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Coronary flow patterns in normal and ischemic hearts: transmyocardial and artery to vein distribution
1Julius Silver Institute, Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa.
Insights
A new model simulates coronary blood flow, revealing how cardiac contraction affects vessel dynamics. It predicts distinct flow patterns during normal and ischemic conditions, including systolic collapse and alternating transmural flow during ischemia.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Computational Biology
Background:
- Coronary blood flow dynamics are complex and difficult to measure directly.
- Understanding these dynamics is crucial for diagnosing and treating cardiac conditions.
- Existing models may not fully capture the interaction between cardiac contraction and coronary circulation.
Purpose of the Study:
- To develop a theoretical model of transmyocardial coronary flow.
- To investigate the impact of extravascular compressive pressure (ECP) on coronary vessels.
- To simulate coronary flow patterns under normal and ischemic conditions.
Main Methods:
- A compartmental model dividing the myocardium into three layers with four vessel-size compartments each.
- Incorporating resistance, compliance, extravascular compressive pressure (ECP), autoregulation, and collaterals.
- Two approaches for ECP: (a) function of left ventricle (LV) pressure, and (b) interstitial fluid pressure using a multilayer muscle-collagen model.
Main Results:
- The model predicts out-of-phase arterial and venous flow patterns.
- It simulates systolic collapse of intramyocardial veins (normal) and arteriolar collapse (ischemia).
- Transmural flow during ischemia shows alternating patterns between layers; the interstitial fluid pressure model for ECP better predicts compressive effects.
Conclusions:
- The developed model accurately describes coronary flow dynamics under normal and ischemic conditions.
- The interstitial fluid pressure approach for ECP is superior in capturing compressive effects during ischemia.
- The interaction between myocardial contraction and coronary circulation is critical and depends on the LV mechanical model used.
Abstract:
The dynamics of the transmyocardial coronary flow patterns during normal and ischemic conditions are complex and relatively inaccessible to measurements. Therefore, theoretical analyses are needed to help in understanding these phenomena. The proposed model employs compartmental division to three layers, each with four vessel-size compartments which are characterized by resistance and compliance. These compartments are subjected to the extravascular compressive pressure (ECP) generated by cardiac contraction, which by modifying the transmural pressure causes changes in cross-sectional area of the vessels in each compartment continuously determining the resistance and capacitance values. Autoregulation and collaterals are also included in order to simulate the flow patterns during regional ischemia. Using these features, the model predicts the typical out of phase arterial and venous flow patterns. Systolic collapse of the large intramyocardial veins during the normal cycle, as well as systolic arteriolar collapse during ischemia are predicted. The transmural flow during ischemia is characterized by alternating flows between the layers. The ECP is considered here is two ways: (a) as a function of left ventricle (LV) pressure, decreasing linearly from endocardium to epicardium and (b) as the interstitial fluid pressure, employing a multilayer muscle-collagen model of the LV. While both of these approaches can describe the dynamics of coronary flow under normal conditions, only the second approach predicts the large compressive effects due to high ECP obtained at very low cavity pressure, resulting from significant muscle shortening and radial collagen stretch. This approach, combining a detailed description of transmural coronary circulation interacting with the contracting myocardium agrees with many observations on the dynamics of coronary flow and suggests that the type of LV mechanical model is important for that interaction.