Applications of the colored microsphere technique in the mammalian coronary microcirculation.
Creators: name: Cicutti, Nicholas.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1994
Subjects: subject: Biology, Animal Physiology.

description: The aim of this dissertation was to provide realistic descriptions of two unique properties of the mammalian coronary microcirculation using our novel application of colored microspheres in myocardium. One important objective was to provide an innovative approach to investigate the controversial issue of whether individual coronary arteries communicate at the microvascular level, thus potentially giving rise to a zone of dual arterial supply. Simultaneous in vivo infusion of two distinctly colored microsphere suspensions into the left anterior descending (LAD; red spheres) and left circumflex (LCx; blue spheres) arteries identified a specific interface region of canine myocardium perfused by both arterial branches. Two distinct zones were delineated, and their widths measured. One region was defined as the Interface Transition Zone (ITZ). This region was formed by microvessels supplied by the individual parent arteries, and separated tissue containing only one or the other colored microspheres. The second region defined as the Boundary Watershed Zone (BWZ) was formed by capillaries containing sphere aggregates of both colors; it was located exclusively within the ITZ. In addition, the ITZ and BWZ were significantly wider in subepicardial than in subendocardial regions. Our subsequent study investigated the potential lability of the coronary watershed zones. As before, two differently colored microsphere suspensions were infused into the LAD (red spheres) and LCx (blue spheres) arteries of nine dogs. Subsequently, the LAD was ligated and a third set (green) of spheres was infused into the LCx. Capillaries perfused exclusively by the LAD before occlusion adjacent to the interface contained green microspheres as well as red/green aggregates, indicating lateral extension of the LCx perfusion territory. Results showed that occlusion caused a 24% expansion of the ITZ and a 48% expansion of the BWZ. In addition, all expansions were significantly greater in subepicardial compared to subendocardial regions. These results demonstrated the capability of microvascular anastomoses in providing blood flow to the periphery of an ischemic region. We also applied our colored microsphere technique for the characterization of coronary capillary flow direction in rat myocardium. Our initial study determined capillary flow direction in two groups of male Sprague-Dawley rats: (1) pressure overload hypertrophy and (2) sham-operated controls. Chronic pressure overload was induced in neonatal rats by aortic constriction. Six weeks postsurgery, both groups received sequential in vivo infusion of two differently colored microsphere suspensions into the left atrial appendage. Histological analysis of 40 $\mu$m serial sections revealed that certain coronary capillaries contained microspheres of both colors. A capillary flow vector was established based on the sequence of colors trapped within each aggregate. Examination of flow vectors among neighboring capillaries enabled the characterization of regional capillary flow direction. Results indicated a predominance in concurrent flow, which decreased significantly over a range of capillary rankings. The percentage of concurrent flow was also significantly lower in subendocardium compared with midmyocardium. This study provided previously unattainable data regarding transmural capillary flow direction and suggested regional adaptations in coronary microvascular flow. (Abstract shortened by UMI.)