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近十年的研究表明，人类睡眠与清醒状态的最大生理差异在于呼吸控制的不同。

Of all the physiological differences in human sleep compared with wakefulness that have been discovered in the last decade, changes in respiratory control are most dramatic.

不仅呼吸系统的运作强度方面有不同，呼吸系统的运作方式方面甚至也有变化。

Not only are there differences in the level of the functioning of respiratory systems, there are even changes in how they function.

在睡眠期间，为保证呼吸而进行的胸腔活动减少了，这让横膈膜的收缩变得更为重要。

Movements of the rib cage for breathing are reduced during sleep, making the contractions of the diaphragm more important.

但是由于卧位的物理学特性，胃部会对横膈膜施加压力，让横膈膜更加难以工作。

Yet because of the physics of lying down, the stomach applies weight against the diaphragm and makes it more difficult for the diaphragm to do its job.

然而，睡眠时还有很多其他的变化能影响呼吸。

However, there are many other changes that affect respiration when asleep.

清醒状态下，呼吸由两套相互作用的系统所控制。

During wakefulness, breathing is controlled by two interacting systems.

第一套系统是一个无意识的新陈代谢系统，它的控制中心是脑干。

The first is an automatic, metabolic system whose control is centered in the brain stem.

这个系统会通过潜意识调节呼吸速率与深度，从而调节血液中的二氧化碳和氧气的水平以及酸碱比。

It subconsciously adjusts breathing rate and depth in order to regulate the levels of carbon dioxide (CO2) and oxygen (O2), and the acid-base ratio in the blood.

第二套系统是主动的行为系统。

The second system is the voluntary, behavioral system.

该系统的控制中心在前脑，它能够调节说话、唱歌和叹气等行为时的呼吸。

Its control center is based in the forebrain, and it regulates breathing for use in speech, singing, sighing, and so on.

它可无视或超控无意识的新陈代谢系统，产生不规则的呼吸模式。

It is capable of ignoring or overriding the automatic, metabolic system and produces an irregular pattern of breathing.

在非快速眼动（NREM）阶段（即眼球没有快速转动的睡眠阶段），呼吸会变得越来越深且越来越有规律，但是呼吸速率也会随之下降，导致总体的空气交换变少。

During NREM (the phase of sleep in which there is no rapid eye movement) breathing becomes deeper and more regular, but there is also a decrease in the breathing rate, resulting in less air being exchanged overall.

之所以会发生这样的情况，是因为在非快速眼动阶段，新陈代谢系统专门控制呼吸，身体使用的氧气较少，产生的二氧化碳也少。

This occurs because during NREM sleep the automatic, metabolic system has exclusive control over breathing and the body uses less oxygen and produces less carbon dioxide.

此外，睡眠期间，无意识的新陈代谢系统对血液中的二氧化碳和氧气浓度的反应没有那么灵敏。

Also, during sleep the automatic metabolic system is less responsive to carbon dioxide levels and oxygen levels in the blood.

发生在睡眠过程中的呼吸控制方面的这一系列变化会导致两种现象的发生。

Two things result from these changes in breathing control that occur during sleep.

第一，睡眠过程中，可能会出现呼吸暂停或减少的现象，因为睡眠和清醒两种状态下的控制机制不同，人的呼吸频率也会随之增加或降低。

First, there may be a brief cessation or reduction of breathing when falling asleep as the sleeper waxes and wanes between sleep and wakefulness and their differing control mechanisms.

第二，完全进入睡眠状态时，非快速眼动阶段期间血液中的二氧化碳含量会增加，氧气含量会减少。

Second, once sleep is fully obtained, there is an increase of carbon dioxide and a decrease of oxygen in the blood that persists during NREM.

人们观察到，在睡眠的各个阶段里，呼吸道方面发生了一些变化。

During all phases of sleep, several changes in the air passages have been observed.

睡眠期间，呼吸要花费平时两倍的力量，因为呼吸道的气流受到了更大的阻力，用来呼吸的肌肉工作效率发生了改变。

It takes twice as much effort to breathe during sleep because of greater resistance to airflow in the airways and changes in the efficiency of the muscles used for breathing.

