Evaluation of 133Xe washout kinetics by controlled pig liver perfusion in vivo

Abstract

The interpretation of multiexponential curves from hepatic tracer washout for estimation of hepatic blood flow (THBF) was investigated, using hepatic 133Xe washout during controlled portal and arterial perfusion of liver in anesthetized pigs. Variations of (1) THBF from 25 to 210 ml/min × 100 g, (2) the proportion of portal to arterial flow, and (3) the site of tracer application were performed. After portal injection the tracer curves were in most cases multiexponential; their analysis revealed that calculation of THBF using k values based on the monocompartmental hypothesis always grossly overestimated total flow. Estimation of THBF by height/area ( H A ), however, reflected the total flow in all cases. Only when hypoventilation or elevation of hepatic venous pressure was performed, did calculation of THBF from k values and H A values reveal similar results. THBF when estimated from H A and from indocyanine green dye extraction gave identical results, both in the controlled perfused liver and in the intact animal. Washout curve analysis after arterial Xe application showed neither a correlation with the total nor with the arterial flow, indicating incomplete mixing of both blood flow components. It is concluded that liver perfusion is multicompartmental and blood flow through the portal and arterial vascular bed is incompletely mixed. Therefore, THBF can be calculated only after portal tracer injection and when the mean transit time concept is applied.