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Distribution of maximum coronary blood flow in the left ventricular wall of anesthetized dogs
Insights
Progressive hemodilution in dogs revealed that endocardial blood flow reserve is lower than epicardial. This finding highlights regional differences in coronary blood flow capacity during reduced blood volume.
Area of Science:
- Cardiovascular Physiology
- Coronary Circulation Research
Background:
- Coronary blood flow distribution is critical for myocardial function.
- Understanding regional differences in blood flow reserve is essential for diagnosing and treating cardiovascular diseases.
Purpose of the Study:
- To investigate the distribution of coronary blood flow in the left ventricular free wall during progressive hemodilution.
- To compare endocardial and epicardial blood flow reserves under conditions of reduced blood volume and maximal vasodilation.
Main Methods:
- Electromagnetic flowmetry to measure blood flow in the circumflex artery.
- Xe-133 and radioactive microspheres to assess regional myocardial blood flow distribution.
- Progressive hemodilution and reactive hyperemia induced by coronary artery occlusion in dogs.
Main Results:
- "Optimum" hemodilution led to a sixfold increase in systolic and threefold increase in diastolic coronary flow, with relative endocardial hypoperfusion.
- During maximal vasodilation, Xe-133 and microsphere distribution indicated uniform epicardial and endocardial flow.
- Arterial blood pressure oscillations influenced coronary flow differently before and during hemodilution.
Conclusions:
- The endocardial blood flow reserve is lower than the epicardial reserve.
- Uniform flow distribution during maximal vasodilation may be due to systolic endocardial perfusion or differential hyperemic period durations.
Abstract:
Blood flow in the circumflex branch of the left coronary artery was recorded by electromagnetic flowmeter. In a group of dogs progressive hemodilution was performed until the diastolic reactive hyperemic response to 10 s occlusion of the circumflex branch disappeared ("optimum" hemodilution). At this degree of hemodilution the distribution of blood flow in the left ventricular free wall was evaluated by measuring tissue activity concentrations of Xe-133 and radioactive microspheres after bolus injection into the aortic root. "Optimum" hemodilution was accompanied by a sixfold increase in systolic coronary flow, a 3-fold increase in diastolic flow and a relative endocardial hypoperfusion. These results indicate that the endocardial blood flow reserve is lower than the epicardial. This conclusion is supported by the influence of spontaneous oscillations of arterial blood pressure (Traube-Hering waves) on systolic and diastolic coronary blood flows before and during "optimum" hemodilution. In another group of dogs maximum coronary vasodilatation was produced by occlusion of the left coronary artery for 10 s. In this group the distribuition of Xe-133 and radioactive microspheres were measured after bolus injection into the aortic root at peak diastolic reactive hyperemia. The epi- and endocardial distribution of both Xe-133 and microspheres was uniform in the left ventricular wall, indicating a uniform flow to these regions. This might be explained by an increased endocardial perfusion during systole due to loss of myocardial contractility or by a decline towards resting level in epicardial flow at the time of injection, corresponding to a shorter duration of the hyperemic period in the epi- than endocardial region.