RHS 371 Audiology 1 Lecture 6 PDF

RHS 371 – Audiology I Lecture 6 Clinical Hearing Assessment Introduction to Pure Tone Audiometry (Audiometer & Testing Environment) Dr Ibrahim almufarrij Prepared by Ms Haifa Basri  Introduction The main disadvantage of TF tests is that they fail to qua...

RHS 371 – Audiology I Lecture 6 Clinical Hearing Assessment Introduction to Pure Tone Audiometry (Audiometer & Testing Environment) Dr Ibrahim almufarrij Prepared by Ms Haifa Basri  Introduction The main disadvantage of TF tests is that they fail to quantify the hearing loss, which leads to the development and introduction to Pure Tone Audiometry. The purposes of the hearing test; ̵ Find the type and extent of hearing loss. ̵ Develop a habilitative and rehabilitative plan to deal with the impact of this hearing loss. To meet these purposes, accurate performance and interpretation of hearing tests are essentials Reliability of any test depends on collaboration between different factors including calibration of equipment, patient performance, and examiner qualification. Pure tone hearing tests performed using Audiometer  Audiometer It’s a basic tool used to evaluate the auditory function of the patients. It’s an electronic device that produces and delivers sounds to the patient. Using the audiometer allows the examiner to: ̵ Know precisely what is presented to the patient. ̵ Ensure the consistency of the sound presented.  Basic Audiometer components and their functions Power switch: Controls the electrical supply to the instrument, usually there is an indicator whether the device is on or off (light). Stimulus dial: Button for presenting the stimuli once (manually). Interrupter: Button that presents the signal to the patient continuously, this should be either in (on) or (off) mode. Frequency control: It allows sweeping between different frequencies for testing. ̵ Most audiometers include the frequencies: 125, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 6000, and 8000 Hz. Stimulus/tone mode switch: To change between different tone types (continues (pure), pulsed, or warble “frequency modulated-FM”).  Masking control: Introduces the needed noise 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 corresponds to a specific SPL. ̵ For example, setting the attenuator at 45 dB HL, means sound coming out of the earphone has 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 50-70 dB HL for bone conduction (some types of equipment might differ slightly). The output selector or transducer: Directs the signal to the Right or Left ear or to the bone vibrator. ̵ Transducers are either Supra-aural earphones, Circum-aural earphones, Insert earphones or Bone conduction vibrator.  Transducers 1. Supra-aural earphones/ Circum-aural: It is known as that because the earphone/cushion is worn over the ear. 2. Inserts: It has an elastic earpiece that can be deeply inserted into the external auditory canal. 3. Bone vibrator: It is usually held against the mastoid process by a spring-like headband. Inserts have advantages over supra-aural headphones: 1. Attenuate the background noise more. 2. More directionality of signals toward TM.  Audiometer types based on the number of channels Audiometers can be: 1. Single-channel. 2. Two channels. Two-channel audiometers are more common. In a two-channel audiometer, the second channel is used to generate the noise whenever masking is needed.  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 portable, easy to move from one place to another. It’s screener, widely used for screening purposes. Pure tone Audiometer  Audiometer types based on its functions 2- Clinical Audiometer (Diagnostic): It includes all features of the pure-tone audiometer plus additional collections to perform more sophisticated tests using tone or more varied signals. It also includes a microphone, inputs for tape and CD players that are used to present recorded tests, a patient’s responding mic, an intercom system, a patient response signal, a computer interface….etc It provides higher frequency testing in the 8000 to 16000Hz range, known as (Extended High-Frequency Audiometer). 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. 5. Any combination of these. Clinical Audiometer  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 is enough to hear a 1000 Hz tone. Refer to the table below to see the normal threshold SPLs.  Normal hearing level in SPL (Jack Katz, Handbook of Clinical Audiology, 7th edition) Freq. 125 250 500 750 1000 1500 2000 3000 4000 6000 8000 Ear- phon e TDH- 13. 47.5 26.5 8.5 7.5 7.5 11.0 9.5 10.5 13.5 13 49/50 5 11. TDH-39 45.0 25.5 8.0 6.5 7.0 9.0 10.0 9.5 15.5 13.0 5 ER3-A 26.5 14.5 6.0 2.0 0.0 0.0 2.5 2.5 0.0 -2.5 -3.5  Hearing Level These values are considered Normal Reference Values or more technically Reference Equivalent Threshold Sound Pressure Levels (RETSPLs). They are the physical intensities needed by normal people to just hear a sound. 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 reference values instead. As all of these values indicate that the sound is just barely audible, they are equally audible, they are heard the same, so we can say they have the same hearing level.  