Biomedical Engineering Reference
In-Depth Information
As the alveoli continue to break down, hyperventilation is unable to compensate for the
decreased surface area for gas exchange. Therefore, the blood oxygen level begins to
decrease and there is an overall constriction of the blood vessels, to account for this low-
ered blood oxygen level. If this continues, the entire cardiovascular system is placed under
high pressure, which places a large load on the heart muscle. To reverse this new load
from the high blood pressure, the heart muscle begins to thicken, which as we have
learned previously will lead to heart failure.
Emphysema is an irreversible condition. The only way to slow its progression is to have
the patient stop smoking and avoid all other lung irritants. It is possible for the patient to
breath bronchodilators to help ventilate the lungs more, but with significant destruction of
alveoli, there is little that physicians can do to reverse the effects of emphysema. Patients
are typically also placed on anti-inflammatory agents to decrease the risk of the inflamma-
tory system from further attacking the damaged alveoli.
9.7.2 Tuberculosis
Tuberculosis results from an infection of the lungs by a specific bacterium. The bacteria
may propagate in the conducting pathways as well as the alveoli. Like most infections, the
patient has a fever and general malaise, but during severe cases the lungs can begin to be
destroyed. As this occurs, the patient will begin to “cough up” blood. There are some simi-
larities between tuberculosis and any other respiratory infection. In general, the defense
mechanisms in the lungs become overwhelmed by the invading pathogens. When the
pathogens begin to grow within the lungs there is a large mucus buildup along the con-
ducting pathways. This tends to increase the resistance to air flow and may disrupt gas
exchange. If the pathogens destroy lung tissue, the surface area for gas exchange reduces
and blood may enter the lung space in extreme conditions.
It has been estimated that one-third of the world's populations (and approximately 5%
of the U.S. population) is currently infected with the bacteria that causes tuberculosis:
Mycobacterium tuberculosis. New tuberculosis infections are occurring at a rate of approxi-
mately one person every 3 seconds, but the death rate from tuberculosis is falling.
Therefore, the absolute number of people with tuberculosis is increasing. The disease is
mostly prominent in developing countries, but more people in developed countries are
contracting the tuberculosis bacteria because their immune systems are compromised by
drug use or other immunosuppressant diseases such as AIDS.
Tuberculosis infections manifest when M. tuberculosis reach the pulmonary alveoli,
where they take over and replicate within alveolar macrophages. It is common for lym-
phatic vessels and blood vessels to transport bacteria to other locations within the body,
but it is the lungs that are most susceptible to degradation from this bacteria. If the tuber-
culosis bacteria enter the bloodstream, patients have nearly a 100% fatality rate. In most
cases of tuberculosis, a granuloma is formed within the lung tissue. The granuloma houses
many immune cells, which release cytokines to help destroy the bacteria and call other
inflammatory cells to the infection site. However, a good portion of the M. tuberculosis can
remain dormant within the granuloma and cause an infection later on.
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