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Regional blood flow and contractile function: are they matched in normal, ischemic and reperfused myocardium?
1Abteilung für Pathophysiologie, Universitätsklinikum Essen, FRG.
Insights
Regional myocardial blood flow and function are matched in hibernating (ischemic) myocardium but unmatched in stunned myocardium. This research explores myocardial adaptation strategies to reduced blood flow.
Area of Science:
- Cardiovascular Physiology
- Myocardial Pathophysiology
Background:
- A central hypothesis posits a balance between myocardial blood flow and contractile function (supply and demand) in natural conditions.
- This balance has been primarily studied at the global ventricular level, with less known about regional dynamics.
Purpose of the Study:
- To examine the relationship between myocardial blood flow and function on a regional level.
- To investigate whether regional flow and function are matched, particularly in conditions of ischemia and adaptation.
Main Methods:
- Analysis of regional myocardial blood flow and function.
- Comparison of flow-function relationships in normal, hibernating, and stunned myocardium.
Main Results:
- Normal myocardium exhibits heterogeneity in blood flow, suggesting similar heterogeneity in metabolic demand and function.
- In hibernating (ischemic) myocardium, regional blood flow and function are matched at a lower level, allowing viability.
- In stunned myocardium, regional blood flow and function are unmatched, despite preserved viability.
Conclusions:
- Regional analysis provides new insights into myocardial adaptation strategies to reduced blood flow.
- Hibernating myocardium demonstrates a matched supply-demand balance, while stunned myocardium shows a mismatch.
- Both hibernation and stunning represent adaptive strategies preserving myocardial viability under ischemic conditions.
Abstract:
One central hypothesis of cardiovascular physiology has been a balance between myocardial blood flow and contractile function during natural conditions, i.e. supply and demand are matched. This hypothesis was derived from studies relating total coronary blood flow to global ventricular function. The present article examines the relationship between myocardial blood flow and function on a regional level. In normal myocardium, considerable heterogeneity of blood flow exists, indicating similar heterogeneity of metabolic demand and potentially also function. However, when the degree of metabolic coupling between flow and function is questioned, there is no evidence whether or not flow and function are matched on a regional level. One closely related hypothesis of cardiovascular pathology has been an imbalance or mismatch between supply and demand during ischemia. Because myocardial function rapidly declines during early ischemia, residual, regional myocardial blood flow and function may be once again matched on a lower level. Such low-level supply-demand balance may persist over prolonged periods of ischemia and permit the myocardium to remain viable, i.e. the myocardium can "hibernate." Analyzing myocardial blood flow and function on a regional level has generated new insight into strategies of adaptation to the adverse situation of reduced blood flow. Whereas in hibernating (ischemic) myocardium, regional myocardial blood flow and function are matched, flow and function appear to be unmatched in reperfused, dysfunctional, i.e. 'stunned' myocardium. "Stunned myocardium" appears once more as a result of a strategy of adaptation, as the preceding ischemia did not induce irreversible myocardial damage but preserved the ischemic myocardium viable, although functionally impaired.