Coronary artery resistance changes depend on how surrounding myocardial tissue is stretched

Deforming the tissue surrounding a coronary artery may change its hydraulic resistance. In excised blocks of dog left ventricular walls we examined how resistance (R) of a maximally dilated branch of a circumflex coronary artery was affected by 10% stretching of the tissue from its unloaded state, first parallel then perpendicular to the vessel axis (with the orthogonal dimension held constant) and finally biaxially. At 30 mmHg transmural pressure (Ptm) R per segment length (mmHg.min.ml-1.cm-1) increased significantly from the unloaded value of 0.0233 +/- 0.0031 (means +/- SE) to 0.0445 +/- 0.0073 and 0.0505 +/- 0.0090 during parallel and biaxial stretch, respectively. At Ptm of 80 mmHg unloaded R decreased to 0.0111 +/- 0.0016 mmHg.min.ml-1.cm-1 but did not change further with stretching. Stretching an isolated circular vessel 10% does not produce nearly this large an increase in R. A finite-element model simulating an epicardial vessel under our experimental conditions qualitatively predicted our results and demonstrated the combined roles of size and shape changes. Simulating a midwall arteriole surrounded by tissue predicted qualitatively similar results as for an epicardial vessel. Thus mechanical interaction between a coronary artery and surrounding tissue depends on both transmural pressure and the direction of stretching.