AN ANATOMIC AND PHYSIOLOGICAL MODEL OF HEPATIC VASCULAR SYSTEM

Hepatic function can be characterized by the activity/time curves obta ined by imaging the aorta, spleen, and liver. Nonparametric deconvolut ion of the activity/time curves is clinically useful as a diagnostic t ool in determining organ transit times and flow fractions. The use of this technique is limited, however, because of numerical and noise pro blems in performing deconvolution. Furthermore, the interaction of par t of the tracer with the spleen and gastrointestinal tract, before it enters the liver, further obscures physiological information in the de convolved liver curve. In this paper, a mathematical relationship is d erived relating the liver activity/time curve to portal and hepatic be havior. The mathematical relationship is derived by using transit time spectrum/residence time density theory. Based on this theory, it is s hown that the deconvolution of liver activity/time curves gives rise t o a complex combination of splenic, gastrointestinal, and liver depend encies. An anatomically and physiologically plausible parametric model of the hepatic vascular system has been developed. This model is used in conjunction with experimental data to estimate portal, splenic, an d hepatic physiological blood flow parameters for eight normal volunte ers. These calculated parameters, which include the portal flow fracti on, the splenic blood flow fraction, and blood transit times are shown to adequately correspond to published values. In particular, the mode l of the hepatic vascular system identifies the portal flow fraction a s 0.752 +/- 0.022, the splenic blood flow fraction as 0.180 +/- 0.023, and the liver mean transit time as 13.4 +/- 1.71 s. The model has als o been applied to two portal hypertensive patients. The variation in s ome of the model parameters is beyond normal limits and is consistent with the observed pathology.