DISAPPEARANCE CURVES OF THE DYE T-1824 AFTER ITS INJECTION INTO THE BLOOD STREAM

Abstract

The course of the disappearance of the blue dye T-1824 after inj. into the blood stream was studied in 100 normal unanesthetized dogs. Spectrophotometric detns. of the dye conc. were made in successive serum samples, beginning within 1 min. after inj., and continuing for at least 1 1/2 hrs. In 6 expts. observations were continued for as long as 26 hrs. Optical densities plotted against time show that although the time-conc. curves may be approximated by a straight line over very limited periods, they cannot be adequately expressed by either the equation c = c0( 1[long dash]T) or c = c, e T where C = conc. at the time t after inj., C0= conc. at the moment of inj. and T is a time constant. Hence the deviation of early points from such an approximated line cannot be accepted as a criterion of incomplete dye dis-tribution in the blood since the line imposed will vary with the period chosen for extrapolation. Dye disappearance may, however, be expressed adequately by a straight line if dye densities are plotted as a function of the square root of time, i.e., c = co(1[long dash]V''t/T). This relationship main- tains after the first 5 or 10 mins. following inj., and for any period up to 24 hrs. Plasma vol. may therefore be calcu-lated by extrapolating the straight line obtained by the square root plot. The plasma volumes thus obtained aver-age 10% less than those calculated by the usual linear extrapolation method. The average % difference cannot be used as a, factor for relating the 2 results, because the differences show considerable variability.