What is the Hearing Level? As these reference values are the softest sound that can be heard, they correspond to the hearing level (HL) of Zero (Reference SPL = 0 dB HL) For instance, At 250 Hz (TDH-49/50)>> 26.5 dB SPL = 0 dB HL, At 2000 Hz (ER3-A) >> 2.5 dB SPL = 0 dB HL.  What is the Hearing Level? As a result, 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 using TDH-49/50 Hz means (55 + 13.5 = 68.5 dB SPL) was internally built. 66 dB SPL at 2000 Hz using inserts means ( 66 - 2.5 = 63.5 dB HL) From dB HL to dB SPL ----- add From dB SPL to dB HL ----- subtract  Sensation Level The intensity level above the threshold level. For example, if the tone is presented at 30 dB SL, means 30 dB above the patient threshold. If the patient threshold is 10 dB HL and we need to present a tone at 10 dB SL, the presentation level is 20 dB HL.  Audiometer calibration Calibration is necessary to ensure that: ̵ The audiometer produces 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, interference, and distortion. Four types of audiometer check/calibration schedules: ̵ Daily listening check. ̵ Psychoacoustic check. ̵ Periodic electronic calibration. ̵ Exhaustive electronic calibration.  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. These checks should be recorded. If any faults are noted, the equipment shall not be used until the fault is corrected. Steps for Daily listening check: In the morning after warm-up (5-10 min) The signal is checked at various intensities (High = 60 dB for AC and 40 dB for BC, Low = 10-15 dB for both) and at all frequencies. Check that the masking noise is approximately correct at all frequencies through both earphones, at a level of 60 dB HL. Check: ̵ Transient clicks or distortion (undesired acoustic signal). ̵ The 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.  2.Psychoacoustic Check It’s done at least once a month. The output from the audiometer is checked. This process is done either with: A. Psychoacoustic (biological) check with a normal-hearing human. B. Psychoacoustic (electro-acoustical) check with a sound level meter. A. 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 500-6000 Hz, the other subjects should be checked. 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. B. Electro-Acoustical Check Performed with a sound level meter and a coupler. The stimulus is presented into a standard 2-cc coupler via an insert earphone of the audiometer. OR Measurements are obtained directly from the audiometer at a fixed attenuator setting. The SPL is measured and compared with the expected ANSI 1996 reference equivalent threshold SPL value. If the difference is > 3 dB, the audiometer should require electronic calibration.  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. 2 CC- coupler and Sound Level Meter  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 S3.6- 1996  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.  Testing environment Sound-isolated chambers. Audiological tests are recommended to be performed in specially constructed, sound-treated (isolated) chambers known as booth or anechoic chambers. Audiological booths are either; Single room. Two-room (patient room and control room).  Single room audiometer Either just the patient inside the booth while the examiner and the equipment outside. OR Both the examiner and the patient are in the same sound- treated room. Recommended test setting  Two-room audiometer (patient room and control room) The patient room needs to be as large as possible: ̵ To fit any accompanied person while testing children or elderly. ̵ To have extra space for a wheelchair. ̵ Important for sound-field testing. The tester’s room needs to be large enough to fit the equipment, the tester, and an observer. Windows provides visual communication between both rooms. Electrical connections are essential to direct the signal from the audiometer to the transducers. A talkback system with a microphone, amplifier, and speaker or earphone is important for examiners to hear their patients when they speak.  Room dimensions should account for door opening and closing, and wheelchair access. The room walls are usually either single-walled or double-walled with dead air space in between, to give more isolation. The window between the patient and the tester should be made of multiple pans of glass with dead air spaces in between (for better Isolation) and moisture-absorbing materials, to absorb any accumulated moisture. A sound-muffled, to reduce the ambient noise. Ventilation system used to allow air entrance and escape. Condescend light is preferable to use to avoid any noisy sound. However, fluorescent light could be used if its noise source is built outside the booth. Subject’s face shall be clearly visible to the examiner. Two room set up Recommended test setting  Noise Level The 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. The ambient noise shall not exceed 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. Check the table below for recommended noise levels using different earphones. Questions?