Sound practical


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How to test hearing functions

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Sound practical

  1. 1. Tests of Hearing
  2. 2. Loud sounds and hearing loss Intense sounds can cause - hair cell death - nerve fiber degeneration
  3. 3. Hearing testing is a means of evaluating an individual's overall hearing function. What is Hearing Testing?
  4. 4. Hearing can be impaired due to lesions in the external ear canal, the middle ear, or the inner ear. The purpose of hearing testing is to evaluate hearing function and, if it is impaired, to attempt to localize the site of lesion.
  5. 5. • Nerve deafness – impairment of the cochlea or impairment of the auditory nerve • Conduction Deafness – impairment of the physical structures that conduct the sound into the cochlea Types of Deafness
  6. 6. destruction of the cochlear or the auditory nerve Nerve Deafness the person becomes permanently deaf
  7. 7. destruction of tympanum- ossicular system Conduction Deafness sound can still be heard via bone (ossicular) conduction
  8. 8. Three different sized tuning forks. The higher pitched forks (such as the 512 Hz fork) are more appropriate for hearing testing. Bedside Testing of Hearing
  9. 9. The single most common office test is a tuning fork test called the Rinne, named after Adolf Rinne, who described this test in 1855. Rinne’s Test
  10. 10. In the Rinne test, a comparison is made between hearing elicited by placing the base of a tuning fork applied to the mastoid area (bone), and then after the sound is no longer appreciated, the vibrating top is placed one inch from the external ear canal (air). Rinne’s Test
  11. 11. Normal Hears vibration in air after bone conduction is over Conduction deafness of one ear Vibration in air is not heard after bone conduction is over Partial nerve deaf- ness of one ear Vibration in air is heard after bone conduction is over Complete nerve deaf- ness of one ear Vibration is not heard on the affected side Rinne’s Test
  12. 12. In the Weber test, a 512 Hz tuning fork is placed on the patient's forehead. If the sound lateralizes (is louder on one side than the other), the patient may have either an ipsilateral conductive hearing loss or a contralateral sensorineural hearing loss. Weber’s Test
  13. 13. Normal Hears equally on both sides Conduction deafness of one ear Sound louder in the diseased ear Partial nerve deaf- ness of one ear Sound louder in the normal ear Complete nerve deaf- ness of one ear Sound heard only in the normal ear Weber’s Test
  14. 14. Audiometry Audiometry is the term used to describe formal measurement of hearing. The measurement is usually performed using an "audiometer" by an "audiologist". In audiometry, hearing is measured at frequencies varying from low pitches (250 Hz) to high pitches (8000 Hz).
  15. 15. Produces pure tones of different frequencies. Is used to determine the nature of hearing disabilities. The audiometer is calibrated so that zero intensity level of sound at each frequency is the loudness that can barely be heard by the normal person (0 db). Audiometer
  16. 16. Audiometry provides a more precise measurement of hearing. Air conduction is tested by having the subject wear earphones attached to the audiometer. Audiometry
  17. 17. Audiometry Pure tones of controlled intensity are delivered to one ear at a time. The subject is asked to raise a hand, press a button, or otherwise indicate when he/she hears a sound. An attachment called a bone oscillator is placed against the bone behind each ear (mastoid bone) to test bone conduction.
  18. 18. Audiogram Frequency Hearing level (dbs) normal -10 +10 100 The minimum intensity (volume) required to hear each tone is graphed, and the results are called an audiogram.
  19. 19. The hearing level is quantified relative to "normal" hearing in decibels (DB), with higher numbers of DB indicating worse hearing. Audiometry
  20. 20. The DB score is not really percent loss, but neverthless 100 dB hearing loss is nearly equivalent to complete deafness for that particular frequency. A score of 0 is normal. It is possible to have scores less than 0, which indicate better than average hearing. Audiometry
  21. 21. Audiogram for a Patient with Normal Hearing
  22. 22. When there is a hearing loss, the next step is to try and determine whether the loss is caused by a sensory problem (sensorineural hearing loss) or a mechanical problem (conductive hearing loss). Audiometry
  23. 23. This distinction is made by using a bone vibrator, which bypasses the mechanical parts of the middle ear. If hearing is better using bone than air, this suggests a conductive hearing loss. Audiometry
  24. 24. Audiogram
  25. 25. Conductive Hearing Loss 0 10 20 30 40 50 60 70 80 90 100 500 1000 2000 3000 4000 6000 8000 dBHearingLevel Frequency (Hz) Left Ear Right Ear BC Left Ear
  26. 26. 0 10 20 30 40 50 60 70 80 90 100 500 1000 2000 3000 4000 6000 8000 dBHearingLevel Frequency (Hz) Left Ear Right Ear BC Left Ear Sensorineural Hearing Loss