Otology & Neurotology 36:373Y381 2015, Otology & Neurotology, Inc.
Voluntary Eardrum Movement: A Marker for Tensor Tympani Contraction? *Margaret Aron, †Duncan Floyd, and *Manohar Bance *Division of OtolaryngologyYHead and Neck Surgery, and ÞNova Scotia Hearing and Speech Centers, Dalhousie University, Halifax, Nova Scotia, Canada Hypothesis: Voluntary eardrum movement (VEM) and resultant tympanometric changes reflect tensor tympani (TT) contraction. Background: TT contraction has been hypothesized to cause symptoms of aural fullness, tinnitus, clicking, and even vertigo despite the lack of understanding of how it functions or what causes it to contract. Identifying tympanometric changes unique to TT contraction can provide a diagnostic tool for identifying its role in pathologic conditions. Methods: Various tympanometric measurements were performed on human subjects who could voluntarily move their eardrums. These were compared with similar tympanometric measurements performed on cadaveric temporal bones while manually tensing the TT and stapedius muscles individually. Results: Eight subjects (14 ears) who could cause VEM were identified. Compared with baseline, VEM resulted in significantly decreased middle ear compliance ( p G 0.01) and middle ear pressure ( p G 0.01) measurements. The compliance changes seen
with VEM were larger than those seen with acoustically stimulated stapedius contraction. Finally, the direction of compliance change with VEM was dependent on the pressure applied to the external auditory canal (EAC), with compliance increasing with positive EAC pressure. This was not seen with stapedius contraction. These findings were reproduced using the cadaveric temporal bone model: larger compliance changes with pull on TT as compared with stapedius with neutral EAC probe pressure; change in direction of compliance changes with varying EAC probe pressure with TT pull, not with stapedius pull. Conclusion: TT contraction produces distinctive tympanometric findings that can be used to support its abnormal contraction in ears with symptoms compatible with TT syndrome. Key Words: ImpedanceVTemporal bone studyVTensor tympaniVTympanic membrane movementVVoluntary contractionVVoluntary ear drum movement. Otol Neurotol 36:373Y381, 2015.
Although contraction of the middle ear muscles (MEMs) (stapedius and tensor tympani [TT]) has been implicated in various otologic conditions, the role of these muscles in these conditions has not been verified and is unclear. The stapedius muscle can be reliably activated by acoustic stimuli, with its effects on middle ear compliance readily demonstrated using impedance audiometry. The physiologic role, contraction inciting factors, and effects on impedance tympanometry for the TT, however, are much less clear. Despite this, TT contraction has been implicated in a number of otologic conditions including tinnitus (1), otalgia, Me´nie`re’s disease (MD), and ‘‘tensor tympani syndrome,’’ a purported syndrome described by Klockhoff (2Y4), characterized by complaints of fullness, tinnitus, vertigo, and dysacusis. If the TT is hypercontracted in some otologic pathologies, potentially we could perform therapeutic TT section in selected patients. In fact, TT sectioning has been reported to
be successful in managing MD (5Y7) as well as some cases of tinnitus (1). Without definitive markers for TT contraction, it becomes a matter of ‘‘faith’’ to assign many otologic pathologies, perhaps spuriously, to the TT. Bance et al. (7) studied the effect of voluntary eardrum movements (VEMs) on middle ear compliance suspected to be caused by TT contraction. This study, however, could not definitively determine if the changes were caused by the TT alone versus stapedius alone versus co-contraction of the two muscles. By comparing VEM and acoustically mediated stapedius contraction in human models with TT and stapedius muscle pull in cadaveric studies, the current study aims to test our hypothesis that VEMs are mediated by TT contraction. If true, the effects on middle ear compliance of VEM could be used as a marker for studying TT contraction. MATERIALS AND METHODS This study was approved by our institutional ethics board.
Address correspondence and reprint requests to Manohar Bance, M.D., M.Sc., F.R.C.S.C., Division of OtolaryngologyYHead and Neck Surgery, Dalhousie University, Room 3184, 3rd Floor Dickson Bldg, VG Site, QEII Health Sciences Centre, 1278 Tower Rd, Halifax, NS, Canada B3H 2Y9; E-mail: [email protected] The authors disclose no conflicts of interest.
Human Studies We identified eight subjects (with 14 ears tested) at our institution who could move their tympanic membrane (TM) voluntarily. This movement was confirmed by direct visualization of TM movement under microscopic visualization.
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Impedance audiometry (Interacoustics Impedance Audiometer Az26) was performed on all subjects to evaluate the effect of this VEM on middle ear compliance using static tympanometry as well as with a modified reflex decay paradigm, as described below, which allowed measurement of acoustic admittance changes during a 10-second window. Measurements were: 1. Static compliance: measured using a 226-Hz probe tone at baseline and then repeated during VEM. For each ear, values are the average of two repeated measurements. 2. Modified reflex decay measurement: Using ‘‘manual’’ settings for reflex decay and applying the following parameters: pressure -1 to +1 daPa (i.e., close to zero external auditory canal [EAC] pressure), probe tone 1,000 Hz (the volume of the probe tone was minimized to 10 dB SPL to eliminate acoustically induced stapedial reflex), and 10-second recording window. This allowed us to record the effect of sequential VEMs on compliance during a 10-second window. 3. Additional investigations were performed as detailed below on three subjects to explore and compare VEM with known stapedius contraction, which can be incited by acoustic stimulation, to determine if stapedius contractions are similar to and could explain the VEMs or whether they differ substantially from the VEMs. The TT does not respond to sound in normal human subjects (7). • First, TMs were examined under the microscope as a 500-Hz sound at 105 dB was delivered to the contralateral ear to observe whether maximal acoustically evoked stapedius reflex (which would be bilateral) resulted in visible TM movement. • Second, the magnitude of compliance change in the modified reflex decay setting with VEMs was compared with the magnitude of the compliance change seen with maximal acoustically induced stapedius contraction.
FIG. 1.
