Perilymphatic Pressure Research Articles

Pressure Gradients Affecting the Labyrinth during Hypobaric Pressure

Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and round windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large pressure gradients toward the chamber and the cerebrospinal fluid compartments, respectively. We conclude that closed cavities with limited pressure release capacities are the cause of the pressure gradients. The strain exerted by these pressure gradients is potentially harmful to the ear.

Why Monitor Perilymphatic Pressure in Meniere's Disease?

Marchbanks R. Why monitor perilymphatic pressure in Meniere's disease?A cohort of 39 patients with confirmed raised intracranial pressure was investigated. Of these patients, 24 (62%) complained of tinnitus and 11 (28%) suffered from paroxysmal rotary vertigo. Intracranial hypertension can occur without the usual headache and visual symptoms. In such cases, the patient may be referred to the otolaryngological clinic and the condition may be mistaken for Meniere's disease or a labyrinthine disorder. The Tympanic Membrane Displacement (TMD) technique now provides a non-invasive method of monitoring the intracranial and perilymphatic pressures. This study provides recommendations for the use of TMD techniques in the otolaryngological clinic for screening, diagnosing and monitoring treatment of patients presenting with raised perilymphatic pressure.

Longitudinal non-invasive perilymphatic pressure measurement in patients with Ménière's disease.

The homeostasis of inner-ear fluids is essential for the functions of hearing and equilibrium. Inner-ear disorders, such as Ménière's disease, are affected by inner-ear pressure. The displacement of the human tympanic membrane can be studied by means of the MMS-10 Tympanic Displacement Analyser (Marchbanks Measurement Systems Ltd., UK) and is thought to be a measure for perilymphatic pressure variations. This measurement was performed in 18 patients with Ménière's disease (20 affected ears) at regular intervals, in order to investigate possible pressure variations in relation to the following symptoms: hearing loss, vertigo, tinnitus and pressure sensation. Symptoms changed independently; changes in symptoms were not significantly related to changes in perilymphatic pressure, as measured by means of the MMS-10 analyser.

Non-invasive perilymphatic pressure measurement in patients with Menière's disease.

The MMS-10 Tympanic Displacement Analyser in a new device to measure the perilymphatic pressure in humans. This instrument was used in 25 patients with Menière's disease (28 affected ears) and a group of 50 young normal hearing subjects. No significant differences were found in perilymphatic pressure measurements between the groups. Although measurement parameters showed large inter-individual variation, the intra-individual correlation was good. In patients with Menière's disease, no relationship was found between perilymphatic pressure, hearing threshold, blood pressure, gender or age.

Cochlear blood flow and labyrinthine pressure: effects of glycerol on the inner ear.

Changes in cochlear blood circulation (CoBC) and perilymphatic pressure (Pp) after administration of physiological saline and 50% glycerol (12 ml/kg) were measured simultaneously in guinea pigs to examine the influence of glycerol on CoBC and Pp. The CoBC was measured by the laser-Doppler method. Although neither CoBC nor Pp changed after administration of physiological saline, glycerol produced a marked increase in CoBC and a slight decrease in Pp in 11 of 15 animals. However, the increase in CoBC was transient; CoBC reached a peak as soon as 30 min after glycerol administration and then returned rapidly to its initial value within 1 h after administration, although the Pp was still decreasing. Therefore, the response of CoBC to glycerol does not seem to be directly related to hyperosmolarity due to glycerol administration.

Tympanogram recorded under cervical compression.

Tympanograms were recorded during compression of cervical veins in 19 normal ears to investigate whether pressure elevation in the middle and inner ears affects acoustic impedance. Upon cervical compression, the peak pressure of the tympanogram shifted to the positive pressure side. The peak amplitude of the tympanogram also changed in a manner similar to that after stapedius muscle contraction. These results suggest that the impedance changes caused by cervical compression reflected changes in both perilymphatic pressure and middle ear pressure.

Perilymph Pressure During Hypobaric Conditions—Cochlear Aqueduct Obstructed

Nine cats with the cochlear aqueduct surgically blocked were anaesthetised, put in a pressure chamber, and stepwise exposed to hypobaric pressure, each of the two steps lasting 5 min. The chamber pressure was reduced to -5 and -7 kPa. Concluding the experiment the cats were observed for 5 min after restoration of atmospheric pressure. The perilymph, tympanic cavity, cerebrospinal fluid, central venous, arterial and surrounding chamber pressures were continuously recorded. Reduced chamber pressure caused relative overpressure within the tympanic cavity, thereby inducing pressure gradients between the chamber, the tympanic cavity, the labyrinth and the cerebrospinal fluid and vascular pressures respectively. Our results demonstrate that hypobaric effects on the labyrinth are mediated via pressure changes in the tympanic cavity and not by systemic, vascular or cerebrospinal fluid influence. Substantial perilymph overpressure lasted throughout the hypobaric conditions. The magnitude and the duration of this overpressure were influenced by the patency of the Eustachian tube whereas the rate of the pressure change in the chamber was of little importance. As atmospheric pressure was restored in the chamber the overpressure in the labyrinth was reversed to underpressure--relative to pre-experimental conditions.

