Components of the "Central " Blood Volume in the Dog

The indicator-dilution method was used in the dog in an attempt to define the proportion of the "central " blood volume contained in the lung vessels. When injections were made into the pulmonary artery with sampling from the femoral artery only half or even less of the calculated blood volume could be accounted for by the lungs. When;i venous injection site was used, the proportion in the lungs was reduced to a third or less. Thus when peripheral sites are used for the inscription of indicator-dilution curves few deductions can be made about either the actual volume or even relative changes in the volume of blood in the lungs. PROVIDED certain conditions are ful-filled, the volume of a vascular compart-ment may be measured by analysis of a dilu-tion curve obtained at the outlet after rapid injection of an indicator at the inlet. In the Stewart-Hamilton method the volume is rep-resented by the product of the cardiac output and the mean transit line of the indicator particles.1 Mathematical proof of the validity of this measurement has been published by Meier and Zierler.2 Attempts have been made in the past to assess changes in the volume of blood in the vessels of the kings by measuring a volume variously termed as "central, " "intratho-racic, " or "cardiopulmonary. " For this measurement an indicator substance is in-jected into the right side of the heart, or pul-monary artery and the resulting changes in concentration of dye are determined at a pe-ripheral artery, usually the brachial or fem-oral. The volume therefore includes the blood not only in the heart and lungs but also in an appreciable, though ill-defined, part of the arterial tree. Others have used a peripheral vein for the injection, the volume thus ob-tained including in addition part of the ve-nous system. In the experiments reported herein, differ-ent components of the so-called central blood From tlio Mnyo Clinic iiiid the Mtiyo Foundation