INTRODUCTION TO PURE (AUDIOMETER & TESTING ENVIRONMENT) TONE AUDIOMETERY. By Mrs. Wedad Alhudaib with many thanks to Mrs.

Transcription

1 INTRODUCTION TO PURE TONE AUDIOMETERY (AUDIOMETER & TESTING ENVIRONMENT) By Mrs. Wedad Alhudaib with many thanks to Mrs. Tahani Alothman

2 Topics : This lecture will incorporate both theoretical information as well as practical demonstration on the following topics: What is the audiometers and its components Audiometer basic types What is the concept of Hearing level and how does it correlate with Reference Equivalent Threshold Sound Pressure Level Audiometer Calibration Testing environment

3 INTRODUCTORY POINTS The main disadvantage of TFs tests is that they fail to quantify the hearing loss The purpose of hearing test is Help to find the type and extent of hearing loss Develop habilitative and rehabilitative plan to deal with the impact of this loss

4 To meet this purpose, accurate performance and interpretation of hearing tests are essentials Reliability of any test is depend on collaboration between different factors like calibration of equipment, patient performance and examiner difficulty Pure tone hearing tests performed using Audiometer

5 AUDIOMETER It s the basic tool used to evaluate the auditory function of the patients. It s an electronic device that produces and delivers sounds to the patient. It allows precise knowing of what presented to the patient and ensures the consistency of the sound presented.

6 BASIC AUDIOMETER COMPONENTS Power switch: Controls the electrical supply to the instrument, usually there is an indicator whether the device is on or off (light ). Interrupter: The button that presented the tone to the patient, this should be either in on or off mode.

7 Stimulus dial: Button for presenting the stimuli once. It should be pressed manually. Frequency control (dial ): It allows sweeping between different frequencies for testing. Most audiometers include the frequencies 125, 250,500,750,1000,1500,2000,3000, 4000, 6000 and 8000Hz.

8 Stimulus or tone mode switch: Used to change between different tone types (continues, pulsed or warble frequency modulated ). Masking control: Allow introduction noise needed for masking Attenuator or hearing level control: Controls the intensity of the test signal. Unlike the volume control, the attenuators are calibrated I.e. each level correspond to specific SPL.

9 For example, setting the attenuator at 45 db HL, means sound coming out of the earphone have a SPL that stands for 45 db HL. Most audiometers have attenuators that are calibrated at 5 db steps. The intensities range from as low as -10 db HL up to 120 db HL for air conduction and about db HL for bone conduction.

10 The output selector or transducer: To direct the signal to the Right or Left ear or to bone conduction vibrator. Transducers are either supra-aural earphones, insert earphones or bone conduction vibrator.

11 TRANSDUCERS 1. Supra-aural earphones: It known as that because the earphone/ cushion combination is worn over the ear. 2. Inserts: It has an elastic earpiece that can be inserted into the external auditory canal. 3. Bone vibrator: It is usually held against the mastoid process by spring like headband.

12 AUDIOMETER TYPES BASED ON NUMBER OF CHANNELS Audiometers can be either a singlechannel or two channels. Tow channels is more common. In two channels audiometer, the second channel used to generate the noise whenever masking needed.

13 AUDIOMETER TYPES BASED ON ITS FUNCTIONS 1- Pure tone Audiometer It s able to produce pure-tones at certain frequencies. It contains the basic Audiometer components. It s easy to move from one place to another (portable) It s widely used for screening purposes

14 PURE TONE AUDIOMETER

15 2- Clinical Auidometer (Diagnostic) It includes all features of Pure-tone audiometer plus additional collections to perform more sophisticated tests using tone or more varied signals. It also includes microphone, inputs for tape and CD players that used to present recorded tests, patient s responding mic, an intercom system, a patient response signal, computer interface.etc

16 It provides higher frequencies testing in the 8000 to 16000Hz range, known as (Extended high frequency audoimeter). It provides a wider variety of output transducers: 1) Right/ Left supra-aural earphone 2) Right/Left inserts 3) The B/C vibrator 4) Loudspeakers and 5) Any combination of these.

17 CLINICAL AUDIOMETER

18 HEARING LEVEL Our actual hearing sensitivity in decibels of SPL is not the same at each frequency. For example, a normal hearing person needs 26.5 db SPL just to hardly hear a 250 Hz tone. However, 7.5 db SPL to just hear a 1000 Hz tone. Refer to the table below to see the normal threshold SPLs.

19 NORMAL HEARING LEVEL IN SPL

20 These values considered as normal reference values or more technically Reference Equivalent Threshold Sound Pressure Levels (RETSPLs). They are the physical intensities needed by the normal people to reach the threshold of hearing.

21 So, the person with hearing loss needs higher SPLs than the normal ones to just hear the sound; the more threshold deviation from these values, the greater hearing loss the patient has. Since It s difficult to have different values at different frequencies like those SPLs, there should be a reference values instead.

22 As all of these values indicate that the sound just barely audible, they are equally audible, they heard the same, so we can say they have same hearing level.