The Influence of Vestibular and Cochlear Aqueducts on Vestibular Response to Middle Ear Pressure Changes in Guinea Pigs

The responses of primary vestibular neurons and perilymphatic pressure changes to middle ear pressure were investigated in guinea pigs with obstructed vestibular or cochlear aqueduct (closed VA or closed CA group) in order to clarify the influence of VA and CA on pressure-induced vestibular response. Although the neural response rates and the amount of perilymphatic pressure change in the closed VA group resembled those in the control group, these values in the closed CA group were higher than in the control group. Patency of the CA had a more significant effect on the vestibular response to middle ear pressure change than patency of the VA.

The Influence of Middle Ear Pressure Changes on the Primary Vestibular Neurons in Guinea Pigs

The responses of primary vestibular neurons and perilymphatic pressure changes to middle ear pressure stimuli in guinea pigs were investigated in order to clarify the direct effects of pressure stimulus on the vestibular apparatus. The vestibular response was related to the amount of middle ear pressure change applied at a rate of +/- 100 mmH2O/s. The neural response rates of vestibular units to positive pressure in the middle ear were significantly larger than those to negative pressure. The time course pattern of the perilymphatic pressure change resembled that of the response of the vestibular units, indicating that the vestibular response is elicited by middle ear pressure via the pressure transmitted in the inner ear.

The Prevalence of Perilymphatic Hypertension in Subjects with Tinnitus: a Pilot Study

This study investigated the prevalence of perilymphatic hypertension (raised perilymphatic pressure) in a population of subjects with tinnitus. A review of the literature showed how changes in perilymphatic pressure could affect tympanic membrane displacement measurements. This review also revealed that perilymphatic hypertension was more likely to occur in young females (less than 45 years) than in other subjects. An experiment was designed to test 32 subjects, who were divided into four groups according to their age and sex. These subjects underwent several routine audiological tests and were then tested with the tympanic membrane measurement system to determine the perilymphatic pressure of both ears. Statistical analysis of the experimental results showed that the young females had raised perilymphatic pressure. This was significantly higher than the perilymphatic pressure of the other test groups and of that of a normal population. The young females also exhibited other symptoms indicative of raised perilymphatic pressure. The raised pressure was thought to be due to an increase in fluid pressure which is more likely to occur in females due to variations in the levels of circulating hormones with menstrual irregularities, pregnancy and the menopause.

Hydrostatic Pressure in the Inner Ear Fluid Compartments and its Effects on Inner Ear Function

The present study summarizes the experimental findings obtained on the pressure in the inner ear fluids and on the effects of pressure changes on cochlear function in the guinea pig. Two types of pressures have to be distinguished in the inner ear fluid compartments: (i) hydrostatic fluid pressure and (ii) superimposed hydrodynamic high frequency (> 100 Hz) sound pressure oscillations. Hydrostatic pressure in the inner ear fluids in guinea pigs is in the order of 200 Pa (2 cm H2O) and shows slow (< 5 Hz) respiratory and pulsatory oscillations as well as considerable physiological variations in the range of -100 to +700 Pa. In normal ears, hydrostatic pressure in the perilymph equals pressure in the endolymph, and pressure changes applied to one compartment are immediately transmitted to the other one. A high compliance of Reissner's membrane seems to be the cause of this endolymphatic-perilymphatic pressure equalization. In experimental endolymphatic hydrops, a unique animal model for Meniere's disease, endolymphatic pressure is higher (100 Pa and above) than perilymphatic pressure. These pressure gradients occur only in late stages of hydrops, probably when Reissner's membrane has lost its high compliance after long standing distension. Positive endolymphatic-perilymphatic pressure gradients are secondary to and not the primary cause of hydrops formation. Changes of hydrostatic pressure do not affect auditory function as long as they stay in the physiological range. This includes the sudden loss of positive inner ear pressure that occurs in perilymph fistulas. The rationale for surgical repair of perilymph fistulas in patients in order to restore the hearing function thus becomes questionable. Other aspects of surgical repair, however, as e.g. prevention of labyrinthitis due to permanently open fistula, could not be investigated in this model, because in guinea pigs even large fistulas heal spontaneously within a few days. In experimental endolymphatic hydrops, deterioration of auditory thresholds was partially correlated to the presence of positive endolymphatic-perilymphatic pressure gradients. A change in pressure, however, occurred later than the first deterioration in auditory function. Therefore positive endo-perilymphatic pressure gradients may contribute to, but are not the only cause of hearing impairment.

