Recent advances in cochlear blood flow measurements.

Changes in blood flow to the inner ear have been thought to influence or underlie a number of cochlear diseases, including some forms of noise-induced hearing loss, sudden hearing loss, and Meniere's disease. Recently, important advances have been made in two technologies for the study of cochlear blood flow. The first is in the area of vital microscopic studies of cochlear microcirculation, and the second is based on the introduction of laser technology in the form of laser Doppler flowmetry. In this report, measurements are given of changes in cochlear circulation caused by carbon dioxide breathing, intravenous phenylephrine injection, systemic hemodilution, positive end expiratory pressure, and direct electrical stimulation of the cochlea. From these changes, we observe that cochlear blood circulation responds to systemic blood pressure alterations and is subject to local flow control mechanisms. Linearity and speed of response of the laser Doppler instrumentation also are shown. These advances show promise for contributing to our knowledge of control mechanisms of inner ear blood flow and for revealing the influence of various pharmacologic agents of potential clinical value.