-
Reliability of a hearing test (4 factors)
calibration, test environment, examiners expertise, patient performance
-
Pure tone audiometry
- tests hearing sensitivity by air and bone conduction
- freq range 125-8000
- intensity range -10 to 120 db HL
-
Test environment
background noise may elevate threshold (can insert headphones or use a sound treated chamber, don't try to measure 0 dB HL)
-
Patient's role: Variables affecting the test
age, education, willingness, motivation, IQ
-
Threshold of hearing sensitivity
the lowest level needed for a person to detect the presence of a signal 50% of the time (barely audible tone)
-
basis for pure tone audiometry
establish auditory thresholds at different frequences
-
two types of false responses
- false negatives: patient may have forgotten their role or misunderstood, can suggest hearing is worse than it is, malingerer
- False Positive: can be frustrating, overly motivated patient
-
patient's position during test
- patient should not be able to see the clinician
- -seat the listener at a right angle to the clinician
-
Air conduction Audiometry
- can only specify the degree of hearing loss not the type
- -
-
Modified Hughson Westlake Method: a compromise between accuracy and time
- measure a threshold for each frequency to get a base
- 1) choose a freq
- 2) adjust the dB to see when they can hear it.
- 3) go up by 10 then once they hear it go down by 5dB to see if they can hear it
- 4)if not then go back up to the original intensity level that they could hear and that becomes your threshold
-
Bone conduction Audiometry
- determines hearing levels at the cochlea
- when used with AC thresholds they can tell us sensorineural hearing loss, conductive hearing loss, mixed hearing loss
-
Why transducer on mastoid process? (2)
- 1. tones are louder at the MP in NH listeners
- 2. each mastoids nearness to the test ear (although we know that it does not just test this one ear but both)
-
masking threshold
40dB, anything higher will cross over to the opposite ear
-
when to mask?
- -when air bone gap is 10dB or greater
- -if the difference between ears is more than 40dB
- -mask the better ear
-
no air bone gap
sensorineural
-
conductive loss
air threshold is out of normal range but bone is within normal range
-
mixed loss
air and bone are both out of normal range, and there is an air bone gap
-
O
right unmasked AC 40 dB threshold
-
X
left unmasked AC 40 dB threshold
-
-
-
-
-
-
-
-
Air reading
can only read up to 100dB on the audiometer
-
bone reading
can only go up to 70dB on the audiometer
|
|