Noninvasive intracranial compliance monitoring. Technical note and clinical results

Although invasive measurement of intracranial pressure (ICP) involving high-resolution waveform analysis allows assessment of intracranial compliance (ICC), it is only feasible in a few selected neurosurgical conditions. Intracranial compliance can be assessed using the high-frequency centroid (HFC), which is the power-weighted mean frequency within the 4 to 15-Hz band of the ICP waveform. The authors have systematically tested the utility, performance, and reliability of a noninvasive monitor of ICC. The underlying principle of this device is that the ICP transmission and its infrasonic waves are transmitted through the inner ear toward the tympanic membrane. If the outer ear is sealed in an airtight fashion, motions of the tympanic membrane cause air pressure fluctuations that can be recorded using a special sensor. The authors compared the HFC calculated from an intraparenchymal ICP sensor with that obtained simultaneously from an ipsilaterally placed noninvasive device during half of a respiratory cycle (peak to baseline) as well as for three random samples of three heart cycles. They analyzed 32 sessions in 13 patients in whom mechanical ventilation had been established. In four (11%) of 36 sessions they could not demonstrate an adequate signal. For the peak-to-baseline cycle, the mean invasively recorded HFC was 8.05 +/- 0.55 Hz (range 6.7-9 Hz) whereas the mean noninvasively recorded HFC was 8.04 +/- 0.49 Hz (range 7-9.3 Hz). The ICP was 8.5 +/- 5 mm Hg (range 2-24 mm Hg). For the three heart cycles randomly sampled, the values were 7.73 +/- 0.51 Hz (range 6.7-8.6 Hz) and 7.76 +/- 0.56 mm Hg (range 6.5-8.8 mm Hg), respectively. This device allows noninvasive assessment of ICC based on the HFC waveform analysis that is equivalent to that obtained by invasive intraparenchymal recording. The monitoring device may become a valuable tool for monitoring parameters in patients in whom placement of an intracranial sensor is not feasible but assessment of ICC as an alternative to ICP measurement is desired.

Can electrocochleography in Meniere's disease be noninvasive?

OBJECTIVES

To evaluate and compare the results of extratympanic and transtympanic electrocochleography (ECochg) in clinically diagnosed cases of Meniere's disease and controls.

DESIGN

Prospective study on 20 clinically diagnosed cases of Meniere's disease and 20 age- and sex-matched controls.

SETTING

Department of Otolaryngology, Head and Neck Surgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India.

METHODS

Electrocochleography was performed by a transtympanic method using a stainless steel needle electrode kept on the promontory and by an extratympanic method whereby the needle electrode was inserted into bony canal skin.

MAIN OUTCOME MEASURES

The various parameters compared were summation potential latency and amplitude, action potential latency and amplitude, and ratio of summation to action potential amplitude (SP/AP).

RESULTS

A significant difference in summation to action potential amplitude ratio (SP/AP) between cases and controls was obtained by both methods. Using 0.29 as a cutoff for SP/AP, the transtympanic method yielded a sensitivity of 100% and a specificity of 90%, whereas the extratympanic method showed corresponding values of 90% and 80%, respectively.

CONCLUSION

Contrary to previous studies, extratympanic ECochg is shown to be an efficacious and a less invasive test as compared with the transtympanic method and can be easily performed in clinical practice.

Changes in the three-dimensional angular vestibulo-ocular reflex following intratympanic gentamicin for Ménière's disease

