I 41 2 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



vein, or jugular vein of dogs after placing loose liga- 

 tures around the portal vein, hepatic artery, and 

 inferior vena cava. After approximately 3 sec the 

 ligatures were tied and the liver removed immedi- 

 ately, transverse sections cut and "wet ashed," and 

 radioactivity determined on the measured aliquots. 

 After injection into the jugular vein, the radioactivity 

 was found uniformly distributed through the liver 

 from right to left. Three-quarters of the radioactivity 

 appeared in the left side of the liver after injection into 

 the splenic vein, and approximately the same pro- 

 portion appeared on the opposite side after injection 

 into the mesenteric vein. Each observation was made 

 but once, under anesthesia, with the abdomen open 

 and after extensive manipulation of the viscera. 

 Hence, application of these data to the situation in 

 man is most uncertain. Nonetheless, there has been a 

 tendency among clinicians to explain the distribution 

 of pathology in human hepatic disease on this basis. 



Barnett & Cochrane (23) have recently pointed 

 out the importance of species and individual anatomic 

 peculiarities in altering lamination. Experiments on a 

 model system proved helpful in evaluating these 

 effects of branching and convergence of tributaries 

 upon the distribution of streamlines at varying rates 

 of flow with different perfusates. For branches like 

 those at the hilum of the liver, they found that the 

 chance that particles in the major trunk "remote 

 from the branch would pass into it are greater with 

 increasing viscosity and decreasing width of the 

 branch," the angle of outflow having little significance 

 at the rates of flow usually prevailing. Thus, for a 

 fluid like blood, small branches would seem likely to 

 be perfused by a fairly representative sample of the 

 total inflow. "Moreover, the manner of formation of 

 the portal vein is important. Where it is formed by a 

 tributary joining a straight main vein (Y) particles 

 are more likely to pass across the portal vein when the 

 rate of flow in the tributary is large and its diameter 

 small. The converse is true where the portal vein is 

 formed by the symmetrical union (Y) of a major and 

 minor tributary, unless the rate of flow in the minor 

 tributary is very high. In both types of junction more 

 crossing-over of the streams occurs when the angle of 

 union is larger than when it is acute." 



Although these considerations are of importance it 

 is probable that local movements of vessels are of 

 even greater significance in determining the extent 

 to which the blood streams commingle in the portal 

 vein in the intact animal and man. In the anesthetized 

 dog secured in the dorsirecumbent position, with the 

 abdomen open and respiratory movements mini- 



mized, it is not surprising that lamination may be 

 detected in the inferior vena cava (132). And even 

 under these circumstances Cole and his associates 

 (89) found that I 131 -labeled rose bengal was uniformly 

 distributed in the liver following injection into four of 

 the different divisions of the portal vein draining the 

 spleen, small intestine, cecum, and colon of the dog. In 

 intact man and dog it has proved a much more elu- 

 sive phenomenon. Portal venography by intrasplenic 

 injection of contrast substance has usually failed to 

 show much evidence of "physiological bilaterality." 

 Streamlining or a filling defect in the shadow of the 

 portal vein at the point of entry of the superior mes- 

 enteric vein attributable to lateral filling by radio- 

 lucent blood from the mesenteric vein has been 

 reported (15, 116) but it is by no means a constant, or 

 even a frequent observation. Indeed, Patrassi and his 

 colleagues (229) claim that injection of contrast sub- 

 stances into the spleen tends rather to make the right 

 lobe more opaque than the left. In addition, they 

 found no significant difference between the transit 

 times from spleen to each of the two lobes when small 

 amounts of sodium para-aminohippurate or red blood 

 cells labeled with radioactive phosphorus were in- 

 jected into the spleen of human subjects. Similar 

 studies in dogs yielded the same results. Incomplete 

 portal venous admixture may therefore be regarded 

 as a potential but unlikely result of the viscous 

 properties ot blood. Hemodynamically it is important 

 chiefly with respect to the movement of red cells and 

 variation of hematocrit within the splanchnic and 

 hepatic vessels. 



Volume and Distensibility 



The potential volume of the vasculature which 

 houses the "circulating blood" of the splanchnic bed 

 may be analyzed dimensionally with the data pub- 

 lished by Mall (206) which have already been 

 employed in determining the major points of vascular 

 resistance. Using data for the length of vessels in the 

 mesenteric circuit from the work of Schleier (261), 

 and estimates of vascular lengths in the liver, the 

 total volume of each vascular category may be com- 

 puted as for cylinders. The internal volume of hepatic 

 and mesenteric arterial inflow tract in a dog of 

 "medium size" (liver weight — ca. 175 g) was found 

 by this means to amount to 4.1 ml; the mesenteric 

 and portal venous systems, 42.6 ml; the sinusoids, 

 32.3 ml; and the hepatic venous outflow tract, 

 4 1. 1 ml. Thus the arteries accounted for some 3.3 per 

 cent of the total, the sinusoids and mesenteric capil- 



