Laser-Doppler assessment of brain microcirculation: effect of local alterations

The objective of this study was to determine whether changes in blood perfusion measured by laser-Doppler (LD) flowmetry correlate with simultaneously measured changes in pial arteriolar diameter after local application of vasoactive agents on the brain surface. A closed cranial window was implanted in anesthetized rabbits. A 0.84-mm-diam LD probe was inserted through one window port and fixed at a distance of 1-2 mm from the cortical surface. The probe detects changes in perfusion within a tissue volume of approximately 1 mm3. The diameter of pial arterioles in the area adjacent to the LD probe was simultaneously measured with a microscope and image-splitting device. Topical application of bradykinin (80 nM to 8 microM), which stimulates the formation of dilator prostaglandins and O2 radicals, induced a dose-dependent arteriolar dilation and increase in LD flow. Topical application of 33 microM 2-chloroadenosine, a stable analogue of adenosine, induced the same degree of pial arteriolar dilation as 8 microM bradykinin but produced a much larger increase in LD flow, probably due to its greater tissue penetration and stability. At 5 min after bradykinin washout the arterioles had nearly returned to their control diameter, whereas LD flow was still increased. Similarly, there was a discrepancy between LD flow and diameter changes after washout of 2-chloroadenosine. We conclude that LD flowmetry is a useful technique for continuous assessment of cortical blood flow in response to topically applied agents.(ABSTRACT TRUNCATED AT 250 WORDS)