Impedance Audiometer AT235 Operation Manual sw ver 2.00200 ver June 2007

Table of Contents Table of Contents ...1 Introduction...3 Intended Use ...3 Precautions...3 General Theory of Impedance Measurements...5 Understanding Tympanograms...6 Classification of Tympanograms ...7 Interpretation of Test Results...10 Tympanometric Curves And Pathologies...10 Reflex Interpretation ...11 Pathways For The Stapedius Reflexes ...13 Reflex Decay Interpretation...15 Examples Of Interpretation...16 Basic Functions ...21 Preparing the Test...21 Test Procedure ...24 Printing Test Results ...25 Connection to PC ...28 Installing Printer Paper ...29 Reflex and Tympanometry...31 Modifying Reflex Test A and B ...34 Ipsilateral and Contralateral reflexes...35 Tympanometry - only...35 Automatic Reflex Test - only ...37 Manual Reflexes...39 Editing Automatic and Manual Reflexes ...40 Manual Reflex Decay ...42 Eustachian Tube Function...44 Automatic and Manual Audiometry ...46 ”Child” Function ...48 Handling of Ear Tips...49 Cleaning of Ear Tips...49 Cleaning of Probe Tip...49 Functions of Buttons ...52 AT235

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Technical Specifications...54 Impedance Measuring system ...55 Reflex and Audiometer Functions ...56 Parts ...58 Connection Panel ...59 Unpacking / Inspection ...60 Contents of Shipment...60 Reporting Imperfections ...61 Care and Maintenance ...61 Trouble Shooting ...63 Frequently Asked Questions...65 Recommended Literature ...68 Dictionary ...70 Appendix A: Main Menu and Setup ...74 Main Setup Menu ...75 Tympanometry Setup Menu ...76 Setup Menu for Reflex Test A and B...78 Reflex Methods ...80 Common Setup Menu ...88 Appendix B: Installing the USB Driver on the PC ...92 Appendix C: General Maintenance Procedures ...95 Return Report...97 Drawing of Front Plate ...99

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Introduction Intended Use The AT235 is an automatic impedance audiometer suited for clinics performing screening, as well as diagnostic work. The test battery includes tympanometry, acoustic reflex testing, ipsilateral and contralateral reflex decay testing, Eustachian tube function test and AC audiometry. The AT235 tympanometer is intended to be used by an audiologist, hearing healthcare professional, or trained technician in a quiet environment (tymp and reflexes) and extremely quiet environment (Audiometry). Careful handling of instrument whenever in contact with patient should be of high priority. Calm and stable positioning while testing is preferred for optimal accuracy. It is recommended that the instrument be operated within an ambient temperature range of 15-35 degree Celsius (59-95 degrees Fahrenheit)

Precautions Notice - Be sure to insert the probe tip in a way which will assure an airtight fit without causing any harm to the patient. Using a proper and clean ear tip is mandatory. Notice - We recommend using a new ear tip for each patient. If the clinician rinses the ear tips they should be subjected to standard disinfecting procedure between patients. This includes physically cleaning the ear tip and use of a recognised disinfectant. Individual manufacturer's instruction should be followed for use of this disinfecting agent to provide an appropriated level of cleanliness. Notice - Be sure to use only stimulation intensities acceptable for the patient. Notice - The transducers (headphones, bone conductor, etc.) supplied with the instrument are calibrated to this instrument exchange of transducers requires a re-calibration.

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If this apparatus is connected to one or more other devices with medical CE marking, to make up a system or pack, the CE marking is only valid also for the combination if the supplier has issued a declaration stating that the requirements in the Medical Device Directive article 12 are fulfilled for the combination. Notice - Never clean the transducer housing with water or insertion instruments. Notice - Do not insert or in any way try to conduct measurements without proper probe eartip in place. Notice - When conducting audiometry using Eartone insert phones – do not insert or in anyway try to conduct measurements without proper foam tip in place. Notice - Although the instrument fulfils the relevant EMC requirements precautions should be taken to avoid unnecessary exposure to electromagnetic fields, e.g. from mobile phones etc. If the device is used adjacent to other equipment it must be observed that no mutual disturbance appears. Notice - Within the European Union it is illegal to dispose electric and electronic waste as unsorted municipal waste. Electric and electronic waste may contain hazardous substances and therefore has to be collected separately. Such products will be marked with the crossed-out wheeled bin shown below. The cooperation of the user is important in order to ensure a high level of reuse and recycling of electric and electronic waste. Failing to recycle such waste products in an appropriate way may endanger the environment and consequently the health of human beings.

