Effect of intracoronary adenosine upon regional blood flow, microvascular blood volume and hematocrit in canine myocardium.

Microvascular blood volume and red cell volume fraction (hematocrit) and their relation to increased coronary blood flow were investigated in the dog heart. In response to intracoronary adenosine infusion into the anterior descending branch (LAD) of the left coronary artery, myocardial blood flow increased markedly in the perfusion zone compared with a region of the left ventricular free wall as supplied with blood from the circumflex branch (Cx) of the left coronary artery. Raising the LAD blood flow by 800% significantly reduced microvascular blood volume in the dilated vascular bed compared with the undilated vascular bed of the Cx. Control microvascular hematocrit averaged 29 +/- 2%. Hematocrit was not only low at control flow but decreased with increased blood flow, average 20 +/- 2%. The volume of red cells contained within microvessels decreased significantly in the adenosine-dilated vascular bed whereas the volume of plasma remained unchanged compared with the control vascular bed. The present data favor the view that such alterations in microvascular blood volume and red cell volume fraction may be due to reduction of the density of red blood cell perfused capillaries and unchanged density of plasma perfused capillaries.