Emphysema

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Emphysema

Emphysema is a chronic lung disease. It is often caused by exposure to toxic chemicals or long-term exposure to tobacco smoke.

Signs and symptoms

Emphysema is characterised by loss of elasticity of the lung tissue; destruction of structures supporting the alveoli; and destruction of capillaries feeding the alveoli. The result is that the small airways collapse during expiration, leading to an obstructive form of lung disease (air is trapped in the lungs in obstructive lung diseases). Symptoms are: shortness of breath on exertion--particularly when climbing stairs or inclines (and later at rest), hyperventilation and an expanded chest. As emphysema progresses, clubbing of the fingers may be observed, a feature of longstanding hypoxia.

Emphysema patients are sometimes referred to as "pink puffers". This is because emphysema sufferers may hyperventilate to maintain adequate blood oxygen levels. Hyperventilation explains why emphysema patients do not appear cyanotic as chronic bronchitis (another COPD disorder) sufferers often do; hence they are "pink" puffers (adequate oxygen levels in the blood) and not "blue" bloaters (cyanosis; inadequate oxygen in the blood).

Diagnosis

Diagnosis is by spirometry (lung function testing), including diffusion testing. Other investigations might include X-rays, high resolution spiral chest CT-scan, bronchoscopy (when other lung disease is suspected, including malignancy), blood tests, pulse oximetry and arterial blood gas sampling.

Pathophysiology

The scientific definition of emphysema is:

"Permanent destructive enlargement of the airspaces distal to the terminal bronchioles without obvious fibrosis".

Hence, the definite diagnosis is made by a pathologist. However, we can easily ascertain clinical diagnosis by history, clinical examination, chest radiography and lung function tests.

In normal breathing, air is drawn in through the bronchial passages and down into the increasingly fine network of tubing in the lungs called the alveoli, which are many thousands of tiny sacs surrounded by capillaries. These absorb the oxygen and transfer it into the blood. When toxins such as smoke are breathed into the lungs, the particles are trapped by the hairs and cannot be exhaled, leading to a localised inflammatory response. Chemicals released during the inflammatory response (trypsin, elastase, etc.) begin to break down the walls of alveoli (alveolar septum). This leads to fewer but larger alveoli, with a decreased surface area and a decreased ability to take up oxygen and lose carbon dioxide. The activity of another molecule called alpha 1-antitrypsin normally neutralizes the destructive action of one of these damaging molecules.

After a prolonged period, hyperventilation becomes inadequate to maintain high enough oxygen levels in the blood, and the body compensates by vasoconstricting appropriate vessels. This leads to pulmonary hypertension. This leads to enlargement and increased strain on the right side of the heart, which in turn leads to peripheral edema (swelling of the peripherals) as blood gets backed up in the systemic circulation, causing fluid to leave the circulatory system and accumulate in the tissues.

Emphysema occurs in a higher proportion in patient with decreased alpha 1-antitrypsin (A1AT) levels (alpha 1-antitrypsin deficiency, A1AD). In A1AD, inflammatory enzymes (such as elastase) are able to destroy the alveolar tissue (the elastin fibre, for example). Most A1AD patients do not develop clinically significant emphysema, but smoking and severely decreased A1AT levels (10-15%) can cause emphysema at a young age. In all, A1AD causes about 2% of all emphysema.

Pathogenesis

While A1AD provides some insight into the pathogenesis of the disease, hereditary A1AT deficiency only accounts for a small proportion of the disease. Studies for the better part of the past century have focused mainly upon the putative role of leukocyte elastase (also neutrophil elastase), a serine protease found in neutrophils, as a primary contributor to the connective tissue damage seen in the disease. This hypothesis, a result of the observation that NE is the primary substrate for A1AT, and A1AT is the primary inhibitor of NE, together have been known as the "protease-antiprotease" theory, implicating neutrophils as an important mediator of the disease.--- However, more recent studies have brought into light the possibility that one of the many other numerous proteases, especially matrix metalloproteases might be equally or more relevant than NE in the development of non-hereditary emphysema.

The better part of the past few decades of research into the pathogenesis of emphysema involved animal experiments where various proteases were instilled into the trachea of various species of animals. These animals developed connective tissue damage, which was taken as support for the protease-antiprotease theory. However, just because these substances can destroy connective tissue in the lung, as anyone would be able to predict, doesn't establish causality. More recent experiments have focused on more technologically advanced, but equally archaic theoretical approaches, using genetic manipulation. Perhaps the most interesting development with respect to our understanding of the disease involves the production of protease 'knock-out' animals, which are genetically deficient in one or more proteases, and assessing whether they would be less prone to the development of the disease. However, the exact pathogenesis of this disease is unlikely to be unravelled in great detail in the near future.

Associations

Emphysema is commonly associated with bronchitis and chronic bronchitis and as it is rather difficult to delineate "pure" cases of emphysema or chronic bronchitis they are classed together into chronic obstructive pulmonary disease(COPD).

See above for alpha 1-antitrypsin deficiency. Severe cases of A1AD may also develop cirrhosis of the liver, where the accumulated A1AT leads to a fibrotic reaction.

Prognosis and treatment

Emphysema is an irreversible degenerative condition. The most important measure that can be taken to slow the progression of emphysema is for the patient to stop smoking and avoid all exposure to cigarette smoke and lung irritants. Pulmonary rehabilitation can be very helpful to optimize the patients quality of life and teach the patient how to actively manage his or her care. It is treated by supporting the breathing with anticholinergics, bronchodilators and (inhaled or oral) steroid medication, and supplemental oxygen as required. Treating patient's other conditions including gastric reflux and allergies may also help the patient's lung function. Supplemental oxygen used as prescribed (20+ hours/day) is the only non-surgical treatment which has been shown to prolong life in emphysema patients. Other medications are being researched. There are lightweight portable oxygen systems which allow patients increasing mobility. Patients fly, cruise, and work while using supplemental oxygen.

Lung volume reduction surgery (LVRS) can improve the quality of life for carefully selected patients. It can be done by several different methods, some of which are minimally invasive. The only known 'cure' for emphysema is a lung transplant, although not many patients are strong enough physically to survive the surgery. The combination of patient's age, oxygen deprivation and the side-effects of the medications used to treat emphysema cause damage to the kidneys, heart and other bodily organs. Transplants also require the patient to take an anti-rejection drug regimen which suppresses immunities and creates new medical issues.

A study published by the European Respiritory Journal suggests that retinoic acid derived from vitamin A can reverse the effects of emphysema in mice by returning elasticity to the alveoli. While vitamin A consumption is not known to be an effective treatment or prevention for the disease, there is a clear possibility for a future cure.

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Pulmonology