9510 Textbook Readings PDF

9510 Textbook Readings ====================== Week 1 ------ *pp 135-136 (Ch 6 intro, The Case History) \ pp 30-32 (General Overview)\ pp 33-35 (Pinna, External Auditory Meatus, Tympanic Membrane)\ Chapter 5 (Hearing threshold, Comparing Air- and Bone-Conduction Thresholds; Basic Audiogram Interpre...

9510 Textbook Readings ====================== Week 1 ------ *pp 135-136 (Ch 6 intro, The Case History) \ pp 30-32 (General Overview)\ pp 33-35 (Pinna, External Auditory Meatus, Tympanic Membrane)\ Chapter 5 (Hearing threshold, Comparing Air- and Bone-Conduction Thresholds; Basic Audiogram Interpretation; Supplemental Pure Tone Tests)* **[Chapter 6: Auditory System and Related Disorders:]** - Hearing impairments are caused by abnormalities of structure and/or function in the auditory system lesions - Hearing loss: manifestations of a lesion somewhere in the ear, as are other symptoms such as pain, ringing in the ears, and dizziness - Interested in: - Nature of the lesion - Severity - Etiology (cause) - Location - Time course (including when it began and how it has progressed). - Idiopathic: specific underlying cause cannot be identified. - Congenital: Disorder is present at birth - May be caused by a genetic problem or other factors that interfere with normal embryological development or occur during the birth process. - Hereditary or genetic: disorder is transmitted by the genetic code that the child inherits from their parents; - Genetic disorders are often present at birth, but others are delayed - Acquired: matter of causation. - Nature of a hearing loss goes hand-in-hand with that of the lesion same cannot always be said about severity and time course. - EX. middle ear infections cause conductive losses, but the magnitude of the hearing loss is not clearly related to the severity of the infection. - EX. hair cell damage due to noise exposure and/or aging is typically underway long before the patient notices (or at least admits to) a hearing problem. - Prelingual impairments occur before the development of speech and language, and have a catastrophic effect serious communicative impairments and interference with academic development. - Post lingual losses develop after speech and language have been established, and have a relatively smaller effect. - Earlier the onset, and the longer the child is deprived of auditory stimulation, the more the loss will interfere with speech and language development **[Case History:]** - Case history includes information about the patient that provides insight into their auditory status and related factors - Contributes to the development of a diagnostic impression, a plan for audiological remediation, and appropriate referrals to other professionals. - Involves obtaining a complete picture of the patient's auditory and communicative status, historical information about factors known to influence or to be related to auditory functioning, and the patient's pertinent medical and family history - Case history is obtained is often a matter of personal style and interviewing skills. - Formal "case history form" that the patient completes in advance, which is then reviewed and discussed with the patient. - Other extreme involves conducting an open-ended interview, - Desirable for the evaluation process to include a functional assessment (self-assessment) scale completed by the patient and/or a parent or spouse **[Chapter 2: Anatomy and Physiology of the Auditory System]** **[General Overview:]** - Auditory system: ear and its associated neurological pathways Anatomical Planes: - Outer ear: pinna and ear canal. - Middle ear: air-filled cavity behind the eardrum, also known as the tympanic cavity. - Notice that the middle ear connects to the pharynx by the Eustachian tube. Medial to the middle ear is the inner ear. - Ossicular Chain: Three tiny bones (malleus, incus, and stapes), known as the ossicular chain, act as a bridge from the eardrum to the oval window, which is the entrance to the inner ear  - Inner ear contains the sensory organs of hearing and balance. - Inner ear: - composed of the vestibule, which lies on the medial side of the oval window - snail-shaped cochlea anteriorly; - three semicircular canals posteriorly. - Entire system is a configuration of fluid-filled tunnels or ducts in the temporal bone, which is descriptively called the labyrinth. - Labyrinth, which courses through the temporal bone, contains a continuous membranous duct within it, so that the overall system is arranged as a duct within a duct. - Outer duct contains one kind of fluid (perilymph) - Inner duct contains another kind of fluid (endolymph). - Cochlea contains: - Organ of Corti: has hair cells that are the actual sensory receptors for hearing - Balance (vestibular) system: semicircular canals and two structures contained within the vestibule, called the utricle and saccule. - Sensory receptor cells are in contact with nerve cells (neurons) that make up the eighth cranial (vestibuloacoustic) nerve - Connects the peripheral ear to the central nervous system - Auditory branch of the eighth nerve is often called the auditory or cochlear nerve, - Vestibular branches are frequently referred to as the vestibular nerve - Eighth nerve leaves the inner ear through an opening on the medial side of the temporal bone called the internal auditory meatus (canal), and then enters the brainstem. - Auditory portions of the nerve go to the cochlear nuclei and the vestibular parts of the nerve go to the vestibular nuclei. - Hearing process: - sounds entering the ear set the tympanic membrane into vibration. - vibrations are conveyed by the ossicular chain to the oval window. - vibratory motion of the ossicles is transmitted to the fluids of the cochlea - stimulate the sensory receptor (hair) cells of the organ of Corti. - hair cells respond, they activate the neurons of the auditory nerve. - signal is now in the form of a neural code that can be processed by the nervous system. - Conductive system: outer ear and middle ear - their most apparent function is to bring (conduct) the sound signal from the air to the inner ear. - Sensorineural system: cochlea and eighth cranial nerve - involves the physiological response to the stimulus, activation of the associated nerve cells, and the encoding of the sensory response into a neural signal. - Central auditory nervous system: aspect of the central nervous system that deals with this neurally encoded message **[Temporal Bone:]** - Temporal bone: most of the structures that make up the ear are contained within - Walls of these structures and all of the bony aspects of the ear, except for the ossicles, are actually parts of the temporal bone itself - Temporomandibular joint: articulation with the mandible is via the highly mobile. - Squamous part: very thin, fan-shaped portion on the lateral aspect of the bone. - Prominent zygomatic process runs anteriorly to join with the zygomatic bone, forming the zygomatic arch - Below the base of the zygomatic process is a depression called the mandibular fossa: accepts the condyle of the mandible to form the temporomandibular joint just anterior to the ear canal. - Petrous part is pyramid-shaped and medially oriented so that it forms part of the base of the cranium. - Extremely hard bone contains the inner ear and the internal auditory meatus through which the eighth cranial nerve - Mastoid part composes the posterior portion of the temporal bone. - Mastoid articulates with the occipital bone posteriorly and with the parietal bone superiorly. - Inferiorly oriented, cone-shaped projection below the skull base called mastoid process. - Mastoid contains an intricate system of interconnecting air cells that vary widely in size, shape, and number - Connected with an anterosuperior cavity called the tympanic antrum, which is located just behind the middle ear cavity. - Opening called the aditus ad antrum connects the antrum with the attic or upper part of the middle ear cavity. - Roof of the antrum (and the middle ear) is composed of a thin bony plate called the tegmen tympani, - Separates them from the part of the brain cavity known as the middle cranial fossa. - Middle ear, antrum, and air cells compose a continuous, air-filled system - Untreated middle ear infection can spread to the mastoid air cell system - Styloid process is an anteroinferior pillar-like projection from the base of the temporal bone that varies widely in size. - Does not contribute to the auditory structures helps speech **[Outer and Middle Ear:]** - Outer ear: pinna and the ear canal, ending at the eardrum - Tympanic membrane: part of the middle ear system, which includes the middle ear cavity and its contents, and "ends" where the ossicles transmit the signal to the inner ear fluids at the oval window. [Pinna:] - Internal structure of the pinna is composed principally of elastic cartilage (except for the earlobe - Contains some undifferentiated intrinsic muscle tissue - Entrance to the ear canal is at the bottom of a large, cup-shaped depression called the concha  [External Auditory Meatus:] - Ear canal is more formally called the external auditory meatus (canal). - \~ 9 mm high by 6.5 mm wide, and is roughly 2.5 cm to 3.5 cm long. - Not quite a straight tube, but has two curves forming a slightly S-like pathway. - Curves usually make it difficult to get an unobstructed view of the eardrum - Necessary to straighten the canal before looking inside with an otoscope - Lined with tight-fitting skin. - Outer third of the canal is different from the inner two-thirds in several ways. - Underlying material is cartilage in the outer third and bone for the remainder of its length. - Bony portion of the canal is derived from - \(1) the tympanic part of the temporal bone, which forms the floor and anterior wall, as well as the inferoposterior wall; - \(2) the squamous part, making up the roof and part of the posterior wall; and - \(3) the condyle of mandible, which contributes to the inferoanterior wall at the temporomandibular joint. - Cartilaginous portion contains hairs as well as a plentiful distribution of sebaceous (oil) and ceruminous (wax) glands, although this is not the case for the bony portion of the canal. - Sebaceous glands are also present in the concha - Secretions serve lubricating and antimicrobial functions, and also help to keep the canal free of debris and even some foreign bodies and insects. [Tympanic Membrane:] - EAM ends at the tympanic membrane or eardrum, which is tilted at an angle of \~ 55° to the canal. - TM: attached to the tympanic sulcus - groove in the bony canal wall, by a ring of fibrocartilaginous connective tissue called the tympanic annulus (or annular ligament). - Ring has a deficiency at the top due to a tiny interruption in the tympanic sulcus known as the notch of Rivinus. - Eardrum is a smooth, translucent, and almost transparent membrane with an average thickness of only \~ 0.074 mm. - It is slightly taller (\~ 0.9 to 1.0 cm) than it is wide (\~ 0.8 to 0.9 cm), and it is concave rather than flat. - Peak of the cone-like inward displacement is called the umbo. - Eardrum is