一些在呼吸时让上呼吸道保持通畅的肌肉在睡眠时往往会变得更加松弛，尤其是在快速眼动（REM）阶段（即眼球快速转动的睡眠阶段）。

Some of the muscles that help keep the upper airway open when breathing tend to become more relaxed during sleep, especially during REM (the phase of sleep in which there is rapid eye movement).

如果没有这样的肌肉活动，人的吸气行为就像从气球里向外抽气一样——狭窄的管路可能会瘪掉。

Without this muscular action, inhaling is like sucking air out of a balloon—the narrow passages tend to collapse.

此外，两侧鼻道的阻力也会轮流变化。

Also there is a regular cycle of change in resistance between the two sides of the nose.

如果有东西将“好”的那一侧堵住了，比如由于过敏或者感冒而引发的的鼻塞，那么阻力将明显增加。

If something blocks the “good” side, such as congestion from allergies or a cold, then resistance increases dramatically.

受这些因素的影响，能将通气的路径从鼻子调整到嘴的这部分肌肉之间复杂的交互功能便丧失了。

Coupled with these factors is the loss of the complex interactions among the muscles that can change the route of airflow from nose to mouth.

其他呼吸调节机制也明显会在睡眠期间停止运作。

Other respiratory regulating mechanisms apparently cease functioning during sleep.

例如，清醒时，当吸气变得更加困难时（比如带着密闭的面罩呼吸），呼吸系统会立刻自动调节，增加呼吸强度。

For example, during wakefulness there is an immediate, automatic, adaptive increase in breathing effort when inhaling is made more difficult (such as breathing through a restrictive face mask).

这种应激反应调节在非快速眼动睡眠阶段是完全不存在的。

This reflexive adjustment is totally absent during NREM sleep.

只有在几次不充分呼吸过后，血液中二氧化碳浓度激增，氧气浓度下降，呼吸强度才会得到调节。

Only after several inadequate breaths under such conditions, resulting in the considerable elevation of carbon dioxide and reduction of oxygen in the blood, is breathing effort adjusted.

最后，对气管中刺激物的应激反应在睡觉时不会体现为咳嗽，而是呼吸暂停。

Finally, the coughing reflex in reaction to irritants in the airway produces not a cough during sleep but a cessation of breathing.

如果刺激足够严重，睡着的人会醒过来，清理呼吸道，重新调节呼吸，然后很可能再度进入睡眠状态。

If the irritation is severe enough, a sleeping person will arouse, clear the airway, then resume breathing and likely return to sleep.

快速眼动阶段的其他的呼吸变化比非快速眼动阶段的呼吸变化还要明显。

Additional breathing changes occur during REM sleep that are even more dramatic than the changes that occur during NREM.

快速眼动阶段空气的交换量比非快速眼动阶段的还要低。这是因为，尽管快速眼动阶段呼吸速率更快，但是快速眼动阶段有短期的浅呼吸或呼吸暂停，该期间内呼吸更不规律。

The amount of air exchanged is even lower in REM than NREM because, although breathing is more rapid in REM, it is also more irregular, with brief episodes of shallow breathing or absence of breathing.

此外，快速眼动期间的呼吸更加依赖于横膈膜的运动，而不是胸腔运动。

In addition, breathing during REM depends much more on the action of the diaphragm and much less on rib cage action.

According to paragraph 1, which of the following can be inferred about the diaphragm during sleep?

According to paragraph 2, all of the following are true of the voluntary breathing system EXCEPT:

The word “exclusive” in the passage is closest in meaning to

According to paragraph 3, which of the following may occur just before NREM sleep begins?

What is the author’s purpose in stating that “inhaling is like sucking air out of a balloon”?

All of the following are mentioned in paragraph 4 as being characteristic of breathing during sleep EXCEPT

According to paragraph 5, what happens during NREM sleep when inhaling is difficult?

