Transmural microcirculatory blood flow distribution in right and left ventricular free walls of rabbits

Within-layer regional myocardial flows in the left and right ventricles (LV , RV) and in LV with increased myocardial workload (beta(1)-adrenoceptor st imulation) were studied transmurally in anesthetized rabbits. Myocardial fl ow distribution was visualized with resolutions between 0.1 x 0.1- and 1 x 1-mm(2) pixels, using digital radiography combined with the H-3-labeled des methylimipramine deposition technique. The spatial pattern of flow distribu tion was quantitated by the coefficient of variation of regional flows (CV, related to global flow heterogeneity) and the correlation between adjacent regional flows (CA, inversely related to local flow randomness). CV was lo wer in LV than in RV [P < 0.05, nonparametric 2-way analysis of variance (N ANOVA)]. When resolution was lowered from 0.1 x 0.1- to 1 x 1-mm(2) pixels, CV decreased by 70% in both LV and RV. CA was higher in LV than in RV (P < 0.05, NANOVA); the interventricular difference in CA was large over the re solutions between 0.4 x 0.4- and 1 x 1-mm(2) pixels. In LV, both CV and CA increased with depth of myocardium (P < 0.05, NANOVA); in subendocardium CV was high comparable with CV in RV (P = 0.47, NANOVA). The enhancement of m yocardial workload decreased CV and tended to decrease CA in LV subendocard ium (P < 0.05, P = 0.06, respectively; NANOVA). We conclude that 1) microre gional flow distribution is less heterogeneous and less random in LV than i n RV; 2) transmurally, in LV subendocardium global flow heterogeneity was t he highest whereas local flow randomness was the lowest, so that clusters o f low- or high-flow regions exist in this LV layer; and 3) global flow hete rogeneity decreased and local flow randomness tended to increase (flow homo genizing occurred) in LV subendocardium with increasing myocardial workload . Thus the distributed pattern of myocardial microregional flows may be ada ptable to local myocardial metabolic change.