The Use of Ascorbate Dilution Curves

AT THE PRESENT time, indicator-dilution curves are one of the most important technics employed in the investigation of the circulation. The earliest of these studies were carried out by the rapid serial collections of blood samples and their subsequent photometric analysis.' This ingenious but cumbersome method was replaced by the continuous withdrawal of blood in front of a photoelectric cell, thus permitting the direct inscription of time-concentration curves.2 Although this approach has greatly facilitated application of the indicator-dilution principle, a number of drawbacks have remained. Most of them are related to the unavoidable physical separation of the intravascular sampling site and the external detector. Thus, the loss of blood may become significant, particularly when multiple dilution curves are necessary. Secondly, distortion of the curve results during transit from sampling site to the detector.3 Finally, it may be difficult to obtain dilution curves from the central circulation, since the blood sample must traverse a long catheter. Accordingly, considerable effort has been directed toward the development of technics that permit placement of the detector directly into the blood stream.-7 Clark and his associatess11 have recently introduced a new group of indicators, chemical reducing agents, that can be detected with intravascular platinum electrodes. This report describes the technics and instrumentation employed in this laboratory with sodium ascorbate as an indicator; particular emphasis is placed on the dilution curves ob-