To test the latter, we first confirmed that the maximal acoustically induced stapedius reflex, tested using an ipsilateral 10-second 500-Hz tone at 105 dB, persisted for the entire 10-second recording of static compliance measurement. Because the static compliance setting uses a much larger scale for compliance (0Y1.5 ml) than does the reflex decay setting (0Y0.2 ml), larger compliance changes could be measured using static compliance settings. Thus, using two probes from two separate tympanometry machines, a 10-second 500-Hz tone at 105 dB was delivered to one ear while static compliance measurements were performed on the other ear during the 10-second window of the incited stapedius reflex contraction. These were compared with baseline static compliance as well as to static compliance changes induced by VEM. • Third, we wished to test the predictions in Figure 1 (see below for further clarification) by measuring compliance change during VEMs and stapedius contraction as a function of the baseline pressure applied to the EAC. As the pressure delivered to the EAC was manually varied, effects on the compliance changes seen with VEM and stapedius contraction were measured and compared. To test this, the middle ear pressure (MEP) at peak admittance (the peak of the tympanometric curve) was measured and denoted as ‘‘peak pressure.’’ Then, using the modified reflex decay setting (as described above), the subject was asked to perform VEMs as the pressure applied to the EAC was manually modified, and static compliance measured, to test the following three conditions: 1. pressure at or near this peak pressure (i.e., EAC and MEP equal; condition in Fig. 1 top row). We predict that VEM will lead to a decrease in TM compliance by tensing the TM, as the TT pulls the TM almost directly medially. 2. pressure more negative than the peak pressure (assuming this moves the TM more laterally, i.e., condition Fig. 1
Model of hypothesis of effect of TT contraction on compliance under varying conditions.
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FIG. 2.
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Middle ear compliance: VEM versus baseline.
around the stapedius muscle via the posterior tympanotomyVin both cases to simulate the in vivo directions of pull of each tendon. Static tympanometry was performed at baseline as well as with incremental force applied to each muscle using 5 to 80 g of incremental weights. Change in compliance, pattern of change, and maximum change were noted and compared for the two muscles. Subsequently, using the reflex decay setting, the applied EAC pressure was varied, exactly as it was in the human studies, and compliance changes were observed when each of the muscle tendons were manually pulled on.
middle row). We predict that this tenses the TM and that VEM contraction, if produced by the TT, would medialize the TM and actually make it more compliant by returning it to a more neutral state. 3. pressure more positive than the peak pressure (assuming this moves the TM more medially, i.e., condition Fig. 1 bottom row). We predict that this would also tense the TM, but that VEM would tense it further, but that the change in compliance with VEM would be less than that seen in condition 1. The same manually modified pressures were then applied to test the effect on compliance changes by the stapedius reflex stimulated by a 10-second 500-Hz tone at 105 dB. Finally, subjects were asked to perform VEMs during stapedius reflex testing as the EAC pressure was modified to see if the VEM and stapedius muscle actions were synergistic or antagonistic.
Paired t-test used to compare compliance and ME pressure values at baseline with those with voluntary TM movement for all ears.
Cadaveric Temporal Bone Studies
RESULTS
We attempted to replicate our live human studies with comparable conditions in four fresh-frozen (non-embalmed) cadaveric temporal bones. Comparing the tympanometric changes seen with pull on the TT and stapedius muscles with those seen in the human study findings would clarify whether changes seen with VEM were consistent with TT or stapedius contraction. The TT and stapedius muscles were exposed through a mastoidectomy with posterior and middle fossa tympanotomies on four fresh cadaveric bones. A suture was then passed around the TT muscle via a drilled out tegmental defect and another was passed
FIG. 3.
Statistical Analysis
Human Studies Movement of the TM could be seen in all subjects under the microscope during VEM. Subjects described hearing a noise described as a ‘‘whooshing’’ or ‘‘wind tunnel sound’’ in the ear during VEM. Six subjects were able to make both TMs move, and thus both ears were measured. Two subjects could only move one of their TMs, thus we recorded 14 ears.
MEP: VEM versus baseline. Otology & Neurotology, Vol. 36, No. 2, 2015
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Static Tympanometry All measured tympanograms, baseline and with VEM, were Type A tympanograms. Figure 2 shows the results of VEM on tympanometry. A statistically significant decrease in peak compliance was measured with VEM (average, 0.53 ml; range, 0.29Y1.39) relative to baseline (average, 0.82 ml; range, 0.42Y1.80) ( p G 0.01). Average MEPs were consistently and statistically significantly more negative with VEM (j53.6 daPa) as compared with baseline (j38.0 daPa) ( p G 0.01) (Fig. 3). Modified Reflex Decay Testing In every case, the modified reflex decay test, performed as described above, demonstrated upward deflections with VEM, consistent with decreased compliance (increased stiffness) in our setup. This is the same deflection direction seen using reflex testing for the normal acoustically evoked stapedius muscle contractions clinically. In 10 of 14 ears, the magnitude of the compliance change with VEM was larger than that which could be recorded on the machine, that is, reached the limits of the available scale for recording compliance changes. A representative example of such a recording is provided in Figure 4. The other four ears also showed upward deflections, however, of smaller amplitude. Additional Investigation on Three Subjects 1. In all three subjects, the stapedial reflex stimulated using a 500-Hz sound at 105 dB did not result in a TM movement visible with the otologic microscope. This differs from the clearly visible VEM movements in the same subjects. 2. In all three subjects, the magnitude of the compliance change with VEM reached the limits of the compliance axis on the modified reflex decay setting (Fig. 4) records compliance changes of up to 0.2 ml. However, the maximal acoustically mediated stapedius reflex also reached these limits, a ceiling effect that makes it difficult to distinguish VEM from stapedius contraction. The stapedius reflex was indeed maintained for the entire 10 seconds of the recording at the limits of the compliance change recording axis. This is important to note because it verifies that we have at least 10 seconds to measure static compliance during
FIG. 4. Example of modified reflex decay testing with VEM. First upward deflection was a rapid VEM. The second is a sustained VEM demonstrating the magnitude of compliance change exceeding the limits of this setting’s scale.
