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 early during expiration, leading to
an obstructive form of lung disease (air is trapped in the lungs in obstructive lung diseases). Features 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. Hypeventilation 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 (cyanois; 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 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. Chemials released
during the inflammatory response (trypsin, elastase, etc.) are released and begin breaking down the walls of alveoli. This leads
to fewer but larger alveoli, with a decreased surface area and a decreased ability to take up oxygen and 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 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 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.
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. 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
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 '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 a anti-rejection drug regimen which suppresses immunities and creates new medical issues.
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