Tethering affects the mechanics of coronary capillaries

Coronary capillaries are extensively tethered to adjacent myocytes by collagen fibers. The influence of this tethering in the beating heart is studied by structural mechanics as applied to the specific morphology of the capillary-myocyte system. The results show considerable effects of the tethering collagen fibers on the capillary deformation, especially during systole and in the deeper myocardial layers. The tethering fibers prevent total systolic collapse, being taut during systole but partially slack during diastole, in agreement with reported observations. At the deeper wall layers, the systolic/diastolic differences in capillary cross-sectional area are predicted to be more pronounced: about 30 and 50% area reduction in arterial and venous ends, respectively, compared with 10 and 20% increase of area in the subepicardial vessels. These predictions comply well with published, experimental data. A parametric investigation shows a variable effect of the capillary-myocyte distance on the dynamics of the capillary area, while the stiffnesses of both the fibers and wall membrane, and the extent of transmural transmission of intramyocardial pressure, have both considerable quantitative effects. These effects are found to be region dependent and vary along the capillary length and from diastole to systole. The results indicate that capillary tethering to the myocardial tissue has significant effect on its mechanics. Tethering should, therefore, be considered in analyzing the dynamics of coronary flow.