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Effect of flow reduction on coronary blood flow heterogeneity
1Department of Physiology and Biophysics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854-5635.
Insights
Reduced coronary blood flow increases spatial heterogeneity in myocardial blood flow. This relationship holds true whether flow is reduced by occlusion or vasoconstriction, indicating flow rate is the primary driver of heterogeneity.
Area of Science:
- Cardiovascular Physiology
- Myocardial Perfusion Dynamics
Background:
- Understanding myocardial blood flow (MBF) heterogeneity is crucial for diagnosing and treating ischemic heart disease.
- Spatial variability in MBF can impact myocardial function and viability.
Purpose of the Study:
- To investigate the relationship between myocardial blood flow and spatial heterogeneity under reduced flow conditions.
- To determine if vasoconstriction alters the relationship between perfusion rate and heterogeneity.
Main Methods:
- Utilized the radioactive microsphere technique in anesthetized open-chest dogs to measure MBF.
- Quantified spatial heterogeneity using the coefficient of variation (CV) of MBF across 50 left ventricular tissue samples.
- Compared MBF heterogeneity under control, 50% coronary artery occlusion, and vasopressin-induced flow reduction.
Main Results:
- Spatial heterogeneity (CV) significantly increased from 18% (control) to approximately 45% under both 50% flow reduction and vasopressin infusion.
- No significant difference in CV was observed between the two reduced flow conditions.
- A significant inverse relationship was found between CV and mean coronary flow (r=0.51), improved with a hyperbolic model (r=0.69).
Conclusions:
- Relative spatial heterogeneity of myocardial blood flow increases as perfusion rate decreases.
- The mechanism of flow reduction (occlusion vs. vasoconstriction) did not significantly alter this inverse relationship.
Abstract:
The purpose of this study was to test the hypothesis that under reduced flow conditions, spatial heterogeneity (segment-to-segment variability) of myocardial blood flow would be inversely proportional to the rate of perfusion and that vasoconstriction would alter this relationship in anesthetized open-chest dogs. A carotid-left circumflex coronary artery shunt was created. Coronary blood flow determinations employed the radioactive microsphere technique. Fifty tissue samples were obtained from the affected left ventricle, including subepicardial and subendocardial samples. The coefficient of variation (CV = 100 x SD/mean), an index of spatial heterogeneity, was computed. Flows were obtained under three separate conditions: control, a 50% flow reduction in the circumflex artery, and vasopressin infusion, in which the administered dose reduced circumflex artery flow by 50%. The within-animal CV increased from a control of 18 +/- 9 to 45 +/- 25 with partial occlusion and 46 +/- 18 with vasopressin. No significant differences in CV were found between the two reduced flow conditions. A significant linear relationship between CV and mean coronary flow was found (r = 0.51, P < 0.001) over the entire range of flows studied (CV = -0.34*flow + 50.91) for control, 50% occlusion, and vasopressin treatment. The correlation was significantly improved (r = 0.69) using the equation CV = (1319.06/flow) + 4.44. Thus, the relative heterogeneity of coronary blood flow increased with reductions in coronary blood flow, regardless of the means of flow reduction.