1.The principle and value of pure tone audiometry

Pure tone audiometry is a core method to determine the smallest hearing (dB HL) perceived by the human ear at various frequencies through air conduction headphones and bone conduction vibrators. It is used to assess the degree and nature of hearing loss (con, sensory neural, or mixed).

• Basic physiology of hearing:

  – Air conduction (AC): Sound is conducted through the external auditory canal →mpanic membrane → auditory ossicles → inner ear → auditory nerve;

  – Bone conduction (BC): Sound directly stimulates the inner ear through the vibration the skull, bypassing the external and middle ear.

• Clinical significance:

  1. Localize the lesion site: The difference in thresholds between air bone conduction can distinguish between conductive deafness, sensory neural deafness, and mixed deafness;

  2. Quantify hearing loss: According to the World Health (WHO-1997) classification standard for hearing impairment, hearing loss is divided into mild (26-40 dB HL), moderate (41-0 dB HL), severe (61-80 dB HL), and profound (>81 dB HL);

  3. Guide the adjustment of hearing: The audiogram can directly map the gain requirements of hearing aids, such as those with a steep high-frequency decline requiring targeted compensation

2.Pure tone audiometry detailed explanation of the entire process

1. Pre-test Preparation

• Environmental Requirements:

  – Soundproof room background noise should be ≤30 dB(A-weighted), and the ambient noise should be regularly checked with a sound level meter;

  – Equipment Calibration: Hearing aids should be calibrated at least once a year to ensure that the frequency (±3%) and intensity (±2 dB) errors are within the standard range.

• Patient Communication and Evaluation:

  – Screening for contraindications: Patients with ear pain, sudden hearing loss in recent days, dizziness, otogenic discharge, etc., need to be referred to an otologist;

  – Collection of medical history: Including the duration of hearing loss, history of otological surgery, history of hearing aid use, etc., which should be recorded in the file.

2. Air Conduction Test (AC)

• Operation Steps:

  1. Wear headphones: Left ear with blue mark, right ear with red mark, to avoid confusion between left and right;

  2. Frequency test sequence:

     – Starting frequency: 1000 Hz (the frequency to which the human ear is most sensitive);

   – Order: 1000 Hz → 2000 Hz → 4000 Hz → 8000 Hz → Retest 1000 Hz → 500 Hz → 250 Hz → 125 Hz;

  3. Threshold Determination:

     – The method of reducing 10 and increasing 5: Reduce the sound pressure level by 10 dB when the patient hears the sound, and increase it by 5 dB when the patient does not hear it, repeat until the same intensity is heard twice;

     – Masking method: When the difference between the hearing of both ears ≥40 dB, masking noise (such as narrowband noise) needs to be applied to the better ear to avoid the interference of “shadow hearing”.

3. Bone Conduction Test (BC)

• Operation Points:

  – Place the bone conduction vibrator at the mastoid process, avoiding contact with the auricle, and avoid pressing the hair;

  – Test frequency range: 250 Hz ~ 4000 Hz (more sensitive to low frequency);

  – The principle of masking is the same as that of air conduction, but it should be noted that the bone conduction vibrator may cause vibratory tactile interference.

3. Common Technical Difficulties and Solutions

1.Testing for Children and Special Populations

• Game Audiometry: Suitable for children aged 3 to 5, improving compliance through games such as “Listen and Place the Blocks”;
• Elderly Patients: Shorten the duration of each test (10 minutes) to avoid hearing fatigue affecting accuracy.

2.Handling Abnormal Results

• Inter-Frequency Threshold Difference > 20 dB Perform additional half-octave frequency tests (e.g., 750 Hz, 1500 Hz, etc.);
• Medical history inquiry a clear history of noise exposure, suspected noise-induced hearing loss, test 3000 Hz, 6000 Hz;
• Abnormal Bone Con Threshold: Check the position of the oscillator, rule out middle ear lesions (such as otosclerosis).

3.Key Points for Interpretation of Audi

4.Practical Case Demonstration

Case 1: High-Frequency Sudden Decline Hearing Loss

• Test Results: Air conduction above 2000 Hz > 60 dB HL, bone conduction thresholds normal;
• Hearing Aid Adjustment Suggestions: Enhance high-frequency compensation combined with frequency shifting function.

Case 2: Conductive Deafness (Otitis Media)

• Test Results: Air conduction thresholds generally > 4 dB HL, bone conduction thresholds normal;
• Treatment Plan: Treat otitis media preferentially, reassess after recovery.

5.Extension: Combination of Pure Tone Audiometry and Hearing Aid Fitting

• Gain Calculation: Set the initial gain value of the aid based on the threshold values of each frequency according to the “1/2 Gain Rule”;
• Effect Verification: Evaluate the compensation effect through pure tone audometry after wearing the hearing aid (sound field test), and the target hearing threshold should be close to 25 dB HL.