The effect of promontorial bone on laser light transmission in measuring capillary blood flow in vivo

Use of laser Doppler flowmetry (LDF) to assess cochlear blood flow (CBF) in experimental animals has elucidated the complex mechanisms in CBF regulati on. Some attempts have been made to measure CBF in humans, although earlier studies produced confusing data about the physical possibility of LDF pene trating the human tympanic cavity promontory. In this study, we used LDF in an attempt to observe capillary blood flow in vivo through the intact huma n promontory in order to develop a method for measuring CBF in human patien ts. Temporal bones from six human cadavers were removed and the promontory overlying the basal turn of the cochlea was drilled off and fixed in 10% fo rmalin. Perpendicular bone thickness was measured at the site of the stria. vascularis. Seven young rats were anesthetized and the carotid artery was cannulated for blood pressure recording. Capillary flow was registered with LDF from two sites, the kidney and the plantar area of a hind limb, using a custom-designed probe with 632.8 nm and 780 nm wavelengths. Intravenous e pinephrine was used to evoke blood flow changes. The same measurements were repeated through the promontorial bone. The light attenuation induced by t he promontorial bone was 79 +/- 28% for the 632.8 nm wavelength, and 22 +/- 15 to 65 +/- 13% for the 780 mn wavelength, depending on the thickness of the bone. The sensitivity in detecting minute changes was 78% and 91-96%, r espectively, for the 632.8 nm and 780 nm wavelengths. This study indicates that it is possible to detect minute changes in capillary blood flow throug h the intact human promontory at the site of the stria vascularis.