but they are less effective against this bodily weakening (PMID 32342470).

Pulmonary rehabilitation is a program that combines exercise training, education, and self-management skills to help short-of-breath individuals move their bodies again. It pairs gradually increasing exercise training tailored to each person with education and self-management methods, and is handled by a multidisciplinary team of medical staff. Pulmonary rehabilitation has been associated with improvements in exercise capacity, quality of life, and breathlessness (PMID 38503466).

Across 17 studies of pulmonary rehabilitation started within 3 weeks of discharge after hospitalization for a flare-up, readmissions decreased and the distance walked in 6 minutes increased by an average of 57m, but no clear difference was seen in mortality, and no adverse events caused by rehabilitation were reported (PMID 38350731). The 2023 guidelines from the American Thoracic Society (ATS) strongly recommend pulmonary rehabilitation both during stable periods of this disease and after hospitalization for a flare-up, while noting that this treatment is underutilized (PMID 37581410).

Medications widen narrowed airways to ease breathlessness, while pulmonary rehabilitation addresses the bodily weakening that drugs cannot easily reach.

Where to Look Further

Methods to catch changes earlier than a standard pulmonary function test exist, but bringing them into clinical practice is still an ongoing process (PMID 40675548).

People with a mild stage of this disease mostly die from cancer and heart and blood vessel diseases, and as the disease gets heavier, deaths from respiratory causes increase (PMID 20854053). The pathway where the heart and lungs are connected by blood can be found in "How the Heart Moves Blood — Four Chambers, Four Doors, Two Loops". The benefits and burdens of lung cancer and lung cancer screening are picked up by another part of this series, "Lung Cancer and Low-Dose CT Screening — Reading a Small Spot in the Picture Over Time".

The principles of how breath goes in and out and the gas exchange happening in the alveoli begin in another part of this series, "How Do We Breathe? — An Upside-Down Tree, and the Leaves Where Air Meets Blood". The narrowing that reverses is covered by "What Is Asthma? — An Airway That Tightens Too Easily, and the Inflammation That Keeps It Swollen", the infections that serve as triggers for flare-ups by "How Do a Cold, the Flu, and Pneumonia Differ? — An Infection That Stays in the Entryway, and One That Reaches the Inner Room", and tuberculosis and the lung damage left behind by it by "What Is Tuberculosis? — The Sleeping Ember, and the Fire That Takes Months to Put Out".

Why the same test result is read differently depending on who it came from is covered by "What a Test Actually Tells You — An Introduction to Sensitivity, Specificity, and Pretest Probability". How to translate the phrase that a risk factor is "several times" higher into a story about real people is found in "If the Risk Was Cut in Half, How Many Fewer People Got Sick? — Relative and Absolute Risk".

Unlike this disease, where breath cannot fully leave, the disease in which the lungs stiffen and expand less — and cases where emphysema and fibrosis come together — continues in "What Is Pulmonary Fibrosis? — Thickening Paper Windows, Scars on the Wall Oxygen Crosses".

