DIAMETERS OF SUBENDOCARDIAL ARTERIOLES AND VENULES DURING PROLONGED DIASTOLE IN CANINE LEFT-VENTRICLES

Using a needle-probe videomicroscope with a charge-coupled device (CCD ) camera, we measured the diameter of subendocardial arterioles and ve nules during prolonged diastole beyond the time point at which coronar y blood flow reached zero. In seven open-chest heart-blocked dogs, a s heathed needle probe with a doughnut-shaped balloon was introduced fro m the left atrial appendage and advanced into the left ventricle throu gh the mitral valve. The tip of the probe was placed gently on the end ocardial surface. Diameters of arterioles (n=16) and venules (n=16) at the beginning of long diastole ranged from 40 to 126 mu m and from 32 to 192 mu m, respectively. After cardiac arrest, the arteriolar diame ter gradually declined with aortic pressure. Arteriolar diameters at z ero flow decreased by 28+/-9% (mean+/-SD) compared with the initial di ameter (P<.01). However, none of the subendocardial arterioles collaps ed at zero flow or at 12 seconds after the beginning of prolonged dias tole (8 to 9 seconds after zero flow) in an additional experiment (n=5 ). In contrast to arteriolar diameter, venular diameter increased duri ng prolonged diastole. Venular diameter at zero flow increased by 14+/ -12% compared with the initial diameter (P<.01). We conclude that duri ng prolonged diastole, when coronary arterial inflow ceases, subendoca rdial arteriolar diameter decreases without any visible collapse, wher eas venular diameter increases.