Perilymphatic pressure dynamics following posture change in patients with Menière's disease and in normal hearing subjects

Effects of body tilt on multifrequency admittance tympanometry

INTRODUCTION

Hydrops and abnormalities of inner fluid pressure are involved in some otologic diseases such as Ménière's disease (MD). However, demonstrating abnormal perilymphatic or endolymphatic pressure is challenging. Multifrequency tympanometry studies in MD patients demonstrated an increase of the width of conductance tympanograms (outside an attack) compared with controls. To confirm that the increase in conductance width is caused by hyperpressure and not hypopressure in these patients tested outside an attack, we assessed the effect of changes in inner ear fluid pressure caused by body tilt on the results of multifrequency admittancemetry tympanograms.

MATERIALS AND METHODS

A multifrequency tympanometry including conductance (G) tympanogram at 2 kHz and resonance frequency measurements were performed in 20 volunteers (40 ears) free of otologic or neurologic disease. The measures were collected in three different positions: vertical, supine, and Trendelenburg positions.

RESULTS

Changes in inner ear fluid pressure caused by body tilt induced an increase in the width of G tympanograms. In the vertical position, the mean value was 141.7 ± 56.5 daPa; in the supine position, it increased to 158 ± 58.3 daPa; and increased even more in the Trendelenburg position (20 degrees), with a mean of 184 ± 69.6 daPa (p < 0.01). Resonance frequency also increased in the Trendelenburg position.We conclude that the increased width of G tympanograms in MD patients outside an attack may be caused by an increase in inner ear fluid pressure.

A Diagnostic Test for Ménière's Disease and Cochlear Hydrops: Impaired High-Pass Noise Masking of Auditory Brainstem Responses

HYPOTHESIS

Endolymphatic hydrops in patients diagnosed with Ménière's disease causes changes in the response properties of the basilar membrane that lead to impaired high-pass noise masking of auditory brainstem responses to clicks.

BACKGROUND

Ménière's disease is defined as the idiopathic syndrome of endolymphatic (cochlear) hydrops, which is an abnormal increase in the volume of cochlear fluid (endolymph) in the inner ear. Accurate detection and diagnosis are important but difficult because of the lack of sufficiently sensitive tests.

METHODS

Two populations were compared: (1) 38 non-Ménière's normal-hearing subjects; and (2) 23 patients who, at the time of testing, continued to have at least three of the four hallmark symptoms (i.e., tinnitus, vertigo, fluctuating hearing loss, and fullness) used in the diagnosis of Ménière's disease. Auditory brainstem responses to clicks presented ipsilaterally with masking noise that was high-pass filtered at various frequencies were recorded.

RESULTS

In the Ménière's patients, the masking noise is insufficient such that an undermasked Wave V is still present at a latency similar to that of Wave V in the response to the clicks alone. In the control non-Ménière's normal-hearing subjects, this undermasked component was either absent or significantly delayed because of the masking noise. The difference in the delays between these populations is such that the distributions do not overlap, resulting in 100% sensitivity and 100% specificity.

CONCLUSION

This test is able to distinguish objectively active Ménière's disease in individuals and may show promise for tracking changes in the severity of the disease caused by progression or treatment.

Perilymphatic pressure measurement in Meniere's disease

The aim of this study was to evaluate the perilymphatic pressure, by means of the MMS-10 Tympanic Displacement Analyzer (TDA), in patients with Meniere's disease (MD). Measurements were performed in 37 patients with MD and in 14 normal-hearing subjects. Data were collected from 3 groups: healthy ears of normal-hearing subjects, unaffected ears of patients with MD, and affected ears of patients with MD. Analysis of the results obtained with the TDA showed no significant differences between the 3 groups. Several hypotheses could explain this lack of difference: 1) perhaps indirect measurement of perilymphatic pressure with the TDA is not relevant; 2) perhaps hyperpressure of the inner ear is not the physiological basis for the clinical triad of MD; or 3) perhaps endolymphatic hydrops does not produce changes in perilymphatic pressure. The results of this series indicate that the TDA is not useful in the evaluation of patients with MD.

The functional and structural outcome of inner ear gene transfer via the vestibular and cochlear fluids in mice

Mice present an ideal model for inner ear gene therapy because their genome is being rapidly sequenced, their generation time is relatively short, and they serve as a valuable model for human hereditary inner ear disease. However, the small size of the mouse inner ear poses a particular challenge for surgical procedures. We have developed a new approach for viral inoculation into the mature mouse inner ear, using a replication-deficient adenovirus expressing the bacterial gene lacZ. We administered the virus through the posterior semicircular canal (canalostomy) and into the cochlea (cochleostomy). Both approaches caused lacZ to be expressed in cells lining the perilymphatic space. One canalostomy case showed gene expression in sensory cells of the crista ampullaris, whereas the cochleostomy group showed gene expression in the sensory cells in the organ of Corti and saccule. Functional tests after the surgery showed that the canalostomy preserved hearing, whereas the cochleostomy did not. Any vestibular function transiently lost after the canalostomy was recovered. Our findings indicate that inoculation of adenovirus vectors into the mouse inner ear through the semicircular canal has the potential to efficiently introduce transgenes to the vestibular system and the cochlea without compromising hearing.

The behavior of evoked otoacoustic emissions during and after postural changes

Click-evoked and stimulus frequency otoacoustic emissions (CEOAEs and SFOAEs, respectively) were studied in humans during and after postural changes. The subjects were tilted from upright to a recumbent position (head down 30 deg) and upright again. Due to the downward posture change, CEOAEs showed a phase increase (80 deg at 1 kHz) and a level decrease (0.5 at 1 kHz), especially for frequency components below 2 kHz. For SFOAEs, the typical ripple pattern showed a positive shift along the frequency axis, which can be interpreted as a phase shift of the inner-ear component of the microphone signal (90 deg at 1 kHz). This also occurred mainly for frequencies below 2 kHz. The altered posture is thought to cause an increase of the intracranial pressure, and consequently of the intracochlear fluid pressure, which results in an increased stiffness of the stapes system. The observed emission changes are in agreement with predictions from a model in which the stiffness of the cochlear windows was altered. For CEOAEs, the time to regain stability after a downward turn was of the order of 30 s, while this took about 20 s after an upward turn. For SFOAEs, this asymmetry was not found to be present (about 11 s, both for up- and downward turns).

The behavior of spontaneous otoacoustic emissions during and after postural changes

Spontaneous otoacoustic emissions (SOAEs) were studied in humans during and after postural changes. The subjects were tilted from upright to a recumbent position (head down 30 degrees) and upright again in a 6-min period. The SOAEs were recorded continuously and analyzed off-line. The tilting caused a change in the SOAE spectrum for all subjects. Frequency shifts of 10 Hz, together with changes of amplitude (5 dB) and width (5 Hz), were typically observed. However, these changes were observed in both directions (including the appearance and disappearance of emission peaks). The most substantial changes occurred in the frequency region below 2 kHz. An increase of the intracranial pressure, and consequently of the intracochlear fluid pressure, is thought to result in an increased stiffness of the cochlear windows, which is probably mainly responsible for the SOAE changes observed after the downward turn. The time for the spectrum to regain stability after a postural change differed between the two maneuvers: 1 min for the downward and less than 10 s for the upward turn.