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Transmural redistribution of coronary resistance during embolization: a clue to intramyocardial small artery
G Pelosi1, G Saviozzi, M G Trivella
1Institute of Clinical Physiology, CNR, Pisa, Italy.
Insights
This study reveals that the subepicardial layer of the left ventricle experiences significantly higher coronary resistance than the subendocardial layer during embolization. This finding helps model the intramyocardial small artery system and its vessel distribution.
Area of Science:
- Cardiovascular Physiology
- Microcirculation Research
- Biomedical Engineering
Background:
- Understanding the vascular architecture of the left ventricular wall is crucial for comprehending coronary blood flow dynamics.
- Previous models described general characteristics of intramyocardial small arteries, necessitating further parameter refinement.
Purpose of the Study:
- To assess the vascular architecture and single vessel resistance distribution in the subepicardial (epi) and subendocardial (endo) layers of the left ventricle.
- To develop and test a branching tree model of the intramyocardial small artery system against experimental coronary resistance data.
Main Methods:
- Coronary embolization in six dogs using 25-micron plastic microspheres injected into the left circumflex artery.
- Assessment of transmural blood flow using 15-micron radioactive microspheres.
- Development of a symmetric dichotomous branching tree model to represent the intramyocardial small artery system.
Main Results:
- Embolization caused a significantly greater increase in subepicardial resistance compared to subendocardial resistance.
- The subepicardial/subendocardial resistance ratio increased substantially with each microsphere injection.
- Experimental data defined parameters for the branching tree model, indicating twofold more terminal vessels in the subendocardium than in the subepicardium.
Conclusions:
- The subepicardial vascular bed exhibits higher resistance than the subendocardial bed in the left ventricle.
- The intramyocardial small artery system can be modeled as a symmetric dichotomous branching tree with a specific distribution of terminal vessels.
- The findings provide insights into the structural basis of regional differences in coronary resistance.
Abstract:
The aim of this study is to assess vascular architecture and the single vessel resistance distribution of the subepicardial (epi) and subendocardial (endo) layers of the left ventricular wall. For this purpose, coronary embolization was performed by injecting three boluses of 25 microns plastic microspheres into the maximally vasodilated left circumflex artery of six dogs; transmural blood flow was assessed by 15-microns radioactive microspheres. A branching tree model of the intramyocardial small artery system--whose general characteristics were described in a previous study (Pelosi et al., 1987, Microvasc. Res. 34, 318-335)--was developed and its parameters were tested against the increase in epi and endo coronary resistance observed during embolization. Embolization produced a significantly greater increase in epi resistance after each bolus injection (from 10.3 +/- 1.1 to 195.6 +/- 32.5 mm Hg/ml/min/g after the last bolus, P less than 0.001) as compared to endo resistance (from 10.3 +/- 2.0 to 56.5 +/- 8.2 mm Hg/ml/min/g after the last bolus, P less than 0.001); as a consequence, the epi/endo resistance ratio increased from 1.09 +/- 0.11 to 1.50 +/- 0.13, 2.48 +/- 0.51, and 3.66 +/- 0.42 (P less than 0.05 for all embolizing injections). The experimental relation (occlusion function) between the number of embolizing beads injected and the epi and endo resistance values was used to define the parameters of the epi and endo branching tree model. Assuming that the embolizing microspheres lodge in vessels of similar resistance (that is similar diameter and length) in the two layers, the experimental results indicate that the intramyocardial small artery system can be depicted as a symmetric dichotomous branching tree with twofold more terminal vessels in the endo than in the epi.