Simultaneous Measurement of Endolymphatic and Perilymphatic Fluid Pressures

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Pressure difference between the endolymphatic and perilymphatic fluid may be more important than the absolute pressure value for the pathophysiology of the inner ear.In this study, endolymphatic and perilymphatic fluid pressures were measured simultaneously in guinea pigs and pressure changes on 1) postural change, 2) anoxia, 3) peroral administration of glycerol, were studied.Without loads, perilymphatic and endolymphatic pressures changed completely identically.When the body of the guinea pig was raised 30°, the endolymphatic pressure rose 0.36 mmHg and the perilymphatic pressure 0.44 mmHg.When respirator was stopped and anoxia was loaded, both pressures rose but the perilymphatic pressure rose much more about 1 mmHg than the endolymphatic pressure. With the relief of anoxia, the endolymphatic pressure rose to 7 mmHg and the perilymphatic pressure to 9 mmHg compared with the beginning and returned to the beginning state in about 6 minutes.Peroral administration of glycerol (50% glycerol, 12 ml/kg) caused pressure decrease of both endolymphatic and perilymphatic fluid but endolymphatic pressure decreased much more than that of the perilymphatic fluid.The largest pressure difference was about 2 mmHg, 30 minutes after the glycerol administration.This study showed that simultaneous recording of perilymphatic and endolymphatic pressure could reveal much more important information about the pathophysiology of the inner ear than the independent recording of both pressures.