23 SO, WHAT IS THE HEARING LEVEL? As these reference values are the softest sound that can be heard, they are corresponding to the hearing level (HL) of Zero ( Reference SPL = 0 db HL) For instances, At 250 Hz >> 26.5 db SPL = 0 db HL, At 2000 Hz >> 11 db SPL = 0 db HL.

24 As a results all of these reference values are built in the audiometer circuit so, when any value dialed in db HL, the audiometer automatically adds these reference values to produce the intended intensity. For example, presenting a 55 db HL tone at 500 Hz means ( = 68.5 db SPL ) was dialed.

25 SENSATION LEVEL The intensity level above the threshold level For example, if tone presented at 30 db SL, means 30 db above patient threshold If patient threshold is 10 db HL and we need to present a tone at 10 db SL, the presentation level is 20 db.

26 AUDIOMETER CALIBRATION o Calibration is necessary to ensure that: The audiometer is producing a pure tone at the specified frequency and intensity The stimulus is present only in the earphone to which it is directed The stimulus is free from unwanted noise, the interference, and distortion

27 CALIBRATION TYPES Four types of audiometer check/calibration schedules: Daily listening check Psychoacoustic check Periodic electronic calibration Exhaustive electronic calibration

28 1.Daily Listening Check Routine and subjective tests They should be carried by someone with sufficiently good hearing to detect any faults. They should be carried out in a normal test room with the equipment set up as installed.

29 These checks should be recorded. If any faults noted, the equipment shall not be used until the fault corrected.

30 STEPS FOR DAILY LISTENING CHECK In the morning after warm up (10 min) Signal is checked at various intensities ( High = 60 db for AC and 40 db for BC, Low = db for both) and at all frequencies Look for transient clicks or distortion (undesired acoustic signal)

31 Ensure that signal is delivered to the correct earphone No cross talk is present Cross talk: when the signal intended for exclusive routing to one earphone is also routed to the other

32 2.PSYCHOACOUSTIC CHECK It s done at least once per month The output from the audiometer is checked This process is done either with: A. Psychoacoustic (biologic) check B. Electro-acoustical calibration check with a sound level meter

33 A. PSYCHOACOUSTIC (BIOLOGIC) CHECK Obtain baseline thresholds on 3-5 normal hearing individuals who will be available for comparison testing throughout the year If on the monthly check, a threshold difference > 5 db HL is found for one of the individuals for any test frequency between Hz, the other subjects should be checked

34 If a shift > 5 db HL in the same direction is confirmed, an electronic calibration of the audiometer is required Monthly results should recorded in a form

35 B. ELECTRO-ACOUSTICAL CALIBRATION CHECK Performed with sound level meter and real-ear coupler Measurements are obtained directly from the audiometer earphone at a fixed attenuator setting and compared with the expected ANSI 1996 reference equivalent threshold SPL value

36 If the difference is > 3 db, the audiometer would require electronic calibration

37 TERMS Sound level meter: An electronic instrument designed to measure sound intensity in db in accordance with an accepted standard ANSI(American National Standards Institute): An association of specialists, manufacturers, and consumers that determines standards for measuring instruments, including audiometers

38 3.PERIODIC ELECTRONIC CALIBRATION It should be done at least one time each year To make sure that the audiometer is meeting the minimum standards defined by ANSI S

39 4.EXHAUSTIVE ELECTRONIC CALIBRATION It s done Every 5 years More comprehensive than the periodic electronic calibration Includes testing of all settings on the frequency and intensity dials Replacing switches, cords, earphone drivers and cushions

40 TESTING ENVIRONMENT Noise Level Noise level needs to be low enough to allow the threshold measurement down to 0 db HL at each tested frequency by both air and bone conduction.

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42 SOUND-ISOLATED CHAMBERS Audiological tests are performed in specially constructed, sound-treating ( isolated ) chambers known as booth or anechoic chambers.

43 Audiological booths are either Single room It s either just the patient inside the booth while the examiner and the equipments outside OR Both the examiner and the patient in the same sound-treated room.

44 One room setup

45 ONE ROOM SETUP

46 Two-room, patient room and control room. The patient room needs to be as large as possible, important for sound field and paediatrics testing. The tester s room needs to be large enough to fit the equipments, tester and an observer. Windows provide visual communication between both rooms

47 Electrical connections are essentials to direct the signal from audiometer to the transducers Talkback system with microphone, amplifier and speaker or earphone is important for examiners to hear their patients when they speak

48 Two room set up

49 TWO ROOM SET UP

50 CONT. TESTING ENVIRONMENT Room dimensions should account for door opening and closing and wheelchair access. The room walls are usually either single walled or doubled wall with dead air space in-between and it gives more isolation.

51 The window between the patient and the tester should be made of multiple pans of glass with dead air spaces in between and moisture observing materials. A sound-muffled ventilation system used to allow air entrance and escaping.

52 Condescend light is preferable to use to avoid any noisy sound. However, fluorescent light could be used if it s noise source built outside the booth. Subject face shall be clearly visible to the examiner.

53 The ambient noise shall not exceeds 35 db (A), otherwise test should not be conducted. db(a), it s a measurement that excludes the effects of lower frequencies and are especially useful in noise level measurements.