It can be inferred from paragraph 5 that a very mild irritation during sleep will likely cause the sleeping person to

The word “considerable” in the passage is closest in meaning to

The word “resume” in the passage is closest in meaning to

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

Look at the four squares  that indicate where the following sentence could be added to the passage. To better understand breathing during sleep, it is, however, helpful to first understand how respiration works in general.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: From the seven statements below, select the statements that correctly characterize breathing during wakefulness and those statements that correctly characterize breathing during sleep. Drag each answer choice you select into the appropriate box of the table. Two of the answer choices will NOT be used. This question is worth 3 points.

Breathing During Sleep Of all the physiological differences in human sleep compared with wakefulness that have been discovered in the last decade, changes in respiratory control are most dramatic. Not only are there differences in the level of the functioning of respiratory systems, there are even changes in how they function. Movements of the rib cage for breathing are reduced during sleep, making the contractions of the diaphragm more important.  Yet because of the physics of lying down, the stomach applies weight against the diaphragm and makes it more difficult for the diaphragm to do its job.  However, there are many other changes that affect respiration when asleep. During wakefulness, breathing is controlled by two interacting systems.  The first is an automatic, metabolic system whose control is centered in the brain stem. It subconsciously adjusts breathing rate and depth in order to regulate the levels of carbon dioxide (CO2) and oxygen (O2), and the acid-base ratio in the blood. The second system is the voluntary, behavioral system. Its control center is based in the forebrain, and it regulates breathing for use in speech, singing, sighing, and so on. It is capable of ignoring or overriding the automatic, metabolic system and produces an irregular pattern of breathing. During NREM (the phase of sleep in which there is no rapid eye movement) breathing becomes deeper and more regular, but there is also a decrease in the breathing rate, resulting in less air being exchanged overall. This occurs because during NREM sleep the automatic, metabolic system has exclusive control over breathing and the body uses less oxygen and produces less carbon dioxide. Also, during sleep the automatic metabolic system is less responsive to carbon dioxide levels and oxygen levels in the blood. Two things result from these changes in breathing control that occur during sleep. First, there may be a brief cessation or reduction of breathing when falling asleep as the sleeper waxes and wanes between sleep and wakefulness and their differing control mechanisms. Second, once sleep is fully obtained, there is an increase of carbon dioxide and a decrease of oxygen in the blood that persists during NREM. But that is not all that changes. During all phases of sleep, several changes in the air passages have been observed. It takes twice as much effort to breathe during sleep because of greater resistance to airflow in the airways and changes in the efficiency of the muscles used for breathing. Some of the muscles that help keep the upper airway open when breathing tend to become more relaxed during sleep, especially during REM (the phase of sleep in which there is rapid eye movement). Without this muscular action, inhaling is like sucking air out of a balloon—the narrow passages tend to collapse. Also there is a regular cycle of change in resistance between the two sides of the nose. If something blocks the “good” side, such as congestion from allergies or a cold, then resistance increases dramatically. Coupled with these factors is the loss of the complex interactions among the muscles that can change the route of airflow from nose to mouth. Other respiratory regulating mechanisms apparently cease functioning during sleep. For example, during wakefulness there is an immediate, automatic, adaptive increase in breathing effort when inhaling is made more difficult (such as breathing through a restrictive face mask). This reflexive adjustment is totally absent during NREM sleep. Only after several inadequate breaths under such conditions, resulting in the considerable elevation of carbon dioxide and reduction of oxygen in the blood, is breathing effort adjusted. Finally, the coughing reflex in reaction to irritants in the airway produces not a cough during sleep but a cessation of breathing. If the irritation is severe enough, a sleeping person will arouse, clear the airway, then resume breathing and likely return to sleep. Additional breathing changes occur during REM sleep that are even more dramatic than the changes that occur during NREM. The amount of air exchanged is even lower in REM than NREM because, although breathing is more rapid in REM, it is also more irregular, with brief episodes of shallow breathing or absence of breathing. In addition, breathing during REM depends much more on the action of the diaphragm and much less on rib cage action.