Учебники / Middle Ear Mechanics in Research and Otology Huber 2006

Fig.1 The CP in response to BC stimuli A) recorded from an ear in the patch-unpatch (SCD Open)-repatch states. B) after the data is smoothed using the loess smoothing algorithm.

To evaluate the reversibility of the e ect of SC opening on CP, we calculate the mean dB di erence in magnitude (20 × log10()) as well as the difference in phase between the patched and the repatched states in the seven ears. The mean dB di erence between the patched and repatched condition (Figure 2A) is not statistically di erent from zero across the measured frequency range. Therefore the preparation was stable and the e ects of SC opening are reversible. There are no statistically significant changes in phaseanglebetweenthepatchandtherepatchstates.Forfrequenciesbelow 500Hz and above 3000Hz the 95% confidence interval includes almost 2 radians; this is a result of an unwrapping artifact due to rapid phase cycling

308 observed in many of the ears.

The di erence in CP between the unpatched and patched conditions in response to BC sound in the same ears is presented as a dB di erence in magnitude (Figure 2B). There is a mean increase in CP as a result of SC opening for frequencies below 1kHz. The increase is near 10dB at 300Hz andisstatisticallysignificant(p<0.05).Additionally,thereisameanphase lead for frequencies between 400Hz and 4000Hz that is significant over a small range of frequencies (1500Hz–1800Hz).

Fig. 2 The mean change in BC CP between A) the patched and repatched conditions and B) the SCD open and patched conditions. The 95% confidence intervals as well as the means are plotted (n=7).

3.2 SCD and air conduction

While the CP produced by BC stimulation was normalized by the stimulus voltage, the CP in response to AC sound stimuli is normalized by PTM [10] because PTM is considered to be the e ective stimulus for AC sound.

Figure 3 shows measurements from an ear in which there is a low-frequency decrease in CP in response to AC sound even as there is a low-frequency increase in CP in response to BC sound. The SCD-induced changes in response to both stimuli are reversible.

309

Fig. 3 Changes in CP in response to both AC and BC sound stimuli in an example ear. A) A reversible increase in sensitivity to BC sound. B) A reversible decrease in sensitivity to AC sound.

The mean di erence between the patched and repatched state in response to AC stimuli in seven ears (Figure 4A) shows a slight decrease that is fairly constant with frequency but is not statistically di erent from zero. The mean di erence in CP between the SC hole and the patched states (Figure 4B) is a decrease of 2–5dB between 500Hz and 4kHz (p < 0.05).

310

4. Discussion

4.1 Summary of results

WeobservedanincreaseinCPsensitivitytoBCsoundafterintroducingSC holesinsevenears(Figure2).WithACsoundweobservedasignificantdecreaseinCPafterSCD.ThesechangesinCParelargestforlowfrequencies, reversible with patching and consistent with previous reports [9, 10].

Our AC and BC results are consistent with an SCD-induced air-bone gap in chinchilla for frequencies below 1kHz. This air-bone gap is largest at the lowest frequencies with a mean near 12dB and is a ected by the increased sensitivity to BC stimuli and the decreased sensitivity to AC stimuli. The repeatability and reversibility observed between the patch- unpatch-repatch conditions (n=7) both within and across animals are consistent with hearing changes that are tied to the mechanical e ects of openingandclosingtheSCDandnotuncontrolledchangesinthesensitivity of the inner ear.

4.2 Comparison to clinical findings

Air-bone gaps of 24 ± 7dB for frequencies between 250 and 4000Hz [5] and a mean air-bone gap of 37dB at 500Hz [3] have been reported in human patients. The air-bone gap we report for chinchilla (12dB) is smaller thanthatobservedclinically.Thisdi erenceisprimarilyduetothesmaller changes in sensitivity to AC as a result of SCD in chinchillas compared to that observed in patients. Interspecies variation may be one reason for the di erence in magnitude of the air-bone gap [10]: 1) the SC hole in chinchilla opens into an air-filled middle-ear air space whereas the SCD in human patients opens into the cranial cavity, and 2) di erences in mid- dle-ear dynamics.

For patients with SCD syndrome, important information can be obtained by fully exploring the sensitivity to both AC and BC sound stimuli.

312Specifically, increased sensitivity to BC stimuli may aid in the di erential diagnosis of SCD syndrome and otosclerosis. In both of these conditions patients may present with a conductive hearing loss, however, patients with SCD syndrome and a conductive hearing loss usually exhibit a supersensitivity to BC stimuli, whereas patients with otosclerosis do not.

5. Conclusions

We have demonstrated an SCD-induced air-bone gap in chinchilla. This air-bone gap is similar in frequency range, though smaller in magnitude, tothatobservedinpatientswithSCDsyndrome.Thereversiblephysiological changes we observed demonstrate that the hearing loss associated with

SCD syndrome results from changes in inner-ear mechanics and should therefore resolve when the dehiscence is patched.

