MRL is acronym for minimum response level. MRL is referring to the supra-threshold stimuli where the children will respond appropiately. Please note that the MRL is not the patient hearing thresholds.

MRL can be useful especially in conditioning the children during the visual reinforcement audiometry testing. 

PLEASE CLICK THE IMAGE BELOW FOR UNDERSTANDING THE PROCEDURE

References: 
1) AUDIOLOGY TEST PROTOCOL For Klinik Audiologi & Sains Pertuturan Fakulti Sains Kesihatan Bersekutu Universiti Kebangsaan Malaysia Kuala Lumpur 2004

During pure tone audiometry testing (PTA), responses from the patient is very crucial in obtaining the correct patient's hearing threshold. The mistake from taking wrong responses from the patient will lead to wrong diagnosis of hearing level. That why, understanding the patient's responses is very important during PTA session.

 Situation where the patient give clear and consistent response during testing:

False responses can be divided into 2 categories:

1) False-positive response
Refer to the patient responds when he should not have responded.

Note: Please do non-stimulus trial to check for false positive response especially in pediatric cases. How? Just don't present the stimulus about 5 seconds to see whether the child wait for stimulus or not.

Situation where patient give false positive response:

Examples:
a) Patient confused by his tinnitus
b) Patient probably not understood the instructions.
c) It could be due to tactile stimulation or acoustic radiation.
d) Clinician presenting the stimulus very rhythmic since the patient can expect the tones at certain times.

2) False negative response
Refer to patient fails to respond when he should have responded.

Situation where patient give false negative response:This patient actually has normal hearing in both ears but he is malingering his response to get poor hearing result.

Examples:
a) Equipment problems (ex: the stimulus cannot be presented at the headphone cord was faulty)
b) Clinician errors that can prevent a signal from reaching the patient (Clinician press the wrong button to present the signal).
c) Some elderly patient, they want to be very sure the signal is there before they will respond.
d) Malingerer patient (patient who trying to make their hearing to be worse for claim SOCSO)
e) Can be due to technical reasons ( collapsing ear canal and standing wave by presenting the pure tone signal through speaker) 

Air conduction testing

The air-conduction tests the entire ear system, the signal from the headphone need to be processed along the outer ear, middle, inner ear and auditory nerve pathway. Thus, all this parts need to be work  normally in order to make air conduction threshold to be normal. If something happen to one of this conduction system it will cause the air conduction threshold to be poor. Thus the air conduction testing is considered to test for both conduction and sensorineural mechanism. Meaning that the air conduction test the whole ear system.

Bone conduction testing

The bone-conduction tests only stimulate the cochlea and above. The signal by the bone conductor will directly stimulates the cochlea and bypassing the outer and middle ear system. Hence, bone conduction testing is considered to test only sensorineural mechanism.

As a deduction

The difference between the air and bone conduction is very important for audiologist to diagnose the type of hearing loss whether it considered to be normal, conductive, sensorineural or mixed hearing loss based on the air-bone gap (AB gap) after masking if needed.

TACTILE RESPONSES

Patient with profound hearing loss who unable to hear the signal being presented might still respond if they sense the vibrations that produced by the bone vibrator or earphones (Nober, 1970). The tactile responses usually occur at low frequencies where our skin is more sensitive to vibration. 

 

Tactile responses can cause 2 problems. 

First problem:

The tactile responses can give wrong impression to the patient's hearing thresholds. For example, the tactile threshold at 250Hz is at 80dB HL but patient actual hearing threshold would have been 90 dBHL or no response. 

Second problem:

The tactile response can create an artificial air-bone gap (A-B gap), thus a sensorineural hearing loss would appear to be mixed hearing loss. For example, suppose a patient should have 70 dBHL sensorineural hearing loss. A tactile response to bone conduction threshold at 40 dBHL could give wrong impression that patient would be have mixed hearing loss. Thus we need to ask the patient if the stimulus was heard (can diagnose as mixed hearing loss) or felt (can diagnose as sensorineural).

Reference: 

 1) Gelfand, S. (2009). Essentials of Audiology. (3rd Edition). New York, NY: Thieme.

Hi I'm back again,

Today I want to share about the selection of appropriate transducer during pure tone audiometry test (PTA) based on my experience in UKM Audiology Clinic.

Basically, our PTA have 3 different types of transducer that we can use in measuring the patient's hearing level (headphone, insert phone and free field). But, how we can choose the best transducer during the hearing test?

Note: Always be flexible in selecting your transducer and you must have a good reason why you choose that transducer in planning your test.

Please choose the headphone as your transducer if you face the situation below:

1) Patient with presented of ear canal atresia or anotia as well as severe ear canal stenosis.

2) Patient with revealed of excessive earwax.

3) Patient with active otitis media.

4) Patient with complaint of earpain or diagnosed with otitis externa.

5) Patient did not want to wear insert phone especially pediatric case. In some pediatric cases, they feel comfortable as fit with earphone even though we learn that insert phone is the comfortable transducer for most pediatric cases.

Please choose the insert phone if you face the situation below:

1) All cases with normal structure of outer ear.

2) Patient with presented of collapsing ear canal especially in elderly cases.

COLLAPSING EAR CANAL

3) Patient with small or abnormal structure of head that prevent us to use headphone as a transducer.

4) Pediatric cases as the insert phone give greater subject comfort.




Please choose the free field if:

1) Patient reluctant to use both headphone and insert phone especially non cooperative children.

2) To get the aided thresholds for the patient with hearing aids or cochlear implants.

3) Sometimes is good to condition the child using the free field first in order to show the parents how to get their children's hearing thresholds. 





 

References: 
1) Gelfand, S. (2009). Essentials of Audiology. (3rd Edition). New York, NY: Thieme. 
2) Katz, J., Medwetsky, L., Burkard, R. & Hood, L. (2009).Handbook of Clinical Audiology (6thEdition).Baltimore, MD: Lippincott, Williams and Wilkins.
3) http://www.rcsullivan.com/www/ears.htm#13.10

 








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