INTRALUMINAL DISTRIBUTION OF 15-MU-M-DIAMETER CARBONIZED MICROSPHERES WITHIN ARTERIAL MICROVESSELS AS DETERMINED BY VITAL MICROSCOPY OF THE GOLDEN-HAMSTER CHEEK POUCH

An assumption inherent in the use of microspheres for measuring regional blood flow is that microspheres distribute uniformly with blood. Published studies suggest that carbonized microspheres, 15-80 μm in diameter, concentrate centripetally in blood flowing through medium-size arteries. The intraluminal distribution of carbonized microspheres within blood flowing through arterial microvessels is not known. To study this problem, the passage of 15-μm-diameter, carbonized microspheres through the arterial vasculature of the golden hamster cheek pouch was cinefilmed. The trajectories of 800 microspheres flowing through 24 vessel segments in 14 different golden hamsters (Mesocricetus auratus) were tabulated. The mean diameter of the observed arterial vessels was 65.2 ± 13.7 (SD) μm. Carbonized microspheres did not distribute homogeneously across the available lumen of the observed microarteries. Comparison of the experimentally determined microsphere distribution against a null hypothesis of a homogeneous density distribution showed a greater than expected concentration of microspheres at the periphery of the available lumen and a less than expected percentage at its center. This disparity was present whether a blunt velocity flow profile or a parabolic velocity profile was convoluted with the density distribution. If flow approximates the parabolic velocity profile, microspheres become markedly underrepresented at the center of the vessel and overrepresented at its periphery. The greater than expected centrifugal distribution of microspheres was related neither to vessl diameter nor to the microsphere velocities studied. If one assumes that erythrocytes are evenly distributed throughout the available arterial lumen (with the exception of a cell-free zone at the periphery), then 15-μm-diameter carbonized microspheres significantly underrepresent the central concentration of erythrocytes and overrepresent the concentration of red blood cells at the microarterial periphery. © 1979.