Audiological Investigations
Audiological investigations help us diagnose the cause and degree of impairment which will help us to rehabilitate the client accurately.
PURE TONE AUDIOMETRY
Pure tone Audiometry is a subjective test because the subject participation is more. It takes 30 minutes to complete the test to find the hearing threshold. In the test the minimum intensity of sound at which a person can respond across different frequencies of sound is identified.
In this test the audiologist present & whistle like sound through ear phones. The patient is asked to press a switch or raise his finger when he hears a tone. The results of the test are plotted as a graph called audiogram. In audiogram, the air conduction threshold indicates the amount of hearing loss and bone conduction indicates which part of the ear is affected.
SPEECH AUDIOMETRY
Speech Audiometry is an essential part of the battery of comprehensive audiometric tests--evaluates speech reception, recognition, and understanding. The pure tone audiogram provides only a partial picture of the patient’s status because it does not give any direct information about his ability to hear & understand speech.
TYMPANOMETRY
Measures the sound reflected from the ear drum while the pressure of the external canal is varied by the operator. It aids in the assessment of outer ear, middle ear and the Eustachian tube. This test should not be performed in infants below the age of 7 months because the suppleness of the cartilage of the external canal may produce misleading results.
REFLEXOMETRY
This is a measure of the stapedial muscle reaction to exposure to high intensity sounds. When the stapedial muscle contracts in response to sound it stiffens the osscicles and the ear drum altering the compliance values which can be measured using an impedance audiometer. The recording is ideally made at a single pressure setting i.e. the pressure which shows the maximum compliance. The reflex on the opposite side also is tested since it is a bilateral reflex. The sound frequencies used to test this reflex are 500, 1000, 2000 and 4000Hz. For screening purposes it is sufficient if 1000Hz is used.
OTOACOUSTIC EMISSION (OAE)
Otoacoustic emissions are sounds, which appear in the ear canal as a by-product of sensory cell activity in the inner ear in response to sound. They are conducted through the middle ear. Their successful stimulation and detection indicates a high degree of normality in the functioning of the middle ear and inner ear. In particular the environment of the inner ear is shown to be healthy. This is a necessary but not in itself a sufficient condition for normal hearing. The signals detected by the cochlea also need to be transmitted effectively through the auditory nerve pathways and to be interpreted correctly by the higher auditory centers.
AUDITORY STEADY STATE RESPONSE (ASSR)
The auditory steady-state response (ASSR) can be thought of as an electrophysiological response to rapid auditory stimuli. The goal of ASSR is to create an estimated audiogram from which questions regarding hearing, hearing loss, and aural rehabilitation can be answered. ASSR allows the hearing care professional to create statistically valid audiograms for those unable or unwilling to participate in traditional behavioral tests. ASSR relies on statistical measures to determine if and when a threshold is present. ASSR design and functionality vary across manufacturers.
AUDITORY BRAINSTEM RESPONSE (ABR)
The sound into the ear is transmitted to the brain for interpretation. The sounds are converted into electrical impulses by the Cochlea these impulses are carried by a pathway. Electrical changes in the various station of the auditory pathway in responses to the sound. These elicited changes can be recorded through electrodes placed on the head of the patient. These electrical impulses in the first 10-15 ms. are known as ABR waves. It is one way to find the hearing sensitivity of the patient. The patient is asked to sleep quickly. Auditory stimulus (clicks) is introduced into the ear.
AIDED AND FREE FIELD AUDIOMETRY
This is similar to Pure tone Audiometry but done using Speaker instead of Headphones. Usually done for client using hearing aid or CI to evaluated the gain level and competency of the Hearing aid.
NEONATAL HEARING SCREENING
Simple tests can be used to check a baby's hearing right after birth. We don't have to wait until children are older to check for hearing loss. Newborn hearing tests are important because a lot of help is available even when a hearing loss is found early in a baby's life.
Hearing screening programs are called "universal" because they are set up to test all babies. All babies can and should have their hearing tested before they leave the hospital, or within 3 weeks of leaving the hospital. If a baby is born at home, a hearing test should be completed before he or she is 2 months old.
When a baby fails the screening tests, he or she is referred for more detailed, diagnostic hearing testing. If a hearing loss is found, then hearing aids and therapy services are started to help the baby learn to listen and speak.
This done for early detection of permanent congenital hearing loss. It describes the use of objective testing methods (usually otoacoustic emission (OAE) testing or automated Auditory Brain Stem Response (AABR) testing) to screen the hearing of well newborns in a particular target region.