often described as having three layers, although more correctly there are four of them. - Most lateral layer of the tympanic membrane is continuous with the skin of the ear canal, - Most medial layer is continuous with the mucous membrane of the middle ear. - Sandwiched between them are two fibrous layers. - One of them is composed of radial fibers reminiscent of the spokes of a wheel - Other layer is made of essentially concentric circular fibers. - TM connected to the malleus - Manubrium attaches almost vertically to the eardrum, with its tip at the umbo - Attachment of the manubrium of the malleus forms the malleal prominence. - Ligamentous bands called the anterior and posterior malleal folds run from both sides of the malleal prominence to the notch of Rivinus, forming a triangular area between them on the eardrum. - Largest part of the tympanic membrane lies outside or below the malleal folds, and is called the pars tensa ("tense part") because it contains all four layers described above. - Superior area of the eardrum between the malleal folds is missing the two fibrous layers, and is called the pars flaccida ("flaccid area") for this reason. It is also known as Shrapnell's membrane. [Middle Ear:] - Middle ear, tympanum, or tympanic cavity: cavity in the temporal bone behind the tympanic membrane - Posterosuperior portion of the middle ear space is usually viewed as an "attic room" above the main tympanic cavity, and is called the epitympanic recess or the attic. - Space accommodates the incus and the malleus. - Floor of the tympanic cavity separates it from the jugular bulb below. - Ceiling is the tegmen tympani, which is the thin bony plate that separates the tympanic cavity from the brain cavity above. - Down on the anterior wall (\~ 3 mm up from the floor) is the opening of the Eustachian tube - Internal carotid artery canal is located on the other side of (i.e., anterior to) the anterior wall, just below the Eustachian tube. - Just above the Eustachian tube is the tensor tympani semicanal, which contains the tensor tympani muscle. - Tensor tympani semicanal and Eustachian tube are separated by a bony shelf or septum. - Curved bony projection on the anterior/medial wall that points into the middle ear space, called the cochleariform process. - Tendon of the tensor tympani muscle bends around the cochleariform process and proceeds in the lateral direction on its way to the malleus (Fig. 2.10).  - Bulge on the medial wall is the promontory of the basal turn of the cochlea. - Oval window of the cochlea (with its attachment to the stapes) is located posterosuperior to the promontory, and the round window of the cochlea is posteroinferior to it. - Facial nerve canal prominence is situated superior to the oval window. - Posterior wall separates the tympanic cavity from the mastoid. - Aditus ad antrum is an opening located superiorly on the rear wall, and provides communication between the epitympanic recess of the middle ear cavity and the antrum of the mastoid air cell system. - Pyramidal eminence or pyramid is a prominence on the posterior wall that contains the body of the stapedius muscle. - Stapedial tendon exits from the apex of the pyramid and proceeds to the stapes. - Fossa incudis is a recess on the posterior wall that accommodates the short process of the incus. - Chorda tympani nerve is a branch of the facial (seventh cranial) nerve that enters the middle ear from an opening laterally at the juncture of the posterior and lateral walls, runs just under the neck of the malleus, and leaves the middle ear cavity via the opening of the anterior chordal canal (of Huguier) that is anterior to the tympanic sulcus. **[Chapter 5: Pure Tone Audiometry]** **[Hearing Threshold:]** - Quantify the degree of a patient's hearing loss in terms of the magnitude of the stimulus needed for them to respond to it. - Smallest intensity of a sound that a person needs to detect its presence is called his threshold for that sound. - Define the threshold as the lowest intensity at which the patient responds to the sound at least 50% of the time - Test sounds used to determine the degree of hearing loss are usually pure tones of different frequencies. - Normal threshold value at each frequency is said to be 0 dB hearing level (HL) - Hearing thresholds are thus given in decibels of hearing level or dB HL - Person has "normal hearing" if their thresholds are close to the norm and a "hearing loss" if the tones must be presented at higher intensities for them to be heard. - Amount of the hearing loss is expressed in terms of how many decibels above 0 dB HL are needed to reach the person's threshold. - Test signals can be presented by air conduction or bone conduction, or in sound field (presenting sound from loudspeakers). **[Air Conduction Testing:]** - Air-conduction testing usually involves presenting the test signals from standard audiometric (supra-aural) earphones - Insert earphones can also be used - Earrings and most eyeglasses (except contact lenses) must be removed for both comfort and proper fitting - Hearing aids should be removed, turned off, and put away during the test. - Chewing gum and candy must be disposed of. - Audiologist should check to see whether putting pressure on the external ear seems to cause the ear canal to close. - Important because the pressure exerted by the earphones might similarly cause collapse of the ear canals, and give the false impression of a conductive hearing loss. **[Bone Conduction Testing:]** - Bone conduction is tested by applying a vibratory stimulus to the skull, which is transmitted to the cochlea and heard as sound. - Bone-conduction vibrator is placed on the mastoid process or forehead, and is held in place by a spring headband. - Before putting the bone vibrator on the patient, one must identify any structural aberrations or other problems that would affect the proper placement. - Hair under the vibrator, oily skin, and oddly shaped or narrow mastoids that make it hard to place the vibrator without it slipping. - Placement variations on the mastoid can result in threshold differences [Occlusion Effect:] - Have been assuming that the ears are not covered by the earphones while bone conduction is being tested. - Typical method results obtained this way are called unoccluded bone-conduction thresholds. - Occluded bone-conduction thresholds are obtained when one or both ears are covered with the earphones. - Stronger signal reaches the cochlea when bone-conduction signals are presented with the ears occluded compared with unoccluded. - Boost is called the occlusion effect. - Occluded bone-conduction thresholds are lower (better) than unoccluded ones, and a given bone-conduction signal will sound louder with the ears covered compared with when the ears are open. - Occlusion effect occurs when the cartilaginous section of the ear canal is occluded, but not when the bony portion is blocked. I - Also absent when there is a disorder of the conductive system. - Occlusion effect can be used clinically to help determine whether a conductive impairment is present in the form of the Bing test - Help determine how much noise is needed for masking during bone-conduction testing - Magnitude of the occlusion effect is found by simply comparing the bone-conduction thresholds obtained when the ears are occluded and unoccluded - Occlusion effect occurs for frequencies up to \~ 1000 Hz, and that it is largest at lower frequencies - Size of the occlusion effect also varies considerably among individuals **[Comparing Air and Bone Conduction Thresholds:]** - Outer and middle ear collectively make up the conductive mechanism and auditory nerve compose the sensorineural mechanism - Comparing the air-conduction thresholds to the bone-conduction thresholds allows us to figure out the type of hearing loss - Fig 8. represents the whole peripheral hearing mechanism. - Divided into two halves, representing the conductive mechanism (outer and middle ear) and the sensorineural mechanism (cochlea and auditory nerve). - Entire ear is tested by air conduction because the signal from an earphone must be processed through the outer, middle, and inner ear and the auditory nerve - All of these parts must be working properly for the air-conduction threshold to be normal, and a problem in any one (or more) of these locations would cause a hearing loss by air conduction - However, it cannot distinguish between a problem coming from one part of the ear versus the other - Bone-conduction signal "bypasses" the outer and middle ear and directly stimulates the cochlea. - Bone conduction is considered to test just the sensorineural mechanism  - Deduce the location of a problem from the following principles: - \(1) air-conduction tests the whole ear, - \(2) bone-conduction tests the sensorineural part of the ear. - Difference between the air- and bone-conduction thresholds implies that there is a problem with the conductive system. - Difference between the air-conduction threshold (AC) and the bone-conduction threshold (BC) at the same frequency is called an air-bone-gap (ABG); that is, AC -- BC = ABG - Fig 5.9a Represents an ear in which the thresholds are 55 dB HL by air conduction and 55 dB HL by bone conduction. - Assumed that the air- and bone-conduction thresholds are both obtained at the same frequency. - Bone-conduction threshold tells us that 55 dB HL of the loss is coming from the sensorineural part of the ear, and the air-conduction threshold indicates that the whole loss is 55 dB HL - Air-bone-gap here is 55 -- 55 = 0 dB. - Figure out that the whole loss is coming from the sensorineural mechanism, and also that the conductive mechanism must be okay sensorineural - Indicated by air- and bone-conduction thresholds that are equal, or at least very close to one another, caused by a disorder of the cochlea or auditory nerve, or both  Air-conduction (Air) and bone-conduction (Bone) thresholds in cases of (a) sensorineural hearing loss, (b) conductive hearing loss, and (c) mixed hearing loss. The difference between the air- and bone-conduction thresholds is called the air-bone-gap (ABG) and represents the part of the loss coming from the conductive mechanism. - Fig. 5.9b air-conduction threshold is 55 dB HL - Bone-conduction threshold is normal at 0 dB HL. - None of the hearing loss is coming from the sensorineural mechanism conductive mechanism as the only possible culprit. - Size of the air-bone-gap in this case is 55 -- 0 = 55 dB. - Conductive hearing loss revealed by a hearing loss by air conduction but no hearing loss by bone conduction. - Also possible to have a hearing loss that is partly due to a sensorineural problem and partly to a conductive problem, called a mixed hearing loss. - Fig. 5.9c. The 55 dB HL air-conduction threshold is the total amount of hearing loss coming from all sources, and the bone-conduction threshold of 30 dB HL represents the part of the loss that is due to problems in the sensorineural mechanism. - 30 dB of the 55 dB HL loss is coming from the sensorineural problem, then the remaining amount of 55 -- 30 = 25 dB (which is the air-bone-gap) must be