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Transmural distribution of capillary morphology as a function of coronary perfusion pressure in the resting canine
K May-Newman1, O Mathieu-Costello, J H Omens
1Institute for Biomedical Engineering, University of California, San Diego, La Jolla 92093-0412, USA.
Insights
Coronary perfusion pressure alters myocardial capillary geometry, affecting blood flow. Canine heart studies show capillaries change shape and size with pressure, not number, influencing intramyocardial capacitance.
Area of Science:
- Cardiovascular Physiology
- Microcirculation Research
- Myocardial Biology
Background:
- Coronary perfusion pressure (CPP) influences myocardial blood volume.
- Microvascular morphology adaptations to CPP are not fully understood.
- Intracoronary myocardial volume changes may relate to microvascular structure.
Purpose of the Study:
- To quantify transmural variations in coronary capillary geometry.
- To assess capillary adaptations to varying coronary perfusion pressure.
- To investigate the relationship between capillary morphology and intramyocardial capacitance.
Main Methods:
- Utilized glutaraldehyde-fixed canine hearts for analysis.
- Employed computer analysis of light microscopic images.
- Measured capillary volume fraction, diameter, numerical density, anisotropy, and sarcomere length.
Main Results:
- Capillary volume fraction (4-6%) showed a transmural gradient (epicardium to endocardium).
- Capillary diameter and shape altered with increasing pressure, not density.
- Effective capillary distensibility was approximately 0.007 mm Hg-1.
- Capillary anisotropy correlated with cross-sectional shape, indicating high orientation.
Conclusions:
- Intramyocardial capacitance is linked to non-homogeneous changes in coronary capillary morphology.
- Capillary distensibility plays a role in regulating myocardial volume under varying perfusion pressures.
- Microvascular structural adaptations are crucial for maintaining cardiac function during CPP fluctuations.
Abstract:
Changes in coronary perfusion pressure lead to alterations in intracoronary myocardial volume that may be associated with regionally altered microvascular morphology. Transmural variations in coronary capillary geometry were quantified as a function of coronary perfusion pressure in glutaraldehyde-fixed canine hearts. Capillary volume fractions, diameter, numerical density, anisotropy, and sarcomere length were measured using computer analysis of light microscopic images of sections taken transverse or longitudinal to the muscle fiber axis. Capillary volume was 4-6% of myocardial wall volume and exhibited a significant transmural gradient, increasing from epicardium to endocardium. Vessels 4 to 5 microns in diameter with a density of 2900 mm-2 appear to increase in diameter and alter their cross-sectional shape with increasing pressure, rather than increasing in number, suggesting an effective distensibility of approximately 0.007 mm Hg-1. Quantification of vessel anisotropy was directly related to cross-sectional shape and demonstrated that the capillaries are highly oriented. These findings indicate that intramyocardial capacitance is at least in part associated with nonhomogeneous changes in coronary capillary morphology with altered perfusion pressure.