The 3-dimensional angular vestibulo-ocular reflexes (AVOR) elicited by rapid rotary head thrusts were studied in 17 subjects with unilateral Ménière's disease before and 2-10 weeks after treatment with intratympanic gentamicin and in 13 subjects after surgical unilateral vestibular destruction (SUVD). Each head thrust was in the horizontal plane or in either diagonal plane of the vertical semicircular canals, so that each head thrust effectively stimulated only one pair of canals. The AVOR gains (eye velocity/head velocity during the 30 ms before peak head velocity) for the head thrusts exciting each individual canal were averaged and taken as a measure of the function of that canal. Prior to intratympanic gentamicin, gains for head thrusts that excited canals on the affected side were 0.91 +/- 0.20 (horizontal canal, HC), 0.78 +/- 0.20 (anterior canal, AC), and 0.83 +/- 0.10 (posterior canal, PC). The asymmetries between these gain values and those for head thrusts that excited the contralateral canals were <2%. In contrast, caloric asymmetries averaged 40% +/- 32%. Intratympanic gentamicin resulted in decreased gains attributable to each canal on the treated side: 0.40 +/- 0.12 (HC), 0.35 +/- 0.14 (AC), 0.31 +/- 0.14 (PC) (p <0.01). However, the gains attributable to contralateral canals dropped only slightly, resulting in marked asymmetries between gains for excitation of ipsilateral canals versus their contralateral mates: HC: 34% +/- 12%, AC: 24% +/- 25%, and PC: 42% +/- 13%. There was no difference in the AVOR gain for excitation of the ipsilateral HC after gentamicin in patients who received a single intratympanic injection (0.39 +/- 0.11, n = 12) in comparison to those who received 2-3 injections (0.42 +/- 0.15, n = 5, p = 0.7). Gain decreases attributed to the gentamicin-treated HC and AC were not as severe as those observed after SUVD. This finding suggests that intratympanic gentamicin causes a partial vestibular lesion that may involve preservation of spontaneous discharge and/or rotational sensitivity of afferents.

Idiopathic inflammatory medial meatal fibrotizing otitis

BACKGROUND

Idiopathic inflammatory medial meatal fibrotizing otitis (IMFO) is rare. Only a few cases with unknown cause have been reported.

OBJECTIVE

To report 3 cases of IMFO as a specific diagnostic entity.

PATIENTS AND METHODS

Two adults and 1 child with bilateral IMFO were observed for several years at the Department of Otorhinolaryngology of Helsinki University Hospital, Helsinki, Finland.

RESULTS

Only the osseous part of the external ear canals was affected by IMFO. The skin and skin organs over the lateral cartilage of the ear canals remained rigorously and constantly uninflamed through the active, relentless progression of the disease over several years, resulting in the formation of a fibrous plug of the medial meatal canal. The middle ears and mastoid air cells were not affected during the active inflammatory phase.

CONCLUSION

IMFO has its own specific pathophysiologic characteristics, and perhaps also etiopathologic characteristics, which are still unknown.

Revision tympanomastoid surgery

We conducted a retrospective study of 50 ears in 48 patients in whom we performed revision tympanomastoid surgery for chronic otitis media. We found that the most common probable causes for the failure of previous surgery were incomplete lowering of the facial ridge (94% of cases), persistent sinodural-angle air-cell disease (92%), persistent tegmental air-cell disease (88%), recurrent or persistent cholesteatoma (66%), persistent mastoid-tip air-cell disease (62%), a small meatus (60%), and persistent hypotympanic air-cell disease (56%). After a mean postoperative follow-up of 26 months, we found no appreciable difference in success rates between patients who had undergone only one previous surgery (93%) and those who had undergone more than one previous surgery (95%) prior to referral to our center. Follow-up hearing data revealed a statistically significant improvement in air and bone conduction and a nonsignificant reduction in the air-bone gap. We conclude that revision mastoid surgery following multiple earlier surgical failures does not carry an appreciably higher risk of failure than does initial revision surgery. Moreover, there appears to have been no change in the causes of failure following mastoid surgery over the past 3 decades.

Daily home tympanometry to study the pathogenesis of otitis media

A study was conducted to define the temporal relationship between a parent-identified cold episode and the diagnosis of otitis media. Forty children were studied in their homes with the use of daily tympanometry, symptom diaries and weekly otoscopy. A total of 136 patients identified colds, and 43 episodes of otitis media were recorded. New episodes of otitis media were observed in 22% of all colds, and 63% of all otitis media episodes occurred during a cold.

