长期噪音刺激损伤听觉功能

导读：据说，人类有着天生的异常敏锐的感觉器官，只是由于生存在一个没有太多自然威胁的环境中，感觉逐渐钝化。然而，更主要的是：人类总是在不知不觉中折磨自己的感官，消耗了与生俱来的天赋。在生活中，有太多破坏敏锐感觉的行为：如放纵于烟酒；如沉湎于电视；又如，让耳朵终日“享受”震天的音乐……来一起看一下这篇文章，想一想，我们是否应该多多地关心一下自己的感觉问题呢？

Scientists are finding what many parents will say they knew all along — loud music hurts kids' hearing. But what moms and dads may not know is that more than 12 percent of children between the ages of six and 19 suffer from noise-induced hearing loss( 过量噪音引发的听力丧失).

So says a Centers for Disease Control study appearing in the July issue of Pediatrics (小儿科).

How Many Kids Are Suffering?

And though hearing experts have suspected for a long time that long-term hearing loss begins in childhood, the study is the first to show how common hearing impairment(听力损伤) is among kids.

"Historically, people have been looking only at adult hearing loss and assuming(自以为) that this is not a problem among children," said Amanda Niskar, a nurse at the CDC and lead author of the study. "What we have found here for the first time is that this is not true. [Hearing loss] is a progression(渐进过程) and it starts when you're very young."

Some hearing experts say the problem of hearing loss in kids will likely worsen, considering rising levels of environmental noise.

Niskar's study, which looked at more than 5,000 kids, measured a preliminary type(初始状态) of hearing loss known as a noise-induced-hearing threshold shift(噪音引发的听力临界变化状态), or NITS. In short, kids with NITS have difficulty hearing certain pitches or levels of sound.

Chronic Exposure Leads to Damage

"The first signs that people notice when they have NITS is that they'll hear an entire conversation, but they'll have difficulty discerning(识别) certain words," Niskar said. "And even if a child has temporary NITS, they might have problems understanding what teachers in a classroom are saying."

Regular exposure to loud noises worsens NITS by damaging nerve cells in the ear called hair cells. As the name suggests, these cells have tiny hairs that detect sound vibrations(声响震动) and turn them into signals sent to the brain. But while soft noises only cause the hairs to vibrate, loud noises can break them.

Brief(短暂的)instances of exposure to loud noise may only temporarily damage these hairs. Niskar said two hours of loud music on headphones or seven minutes next to the speakers at a rock concert result in NITS that may last for only a few days. However, chronic exposures can damage the hair cells — and hearing — permanently.

Turn Down the Music

Scientists agree loud music is one of the most common culprits(罪魁祸首).

"The most important point in the study is that the percentage of kids with damaged hearing increases with age," said Dr. Steven Rauch, an associate professor of otolaryngology(耳鼻喉科学) at Harvard Medical School. "By late adolescence, more than 15 percent of kids had hearing damage. In that group, the obvious source is music."

Rauch added loud noises in the environment are becoming more and more common. This means today's kids could have more hearing problems later on in life if they do not protect their ears, he said.

"The thing to remember is that noise injuries are 100 percent preventable with judicious(谨慎的) exposure to noise," Rauch said. "The key thing for parents to tell their kids is not to turn it up so loud."