COPD

TL;DR. Chronic obstructive pulmonary disease is the slow destruction of the lung by inhaled particles, most often tobacco smoke, over decades. Two things happen at once. The small airways become chronically inflamed, thickened, and clogged with mucus, and the walls between the alveoli are digested away, so the lung loses both its surface area for gas exchange and the elastic recoil that normally holds the small airways open. The result is air trapping: patients can get air in and cannot get it out, so the lungs inflate and the chest works harder for less oxygen. Unlike asthma, it does not reverse. It is the fourth leading cause of death worldwide, and stopping smoking is the only intervention that slows the decline.

Key takeaways

• COPD killed about 3.5 million people in 2021, roughly 5 percent of all global deaths, making it the fourth leading cause of death, with over 200 million people affected.
• Smoking is the dominant cause in high-income countries, but roughly a quarter to a third of COPD worldwide occurs in never-smokers, driven by household air pollution from cooking with solid fuels, occupational dust, and childhood lung development.
• Emphysema destroys alveolar walls; chronic bronchitis clogs airways. Most patients have both.
• Stopping smoking is the only intervention proven to slow the rate of lung function decline. Every other treatment improves symptoms, exacerbations, or survival without changing the underlying trajectory.
• Pulmonary rehabilitation produces larger improvements in breathlessness and exercise capacity than any drug, and is chronically underused.
• Too much oxygen can kill people with COPD, which is why oxygen is prescribed to a target saturation range rather than given freely.

What it is

In short: Largely irreversible airflow obstruction from inhaled particles, diagnosed on a breathing test, and a smoker's daily cough is its early stage.

COPD is persistent, largely irreversible airflow limitation caused by an abnormal inflammatory response to inhaled particles. It is diagnosed by spirometry: a post-bronchodilator FEV1/FVC ratio below 0.70, meaning less than 70 percent of the air a person can exhale comes out in the first second.

Two overlapping processes:

Most patients have elements of both. Severity is graded by FEV1 as a percentage of predicted (GOLD stages 1 to 4), and modern classification also uses symptom burden and exacerbation history, because those predict outcomes better than FEV1 alone.

Don't be confused: "smoker's cough" is not a benign category, it is early COPD. A daily productive cough in a smoker is chronic bronchitis, and chronic bronchitis in a smoker is the beginning of a progressive disease. COPD is typically diagnosed a decade or more after it starts, once half of lung function is gone, because people attribute breathlessness to ageing or being unfit and reduce their activity to match. Spirometry in a symptomatic smoker over 40 is how this gets caught while quitting still helps most.

The history

In short: One study in 1977 produced the curve that still explains it: quitting returns the rate of decline to normal without recovering what was lost.

Emphysema was described anatomically by Giovanni Battista Morgagni in the eighteenth century and illustrated by René Laennec, who also invented the stethoscope, in the early nineteenth.

The disease's modern epidemiology is essentially the history of manufactured cigarettes. Cigarette production industrialised from the 1880s, consumption rose through both world wars, and lung disease followed with a lag of two to four decades. The causal link was established in the 1950s by Doll and Hill in the UK and by Wynder and Graham in the US, and codified by the 1964 US Surgeon General's report.

Two other threads matter:

The Fletcher and Peto study (1977) followed British working men for eight years and produced the curve that still shapes how COPD is explained: lung function declines with age in everyone from about 25, susceptible smokers decline two to three times faster, and stopping smoking returns the rate of decline to normal without recovering what was lost. That curve is the argument for quitting at any age and the argument for finding the disease early.

Alpha-1 antitrypsin deficiency, identified in 1963, gave the mechanistic explanation. Alpha-1 antitrypsin is a protein made by the liver that neutralises neutrophil elastase, an enzyme that digests elastin. People who inherit a deficiency have unopposed elastase activity and develop emphysema early, often in their thirties and forties, and much worse if they smoke. This established the protease-antiprotease imbalance model of emphysema, which turned out to explain smoking-related disease as well: smoke both recruits neutrophils and inactivates antiprotease defences.

What actually goes wrong

In short: Enzymes digest the lung's elastic scaffolding, so air goes in and cannot come out, and the trapped air is what causes the breathlessness.

Inhaled particles cause chronic inflammation. Smoke activates airway epithelial cells and macrophages, recruiting neutrophils, macrophages, and CD8 T cells. These release proteases (neutrophil elastase, matrix metalloproteinases) that digest the elastin and collagen scaffolding of the alveolar walls.