[Atrophy of the tympanic membrane in contact with hydroxyapatite prosthesis: physiopathologic approach]

The implantation of ossicular replacement prothesis made of dense hydroxyapatite (HA) appears to be a wider method of reconstruction of ossicular chain damaged by suppurative processes or surgery. A review of 19 patients who underwent implantation of HA prosthesis disclosed 4 cases of extrusion and 3 cases of atrophy. When X-ray diffraction analysis of explanted commercially available prosthesis made of dense HA was compared with the results with porous implants and with HS powder employed in the manufacture of both, is suggested that tympanic membrane atrophy could be caused by mechanical and/or chemical factors.

Efficacy of increased gentamicin concentration for intratympanic injection therapy in Ménière's disease

OBJECTIVES

Update of ongoing case series of intratympanic gentamicin use in intractable Ménière's disease. Comparison of the treatment results of two gentamicin concentrations: 30 mg/ml and 40 mg/ml.

STUDY DESIGN

Retrospective case-matched review of an ongoing protocol.

SETTING

Ambulatory visits in an office setting.

PATIENTS

Eighty-seven patients were included in this study according to the 1995 guidelines of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) for reporting treatment results of Ménière's disease.

INTERVENTION

Intratympanic injection of a buffered gentamicin solution (30 mg/ml) was used in 44 patients (Group 1) in years 1992 to 1995. Stock gentamicin solution (40 mg/ml) was used in 43 patients (Group 2) in years 1996 to 1999. Treatment was titrated for each patient, and the hearing was strictly monitored. The endpoint of treatment was the complete cessation of vertigo spells.

MAIN OUTCOME MEASURES

Hearing results, vertigo control scores, and ice water caloric testing responses were analyzed after 24 months of follow-up. Thirty-two patients from each group were selected for case-matched statistical analysis.

RESULTS

Four or fewer gentamicin injections were used in 70% of Group 1 patients and 96% of Group 2 patients. In Group 1, vertigo control was achieved in 81% of patients, and the hearing remained the same or was improved in 68% of patients. In Group 2, vertigo control was achieved in 72% of patients, and the hearing remained the same or was improved in 81% of patients. Treatment was aborted in four patients of Group 2 for early reversible hearing loss, and 31 of 39 patients (79%) who completed the protocol experienced lasting vertigo control. There was a trend for longer-lasting vertigo control in the Group 2 patients.

CONCLUSION

It was concluded that increasing the gentamicin concentration to 40 mg/ml probably produces similar rates of vertigo control as those of the lower dose, at least initially, but requires fewer injections. The higher dose did not increase the risk of hearing loss if treatment was stopped at the first indication of injury. A larger study is needed to confirm the trend of improved long-term hearing results in patients treated with the 40 mg/ml solution.

Use of homograft dehydrated temporal fascia in tympanoplasty

OBJECTIVE

To investigate the results of myringoplasty operations using homograft dehydrated fascia temporalis (Tutoplast) and compare these with those performed with autograft fascia temporalis.

STUDY DESIGN

Prospective cohort.

SETTING

University hospital.

PATIENTS

Forty-three adult patients (> or =18 years of age) with central, dry perforations of pars tensa with intact ossicular chains.

INTERVENTION

Tympanoplasty with an endaural approach and underlay technique was performed. Homograft dehydrated temporal fascia was used in 22 patients, and autograft was used in the remaining 21 patients.

MAIN OUTCOME MEASURES

Preoperative and postoperative air-bone gap and speech reception threshold levels and postoperative compliance values of the homograft and autograft groups were compared.

RESULTS

Postoperative perforations were encountered in two patients (9.1%) from the homograft group and three patients (14.2%) from the allograft group. Significant postoperative improvements in air-bone gap and speech reception threshold values were detected for both groups (p < 0.05). Although the mean compliance of the tympanic membranes was significantly lower in the homograft group, no statistically significant difference was observed between groups when the postoperative air-bone gap and speech reception threshold values were compared.

CONCLUSION

Homograft temporal fascia can be used in tympanoplasty with the same success rate of autograft temporal fascia without impeding hearing. Its main advantages are the reduction in the duration of surgery and the length of preauricular and postauricular incisions. However, the advantages of the dehydrated homograft temporal fascia should be weighed against its cost and risk of transmission of viral and prion-mediated diseases.

