Evidence for long-term fluctuations in regional blood flow within the rabbit left ventricle.

The regional distribution of coronary perfusion within the left ventricle is markedly heterogenous. The perfusion pattern is composed of both spatial and temporal variations in perfusion among single myocardial samples. Previous investigators have mostly studied short-term (< 1 min) temporal variability. The aim of this study was to quantify long-term fluctuations in perfusion to single samples within the rabbit left ventricle. Coronary perfusion was estimated from the deposition of microspheres in myocardial samples (range 32-96 mg). Two batches of microspheres were infused either simultaneously or sequentially over specified periods of time. The paired values for regional perfusion were compared and Kendalls correlation coefficient (tau) calculated. The assumption being that the lower tau, the higher degree of temporal perfusion variability was present. The tau for paired values of regional myocardial perfusion based on two sequential infusions lasting either 10 s, 5, 10 or 30 min, averaged 0.40, 0.55, 0.80 and 0.80, respectively. No difference was detected between awake and anaesthetized animals. The tau for two simultaneous infusions averaged 0.95 irrespective of the duration of the infusion, indicating negligible methodological error. The coefficient of variation for spatial perfusion heterogeneity ranged from 0.3 to 0.4 irrespective of the infusion duration. The findings suggest that regional coronary vasomotion is characterized by a wide range of cycle times, some of which have cycle times of more than 30-min duration. Although part of the regional perfusion heterogeneity was due to long-term fluctuations in perfusion, temporal variations with cycle times less than 5 and 10 min, respectively, were more prominent.