due to problems in the conductive system - Sensorineural part of a mixed loss is shown by the bone-conduction threshold, and its conductive component is represented by the air-bone-gap. - Air-bone-gap should be 0 dB unless there is a problem with the conductive mechanism. - Not always the case, which is why it is suggested from the outset that the air-bone-gap should be at least 10 dB wide before it is considered significant. - Why? - Test-retest reliability - Given clinical threshold measurement is generally considered to be reliable within ± 5 dB. - Applying ± 5 dB of variability to both the air- and bone-conduction measurements at the same frequency means that the spread between them (the air-bone-gap) can be as wide as 10 dB. - Statistical relationship between air- and bone-conduction thresholds: - Mean air-conduction threshold that equals the mean bone-conduction threshold. - Air- and bone-conduction thresholds are equal in normal ears on average, so that the normal air-bone-gap is 0 dB on average. - Must also be normal ears with at least some amount of air-bone-gap, and even ears in which bone conduction is poorer than air conduction - Most air- and bone-conduction thresholds are within ± 10 dB of each other - Be wary of the fact that bone conduction may be worse than air conduction because of an error. This often occurs if the bone vibrator slips or if it was improperly placed when it was applied. [Basic Audiogram Interpretation:] - Typical normal audiogram is shown in Fig. 5.10. - All of the air-conduction thresholds are in the vicinity of 0 dB HL for both ears. - Air- and bone-conduction thresholds are very close to one another at each frequency no significant air-bone-gaps. - Why do we bother testing bone conduction in a case such as this one, where the hearing is clearly normal? - Because 0 dB HL is the average threshold for normal people, so that thresholds lower than 0 dB HL are expected to be found in many people, especially in children - Middle ear problem in a person who normally has --10 dB HL thresholds can cause these thresholds to shift up to 5 or 10 dB HL. Here, the hearing sensitivity is within the normal range but there is also a conductive disorder. - Testing bone conduction would show a 15 to 20 dB air-bone-gap, thus revealing the problem. - Omitting bone-conduction testing would cause such a conductive impairment to be missed. - - Pure tone average (PTA) is usually calculated for each ear. - PTA, which is simply the mean of the air-conduction thresholds at 500, 1000, and 2000 Hz, is an attempt to summarize the degree of hearing loss - Table 5.2 Typically used categories to describe the degree of hearing loss based on the pure tone average  - Pure tone average was originally based on the 500, 1000, and 2000 Hz thresholds because it often agrees with hearing ability for speech - PTA is usually compared with a measure of hearing for speech called the speech recognition (reception) threshold (SRT),3 and significant differences between the PTA and SRT are of clinical significance - 500, 1000, and 2000 Hz have come to be known as the "speech frequencies." misnomer because adequate speech recognition actually depends on a much wider range of frequencies - Three-frequency pure tone average often fails to agree with the SRT, especially when the shape of the pure tone audiogram slopes sharply. - Two-frequency pure tone average based on the best two of these three frequencies (usually 500 and 1000 Hz) is often used instead of the three-frequency PTA under these circumstances - Air-conduction thresholds in Fig. 5.11 reveal that this patient has a hearing loss in both ears. - A loss in both ears is said to be bilateral. - Left ear was tested at 1500 Hz because there was a spread of ≥ 20 dB between the thresholds at 1000 and 2000 Hz. - Three-frequency pure tone averages are 52 dB HL in the right ear and 50 dB HL in the left ear, so that the degree of hearing loss would be considered moderate according to Table 5.2. - Audiogram has quite a slope, we would also calculate two-frequency PTAs based on 500 and 1000 Hz. - These are 45 dB HL for the right ear and 40 dB HL for the left. - Type of loss in this example is sensorineural because the air- and bone-conduction thresholds are essentially the same at each frequency, that is, there are **no significant air-bone-gaps.** - Configuration (shape) of the audiogram slopes downward with increasing frequency - Interpretation of this audiogram would read as follows: "Moderate sloping sensorineural hearing loss, bilaterally," - Moderate describes the severity, sloping describes the configuration, and sensorineural describes the type of hearing loss.  - Example of a bilateral conductive hearing loss. - Air-conduction thresholds are between 25 and 50 dB HL, but all of the bone-conduction thresholds are in the vicinity of 0 dB HL. - Losses would be considered to be in the mild range because the pure tone averages are 30 dB HL for the right ear and 38 dB for the left ear. - Broad terms, the configurations of these losses could be described as flat; however, notice that there is a slight tent-like shape for the right ear. - Fig. 5.13 has a unilateral conductive hearing loss because it involves just one ear - Impaired right ear has a mild hearing loss with a fairly flat configuration and a pure tone average of 32 dB HL. - Hearing loss in the right ear is conductive because the bone-conduction thresholds approximate 0 dB HL in both ears  - Audiogram of a patient with normal hearing in his right ear and a sensorineural hearing loss in his left ear - Hearing loss is sensorineural because the air- and bone-conduction thresholds are essentially the same. - No response at the maximum testable bone conduction levels of 70 dB HL for both 2000 and 4000 Hz. - Not a problem at 2000 Hz, where the air-conduction threshold is only 75 dB HL, but we really do not know for sure whether or not there is an air-bone-gap at 4000 Hz, where the air-conduction threshold is 90 dB HL. - Normal right ear shown in Fig. 5.14 has a pure tone average of 0 dB HL. - Impaired left ear has a three-frequency pure tone average of 38 dB HL and a two-frequency PTA of 20 dB HL. - Even if one of these averages agrees with the speech reception threshold, both of them clearly understate the amount of hearing loss in the higher frequencies. - Shows how misleading it can be to describe a hearing loss solely on the basis of the pure tone average. - One might interpret this audiogram as indicating "a unilateral severe high-frequency hearing loss in the left ear, with normal hearing sensitivity in the right ear." - "Severe" designation here is borrowed from the degrees of loss shown in Table 5.2. - Technically a misuse of the term because the degrees of loss shown in the table really apply only to the traditional pure tone average, and are intended to imply how much the hearing loss affects overall sensitivity for speech - Bilateral asymmetrical sensorineural hearing loss hearing loss in both ears, but the thresholds are worse in one ear than in the other. - Right ear has a two-frequency pure tone average of 48 dB HL and a three-frequency PTA of 55 dB HL, and is noticeably worse than the left ear, which has two- and three-frequency PTAs of 28 and 32 dB HL,  - Mixed hearing loss occurs when both sensorineural and conductive impairments coexist in the same ear. - Bone-conduction thresholds show the sensorineural portion of the loss, and the conductive component is represented by the air-bone-gap. - Overall extent of the hearing loss is shown by the air-conduction thresholds. - Bilateral mixed hearing loss in which the pure tone averages are 67 dB HL in the right ear and 75 dB HL in the left ear. - Bone-conduction thresholds show that the sensorineural components are similar for the two ears, sloping from \~ 10 to 15 dB HL at 250 Hz down to 55 to 60 dB HL at 4000 Hz. - Air-bone-gaps are also similar for the two ears and also from one frequency to the other in this audiogram. **[Supplemental Pure Tone Tests:]** [Occlusion Effect and Audiometric Bing Test:] - Occlusion effect - \(1) causes a low-frequency bone-conduction threshold to be lower (better) than it would be with the ear uncovered, and - \(2) occurs when the conductive mechanism is normal but not when there is a conductive disorder - Bing test was originally a tuning fork technique used to determine whether the occlusion effect is present (see below). - Audiometric Bing test uses a bone-conduction vibrator in place of a tuning fork. - Because the audiometric Bing test also reveals the size of the occlusion effect - Audiometric Bing Test: - Bone-conduction thresholds are obtained in the regular way, with the ears uncovered. - Low-frequency (\< 1000 Hz) thresholds are then retested while the test ear is occluded - Other earphone is located on the opposite side of the head (usually between the opposite ear and eye), not covering the other ear. - Audiometric Bing test is positive if the occluded thresholds are significantly better (lower) than the unoccluded thresholds. - Positive result means that the occlusion effect is present, and suggests that a conductive disorder is not present. - Would occur when the ear is normal or when the hearing loss is sensorineural. - Size of the occlusion effect is simply the difference between the occluded and unoccluded thresholds at any given frequency. - Test is negative if the occluded and unoccluded thresholds are essentially the same, indicating that the occlusion effect is absent. - Result suggests that there is a problem with the conductive mechanism and implies that the hearing loss is either conductive or mixed. [Tuning Fork Tests:] Schwabach Test: - Technique for estimating a patient's hearing sensitivity by bone conduction. - Has two principal characteristics: - \(1) it makes use of the fact that the tone produced by a tuning fork becomes softer with time after it has been struck due to damping, - \(2) the patient's hearing is expressed in relative terms compared with the examiner's hearing ability - Done by timing how long the tuning fork is heard by the patient and how long it is heard by the examiner - Placing the base of the vibrating fork on the patient's mastoid process until the tone fades away. - Clinician then moves the fork to their own mastoid and times how long they can hear it - Patient will: - hear the tone (1) for a shorter period of time if the patient has a sensorineural loss; - \(2) for a longer period of time (or perhaps the same length of time) if the patient has a conductive loss; and - \(3) for the same amount of time if the patient has normal hearing - outcomes are problematic when dealing with mixed losses - validity is completely dependent on the tenuous assumption that the examiner really has normal hearing Weber Test: - Determine whether a unilateral hearing loss is sensorineural or conductive. It is a - lateralization test because the patient is asked to indicate the direction from which a sound appears to be coming. - Before starting this test, the patient should be advised that it is possible for the tone to be heard from the good side or the poorer