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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. The result is that the small airways collapse early during exspiration, leading to an obstructive form of lung disease. Features are: shortness of breath on exertion (and later in rest), cyanosis and an expanded chest. Often clubbing of the fingers is observed, a feature of longstanding hypoxia.
Emphysema patients are occasionally referred to as "blue bloaters", a slightly derogatory term that combines their cyanosis with another feature, namely the tensing of the upper airways to create a positive end-expiratory pressure (PEEP) and keep the small airways open.
Diagnosis
Diagnosis is by spirometry (lung function testing), including diffusion testing. Other investigations might include X-rays, bronchoscopy (when other lung disease is suspected, including malignancy), blood tests and arterial blood gas sampling.
Pathophysiology
The scientific definition of emphysema says 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. Instead, they remain in the lungs, clogging up the oxygen exchange mechanism and severely restricting the airflow. This damage causes the symptoms of emphysema.
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 clincally 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 primarily 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. Needless to say, these poor 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 technilogically 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.
Given the complex nature of the composition of tobacco smoke, the poor correlation between existing animal models used in research and humans, complex nature of the proteolytic/antiproteolytic properties in the body, various other substances that may be involved (e.g., oxidants), together with differences in potential routes to disease development between different individuals, it may prove to be simpler and more logical to convince smokers to cut down rather than attempting to deduce the pathogenesis of this man-made disease of little biological scientific relevance, as opposed to continuing to pour money into more scientifically inane research that hasn't progressed significantly in the past fifty years into this perfectly preventable disease. This of course aside from the fact that even if the pathogenesis were deduced, to be able to treat the underlying cause with whatever barely effective yet expensive IV injection or inhalant treatment is concocted in the future, may not prove to be practical or worthwhile.
Associations
Emphysema is commonly associated with 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 also develop cirrhosis of the liver, where the accumulated A1AT leads to a fibrotic reaction.
Prognosis and treatment
Emphysema is an irreversible degenerative condition. It is treated by supporting the breathing with bronchodilators and steroid medication, and supplemental oxygen is often required. The only 'cure' for emphysema is a lung transplant, although not many patients are strong enough physically to survive the surgery. The combination of oxygen deprivation and the side-effects of the medications used to treat emphysema cause damage to the kidneys, heart and other bodily organs.
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