FIG. 5. Compliance change from baseline with VEM and with stapedius contraction (stimulated by maximal acoustic stimulus).
activation of the stapedial reflex, and so measurements of static compliance during maximal acoustic stimulation were not contaminated by a significant decay of the stapedial reflex during testing. The static tympanometry allows us to measure compliance changes of up to 1.5 ml. In all cases, stapedius contraction resulted in a decrease in peak compliance relative to baseline. However, changes seen with VEMs were larger than the change seen with stapedius contraction in response to maximal acoustic stimulation in all cases (Fig. 5). Thirdly, there were distinct differences in the action of the acoustically evoked stapedius muscle as compared with VEM when we observed these under varying EAC pressures. These are shown in Figure 6. • When applied EAC pressure approximated baseline ME pressure, both stapedius contraction and VEM resulted in a decreased compliance, that is, upward deflection. • When applied EAC pressure was relatively positive to ME pressure, the compliance decreased, once again, for both the stapedius contraction and VEM, but the change was less than that at peak pressure, as predicted for TT contraction in Figure 1 (bottom row). • When applied EAC pressure was relatively negative, a clear difference was seen between acoustically evoked stapedius contraction’s effect on compliance and that seen with VEM. With the TM bowed laterally by negative EAC pressure, VEMs increased compliance: the opposite of what was seen with neutral and positive EAC pressure. This is as predicted by our model in the middle row of Figure 1. Importantly, in this condition, the stapedial acoustic reflex still produced a decrease in compliance. • To further corroborate this difference, we tried to evoke both stapedial and VEM responses simultaneously: the subject was asked to perform a VEM while the stapedius was contracting in response to acoustic stimulation under all EAC pressure conditions. When neutral EAC pressure was applied, VEM caused a further decrease in compliance when superimposed on the stapedius reflex. This was also the case when the EAC pressure was positive, that is,
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FIG. 6. Comparing stapedius contraction (left) to VEM (right) under varying EAC pressures in live humans. In all figures, the arrow denotes the onset of a typical VEM or a typical stapedial response. Top: Baseline tympanogram provides baseline MEP. Row 1: decreased compliance (upward deflection) with both stapedius and VEM when the applied EAC pressure is similar to baseline MEP. Row 2: Relatively positive EAC pressure results in decreased compliance with both stapedius contraction and VEM movement. With both stapedial and VEM, the magnitude of compliance change is smaller than when EAC pressure resembles ME pressure in the top row. Row 3: relatively negative EAC pressures result in decreased compliance with stapedius contraction of progressively smaller magnitude as EAC pressure becomes more negative. VEM, however, results in increased compliance when applied EAC pressure is relatively negative. This is indicated by an upward deflection at the onset of the VEM rather than a downward deflection. Results support the predictions depicted in Figure 1.
pushing the TM inward. However, when relatively negative pressures were applied to the EAC, the decrease in compliance caused by stapedius contraction was opposed by VEM, that is, VEM caused a reversal of the compliance change induced by stapedial contraction (Fig. 7). Cadaveric Temporal Bone Studies Four fresh-frozen cadaveric temporal bones were used for this study. Unfortunately, the stapedius muscle tore while inserting its suture in one bone. We thus were able to measure compliance changes from force applied to four TT and three stapedius muscles. For each applied force, the change in compliance caused by pulling on the TT was greater than that with the stapedius muscle. Furthermore, the maximal compliance change was reached with lighter loads on the stapedius
muscle than on the TT muscle, and the maximum compliance change seen with pull on the stapedius muscle was consistently smaller than the maximum compliance change seen with pull on the TT muscle (Fig. 8). Pulling on the TT resulted in a more negative measured peak MEP measurement than did pulling on the stapedius (Fig. 9). Using the reflex decay setting and manually pulling on each of the muscles while varying EAC pressures reproduced the same findings as those seen in the human study: decrease in compliance with pull on both muscles with both ambient and positive EAC pressure. For the negative EAC pressure condition, the stapedius tendon pulling resulted, as seen in the human subjects and predicted in our model, in a decrease in compliance, in contradistinction to pulling on the TT, which resulted in an increase in compliance. Again, this is in keeping with human VEMs and our model prediction. Otology & Neurotology, Vol. 36, No. 2, 2015
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FIG. 7. VEM superimposed on acoustically induced stapedius contraction at varying EAC pressures. Initial compliance deflection represents stapedius reflex, gray lines indicate the timing of VEM. Top: Baseline tympanograms. Row 1: EAC pressure 51 daPa, that is, close to baseline MEP. VEM results in further decreased compliance than that caused by stapedius contraction. Row 2: Relatively positive EAC pressure (+106 daPA) results in a smaller decrease in baseline compliance with stapedial contraction (arrow) and, again, VEM results in an even further decrease in compliance. Rows 3 and 4: With progressively negative EAC pressure (upper row, j29 daPa; lower row, j141 daPa), stapedial contraction results in progressively smaller decreases in compliance and VEM results in a deflection in the opposite direction from the stapedius-induced contraction.
The magnitudes of the compliance changes in different conditions reflected those seen in the human studies (Fig. 10). Please note that, using the tympanometry machine in the cadaveric laboratory settings as compared with the one used in the patient clinic (Fig. 10), an upward deflection indicates increased compliance and a downward deflection indicates decreased compliance, that is, the opposite of Figures 6 and 7. DISCUSSION The TT muscle is a relative mystery compared with the stapedius muscle. The results of this study shed some light on its effects on middle ear compliance and pressure
that are distinct from those seen with stapedius muscle contraction. This study supports our hypothesis that VEMs are mediated by contraction of the TT muscle and can be used as a model to study the effects of TT contraction. Many findings support the fact that VEM is caused by a process distinct from stapedius muscle contraction, likely from TT contraction. Firstly, compliance changes with VEM are of a larger magnitude than those seen with stapedius contraction. They cause visible movements of TM, and larger static compliance change, as compared with stapedial muscle contractions, and this is seen both in live subjects and in temporal bones when pulling on the respective muscles (Figs. 2, 8). Furthermore, the increase in
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FIG. 8.
Temporal bone study: effect on compliance of applying progressive weights on stapedius and TT muscles.
compliance seen with VEM with relatively negative EAC pressure is clearly distinct from what is seen with stapedius contraction (Figs. 6, 7, and 10), and is the first time this has been reported. In addition, VEM results in the compliance peak, shifting to a more negative position, as reflected by measurement of a more negative MEP on tympanometry in the VEM state as compared with the resting state (Figs. 3 and 9). This does not occur with stapedius contraction. We hypothesize that this is caused by the fact that a TM tensed by contraction of the TT requires relatively more negative EAC pressure to bring it back to its most compliant state, so that peak admittance is measured at a more negative EAC pressure. In addition, the tympanogram pressure tracing is asymmetric on either side of its peak with TT contraction (Fig. 11) when compared with the baseline and stapedius tracings. This, we hypothesize, occurs because the TM is medialized by the TT, and so negative EAC pressures (which bring it out to a more neutral position) actually do not decrease compliance as much as positive pressures, which tense the TM even further. This asymmetry is another marker of a tonically contracted TT.
FIG. 9.
