Hearing Development Is Crucial During Second Half of Fetal Development

• Outline Chapter 10 Hearing Development and Deafness

• Hearing development is crucial during second half of fetal development.

• Functional hearing appears at 25-27 weeks gestation.

• Baby is exposed to sounds in the uterus and can hear mother’s voice.

• Exposure to loud noises can induce abnormalities.

• Crucial to start early intervention by the age of 6 months for infants with hearing loss.

• 95% of deaf infants are born to families with normal hearing

• The auditory system has 3 structures: a) Peripheral elements= outer, middle and inner ear. b) Auditory nerves c) Auditory regions of the brain

• Hearing range: range of frequencies that can be heard by humans, and it is commonly given as 20 to 20,000 Hz. A basic measure of hearing is afforded by an audiogram.

• Frequency/Pitch is measured in hertz (Hz). The most important sounds we hear every day are in the 250 to 6,000 Hz range.

• Sound intensity or loudness, is measured in decibels (dB). A person with hearing within the normal range can hear sounds ranging from 0 to 140 dB.

Hearing screenings

• OAE (Otoacoustic emissions)- Sound measured with a small probe inserted into the ear canal. Sounds given off by the inner ear allow the cochlea to be stimulated by the sound and the outer hair cells vibrate. The vibration produces a nearly inaudible sound that echoes back into the middle ear.

• ABR ( Auditory Brainstem Response)- sounds are played into baby's ears. Band-aid like electrodes are placed on the baby's head to detect responses. This test measures how the hearing nerve responds to sounds and can identify babies who have a hearing loss. Recommended for NICU settings as is more reliable.

Types of Hearing Impairment

1) Conductive hearing loss- blockage of sound transmission in the outer and middle ear. Caused by malformations,

fluid or debris.

2) Sensorineural hearing loss- loss of sound transduction in the inner ear to transmit to auditory nerve.

3) Neural hearing loss – auditory neuropathy. Dysfunction of the inner hair cells and auditory nerve

4) Mixed hearing loss- combined conductive with sensorineural deficits.

Severity of Hearing Loss

• Mild

• Moderate

• Severe

• Profound

• Hearing loss can be unilateral or bilateral.

• Risk factors associated with hearing loss: lack of follow up from initial findings, miscommunication on screening results, developmental delays, family history, NICU complications, in-utero infections, craniofacial anomalies, genetic syndrome, postnatal infections, neurodegenerative disorders, head trauma, chemotherapy, recurrent otitis media.

• Genetic causes

– For approximately 80% of children with hereditary hearing loss, the loss is inherited as an autosomal recessive trait

– More than 200 documented inherited syndromes are associated with deafness

Other Causes:

• Environmental exposures to viruses, bacteria, and other toxins prior to or following birth

• Severe respiratory or cardiopulmonary disease in neonate

• Very low birth weight

• Infections during pregnancy, infancy, and childhood

• Some antibiotics used to treat severe bacterial infections and chemotherapy drugs can cause bilateral hearing loss • Otitis media/ middle ear infection with fluid accumulation

• Skull base fractures

• Noise exposure: sudden, explosively loud noises (firecrackers or fireworks) or repeated exposure to very loud sounds over time (iPod at high-intensity levels or attending live rock music concerts)

• Children with intellectual disabilities are at increased risk for hearing loss, especially when genetic condition is cause of disability

• Factors indicating possible hearing loss

• Parental concerns

• Lack of hearing milestones

• Signs of hearing loss in deaf or hard-of-hearing child

• Baby does not awaken to loud noises,

• babbling does not become meaningful,

• Delay in receptive language

Types of Interventions

• Medical and surgical treatments

• Audiology monitoring

• Early intervention services/Low Incidence Programs

• Speech and Language services

• Frequency modulated devices

• Hearing aids and cochlear implants