Considerations in use of microspheres for flow measurements in anesthetized rat.

The results of single injections of different doses of microspheres (60,000, 100,000, and 375,000) demonstrated a significant reduction in measured heart and kidney blood flows as a function of the number of microspheres injected. Measured flow to other organs was unaffected by a single injection of these doses of microspheres. The injection of microspheres at a faster rate (0.8 ml/min microsphere injection; 1.0 ml/min flush) resulted in higher calculated heart flow when compared with the slow rate (0.2 ml/min microsphere injection; 0.25 ml/min flush). A significant decrease (approximately 21%) in measured blood flow to the right side of the brain that was observed in all the groups is due to the occlusion of the right carotid artery by the cannulation procedure. Intra-aortic injection of microspheres resulted in reduced measured brain blood flow when compared with intraventricular injections. Accurate and reliable heart and brain blood flows were not obtained with intra-aortic injection of microspheres. However, intra-aortic injection of microspheres does provide accurate and reliable flow measurements for more distal organs.