Intensity-dependent changes in oxygenation of cochlear perilymph during acoustic exposure

This study examined the effects of acoustic exposure at different intensities on local oxygenation of the cochlea. The oxygen partial pressure (pO 2) of perilymph in the basal scala tympani was measured polarographically in anesthetized guinea pigs exposed to either wide-band noise at 85 dB SPL or a 10 kHz pure tone at 90, 105, or 125 dB SPL for 1 h. Cochlear temperature, heart rate, arterial blood pressure and acid-base status were monitored. The cochlear microphonics (CM) and compound action potentials (CAP) were recorded before and after exposure. There were clear intensity-dependent differences in the effect of acoustic exposure on perilymphatic oxygenation. Moderate exposure intensities (85–90 dB SPL) were found to increase the pO 2 by an average of about 20% of the initial level. In contrast, high intensity acoustic exposure (125 dB SPL) resulted in a mean decrease of about 20%. These changes persisted within a subsequent 30-min post-exposure period. There was no significant change in cochlear temperature and cardiorespiratory variables during and after any of the exposures as compared to the controls. CM and CAP amplitudes showed an extensive loss after acoustic overstimulation (125 dB SPL), but no permanent change with lower exposure intensities. These findings suggest that intracochlear oxygenation plays an important role in inner ear physiology during acoustic stimulation.

PRESSURE TRANSFER BETWEEN THE PERILYMPH AND THE CEREBROSPINAL FLUID COMPARTMENTS IN CATS

This is a review of our studies of the labyrinthine fluid pressure in cats subjected to pressure changes in the middle ear (implosive routes) and the cerebrospinal fluid compartment (explosive routes) as well as to changes in vascular and ambient pressures. The perilymph, cerebrospinal fluid (CSF), middle ear, venous and arterial pressures were measured with the cochlear aqueduct (CA) patent as well as surgically blocked. Experiments on explosive pressure changes revealed that the perilymph pressure was regulated by the CSF in case of CA patency. The CSF influence was dominant enough to obscure any direct effect on the labyrinth from other sources. With the CA obstructed the CSF influence on the labyrinth was apparently mainly via the endolymphatic sac and duct although limited and much delayed. Systemic arterial pressure changes had a pronounced influence on the perilymph pressure, but this effect was revealed only when the CSF influence was reduced by CA obstruction. Experiments on implosive and ambient pressure changes suggested that there was no fundamental difference in the perilymph response to equivalent levels of implosive versus hypobaric pressure. Three factors determined the effect of implosive and hypobaric pressure: the patency of the CA, the rate of the pressure change, and the eustachian tube function.

Measurements of perilymphatic oxygen tension in guinea pigs exposed to loud sound

Using different types of custom-made oxygen-sensitive microelectrodes, the perilymphatic oxygen partial pressure (PO2) was determined in anesthetized guinea pigs. Cochlear temperature, heart rate, and arterial blood pressure and acid-base status were monitored. The PO2 in the basal scala tympani perilymph (200 microns below the round window membrane) was found to be 53 +/- 17 mmHg (mean +/- SD) in 33 normal animals. In 11 guinea pigs exposed to loud sound for 15 min (10 kHz pure tone, 125 dB SPL) there was on average a continuous decline in the perilymphatic PO2, which was significant only 30 min post-exposure. A considerable variation in response was found in individual animals. Mean arterial blood pressures showed a slightly increasing time course, while heart rates did not change significantly during the whole period of the experiment. Arterial acid-base status and PO2 values remained within normal limits and did not change significantly. Cochlear microphonics and compound action potentials were substantially decreased after acoustic overstimulation. The results are discussed with due consideration of sources of error.

The measurement and manipulation of intralabyrinthine pressure in experimental endolymphatic hydrops

Three to four months after unilateral surgical ablation of the endolymphatic duct and sac, endolymphatic and perilymphatic pressures were measured in both the normal and hydropic ears of 11 guinea pigs. In normal ears, endolymphatic pressure always approximated perilymphatic pressure. Endolymphatic pressure exceeded perilymphatic pressure in all ears with hydrops, except one in which these pressures were equal. The effect of postural inversion on inner ear pressures were studied in both normal and hydropic inner ears. Normal ears showed endolymphatic and perilymphatic pressure to rise equally during this maneuver. In hydropic ears, the difference between endolymphatic and perilymphatic pressure was notably reduced from measurements obtained in the prone position. This study indicates that an alteration in pressure regulation within the inner ear may be important in the pathogenesis and manifestation of experimental endolymphatic hydrops in the guinea pig. Physiologic mechanisms and clinical implications of these results are described.

