The effects of microsphere injections into the left atrium on the myocardial blood supply measured by thermal conductance probes

Abstract

Former experiments with thermal conduction probes showed signs of reductions or increases of myocardial perfusion shortly after injection of microspheres into the left atrium. Because of this, 210 measurements made during experiments on 66 dogs under propionylpromazine/pentobarbital narcosis were newly analysed to verify a possible influence of microspheres (9 μm 0) injected into the left atrium on microcirculation. Using 20 additional dogs in identically performed experiments, the myocardial perfusion was measured using thermal conductance probes, following injections of isotonic NaCl solution (8 ml each), Ringer's solution, 5% glucose, the subject's blood, and isotonic NaCl solution mixed with the surface-active substance Tween 80®. These suspension media were injected both with and without unlabelled microspheres (8.6 μlm Q1). The results led to the following conclusions: An obligatory decrease in the blood supply as the result of a mechanical blocking of capillaries by microspheres can be ruled out. The particles, the suspension media, and a suspension temperature not sufficiently adjusted to the body temperature induce reactive negative or positive changes in the microcirculation of the myocardium. This was found in approx. 45%-75% of cases. Solutions containing particles cause, in the majority of cases, a decrease. The suspension medium with the smallest effect proved to be isotonic NaCl solution. From the results one can conclude that artefacts may arise from the application of the heat conductance probe method when the temperatures are not perfectly matched. However, the injected solution itself can often lead to various reactions in microcirculation which may last up to 5 min. It is advisable to allow at least 6 min to elapse after reactive changes have faded before administering the next injection. In no case could the effects observed using the thermal conductance probes be confirmed by another measurement parameter (ECG, heart frequency, left ventricular pressure, dp/dt_max, aortic pressure).