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MEASURING
BONE CONDUCTION WITH THE SAL TECHNIQUE
William DAMMAN oto-vestibular lab
E.N.T. department / A.Z. St.-Jan BRUGGE
N.O.K.-afdeling St.-Janshospitaal. (1935 – 1977)
Vibrator position in bone conduction threshold measurements :
- vibrator on test ear mastoid :
- relative mastoid bone conduction
- RAINVILLE method
- vibrator on forehead :
- frontal bone conduction with occlusion
- SAL technique
SAL test :
- described by JERGER & TILLMAN (1960)
- eliminates associated masking problems
(cfr. ”masking dilemma”)
- vibrator on forehead
- headphones on both ears
- same position for L- and R-bone conduction
threshold measurement
- present a fixed NB-noise (*) by means of a bone vibrator placed at the forehead
x dB NB-noise * = x dB NB-noise
- in a normal hearing person the AC threshold will be shifted by … dB
x dB NB-noise * = x dB NB-noise
AC threshold = 0 dB = 40 dB new AC threshold = 40 dB
- by applying the same NB-noise intensity (x dB) for the other BC test frequencies,
we become a set of normal AC threshold shifts
- repeat these measurements in 10 normal ears and obtain a mean AC threshold shift for all BC test frequencies,
35 45 40 30 40 dB
- repeat these measurements in 10 normal ears and obtain a mean AC threshold shift for all BC test frequencies,
35 45 40 30 40 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
- obtain AC thresholds for both ears
100 dB
= 40 dB
60 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
- present the same fixed NB-noise (x dB) as while collecting the normative data
100 dB
= 40 dB
60 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
= 30 dB
- obtain new AC thresholds for the BC test frequencies when this masking noise is present
100 dB
= 40 dB
60 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
= 30 dB
- patient’s threshold shift is compared with normal threshold shift
100 dB
= 40 dB
60 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
= 30 dB
- this difference is a measure of the sensorineural acuity level (SAL).
]
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
[
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
]
- we can use the SAL technique for
conductive hearing losses
sensorineural hearing losses
- the normal AC threshold shifts are also the max. BC thresholds that You can determine with this x dB NB-noise
50 dB ?
90 dB
= 40 dB
50 dB ?
= 0 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz 35 45 40 30 40 dB
- the normal AC threshold shifts are also the max. BC thresholds that You can determine with this x dB NB-noise
- adapt the x dB noise level to the hearing loss
50 dB ?
90 dB
= 40 dB
50 dB ?
= 0 dB
SAL (x dB NB-noise) 250 500 1000 2000 4000 Hz
x = 40 dB 35 45 40 30 40 dB
x = 60 dB 55 65 60 50 60 dB
Disadvantages of the SAL test :
- SAL-results do not always precisely agree with classical BC audiometry
- limited value in cases of severe sensorineural
hearing loss
Advantages of the SAL test :
- eliminates masking problems (cfr. ‘masking dilemma’)
- absence of concern over occlusion effect
- easier for young children than conventional
masked BC audiometry
- valuable cross-check for conventional
masked BC-audiometry
- SAL technique and functional hearing loss
Oto-vestibular lab AZ Sint-Jan Hospital BRUGGE
Janne DEDEYNE
Lore BLEYAERT Marie MUYLLE
William DAMMAN
