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An investigation of the circulation of blood in the eyes of diver has produced the strongest evidence that tissue damage caused

admin2013-01-22  64
问题     An investigation of the circulation of blood in the eyes of diver has produced the strongest evidence that tissue damage caused by diving is more common and more severe than had been previously thought. Of the 26 professional divers studied, all had abnormal retinas. None of the divers taking part in the study had visual problems as a result of their damaged retinas but Alan Bird of Moorfields Eye Hospital in London said that he "would not be surprised to find divers whose damage has progressed far enough to affect their vision".
    Evidence has mounted during recent years to show that exposure to pressure during diving subtly damages the central nervous system. Doctors believe that the damage is due to obstruction in the flow of blood through the tissues. People who take up diving as a sport know they are at risk of getting "the bends" or an air embolism, but if they follow the correct procedures, the risk is very low. All professional divers know they also run the risk of bone necrosis. About 5 per cent of them develop small dead patches in their bones. Active professional divers have their thighs and upper arms X-rayed as part of their annual medical examination.
    Doctors have been concerned diving-caused dead patches to appear on bones; other tissues may be suffering a similar fate. Their concern increased in the early 1950s. Detailed neurological examinations and tests of the memory and reactions of experienced professional divers suggested that some of them might have slight damage to the brain and spinal cord. In order to determine the size of the problem, the researchers needed a method of looking for the damage in a large sample of divers that did not involve surgery. The damage which occurs in the tissue of both the bones and the nerves of divers is similar. Damages of the retina which doctors can see using the technique are known as retinal angiography. The process involves injecting fluorocein dye into the blood stream and photographing the back of the eye through the pupil. The technique can provide a detailed photograph of the two vascular systems supplying blood to their retina without causing too much discomfort to the patient.
    The researchers suggested three mechanisms to explain how diving causes this obstruction. When divers come back to the surface, air bubbles sometimes form in their lungs. Bubbles forming in the lungs trigger changes in the body’s clotting mechanism which could result in minute clots. The researchers hope that clues to the cause of the obstruction will come from investigations into the individual differences between divers. Some of the divers studied had relatively little damage even though they had been diving for many years and done a great deal of deep diving. On the other hand, a few inexperienced divers had quite extensive damage.
Damage to the retina is caused by ______ .
选项 A、obstructions to blood circulation
B、loss of pigment in the epithelium
C、pressure on the central nervous system
D、All of the above
答案A
解析 这道题可以用排除法。B、D信息根本没有提到，所以排除B和D。个别学生选择了C，根据是文中的信息：最近几年中不断有证据表明跳水过程中承受的压力对中枢神经系统有难以观察的损害。然而问题问的是视网膜的损害，因此我们判断答案是A。
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