Elastic recoil is lost. A normal lung is a stretched elastic bag: it empties passively because it recoils. Emphysema destroys that elasticity, so exhalation becomes an active, effortful process.

Small airways collapse on expiration. The alveolar walls also act as guy ropes holding the small airways open. Destroy them and the airways collapse during exhalation, trapping air behind them.

Hyperinflation follows. Each breath in adds air that cannot fully come out. The lungs and chest inflate, the diaphragm is pushed down and flattened, and a flattened diaphragm is mechanically inefficient. This is why patients with severe COPD sit leaning forward with arms braced: it lets accessory muscles help. It is also why dynamic hyperinflation during exercise causes breathlessness out of proportion to oxygen levels, and why bronchodilators help even when they change FEV1 very little, by reducing trapped volume.

Gas exchange fails. Destroyed alveoli mean less surface area. Ventilation and blood flow become mismatched. Late in the disease, carbon dioxide accumulates because ventilation cannot be increased enough.

Systemic consequences. COPD is not confined to the lungs: it is associated with muscle wasting, weight loss, osteoporosis, depression, anaemia, and cardiovascular disease, partly through shared risk factors, partly through systemic inflammation, and partly through the deconditioning spiral described below.

The deconditioning spiral is central to why rehabilitation works. Breathlessness leads to avoiding exertion, avoidance leads to muscle deconditioning, deconditioned muscles demand more ventilation for the same task, which causes more breathlessness at lower workloads. Breaking that loop with supervised exercise produces improvements no drug matches.

What it does to the body

In short: A shrinking life punctuated by exacerbations, each of which accelerates the decline and carries a real risk of death.

Symptoms: chronic productive cough, breathlessness on exertion that progresses over years to breathlessness at rest, wheeze, chest tightness, fatigue, and weight loss in advanced disease.

Exacerbations are acute worsenings, usually triggered by viral or bacterial infection or by air pollution. They matter more than any single measurement: each severe exacerbation is associated with accelerated lung function decline, and the risk of death after a hospitalised exacerbation is substantial. Frequent exacerbators are a distinct phenotype and are treated more aggressively.

Advanced disease brings cor pulmonale (right heart failure caused by high pressure in the pulmonary circulation, producing leg swelling and raised neck veins), respiratory failure with low oxygen and high carbon dioxide, profound exercise limitation, and dependence on others.

Breathlessness in advanced COPD is often as severe as in advanced cancer, and it is treated far less well, partly because the trajectory is a long decline with sharp dips rather than a predictable terminal phase, which makes clinicians reluctant to introduce palliative care.

Is it deadly?

Yes. COPD is the fourth leading cause of death worldwide, killing roughly 3.5 million people in 2021, about 5 percent of all deaths.

• Prognosis is best predicted by composite indices (such as BODE: body mass index, obstruction, dyspnoea, exercise capacity) rather than FEV1 alone.
• Hospitalised exacerbations carry in-hospital mortality of several percent and one-year mortality that can approach a quarter in severe disease.
• Continued smoking roughly doubles the rate of decline compared with quitting.
• Long-term oxygen therapy in patients with chronic severe hypoxaemia is one of the few treatments shown to extend life, based on trials from the early 1980s, and only in that specific group.

Is it contagious?

No. COPD cannot be transmitted from person to person.

Two related points. The infections that trigger exacerbations are contagious: respiratory viruses and bacteria such as Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis. And secondhand smoke causes COPD in people who never smoked, which is transmission of the cause rather than the disease. In much of the world, household air pollution from cooking fires exposes whole families, especially women and young children, which is why COPD in never-smoking women is common in South Asia and sub-Saharan Africa.

Who gets it

In short: Smoking dominates where cigarettes are common, and a quarter to a third of cases worldwide occur in people who never smoked.

Smoking is the dominant cause where cigarettes are common: roughly 20 to 40 percent of long-term smokers develop COPD, and the variation in susceptibility is genetic and developmental. Pipe, cigar, waterpipe, and cannabis smoking all contribute.

Never-smoker COPD accounts for roughly a quarter to a third of cases globally, and its causes are:

Sex. Historically male-dominated because of smoking patterns, now converging, and in some countries female prevalence exceeds male. Women appear to be more susceptible to a given smoking exposure.

