QUANTIFICATION OF MYOCARDIAL BLOOD-FLOW WITH ULTRASOUND-INDUCED DESTRUCTION OF MICROBUBBLES ADMINISTERED AS A CONSTANT VENOUS INFUSION

Background-Ultrasound can cause microbubble destruction. If microbubbl es are administered as a continuous infusion, then their destruction w ithin the myocardium and measurement of their myocardial reappearance rate at stead Il state will provide a measure of mean myocardial micro bubble velocity. Conversely, measurement of their myocardial concentra tion at steady state will provide an assessment of microvascular cross -sectional area. Myocardial blood now (MBF) can then be calculated fro m the product of the two. Methods and Results-Ex vivo and in vitro exp eriments were performed in which either now was held constant and puls ing interval (interval between microbubble destruction and replenishme nt) was altered, or vice versa. In vivo experiments were performed in 21 dogs. In group 1 dogs (n=7), MBF was mechanically altered in a mode l in which coronary blood volume was constant. In group 2 dogs (n=5), MBF was altered by direct coronary infusions of vasodilators. In group 3 dogs (n=9), non-now-limiting coronary stenoses were created, and MB F was measured before and after the venous administration of a coronar y vasodilator. In all experiments, microbubbles were delivered as a co nstant infusion, and myocardial contrast echocardiography was performe d using different pulsing intervals. The myocardial video intensity ve rsus pulsing interval plots were fitted to an exponential function: ga mma=A(1-e(-beta t)), where A is the plateau video intensity reflecting the microvascular cross-sectional area, and beta reflects the rate of rise of video intensity and, hence, microbubble velocity. Excellent c orrelations were found between now and beta, as well as now and the pr oduct of A and beta. Conclusions-MBF can be quantified with myocardial contrast echocardiography during a venous infusion of microbubbles. T his novel approach has potential for measuring tissue perfusion in any organ accessible to ultrasound.