美国儿科学会（政策）：预防婴儿、儿童及青少年过多暴露噪音（第三部分）

（上接第二部分）

Children’s Unique Susceptibilities

Noise exposure is a pediatric issue because of the susceptibility of the developing auditory system and because effects on hearing and quality of life at early developmental stages can affect a child’s life trajectory. Studies in immature laboratory animals reveal heightened susceptibilities to noise compared with adult animals, illustrating the concept of “critical periods” of vulnerability.¹⁶ External ear anatomy in young children differs from adult anatomy; smaller ear canals more greatly intensify higher frequency sounds.¹⁷ Children have differences in behavior and development, with long life spans during which cumulative exposures may manifest. Children and youth often have excessive exposures through PLDs. Children with developmental differences, such as those with autism spectrum disorder, often have increased sensitivity to noise^18,19; they may display atypical play methods with noisy toys, such as prolonged and repetitive use, potentially increasing risk of hearing damage.²⁰ Hyperacusis (increased sensitivity to sound at levels that would not trouble most individuals), misophonia (excessive and inappropriate emotional responses to specific “trigger” sounds), and phonophobia (phobia to specific sounds or classes of sounds) have been described in these children. Auditory processing issues are also reported in children with attention-deficit/hyperactivity disorder (ADHD), including hypersensitivity and hyposensitivity to sounds.^21,22 

Noise Effects

Hearing Loss

Sensorineural hearing loss (SNHL) is caused by damage to the hair cells of the cochlea or to the auditory nerve. Excessive noise exposure is one cause of SNHL. Damage to hair cells is permanent and usually cannot be restored with medical treatment.^23,–25 NIHL can occur after high-intensity traumatic noises or after less-loud noises experienced over time. SNHL can occur after a single loud sound near the ear. Hearing loss more commonly results over time from damage caused by repeated exposures to loud sounds. The louder the sound, the shorter the amount of time it takes for damage to occur. The longer the exposure, the greater the risk for hearing loss (especially if hearing protection is not used or if there is not enough time for the ears to rest between exposures).²⁶ Continuous exposure to hazardous noise levels tends to cause maximum damage to high-frequency areas of the cochlea and is usually most severe around 4000 Hz.

NIHL impacts understanding of speech. Consonants are disproportionately affected in higher frequencies, whereas lower frequency vowel sounds remain relatively normal. Because softly spoken, high-frequency consonants such as “f,” “s,” and “h” convey more of the intelligibility of words in speech compared with vowels, an individual with NIHL can have difficulty understanding in background noise and when following higher-pitched voices.

Hearing Loss in Adults

Hearing loss is the third most common chronic physical condition in US adults. Hearing loss is linked to cognitive decline, Alzheimer disease, dementia, and Parkinson disease.^27,28 The Centers for Disease Control and Prevention analyzed data collected from adults ages 20 to 69 years using questionnaires and audiometric tests to determine the presence of audiometric notches indicative of NIHL. An audiometric notch is a deterioration in the hearing threshold (the softest sound a person can hear); high-frequency notches suggest NIHL. Nearly 1 in 4 adults (24%) had notches, suggesting a high prevalence of NIHL. People with NIHL often did not recognize this: almost one-quarter of participants reporting good or excellent hearing had bilateral (5.5%) or unilateral (18.0%) notches. This study indicates that NIHL hearing loss is a significant but often unrecognized problem in adults.⁶ The high prevalence of notches (almost 1 in 5) among young adults suggests that early life interventions are needed.

Hearing Loss in Children and Adolescents

Several studies confirm that hearing loss is common in children, adolescents, and young adults. Even small amounts of hearing loss can have profound, negative effects on speech, language comprehension, communication, classroom learning, and social development.^29,30 

One study using national data examined changes in hearing loss prevalence in US children and adolescents (12 to 19 years old) from 1988 to 2010 and associated risk factors including reported noise exposures. The prevalence of hearing loss of >15 dB increased from 17.0% to 22.5% from 2007 to 2008 but decreased to 15.2% from 2009 to 2010. The most current data, thus, illustrated that about 1 in 6 middle and high school students had evidence of hearing loss. This study did not demonstrate a consistent association between exposure to loud music with an increased risk of hearing loss.³¹ 

Studies in youth do not consistently show positive associations between reported noise exposure and hearing loss. Adolescents and young adults, however, typically underestimate symptoms caused by loud sound, tinnitus, and temporary hearing impairment during music exposure. Youth typically underreport concern for these symptoms.³² Although more research is needed to demonstrate the association of noise exposure with early hearing loss, it is likely that noise contributes to hearing loss in children and adolescents. Pediatricians, therefore, may play important roles in counseling about preventable noise exposures.

（未完待续，下接第四部分）