Intravital Microscopic and Laser Doppler Method Estimates of Cochlear Blood Flow

Cochlear blood flow (CoBF) was measured by intravital microscopy (IVM) and laser Doppler (LD) methods in normal guinea pigs and after a single norepinephrine (NE) injection into the carotid artery. CoBF changed in proportion to BP changes in normal animals. CoBF values by LD correlated well (r = 0.67) with CoBF measured by IVM when BP changed in the 35 and 70 mm Hg range. A linear regression line was obtained as y = 1.407X-2.996. No correlation was found between the diameters of radiating arterioles (RA) and blood volume (i.e., the hemoglobin concentration index). NE injection into the carotid artery induced the formation of sludge at RA, resulting in decreased local CoBF. A decrement in CoBF was also observed by LD after injection. Although similar patterns of CoBF changes were obtained by these two methods after injection, the degree of CoBF change by LD appeared to be lower than that by IVM. Our result indicates that the combination of these two methods provides a better understanding of cochlear circulation.