side - Putting the base of the vibrating tuning fork somewhere on the midline of the skull, most commonly on the center of the forehead - Audiometric Weber test uses the bone-conduction vibrator instead of tuning forks - Patient is asked to indicate where the tone is heard. - Hearing the tone in the better ear implies that there is a sensorineural loss in the poorer ear, whereas hearing the tone in the poorer ear suggests a conductive loss in that ear. - Tone is heard in the middle of the head, "all over," or equally in both ears when the patient has normal hearing - Mixed loss, the tone will be lateralized to the better ear if its level is below the poorer ear's bone-conduction threshold - Fail to detect the conductive component of a mixed loss in such cases - Works for several reasons, - All of which are related to the idea that the bone-conduction tone from the tuning fork reaches both cochleae at the same intensity. - Tone lateralizes to the better ear with sensorineural losses for either of two reasons: - \(1) The tone will only be heard in the better ear if its level is lower than the bone-conduction threshold of the poorer ear. - \(2) The second mechanism is due to the Stenger effect, which means that a sound presented to both ears is perceived only in the ear where it is louder. - Intensity of the tone from the tuning fork will have a higher sensation level in the better ear than in the impaired ear - Will be louder in the better ear and will be perceived there. - Several factors can explain why a bone-conduction tone would be louder in (and thus lateralized to) the poorer ear - \(1) outer ear obstructions (e.g., impacted cerumen) may cause an occlusion effect, - \(2) mass loading of the middle ear system caused by effusions or ossicular chain interruptions may lower its resonance, and - \(3) phase advances may be caused by fixations or interruptions of the ossicular chain. Bing Test: - Used to determine if closing off the patient's ear canal results in an occlusion effect - Patient is asked to report whether a tuning fork sounds louder with the ear canal open or closed. - Base of a vibrating tuning fork is held against the patient's mastoid process. - Tester then presses the tragus down over the entrance of the ear canal to occlude it. - Usual technique is to alternately occlude and unocclude the ear canal to help the patient make a reliable louder/softer judgment - Ask whether the tuning fork sounds louder when the ear is closed and softer when the ear is open - Important to avoid pressing too hard when closing-off the ear canal for the Bing test because doing so can inadvertently change it into a test of the effect of pressure in the ear canal known as the Gellé test - Outcome of the tuning fork Bing test is based completely on a subjective judgment of louder versus not louder. - If the occlusion effect is present, covering the ear canal should cause the tuning fork to sound louder. - Positive result and implies that the ear is either normal or has a sensorineural hearing loss. - Negative result occurs if closing off the ear canal fails to make the tuning fork sound louder, and implies that there is either a conductive or mixed hearing loss. Rinne Test: - Tuning fork procedure that compares hearing by air conduction and by bone conduction - Rinne test is based on the idea that the hearing mechanism is normally more efficient by air conduction than it is by bone conduction. - Tuning fork will sound louder by air conduction than by bone conduction. - Air conduction advantage is lost when there is a conductive hearing loss, in which case the tuning fork sounds louder by bone conduction than by air conduction. - Asking the patient to indicate whether a vibrating tuning fork sounds louder when its base is held against the mastoid process (bone conduction) or when its prongs are held near the pinna, facing the opening of the ear canal (air conduction). - After striking the fork, the clinician alternates it between these two positions - Outcome of the Rinne test is traditionally called "positive" if the fork is louder by air conduction - Implies that the ear is normal or has a sensorineural hearing loss. - Results are called "negative" if bone conduction is louder than air conduction, which is interpreted as revealing the presence of a conductive abnormality - Examiner is often concerned with identifying a conductive loss with this test. - Clinicians prefer to describe Rinne results as "air better than bone" (AC \> BC) versus "bone better than air" (BC \> AC). - AC \> BC implies normal hearing or sensorineural impairment, and BC \> AC implies a conductive disorder. - More accurate way to administer the Rinne test involves timing how long the patient can hear the tuning fork at the two locations. - In this case, the results are - \(1) positive (AC \> BC) when the tone is heard longer by air conduction, and - \(2) negative (BC \> AC) when it is heard longer by bone conduction. **[Week 2:]** *Textbook:\ pp. 187 -- 196 (through and including vascular pulsing)\ pp. 200 - 211 (start at The Acoustic Reflex; stop at Immittance Assessment in Infants)\ pp.212 (start ET tests) -- 215.\ Articles:\ Required:\ [[Hunter L Acoustic Immittance.pdf]](https://westernu.brightspace.com/d2l/common/dialogs/quickLink/quickLink.d2l?ou=26186&type=coursefile&fileId=Lessons%2f2+Immittance+Acoustic+Reflex+Testing%2fHunter+L+Acoustic+Immittance.pdf)\ * **Chapter 7: Acoustic Immittance Assessment:** - Acoustic impedance (Za) is the opposition to the flow of sound energy, measured in ohms. - Ratio of sound pressure (P) to sound flow, or volume velocity (U); or - Za = P/U - Acoustic admittance (Ya), expressed in acoustic millimhos (mmhos). - Ease of sound flow - Ya = U/P - Acoustic impedance is composed of - \(1) a frictional component called **acoustic resistance (Ra),** - \(2) a stiffness component called **negative (stiffness) acoustic reactance (--Xa**), and - \(3) a mass component called **positive (mass) acoustic reactance (+ Xa).** - Their reciprocals are respectively the components of acoustic admittance: - \(1) acoustic conductance (Ga), - \(2) positive (compliant or stiffness) acoustic susceptance (+ Ba), and - \(3) negative (mass) acoustic susceptance (--Ba). - The immittance of the ear is derived from its various sources of mechanical and acoustical springiness, mass, and resistance: - \(1) The stiffness (springiness) components come from the volumes of air in the outer ear and middle ear spaces, the tympanic membrane, and the tendons and ligaments of the ossicles. - \(2) The mass components are due to the ossicles, the pars flaccida of the eardrum, and the perilymph. - \(3) Resistance (friction) is introduced by the perilymph, the mucous membrane linings of the middle ear spaces, the narrow passages between the middle ear and mastoid air cavities, and also by the tympanic membrane and the various middle ear tendons and ligaments. - Contractions of the middle ear muscles also change the immittance of the ear, usually by increasing the stiffness component. - Admittance measurements are employed clinically because they are more straightforward than those using impedance. - The acoustic admittance characteristics of the ear can be assessed using a device such as the one described in Fig. 7.1.  - AI measured by inserting an ear piece called a **probe tip** into the ear canal. - Probe tip is encased in a flexible plastic cuff to create an airtight connection between the ear canal and the probe tip, called a **hermetic seal**. - Probe tip includes four tubes. - One tube is connected to a receiver (loudspeaker), which is used to deliver a tone into the ear canal. This sound is called the probe tone. - Second tube is connected to a measuring microphone and is used to monitor the probe sound within the ear canal. - Third tube is connected to an air pressure pump and manometer (pressure meter), - Fourth tube connects to another receiver used to present stimuli for testing the acoustic reflex. - A second earphone goes to the opposite ear and is used for acoustic reflex tests. - The latter earphone may be a standard audiometric earphone or an insert receiver, depending on the device being used. - AA (in mmhos or mL) measured with such a device is displayed on a video screen or meter and can be plotted on paper. Fig. 7.2 shows a photograph of a typical clinical acoustic immittance instrument. - Introduce an 85 dB sound pressure level (SPL) probe tone into the ear canal, where it will be affected by the admittance properties of the ear. - Will be revealed as an increase or decrease in the level of the probe tone as it is monitored by the measuring microphone. - Instruments called **bridges** involve a manual intensity adjustment to bring the probe tone level in the ear to 85 dB SPL, whereas those referred to as meters use an automatic volume control to keep the probe level at 85 dB SPL. - In addition to measuring overall admittance (Y), most admittance meters also provide separate measurements of susceptance (B) and conductance (G). - Done by analyzing the monitored signal in terms of in-phase (for G) and out-of-phase (for B) components. - **Most routine immittance tests use a 226 Hz (or a 220 Hz) probe tone**. - Low-frequency chosen because they are sensitive to changes in stiffness reactance, comprising a major part of the normal ear's impedance. - In addition, admittance devices are calibrated in terms of the admittance of an equivalent volume of air. - When the meter indicates that the admittance of an ear is 1.8 mmhos at 226 Hz, it means that the admittance of the ear corresponds to that of a 1.8 ml volume of air. - Why? - Suppose we have several stainless-steel containers (i.e., hard-walled cavities) with various volumes, ranging from perhaps 0.2 to 2.5 ml. - Air volume in such a cavity constitutes an acoustical spring, so that its admittance is essentially a compliant susceptance (and its impedance a stiffness reactance). - Inserting our probe tip into each of these containers would show that admittance increases (or the impedance decreases) as the volume of the cavity becomes larger. - Repeating this experiment with different probe tone frequencies in the same cavity would result in different amounts of admittance at each frequency. - This reflects the fact that admittance depends on frequency. - We would also find that admittance (in mmhos) is equal to the volume (in ml when the probe tone is 226 Hz). - **For example, the acoustic admittance (Ya) at 226 Hz will be 2.0 mmhos for a 2 ml container, 1.2 mmhos for a 1.2 ml container, 0.3 mmhos for a 0.3 ml container, etc.