Wei K, Jayaweera A R, Firoozan S, Linka A, Skyba D M, Kaul S
Cardiovascular Division, University of Virginia School of Medicine, Charlottesville 22908, USA.
Circulation. 1998 Feb 10;97(5):473-83. doi: 10.1161/01.cir.97.5.473.
Ultrasound can cause microbubble destruction. If microbubbles are administered as a continuous infusion, then their destruction within the myocardium and measurement of their myocardial reappearance rate at steady state will provide a measure of mean myocardial microbubble velocity. Conversely, measurement of their myocardial concentration at steady state will provide an assessment of microvascular cross-sectional area. Myocardial blood flow (MBF) can then be calculated from the product of the two.
Ex vivo and in vitro experiments were performed in which either flow was held constant and pulsing interval (interval between microbubble destruction and replenishment) 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 model 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-flow-limiting coronary stenoses were created, and MBF was measured before and after the venous administration of a coronary vasodilator. In all experiments, microbubbles were delivered as a constant infusion, and myocardial contrast echocardiography was performed using different pulsing intervals. The myocardial video intensity versus pulsing interval plots were fitted to an exponential function: y=A(1-e[-betat]), 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 correlations were found between flow and beta, as well as flow and the product of A and beta.
MBF can be quantified with myocardial contrast echocardiography during a venous infusion of microbubbles. This novel approach has potential for measuring tissue perfusion in any organ accessible to ultrasound.
超声可导致微泡破坏。如果以持续输注的方式给予微泡，那么它们在心肌内的破坏以及在稳态下心肌再出现率的测量将提供平均心肌微泡速度的一种测量方法。相反，在稳态下测量它们的心肌浓度将提供微血管横截面积的评估。然后可以通过两者的乘积计算心肌血流量（MBF）。
进行了体外和体内实验，其中要么流量保持恒定而改变脉冲间隔（微泡破坏与再充盈之间的间隔），要么反之。在21只犬身上进行了体内实验。在第1组犬（n = 7）中，在冠状动脉血容量恒定的模型中机械改变MBF。在第2组犬（n = 5）中，通过直接冠状动脉输注血管扩张剂来改变MBF。在第3组犬（n = 9）中，制造非血流限制性冠状动脉狭窄，并在静脉给予冠状动脉血管扩张剂前后测量MBF。在所有实验中，微泡以恒定输注方式给予，并使用不同的脉冲间隔进行心肌对比超声心动图检查。心肌视频强度与脉冲间隔的关系图拟合为指数函数：y = A(1 - e[-βt])，其中A是反映微血管横截面积的平台视频强度，β反映视频强度的上升速率，进而反映微泡速度。在流量与β之间以及流量与A和β的乘积之间发现了极好的相关性。
在静脉输注微泡期间，可通过心肌对比超声心动图对MBF进行定量。这种新方法具有测量超声可及的任何器官组织灌注的潜力。