Deprivation. COPD is one of the most socially patterned diseases, tracking smoking, occupation, housing, and air quality.

Treatment, and how it works

In short: Only stopping smoking changes the trajectory, and pulmonary rehabilitation improves breathlessness more than any inhaler does.

Stopping smoking

The only intervention that changes the disease's trajectory. It reduces the rate of FEV1 decline back toward normal, reduces exacerbations and mortality, and works at any age and any disease stage. Combining pharmacotherapy (varenicline, nicotine replacement, cytisine, bupropion) with behavioural support is far more effective than advice alone (Chapter 43). Nothing else in this section comes close.

Inhaled drugs

The eosinophil-guided use of inhaled steroids is a good example of moving from "everyone with the disease gets the drug" to "the subgroup in whom it works gets the drug," and it reduced a great deal of avoidable pneumonia.

Non-drug treatment, which is where the largest gains are

Pulmonary rehabilitation: a supervised programme of exercise training plus education, usually 6 to 12 weeks. It improves breathlessness, exercise capacity, and quality of life more than any inhaler, and reduces hospital admissions when delivered after an exacerbation. Uptake is poor almost everywhere, and referral rates are low, which is one of the clearest gaps between evidence and practice in respiratory medicine.

Vaccination: influenza, pneumococcal, COVID-19, and RSV vaccines reduce exacerbations and hospitalisation.

Long-term oxygen therapy: for patients with sustained resting hypoxaemia (oxygen saturation persistently at or below about 88 percent), used at least 15 hours a day, it improves survival. It does not help breathlessness in patients who are not hypoxaemic, and it is frequently requested and prescribed for that purpose without benefit.

Non-invasive ventilation during acute exacerbations with respiratory acidosis, which reduces the need for intubation and reduces mortality. It is one of the most effective acute treatments in respiratory medicine.

Nutrition and muscle: weight loss and muscle wasting predict mortality independently. Nutritional support and resistance training matter.

Surgical and bronchoscopic options for selected patients: lung volume reduction surgery or endobronchial valves, which remove or collapse the most destroyed regions so the remaining lung and the diaphragm work more efficiently. In carefully chosen patients with upper-lobe-predominant emphysema and low exercise capacity, surgery improved survival. Lung transplantation for a small number.

Palliative care: opioids at low dose genuinely relieve refractory breathlessness, are safe when titrated appropriately, and are underused because of unwarranted fear of respiratory depression. Handheld fans directed at the face reduce breathlessness through trigeminal nerve stimulation, cost nothing, and are supported by trial evidence.

Exacerbations

Short course of oral corticosteroids (5 days is as good as longer), antibiotics when sputum is purulent or the patient is severely unwell, increased bronchodilators, controlled oxygen, and non-invasive ventilation if carbon dioxide is rising with acidosis. Every exacerbation should prompt review of inhaler technique, smoking status, vaccination, and rehabilitation referral.

Controlled oxygen deserves emphasis. In patients with chronic carbon dioxide retention, giving high-flow oxygen can worsen hypercapnia (mainly by increasing ventilation-perfusion mismatch, and partly by reducing hypoxic respiratory drive) and cause a fall in consciousness and respiratory arrest. A randomised prehospital trial found significantly higher mortality with high-flow oxygen than with titrated oxygen. So oxygen is prescribed to a target saturation of roughly 88 to 92 percent in at-risk patients, and this is one of the few places in medicine where more of an apparently benign treatment kills people.

What treatment costs

• LAMA/LABA inhalers: dry mouth, urinary retention (LAMA), tremor and palpitations (LABA). Generally well tolerated.
• Inhaled corticosteroids in COPD: increased pneumonia risk, oral thrush, hoarseness, and at high doses the systemic effects listed in Chapter 44. This is why they are targeted rather than universal.
• Oral corticosteroids: repeated courses accumulate real harm (diabetes, osteoporosis, cataract, infection), which is why exacerbation courses are kept short.
• Oxygen: fire risk (smoking while on oxygen causes serious burns), dryness, restricted mobility, and the hypercapnia risk above.
• Roflumilast (a phosphodiesterase-4 inhibitor for severe chronic bronchitis with frequent exacerbations): diarrhoea, weight loss, nausea, and mood effects, which limit its use.
• Long-term azithromycin for frequent exacerbators: reduces exacerbations, at the cost of hearing loss in some, QT prolongation, and selection for macrolide resistance.