** [Immittance at the Plane of the Eardrum] - Immittance of the middle ear because it provides information about - \(1) middle ear pathologies and - \(2) middle ear muscle contractions due to the acoustic reflex. - Probe tip monitors the immittance of the ear from the perspective of its location, which is in the general vicinity of the ear canal entrance. - The probe tip measures the total immittance of the ear, which includes the combined effects of the outer ear and the middle ear. - Problem because ear canal volume (size) is usually not clinically relevant, yet its influence on the total immittance value (at the probe tip) is often big enough to cloud the effects of the clinically significant middle ear immittance value. - For example, a patient with abnormally low middle ear admittance due to a conductive disorder may have a normal total admittance value due to a large ear canal volume. - Another individual whose middle ear is normal might seem to have unusually low total admittance because their ear canal volume is quite small. - Third patient might have low total admittance due to otitis media when first evaluated. The middle ear problem might be completely resolved (i.e., the middle ear immittance has returned to normal) when they return for reassessment, but the total Ya might still be abnormally low simply because their outer ear volume was made to appear smaller by a very deeply inserted probe tip. This can happen because the volume under the probe tip will be different depending on how deeply it has been inserted. - Must remove the outer ear component from the total admittance value at the probe tip to get an undistorted representation of the middle ear's admittance at the eardrum. In other words, removing the effect of the ear canal moves the measurement location from the end of the probe tip to the plane of the tympanic membrane. - Achieve this goal by taking advantage of the fact that total admittance (YTOTAL) is simply the sum of the admittances of the outer ear (Y0E) and the middle ear (YME)1: - YTOTAL = YOE + YME - Subtracting the admittance of the outer ear from the total admittance leaves the middle ear admittance, which is the value that we need: - YME = YTOTAL + YOE - The procedure for determining the admittance of the middle ear (i.e., at the plane of the ear drum) is simple and straightforward: - \(1) measure the total admittance (YTOTAL) of the ear (Fig. 7.3a). - \(2) measure the ear's admittance again while pressure is being exerted on the tympanic membrane. - This measurement reflects the admittance of the outer ear (or ear canal) alone, and is depicted in Fig. 7.3b. - Pressure change is accomplished using the pressure pump connected to one of the tubes in the probe tip. - Heightened air pressure puts the eardrum under so much tension that it acts like a hard wall, so that essentially no sound energy can be transmitted into the middle ear. - Prevents the probe tip from measuring the admittance of the middle ear. - In this case, we say that the middle ear has been excluded from the measurement. - Hence, the admittance obtained under these conditions comes from the outer ear alone. **Tympanometry** - Tympanometry involves measuring the acoustic admittance of the ear with various amounts of air pressure in the ear canal. - We control the amount of air pressure in the ear canal because the probe tip makes a hermetic seal with the ear canal, and one of its tubes is connected to an air pump and manometer. - Amount of air pressure is expressed in terms of **dekapascals (daPa)** or of millimeters of water pressure (mm H~2~O),[^^](https://jigsaw.vitalsource.com/books/9781638531067/epub/OEBPS/Text/Chapter07.xhtml?favre=brett#c007_r2) relative to the atmospheric pressure in the room where the test is being done. - *0 daPa* implies that the pressure in the ear canal is equal to the atmospheric pressure,  - *positive pressure* (e.g., + 100 daPa) means that the ear canal pressure is greater than atmospheric pressure, - *negative pressure* (e.g., --100 daPa) means it is less than atmospheric pressure. - This information is shown on a diagram called a **tympanogram** (**[[Fig. 7.4]](https://jigsaw.vitalsource.com/books/9781638531067/epub/OEBPS/Text/Chapter07.xhtml?favre=brett#fig7.4)a**), with admittance in mmhos or (or equivalent volume in ml) on the *y*-axis, and pressure in daPa (or mm H~2~O) on the *x*-axis. - \(1) first step in tympanometry is to properly insert the probe so that it makes a hermetic seal with the external auditory meatus. - \(2) probe tip should face the drum and not the ear canal wall, and the path to the tympanic membrane should not be blocked. Cerumen will be problematic if it gets into the probe tip tubes or completely obstructs the path to the tympanic membrane, but the simple presence of some wax is usually not a problem. - \(3) select the probe tone frequency and the admittance parameter(s) to be measured. We will measure overall acoustic admittance (*Y*) with a 226 Hz probe tone. - \(4) 226 Hz probe tone is turned on and the pressure in the ear canal is then raised to + 200 daPa. - This amount of positive pressure is usually assumed to tense the eardrum sufficiently to prevent the admittance of the middle ear from being measured - A useful analogy is to imagine that the + 200 daPa pressure causes the tympanic membrane to become "opaque" to sound, so that the probe cannot "see" the middle ear through it. - **Admittance obtained at + 200 daPa is assumed to represent just the outer ear**. - In **[[Fig. 7.4]](https://jigsaw.vitalsource.com/books/9781638531067/epub/OEBPS/Text/Chapter07.xhtml?favre=brett#fig7.4)a**, the admittance at + 200 daPa is 1.0 mmho *(point 1)*. This means that the acoustic admittance of the outer ear is 1.0 mmho, and that the ear canal volume is 1.0 ml because mmhos equals volume at 226 Hz. - \(5) Air pressure is then decreased at a steady rate while we continue to measure the admittance. Notice that the tympanogram curve slowly rises as the pressure decreases below + 200 daPa. The total admittance rises by \~ 0.1 mmhos, to reach 1.1 mmhos, when the pressure is + 100 daPa *(point 2)*. It then increases more rapidly as the pressure drops further, and achieves 1.75 mmhos at 0 daPa, or at atmospheric pressure *(point 3)*.  - Why is this happening and what does it mean? - As the pressure in the ear canal is steadily reduced, the tension on the tympanic membrane also diminishes. - Middle ear is no longer being completely blocked from the view of the probe tip. - Probe tip is now picking up more and more of the middle ear's admittance. - Less the pressure, the less the tension on the eardrum, and the more the middle ear contributes. - It is as though the eardrum has changed from being completely "opaque" to being progressively more "translucent." - Because we know that 1.0 mmho is coming from the ear canal, we can deduce that the additional amounts of admittance (above 1.0 mmho) must be coming from the middle ear. - Hence, the 1.75 mmhos of total admittance at 0 daPa represents 1.0 mmho from the ear canal and 0.75 mmhos from the middle ear. - \(6) pressure continues to be reduced below 0 daPa. Air is now being pumped out of the ear canal instead of into it, so that the pressure is becoming increasingly negative. We see that the admittance continues rising until it reaches a maximum of 1.85 mmhos when the pressure in the outer ear is --15 daPa (point 4). The total admittance then begins to fall again as the negative pressure increases. - \(7) The **maximum point is called the peak of the tympanogram**. This is where there is no longer any tension being imposed on the tympanic membrane, so that it becomes "transparent," allowing the probe tip to "see" all of the middle ear admittance. - Because we know that the maximum (or peak) total admittance is 1.85 mmhos and that the outer ear admittance is 1.0 mmho, we can deduce that the middle ear admittance is 0.85 mmhos. (The **middle ear admittance is often referred to as the static admittance**, or more accurately as peak-compensated static admittance, discussed below.) - By reducing the pressure below 0 daPa we are actually increasing the negative pressure. - Causes the admittance to fall to 1.2 mmhos at --100 daPa (point 5), and to 1.0 mmho at --200 daPa (point 6). - Falling admittance values indicate that the negative pressure is tensing the tympanic membrane, so that it again becomes progressively more "opaque" to sound. Continuing to increase the negative pressure causes the admittance to fall to only 0.9 mmhos at --300 daPa (point 7), which is the lowest pressure used here. Thus, the admittance at --300 daPa is actually smaller than it was at + 200 daPa. This means that the middle ear can be excluded from the measurement by applying either positive or negative pressure (i.e., at point 1 or 7; these two points are often called the positive and negative "tails"). - Even though many audiologists use + 200 daPa to estimate outer ear volume, the lowest point on the tympanogram is often obtained at --300 to --400 daPa. - Compared with + 200 daPa, it has been shown that --400 daPa more effectively removes the middle ear admittance and thus provides a more accurate measure of the outer ear volume - It is suggested that - \(1) tympanograms should be obtained over a pressure range from + 200 daPa down to --400 daPa (or at least --300 daPa) and that - \(2) the admittance of the middle ear should be based on (a) the tympanogram peak as the total admittance value and (b) the lower of the two "tails" as the outer ear admittance value. - Because the y-axis shows admittance in mmhos (or equivalent volume in mL), the overall height of the peak relative to 0 mmhos gives total admittance, and the overall height of the "tail" (at + 200 daPa or --300 daPa) gives the outer ear (canal) volume. The height of the tympanogram's peak above its own baseline (i.e., one of the two tails) gives the middle ear admittance. - The peak of the tympanogram also provides us with an estimate of the pressure within the middle ear, which is --15 daPa in this example. - Here is why: - Recall that we exclude the middle ear by using air pressure to stress the eardrum. - Stress occurs because there is more pressure on one side of the tympanic membrane than on the other (higher pressure in the outer ear than in the middle ear, or vice versa). - Admittance will be highest (the peak) when the eardrum is not experiencing any stress due to a pressure difference. - The positive or negative pressure used to obtain the peak pressure should be the same as the pressure that exists on the other side of the eardrum, that is, within the middle ear. This is so because having the same pressure on both sides of the eardrum will result in the least tension on the eardrum, and hence the highest total admittance value, so that the tympanogram peak provides us with an estimate of the pressure inside the middle ear. Interpreting 226 Hz (Low-Frequency) Tympanograms: - Major considerations that come into play when interpreting 226 Hz (or 220 Hz) tympanograms include - static acoustic admittance, - tympanometric gradient or width, - ear canal volume, the pressure at which the tympanometric peak occurs, - shape of the tympanogram. - The most widely utilized tympanogram classification system was originated by Jerger (1970). Fig. 7.5 shows most of the tympanogram types in this system. - Types were based on relative tympanograms obtained with an immittance bridge, and this format is retained in the figure. Notice that these tympanograms are expressed in arbitrary compliance units instead of absolute admittance in mmhos (static acoustic admittance and ear canal volume were