Temporal and spatial heterogeneity of myocardial perfusion

Using the microsphere technique (15±5μ) the spatial and temporal heterogeneity of myocardial blood flow was explored in the canine heart. Injections of microspheres were made directly into a pump perfused left coronary artery using two experimental protocols. In the first study, 4 types of microspheres were injected simultaneously (sim), ¹²⁵I, ¹⁴¹Ce, ⁹⁵Nb and ⁸⁵Sr and in the second, the four types of microspheres were injected at 10 to 20 second intervals (seq) under conditions of constant coronary and systemic haemodynamics. After completion of the study, the perfused myocardium was sectioned into 150 sections each containing at least 2000 microspheres of each type. Flow per gram was computed for each section for each isotope. The mean variance for a sample was 0.005 for sim and 0.029 for seq. This difference was significant (p<.025) when subjected to 3 way analysis of variance. A periodicity of flow of between 45 and 90 seconds was detected. Thus, spatial heterogeneity of perfusion can be demonstrated in the normally autoregulating heart and a flow cycle of approximately one minute exists.