Pressure Gradients Affecting the Labyrinth during Hypobaric Pressure

Abstract

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.

Ear Canal Pressure Variations Versus Negative Middle Ear Pressure: Comparison Using Distortion Product Otoacoustic Emission Measurement in Humans

“…A negative MEP pulls the tympanic membrane toward the middle ear cavity. A similar displacement of the oval and round windows should occur according to directly measured stapes displacement (Murakami et al 1997) and inner ear pressure change (Konradsson et al 1997;Feijen et al 2002) with MEP variations. As a result, the ossicular chain is compressed (the ossicular ligaments stretched) with a negative MEP.…”

“…It has been verified by Flisberg et al (1963) in a human study that Ͻ10% of an experimentally introduced MEP at Ϯ50 mm Hg transfers to the closed ear canal. In an animal study (Konradsson et al 1997), it was also estimated that approximately 20 to 25% of ambient air pressure at Ϫ40 to Ϫ52 mm Hg in a pressure chamber transferred into the middle ear (1 mm Hg Ϸ 13.60 mm H 2 O and 1 mm H 2 O ϭ 0.98 daPa).…”

“…The perilymphatic fluid pressure of the inner ear can be varied momentarily by a negative MEP arising from a negative ambient pressure in cats (Konradsson et al 1997), which is quickly equilibrated through the cochlear aqueduct to the cerebrospinal fluid. It has been measured that time constants for the inner ear pressure recovery are 15 and 2.5 sec, respectively, for positive and negative MEPs of 500 to 600 mm H 2 O in guinea pigs (Feijen et al 2002).…”

Inner ear pressure changes following square wave intracranial or ear canal pressure manipulation in the same guinea pig

“…A temporary shift in intracranial pressure after neurosurgery can cause a temporary shift in the hearing level [18]. The influence of ambient pressure changes on cochlear and vestibular function has been indicated in several reports of aerospace and underwater medicine, as well as in studies on the effects of pressure chamber treatment of Menière's disease [5,10].…”

Inadequate opening capacity of the eustachian tube in Meniere's disease

“…Rapid pressure changes in the ME cavity are transmitted to the inner ear fluids. The effects of pressure changes on the inner ear fluids are governed by the complex interaction between the rate of pressure change, the patency of the ET and the cochlear aqueduct, and the characteristics of the endolymphatic sac [5,6]. Inadequate functioning of the ET and a negative ME pressure are regarded as the origin of several chronic ME diseases, such as secretory otitis media, retraction of the tympanic membrane and cholesteatoma.…”