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Other than stapedius contraction, the other possible ways that middle ear compliance can be decreased dynamically include TT contraction and/or the flow of air through the eustachian tube. If eustachian tube pumping or opening was responsible for the changes we see with VEMs, we would expect to see increasing ME pressures associated with the decreased compliance in VEMs, as a gas bolus enters the middle ear and tenses the TM; however, the opposite is seen in VEMs. Also, any inflow of air into the middle ear should actually increase its compliance when the EAC is at positive pressure as it equalizes the pressures in the middle and external ear and returns the eardrum to a more neutral, more compliant, position; however, this did not occur. The measured increase in compliance with VEM at negative EAC pressure was also the opposite of what might be expected if air was being pumped into the middle ear, as this would further increase the relative pressure difference between the EAC negative pressure and the positive MEP, resulting in further stiffening of the TM. For these reasons, we do not think that the measured compliance changes were caused by pumping air into the middle ear. Anecdotally, we have
Temporal bone study: effect on MEP of applying progressive weights on stapedius and TT muscles. Otology & Neurotology, Vol. 36, No. 2, 2015
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FIG. 10. Temporal bone study: Compliance changes when pulling on TT and stapedius muscle at varying EAC pressures. Initial change in deflection should be noted, at onset of black pencil line, which denotes time when tendon pulled on. On this machine, the directions are reversed from previous: an upward deflection indicates an increase in compliance, and a downward deflection indicates a decrease in compliance. Note a similar change in compliance direction in all situations except with negative EAC pressure: stapedius and TT compliance changes are in opposite directions. The magnitude of compliance change with stapedial traction is smaller than that with TT traction.
FIG. 11. With VEM or TT pull, an asymmetry is noted on either side of the compliance peak. Arrow points to a more gradual slope of compliance descent on the negative side of the peak in both human and cadaver models. This asymmetry is not seen in the baseline or stapedius contraction measurements. Otology & Neurotology, Vol. 36, No. 2, 2015
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MARKER FOR TENSOR TYMPANI CONTRACTION also seen a few patients who can move their TM with a ventilation tube in place, again making it very unlikely that this TM movement is caused by pumping air into the middle ear. This leads us to believe that it is, indeed, contraction of the TT muscle that is mediating these VEMs. This is further supported by the findings of the temporal bone study under controlled conditions. In all tested conditions, the findings produced with TT pull reproduced those seen with VEM and those seen with stapedius pull reproduced those seen with acoustically induced stapedius contraction in the human studies. Understanding the tympanometric changes that occur with TT contraction provides clinicians with potential diagnostic markers for identifying patients whose symptoms may be caused by pathologic contraction of the TT muscle. For cases of nonpulsatile ‘‘clicking’’ type tinnitus, objective movement of the TM may be documented using the modified reflex decay test used in this study. To test whether or not the clicking is caused by TT contraction, we would recommend that recordings be performed with both neutral and negative EAC pressures. We would expect that TT-induced contractions would result in decreased compliance during the clicking noise at neutral pressure and increased compliance at negative external ear canal pressure. This is the first time a test has been proposed to separate these muscles’ actions. For MD or TT syndrome, however, the TT has been hypothesized to be in a tonically contracted state. Unfortunately, given the wide range of normal ME compliance values, we have not been able to identify absolute threshold cutoffs for ME compliance, below which TT contraction would be suspected. Furthermore, in those clinical situations where tonic TT contraction is implicated, we do not have baseline/normal values of the symptomatic ear before the hypothesized TT contraction, with which to compare. In cases with unilateral symptoms, however, we propose using the ME compliance of the contralateral, asymptomatic, ear as a baseline value. If TT contraction is implicated in the pathophysiology of the symptomatic ear, its compliance should be lower than the contralateral asymptomatic ear. If the symptomatic ear’s compliance is greater than the asymptomatic ear, it is extremely unlikely for TT contraction to be the cause for the symptoms. Thus, TT section can be more appropriately directed to ears where it is more likely to be of symptomatic benefit. Finally, the findings of this study shed a new light on the mechanism of action of the TT muscle and how it affects
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ME compliance as compared with the stapedius muscle. For the first time, we propose a test that can distinguish TT from stapedial contraction, that is, to measure the effects of contraction with neutral and negative EAC pressure. The empirical findings are in keeping with our model presented in Figure 1. From the results of this study, we developed a clearer understanding of TT contraction, including its effect on ME compliance and the mechanism by which it does so. Specifically, the TT muscle acts quite differently on the middle ear than does the stapedius muscle. These findings can now be used to better identify patients who may have abnormal TT contraction contributing to their slew of otologic complaints and offer them guided therapy in the way of TT section. CONCLUSION We suggest that markers of a contracted TT include 1) low static compliance; 2) mildly negative MEP measured with tympanometry; 3) asymmetric tracing on the tympanometric pressure sweep curve; 4) if contraction/ relaxation cycles can be seen on a tympanometric tracing, they should reverse direction when negative EAC pressure is applied. In addition, VEMs in humans are likely mediated by the TT, and not the stapedius muscle, and can be used as a model to study the actions of the TT. REFERENCES 1. Bento RF, Sanchez TG, Miniti A, Tedesco-Marchesi AJ. Continuous, high-frequency objective tinnitus caused by middle ear myoclonus. Ear Nose Throat J 1998;77:814. 2. Klockhoff I. Middle ear muscle reflexes in man. A clinical an experimental study with special reference to diagnostic problems in hearing impairment. Acta Otolaryngol Suppl 1961;164:1Y92. 3. Klockhoff I. Tensor Tympani Syndrome: A Source of Vertigo. Uppsala, Sweden: Meeting of Barany Society, 1978. 4. Klockhoff I. Impedance fluctuation and a tensor tympani syndrome. Proceedings of the 4th International Symposium on Acoustic Measurements, Lisbon 1979;69Y76. 5. Franz P, Hamzavi J-S, Schneider B, Ehrenberger K. Do middle ear muscles trigger attacks of Me´nie`re’s disease? Acta Otolaryngol 2003;123:133Y7. 6. Loader B, Beicht D, Hamzavi J-S, Franz P. Tenotomy of the middle ear muscles causes a dramatic reduction in vertigo attacks and improves audiological function in definite Meniere’s disease. Acta Otolaryngol 2012;132:491Y7. 7. Bance M, Makki FM, Garland P, Alian WA, van Wijhe RG, Savage J. Effects of tensor tympani muscle contraction on the middle ear and markers of a contracted muscle. Laryngoscope 2013;123:1021Y7.