What the person can do

In short: Stop smoking, do rehabilitation, keep moving despite the breathlessness, and get vaccinated every year.

• Stop smoking. Everything else is secondary. Use the medications and support, since willpower alone succeeds a few percent of the time and combined treatment several times more often.
• Do pulmonary rehabilitation, and ask for referral if it is not offered. Then keep exercising after it ends, because the benefit fades without maintenance.
• Keep moving daily. Breathlessness on exertion is not damaging the lungs. Avoiding exertion is what makes it worse.
• Get vaccinated every year.
• Learn your inhaler technique, and have it checked. Many people with COPD have insufficient inspiratory flow for dry powder devices and should be using a different type.
• Have a written action plan with a rescue supply of steroids and antibiotics if you are a frequent exacerbator, and know when to use it and when to seek help.
• Improve indoor air: ventilation when cooking, avoid solid fuel indoors where alternatives exist, address damp.
• Get tested for alpha-1 antitrypsin deficiency if you are young at diagnosis, a never-smoker, or have a family history. It changes screening for relatives and, in some countries, treatment.
• Ask about breathlessness relief if it is severe, including a handheld fan, breathing techniques, and low-dose opioids where appropriate.

Living with it

In short: The decline is slow enough to be mistaken for ageing, and anxiety and depression worsen breathlessness through a loop worth treating.

COPD produces a distinctive kind of shrinking life: the person stops climbing stairs, then stops going out, then stops washing without a rest. Because the decline is slow, it is often rationalised as ageing until it is severe. Anxiety and depression are very common and worsen breathlessness through hyperventilation, creating another loop worth treating.

Carers often take on substantial physical work, and the household becomes organised around avoiding exertion. Advance care planning is particularly valuable in COPD because of the unpredictable trajectory: patients can survive several near-fatal exacerbations, which makes it hard to know when to have the conversation, so the answer is to have it early and revisit it.

Stigma is a specific problem here. COPD attracts a "self-inflicted" judgement that reduces both research funding and the sympathy patients receive, despite most smokers having started as children in an era of heavy marketing, and despite the large minority who never smoked at all.

What's next

• Biologics. Dupilumab, which targets the interleukin-4 receptor, reduced exacerbations in patients with COPD and elevated eosinophils in phase 3 trials, the first biologic to succeed in COPD after a long run of failures. This extends the eosinophil-guided logic further.
• Early detection and early intervention, on the argument that finding COPD at stage 1 in a smoker and getting them to quit is where nearly all the preventable disability lies.
• Regeneration: attempts to regrow alveolar tissue, currently early-stage and unproven.
• Clean cooking. For global mortality, replacing solid fuel stoves with clean cooking energy is the largest available intervention and is an energy and development problem rather than a medical one.
• Tobacco control, which remains the highest-yield policy: taxation, plain packaging, advertising bans, smoke-free environments, and cessation support all have strong evidence.

Sources and notes

Mortality and prevalence figures: WHO and Global Burden of Disease 2021 estimates (about 3.5 million deaths, roughly 5 percent of global deaths, fourth leading cause; approximately 213 million prevalent cases). GOLD (Global Initiative for Chronic Obstructive Lung Disease) reports for diagnosis, classification, and treatment. Fletcher and Peto: BMJ, 1977. Alpha-1 antitrypsin deficiency: Laurell and Eriksson, 1963. Long-term oxygen therapy survival benefit: Nocturnal Oxygen Therapy Trial (1980) and MRC trial (1981). Titrated versus high-flow oxygen in prehospital COPD: Austin et al., BMJ, 2010. Lung volume reduction surgery: National Emphysema Treatment Trial, NEJM, 2003. Pulmonary rehabilitation efficacy: Cochrane reviews. Short-course steroids: REDUCE trial, JAMA, 2013. Dupilumab in COPD: BOREAS and NOTUS trials, NEJM, 2023 and 2024. Never-smoker COPD proportion: varies by region and study, commonly cited as a quarter to a third globally.

Open questions. Why only a minority of smokers develop COPD is not fully explained. No treatment yet regenerates destroyed alveolar tissue. The optimal role of inhaled corticosteroids in COPD is still being refined.

Next: the immune system attacking things that were never a threat. 👉