LAMINAR ANALYSIS OF CEREBRAL BLOOD-FLOW IN CORTEX OF RATS BY LASER-DOPPLER FLOWMETRY - A PILOT-STUDY

Laser-Doppler flowmetry (LDF) is a reliable method for estimation of r elative changes of CBF. The measurement depth depends on wavelength of the laser light and the separation distance of transmitting and recor ding optical fibers. We designed an LDF probe using two wavelengths of laser light (543 nm and 780 nm), and three separation distances of op tical fibers to measure CBF in four layers of the cerebral cortex at t he same time. In vitro comparison with electromagnetic flow measuremen ts showed linear relationship between LDF and blood flow velocity at f our depths within the range relevant to physiologic measurements. Usin g artificial brain tissue slices we showed that the signal for each ch annel decreased in a theoretically predictable fashion as a function o f slice thickness. Application of adenosine at various depths in neoco rtex of halothane-anesthetized rats showed a predominant CBF increase at the level of application. Electrical stimulation at the surface of the cerebellar cortex demonstrated superficial predominance of increas ed CBF as predicted from the distribution of neuronal activity. In the cerebellum hypercapnia increased CBF in a heterogeneous fashion, the major increase bring at apparent depths of approximately 300 and 600 m u m, whereas in the cerebral cortexl hypercapnia induced a uniform inc rease. In contrast, the CBF response to cortical spreading depression in the cerebral cortex was markedly heterogeneous. Thus, real-time lam inar analysis of CBF with spatial resolution of 200 to 300 mu m may be achieved by LDF. The real-time in depth resolution may give insight i nto the functional organization of the cortical microcirculation and a daptive features of CBF regulation in response to physiologic and path ophysiologic stimuli.