DOG-MODEL FOR CEREBROVASCULAR STUDIES OF THE PROXIMAL-TO-DISTAL DISTRIBUTION OF SEQUENTIALLY INJECTED EMBOLI

This study was undertaken to determine whether microemboli injected in a predetermined sequence would maintain that sequence once they came to rest in brain microvessels. If so, the injection of different-color ed microspheres at different times could be used to bracket-in-time em boli that are known to be released into the circulation during cardiop ulmonary bypass. We injected different-colored microspheres into the a rterial circulation of anesthetized dogs before and after the injectio n of fat emboli and before and after cardiopulmonary bypass. Coronal s lices of the dog brains were embedded in celloidin, sectioned at 100 m u m, and stained for alkaline phosphatase. The afferent cerebrovascula ture stained dark brown against a light background, and the proximal/d istal orientation of many of the arterioles could be determined by fol lowing their course within the thick sections. When different types of emboli were found in a single arteriole, they appeared in the order i njected or the order of occurrence in the bypass protocol in 99.3% of the 867 such arterioles counted. Therefore, the microemboli maintained their ordered sequence with only a very small degree of mixing. Once they came to rest, there was not sufficient collateral blood how in th e brain microvessels to move them into disordered positions. This dog model should facilitate studies of the time of release of microemboli within narrower windows of time during cardiopulmonary bypass. (C) 199 5 Academic Press, Inc.