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Immittance Testing

PostedNovember 21, 2024
UpdatedNovember 21, 2024
Bysageaudiology_mqc6dy

Immittance Testing

Overview

Immittance testing evaluates middle ear function through tympanometry and acoustic reflex measures. This protocol establishes standards for conducting these measurements.

Equipment Requirements

  • Calibrated immittance bridge
  • Probe tips of various sizes
  • Disposable specula
  • Recording system
  • Sound-treated environment

Pre-Test Procedures

  1. Equipment Check
    • Daily calibration verification
    • Probe tip inspection
    • Air pressure system check
    • Leak detection test
  2. Patient Preparation
    • Otoscopic examination
    • Clear instructions on:
      • Staying still
      • Avoiding swallowing/talking during test
      • Expected pressure sensations

Testing Protocol

Tympanometry

  1. Probe Insertion
    • Select appropriate probe tip size
    • Obtain hermetic seal
    • Verify probe placement stability
  2. Measurement Parameters
    • Probe tone: 226 Hz (adults)
    • Pressure sweep: +200 to -400 daPa
    • Sweep rate: 50 daPa/sec
    • Direction: positive to negative pressure
  3. Recording Sequence
    • Initial sweep
    • Repeat if poor seal/noise
    • Document peak pressure, compliance, gradient

Acoustic Reflex Testing

  1. Threshold Measurement
    • Initial presentation at 95 dB HL
    • Test frequencies: 500, 1000, 2000, 4000 Hz
    • Observe for 0.02-0.15 ml deflection
    • Bracket threshold in 5 dB steps
  2. Reflex Decay
    • 10-second stimulus at 10 dB SL
    • Monitor amplitude change
    • Test at 500 and 1000 Hz

Documentation

  • Record tympanogram type (A, As, Ad, B, C)
  • Note peak pressure points
  • Document acoustic reflex thresholds
  • Record presence/absence of decay
  • Note any procedural modifications

Measurement Parameters

  1. Normal Values
    • Peak pressure: ±50 daPa
    • Static compliance: 0.3-1.4 ml
    • Gradient: 50-110 daPa
    • Ear canal volume: 0.6-2.0 ml
  2. Pediatric Considerations
    • 1000 Hz probe tone < 6 months
    • Modified compliance ranges
    • Faster sweep rates

Quality Control

  • Daily biological checks
  • Regular calibration verification
  • Document ambient conditions
  • Equipment maintenance log

Special Considerations

  1. Contraindications
    • Recent ear surgery
    • Acute otitis externa
    • Perforated tympanic membrane
    • Excessive cerumen
  2. Modifications
    • PE tubes present
    • Young children
    • Tympanic membrane abnormalities

References

  • ASHA Guidelines for Immittance Testing
  • ANSI S3.39 Specifications for Instruments to Measure Aural Acoustic Impedance
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