Evaluation of the role of respiratory viruses in acute myringitis in children less than two years of age

BACKGROUND

The etiology of acute myringitis remains controversial although it is usually encountered in connection with acute otitis media (AOM). In most cases of acute myringitis a bacterial pathogen has been detected in the middle ear fluid, but the role of respiratory viruses has remained unclear. Our objective was to investigate the etiologic role of viruses in the pathogenesis of acute bullous and hemorrhagic myringitis in children <2 years of age.

METHODS

A prospective longitudinal cohort study of 2028 children ages 7 to 24 months in primary care in the Finnish Otitis Media Vaccine Trial. Nasopharyngeal aspirate (NPA) and middle ear fluid (MEF) samples taken at the time of the diagnosis were examined by a time-resolved fluoroimmunoassay for antigen detection of adenoviruses; influenza viruses A and B; parainfluenza viruses 1, 2 and 3; and respiratory syncytial virus and by reverse transcription polymerase chain reaction for human rhinovirus and human enterovirus.

RESULTS

Eighty-two children with bullous myringitis and 37 children with hemorrhagic myringitis were diagnosed during the 18-month follow-up period. In bullous myringitis a respiratory virus was detected in 70% of NPA samples and in 27% of MEF samples. In hemorrhagic myringitis 57% of NPA samples and 28% of MEF samples were virus-positive. The viral distribution was similar to that of AOM (virus positive 64% of NPA and 37% of MEF).

CONCLUSIONS

We could not confirm any specific respiratory virus to be the etiologic agent in acute myringitis. The etiology of acute myringitis is similar to that of AOM in children <2 years of age.

Hearing loss and middle ear involvement in rheumatoid arthritis

In this controlled study, hearing and middle ear functions were investigated in 37 patients with rheumatoid arthritis (RA) and 35 controls in order to study the prevalence and the nature of hearing loss in RA. The prevalence of the hearing impairment was significantly higher in the RA group, and the majority was bilateral (P<0.001). Of the patients, 35.1% had sensorineural (SN), 24.3% had conductive loss, and 10.8% had a mixed type of hearing loss. The hearing loss was positively correlated to the Steinbrocker functional index. The prevalence of abnormal tympanograms was 37.8%, while it was 17.1% in the control group. The probable site of involvement responsible for the SN loss was the cochlea, and discontinuity of the ossicles, rather than stiffness, was responsible for the conductive hearing loss. The presence of a mixed type of hearing loss suggested a multifocal involvement of the audiologic system in RA.

[YAG-Nd laser: effects of radiation on acoustic analyser function in experimental animals]

Effects of laser radiation on the function of the internal ear receptors were studied using short-latent acoustic evoked potentials (SLAEP) of rabbit truncus cerebri. Contact laser impact in the area of the medial wall of the tympanic cavity in one of the ear was made after registration of baseline SLAEP. The other ear served control. It was found that YAG-Nd laser radiation had the receptor damage threshold within 7-8 W. Assessment of laser energy reaching receptors of the animals' labyrinth was carried out by the thickness of the bone of tympanic medial wall in the rabbit middle ear. Differences in the above thickness in humans and rabbits and calculated transmission factors for laser radiation of the bone tissues indicate that radiation power 14-16 W may appear critical in manipulations on human middle ear.

Clinical applications of a finite-element model of the human middle ear

Computer-generated models are increasingly being used in otolaryngology for teaching purposes, preoperative planning, and clinical simulations, especially when dealing with small, complex areas such as the middle ear. One technique used to analyze the mechanics of complex models is the finite-element method, whereby the system of interest is divided into a large number of small, simple elements. The mechanical properties and applied forces are represented by functions defined over each element, and the mechanical response of the whole system can then be computed. We present a unique three-dimensional finite-element model of the human eardrum and middle ear. Our model takes advantage of phase-shift moiré shape measurements to precisely define the shape of the eardrum. The middle ear geometry is derived from histologic serial sections and from high-resolution magnetic resonance microscopy of the human ear. We discuss the importance of this model in terms of understanding and teaching the mechanics of the human middle ear, simulating various pathologic conditions, and designing ossicular prostheses.

Wideband reflectance tympanometry in chinchillas and human

Wideband reflectance tympanometry was performed on twelve chinchillas ears. The complex input impedance of the middle ear, multifrequency admittance tympanograms, reflectance patterns (reflectance versus frequency), and reflectance tympanograms (reflectance versus ear-canal air pressure) were analyzed and compared to human data. The complex impedance of the chinchilla ear has a lower stiffness reactance at low frequencies, a higher mass reactance at high frequencies, and a lower resistance compared to the human. Multifrequency admittance tympanograms from chinchillas follow the same sequence of patterns as humans for low frequencies (<2 kHz). At higher frequencies tympanograms from both species are poorly organized and do not follow a consistent sequence of patterns. Reflectance patterns of chinchillas and humans are different. However, both species show high reflectance at low frequencies, regions of lower reflectance in mid-frequencies (2-6 kHz), and high reflectance at high frequencies (>8 kHz). Reflectance tympanograms for the two species show a single, centrally located minimum at low frequencies (<2 kHz) and are substantially different at higher frequencies. Results are shown for two animals that underwent eustachian tube obstruction. Reflectance patterns obtained with different ear-canal air pressures are substantially different. Reflectance results at any single ear-canal pressure (including ambient pressure) do not completely characterize the effects of middle-ear pathology.

Cartilage palisade tympanoplasty and diving

OBJECTIVE

To determine whether a patient with a serious defect of the tympanic membrane (TM) will be able to dive after surgery.

PATIENTS AND METHODS

The authors describe three patients who were divers with serious defects of the TM (more than 75% of TM). In all three cases, cartilage palisade tympanoplasty was used to reconstruct the TM.

RESULTS

Six months after surgery, the patients passed clinical examinations, audiograms (hearing restored to normal), tympanometry (increased stiffness of the TM), and pressure tolerance tests in hyperbaric chamber (30-m immersion was simulated for 4 minutes), and they began to dive again. Approximately 2 years after the surgery, all three patients are able to dive without any difficulties.

CONCLUSION

The authors conclude that patients can dive after cartilage palisade tympanoplasty.

The clinical evaluations of pathophysiology for congenital middle ear cholesteatoma

PURPOSE

Congenital middle ear cholesteatoma (CMEC) is less common than the acquired variety. Many theories have been put forward to explain the pathophysiology of CMEC; however, none of them have been convincingly proven thus far. This clinical study was performed to analyze the case reviews; assess the characteristic features of CMEC, and evaluate the correlation between those features and the pathophysiology of CMEC.

METHODS

The medical records of patients who underwent otologic procedures at the hospitals of the Catholic University, Seoul, Korea, from January 1993 to November 1998 have been reviewed.

RESULTS

Of the 14 patients, 3 had cystic lesions isolated to the anterosuperior quadrant of the mesotympanum. The lesions were easy to remove and did not affect the patients' hearing. Eleven patients had more extensive disease with posterior mesotympanum involvement; the lesions were large, were often too extensive to indicate a formative site, and caused ossicular damage.

CONCLUSION

CMEC manifests in 2 distinctive forms according to the formation site. This distinctive formation site suggests that the pathophysiology of posterior lesions may be different from that of anterior ones. For early diagnosis of CMEC, a screening program should be established for children to prevent more extensive disease.

Pars tensa and pars flaccida retractions in persistent otitis media with effusion

OBJECTIVE

In children with otitis media with effusion (OME), to investigate the incidence of, and any association, between retractions of the pars tensa and pars flaccida; to assess the effect of pars tensa and pars flaccida retractions on the hearing; to investigate risk factors for retractions; and to document the natural history of such retractions over a 12-week 'watchful aiting" period.

STUDY DESIGN

Prospective, observational study.

SETTING

Sixteen departments of otolaryngology in hospitals in the U.K.

PATIENTS

A cohort of 1,267 children aged 3.25 to 6.75 years with confirmed OME. None had previously received surgical intervention.

INTERVENTIONS

Follow-up over a "watchful waiting" period of 12 weeks.

MAIN OUTCOME MEASURES

Otoscopy and pure-tone audiometry.

RESULTS

Retraction of the pars tensa to the incus or promontory occurred in 8% of the better-hearing ears and 10% of the poorer-hearing ears. Pars flaccida retraction to the malleus or farther occurred in 4.5% of the better-hearing ears and 5.5% of the poorer-hearing ears. Retractions were not associated with a longer history of hearing problems. Pars tensa or pars flaccida retraction in association with OME did not materially affect the hearing. Pars tensa retractions, followed up over a 12-week period, resolved in 69% of the better-hearing ears and 65% of the poorer-hearing ears. In 14% and 10% of ears, respectively, the OME had also resolved.

CONCLUSIONS

There is minimal evidence to support the concept that pars tensa or pars flaccida retractions are a strong or relevant marker for the severity or evolution of OME in children. Prospective studies over a longer period of follow-up are required to confirm this.

Hyperectasis: the hyperinflated tympanic membrane: the middle ear as an actively controlled system

OBJECTIVE

To describe and analyze a middle ear condition in which the steady state of the middle ear pressure is elevated above the atmospheric pressure. SETTING AND STUDY DESIGN: This is a long-term survey of 59 patients from a private clinic who were observed on routine examination to have a ballooned out (hyperinflated) tympanic membrane.

INTERVENTION

All patients underwent hearing tests, tympanometry, and Shullers (lateral) mastoid radiography.

MAIN OUTCOME MEASURES

A hyperinflated tympanic membrane indicates a middle ear pressure that is higher than atmospheric pressure. The ballooned tympanic membrane returns to its physiological level after being punctured. This pressure situation is the reverse or opposite of atelectasis and is therefore termed hyperectasis. Hyperectasis, like atelectasis, is associated with a poorly pneumatized mastoid.

RESULTS

Fifty-nine hyperectatic ears persisted in their hyperinflated state for weeks, months, or even years. The hyperectasis was preceded by atelectasis, and both conditions occasionally changed one into the other. The ballooned part of the tympanic membrane is usually thin and "scarred." Hyperectasis is not a rare situation and, once recognized, can be readily encountered in an otologic clinic.

CONCLUSIONS

Like most biologic systems (e.g., blood pressure, temperature), the middle ear's central feature, i.e., pressure, also has a dynamic character vacillating up and down. It is conceivable that middle ear pressure is also actively regulated and controlled with the aid of a feedback mechanism. Passage of gas through the eustachian tube or absorption by diffusion-perfusion is also at least partly an active process. The up and down middle ear pressure vacillations are usually clinically benign and do not lead to any pathologic features as long as they are buffered by an accompanying normal mastoid pneumatization. It is the ear with a nonpneumatized mastoid that has limited ability to buffer pressure changes and that will present as an atelectasis, a retraction pocket, or (eventually a cholesteatoma) or their reverse, a hyperectatic tympanic membrane.

Evaluation of eardrum laser doppler interferometry as a diagnostic tool

OBJECTIVES

Laser Doppler interferometry (LDI) of the eardrum allows noncontact optical analysis of its vibrations in response to sound. Although LDI has been widely used in research, it has not yet been introduced into clinical practice as an adjunctive test for otological workup. The aim of this study was to evaluate LDI as a diagnostic tool in the clinical sphere.

STUDY DESIGN

Prospective.

METHODS

A measurement system was developed based on a commercially available scanning He-Ne laser Doppler interferometer. The study included 129 eardrums of 79 subjects that were divided into 3 groups: 1) normal subjects and 2) patients with sensorineural and 3) conductive hearing loss (HL). All the patients suffering from conductive HL underwent ossiculoplasty, which allowed confirmation of the final diagnosis, and patients were assigned accordingly to the subgroups malleus fixation, incus luxation, and stapes fixation.

RESULTS

The modified LDI system allowed bilateral evaluation of a subject within 30 minutes. No significant difference between normal subjects and patients having sensorineural HL were found. However, it was possible to distinguish between normal subjects and patients with conductive HL. Furthermore, the system had the ability to differentiate between various middle ear diseases. These groups differed statistically significantly in terms of manubrium vibration amplitude and resonance frequency. In malleus fixation significant differences in tympanic membrane movement patterns were found.