Otology & Neurotology, Vol. 36, No. 2, 2015
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Voluntary Eardrum Movement: A Marker for Tensor Tympani Contraction? *Margaret Aron, †Duncan Floyd, and *Manohar Bance *Division of OtolaryngologyYHead and Neck Surgery, and ÞNova Scotia Hearing and Speech Centers, Dalhousie University, Halifax, Nova Scotia, Canada Hypothesis: Voluntary eardrum movement (VEM) and resultant tympanometric changes reflect tensor tympani (TT) contraction. Background: TT contraction has been hypothesized to cause symptoms of aural fullness, tinnitus, clicking, and even vertigo despite the lack of understanding of how it functions or what causes it to contract. Identifying tympanometric changes unique to TT contraction can provide a diagnostic tool for identifying its role in pathologic conditions. Methods: Various tympanometric measurements were performed on human subjects who could voluntarily move their eardrums. These were compared with similar tympanometric measurements performed on cadaveric temporal bones while manually tensing the TT and stapedius muscles individually. Results: Eight subjects (14 ears) who could cause VEM were identified. Compared with baseline, VEM resulted in significantly decreased middle ear compliance ( p G 0.01) and middle ear pressure ( p G 0.01) measurements. The compliance changes seen
with VEM were larger than those seen with acoustically stimulated stapedius contraction. Finally, the direction of compliance change with VEM was dependent on the pressure applied to the external auditory canal (EAC), with compliance increasing with positive EAC pressure. This was not seen with stapedius contraction. These findings were reproduced using the cadaveric temporal bone model: larger compliance changes with pull on TT as compared with stapedius with neutral EAC probe pressure; change in direction of compliance changes with varying EAC probe pressure with TT pull, not with stapedius pull. Conclusion: TT contraction produces distinctive tympanometric findings that can be used to support its abnormal contraction in ears with symptoms compatible with TT syndrome. Key Words: ImpedanceVTemporal bone studyVTensor tympaniVTympanic membrane movementVVoluntary contractionVVoluntary ear drum movement. Otol Neurotol 36:373Y381, 2015.
Although contraction of the middle ear muscles (MEMs) (stapedius and tensor tympani [TT]) has been implicated in various otologic conditions, the role of these muscles in these conditions has not been verified and is unclear. The stapedius muscle can be reliably activated by acoustic stimuli, with its effects on middle ear compliance readily demonstrated using impedance audiometry. The physiologic role, contraction inciting factors, and effects on impedance tympanometry for the TT, however, are much less clear. Despite this, TT contraction has been implicated in a number of otologic conditions including tinnitus (1), otalgia, Me´nie`re’s disease (MD), and ‘‘tensor tympani syndrome,’’ a purported syndrome described by Klockhoff (2Y4), characterized by complaints of fullness, tinnitus, vertigo, and dysacusis. If the TT is hypercontracted in some otologic pathologies, potentially we could perform therapeutic TT section in selected patients. In fact, TT sectioning has been reported to
be successful in managing MD (5Y7) as well as some cases of tinnitus (1). Without definitive markers for TT contraction, it becomes a matter of ‘‘faith’’ to assign many otologic pathologies, perhaps spuriously, to the TT. Bance et al. (7) studied the effect of voluntary eardrum movements (VEMs) on middle ear compliance suspected to be caused by TT contraction. This study, however, could not definitively determine if the changes were caused by the TT alone versus stapedius alone versus co-contraction of the two muscles. By comparing VEM and acoustically mediated stapedius contraction in human models with TT and stapedius muscle pull in cadaveric studies, the current study aims to test our hypothesis that VEMs are mediated by TT contraction. If true, the effects on middle ear compliance of VEM could be used as a marker for studying TT contraction. MATERIALS AND METHODS This study was approved by our institutional ethics board.
Address correspondence and reprint requests to Manohar Bance, M.D., M.Sc., F.R.C.S.C., Division of OtolaryngologyYHead and Neck Surgery, Dalhousie University, Room 3184, 3rd Floor Dickson Bldg, VG Site, QEII Health Sciences Centre, 1278 Tower Rd, Halifax, NS, Canada B3H 2Y9; E-mail: [email protected] The authors disclose no conflicts of interest.
Human Studies We identified eight subjects (with 14 ears tested) at our institution who could move their tympanic membrane (TM) voluntarily. This movement was confirmed by direct visualization of TM movement under microscopic visualization.
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Impedance audiometry (Interacoustics Impedance Audiometer Az26) was performed on all subjects to evaluate the effect of this VEM on middle ear compliance using static tympanometry as well as with a modified reflex decay paradigm, as described below, which allowed measurement of acoustic admittance changes during a 10-second window. Measurements were: 1. Static compliance: measured using a 226-Hz probe tone at baseline and then repeated during VEM. For each ear, values are the average of two repeated measurements. 2. Modified reflex decay measurement: Using ‘‘manual’’ settings for reflex decay and applying the following parameters: pressure -1 to +1 daPa (i.e., close to zero external auditory canal [EAC] pressure), probe tone 1,000 Hz (the volume of the probe tone was minimized to 10 dB SPL to eliminate acoustically induced stapedial reflex), and 10-second recording window. This allowed us to record the effect of sequential VEMs on compliance during a 10-second window. 3. Additional investigations were performed as detailed below on three subjects to explore and compare VEM with known stapedius contraction, which can be incited by acoustic stimulation, to determine if stapedius contractions are similar to and could explain the VEMs or whether they differ substantially from the VEMs. The TT does not respond to sound in normal human subjects (7). • First, TMs were examined under the microscope as a 500-Hz sound at 105 dB was delivered to the contralateral ear to observe whether maximal acoustically evoked stapedius reflex (which would be bilateral) resulted in visible TM movement. • Second, the magnitude of compliance change in the modified reflex decay setting with VEMs was compared with the magnitude of the compliance change seen with maximal acoustically induced stapedius contraction.
FIG. 1.
