| Objective: To determine the minimal ischemic burden for evoking maximal opening of native coronary collateral circulation through studying the effect of different ischemic burden on the opening of the collateral circulation.Methods: Forty-nine adult New Zealand rabbits (2.5 ?0.5kg) were subjected to complete occlusion of left ventricle coronary artery (LVA) with different ischemic burden. Coronary collateral blood flow (CCBF) was measured with microsphere technique. ECG and morphology of the normal and ischemic myocardium were adopted as the criteria of myocardial ischemia and reperfusion.Result: (1) Pathology: Myocardial cells degeneration was found in the 8min and 20min-occlusion groups and no thrombus found in all subjects. (2) CCBF increased at the onset of occlusion and reached the maximal at 2min (p<0.05). A trend of decrease was shown with the occlusion prolonging to 4, 5, 8, 10 and 20min (p>0.05). (3) CCBF after one 2-min occlusion increased more significantly than the value of pre-occlusion but decreased gradually to the baseline at 2min after reperfusion. (4) CCBF after three repetitive 2-minute occlusions with 5 to 30min interval did not show any further increase (p>0.05).Conclusion: The data suggest that the fully opening of native collateral circulation after artery occlusion requires 2min duration and maintains no more than 2 minutes, which is not augmented by increase of the ischemic burden.
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