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General Theory of Impedance Measurements To understand impedance measuring from a popular point of view it is sufficient to know that a sound of 226 Hz. presented into a cavity like the human ear will produce different SPLs depending on the volume of the cavity. By measuring changes in the SPL, equivalent volume changes can be established. Presenting a high positive or negative air pressure to the outer ear canal will stiffen the tympanic membrane, thus creating a cavity acoustically consisting of only the outer ear canal. In this way the equivalent volume of the outer ear canal can be established. By gradually varying the air pressure from a positive pressure to a negative the tympanic membrane and the attached ossicular chain will gradually become more and more mobile, showing more compliance to the sound pressure waves. The sound passage to the middle ear will then be less and less reduced or impeded by the tympanic membrane, and the impedance is said to be lower. The lowest impedance will be obtained when the air pressure is equal on both sides of the tympanic membrane, thus showing the highest compliance to the sound waves. In this state, the cavity responding to the introduced sound will be comprised of the outer ear canal as well as the middle ear. This will reveal the total equivalent volume of the outer- and middle ear. The equivalent volume of the middle ear, also called the compliance, is easily derived by subtracting the two volume measurements above. This is done automatically on the AT235 and the result is presented as "Compliance", measured in ml. The impedance curve, drawn by a gradual sweep across a wide pressure range, can reveal a great deal of information about the state of the middle ear, the tympanic membrane, and the ossicular chain. The above principle for measuring the stiffness of the tympanic membrane can also be used to detect tympanic membrane stiffness, caused by contraction of the middle ear muscles. This is usually referred to as the "Stapedius Reflex". The normal ear will, when subjected to loud signals, reflexively contract the Stapedius muscle (and in some cases the tensor tympani muscle). This will immobilise the tympanic membrane somewhat and this change of impedance is AT235

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detectable as explained above and a reflex recording of the impedance change can be presented. Such a reflex is called a Stapedius reflex, as the Stapedius muscle contraction is the dominant factor in creating this impedance change. Reflex measurements are normally carried out with air pressure in the outer ear canal set for maximum compliance. This Stapedius reflex can be elicited both ipsilateral and contralateral, and has great diagnostic value. Together with the impedance curve measurement the integrity of the complete middle ear system can be evaluated.

Understanding Tympanograms General Considerations: A given curve drawn in a co-ordinate system will always have its shape dictated by the vertical and horizontal graduations. The printout of the AT235 complies with the international standards in this respect, and therefore may not produce tympanogram shapes directly comparable to other instruments if these do not meet the standard requirements. The Peak: The peak of the tympanogram will horizontally be placed at the air pressure of the middle ear, as equal pressures on both sides of the tympanic membrane produces the highest compliance of the system. A slight deviation of the peak in the direction of the air pressure sweep may be experienced, due to an inherent hysteresis of the middle ear and the test equipment. A slower sweep speed may diminish the offset. The Height: The height of the tympanogram from its more or less horizontal bottom line (measurements made from start pressure) to the top shows the difference in compliance between stiffened tympanic membrane and max. compliance. This difference is referred to as "compliance" and is a measure for the equivalent volume of the middle ear.

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Equivalent Volume: The term "Equivalent Volume", in which compliance is measured, should be understood clearly in order to avoid misinterpretation of test results. The unit of measurement is cm3 (or ml.) but this does not mean that e.g. the middle ear has this exact internal volume. It means that the middle ear, as seen from the outer surface of the tympanic membrane, reacts the same way as a hard walled cavity of this exact volume would react. Compared to a hard walled cavity a normal middle ear incorporates at least three major differences. One is friction due to the ligaments connected to the ossicles (resistance). The second is stiffness caused by the elastic qualities of the eardrum and the enclosed air and by a fluid pressure from the inner ear exerted on the stapes (stiffness reactance). The third is the mass of the eardrum and the ossicles (mass reactance). At 226 Hz the stiffness component is by far the most dominant factor and is therefore the subject of measurement. The Shape: The shape of the tymp curve will change when the stiffness of the system is changed (e.g. by ossicular chain disruption, otitis media, etc.), and this is a primary reason for the diagnostic value of this measurement. However, normal ears show a great variety of tymp shapes so this should never be taken as the only basis for making a diagnosis. Furthermore, two different abnormalities may have opposing effects, resulting in a normal shape of the tymp curve.