Source Papers

• "Goals of COPD treatment: Focus on symptoms and exacerbations." (2020) — PMID 32250871 — Common symptoms are shortness of breath, cough, and phlegm; flare-ups are mainly triggered by respiratory infections and environmental factors.
• "Diagnosis and early detection of COPD using spirometry." (2014) — PMID 25478197 — The diagnostic criterion is FEV1/FVC, severity is FEV1, most results are reproducible by a trained tester, it is largely underdiagnosed in primary care, symptoms are not a reliable indicator, early diagnosis is valuable because it allows risk factors like smoking to be addressed promptly, and small airway disease often exists widely before it shows up in indicators.
• "Chronic obstructive pulmonary disease." (2014) — PMID 24692133 — Airflow limitation is not fully reversible, it involves a varied mix of obstructive changes in the small airways and destructive changes in the respiratory bronchioles and alveoli, there is a decrease in blood vessels in the walls between alveoli in emphysema, blockage is recorded as a decrease in FEV1/FVC, overinflation is linked to expiratory flow limitation, FEV1 is most widely used for monitoring progress, and an increase in FVC is also evidence of bronchodilation.
• "Towards early detection and disease interception of COPD across the lifespan." (2025) — PMID 40633975 — COPD definition (persistent and often progressive airflow limitation due to airway and/or alveolar abnormalities), and lung function trajectories starting early in life are also an important pathway.
• "Small Airways Disease in Patients With COPD." (2026) — PMID 40675548 — Small airways are the main site of disease progression and airflow limitation, and sensitive techniques contribute to early detection, but a gap remains in introducing them to clinical practice.
• "Optimizing chronic obstructive pulmonary disease management in primary care." (2011) — PMID 21079536 — Symptoms are similar to asthma and heart disease, creating a risk of misdiagnosis; pulmonary function tests are the best way to separate the three; asthma is fully reversible while COPD is not; and inhaler use education and regular check-ups are important.
• "Natural history and mechanisms of COPD." (2021) — PMID 33506971 — Smoking is the strongest trigger; the two pathways are a rapid decline after a normal peak versus a low peak (with a normal or slightly fast decline); continued smoking is strongly linked to progression, structural damage, and a poor prognosis; and other factors include tuberculosis sequelae and a combination of structural and inflammatory changes.
• "Towards the elimination of chronic obstructive pulmonary disease: a Lancet Commission." (2022) — PMID 36075255 — Smoking has been identified as a major risk factor for over 50 years, and post-bronchodilator pulmonary function tests are insensitive to early changes, underused, frequently misread, and fail to predict symptoms.
• "Global, regional, and national prevalence of, and risk factors for, COPD in 2019." (2022) — PMID 35279265 — Covering 260 sites in 65 countries, the 2019 prevalence among those aged 30 to 79 was 10.3% by the GOLD definition and 7.6% by the LLN definition, with male sex, smoking, low body weight, biomass, and occupational dust/smoke identified as risk factors.
• "Chronic obstructive pulmonary disease in never-smokers." (2022) — PMID 35427530 — Roughly half of global COPD is due to non-smoking factors (varying by region: air pollution, occupation, uncontrolled asthma, secondhand smoke, infections, and low socioeconomic status), impaired lung growth in childhood is linked to increased risk, and non-smoker COPD features milder symptoms and airflow limitation with less emphysema, though flare-ups can be frequent.
• "Chronic obstructive pulmonary disease in non-smokers." (2009) — PMID 19716966 — 25% to 45% of COPD cases are in non-smokers, with about 3 billion people exposed to biomass smoke versus 1.01 billion smokers, making biomass potentially the world's largest risk factor.
• "Non-smoking-related chronic obstructive pulmonary disease: a neglected entity?" (2012) — PMID 22845669 — Candidate risk factors for non-smoker COPD include genetics, longstanding asthma, outdoor air pollution, secondhand smoke, biomass, occupational exposure, repeated respiratory infections in childhood, and tuberculosis.
• "Sex differences in COPD characteristics: KNHANES 2007-2018." (2024) — PMID 38092558 — About 89% of men with COPD in Korea have a smoking history, while 86% of women are non-smokers.
• "Distinct trajectories of lung function from childhood to mid-adulthood." (2024) — PMID 38499347 — In 865 individuals measured 10 times between ages 9 and 45, trajectories were mostly established before puberty, the three lowest FEV1 trajectories (19%) accounted for 55% of airflow obstruction at age 45, and accelerated decline trajectories were linked to smoking and obesity.
• "Childhood predictors of lung function trajectories and future COPD risk." (2018) — PMID 29628376 — In 2,438 people in Tasmania followed from ages 7 to 53 across six trajectories, early-life predictors included asthma, bronchitis, pneumonia, allergic rhinitis, eczema, parental asthma, and maternal smoking, with personal smoking and adult asthma increasing the effect, and three trajectories accounting for 75% of the COPD burden through modifiable early exposures.
• "Combined Impact of Smoking and Early-Life Exposures on Adult Lung Function Trajectories." (2017) — PMID 28530117 — In the 1946 British birth cohort, FEV1 loss from lower respiratory infections in infancy and overcrowded housing was seen only in those with a smoking history and was not apparent in non-smokers.
