A Slide Rule for Time Conversion for Bromsulphalein (BSP) Retention Studies

In blood plasma, the concentration of injected Bromsuiphalein is indicated by x at any time, t. The two quantities are related by the first-order equation In x = kt (k is a constant). A specialized log-log slide rule has been developed to permit the rapid direct calculation of x at some value of t, when the value of x at some other time is known. THE Bromsulphaleimm (BSP) test of Rosenthal ammd White (1) has undergone several modifications (2) imi the 40 years following its in-troduction. Like most drugs, BSP is removed from blood plasma at a rate which is proportional to its concentratiomi, that is, a first-order reactiomi (3). As would be expected for a first-order reaction, a graph of In (BSP) or log (BSP) vs. time results iii a straight line. This graph is used in the BSP clearance test (4-6). In this hospital the BSP test is usually performed by determining the per cent retemition of BSI ’ 43 mm. after time ihmtravenous injection of a 5 mg./kg. body weight dose. The procedure is very much like that of Woottomi (7), although we use a nomogramt relating volume of BSP dye solution used to body weight. Because of the large size of many hospitals it is not always possible to collect a blood specimen exactly 43 mm. after the injectioim of the BSP dye solution. However, it is always possible to note the exact time at which time blood sample was drawn. The problem then resolves itself into the simple one of deter-mining what fraction of BSP was retained 43 mm. after injectioim even though blood collection was made at some other knowmm time. Time solu-tion to the problem follows from the equations governing the system. If y equals time concemmtration of BSP retained in blood plasma in th