A Major Pitfall in the Interpretation of "Central Blood Volume"

Abstract

During reactive hyperemia of the legs of normal subjects, the "central blood volume" increased 569 ml. when measured from a hrachial arterial sampling site but decreased 144 ml. when measured from the femoral artery. This study demonstrates that changes occurring within the peripheral arterial system can profoundly influence "central blood volume" measurements which are made from a peripheral arterial sampling site. Failure to recognize the inconstancy and the potential magnitude of the arterial contribution is a major pitfall in the interpretation of the calculated "central blood volume." It is suggested that changes in either arterial volume or arterial flow distribution may alter the "central blood volume" but that the distribution effect is the more probable cause of the changes seen in this study. Alterations in "central blood volume," which result from changes within the peripheral vasculature, cannot be readily distinguished from those caused by changes in the volume of blood in the heart and lungs. Peripheral effects can be avoided if the indicator is injected into the right auricle and sampling is done from the root of the aorta.