• "Recent Prevalence of and Factors Associated With COPD: KNHANES 2015-2019." (2023) — PMID 37038644 — Among 15,613 individuals, the prevalence was 12.9%, reaching nearly one-third in those aged 70 and older, and a history of tuberculosis was associated with COPD.
• "Prevalence of chronic obstructive lung disease in Korea using data from the fifth Korea national health and nutrition examination survey." (2015) — PMID 26019762 — Among 8,969 people aged 40 and older, the 2010–2012 prevalence was 13.7% (23.3% of men, 6.5% of women), rising each year, and was associated with male sex, older age, heavier smoking, lower education, and lower body mass index.
• "Definition, epidemiology and natural history of COPD." (2007) — PMID 17978157 — Smoking is the main risk factor, severe alpha-1 antitrypsin deficiency is rare, continued exposure leads to a faster decline, and smoking prevention and cessation are the most important measures.
• "GOLD Science Committee recommendations for the use of pre- and post-bronchodilator spirometry for the diagnosis of COPD." (2025) — PMID 39638416 — Suspect in individuals with symptoms and exposures, confirm with a post-bronchodilator FEV1/FVC <0.7, use pre-bronchodilator values to rule out and post-bronchodilator values to confirm, and remeasure results near the threshold.
• "The Diagnosis and Treatment of COPD and Its Comorbidities." (2023) — PMID 36794439 — The LLN is better than a fixed 0.7 cutoff at avoiding overdiagnosing or missing diagnoses (German review).
• "Underdiagnosis and Overdiagnosis of COPD." (2018) — PMID 29979608 — Persistent airflow limitation is present in 10% to 12% of people aged 40 and older, only 20% to 30% of them are diagnosed, about 70% may be undiagnosed, and 30% to 60% of those diagnosed by doctors do not actually have COPD.
• "Undiagnosed and 'overdiagnosed' COPD using postbronchodilator spirometry in primary healthcare settings." (2023) — PMID 37130651 — Only 50% to 75% of COPD cases in primary care records show airflow limitation, some may be treatments for asthma or other diseases, and the data are heterogeneous and of moderate quality.
• "Under- and over-diagnosis of COPD: a global perspective." (2019) — PMID 30838057 — Failing to perform a pulmonary function test is the strongest predictor of a wrong COPD diagnosis, and diagnosis requires a combination of symptoms, blockage that remains even after a bronchodilator, and a history of risk factor exposure.
• "Prognosis of asymptomatic and symptomatic, undiagnosed COPD in the general population in Denmark." (2017) — PMID 28389225 — Among 32,518 high-risk individuals, 11% met the criteria, of whom 78% were undiagnosed; over a median of 6.1 years, symptomatic undiagnosed cases had increased exacerbations, pneumonia, respiratory mortality, and all-cause mortality, while asymptomatic undiagnosed cases had increased exacerbations and pneumonia (with respiratory mortality not significant).
• "Chronic obstructive pulmonary disease exacerbation fundamentals." (2021) — PMID 33893708 — Definition of exacerbation (an acute worsening of respiratory symptoms requiring additional treatment), based on criteria of shortness of breath and phlegm volume/purulence, involving infections and pollutants.
• "Exacerbations of COPD." (2016) — PMID 26937187 — Acute flare-ups exceeding normal daily fluctuations have large and long-lasting effects on health status and adverse effects on lung function, and many go unreported and untreated, leading to a worse prognosis.
• "Acute COPD exacerbations." (2014) — PMID 24507843 — Most flare-ups are triggered by viral or bacterial infections, preventing flare-ups is a core goal of treatment, and methods include drug and non-drug prevention.
• "Acute exacerbation of COPD." (2016) — PMID 27028990 — Triggers are infections and the environment (air pollution and weather), and evaluation involves oxygen saturation, sputum cultures, chest X-rays, and blood inflammation markers, with severe cases requiring hospitalization, oxygen, or non-invasive ventilation.
• "Implications of Cardiopulmonary Risk for the Management of COPD." (2024) — PMID 38664329 — Flare-ups can wear down lung function and increase the risk of subsequent flare-ups and cardiovascular events, leading to premature death.
• "Management of COPD exacerbations: an ERS/ATS guideline." (2017) — PMID 28298398 — Recommends treatments for flare-ups, such as strongly recommending non-invasive mechanical ventilation for acute respiratory failure.
• "Exacerbations of COPD." (2018) — PMID 29540496 — Severe flare-ups are linked to poor survival, smoking cessation is central to preventing flare-ups, and influenza and pneumococcal vaccinations are recommended.
• "COPD: early diagnosis and treatment to slow disease progression." (2015) — PMID 25363328 — Reviewing research on early and mild COPD, smoking cessation reduces the rate of lung function decline at all stages with greater effect the earlier it is done, data suggest long-acting bronchodilators can slow the decline, and there are many unresolved questions regarding the best treatment for mild COPD.
• "Management of severe COPD." (2004) — PMID 15351196 — Other than smoking cessation, there are no methods or drugs that alter the rate of lung function decline and disease progression.
• "Mortality in COPD: causes, risk factors, and prevention." (2010) — PMID 20854053 — Mortality in mild COPD is mainly from cancer and cardiovascular disease, non-malignant respiratory mortality increases with severity, and smoking cessation increases survival.
• "GOLD 2026: Transforming COPD Management." (2026) — PMID 41806208 — Identifies smoking cessation, pulmonary rehabilitation, and vaccination as core strategies that alter the disease course, introduces dual bronchodilation as the first step, places inhaled steroids in selected patients, and notes limitations in efficacy, cost, and generalizability.
