(347h) Measurements of Pulsatile Hemodynamics In Brain Microvessels

Experimental measurements are reported of blood flow in the microcirculation of the brain cortex.  We use two-photon excited fluorescence (2PEF) microscopy to measure cortical blood flow in anesthetized rats.  2PEF is a nonlinear optical technique that allows detection of fluorescence from a point in highly scattering samples such as neural tissue.  By rapidly scanning the detection point throughout the sample, an “image” can be detected deep inside the cortex of a live animal.

We exploit this technique to track the motion of individual red blood cells inside arterioles, capillaries, and venules in the cortex with precision that is unmatched by other in vivo measurement methods.  Furthermore, we correlate the blood cell speed with heartbeat and respiration measurements to extract detailed information about time-dependent blood flow in individual vessels and at vessel bifurcations.  Measurements are made in surface vessels and in capillaries deep in the brain tissue.

Time-averaged blood flow speed decreases with vessel diameter in arterioles and in capillaries, and increases in venules.  Blood flow speed decreases with inspiration by about 20% across all parts of the cardiac cycle.

These results show that hemodynamics in the brain cortex can be resolved with high spatial and temporal resolution in vivo, which is a critical step toward identifying and quantifying cerebral blood flow abnormalities associated with a variety of hematological disorders.