To test the latter, we first confirmed that the maximal acoustically induced stapedius reflex, tested using an ipsilateral 10-second 500-Hz tone at 105 dB, persisted for the entire 10-second recording of static compliance measurement. Because the static compliance setting uses a much larger scale for compliance (0Y1.5 ml) than does the reflex decay setting (0Y0.2 ml), larger compliance changes could be measured using static compliance settings. Thus, using two probes from two separate tympanometry machines, a 10-second 500-Hz tone at 105 dB was delivered to one ear while static compliance measurements were performed on the other ear during the 10-second window of the incited stapedius reflex contraction. These were compared with baseline static compliance as well as to static compliance changes induced by VEM. • Third, we wished to test the predictions in Figure 1 (see below for further clarification) by measuring compliance change during VEMs and stapedius contraction as a function of the baseline pressure applied to the EAC. As the pressure delivered to the EAC was manually varied, effects on the compliance changes seen with VEM and stapedius contraction were measured and compared. To test this, the middle ear pressure (MEP) at peak admittance (the peak of the tympanometric curve) was measured and denoted as ‘‘peak pressure.’’ Then, using the modified reflex decay setting (as described above), the subject was asked to perform VEMs as the pressure applied to the EAC was manually modified, and static compliance measured, to test the following three conditions: 1. pressure at or near this peak pressure (i.e., EAC and MEP equal; condition in Fig. 1 top row). We predict that VEM will lead to a decrease in TM compliance by tensing the TM, as the TT pulls the TM almost directly medially. 2. pressure more negative than the peak pressure (assuming this moves the TM more laterally, i.e., condition Fig. 1
Model of hypothesis of effect of TT contraction on compliance under varying conditions.
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FIG. 2.
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Middle ear compliance: VEM versus baseline.
around the stapedius muscle via the posterior tympanotomyVin both cases to simulate the in vivo directions of pull of each tendon. Static tympanometry was performed at baseline as well as with incremental force applied to each muscle using 5 to 80 g of incremental weights. Change in compliance, pattern of change, and maximum change were noted and compared for the two muscles. Subsequently, using the reflex decay setting, the applied EAC pressure was varied, exactly as it was in the human studies, and compliance changes were observed when each of the muscle tendons were manually pulled on.
middle row). We predict that this tenses the TM and that VEM contraction, if produced by the TT, would medialize the TM and actually make it more compliant by returning it to a more neutral state. 3. pressure more positive than the peak pressure (assuming this moves the TM more medially, i.e., condition Fig. 1 bottom row). We predict that this would also tense the TM, but that VEM would tense it further, but that the change in compliance with VEM would be less than that seen in condition 1. The same manually modified pressures were then applied to test the effect on compliance changes by the stapedius reflex stimulated by a 10-second 500-Hz tone at 105 dB. Finally, subjects were asked to perform VEMs during stapedius reflex testing as the EAC pressure was modified to see if the VEM and stapedius muscle actions were synergistic or antagonistic.
Paired t-test used to compare compliance and ME pressure values at baseline with those with voluntary TM movement for all ears.
Cadaveric Temporal Bone Studies
RESULTS
We attempted to replicate our live human studies with comparable conditions in four fresh-frozen (non-embalmed) cadaveric temporal bones. Comparing the tympanometric changes seen with pull on the TT and stapedius muscles with those seen in the human study findings would clarify whether changes seen with VEM were consistent with TT or stapedius contraction. The TT and stapedius muscles were exposed through a mastoidectomy with posterior and middle fossa tympanotomies on four fresh cadaveric bones. A suture was then passed around the TT muscle via a drilled out tegmental defect and another was passed
FIG. 3.
Statistical Analysis
Human Studies Movement of the TM could be seen in all subjects under the microscope during VEM. Subjects described hearing a noise described as a ‘‘whooshing’’ or ‘‘wind tunnel sound’’ in the ear during VEM. Six subjects were able to make both TMs move, and thus both ears were measured. Two subjects could only move one of their TMs, thus we recorded 14 ears.
MEP: VEM versus baseline. Otology & Neurotology, Vol. 36, No. 2, 2015
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Static Tympanometry All measured tympanograms, baseline and with VEM, were Type A tympanograms. Figure 2 shows the results of VEM on tympanometry. A statistically significant decrease in peak compliance was measured with VEM (average, 0.53 ml; range, 0.29Y1.39) relative to baseline (average, 0.82 ml; range, 0.42Y1.80) ( p G 0.01). Average MEPs were consistently and statistically significantly more negative with VEM (j53.6 daPa) as compared with baseline (j38.0 daPa) ( p G 0.01) (Fig. 3). Modified Reflex Decay Testing In every case, the modified reflex decay test, performed as described above, demonstrated upward deflections with VEM, consistent with decreased compliance (increased stiffness) in our setup. This is the same deflection direction seen using reflex testing for the normal acoustically evoked stapedius muscle contractions clinically. In 10 of 14 ears, the magnitude of the compliance change with VEM was larger than that which could be recorded on the machine, that is, reached the limits of the available scale for recording compliance changes. A representative example of such a recording is provided in Figure 4. The other four ears also showed upward deflections, however, of smaller amplitude. Additional Investigation on Three Subjects 1. In all three subjects, the stapedial reflex stimulated using a 500-Hz sound at 105 dB did not result in a TM movement visible with the otologic microscope. This differs from the clearly visible VEM movements in the same subjects. 2. In all three subjects, the magnitude of the compliance change with VEM reached the limits of the compliance axis on the modified reflex decay setting (Fig. 4) records compliance changes of up to 0.2 ml. However, the maximal acoustically mediated stapedius reflex also reached these limits, a ceiling effect that makes it difficult to distinguish VEM from stapedius contraction. The stapedius reflex was indeed maintained for the entire 10 seconds of the recording at the limits of the compliance change recording axis. This is important to note because it verifies that we have at least 10 seconds to measure static compliance during
FIG. 4. Example of modified reflex decay testing with VEM. First upward deflection was a rapid VEM. The second is a sustained VEM demonstrating the magnitude of compliance change exceeding the limits of this setting’s scale.
