Audiogram, Audiometry, Pure-Tone Audiometry

  • Preparation
  1. Patient should avoid loud noise exposure for 14 hours prior to testing (e.g. music via headphones, motorcycle)
  2. Testing environment should be quiet
    1. Formal audiology evaluations are typically performed in a sound proof booth
  3. Testing varies by indication
    1. Clinic Hearing screening is often performed with a handheld device (or online/webapp)
    2. Threshold search Audiometry may be used to program Hearing Aids
    3. Comprehensive Audiometry differentiates between conductive, sensorineural and mixed Hearing Loss
  • Technique
  • Pure-Tone Audiometry
  1. Screening (typical handheld device)
    1. Hearing frequencies tested: 500 to 4000 Hz (speech spectrum)
    2. Loudness tested: 25-30 DB in adults (15-20 DB in children)
  2. Threshold Search Audiometry (Hughson-Westlake Method, by audiologist)
    1. Start with the better Hearing ear
    2. Hearing is tested in each ear at frequencies between 250 Hz to 8000 Hz
      1. Frequencies tested at one octave intervals: 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, 8000 Hz
      2. Typical sequence: 1k, 2k, 3k, 4k, 8k, 1k, 500, 250
    3. Each frequency is tested at volumes between 0-90 decibels (logarithmic, loudness doubles every 10 decibels)
      1. Start with an easily heard DB level
      2. Test each heard tone again at 10 DB lower until no response
      3. Then increase by 5 DB, testing until tone heard again
  3. Comprehensive Audiometry (by audiologist, typically in a sound proof room)
    1. Air and bone testing differentiates conductive, sensorineural and mixed Hearing Loss
      1. Pure tone air conduction via headphones
      2. Pure tone bone conduction via device applied to mastoid bone
    2. Tympanometry
    3. Speech-reception threshold and word recognition
  • Findings
  • Audiogram Graph
  1. Audiogram axes
    1. Horizontal (X-Axis): Increasing frequencies (Hertz) from left to right
    2. Vertical (Y-Axis): Increasing sound intensity (decibels) from soft (top) to loud (bottom)
  2. Thresholds
    1. Softest sound heard per frequency 50% of the time is recorded as threshold on the graph
  3. Symbols
    1. Four symbols are used (2 for air L/R, 2 for bone L/R)
    2. For each frequency, these 4 symbols are plotted, representing thresholds (left and right ears, air and bone)
  4. Interaural Attenuation
    1. Sound waves lose acoustic energy as they travel transcranially to the contralateral ear
    2. In Hearing Testing, soft sounds are not typically heard by the opposite ear
  5. Cross Hearing
    1. Good ear detects sounds presented only to the bad ear despite interaural attenuation
      1. Results in False Negative testing of the bad ear
      2. Overcome by masking procedure
    2. Cross Hearing occurs when there is a large threshold discrepancy between ear Hearing thresholds
      1. Bad ear threshold exceeds the good ear threshold by >40 dB (55 dB for insert earphones)
      2. Loud sounds presented to bad ear overcomes interaural attenuation
  6. Masking
    1. When testing the bad ear, noise is the presented to the good ear to block cross Hearing
  • Interpretation
  1. Normal Hearing
    1. All frequencies are heard at 20 decibels or less
  2. Hearing Loss across all frequencies (typically 40 DB loss)
    1. Conductive Hearing Loss (e.g. Cerumen Impaction)
    2. Otosclerosis
  3. Low frequency Hearing Loss
    1. Meniere's Disease (severe)
  4. Low to mid-frequency Hearing Loss (with bone conduction better than air conduction)
    1. Tympanic Membrane Perforation
  5. High frequency Hearing Loss
    1. Noise-Induced Sensorineural Hearing Loss (4000 Hz and higher)
    2. Age-Related Hearing Loss - Presbycusis (2000 Hz and higher)
  • Resources
  1. Audiogram of normal sounds
    1. http://www.nmit.edu.au/Content/images/centre_of_excellence/frequency_intensity_of_sounds.jpg