• "E-Cigarettes and Cardiopulmonary Health: Review for Clinicians." (2022) — PMID 35041473 — Marketed without evidence, trials combined with counseling suggest reduced smoking while observational meta-analyses show no link to smoking cessation, nicotine dependence does not decrease, lung function mostly shows no change but lung disease biomarkers increase, long-term studies are needed, and clinicians should discourage use by non-smokers and youth as well as dual use that does not reduce smoking.
• "The 2007 GOLD Guidelines: a comprehensive care framework." (2009) — PMID 19650945 — Inhaled bronchodilators are the most effective way to reduce the work of breathing and relieve shortness of breath.
• "Sarcopenia Associated with COPD." (2019) — PMID 31223602 — A vicious cycle of decreased activity leading to decreased muscle mass and worsened exercise capacity.
• "Exercise and COPD." (2020) — PMID 32342470 — Drug therapy improves shortness of breath but has limited effectiveness against physical deconditioning, whereas rehabilitation improves shortness of breath, fatigue, and quality of life.
• "Review of the Evidence for Pulmonary Rehabilitation in COPD." (2024) — PMID 38503466 — A multidisciplinary program of individualization, progressive exercise training, education, and self-management, linked to improved exercise capacity, quality of life, and shortness of breath, though participation is low.
• "Do pulmonary rehabilitation programmes improve outcomes in patients with COPD posthospital discharge for exacerbation." (2024) — PMID 38350731 — Across 17 studies starting within 3 weeks of discharge, there was reduced readmission (OR 0.48), a 6-minute walk distance increase of +57m, no significant effect on mortality, and no intervention-related side effects.
• "Pulmonary Rehabilitation for Adults with Chronic Respiratory Disease: ATS Clinical Practice Guideline." (2023) — PMID 37581410 — Strongly recommends pulmonary rehabilitation for stable COPD and following hospitalization for a flare-up, though it is underused.
• "Chronic bronchitis and chronic obstructive pulmonary disease." (2013) — PMID 23204254 — Chronic bronchitis is caused by mucus hypersecretion and hyperproduction from goblet cells, which blocks the small airway lumen and worsens airflow limitation, with emphysema and chronic bronchitis forming the two ends of a spectrum and most cases lying in between.
• "Pathophysiology of airflow limitation in chronic obstructive pulmonary disease." (2004) — PMID 15325838 — Airflow limitation is the result of an increased time constant for the lungs to empty, caused by increased small airway resistance and increased compliance from emphysema destruction.
• "Effects of smoking intervention and the use of an inhaled anticholinergic bronchodilator on the rate of decline of FEV1. The Lung Health Study." (1994) — PMID 7966841 — In 5,887 smokers aged 35 to 60 with mild obstruction across 10 centers in the US and Canada over a 5-year randomized trial, the smoking cessation intervention group had a smaller FEV1 decline (mostly in the first year, with the maximum in continuous quitters), while bronchodilators had no effect on the long-term decline.
• "Early intervention in chronic obstructive pulmonary disease. A review of the Lung Health Study results." (1996) — PMID 8637302 — Quitting smoking in early COPD initially improves lung function, after which the annual rate of decline approaches normal.
• "The effects of a smoking cessation intervention on 14.5-year mortality: a randomized clinical trial." (2005) — PMID 15710956 — In the 14.5-year Lung Health Study, all-cause mortality in the smoking cessation intervention group versus the control group was 8.83 versus 10.38 per 1,000 person-years, with a 5-year cessation rate of 21.7% versus 5.4%, and the results applied only to people with airway obstruction.
• "Treatment of Tobacco Smoking: A Review." (2022) — PMID 35133411 — About 70% of smokers want to quit and make an average of about 6 attempts before achieving long-term cessation, behavioral counseling and medications are each effective and most effective when used together (6-month cessation rate of 15.2% versus 8.6%).
• "Effectiveness of smoking cessation interventions among adults: an overview of systematic reviews." (2024) — PMID 38997788 — Across 22 Cochrane systematic reviews, medication and behavioral interventions increased smoking cessation, with some drugs showing small and mild side effects.
• "Performance and Interpretation of Office Spirometry." (2021) — PMID 34752275 — Spirometry evaluates vital capacity and expiratory flow rates and provides both numeric data and a graphic depiction of airflow; characteristic patterns help identify lung disease and reversibility.
• "Use of flow volume curve to evaluate large airway obstruction." (2022) — PMID 35130676 — The flow-volume loop plots airflow against lung volume during maximal inspiration and expiration; characteristic loops in obstructive and restrictive disorders; spirometry should be interpreted with flow-volume and volume-time curves as well as values.
• "The Concavity of the Maximal Expiratory Flow-Volume Curve Reflects the Extent of Emphysema in Obstructive Lung Diseases." (2019) — PMID 31511572 — A concave maximal expiratory flow-volume curve is a spirometric feature of COPD; an index of concavity was associated with the extent of emphysema on CT.
• "Concavity of the maximal expiratory flow-volume curve, and incidence of COPD and respiratory symptoms: a population-based cohort study." (2026) — PMID 41532089 — Tasmanian cohort, 852 people at age 45 followed for 8 years; greater concavity linked to later wheeze and exertional dyspnoea; post-bronchodilator FEV1/FVC was more sensitive and specific for incident COPD.