Introduction

Chronic obstructive lung disease (COLD), also known as chronic obstructive pulmonary disease (COPD), is characterized by a limitation of the airflow in the lung, which develops over time and is not totally reversible.

COLD is associated with a set of breathing-related symptoms:

  • Chronic cough
  • Spitting or coughing mucus (phlegm)
  • Being out of breath when doing physical activities

The ability to exhale (breath out) gets worse over time.

Normal lungs and alveoli picture
The lungs are located in the chest cavity and are responsible for respiration. The alveoli are small sacs where oxygen is exchanged in the lungs.

The two major diseases in this category are emphysema and chronic bronchitis, both covered in this report. Asthmatic bronchitis, the other major COLD, is a condition that develops when a person with asthma is exposed to irritants, such as smoking, and develops a chronic cough. [For more information, see In-Depth Report #04, Asthma in adults.]

Because smoking is overwhelmingly the cause of both emphysema and chronic bronchitis, they often develop together and frequently require similar treatments and approaches. As chronic bronchitis often coincides with emphysema, it is frequently difficult for a physician to distinguish between the two.

Emphysema

Emphysema is a disease marked by destruction in the alveoli, grapelike clusters of air sacs at the end of the smallest airways (the bronchioles) in the lung. It generally takes the following course:

  • The walls of the alveoli become inflamed and damaged; over time they lose elasticity (the ability to stretch and shrink), and pockets of dead air (called bullae) form in the injured areas. These pockets are formed by damaged alveoli that merged, and have become irregular in shape.
  • The pockets interfere with the normal working of the lungs, making breathing out more difficult.
  • Inhalation (breathing in) is not impaired. Until the late stages of the disease, oxygen and carbon dioxide levels are normal.
Chronic Obstructive Lung Disease picture

Click the icon to see an image of emphysema.

Chronic Bronchitis

Chronic bronchitis is defined as coughing and overproduction of mucus for at least 3 months, during at least 2 consecutive years. In chronic bronchitis, the disease process is generally marked by the following characteristics:

  • Irritation of the bronchial tubes (from smoking, air pollution, etc.) causes mucus production. The mucus is cleared through coughing.
  • Constant coughing causes damage to the bronchial tubes. The tubes swell and thicken, leaving less room for air flow.
  • The reduced airflow into the lungs usually leads to lung damage that results in emphysema.
Chronic Obstructive Lung Disease picture

Click the icon to see an image depicting bronchitis.

The Lungs

The lungs are two spongy organs surrounded by a thin, moist membrane called the pleura. Each lung is composed of smooth, shiny lobes; the right lung has three lobes, and the left has two. About 90% of the lung is filled with air; only 10% is solid tissue.

When a person inhales, air travels through the following pathways into the lungs:

  • Air is carried from the trachea (the windpipe) into the lung through flexible airways called bronchi.
  • Like the branches of a tree, bronchi divide successively into over a million smaller airways called bronchioles.
  • The bronchioles lead to grape-like clusters of microscopic sacs called alveoli.
  • In each adult lung there are millions of these tiny alveoli. The thin membrane of the alveoli allows oxygen and carbon dioxide to pass to and from capillaries.
  • During deep inhalation, the elastic alveoli unfold and unwind to allow this passage to occur.

Capillaries, the smallest of our blood vessels, carry blood throughout the body. Red blood cells carry oxygen throughout the body, and return carbon dioxide to the lungs; white blood cells are the critical infection fighters in our body.

Chronic Obstructive Lung Disease picture

Click the icon to see an image of normal lungs.
Review Date: 4/28/2006
Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital