Intracochlear Pressure Research Articles

Druckrelationen zwischen endokraniellen und intracochleären Flüssigkeitsräumen bei Patienten mit Innenohrerkrankungen*

Intracranial pressure is transmitted to the perilymph of the cochlea via the cochlear aquaeduct and via Reissner's membrane to the endolymph. The "Tympanic Membrane Displacement Analyser (TDA)" is a new device that may be a useful non-invasive method to show intracranial and intracochlear pressure changes indirectly measured by tympanic membrane displacement during stapedial reflex contraction. The TDA was utilised in 20 normal persons and in 29 patients with unilateral diseases of the inner ear. No significant differences in the tympanic membrane displacement were found between patients with sensorineural hearing loss, patients with Ménière's disease, and normal persons.

Die nicht-invasive Beurteilung des intracochleären Druckes - Teil 2: Untersuchungsbefunde von Patienten mit M. Ménière, fluktuierendem Tieftongehör sowie peripher-vestibulären Schwindelattacken

The tympanic membrane displacement technique (TMD) is aimed at evaluating intracochlear and intracranial pressure changes non-invasively. Therefore, the present paper describes the findings in patients with Ménière's disease where an increase in volume of the endolymphatic spaces is discussed. It should be investigated to which extent a change in the intracochlear pressure corresponds to different stages of the disease. It could be described that the intracochlear pressure does change over a certain period of persisting Ménière's, but that there is no extensive increase in intracochlear pressure between the attacks. The glycerol test as well as the acute attack (case report on one patient) are, however, characterised by distinct patterns. The same holds true for the late-stage Ménière's. It could be demonstrated that the functional patency of the cochlear aquaeduct in patients with long-term Ménière's history is reduced. This finding is surprising and should be investigated further. In essence, the TMD technique enables to better characterise Ménière patients, but it should not be a tool of routine diagnosis of the disease. In some audiological patients, it can also be beneficially applied (10).

Noninvasive assessment of intracochlear pressure and patency of the cochlear aqueduct in normal probands with TMD (tympanic membrane displacement) analysis

The intracochlear pressure cannot yet be evaluated in patients with certain audiological neuro-otological diseases. However, it seems to be of importance in the diagnosis and pathogenesis of Ménière's disease and related disorders. The present paper is aimed at introducing a setup to indirectly assess intracochlear and intracranial pressure changes and the design and philosophy of this technique. It is possible to describe a normal range of the measured values in healthy controls although large interindividual variations occur. In addition, the positional changes of the registered parameters enable assessment of the patency of the cochlear aquaeduct. This seems to be important in some diseases, such as stapes gusher.

Experimental Look at Cochlear Mechanics: Approche expérimental de la mécanique cochléaire

The mechanisms by which the organ of Corti is stimulated by acoustic stimuli are discussed on the basis of experimental observations. This discussion refers to the resonance theory as well as to the traveling wave (TW) theory. The measurement of the basilar membrane displacements, of the cochlear micro-phonic (CM) responses to pure tones and impulses, and the recording of the intracochlear acoustic pressure seem to indicate that, at least in the basal part of the cochlea and for frequencies up to the characteristic frequency of a given location, the cochlear responses do not exhibit large phase lags and long delays which characterize the one-dimensional long-wave models (in which a TW transports the energy along the cochlear partition). These experimental observations suggest that the cochlear partition is excited simultaneously as a whole, more or less like a bank of resonators, as proposed a long time ago by Helmholtz.

Intracochlear pressures resulting from brief high intensity stimuli

A previous study has shown similar hearing loss and cochlear injury from exposures to impulses differing in peak pressure, but having the same energy and Fourier pressure spectrum. Nonlinear processes in the middle ear or transmission through the external and middle ear may render different stimuli more similar once they reach the cochlea, thus accounting for the equivalent injury observed. In order to explore this possibility, pressures in the basal turn of the cochleas of eight anesthetized chinchillas were measured for impulses presented at levels between 88‐and 147‐dB peak. This included the impulses used in the previous injury study. While nonlinearities were noted at the higher intensities, there was a remarkable preservation of the pressure‐time histories. In addition to these impulse stimuli, intracochlear pressures were measured using brief tone pips whose envelope was Gaussian. Frequencies of 700, 1375, 2000, 2700, and 4100 Hz were chosen to span the frequency response of the speaker. With these stimuli, nonlinearities appeared as both harmonic and subharmonic distortion as the intensities increased.

Effect of prazosin and 'intracranial hypertension' on cochlear blood flow.

The cochlear and cerebral blood flow were simultaneously measured with the microsphere method in albino rabbits before and after administration of prazosin (0.5 mg/kg body weight) and before and during an increase in intracranial pressure (ICP) and intracochlear pressure. Increments in ICP were induced by intracranial infusion of Ringer solution prewarmed to body temperature. The increments were accompanied by an intravenous administration of prazosin to abolish the Cushing effect. The cochlear blood flow was unaffected by the intravenously administered prazosin. A decrease was found when the perfusion pressure of the cochlear, i.e. mean arterial blood pressure minus ICP fell below 5 kPa.

Persistence of auditory nerve response and absence of brain-stem response in severe cerebral ischaemia

Cerebral ischaemia, in which the brain-stem components of the ABP were isoelectric, was accompanied by the paradoxical persistence of the compound action potential of the auditory nerve (wave 1). This ischaemia was induced in cats by reducing mean arterial blood pressure and elevating intracranial pressure, resulting in decreased cerebral perfusion pressure (CPP). This is unexpected since the inner ear is supplied by a branch of an intracranial artery. To study this phenomenon, CPP was manipulated and when average CPP was 13.5 mm Hg, only wave 1 remained. In 7 of 9 experiments, clamping of both common carotid arteries did not abolish wave 1. Experiments with radioactive tracers demonstrated a remaining residual blood flow through the inner ear. This remaining auditory nerve response is probably not due to a very low metabolism of the inner ear or to the cochlea being supplied by anastosomes from the middle ear, supplied by the external carotid artery. The residual cochlear blood flow and the persistent wave 1 can probably be explained in the following way at low CPPs the smaller intracranial blood vessels collapse so that the brain tissue is not perfused, leading to loss of the brain-stem components of the ABP. However, flow still persists in the larger intracranial arteries. This blood preferentially flows to the cochlea since the intracochlear pressure is slightly below the intracranial pressure due to the presence of the oval and round windows. Thus a sufficient blood flow to the cochlea is maintained, with sparing of wave 1.

Effects of perilymph viscosity on low-frequency intracochlear pressures and the cochlear input impedance of the cat.

Cochlear model calculations are shown to be in reasonable agreement with recent low-frequency measurements of intracochlear pressures and the cochlear input impedance of the cat [V. Nedzelnitsky, J. Acoust. Soc. Am. 68, 1676-1689 (1980); T. J. Lynch, III, V. Nedzelnitsky, and W. T. Peake, J. Acoust. Soc. Am. 72, 108-130 (1982)]. Included in the cochlear model are perilymph viscosity, the measured variation of the area of the scala vestibuli with distance from the stapes [P. Dallos, J. Acoust. Soc. Am. 48, 489-499 (1970)], and finite impedance of the round window membrane. The WKB approximation and its extension to the low-frequency region is used in order to exhibit explicitly the dependence of the model results on the cochlear parameters.