measured separately). - Jerger's (1970) classical 220 Hz (226 Hz) typanogram types: - **Type A** - distinctive peak in the vicinity of atmospheric pressure and were typical of patients with normal middle ears, as well as those with otosclerosis. - If the type A tympanogram had a very shallow peak, it was classified as type AS, which was generally associated with otosclerosis but could also occur with otitis media. - Very high (deep) type A tympanograms were designated as type AD. These were found in otherwise healthy ears that had scarred or flaccid eardrums, or in cases of ossicular interruptions. - Type ADD tympanogram was so deep that the peak was off-scale, and was found in ears with ossicular discontinuities. - **Type B** - tympanograms were essentially flat across the pressure range, and were characteristic of patients with middle ear fluid and cholesteatoma. - Type B tympanograms can also be caused by entities such as eardrum perforations or impacted cerumen (or other obstructions) in the ear canal. - **Type C** - tympanograms had negative pressure peaks beyond --100 daPa (mm H2O), indicating negative middle ear pressure. - Associated with Eustachian tube disorders, and were also found in cases of middle ear fluid. - Not shown in the figure are tympanograms with notched peaks, which were classified as t**ype D** if the notch was narrow and **type E** if it was wide. These are rare occurrences when using 226 Hz (220 Hz) probe tones. - **Type D** was associated with hypermobile or scarred (but otherwise normal) eardrums, - **Type E** was found in cases of ossicular disruption. Static Acoustic Immittance: - Static acoustic immittance is the immittance of the middle ear at some "representative" air pressure. - Originally considered to be the middle ear impedance or admittance obtained under conditions of atmospheric pressure. - This point might seem confusing because we pressurized the ear to figure out the middle ear admittance. - **Remember that the total admittance can be measured without applying any pressure, that is, at atmospheric pressure of 0 daPa.** - Pressure is used to stiffen the eardrum to obtain the outer ear component. - "pressurized" outer ear value is then removed from the total admittance at atmospheric pressure, leaving the middle ear admittance at the eardrum, which is also at atmospheric pressure. - In any case, this is the situation that presumably exists in the patient's ear "under regular conditions" when the probe tip is not there. - On the tympanogram, it is the value of YME obtained at 0 daPa, which is 0.75 mmhos in Fig. 7.4a (point 3). - We will call this measurement "**atmospheric static."** The alternative approach is to measure static admittance at whatever pressure corresponds to the peak of the tympanogram - We will call this value "**peak static**." (More accurately, it is the peak-compensated static admittance.) - It occurs at --15 daPa in Fig. 7.4a, where YME is 0.85 mmhos (point 4). The peak static method is preferred because it provides a more stable picture of middle ear admittance - Static acoustic admittance measurements obtained from a patient are compared with the applicable normative admittance values. - These norms are usually expressed as 90% normal ranges, - Infants younger than about 6--9 months old are tested using higher-frequency probe tones, and are discussed later in this chapter. Table 7.1 Representative 90% normal ranges for peak static acoustic admittance (mmhos) using 220 and 226 Hz probe tones  - Given static admittance measurement is considered to be - \(1) within normal limits if it falls within the normal range, - \(2) abnormally low if it falls below the lower limit of the normal range, - \(3) abnormally high if it is above the upper limit of the normal range. - Seven tympanograms in Fig. 7.6 show static admittance values ranging from 2.6 mmhos for the tympanogram with the highest peak down to only 0.1 mmhos for the lowest one, which is close to being flat. - Values are the distances in mmho between the height of the peaks and the ear canal volume of 1.0 mmho measured at + 200 daPa. - Let us compare these to the normal range for adults in Table 7.1. - Tallest tympanogram is abnormally high because its static admittance (2.6 mmhos) is well above the upper limit of 1.66 mmhos. - Static value for the second tympanogram from the top is 1.7 mmhos, which is right on the upper limit (rounded to the nearest tenth of an mmho). We would probably consider it to be just within normal limits, especially if there is no air-bone-gap on the audiogram. (It is also within the upper limit of 1.75 mmhos in Table 7.3.) - Third and fourth curves have static values of 1.3 and 0.9 mmhos and are clearly within normal limits. - Next tympanogram (third from the bottom) shows a static admittance value of 0.4 mmhos, which is just above the lower limit of 0.37. (Even though 0.4 mmhos is below the 0.5 mmhos lower limit in Table 7.3, most clinicians use lower limits closer to those in Table 7.1, and some use even lower criteria taken from other studies.) - Second tympanogram from the bottom in Fig. 7.6 reveals static admittance of 0.2 mmhos, and the static admittance shown on the lowest one is 0.1 mmhos. Both of these are abnormally low compared - Abnormally low static acoustic admittance means abnormally high impedance, associated with: - middle-ear disorders such as otitis media, cholesteatoma, and otosclerosis. - Abnormally high static admittance (and thus abnormally low impedance) - often associated with middle-ear disorders such as ossicular discontinuity. - If we apply the classical tympanogram types to the examples in Fig. 7.6, we would categorize those having static admittance within the normal range as type A. - Tympanogram with abnormally high admittance would be classified as either type AD or ADD. - Two tympanograms with abnormally low admittance would be classified as AS, although the lowest one might be considered "flat" enough to be categorized as type B. - Notice that the tympanograms in this group have peaks at 0 daPa, so that the type A categories are straightforward. Tympanometric Gradient and Width: - See in Fig. 7.6 that the **tympanogram peak becomes smaller as the static admittance becomes lower**. - If the admittance becomes low enough, then there will be no discernible peak, so that the tympanogram is described as flat. - Common finding in ears with otitis media and cholesteatoma, where the static admittance may be as low as 0.06 or less - The flatness (versus peakedness) of a tympanogram can also be quantified by its gradient, which describes the relationship of its height and width. - **Gradient** was originally calculated in terms of arbitrary units of compliance (Brooks 1969), as shown in Fig. 7.7a, and is determined as follows: - \(1) Draw a horizontal line where the width of the tympanogram is 100 mm H2O (or daPa). - \(2) Measure the height of the peak above this line (hp), as well as the total height (ht) of the tympanogram from its peak to its baseline. - In the figure, hp is 3.6 compliance units and ht is 8 units. - \(3) **Find the gradient by dividing hp/ht**, which is 3.6/8 = 0.45 in the figure. The same procedure can be used to calculate the gradient of absolute tympanograms, except that the heights are measured in terms of mmhos or ml.  - Tympanometric gradients less than 0.2 are considered to be abnormally low are associated with the presence of middle ear fluid - Another way to quantify the flatness of a tympanogram is to determine the tympanometric width which is simply the width of the tympanogram in daPa measured at 50% of its static acoustic admittance value. - **Method for determining tympanometric width** is illustrated by the example in Fig. 7.7b. - Static admittance value is measured at the tympanogram peak and is found to be 0.85 mmhos in this example. - We measure down 0.425 mmhos from the peak because this distance is half the static value, and draw a horizontal line intersecting both sides of the tympanogram. - Next, we draw vertical lines from these intersection points down to the x-axis. The tympanogram width is the distance between these two lines. - In the example the tympanogram width is 80 daPa because the vertical lines cross the x-axis at --40 daPa and + 40 daPa (which are 80 daPa apart). - Tympanometric widths that are too wide are associated with middle ear effusion, and normative data may be used to help determine when this is the case - Representative upper cutoff values for tympanometric width are 235 daPa for infants and 200 daPa for 1-year-olds through school-age children (ASHA 1997). - Typical 90% normal ranges for adults are 51 to 114 daPa (Margolis & Heller 1987) and 48 to 134 daPa (Shahnaz & Polka 1997). Ear Canal Volume: - Tympanograms with extremely small or absent peaks are often referred to as essentially flat. - Usually attributed to extremely low middle ear admittance, and are typically associated with middle ear pathologies such as otitis media and cholesteatoma. - We can reach this conclusion only if the volume (admittance at 226 Hz) measured at + 200 daPa (or at --300 or --400 daPa) is attributable to the ear canal. - **If the volume is too large**, then the flat tympanogram may be due to such causes as - \(1) a perforated tympanic membrane; - \(2) a patent myringotomy tube, if one is present; or - \(3) the absence of a hermetic seal. It is reasonable to consider the volume to be larger than normal when it exceeds 2.0 ml (mmhos) in children and 2.5 ml (mmhos) in adults - Volumes that are too small: - \(1) a clogged probe tip; - \(2) a probe tip that is pushed against the canal wall; - \(3) impacted cerumen or another obstruction in the ear canal; and - \(4) a clogged myringotomy tube if one is present. These cases are usually identified by volumes at or close to 0 ml (mmhos). - Fig. 7.8 demonstrates how the flat tympanograms associated with tympanic membrane perforation, otitis media with effusion, and a clogged probe tip are differentiated on the basis of their ear canal volumes. - Important to keep this issue in mind when tympanograms are classified by type because the letter designation does not account for the ear canal volume. For example, we could not attribute the type B tympanogram in Fig. 7.5 to middle ear effusion unless we also know the ear canal volume. Tympanometric Peak Pressure: - Pressure on the outer ear side of the eardrum is generated and measured using the air pump and manometer connected to the probe tip. - Tympanogram peak occurs when the same pressure exists on both sides of the tympanic membrane. - Ear canal pressure corresponding to the tympanogram peak is also an estimate of the pressure within the middle ear. - Fig. 7.9 shows otherwise identical tympanograms with peak pressures of 0, --50, --150, and --250 daPa. - Notice how increasingly negative tympanometric peak pressures are shown moving to the left of 0 daPa. - Even though "tympanometric peak pressure" and "middle ear pressure" are often used interchangeably, we distinguish between the two terms here to point out that they are not always the same, especially when the patient