Chronic obstructive pulmonary disease, or COPD, is a group of chronic lung diseases that makes breathing difficult. It is a progressive condition, meaning that it gets worse over time. COPD has a range of effects on the lungs that reduce their ability to take in oxygen and distribute it to organs in the bloodstream.

The diseases that makeup COPD include emphysema, chronic bronchitis, and refractory asthma. Each of these has different effects on the lungs and respiratory system.

According to the American Lung Association, it is the third leading cause of death from disease in the United States. COPD typically causes coughing that produces large amounts of mucus, shortness of breath, and other symptoms.

In this article, we explain the pathophysiology of COPD. Pathophysiology describes the changes a disease or condition causes in a person’s physical function as it develops.

We also explore the symptoms these changes cause and how to manage them.

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A person with COPD may have airways that have become clogged.

COPD reduces lung function by damaging the airways and air sacs in the lungs.

When a person with healthy lungs inhales air, it travels down their windpipe and into the airways of the lungs, known as bronchial tubes.

Inside the lungs, the bronchial tubes branch into thousands of smaller, thinner channels called bronchioles.

At the end of these tubes are bunches of tiny round air sacs called alveoli. There are more than 300 million alveoli in the lungs. Larger lungs have more alveoli.

Capillaries are small blood vessels that surround the walls of the air sacs. Once air makes its way to the air sacs, oxygen passes through the walls of the air sac into the capillaries that transport blood.

At the same time, carbon dioxide moves from the capillaries into the air sacs. These events happen at the same time, and scientists refer to this as gas exchange.

Healthy air sacs are elastic and very stretchy. As a person breathes in, the air sacs fill up with air like a balloon. As they breathe out, the air sacs deflate due to the air moving out. The body uses energy to blow the air sacs up but does not use any energy to empty them as they return to their original size.

People with COPD have less air flowing in and out of the airways. Several physical problems in the lungs can contribute to this:

  • the airways and air sacs have lost their stretchiness
  • the walls between the air sacs are partially or completely damaged
  • the walls of the airways become inflamed and thickened
  • the airways produce more mucus, causing them to clog

COPD incorporates several conditions: Chronic bronchitis, emphysema, refractory asthma, or a combination of all three.

Each leads to a different problem with the airways and air sacs.

Here, learn more about the anatomy of the lungs.

Chronic bronchitis

Chronic bronchitis results from an increase in swelling and mucus production in the breathing tubes or airways. This results in the lining of the airways being constantly irritated and inflamed.

Tiny hairs, or cilia, line the tubes of the airways. These help move mucus along the airways so that coughing can remove it from the lungs. When prolonged damaged causes the cilia to lose function or disappear altogether, the lungs cannot move mucus as easily.

The extra swelling and mucus make the inside of the breathing tubes smaller than usual, making breathing more difficult.

Read more on bronchitis.


Emphysema causes damage to the air sacs in the lungs and the walls between them. This causes the sacs to lose their stretchiness and trap air instead.

It becomes increasingly difficult to expel all air from the lungs, and they no longer empty efficiently. This leads to the presence of more air than usual. This phenomenon is called air trapping and causes the lungs to hyperinflate.

When there is extra air in the lungs, breathing takes additional effort, which contributes to shortness of breath.

Damage means that the air sacs that typically support the airways and breathing process are unable to open fully during inhalation or exhalation.

The damage can also destroy the walls of the air sacs, resulting in larger, less efficient air sacs instead of the smaller ones. This reduces gas exchange within the lungs.

People with COPD have difficulty emptying the lungs, which can lead to shortness of breath or extreme fatigue.

Find out more about emphysema.

Refractory asthma

This is a severe type of asthma that does not resolve in response to asthma medications.

Asthma presents in attacks of symptoms that cause the airways to become tighter and more swollen. People with refractory asthma cannot return the airways to their natural state using medications.

Here, learn more about severe asthma.

COPD can develop due to many different factors, but the most common cause is cigarette smoke.

Other common risks include environmental and genetic factors. Inhaling any pollutant can cause COPD, whether it is cigarette smoke, industrial chemicals, cooking fumes, or heavy air pollution.

Genetics may also play a role in the development of COPD, even for those who have not had exposure to pollutants. Experts suspect that genetics also contribute to some people being more sensitive to the effects of cigarette smoke and pollutants than others.

People often mistake shortness of breath or an on-going cough as symptoms of another condition. For this reason, many people do not know they have COPD until it becomes more advanced.

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A long term cough is one symptom of COPD.

It is essential to note the warning signs of COPD and consult a doctor if they appear. Common symptoms include:

  • a long term cough
  • shortness of breath while performing daily activities
  • frequent respiratory infections
  • a blue tint in the lips or fingernail beds
  • fatigue
  • producing more mucus than usual
  • wheezing
  • a feeling of tightness in the chest

People who have mild COPD symptoms may not notice them at first, or they may not cause significant disruption to daily life. These people may be able to manage early symptoms with lifestyle changes to help make breathing easier.

The severity of COPD depends on the extent of lung damage. If people who smoke continue to do so, lung damage will progress at a much faster rate. The effects of COPD on other systems and organs also provide vital clues about how severe the disease may be.

Severe COPD can cause additional symptoms, such as:

  • swelling in the ankles
  • feet, or legs
  • weight loss
  • reduced muscle strength and endurance

It can lead to hypoxia, which means that not enough oxygen is reaching vital organs, such as the brain and heart. This can lead to problems with thought processes, confusion, and high blood pressure in the blood vessels around the lungs.

Doctors track the decline of lung function in COPD by measuring the amount of air that a person can forcibly exhale in one second (FEV1). This amount decreases as COPD gets worse.

Acute exacerbation of COPD is a flare-up or episode in which a person’s breathing becomes worse than usual, and they struggle to maintain their oxygen levels.

These episodes occur due to sudden blockage in the airways, which makes COPD symptoms worse.

An infection in the airways or elsewhere the body usually triggers an exacerbation. Exacerbations can be an emergency and may cause further lung damage, which makes COPD progress more quickly.

It is important for those affected to seek treatment as needed. People can avoid exacerbations by knowing the warning signs and taking action immediately.

Symptoms of a flare-up include:

  • increased amounts of mucus that may be thicker and darker in color than usual
  • extreme shortness of breath
  • fever
  • confusion or intense fatigue
  • excessive coughing or wheezing

Certain medications and exposure to pollutants or irritants can also cause exacerbations. People who smoke tend to have more exacerbations than those who do not.

Read more on COPD exacerbations here.