Acknowledgments

We thank M.E. Ravicz, W.T. Peake, S.N. Merchant and H.H. Nakajima for their input and advice. This work was supported by the NSF and the NIDCD.

References

1.K. Brantberg, J. Bergenius, L. Mendel, H. Witt, A. Tribukait, and J. Ygge., Symptoms, findings and treatment in patients with dehiscence of the superior semicircular canal. Acta Otolaryngol, 121: 68–75, 2000

2.P. Cremer, L. Minor, J. Carey, and C. Santina., Eye movements in patients with superiorcanaldehiscencesyndromealignwiththeabnormalcanal.Neurology,55: 1833–1841, 2000

3.A. Mikulec, M. McKenna, M. Ramsey, J. Rosowski, B. Herrmann, S. Rauch, H. Curtin, and S. Merchant., Superior semicircular canal dehiscence presenting as conductive hearing loss without vertigo. Otol. and Neurotol., 25: 121–129, 2004

4.L. Minor., Superior canal dehiscence syndrome. Amer. J. of Otol., 21: 9–19, 2000

5.L. Minor, J. Carey, P. Cremer, L. Lustig, and S. Streubel., Dehiscence of bone overlying the superior canal as a cause of apparent conductive hearing loss. Otol. and Neurotol., 2003

6.L. Minor, D. Solomon, J. Zinreich, and D. Zee., Sound and/or pressure-induced vertigo due to bone dehiscence of the superior semicircular canal. Arch Otolaryngol Head Neck Surg, 124: 249–258, 1998

7.J. Rosowski, J. Songer, H. Nakajima, K. Brinsko, and S. Merchant., Investigations

8.J. Songer., Superior Canal Dehiscence: Auditory Mechanisms. PhD thesis, Massachusetts Institute of Technology, 2006

9.J. Songer, K. Brinsko, and J. Rosowski., Superior semicircular canal dehiscence and bone conduction in chinchilla. In K. Gyo, H. Wada, N. Hato, and T. Koike, editors, The proceedings of the Third International Symposium on Middle Ear Rea-

search and Oto-Surgery, pages 234–241. World Scientific, 2004

10. J. Songer and J. Rosowski., The e ect of superior canal dehiscence on cochlear potential in response to air-conducted stimuli in chinchilla. Hear. Res., 210: 53–62, 2005

11. J. Songer and J. Rosowski., The e ect of superior-canal opening on middle-ear input admittance and air-conducted stapes velocity in chinchilla. J. Acoust. Soc. Amer., 120: 258–269, 2006

EPIDEMIOLOGY OF PRESSURE REGULATION. INCIDENCE

OF VENTILATION TUBE TREATMENTS AND ITS PRELIMINARY CORRELATION TO SUBSEQUENT EAR SURGERY

Michael Gaihede1, Kirsten Hald1, Mette Nørgaard2, Pia Wogelius2, Daniel Buck2, Kjell Tveterås1

Department of Otolaryngology, Head and Neck Surgery1 and

Department of Clinical Epidemiology2, Aalborg University Hospital, Hobrovej 18–22, DK 9000 Aalborg, Denmark

Michael Gaihede, mlg@rn.dk, Phone +45 9932 2911, Fax +45 9932 2938 Kirsten Hald, kirsten.hald@rn.dk, Phone +45 9932 2911, Fax +45 9932 2938 Kjell Tveterås, kt@rn.dk, Phone +45 9932 2911, Fax +45 9932 2938

Mette Nørgaard, m.noergaard@rn.dk, Phone +45 9932 6903, Fax +45 9932 6914 Pia Wogelius, pia.wogelius@rn.dk, Phone +45 9932 6894, Fax +45 9932 6914 Daniel Buck, DB@DCE.AU.DK, Phone +45 9932 6903, Fax +45 9932 6914

Corresponding author: Michael Gaihede

314Keywords: ventilation tubes, incidence, secretory otitis media, otitis media sequelae, otosurgery

Purpose: Treatment with ventilation tubes (VT) in secretory otitis media and related conditions is a very common procedure based on the rationale of equilibrating the middle ear pressure (MEP) with ambient. Repeated VT treatments are also common in more severe cases, which increase the risk of permanent perforation of the tympanic membrane. The purpose of the present study was to describe the current incidence of VT treatments in children (<15 years) during 2000 to 2005 in a Danish County as well as the number of children subsequently admitted to a tertiary hospital setting for subsequent reconstructive ear surgery.

Materials and Methods: Database information was obtained from the County Health Authorities with information on all VT treatments in children in primary otological practices for the period. Cross reference of this information for year 2000 was made with our database on ear surgery for the identification of patients, who subsequently had been referred for surgery to our department.