Model calculations of low‐frequency intracochlear pressures and the cochlear input impedance of the cat and guinea pig

Recent low‐frequency measurements of intracochlear pressures and the cochlear input impedance of the cat [V. Nedzelnitsky, J. Acoust. Soc. Am. 68, 1676–1689 (1980); T. J. Lynch, III, V. Nedzelnitsky, and W. T. Peake, J. Acoust. Soc. Am. 72, 108–130 (1982)] and the guinea pig (A. Dancer and R. Franke, Hear. Res. 2, 192–205 (1980)] are shown to be in reasonable agreement with the results of cochlear model calculations. Included in the cochlear model are perilymph viscosity, the measured variation of the area of the scala vestibuli with distance from the stapes [P. Dallos, J. Acoust. Soc. Am. 48, 489–499 (1970)], and the finite impedance of the round window membrane. Approximate analytic expressions for the fluid pressures in the scalae are derived so as to explicitly exhibit the dependence of the model results on cochlear parameters. [This work was supported by NSF.]

The effect of intracranial hypertension on cochlear blood flow.

The cochlear blood flow was investigated in rabbits with the microsphere method before and during an induced increase of intracerebral and intracochlear pressures. The increase was accomplished by infusing Ringer solution into the lateral cerebral ventricles. The cochlear blood flow was found to autoregulate in response to decreases in perfusion pressures down to 5-6 kPa. This finding is discussed in relation to known effects of intracochlear and intracranial pressure on hearing.

Sound pressures in the basal turn of the cat cochlea.

Techniques were developed for measuring sound pressure in the cochlea with calibrated, liquid-filled, piezoelectric probe microphones. Sound pressures were measured in scala vestibuli and scala tympani in the basal turn in 25 cats for tones from 20--10 000 Hz. Control experiments indicated that intracochlear pressures were essentially uninfluenced by the measuring technique, and were conducted to the cochlea via the ossicular chain. Intracochlear pressures are linearly related to pressure at the tympanic membrane for tone levels at least as high as 105 dB SPL, and are relatively independent of depth of probe insertion in the scalae. The transfer ratio of sound pressure in scala vestibuli to that at the tympanic membrane increases in magnitude over the frequency range 50--1000 Hz to reach a maximum value of 15--30 dB, and decreases at higher frequencies, thus demonstrating that the middle ear provides a frequency-dependent pressure gain. At frequencies below 40 Hz, the pressures in scala vestibuli and scala tympani are approximately equal and are both determined by the round-window membrane compliance. At frequencies above 100 Hz, the round-window membrane impedance is small compared to the acoustic input impedance of the cochlea, and the pressure in scala vestibuli considerably exceeds that in scala tympani; consequently, the pressure difference across the cochlear partition is approximately equal to the pressure in scala vestibuli.

Glycerol effects on the perilymphatic and cerebro-spinal fluid pressure.

Glycerol has been injected intravenously in guinea pig and its effects on the pressure in the cochlear fluids have been studied. Simultaneously, arterial and cerebro-spinal pressures have been recorded. Glycerol lowered the intracochlear as well as cerebro-spinal and blood pressures, the latter only temporarily. Different possible mechanisms for the glycerol effect on the intracochlear pressure and its transient effect on hearing in Menière's disease are discussed.

Changes in the Cochlear Microphonic of the Guinea Pig Produced by Mechanical Factors in the Inner Ear

The cochlear microphonics of the guinea pig have been recorded by means of differential intracochlear electrodes located in various turns of the cochlea. Since it has been shown by Békésy that the cochlear-microphonic voltage is proportional to the displacement of the basilar membrane, it is, thus, possible to study the changes in the mechanical movements of the cochlear partition. Mechanical alterations were produced by increase of the fluid pressure inside the cochlea and by local pressure on the basilar membrane. Increased intracochlear pressure produces a selective decrease in the microphonics recorded from the apical part of the cochlea, and when this decrease becomes very large a phase shift is also observed. Touching the basilar membrane with a guinea-pig hair in the basal turn modifies the potential recorded in the same region, but leaves unchanged the microphonics recorded in the upper parts. Pressing on the basilar membrane in the second turn modifies the microphonics recorded in the apical part, but not the microphonics of the basal turn. Rather large destructions of the apical parts of the cochlea modify only slightly, or not at all, the microphonics from the basal part of the cochlea. These various effects are discussed in the light of the mechanisms and the models described by Békésy.