FIG. 5. Compliance change from baseline with VEM and with stapedius contraction (stimulated by maximal acoustic stimulus).
activation of the stapedial reflex, and so measurements of static compliance during maximal acoustic stimulation were not contaminated by a significant decay of the stapedial reflex during testing. The static tympanometry allows us to measure compliance changes of up to 1.5 ml. In all cases, stapedius contraction resulted in a decrease in peak compliance relative to baseline. However, changes seen with VEMs were larger than the change seen with stapedius contraction in response to maximal acoustic stimulation in all cases (Fig. 5). Thirdly, there were distinct differences in the action of the acoustically evoked stapedius muscle as compared with VEM when we observed these under varying EAC pressures. These are shown in Figure 6. • When applied EAC pressure approximated baseline ME pressure, both stapedius contraction and VEM resulted in a decreased compliance, that is, upward deflection. • When applied EAC pressure was relatively positive to ME pressure, the compliance decreased, once again, for both the stapedius contraction and VEM, but the change was less than that at peak pressure, as predicted for TT contraction in Figure 1 (bottom row). • When applied EAC pressure was relatively negative, a clear difference was seen between acoustically evoked stapedius contraction’s effect on compliance and that seen with VEM. With the TM bowed laterally by negative EAC pressure, VEMs increased compliance: the opposite of what was seen with neutral and positive EAC pressure. This is as predicted by our model in the middle row of Figure 1. Importantly, in this condition, the stapedial acoustic reflex still produced a decrease in compliance. • To further corroborate this difference, we tried to evoke both stapedial and VEM responses simultaneously: the subject was asked to perform a VEM while the stapedius was contracting in response to acoustic stimulation under all EAC pressure conditions. When neutral EAC pressure was applied, VEM caused a further decrease in compliance when superimposed on the stapedius reflex. This was also the case when the EAC pressure was positive, that is,
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FIG. 6. Comparing stapedius contraction (left) to VEM (right) under varying EAC pressures in live humans. In all figures, the arrow denotes the onset of a typical VEM or a typical stapedial response. Top: Baseline tympanogram provides baseline MEP. Row 1: decreased compliance (upward deflection) with both stapedius and VEM when the applied EAC pressure is similar to baseline MEP. Row 2: Relatively positive EAC pressure results in decreased compliance with both stapedius contraction and VEM movement. With both stapedial and VEM, the magnitude of compliance change is smaller than when EAC pressure resembles ME pressure in the top row. Row 3: relatively negative EAC pressures result in decreased compliance with stapedius contraction of progressively smaller magnitude as EAC pressure becomes more negative. VEM, however, results in increased compliance when applied EAC pressure is relatively negative. This is indicated by an upward deflection at the onset of the VEM rather than a downward deflection. Results support the predictions depicted in Figure 1.
pushing the TM inward. However, when relatively negative pressures were applied to the EAC, the decrease in compliance caused by stapedius contraction was opposed by VEM, that is, VEM caused a reversal of the compliance change induced by stapedial contraction (Fig. 7). Cadaveric Temporal Bone Studies Four fresh-frozen cadaveric temporal bones were used for this study. Unfortunately, the stapedius muscle tore while inserting its suture in one bone. We thus were able to measure compliance changes from force applied to four TT and three stapedius muscles. For each applied force, the change in compliance caused by pulling on the TT was greater than that with the stapedius muscle. Furthermore, the maximal compliance change was reached with lighter loads on the stapedius
muscle than on the TT muscle, and the maximum compliance change seen with pull on the stapedius muscle was consistently smaller than the maximum compliance change seen with pull on the TT muscle (Fig. 8). Pulling on the TT resulted in a more negative measured peak MEP measurement than did pulling on the stapedius (Fig. 9). Using the reflex decay setting and manually pulling on each of the muscles while varying EAC pressures reproduced the same findings as those seen in the human study: decrease in compliance with pull on both muscles with both ambient and positive EAC pressure. For the negative EAC pressure condition, the stapedius tendon pulling resulted, as seen in the human subjects and predicted in our model, in a decrease in compliance, in contradistinction to pulling on the TT, which resulted in an increase in compliance. Again, this is in keeping with human VEMs and our model prediction. Otology & Neurotology, Vol. 36, No. 2, 2015
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FIG. 7. VEM superimposed on acoustically induced stapedius contraction at varying EAC pressures. Initial compliance deflection represents stapedius reflex, gray lines indicate the timing of VEM. Top: Baseline tympanograms. Row 1: EAC pressure 51 daPa, that is, close to baseline MEP. VEM results in further decreased compliance than that caused by stapedius contraction. Row 2: Relatively positive EAC pressure (+106 daPA) results in a smaller decrease in baseline compliance with stapedial contraction (arrow) and, again, VEM results in an even further decrease in compliance. Rows 3 and 4: With progressively negative EAC pressure (upper row, j29 daPa; lower row, j141 daPa), stapedial contraction results in progressively smaller decreases in compliance and VEM results in a deflection in the opposite direction from the stapedius-induced contraction.
The magnitudes of the compliance changes in different conditions reflected those seen in the human studies (Fig. 10). Please note that, using the tympanometry machine in the cadaveric laboratory settings as compared with the one used in the patient clinic (Fig. 10), an upward deflection indicates increased compliance and a downward deflection indicates decreased compliance, that is, the opposite of Figures 6 and 7. DISCUSSION The TT muscle is a relative mystery compared with the stapedius muscle. The results of this study shed some light on its effects on middle ear compliance and pressure
that are distinct from those seen with stapedius muscle contraction. This study supports our hypothesis that VEMs are mediated by contraction of the TT muscle and can be used as a model to study the effects of TT contraction. Many findings support the fact that VEM is caused by a process distinct from stapedius muscle contraction, likely from TT contraction. Firstly, compliance changes with VEM are of a larger magnitude than those seen with stapedius contraction. They cause visible movements of TM, and larger static compliance change, as compared with stapedial muscle contractions, and this is seen both in live subjects and in temporal bones when pulling on the respective muscles (Figs. 2, 8). Furthermore, the increase in
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FIG. 8.
Temporal bone study: effect on compliance of applying progressive weights on stapedius and TT muscles.
compliance seen with VEM with relatively negative EAC pressure is clearly distinct from what is seen with stapedius contraction (Figs. 6, 7, and 10), and is the first time this has been reported. In addition, VEM results in the compliance peak, shifting to a more negative position, as reflected by measurement of a more negative MEP on tympanometry in the VEM state as compared with the resting state (Figs. 3 and 9). This does not occur with stapedius contraction. We hypothesize that this is caused by the fact that a TM tensed by contraction of the TT requires relatively more negative EAC pressure to bring it back to its most compliant state, so that peak admittance is measured at a more negative EAC pressure. In addition, the tympanogram pressure tracing is asymmetric on either side of its peak with TT contraction (Fig. 11) when compared with the baseline and stapedius tracings. This, we hypothesize, occurs because the TM is medialized by the TT, and so negative EAC pressures (which bring it out to a more neutral position) actually do not decrease compliance as much as positive pressures, which tense the TM even further. This asymmetry is another marker of a tonically contracted TT.
FIG. 9.
