The effect of increased inner ear pressure on tympanic membrane vibration

It has been suggested that increased inner ear pressure can affect the stiffness of the tympano-ossicular conductive system. However, the published literature contains few studies on changes of middle ear mechanics caused by increased inner ear pressure. In this study, we evaluated the effects of increased inner ear pressure on tympanic membrane vibration in guinea pigs using a laser Doppler vibrometer (LDV).

We used 10 male guinea pigs (weighing 250 g each) with normal eardrums and Preyer reflexes were used for the experiment. Inner ear pressure was modified by two approaches--directly via a tube placed in the inner ear (n=5) and indirectly via a tube placed in the subaracnoid space (n=5). Slow uniform pressure (microl/min) was infused until constant pressure was maintained. At this time, an artificial endolymph or perilymph was injected with a constant pressure of 100 and 300 mm H2O. We measured the umbo velocity using a LDV.

A positive pressure load decreased the umbo vibration at low frequencies but did not change the umbo vibration at mid and high frequencies. The umbo velocity had a greater reduction for an endolymphatic pressure load than for a perilymphatic pressure load. The largest change in velocity was noted at a frequency of 0.1 kHz. There was no significant change in velocity at higher frequencies, except for 5 kHz.

LDV is a good tool to analyze middle ear function and it has the potential indirectly to diagnose an increase in endolymphatic or perilymphatic pressure.