Impedance Audiometry Dnb Ent 2011, 2018
- 1. Discuss the principle of Impedance Audiometry
- 2. Basic Principle:
- 3. Static Acoustic Immittance or Static Acoustic Compliance:
- 4. Procedure:
- 5. Tympanometry:
- 6. Describe different types of curves of impedance audiometry and its importance in clinical practice.
- 7. Types of Tympanogram
- 8. Types of Tympanogram details
- 9. Briefly describe the stapedial reflex pathway. What are the applications of Impedance Audiometry in otological practice​1,2​?
- 10. B. Non-Acoustic reflex pathway:
- 11. What are the applications of Impedance Audiometry in otological practice​2​?
Discuss the principle of Impedance Audiometry. Describe different types of curves of impedance audiometry and its importance in clinical practice. Briefly describe the stapedial reflex pathway. What are the applications of Impedance Audiometry in otological practice?
Discuss the principle of Impedance Audiometry
Basic Principle:
Th basic principle of impedance audiometry (IA) is that of measuring the amount of current require to maintain a specified SPL in cavity. The system works on the principle that in a hand walled cavity has calibrated tone applied to it. The SPL developed inside the cavity depends on the volume of that cavity. If the cavity volume is larger, the intensity of the tone most be large to obtain the given SPL within the cavity. If the cavity size is smaller, the intensity of the tone required to obtain the same SPL will be smaller.
Working of Impendence system (Figure):
All the impedance system has three units.
- To produce acoustic signal
- To induce and vary the air pressure
- To analyse or measure the pick-up reflected sound energy in the form of SPL or acoustic immittance or electrical current equivalent
All the pressure system or the manometers have the facility to induce air pressure from positive to negative pressure ranges changing from +200dapa to -300 or -400 dapa pressure. Few systems have extendable pressure manometer up to -600 dapa.
The standard probe tone signal generated through immittance system is 226Hz. A low frequency probe tone of 85dB or 90dBSPL. Some system even has additional probe tone frequencies. Such as 660Hz, 800Hz, and 1000Hz of 75, 77, and 78dBSPL. (Madsen Zodiac,1980 Immittance system consists of 226Hz probe tone and Maico MI34 tympanometer. GSI 33 system has extra high frequency probe tones).
The third unit of basic impedance audiometer consist of a sensitive microphone to pick up the SPL reflected back and convert into equivalent electrical signal through the rectifier and feed it to analysing system which makes synchronized comparison of applied electrical signal and the reflected electrical signal through a balanced meter system. The difference between these two SPL (cc, ml or microliters of c3) are constantly displayed by the compliance meter system
The reflexes eliciting system i.e ipsilateral is generated by the same signal generator and delivered through the same probe opening in majority of equipment but in few, separate fourth opening within the probe is reported. A contralateral reflex signal generation is through separate audiometer oscillator circuit.
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