Emphysema is a degenerative lung disease in which the air sacs in the lungs become damaged and replaced with tough, fibrous ‘scar’ tissue. The vast majority of cases are caused by smoking, though other types of air pollution can be responsible for emphysema.
Emphysema is one of a set of respiratory conditions that includes bronchitis, asthma and bronchiectasis. Together they are responsible for chronic obstructive pulmonary disease (COPD). Emphysema is not reversible, though it will not get worse if the factor that is causing it is removed – if someone stops smoking, for example. Emphysema affects more males than females, and tends to occur after many years of smoking.
Symptoms of emphysema
As you might expect, emphysema develops gradually, with symptoms hardly noticeable at first. As the disease progresses the following symptoms appear:
Breathlessness, even after mild exertion
A permanent wheeze
Difficulty in breathing out: this is normally effortless as exhaling is a passive process. As emphysema worsens, breathing out takes an increasing amount of effort.
Mild emphysema may go undiagnosed for years. In the later stages, those affected become breathless most of the time, and the increased effort to breathe out results in the development of a flattened diaphragm and a barrel chest.
What causes emphysema?
Emphysema is caused by a process called lung fibrosis, which is a response to long-term tissue damage. The air sacs, or alveoli, are made from thin, delicate epithelial cells that are perfectly adapted for gas exchange. When damaged, these cells become replaced by thicker, tougher tissue.
Lung tissue has a natural elasticity so that when the air sacs have been inflated, they keep their shape and recoil to expel air. In emphysema, the cellular architecture is lost and the air sacs tend to collapse upon exhalation. The result is that air becomes trapped and air flow is obstructed.
Fibrosis of the lung tissue has several important consequences:
Gas exchange becomes much less efficient and less oxygen is loaded into the blood
Lung elasticity is lost
Exhalation requires effort by the muscles in the ribcage
A permanent wheeze can develop in severe cases due to air trying to get in and out through narrowed airways.
Emphysema: the mechanism of disease
The exact mechanism that leads to the development of emphysema is unclear but it seems to involve the action of enzymes. When a noxious gas such as cigarette smoke is inhaled, the airways become irritated and inflamed. Enzymes such as elastase and trypsin are released from white blood cells. Both of these enzymes break down proteins and when they come into contact with tissue, they damage the cells.
When this happens in the lungs, it causes the dividing walls (the septa) between different alveoli to rupture. Because the alveolar walls are normally under a certain amount of elastic tension, the loss of an alveolar wall creates a space in the lung tissue that is larger than the two original alveoli.
When several alveolar walls rupture, the result is a large open air space called a bulla (plural = bullae). The surface area of the damaged area of lung is drastically reduced, as is the air flow to the surrounding healthy alveoli.
To compensate for this loss of lung function, someone with emphysema must make more of an effort to breathe, hence the barrel chest and flattened diaphragm.
To combat the action of protein-digesting enzymes, the body makes an enzyme called alpha 1-antitrypsin (AAT). Some people have a genetic condition in which they cannot make AAT, and this can cause smokers to develop emphysema much earlier than normal.
Advanced emphysema usually leads to significantly lower amounts of dissolved oxygen in the blood. To compensate, breathing becomes deeper and more frequent. The arteries in the lung begin to constrict, making it harder for the heart to force blood through the pulmonary circulation. This leads to a condition called pulmonary hypertension, which results in an enlargement of the right side of the heart. This can eventually lead to heart failure.
A DLCO test (diffusion capacity of the lung for carbon dioxide) can be carried out to confirm emphysema and to provide a differential diagnosis against asthma or bronchitis. This measures the speed of diffusion of gases across the alveolar membrane. The value will be decreased in someone with emphysema, but normal in someone with bronchitis or asthma.
Other diagnostic tests that can be done include:
Oximetry: a measurement of the blood’s oxygen saturation, which should be over 90%.
Complete blood cell count, which will detect elevated number of red blood cells. The body responds to low oxygen levels by making extra red blood cells.
Assessing the severity of emphysema
Someone with the symptoms of emphysema is monitored to see how the disease is progressing over time. The severity of the underlying lung fibrosis is usually assessed by spirometry, which measures a person’s ability to exhale.
The peak flow (FEV1) value is compared to the expected value for someone of the same sex, age and size who does not have lung disease. The bigger the difference, the more advanced the emphysema.
X-rays can help to assess changes to lungs and surrounding structures, in particular the flattened diaphragm.
How is emphysema treated?
The most important action you can take if you have early symptoms of emphysema is to prevent further damage, which usually means stopping smoking. Exercise is hugely beneficial, and pulmonary rehabilitation programmes are available that combine exercises with education about proper breathing techniques and the correct use of medication.
Several medications are available that will relieve the symptoms of emphysema:
Bronchodilators: drugs that dilate the small airways (terminal bronchioles) and open up the airways. Short or long acting bronchodilators are available, usually delivered via inhaler or nebuliser
Steroids: these are also delivered via inhaler (or nebuliser). They minimise the inflammatory response in the airways. Their action is cumulative and it takes up to two weeks for them to have the desired effect
Alpha 1-antitrypsin can be given to patients who are unable to make their own
Antibiotics are given to eliminate any lung infections – indicated by coloured phlegm. Uninfected phlegm is clear
Oxygen. Breathing pure oxygen can help to relieve symptoms in people with very advanced and severe emphysema by raising blood oxygen levels.
Surgery for emphysema
As with chronic obstructive pulmonary disease, there is no cure for emphysema. Surgery is only considered in extreme and severe cases. It involves two main procedures:
Lung volume reduction surgery: this is done to remove the more damaged areas of lung tissue, allowing improved air flow to the healthier areas
Lung transplant: this is usually only considered in young patients. To prevent rejection, recipients will have to take immunosuppressant drugs for the rest of their lives.