Classification of Tympanograms Tympanograms can be classified according to compliance (height, measured in ml. or cm3), pressure at compliance maximum (measured in daPa), rate of compliance change (gradient in %), and shape. Please refer to the chapter "Examples of Interpretations" in this manual for illustrations of the classic curve categories, and the names given to them by Liden and Jerger. On the following pages a more detailed description of each category is presented. AT235

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Type "A" characteristics: The tymp curve shows a clear compliance peak within the pressure range of ± 50 daPa for adults. For children the middle ear pressure may be considered normal down to -150 daPa negative pressure. Normal ears often show type "A" tympanograms. Type "AD" characteristics: The type AD tympanogram is essentially a type A tympanogram in which the curve is very high and may be outside the range of the instrument / recording chart. Peak is within the pressure range of type A of ± 50 daPa. The very mobile eardrum can reproduce various curves. It can represent ossicular discontinuity, flaccid eardrum or a combination of both. Peaking and notching outside the test range is possible. Note: The type AD curve may reveal itself as being a type D curve, if a higher probe tone, e.g. 800 Hz, is used. Type "AS" characteristics: The type As tympanogram is essentially a type A tympanogram in which the curve is much shallower than usual. Peak is within the pressure range of type A of ± 50 daPa. For children the middle ear pressure may be acceptable down to -150 daPa negative pressure. The pathology could be immobile stapes due to otosclerosis (no reflexes), some form of otitis media, thick or scarred eardrum, or just a normal variant. Infants’ ears may show this small compliance. Type "B" characteristics: Low compliance without peak identification. Middle ear pressure is unknown, probably negative. The type "B" is flat, going slightly upwards by negative pressure. It may be associated with ears having extremely stiffened middle ear systems. Indication of fluid (serous or adhesive otitis media), retracted eardrum, blockage of the external ear canal, or perforated eardrum e.g. with drainage tube. Note: Ears with type B tympanograms should be tested for peak identification down to -600 daPa.

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Type "C" characteristics: Normal compliance peak with peak identification in the negative pressure range, e.g. below -50 daPa for adults (Bluestone) and below -150 daPa for infants (Liden) .The type C curve shows all the characteristics of normal type A, AD and AS curves. The type C curve indicates poor Eustachian tube function with possible developing or resolving middle ear effusion. Type "D" characteristics: Depicted by a deep curve with a small notch at the peak. Middle ear pressure ± 100 daPa. This curve does not necessarily indicate a pathological ear. Healed perforation of tympanic membrane, fixation of parts of the bones after ossicular discontinuity, flaccid eardrum with ear wax, or maybe a ventilation tube blocked with ear wax and healed middle ear, can cause peaking and notching, resulting in many shapes at the top of the maximum compliance curve. The curve could also be a narrow type E (W shaped) tympanogram. Note: May be better detected with an 800 Hz probe tone. Type "E" characteristics: Depicted by a broad, deep, often multiple notching. "W" shaped. This tympanogram is usually caused by ossicular discontinuity, but may also indicate restored ossicular chain one year or more after stapedectomy. Note: May be better detected with an 800 Hz probe.

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Interpretation of Test Results Tympanometric Curves And Pathologies - According to Feldmann Peak Pressure Negative Pressure:

Positive Pressure:

Normal Pressure:

1) Ossicular bone 1) Blocked fixation Eustachian 2) Adhesive fixation tube 3) Ossicular 2) Serous discontinuity otitis media 4) Middle ear tumour 5) Eardrum abnormality

Absence of Pressure Peak:

1) Middle ear 1) Early effusion acute otitis 2) Open tymp. media membrane 3) Artifact

Amplitude Increased Amplitude: 1) Eardrum abnormality 2) Ossicular discontinuity

Decreased Amplitude:

Unchanged Amplitude:

1) Ossicular fixation bony or adhesive 2) Serous otitis media 3) Cholesteatoma, polyps, granuloma 4) Glomus tumours

1) Blocked Eustachian tube 2) Early acute otitis media

Shape ...Slopes... Increased slope: Decreased / Flattened slope: 1) Eardrum abnormality 2) Ossicular 1) Serous otitis discontinuity 2) Ossicular fixation 3) Tumours of middle ear