has a flaccid tympanic membrane  - Abnormally negative tympanometric peak pressures are associated with Eustachian tube disorders - Can occur either with or without the presence of middle ear fluid. - Amount of negative pressure needed to consider the tympanometric peak pressure abnormally negative is not clearly identifiable in the literature. Suggested cutoff values vary widely, including values such as --25 daPa, --30 daPa (Feldman 1975), --50 daPa (Porter 1972), --100 daPa (Jerger 1970; Jerger, Jerger & Mauldin 1972; Jerger, Jerger, Mauldin, & Segal 1974; Fiellau-Nikolajsen 1983; Silman, Silverman, & Arick 1992), --150 daPa (Renvall & Liden 1978; Davies, John, Jones, & Stephens 1988), --170 daPa (Brooks 1969), and about --200 daPa (AAA 2020). - **In practice, --100 daPa appears to be a reasonable "cutoff value" for tympanometric peak pressure**. - Lower pressures suggest the possibility of Eustachian tube dysfunction. - Unfortunately, there does not seem to be a particular tympanometric peak pressure cutoff value that successfully distinguishes between the presence and absence of middle ear effusion. - One can sometimes follow the course of recovery from a case of otitis media as tympanometric peak pressures that become progressively less negative over time (Feldman 1976). - This course of events can be seen in stylized form by imagining that the series of tympanograms in Fig. 7.9 follows a sequence going from --250 daPa toward 0 daPa over a period of several days. - Unlike the situation for negative middle ear pressure, the significance of abnormally high positive peak pressures (e.g., \> 50 daPa) is not clear. - In addition, positive peak pressure has also been associated with nonpathological causes such as rapid elevator rides, crying, or nose blowing (Harford 1980). [Tympanogram Shape:] - Low-frequency probe tones like 226 Hz are mainly sensitive to changes in stiffness (or compliance). - Shapes of most 226 Hz (220 Hz) tympanograms do not provide much information because they are usually single-peaked or flat. - Infrequent exception is the presence of a notch in the tympanogram peak. - Notched tympanograms are produced when mass becomes a significant component of the ear's immittance, which occurs near and above its resonant frequency. - For this reason notching is common with high-frequency probe tones (e.g., 660 or 678 Hz; - Notching of the 226 Hz tympanogram is abnormal because it means that something is causing mass to play a greater than normal role in the ear. These changes can be produced by a scarred or flaccid tympanic membrane (even in an otherwise normal ear), as well as abnormalities such as ossicular discontinuities (which produce substantial hearing losses). - These are the aberrations associated with type D and E tympanograms. [Vascular Pulsing:] - Most tympanograms are smooth, they sometimes have regular ripples or undulations that are synchronized with the patient's pulse, which is their origin. - Medical referral is indicated when vascular pulsing is present on the tympanogram because it tends to occur in patients with glomus jugulare tumors (Feldman 1976). 678 Hz (660 Hz) Tympanograms - "High-frequency" tympanograms are obtained with probe tones higher than the traditional "low-frequency" 226 Hz (or 220 Hz) probe tone. - "high-frequency" probe tone is usually 678 Hz (or 660 Hz), but we will see below that 1000 Hz probes are used with infants. - Combined use of 226 Hz and 678 Hz tympanograms is sometimes called multiple frequency (or multifrequency) tympanometry. - Term is also used to describe various tympanometric methods that involve testing at many frequencies to arrive at the resonant frequency of the ear and other measures. - Abnormally high resonant frequencies are associated with stiffening disorders, such as otosclerosis, - Abnormally low resonant frequencies are associated with disorders that increase the mass component of the system, like ossicular discontinuity. - Separate tympanograms are obtained for susceptance (B) and conductance (G) when testing at 678 Hz (or 660 Hz) instead of a single admittance (Y) tympanogram. - Depending on the instrumentation used, the B and G tympanograms may be obtained simultaneously (which is preferred), or they may be done one after the other. In either case, the interpretation is easier when they are plotted on the same tympanogram form. Normal 678 (660) Hz Tympanograms - In contrast to 226 Hz tympanograms, 678 Hz (660 Hz) B-G tympanograms are interpreted on the basis of their shapes and configurations (or morphology). - Four types of normal 678 Hz B-G tympanograms - Named on the basis of the number of positive and negative peaks and must also meet a criterion for tympanogram width. - \(1) normal type of 678 Hz tympanogram is called 1B1G - there is one peak for the B tympanogram and one peak for the G tympanogram (Fig. 7.10a). - other three normal variations involve notches on one or both of the tympanograms. - \(2) normal type has a notched peak on the B tympanogram and a single peak on the G tympanogram. - notch on the B tympanogram can be viewed as two positive peaks with a negative peak between them. The convention is to count these "peaks" or "extrema" (in both directions). - This normal variation is called 3B1G because B has three peaks and G has one peak (Fig. 7.10b). - \(3) normal variation is called 3B3G because there are three peaks on both tympanograms (Fig. 7.10c). The - \(4) last type of normal 678 Hz (or 660 Hz) configuration is called 5B3G because it has five peaks on the B tympanogram and three peaks on the G tympanogram (Fig. 7.10d). - Table 7.4 Percentages of normal 678 Hz (or 660 Hz) B-G tympanograms  **The Acoustic Reflex** - Presenting a sufficiently intense sound to either ear results in the contraction of the stapedius muscle in both ears acoustic or stapedius reflex. - Reflexive muscle contraction stiffens the conductive mechanism via the stapedius tendon, and therefore changes the ear's immittance. - Acoustic reflex is easily measured because the immittance change is picked up by the probe tip and displayed on the immittance device meter. Acoustic Reflex Arc: - Acoustic reflex arc was described by Borg (1973), and its basic features are shown in Fig. 7.14. - Follow this pathway assuming that the right ear was stimulated. - Afferent (sensory) part of the arc involves the auditory (eighth) nerve from the right ear, which goes to the right (ipsilateral) ventral cochlear nucleus. - Neurons then go to the superior olivary complexes on both sides of the brainstem. - Right and left superior olivary complexes (SOC) send signals to the facial (seventh) nerve nuclei on their respective sides. - Finally, the efferent (motor) legs of the acoustic reflex arc involve the right and left facial nerves, which direct the stapedius muscles to contract in both ears. - The acoustic reflex involves the stapedius muscles. - While the tensor tympani muscles do respond to extremely intense sounds, this is actually part of a startle reaction, and the accumulated evidence reveals that the acoustic reflex in humans is a stapedius reflex (Gelfand 2018). - Certain kinds of nonacoustic stimulation also elicit contractions of the stapedius muscles (e.g., tactile stimulation of the external ear) or of both middle ear muscles (e.g., an air puff to the eye). Acoustic Reflex Tests - Basic acoustic reflex testing procedure involves presenting a sufficiently intense tone or noise to activate the reflex, and observing any resulting immittance change, which is usually seen as a decrease in the ear's admittance (i.e., an increase in its impedance). - Immittance change caused by the contraction of the stapedius muscle is measured in the ear containing the probe tip, which is called the probe ear. - Ear receiving the stimulus used to activate the reflex is called the stimulus ear. - Either ear can be the stimulus ear because the stimulus can be delivered from the receiver in the probe tip (the fourth tube described earlier) or the earphone on the opposite ear. - Ipsilateral or uncrossed acoustic reflex is being measured when the stimulus is presented to the probe ear, which is the same ear in which the immittance change is being monitored. - Contralateral or crossed acoustic reflex is being measured when the probe tip is in one ear and the stimulus is presented to the opposite ear. - Easy to identify whether the right or left ear is being tested for the ipsilateral reflex because the reflex is activated and monitored in the same (probe) ear. - Can be confusion about which ear is the "test ear" with contralateral reflexes because the stimulus and probe are in opposite ears. - Both ears (and the reflex pathway between them) are really being tested with the contralateral reflex. - Convention is to identify a contralateral acoustic reflex according to the stimulated ear. - "right contralateral acoustic reflex" means that the stimulus is in the right ear (with the probe in the left ear), - "left contralateral acoustic reflex" means that the stimulus is in the left ear (with the probe in the right ear). - Another way to avoid confusion is to describe the test results as, for example, "stimulus right" or "probe left." - The usual reflex testing order is to do the left contralateral and right ipsilateral reflexes while the probe is in the right ear (Fig. 7.15a), and then to reverse the headset and do the right contralateral and left ipsilateral reflex test while the probe is in the left  - Variety of acoustic reflex tests are regularly used in clinical assessment. - Two basic measurements are discussed here: - acoustic reflex threshold, which is the lowest stimulus level that produces a reflex response, - acoustic reflex decay, which is a measure of how long the response lasts if the stimulus is kept on for a period of time. - More advanced techniques include - \(1) acoustic reflex magnitude and growth functions (how the size of the response depends on stimulus level); - \(2) acoustic reflex latency (the time delay between the stimulus and the reflex response); - \(3) nonacoustic reflexes (middle ear muscle reflexes that are stimulated tactually, electrically, or with air puffs instead of sound). Acoustic Reflex Threshold: - Acoustic reflex threshold (ART) testing involves finding the lowest level of a stimulus that causes a measurable change in acoustic immittance. - Fig. 7.17 shows the measurement of an ART under laboratory conditions and illustrates several characteristics of the reflex response. - The immittance changes attributed to the reflex are associated in time with the stimulus presentations, and that the magnitude of the reflex response increases as the stimulus level is raised above the ART. - May also say that the ART is the smallest discernible immittance change that is associated in time with the presentation of a stimulus, and that responses should also be present (and generally larger) at higher stimulus levels. - Clinical ARTs are usually obtained using pure tone stimuli at 500, 1000, and 2000 Hz. - Some clinicians also use 4000 Hz, it is not recommended because even young people with normal hearing experience