otometrics MADSEN Midimate 622, Руководство пользователя

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6. PURE TONE AUDIOMETRY
6.1 AIR CONDUCTION THRESHOLD MEASUREMENTS
Pure tones for threshold measurements are selected by the frequency
switch, the digital display showing the frequency selected. In addition, the
following functions are available via the softkeys:
Continuous, Pulsing and Warble Tones (Softkey 2)
Masking On/Off (Softkey 4)
Via Options Menu (Softkey 3):
1.5 second minimum tone presentation (Softkey 1)
1 dB / 5 dB Resolution (Softkey 2)
Data Transfer or Printout (Softkey 3)
HL Lock On/Off (Softkey 4)
Audible Patient Response Signal On/Off (Softkey 5) .
The test normally starts at 1000 Hz in the better ear and continues with the
higher frequencies. Then the test is continued on 750-500-250 and 125 Hz.
The same is repeated for the opposite ear. If the difference between the two
ears is more than 55-60 dB, the test should be repeated using masking.
6.2 THE NEED FOR MASKING
The need for masking in air conduction tests may be explained as follows:
In addition to providing air conducted sound to the outer ear canal, the
moving-coil earphone also presents a vibrating mass in contact with the
head. The earphone behaves like a bone vibrator and will conduct sound
through the skull.
If the air conduction intensity in the earphone is 40-60 dB, it may be expected
that the earphone will also convey bone-conducted sound to the skull at a
level corresponding to approximately 0 dB. In relation to the two ears, the
attenuation or loss through the skull is negligible (only 2-3 dB). In certain
circumstances, therefore, the patient may respond to a pure tone signal
applied by the earphone to one ear whereas it is actually being heard in the
opposite ear by bone conduction. The application of masking as described
ensures that the untested ear is not confused with the tested ear. On the
assumption that the nature of the patient's hearing loss is unknown, the
masking routine is essential.
6.3 AIR CONDUCTION THRESHOLD MEASUREMENTS WITH MASKING
To enable Masking, select the following from the Select Function Menu:
Tone, Air, Left and the following display will appear:
(Tone, Air, Left) Masking ?:
No Mask Air Ipsi Bin.S+M
MIDIMATE 622 OPERATION MANUAL 6. Pure Tone Audiometry
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