measuring bone conduction with the sal technique · -frontal bone conduction with occlusion -sal...

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