Air Conduction
Prior to a hearing test, these 3 landmarks should be viewable during otoscopy in a normal, healthy ear.
What are the cone of light, the malleus, pars flaccida (sometimes incus)
This is the interaural attention value expected using supra-aural headphones.
What is 40 dB
Right ear bone conduction stimulates these structures.
What is right ear outer middle and inner ear and simultaneous left ear outer, middle and inner ear.
For good agreement with a 45 dB PTA, the SRT should be:
What is 39-51
Excessive mobility on a tympanogram is typically identified through this measure.
What is increased compliance (admittance), identified as a Ad tymp
This type of transducer can limit the occlusion effect during AC testing.
What is insert headphones.
This type of noise is used for masking pure tones because it is most effective.
What is narrow band noise
The middle ear contribution to bone conduction is relatively minor, but can be explained in this way.
What is inertial. As the skull vibrates, the supporting structures function like springs. The inertial force of the ossicular mass creates extra fluid displacement within the cochlea.
Dynamic range is thought to be the patient's usable listening range. In contrast to normally hearing individuals, in patients with conductive hearing loss, the dynamic range is changed in this way:
What is shifted, but similarly wide. Conductive hearing loss means that the sounds like likely need to be louder (explaining the shift), but recruitment does not limit the max so the width is largely unaffected. This is in contrast to SNHL where the min and the max of usable range is altered.
This is a common cause of a Type B tympanogram with a large ear canal volume.
What is a perforated ear drum.
Lateralization to the right ear during the weber test is interpreted as:
What is better hearing in the right ear, or conductive hearing loss in the right ear.
This is how we identify the need to mask for air conduciton:
AC Test Ear – ________ > IA
what is the BC Nontest Ear
If the ear canal is occluded, bone conducted SPL is changed in this way.
What is increased; the SPL is increased because of the occlusion effect. Here the occlusion traps predominately low frequency sound in the ear canal and often creates the sensation of increased loudness.
Using the 40 dB method, for a patient with a 45 dB SRT, WRS should be assessed at this level.
What is 85 dB.
Type B tymp with abnormal low ECV might be explained how:
What is probe placement. Here the probe may be against the canal wall so volume cannot be measured, and therefore compliance cannot be determined or is absent.
Flat SNHL, PTA = 55. This is the likely degree
What is moderate.
2Khz air conduction: R: 70, L: 10
2Khz bone conduction: R: 60, L: 10
This is the initial AC masking level noise in the NTE.
What is 20 dB HL.
Initial AC masking level calculation = AC Nontest ear + 10 dB
Here that would mean 10+10 = 20
Loudness growth is different between AC and BC stimuli in this way.
What is retrocochlear lesions and neural presbycusis
The cause of significant negative ME pressure and TM retraction might be explained this way:
What is eustachian tube dysfunction. If the ET is blocked, it prevents air from entering the middle ear to equalize the pressure with the outside air.
What is conductive; here the fluid restricts TM mobility and sound energy transfer is reduced from the middle ear space to the cochlea when measured via air conduction. This loss of sound energy is described by increased (worsened) air conduction thresholds. In contrast, bone conduction will likely not be affected and will be within normal limits given that most of the bone-conducted signal bypasses the immobilized TM.
500 hz air conduction: R: 60, L: 20
500 hz bone conduction: R: 40, L: 10
This is the initial BC masking level noise in the NTE.
What is 40 dB of masking in the left ear.
Initial BC masking level calculation = AC Nontest Ear +10 dB +OE
Here that would mean 20+10+10(which is the OE value at 500)
Air bone gaps are different for patients with outer ear occlusion in comparison to patients with middle ear disorders because:
What is the presence of the occlusion effect. For an occluded ear, the ABG can be explained by the occlusion effect (trapped LF sounds). In this instance the bone line is improved primarily.
For a middle ear disorder (e.g., otosclerosis), the ABG can be explained by increased stiffening of the TM and ossicles. Here the AC line is worsened primarily though in some cases the BC line an also be affected.
Dubno's WRS predictions use this information to predict word recognition ability.
What is PTA. Dubno's research defined confidence limits for maximum word-recognition scores (PBmax) to help determine if a patient's score is unusually low for their degree of hearing loss. Scores outside this region might be explained by additional pathology that requires investigation.
Changes in stiffness influences the transfer of energy through the middle ear in this way.
What is shifting resonant frequency. If stiffness is increased, this will shift the resonant frequency higher (lower frequencies will be affected); if stiffness is decreased, this will shift the resonant frequency lower (higher frequencies will be affected).