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Smoothness: Altered smoothness: 1) Eardrum abnormality 2) Ossicular discontinuity 3) Vascular tumours 4) Patulous Eustachian tube

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Reflex Interpretation Figure 1:

Onset and Offset: As judged on the normal reflex these measurements have little or no diagnostic value (See Decay Test). The attention should be drawn to the fact that instrument variation exists in these parameters. Roughly, it can be said that the more steep the onset and offset slopes, the faster is the instrument. Especially older instruments had rather flat slopes. Noise: Acoustical signals showing up in the reflex recording, yet irrelevant to the Stapedius reflex. As the reflex measurements are based on observing the change in sound intensity of a 226 Hz tone, as explained in "Popular Introduction to Impedance", it is possible that environmental noise of this frequency entering the ear will show up as part of the test result. This is a problem inherent to the measuring method and therefore common to all normal impedance meters. Heart beat, talking and external noises are common causes of noise peaks seen on the reflex curve. A negative reflex may occur due to the following interference of noise: Prior to recording the reflex activity an acoustic reference level is measured in the ear canal without any Stapedius activity. The difference between this reference level and the AT235

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level present when the Stapedius muscle is active is recorded as a reflex. If, however, external noise was entering the ear only during reference level measurement, and not during reflex measurement, the level may actually be lower during the reflex, thus resulting in a negative reflex. This is of course not a valid measurement. The negative reflex is an extreme situation, but noise will always distort the measurements to a certain degree and should therefore be avoided. Negative Onset: It is quite common to see reflexes start out with a small negative deflecting dip. In ears with stapedial otosclerosis this dip with an additional dip at the end of the stimulation can be the only reaction left from the contraction of the Stapedius muscle. Some tumour ears have been reported to give only the negative onset, but no further reaction. Reflex Threshold: For a given stimulus the lowest level that elicits a detectable reflex. This is not an absolute measurement as no exhausting norm exits defining stimuli and related reflex characteristics. Therefore, differences in test setups and reflex evaluation will produce somewhat different results. It is not uncommon to report the reflex threshold as the intensity which produces a 1% or 2% change in equivalent volume (Test "A" with 2% sensitivity). It should be noted that a visual examining of reflex test might reveal some Stapedius muscle action, also at slightly lower stimulus intensities. This procedure (see "Example of Popular Fixed Intensity Reflex Test") is recommended for establishing the absolute reflex threshold. Generally, noise stimuli elicit reflexes at lower levels than pure tones do.

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Pathways For The Stapedius Reflexes Figure 2:

The Nature of the Reflex: The Stapedius muscle reflex is elicited binaurally via monaural stimulation (Ipsilateral stimulation via the impedance probe contralateral stimulation via the headphone). The average reflex threshold is 85 dB HL (70 dB - 100 dB) for normal ears of 20 year old patients when pure tones are used as stimulus. Noise as stimulus produces a threshold approx. 10-20 dB lower as noise is made out of many simultaneous tones together carrying more energy. Increased stimulation level will produce a stronger reflex. Cochlear and retrocochlear pathology may show less rapid growth of reflex amplitude versus stimulation amplitude. Primarily, a reflex test shall answer these questions: AT235

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• Is the reflex absent or present? • If present, is it present both contralateral and ipsilateral? • What is the threshold of the reflex? If the test shows normal reflex thresholds and a normal tympanogram is present, the middle ear will usually be classified as healthy. One exception, though, is the early stage of otosclerosis. Non Acoustic Stimulation: The Tensor Tympany muscle of the middle ear can produce a reflex elicited by a non acoustic stimulus or by an acoustic stimulation loud enough to have a startling effect on the patient. As the tensor reflex is a startle response, it will decrease and disappear after a few equal stimulations. Even though the tensor reflex is regarded late and unstable compared to the Stapedius reflex, it may be useful in testing deaf or hard of hearing patients. Below is shown the tactile sensitive area of the face to be stimulated with e.g. a piece of wool. Stimulation may also be a blow of air into the eye region of the patient. Figure 3:

Air

Touch

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Reflex Decay Interpretation Figure 4:

Reflex Decay: Reflex decay is calculated as the reduction of size of the acoustic reflex during the first 10 seconds of muscular contraction. Most normal ears will be able to maintain a Stapedius contraction for 10 seconds or longer for frequencies below 1000Hz, at a level 10dB above reflex threshold. A high reflex decay score could indicate VIIIth nerve disorders. Another way of stating the reflex decay is by finding the number of seconds it takes before the Stapedius contraction falls to 50% of its initial maximum. Note: If a decay score is obtained, you should assure that it is not due to an improper seal, which might produce an artefact similar to a decaying curve. See the chapter “Preparing the Test” for details of fitting the probe. The fact that the light band of the probe goes off, and the test starts is not an absolutely certain indication of a fit good enough to produce valid decay test results. This is due to the prolonged test time and the high sensitivity of the test. Also great care should be taken to have the probe kept in a very fixed position relative to the ear during testing.

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Examples Of Interpretation In the following, some typical compliance curves, reflex curves and the possibly associated pathology are shown. The curves are idealised and only one expected pathology is described for each combination of tympanogram and reflex. A combination of variables always has to be taken into consideration. E.g. the combination of a stiff middle ear system and a floppy eardrum may result in a tympanogram falling within the normal category. The interpretations stated here are generalised examples taken from the currently available literature and they can, of course, vary with each individual case. The diagnostic value of tympanograms showing a "D" or "E" shape is reduced today. A probe tone higher than 226 Hz has been preferred for these particular tympanograms.

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Pathology

: Normal ear.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Cochlea lesion.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Normal. -100 daPa to +100 daPa. Present. Present. No hearing loss.

Normal. -100 daPa to +100 daPa. Present. Present or absent. Sensory neural hearing loss.

Pathology

: Retrocochlear lesion.

Volume Pressure Ventilation Reflex Audiogram

: Normal. : -100 daPa to +100 daPa. : Present. : (Abnormal Decay.) : Sensory neural hearing loss (May be unilateral).

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Pathology

: Supranormal eardrum (floppy) or atrophic/scarred eardrum.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Disrupted ossicular chain peripheral to stapes muscle attachment.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Disrupted ossicular chain medial to stapes muscle attachment.

Volume Pressure Ventilation Reflex

: : : :

Audiogram

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Normal. -100 daPa to +100 daPa. Present. Present. Normal.

Normal. -100 daPa to +100 daPa. Present. Absent. Conductive loss.

Normal. -100 daPa to +100 daPa. Present. Absent (Present by contralateral stimulation). : Conductive loss.

Pathology

: Disruption of ossicular chain with bones fixated to the tympanic membrane, resonating. Supranormal eardrum (floppy).

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Normal. -100 daPa to +100 daPa. Present. Absent / Present. Conductive loss.

Pathology

: Scarred and healed (abnormal) eardrum.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

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Normal. -100 daPa to +100 daPa. Present. Present. Normal.

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AT235

Pathology

: Fluid in the middle ear, or serous otitis media.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Ear wax in the external ear canal (Obturating cerumen).

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Perforated tympanic membrane - defect or ventilated tympanotomy. Traumatic rupture.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Otosclerosis or stapes fixation.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Adhesive otitis media. Adhesive ossicular fixation (glue ear).

Volume Pressure Ventilation Reflex Audiogram

: : : : :

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Normal. Peak not obtainable. Absent or elevated (rare). Mild to moderate conductive loss.

Low Normal. Absent. Mild to moderate conductive loss.

Normal / High Not obtainable. Absent (peaks). Mild to moderate conductive loss (20 dB).

Normal. -100 daPa to +100 daPa. Present. Absent or elevated (rare). Moderate conductive loss.

Normal. Negative / moderate. Absent. Moderate conductive loss.

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Pathology

: Moderate fluid in the middle ear.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Impact fluid in the middle ear.

Volume Pressure Ventilation Reflex Audiogram

: : : : :

Pathology

: Blockage of Eustachian tube; fluid in the middle ear may be present.

Volume Pressure Ventilation Reflex Audiogram

: Normal. : Negative. : Absent or poor : Absent or elevated (rare). : Mild to moderate conductive loss.

Normal. Negative / negative. Mild conductive loss.

Normal. Not obtainable. Absent. Moderate conductive loss.

Pathology: Acute Serous Otitis Media: Positive middle ear pressure is rarely observed in tympanometry. Usually it is a consequence of sneezing or valsalvation. One pathological condition that may cause positive pressure in the middle ear is acute serous otitis media in the early stage. A typical acute serous otitis media may develop according to the tympanograms outlined below:

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