Two hemodynamic problems commonly associated with the microsphere technique for measuring regional blood flow in rats

The purpose of this study was to reevaluate two major steps associated with the radioactive microsphere technique in rats; the hemodynamic effects of the solutions used to inject the microspheres, and the hemodynamic effects of repeated blood withdrawals. With regard to the first, Flaim et al. (1978) have shown that 1.0 ml of 10% dextran injected into the rat may result in a severe pressure drop. The present study showed that even 0.1 ml of 10% dextran caused significant hypotension 46% of the time. Six other mediums were also tested as possible suspending media. It was concluded that a dextrose solution (sp gr 1.3) was the best microsphere injection medium based on the length of time the microspheres stayed mixed in the solution and the minimal hemodynamic alterations caused during injection. With regard to the second concern, cardiac output decreased approximately 7% with each reference sample withdrawal. When volume was replaced with a Ficoll-70 solution, cardiac output decreased less than 3%. These data show that repeated blood withdrawals are possible as long as the volume of blood is replaced. Thus, several isotopes can be injected in the same rat to allow measurement of regional blood flow under different experimental conditions.