CONCLUSIONS

Our LDI is applicable in clinical otological practice and serves as a valuable addition to the routine audiological investigations for preoperative evaluation of the mobility and integrity of the ossicular chain.

Tympanometric hysteresis effect and errors in middle ear pressure determination--a preliminary study in children with secretory otitis media

Previous tympanometric studies on middle ear pressure (MEP) have revealed the hysteresis effect, which is illustrated in bidirectional tympanometries by the different peak pressures for either direction. This leads to an error in determination of MEP, which has been reported to be 10-25 daPa in normal ears, but experimental data have suggested that this error may be increased in ears with secretory otitis media (SOM). This was investigated in a group of 18 children with SOM by bidirectional tympanometries. The peak pressure difference (PPD) was calculated and found to be 75 daPa in the group of SOM, which was significantly larger than in normal ears (mean = 3 daPa) (p < 0.001). The maximum PPD in the SOM group was 205 daPa, indicating an error in MEP determination of more than 100 daPa. Hysteresis is related to the viscous properties of the middle ear system, and the increased hysteresis in SOM ears can be explained by the additional viscosity of the middle ear effusion. In order to improve the accuracy of MEP estimation it is suggested that in ears with SOM, the mean pressure of bidirectional tympanometries should be applied.

Perilymphatic pressure measurement in patients with Menière's disease

The MMS-10 Tympanic Displacement Analyser is a new device for measuring perilymphatic pressure in humans. This instrument was used in 70 patients with Menière's disease (44 affected ears) and a group of 50 young normal hearing subjects. No significant differences in perilymphatic pressure measurements were found between the groups. Although measurement parameters showed large inter-individual variation in a subgroup of 25 patients, the intra-individual correlation in the subgroup was good. In patients with Meniere's disease no relationship was found between perilymphatic pressure, hearing thresholds, blood pressure, gender or age. There was no difference between unilaterally and bilaterally affected patients.

Biomechanical aspects in implantable microphones and hearing aids and development of a concept with a hydroacoustical transmission

The middle ear functions as a sensitive pressure receptor. This implies that it not only transmits sound pressure waves with molecule-sized vibrational amplitudes, but that it also reacts to the million times larger variations of ambient air pressure. This pressure induces movements of the tympanic membrane and of the attached ossicular chain of up to 1,000 microm. Any artificial device that contacts these sound-transporting elements, be it a receiver for an implantable microphone or a transducer for an implantable hearing aid, has to respect these two different modes of biomechanical behavior. A hydroacoustical transmission system has therefore been developed consisting of a water-filled flexible tube, which contacts the ossicular chain with a balloon tip, and which is connected to a piezo-electric transducer at its other end. This soft contact prevents a localized pressure load and does not restrain the free movement of the underlying ossicle during ambient pressure variations. Temporal bone experiments showed that the device transmits vibration energy in good acoustical quality. The device can also be used in a reverse mode, working as a microphone, for example for a totally implantable hearing aid or a cochlear implant. This microphone concept has the advantage that it incorporates the biologic sound receiving components (the tympanic membrane and the ossicular chain micromechanics) into a technical device.

Rupture pressures of membranes in the ear

The rupture pressures of the tympanic membrane, Reissner's membrane, the round window membrane, and the annular ligament have all been measured in cadaver ears from Norwegian cattle. For the tympanic membrane, a static overpressure was applied to the ear canal; for Reissner's membrane, to the endolymph; and for the round window membrane, to the perilymph. The rupture pressure of the annular ligament equals the rupture force to the footplate divided by the area of the oval window. The mean rupture pressures are 0.39 atm for the tympanic membrane, 0.047 atm for Reissner's membrane, greater than 2 atm for the round window membrane, and 29.4 atm for the annular ligament. This last pressure corresponds to 0.68 kilogram force applied to the footplate. The ruptures of the tympanic membrane appeared without exception as small tears in the pars flaccida. The rupture pressure of the tympanic membrane was also measured in a few ears from foxes.