Abstract
The dynamics of the distribution of creatinine infused into 5 anesthetized, heparinized dogs in moderate diuresis were analyzed in terms of the simplest serial compartmental model (4 chambers with passive exchanges) which would describe the data accurately. During 3-hr experiments, the intravenous infusion rate was continuously varied over a wide range, resulting in large variations in arterial plasma concentration (measured continuously by AutoAnalyzer), thus providing an exacting test of the model. Input into first chamber of the model was the experimental rate of creatinine infusion. Output, also from this chamber, was determined by matching the integral of the product of clearance times the concentration of the first chamber (delayed 2 min) to the observed creatinine output measured over 10-min periods. The concentration in this chamber, after passing through a dispersive delay line analogous to the AutoAnalyzer, was matched to the observed AutoAnalyzer record by varying the volumes of the chambers and the passive exchange rates. This simple model provides an accurate description of the observed creatinine concentration and output and therefore can be used either as a building block in more extensive descriptive systems or as a basis for summarizing and comparing data obtained under varied physiological or pathological conditions.