Pressure Relationship between Perilymph and Endolymph Associated with Endolymphatic Infusion

The pressure difference between the perilymph and the endolymph following infusion of artificial endolymph into the endolymphatic space was studied in guinea pigs. Both the perilymphatic and the endolymphatic pressures were measured simultaneously with use of two sets of a servo-nulling system. Endolymphatic infusion caused pressure increases in both the endolymphatic and the perilymphatic spaces, but no measurable pressure difference between them. Soon after the endolymphatic infusion, both pressures returned nearly to the initial levels. We conclude that 1) the endolymphatic and the perilymphatic pressures are very closely related, and 2) if a physiologically significant pressure difference exists between endolymph and perilymph in endolymphatic hydrops, it is below the resolving power of the methods used in this study (+/- 0.1 mm Hg).

Transmission of cerebrospinal fluid pressure changes to the inner ear and its effect on cochlear microphonics

Alterations in inner ear fluid pressure and cochlear microphonics (CM) associated with increased cerebrospinal fluid (CSF) pressure were studied in the guinea pig. Hydrostatic pressure in the endolymph and perilymph of the cochlea were measured by use of a servo-controlled micropipet system. Endolymphatic and perilymphatic pressure increased in a linear manner with little or no time lag following pressure increases of 0-50 mm Hg. There was no pressure gradient between the endolymph and perilymph. CM in response to 500 Hz and 4000 Hz tone bursts was recorded before, during and after CSF pressurization. The input-output function of CM showed suppression of 2-8 dB in both maximum output and sensitivity unless the increase in CSF pressure exceeded a level which reduced the cochlear blood flow.

Effects of Hydrostatic Pressure on Sensory Discharge in Frog Semicircular Canals

The effects of endolymphatic and perilymphatic pressure changes on resting and mechanically evoked responses were studied in isolated posterior semicircular canals of the frog. The results demonstrated that ampullar receptors are extremely sensitive to hydrostatic pressure changes (0.25 mm H2O were sufficient to produce distinct changes), being inhibited by endolymphatic pressure increases and facilitated by perilymphatic ones. Intracellular recordings from single afferent axons showed that the effects of hydrostatic pressure result from a modified transmitter release from the synaptic pole of the hair cells. Unlike resting activity, mechanically evoked activity was always depressed in the presence of a hydrostatic pressure. This indicates that the sensitivity of ampullar receptors to mechanical stimuli, i.e. the gain of the conversion process, is maximal when no pressure is present between the inner and the outer fluid. The possible action of hydrostatic pressure on vestibular receptors is discussed.

Effects of Perilymph Volume Adjustments on Cochlear Blood Flow in the Guinea Pig

Previous research suggests a potential relationship between perilymphatic pressure (Pp) and cochlear blood flow (CBF); however, the alterations in Pp necessary to produce changes in CBF have not been adequately described or quantified. The effects of perilymph volume changes on systemic blood pressure (BP) and CBF were presently investigated in the guinea pig cochlea. Five microliters of perilymph were displaced in each of three conditions: viz. evacuation of 5 microliters from the cochlea; replacement of these 5 microliters; and finally the addition of 5 microliters of artificial perilymph into the cochlea. All perilymph volume adjustments were completed in 1-microliter increments during which changes in CBG and BP were recorded. Significant alterations in CBF were observed during 1-microliter perilymph volume adjustments in each condition with no significant changes in systemic BP. The results from this study support our hypothesis that an inverse relationship exists between CBF and Pp in that decreases in perilymph volume yielded elevations in CBF while increases in perilymph volume yielded reductions in CBF.

The effects of pressure on cochlear microphonics in experimentally induced hydropic ears in the guinea pig

The effect of perilymphatic pressure on the cochlear microphonics (CM) threshold was examined in guinea pigs with experimentally induced hydrops. When a pressure of 300 mm H2O was applied to the scala tympani of the basal turn, the 500 Hz CM threshold shifts in ears during the 1st week following obliteration of the endolymphatic sac and duct were significantly smaller when compared with shifts in normal ears. Larger threshold shifts were then regained at 4-12 weeks after surgery. When acetazolamide was administered to hydropic animals, the effect of the increase of perilymphatic pressure on the CM threshold was also investigated. During the 1st postoperative week (4-7 days after surgery), CM threshold shifts were larger when compared to changes in hydropic animals without medication. The CM depression as the result of pressure is probably due to a mechanical effect on the intracochlear partition.