WONDERFUL INFORMATION
Compiler: C.K.Mohamed/Tellicherry

 EMBOLISM

 EPIDEMIOLOGY

Medical term, literally meaning 'a plug', that is used to indicate any condition in which matter passes along a blood vessel to another part of the body, where it blocks the vessel and thus cuts off the blood supply, or damages the tissues in some other way.

An embolus may be formed by blood clot, by tumour tissue, by fragments of infected material, by air. which has entered a blood vessel, or by liquids administered by injection.

Pulmonary embolism is a common cause of serious illness or even death. It occurs when a clot passes up the veins that return blood from the legs and lower trunk. The clot will pass readily through the right side of the heart, and enter the pulmonary artery, which carries blood to the lungs. Being far too big to traverse the pulmonary blood vessels, it will then become jammed.

A large embolism of this type will cause immediate death. More commonly, the patient feels a sudden pain in the chest, and collapses in a state of shock. Very small emboli may cause only a short episode of breathlessness or fever, perhaps associated with blood-stained sputum. Such relatively minor manifestations of pulmonary embolism are often overlooked or mistaken for the symptoms of some other condition. Any patient with even a small pulmonary embolism should be treated in hospital, since the condition is potentially lethal.

Most commonly, a pulmonary embolus arises from a thrombosis in the veins of the calf. This is particularly likely to happen in anyone who is confined to bed for a few days without the opportunity to exercise his legs. This condition is also seen in pregnant women, and very occasionally in those on the contraceptive pill.

Cerebral embolism is also quite common. This is a type of stroke caused by matter obstructing the blood vessels that lead to the brain. The embolus may be formed of clot material, of degenerative tissue that has sloughed off the wall of an artery, of fragments of a tumour, or of pieces of an infected vegetation on a heart valve.

Air embolism occurs when an air bubble gets into a blood vessel. Causes include accidents during blood transfusion, intravenous infusion, or surgery particularly in the region of the head and neck. Amateur attempts at abortion by means of a uterine syringe may cause massive air embolism and sudden death. Divers .(both hard-top and. skin-divers) and compressed-air workers are also liable to air embolism if they undergo too rapid decompression.

The symptoms of air embolism vary greatly, depending on the site at which the bubble or bubbles lodge. They include sudden death, collapse, shock, unconsciousness, paralysis, and severe pain in various parts of the body. In the case of a diver or compressed-air worker, immediate recompression in a compression chamber may be life-saving.

The field of science dealing with the relationships of the various factors that determine the frequencies and distributions of an infectious process or disease or physiological state in a human community. Epidemiology is therefore far more than the study of epidemics of infectious diseases. The subject has grown greatly in scope, and is now being used in an attempt to determine the cause of diseases of unknown aetiology such as multiple sclerosis.

The most obvious application of epidemiology is in the study of an outbreak of an infectious disease such as diphtheria or influenza. An epidemic may be defined as a disease that attacks many people at the same time in a locality. It is widely diffused and has a tendency to spread rapidly. Epidemics occur either sporadically or, in the case of common diseases such as influenza, every few years, with occasional pandemics in which major parts of the world are involved. Pandemics of influenza appeared in 1918-1919, 1957, and 1969-1970.

When an outbreak of an infectious disease occurs, many factors must be considered. The type and virulence of the infecting organism are determined, for these vary and may play an important part in the spread of the infection. For example, recent pandemics of influenza have been due to the appearance of new Asian variants of influenza A virus. Secondly, it is important to know the number of carriers of the organism, as healthy carriers may play an important part in maintaining an epidemic. There is evidence that in outbreaks of meningococcal meningitis the carrier incidence of this organism has become much higher than usual. It is also important to know what proportion of the community has been immunized against the disease, for there is strong evidence that if this proportion drops to a critical level in the case of a disease such as diphtheria, an outbreak will occur. Among other factors investigated are the general health of the population, the type of living conditions (overcrowding in particular), the presence or absence of animal or in- sect carriers of the disease, the geographical incidence of the disease, and any particular racial susceptibilities.

Epidemiological study of an obscure disease such as multiple sclerosis may throw important light on the cause of the condition. It is known that multiple sclerosis is commoner in temperate climates, and reasons for this are being sought. The diet, natural environment, and general habits of peoples in different parts of the world are being studied, as well as genetic studies of blood groups, conjugal incidence, and the association of multiple sclerosis with trauma, infections, and other diseases. Epidemiology also involves investigating the factors controlling a physiological state such as blood pressure.