Under certain circumstances, the human body must cope with gases at greater-than-normal atmospheric pressure. For example, gas pressures increase rapidly during a drive made with scuba gear because the breathing equipment allows divers to stay underwater longer and dive deeper. The pressure exerted on the human body increases by 1 atmosphere for every 10 meters of depth in seawater, so that at 39 meters in seawater a diver is exposed to pressure of about 4 atmospheres. The pressure of the gases being breathed must equal the external pressure applied to the body, otherwise breathing is very difficult. Therefore all of the gases in the air breathed by a scuba diver at 40 meter are present at five times their usual pressure. Nitrogen, which composes 80 percent of the air we breathe, usually causes a balmy feeling of well-being at this pressure. At a depth of 5 atmospheres, nitrogen causes symptoms resembling alcohol intoxication, known as nitrogen narcosis. Nitrogen narcosis apparently results from a direct effect on the brain of the large amounts of nitrogen dissolved in the blood. Deep dives are less dangerous if helium is substituted for nitrogen, because under these pressures helium does not exert a similar narcotic effect.

As a scuba diver descends, the pressure of nitrogen on the lungs increases. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues The reverse occurs when the diver surfaces, the nitrogen pressure in the lungs falls and the nitrogen diffuses from the tissues into the blood, and from the blood into the lungs. If the return to the surface is too rapid, nitrogen in the tissues and blood cannot diffuse out rapidly enough and nitrogen bubbles are formed. They can cause severe pains, particularly around the joints.

Another complication may result if the breath is held during ascent. During ascent from a depth of 10 meters, the volume of air in the lungs will double because the air pressure at the surface is only half of what it was at 10 meters. This change in volume may cause the lungs to distend and even rupture. This condition is called air embolism.

To avoid this event, a diver must ascend slowly, never at a rate exceeding the rise of the exhaled air bubbles, and must exhale during ascent.

It can be inferred from the passage that which of the following presents the greatest danger to a diver?

Câu hỏi liên quan

• The word “this” in paragraph 3 refers to ...............

• In the first paragraph, the word “emerged” is closest in meaning to____.

• The word “excluded” is closest meaning to ___________ .

ZUNIA12

• What is the purpose of the paragraph 1?

• The phrase “of no consequence” means ________.

• The purpose of the projects mentioned is .................

• The “ English cousin” in the second paragraph refers to a_______.

• Based on the passage, what is probably true about the south of France?

• The word “hurdles” can be best replaced by ...............

• What of the following statement is true about life in the future?

• According to the passage, a regional university rector in Germany is elected by _____.

• According to the passage, copyright law is _______

• The expression catch a whiff is closest in meaning to________.

• The word formulaic is closest in meaning to___________.

• The statement: "Colloquialisms, on the other hand, are familiar words and idioms that are understood by almost all speakers of a language and used in informal speech or writing, but not considered acceptable for more formal situations." means:

• The expression “traditional methods of teaching” is the first sentence refers to ______

• In the first paragraph, the word "elements" is closest in meaning to .............

• All of the following are TRUE about long – term memory EXCEPT that ..........

• The word “sensational” is closest in meaning to ...........

• People thought Merlin was a dreamer because he ..............