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Test For Hearing

  • Pure Tone Audiometry
  • Pure tone audiometry (PTA) is a test designed to determine the hearing threshold in the way of air and bone in a range of frequencies. In other words, PTA shows the status of the auditory cells in the cochlea of the inner ear.
  • What is PTA for?    
  • The aim of the test is to determine the threshold of hearing, ie. the minimum volume that the patient hears. The test result is the graph –Audiogram, hearing threshold curve for air and bone conduction, on the basis of which it is possible to determine the size of hearing loss.    
  • How is the PTA performed?    
  • Pure tone audiometry is completely non-invasive. It is carried out in special headphones for air and bone conduction, separately for the right and left ear. Each ear receives sounds with certain frequency (pitch) and volume.    
  • The test is conducted in cooperation with the patient and allows to pre-determine the nature and depth of hearing loss.    
  • It is one of the simplest and most common hearing tests, providing valuable information on the hearing. The patient does not need to specifically prepare for the study.
  • Impedance
Impedance audiometry is an objective method based on the measurement of the pressure in the middle ear, stapedius reflexes, and tension of the tympanic membrane. It is one of the most common and most accurate methods for testing the middle ear.

What is the purpose of Impedance Audiometry –

Impedance audiometry covers following tests:
        
  • tympanometry, which measures the pressure in the middle ear    
  • measuring the reflex of the stapedius    
  • Eustachian Tube Function Test
Basically, this test assesses the patency of the middle ear. This study is very helpful for the diagnosis of:
        
  • presence of infectious fluids in the middle ear    
  • otitis media with effusion    
  • hypertrophy of adenoids or tonsils    
  • Eustachian tube dysfunction    
  • otosclerosis    
  • ossicular chain fracture    
  • facial palsy
How is the impedance audiometry performed?

Impedance audiometry is completely painless and non-invasive, but it requires a small mobility during the measurement. It involves inserting the probe tube into the ear. The Tube is ended with a cap matched to the size of the ear.
        
  • Tympanometry is based on measuring the acoustic resistance and pressure in the middle ear. Tympanometry is performed by changing the pressure in the external auditory canal to obtain such pressure that prevails in the middle ear. This causes the impedance of the middle ear to be the smallest, and the compliance of the tympanic membrane is the greatest.    
  • Stapedius reflex test is performed automatically, by providing middle and high-frequency stimulus sounds (500, 1000, 2000 and 4000 Hz).
  • Eustachian tube patency test involves inserting a tympanometer probe in the ear canal. It’s the output pressure in the tympanic cavity being tested. While the patient clogging his nose and swallowing saliva causes a negative pressure in the tympanic cavity, the ear pressure is measured again. The patient exhales while closing the mouth and clogging his nose, which causes a positive ear pressure generation. The last measurement of the pressure in the tympanic cavity is performed
   
  • OAE
Otoacoustic emissions is a response of cochlear auditory cells to tonal pulse or cracks provided by the probe. Otoacoustic emission occurs in all good hearing, also in newborns.
        
  • Indications for testing:
    
  1. Assessment of the inner ear.    
  2. hearing screening for infants    
  • Topodiagnostic assessment of hearing loss    
  1. Monitoring changes in hearing after taking ototoxic medications.    
  2. Detection of functional deafness.    
  3. Tinnitus diagnostics.   
  • What is otoacoustic emission performed for
Otoacoustic emissions (OAE) is a non-invasive, objective and easy method of assessing the activity of the cochlea. It involves recording responses in frequencies other than the frequency of the administered stimulus. Aside from using OAE in screening newborns, it has found its rightful place in the set of topodiagnostic tests of hearing disorders. The credibility of OAE test depends on the limitations of the method and the measurement conditions. One of them is the correct aeration of the middle ear, and impaired conduction system ensuring the sound will reach the inner ear. Pressure disturbance in the tympanic cavity and in the external auditory canal may affect the response parameters of OAE.    
  • How is the OAE performed?
The test involves placing a probe in the ear canal. The probe consists of a small speaker that emits sounds and a small, highly sensitive microphone recording otoacoustic emission. When the stimulus sound coming from the speaker moves the hair cells, which produce secondary sound picked up by the microphone. OAE test should be carried out in a soundproof room. The test is completely non-invasive but requires low mobility of the child during the examination, as well as special acoustic conditions (silent room or cubicle).
        
  • BERA
  • BERA (Brainstem Evoked Response Audiometry) is an electro-physiological test procedure to measure the responses of brain waves stimulated by a clicking sound to identify the central auditory or hearing pathways of the brainstem.
What are the indications of BERA
        
  1. Detection of hearing lossin children less than 05 years and difficult to test adults.    
  2. To detect Magnitude of hearing loss.    
  3. Rough idea of types of hearing loss -  Conductive/Sensorineural hearing loss.    
  4. Site of the lesion i.e  Retrocochlear/Cochlear.    
  5. To study any central auditory pathway defects.
How is BERA done

BERA is electrophysiological test of hearing in which electrical activity of hearing pathway is detected with the help of electrodes in response to sound stimulus.   03 Electrodes are used to record electrical activity which are reference electrode, ground electrode & active electrode.
Is there any need of sedation?
Yes,in children there is need of sedation. It is usually done with Trichlofos or promethazine.

Interpretation of BERA
BERA is objective test of hearing in which electric potential are recorded from entire hearing pathways in the form of different wave patterns in response to sound stimulus. These waves are studied for latency, periodicity, and other characteristics. There are different waves starting from I,II, III, IV, V, VI & VII  waves are recorded.
        
  • ASSR    
  • Auditory Steady State Response (ASSR) is an objective test used for evaluation of hearing ability in children too young for traditional audiometric testing. Most children are referred for ASSR after a newborn hearing screen in the hospital indicates the possibility of hearing loss. Early intervention strategies, such as hearing devices or cochlear implantation, are necessary for development of speech and language skills in a child with hearing impairment. The results obtained from ASSR testing can be used to estimate the behavioral pure-tone audiogram. This information is essential in the management of children with hearing loss.    
  • The person being tested must be very quiet and still in order to obtain reliable ASSR results. Often, testing is performed under sedation or in natural sleep if the person is under 6 months of age. Results are obtained by measuring brain activity while the person listens to tones of varying frequency (pitch) and intensity (loudness).
The brain activity is recorded using electrodes taped on the forehead and behind each ear. The use of electrodes eliminates the need for active participation of the patient (i.e., pushing a response button every time a tone is activated). The results are detected objectively using statistical formulas that determine the presence or absence of a true response. Similar to traditional audiometric testing, threshold is determined as the lowest level at each frequency at which a response is present. ASSR provides an accurate, frequency-specific estimate of the behavioral pure-tone audiogram.