[Ossicular vibration changes associated with pressure changes in inner ear and cerebrospinal fluid in guinea pigs]

The effects of increase in the inner ear and cerebrospinal fluid (CSF) pressures on the vibration of the ossicular chain were studied in guinea pigs by using a laser doppler vibrometer. Velocity of the malleus umbo and that of the incus long crus in response to a constant sound stimulus of 90dB SPL at the tympanic membrane were measured at 13 frequencies between 0.125 kHz and 10 kHz. Loading pressures to the inner ear and the CSF were adjusted by changing the height of a saline bottle hooked up to the respective site by a 24G Teflon catheter. The pressure was monitored with a pressure transducer placed in the catheter. Positive and negative pressure loads to the inner ear decreased the velocity of the umbo at low and high frequencies. The maximum change was 4.7 dB at 0.125 kHz with a positive pressure load of 400 mmH2O. Similar results were obtained for the umbo and the long crus by a positive pressure load to the CSF, with the exception that the umbo velocity showed no change at higher frequencies. These results suggest that the inner ear and CSF pressure changes affect not only the function of the organ of Corti but also the vibration of the ossicular chain. These changes occurred mainly at lower frequencies.