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Other than stapedius contraction, the other possible ways that middle ear compliance can be decreased dynamically include TT contraction and/or the flow of air through the eustachian tube. If eustachian tube pumping or opening was responsible for the changes we see with VEMs, we would expect to see increasing ME pressures associated with the decreased compliance in VEMs, as a gas bolus enters the middle ear and tenses the TM; however, the opposite is seen in VEMs. Also, any inflow of air into the middle ear should actually increase its compliance when the EAC is at positive pressure as it equalizes the pressures in the middle and external ear and returns the eardrum to a more neutral, more compliant, position; however, this did not occur. The measured increase in compliance with VEM at negative EAC pressure was also the opposite of what might be expected if air was being pumped into the middle ear, as this would further increase the relative pressure difference between the EAC negative pressure and the positive MEP, resulting in further stiffening of the TM. For these reasons, we do not think that the measured compliance changes were caused by pumping air into the middle ear. Anecdotally, we have
Temporal bone study: effect on MEP of applying progressive weights on stapedius and TT muscles. Otology & Neurotology, Vol. 36, No. 2, 2015
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FIG. 10. Temporal bone study: Compliance changes when pulling on TT and stapedius muscle at varying EAC pressures. Initial change in deflection should be noted, at onset of black pencil line, which denotes time when tendon pulled on. On this machine, the directions are reversed from previous: an upward deflection indicates an increase in compliance, and a downward deflection indicates a decrease in compliance. Note a similar change in compliance direction in all situations except with negative EAC pressure: stapedius and TT compliance changes are in opposite directions. The magnitude of compliance change with stapedial traction is smaller than that with TT traction.
FIG. 11. With VEM or TT pull, an asymmetry is noted on either side of the compliance peak. Arrow points to a more gradual slope of compliance descent on the negative side of the peak in both human and cadaver models. This asymmetry is not seen in the baseline or stapedius contraction measurements. Otology & Neurotology, Vol. 36, No. 2, 2015
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MARKER FOR TENSOR TYMPANI CONTRACTION also seen a few patients who can move their TM with a ventilation tube in place, again making it very unlikely that this TM movement is caused by pumping air into the middle ear. This leads us to believe that it is, indeed, contraction of the TT muscle that is mediating these VEMs. This is further supported by the findings of the temporal bone study under controlled conditions. In all tested conditions, the findings produced with TT pull reproduced those seen with VEM and those seen with stapedius pull reproduced those seen with acoustically induced stapedius contraction in the human studies. Understanding the tympanometric changes that occur with TT contraction provides clinicians with potential diagnostic markers for identifying patients whose symptoms may be caused by pathologic contraction of the TT muscle. For cases of nonpulsatile ‘‘clicking’’ type tinnitus, objective movement of the TM may be documented using the modified reflex decay test used in this study. To test whether or not the clicking is caused by TT contraction, we would recommend that recordings be performed with both neutral and negative EAC pressures. We would expect that TT-induced contractions would result in decreased compliance during the clicking noise at neutral pressure and increased compliance at negative external ear canal pressure. This is the first time a test has been proposed to separate these muscles’ actions. For MD or TT syndrome, however, the TT has been hypothesized to be in a tonically contracted state. Unfortunately, given the wide range of normal ME compliance values, we have not been able to identify absolute threshold cutoffs for ME compliance, below which TT contraction would be suspected. Furthermore, in those clinical situations where tonic TT contraction is implicated, we do not have baseline/normal values of the symptomatic ear before the hypothesized TT contraction, with which to compare. In cases with unilateral symptoms, however, we propose using the ME compliance of the contralateral, asymptomatic, ear as a baseline value. If TT contraction is implicated in the pathophysiology of the symptomatic ear, its compliance should be lower than the contralateral asymptomatic ear. If the symptomatic ear’s compliance is greater than the asymptomatic ear, it is extremely unlikely for TT contraction to be the cause for the symptoms. Thus, TT section can be more appropriately directed to ears where it is more likely to be of symptomatic benefit. Finally, the findings of this study shed a new light on the mechanism of action of the TT muscle and how it affects
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ME compliance as compared with the stapedius muscle. For the first time, we propose a test that can distinguish TT from stapedial contraction, that is, to measure the effects of contraction with neutral and negative EAC pressure. The empirical findings are in keeping with our model presented in Figure 1. From the results of this study, we developed a clearer understanding of TT contraction, including its effect on ME compliance and the mechanism by which it does so. Specifically, the TT muscle acts quite differently on the middle ear than does the stapedius muscle. These findings can now be used to better identify patients who may have abnormal TT contraction contributing to their slew of otologic complaints and offer them guided therapy in the way of TT section. CONCLUSION We suggest that markers of a contracted TT include 1) low static compliance; 2) mildly negative MEP measured with tympanometry; 3) asymmetric tracing on the tympanometric pressure sweep curve; 4) if contraction/ relaxation cycles can be seen on a tympanometric tracing, they should reverse direction when negative EAC pressure is applied. In addition, VEMs in humans are likely mediated by the TT, and not the stapedius muscle, and can be used as a model to study the actions of the TT. REFERENCES 1. Bento RF, Sanchez TG, Miniti A, Tedesco-Marchesi AJ. Continuous, high-frequency objective tinnitus caused by middle ear myoclonus. Ear Nose Throat J 1998;77:814. 2. Klockhoff I. Middle ear muscle reflexes in man. A clinical an experimental study with special reference to diagnostic problems in hearing impairment. Acta Otolaryngol Suppl 1961;164:1Y92. 3. Klockhoff I. Tensor Tympani Syndrome: A Source of Vertigo. Uppsala, Sweden: Meeting of Barany Society, 1978. 4. Klockhoff I. Impedance fluctuation and a tensor tympani syndrome. Proceedings of the 4th International Symposium on Acoustic Measurements, Lisbon 1979;69Y76. 5. Franz P, Hamzavi J-S, Schneider B, Ehrenberger K. Do middle ear muscles trigger attacks of Me´nie`re’s disease? Acta Otolaryngol 2003;123:133Y7. 6. Loader B, Beicht D, Hamzavi J-S, Franz P. Tenotomy of the middle ear muscles causes a dramatic reduction in vertigo attacks and improves audiological function in definite Meniere’s disease. Acta Otolaryngol 2012;132:491Y7. 7. Bance M, Makki FM, Garland P, Alian WA, van Wijhe RG, Savage J. Effects of tensor tympani muscle contraction on the middle ear and markers of a contracted muscle. Laryngoscope 2013;123:1021Y7.
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