What is emphysema?
Emphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema the lung tissues necessary to support the physical shape and function of the lung are damaged. It is included in a group of diseases called chronic obstructive pulmonary disease or COPD (pulmonary refers to the lungs). Emphysema is called an obstructive lung disease because the destruction of lung tissue around smaller airways, called bronchioles, makes these airways unable to hold their shape properly when you exhale. This makes them inefficient at transferring oxygen into the blood, and in taking carbon dioxide out of the blood.
The NHS says around 900,000 people in the UK have been diagnosed with COPD and about two million people have the condition but have not been diagnosed. COPD causes 25,000 deaths a year.
Emphysema changes the anatomy of the lung in several important ways.
Normally, the lungs are very spongy and elastic. When a breath is taken, the chest wall expands, expanding the sponge. Just as a squeezed sponge will draw water into it when released, suction draws air into the lungs when the chest wall expands. Air is brought though the trachea (windpipe) and bronchi (the main air tubes going to right and left lungs). These tubes divide into smaller and smaller tubes, finally ending in alveoli. Alveoli, the tiniest structures in the lung, are very small air sacs that are arranged like a bunch of grapes. The alveoli are at the ends of the smallest tubes called bronchioles. The alveoli and the bronchioles are very important structures for the lungs to function properly. It is these structures that are damaged by emphysema.
A sponge works to pick up water because all the tiny little holes expand at once after being squeezed. If the holes were larger, the sponge would not pick up as much water. This is because a larger hole cannot expand enough by itself to equal the action of multiple smaller ones. Thinking of the lungs as a sponge in this way, it becomes easier to see how emphysema acts to cause impaired lung function. Lungs require an elastic quality, so that they can expand and contract well. Also, as with the holes of the sponge, the lungs need many alveoli (hundreds of millions, in fact) to draw enough air into them. The fewer and the bigger the alveoli, the less effectively they perform.
Cigarette smoking is by far the biggest culprit for people developing emphysema, and it is also the most preventable cause. Other risk factors include a deficiency of an enzyme called alpha-1-antitrypsin, air pollution, airway reactivity, heredity, male sex and age.
- The importance of cigarette smoking as a risk factor for developing emphysema cannot be overemphasised. Cigarette smoke contributes to this disease process in two ways. It destroys lung tissue, which is the cause of the obstruction, and it causes inflammation and irritation of airways that can cause the disease to get worse.
- Destruction of lung tissue occurs in several ways. First, cigarette smoke directly affects the cells in the airway responsible for clearing mucus and other secretions. Occasional smoking temporarily disrupts the sweeping action of tiny hairs called cilia that line the airways. Continued smoking leads to damage to the cilia that prevents them working properly to clear secretions. Long-term exposure to cigarette smoke causes the cilia to disappear completely from the cells lining the air passages. Without the constant sweeping motion of the cilia, mucus secretions cannot be cleared from the lower respiratory tract. Furthermore, smoke causes mucus secretion to be increased at the same time that the ability to clear the secretions is decreased. The resulting mucus build-up can provide bacteria with a rich source of food and lead to infection.
- The immune cells in the lung, whose job it is to prevent and fight infection, are also affected by cigarette smoke. They cannot fight bacteria as effectively or clear the lungs of the many particles (such as tar) that cigarette smoke contains. In these ways cigarette smoke sets the stage for frequent lung infections. Although these infections may not even be serious enough to require medical care, the inflammation caused by the immune system constantly attacking bacteria or tar leads to the release of destructive enzymes from the immune cells.
Over time, enzymes released during this persistent inflammation leads to the loss of proteins responsible for keeping the lungs elastic. In addition, the tissue separating the air cells (alveoli) from one another is also destroyed. Over years of chronic exposure to cigarette smoke, the decreased elasticity and destruction of alveoli leads to the slow destruction of lung function. And if that isn’t enough of a reason to stop, remember that cigarette smoke is also carcinogenic, meaning that it leads to lung cancer. In the UK, cigarette smoking causes 90% of lung cancer in men and 83% in women, according to Cancer Research UK. It is also responsible for most cancers of the larynx, oral cavity and pharynx, oesophagus and bladder.
- Alpha-1-antitrypsin is a substance that fights a destructive enzyme in the lungs called trypsin. Trypsin is a digestive enzyme, most often found in the digestive tract, where it is used to help the body digest food. It is also released by immune cells in their attempt to destroy bacteria and other material. People with alpha-1- antitrypsin deficiency cannot fight the destructive effects of trypsin once it is released in the lung. The destruction of tissue by trypsin produces similar effects to those seen with cigarette smoking. The lung tissue is slowly destroyed, thus decreasing the ability of the lungs to perform appropriately.
- Air pollution acts in a similar manner to cigarette smoke. The pollutants cause inflammation in the airways, leading to the destruction of lung tissue.
- Abnormal airway reactivity, such as bronchial asthma, has been shown to be a risk factor for the development of emphysema.
- Men are more likely to develop emphysema than women, although the number of women developing COPD is increasing.
- Older age is a risk factor for emphysema. Lung function normally declines with age. Therefore, it stands to reason that the older the person, the more likely it is that they will have enough lung tissue destruction to produce emphysema.