elevated ARTs at this frequency due to rapid adaptation (Gelfand 1984). - Pure tone ARTs are obtained by changing the intensity of the stimulus in 5 dB steps while watching for admittance changes caused by the stimuli. - These admittance changes are observed by watching for deflections on the admittance device meter, and the ART is considered to be the lowest intensity causing a deflection that can be distinguished from the background activity on the meter. - This approach is often called "visual monitoring with 5 dB steps." - It is sometimes necessary to test reflex thresholds using broadband noise (BBN) stimuli. - Unlike pure tone ART testing, which can use visual monitoring with 5 dB steps, 1 or 2 dB steps and recorded responses are needed to accurately measure ARTs for broadband noise stimuli even for clinical purposes. - Due to the very small size of the reflex response at and just above the ART when broadband noise is used - These small reflex responses are often missed with visual monitoring, and the lowest level at which they occur is obscured with 5 dB steps. - As a result, visual monitoring with 5 dB steps often causes the normal BBN ART to appear higher (poorer) than it really is, and also shrinks the size of the normal 20 dB noise-tone difference The acoustic reflex threshold is the lowest stimulus level resulting in an observable immittance change that is "time-locked" to a stimulus presentation. These data were obtained under laboratory conditions, using 1 dB stimulus steps and simultaneous recording of the stimulus presentations ("event marker") and reflex responses. - Normal ARTs with a 220 or 226 Hz probe tone occur between \~ 85 and 100 dB SPL for pure tones and \~ 20 dB lower when the stimulus is broadband noise - Most clinical measurements involve pure tone ARTs. - Table 7.5 shows a representative set of contralateral and ipsilateral ARTs (in dB HL) for people with normal hearing. - Acoustic reflex thresholds based on wideband reflectance measurements generally have been found at lower (better) stimulus levels, although the size of the difference varies between studies ( - The difference between the ARTs for pure tones and broadband noise is the basis of many methods that attempt to identify or predict hearing loss from ARTs as discussed below.  Acoustic Reflex Decay - Also common practice to test for acoustic reflex decay (or adaptation), which is a **measure of whether a reflex contraction is maintained or dies out during continuous stimulation** - Reflex decay is tested at both 500 and 1000 Hz. - Higher frequencies are not tested because even people with normal hearing can have rapid reflex decay above 1000 Hz. - Test involves presenting a stimulus tone continuously for 10 seconds at a level 10 dB above the reflex threshold. - Magnitude of the reflex response will either stay the same or decrease over the course of the 10 second stimulus, as shown in Fig. 7.18. - Central issue is whether the response decays to half of its original magnitude. - If the magnitude of the reflex response does not decrease to 50% of its original size during the 10 second test period (Fig. 7.18a,b), then the **outcome is considered negative**. - **Test is considered positive** if the magnitude of the reflex response does decay by 50% or more within this time period (Fig. 7.18c). Conductive Hearing Loss: - Conductive hearing losses cause acoustic reflexes to be either "elevated" or "absent." - By "elevated" we mean that the ART is higher than normal, that is, it takes more intensity to reach the reflex threshold than would have been needed if there was no conductive loss. - An "absent" reflex means that a reflex response cannot be obtained, even with the most intense stimulus available (which is usually 125 dB HL on most modern immittance devices). The effects of conductive loss can be summarized by two basic rules: - \(1) Probe-ear rule - The presence of conductive pathology in the probe ear causes the acoustic reflex to be absent. - Even though the stapedius muscle itself may actually be contracting, presence of the pathology prevents us from being able to register any change in acoustic admittance that can be picked up by the probe tip. - Chances of having a measurable acoustic reflex fell to 50% when the air-bone-gap in the probe ear (averaged across frequencies) was only 5 dB. - \(2) Stimulus-ear rule - A conductive loss in the stimulus ear causes the ART to be elevated by the amount of the conductive impairment. - Occurs because the amount of the stimulus that actually reaches the cochlea will be reduced by the amount of the air-bone-gap. - For example, suppose an otherwise normal-hearing patient develops otitis media with a 25 dB air-bone-gap. - 25-dB air-bone-gap causes the signal reaching their cochlea to be 25 dB weaker than the level presented from the earphone. - If the patient's ART would normally have been 85 dB HL (without the conductive loss), then the stimulus would now have to be raised by 25 dB to 110 dB HL to reach their cochlea at 85 dB HL. - Hence, the patient's ART would now be elevated to 110 dB HL. - In addition, if the air-bone-gap is large enough, then the ART will be elevated so much that the reflex will be absent. - Occurs because the highest available stimulus level cannot overcome the size of the air-bone-gap and still deliver a large enough signal to the cochlea. - Chances of having an absent acoustic reflex reached 50% when the conductive loss (averaged across frequencies) was 27 dB in the stimulus ear. - Occurred because the (otherwise normal) average ART of \~ 85 dB HL plus an average air-bone-gap of 27 dB is more than 110 dB HL, which was the highest stimulus level available at that time. - Modern immittance instruments allow testing up to 125 dB HL, so that the 50% point for absent reflexes is not reached until there is a 42 dB air-bone-gap in the stimulus ear (Gelfand 1984). - Following acoustic reflex configurations result from the two principles just described: - For unilateral conductive losses, contralateral acoustic reflexes tend to be - \(1) absent when the probe is in the pathological ear, - \(2) elevated or absent when the probe is in the normal ear. - Contralateral acoustic reflexes tend to be absent in both ears when there is a bilateral conductive impairment. - Ipsilateral acoustic reflexes are affected by both principles at the same time; - that is, the air-bone-gap reduces the effective level of the stimulus that actually reaches the cochlea, - the conductive pathology prevents an immittance change from being monitored even if the reflex is activated. - Consequently, ipsilateral acoustic reflexes tend to be absent when testing an ear with a conductive disorder, regardless of the condition of the opposite ear. These findings are illustrated in Fig. 7.19 for a unilateral conductive loss and in Fig. 7.20 for a bilateral conductive disorder.  Configuration of contralateral and ipsilateral acoustic reflexes in unilateral conductive hearing loss. The conductive loss affects the right ear in this example. Contralateral reflexes are absent with the probe in the abnormal ear ("probe ear rule," a), and are elevated (or absent) with the probe in the good ear and the contralateral stimulus going to the bad ear ("stimulus ear rule," b). The ipsilateral reflexes are absent when the probe is in the abnormal right ear (a), and normal when the probe is in the normal left ear (b). (a,b) Both contralateral and both ipsilateral reflexes tend to be absent when there is a bilateral conductive disorder. Sensorineural Hearing Loss: - Acoustic reflex thresholds depend on hearing sensitivity in a rather peculiar way - In this context "hearing sensitivity" represents a continuum going from normal hearing through various magnitudes of sensorineural hearing loss due to cochlear disorders. - Fig. 7.21, Fig. 7.22, and Fig. 7.23 show the 10th, 50th, and 90th percentiles of the ARTs at 500, 1000, and 2000 Hz for patients who have normal hearing or sensorineural losses associated with cochlear disorders. - For example, Fig. 7.21 provides the following information about patients who have hearing thresholds of 5 dB HL at 500 Hz: 10% of them have ARTs up to 75 dB HL, 50% have ARTs up to 85 dB HL, and 90% have ARTs up to 95 dB HL. - Similarly, Fig. 7.22 shows that among patients who have thresholds of 60 dB HL at 1000 Hz, 10% have ARTs up to 85 dB HL, 50% have ARTs up to 95 dB HL, and 90% have ARTs up to 110 dB HL. - Using the median (50th percentile) curves as a guide, we see that pure tone acoustic reflex thresholds - \(1) are about the same for people with normal hearing and sensorineural hearing losses of cochlear origin up to roughly 50 dB HL, and - \(2) become progressively higher as the amount of cochlear hearing loss increases above about 50 dB HL. The corresponding values for the 2000 Hz stimulus are shown in Fig. 7.23.  Fig. 7.21 Tenth, 50th, and 90th percentiles of acoustic reflex thresholds for a 500 Hz stimulus as a function of the hearing level at 500 Hz for people with normal hearing and sensorineural hearing losses of cochlear origin. Fig. 7.22 Tenth, 50th, and 90th percentiles of acoustic reflex thresholds for a 1000 Hz stimulus as a function of the hearing level at 1000 Hz for people with normal hearing and sensorineural hearing losses of cochlear origin.  Fig. 7.23 Tenth, 50th, and 90th percentiles of acoustic reflex thresholds for a 2000 Hz stimulus as a function of the hearing level at 2000 Hz for people with normal hearing and sensorineural hearing losses of cochlear origin. - Well established that patients with retrocochlear pathologies have acoustic reflexes that are elevated, often to the extent that the reflex is absent - However, the decision about when an ART is "elevated" must account for the fact that the ARTs depend on the magnitude of the hearing loss in patients who do not have retrocochlear involvement. - The 90th percentiles provide us with upper cutoff values for ARTs that meet this need. - Many prior inconsistencies about the diagnostic usefulness of the reflex were resolved by the introduction of 90th percentiles that account for the degree of hearing loss - Two sets of 90th percentile values are shown in Table 7.6 because both are in common use and distinguish between cochlear and retrocochlear ears with considerable success - In practice, the patient's ARTs are compared with the respective 90th percentiles that apply to their hearing thresholds for the frequencies tested. - If an ART falls on or below the relevant 90th percentile, then it is considered to be essentially within the normal and/or cochlear distribution. - ARTs that fall above the applicable 90th percentiles are considered elevated because only a small proportion of normal and/or cochlear-impaired ears have ARTs that are so high. - If the abnormally elevated or absent reflexes are not attributable to a conductive disorder, then the patient is considered to be at risk for eighth nerve pathology in the ear that receives the stimulus. - In contrast, many patients with functional impairments (Chapter 14) have ARTs that are below the 10th percentiles - Abnormal ref