Role of autoregulation in spatial and temporal perfusion heterogeneity of canine myocardium

Spatial heterogeneity, the region-to-region variation in flow at an instant, and temporal heterogeneity, the time variation of flow in a small region of myocardium, were investigated with radioactive labeled microspheres in 111 regions of left ventricular myocardium. The error of the method was measured by simultaneously injecting four differently labeled microspheres (15 ± 5 (SD) μm). The coefficient of variation (CV) was 6.5 ± 1.0%. Spatial variation with autoregulation intact was 21.7 ± 1.4% (CV); with autoregulation abolished and low perfusion pressure, it was 34.3 ± 3.7%; and with normal perfusion pressure, 30.8 ± 6.4% (differences not significant). This degree of variation was similar in the entire left ventricle and its layers. Forces which tended to cause vessel closure (low perfusion pressure, ventricular systolic pressure, and ventricular diastolic pressure) tended to increase CV. Temporal heterogeneity as measured by 20-s intervals between microsphere injections was 11.1 ± 1.0% (CV) with autoregulation, 9.8 ± 1.3% (P<0.05) with autoregulation abolished, and 8.4 ± 0.8% (P<0.05) when perfusion pressure was restored. A periodicity of flow cycles of 30-90 s was suggested by the data. These results suggest that spatial heterogeneity is less influenced by autoregulation than by hydraulic considerations, whereas temporal heterogeneity is a component of autoregulation.