Results:TheincidenceofVTinsertionswasdeterminedforthegroupofchildrenborn in 2000 and followed for a 6-year period. The incidence peaked between the age of 1 to 2 years at 137 per 1,000 children, while the cumulated incidence was 28 %. Repeated insertions were found amounting to 45, 22, and 11 % for 2nd, 3rd, and 4th+ insertions, respectively. A total of 3544 children were treated with one or more VTs in 2000; in the following observation period 40 of these were identified in our department. A total of 45 surgical procedures were performed in these children: 39 myringoplasties (87 %), 5 tympanoplastytypeII(11%),1tympanoplastytypeIII(2%);cholesteatomawasfound in 9 cases (20 %).

Conclusions: The incidence of VT insertions was high amounting to 28 % by the age of 6 years. Reinsertions were also high and likely to be correlated to subsequent referrals of patients for reconstructive otosurgery. During our limited period of follow up only few children (1 %) were submitted for ear surgery, where the majority had simple myringoplasties (87 %), while the remaining cases consisted of more severe caseswith structuraldamage.Futurestudiesincludingalongerobservationperiodwill increase this number and provide measures of the correlation between the incidence of VT insertions and reinsertions and the need for subsequent otosurgery reflecting complications and sequelae of SOM and VT. Such numbers describe a more complete measure of the epidemiological weight of SOM and the necessity of basic research in MEP regulation.

1. Introduction

The most common indication for treatment with ventilation tubes (VT) is chronic secretory otitis media (SOM) based on ventilation and equilibra- 315 tion of negative middle ear pressure. Since SOM is frequent with a cumu-

lated incidence of >80 % by the age of 4 years [1], insertions of VTs are similarly frequent accounting for the largest number of surgical procedures in children. Though short term e ects in hearing and behaviour have been documented, long term e ects seem absent and due to risks of complications watchful waiting has been suggested for the majority of children [2– 4]. Moreover, the international costs related to insertions of VTs in chronic SOM are high amounting to approximately US $ 2 billion in the United States, and hence, the analysis of the clinical outcome is important [5].

In recurrent or chronic SOM repeated VTs are often employed, which is correlated to increased rates of complication. In particular, permanent

perforation of the tympanic membrane (TM) can be found in up to 24 % of cases treated with long-term T-tubes [6]. Moreover, patients with repeated VT insertions also represent the cases with more severe courses of SOM related to the development of sequelae like retraction of the tympanic membrane, atelectasis, and cholesteatoma [7]. These patients are likely candidates for proper ear surgery either because of simple perforations of the TM or more extended reconstruction due to more severe courses and relatedsequelae.Thus,thesepatientsconstitutealargerpartofthepatients later referred to otosurgical centres.

The current study was conducted in order to describe these aspects by determining the rate of VT insertions including repeated VTs and their correlation with the subsequent referral of these patients to our departmentforotosurgicalprocedures.TheseaspectsofVTtreatmentwouldadd to the overall description of indications, benefits and costs of VT treatments [5].

2. Materials and Methods

ThestudywasconductedinNorthJutlandCounty,Denmark,during2000– 2005. Since 1968 a 10-digit civil registration number has been assigned to all Danish citizens shortly after birth, and this allows unambiguous linkage between datasets.

2.1 VT database

InformationaboutVTinsertionswasobtainedfromtheHealthAuthorities of North Jutland County. This database covers all surgeries by the private ENT-practioners in our county and includes information on civil registration number, date and type of surgery (uni or bilateral). We included children up to the age of 15 years. Based on these data the incidence of VT

316insertions could be determined as well as the proportion of reinsertions. It should be noted that the vast majority of VT insertions in Denmark (more than 95 %) are performed by private ENT-practioners, whereas these are not engaged in proper otosurgery, which is restricted to hospital settings.

2.2 Ear surgery database

Systematic registration of all ear surgery is taking place in our department coveringtheotosurgicalserviceoftheentirecounty.Thisdatabaserelatesto thesamecivilregistrationnumbersastheVTdatabaseanditcontainstypes of surgery and extent of pathology. Thus, patients treated with VT inserted in 2000 and subsequently referred during 2000 to 2005 could be identified and described.

2.3 Statistics Denmark

From Statistics Denmark we obtained information on the number of residents in North Jutland County born in the year 2000.

3. Results

Among 5769 children born in 2000 a total of 1610 (28 %) had at least one VT inserted during the study period. From this group the incidence of VT insertions according to age was determined (Fig. 1); maximum incidence of 137 VTs per 1,000 children was found at 1-year. The proportion of these children, who had more VTs inserted during the study period, is described in Fig. 2, where the last group (4+) describes 4 or more surgeries. For simplicity, uni and bilateral VTs have been described together (overall ratio = 1:4).

317

Fig. 1 First time insertions of VT’s according to age among 1,610 children born in 2000 (0 → 0 to < 1 years; etc.). The cumulated incidence over time until the end of the 5th year was 28 %.