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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



what probably remains to this day the most complete 

 study of the flow of blood through the mesenteric 

 organs. He placed a stromuhr in the portal veins of 

 dogs anesthetized with ether and obtained a mean 

 blood flow divided by the mean body weight of 14.3 

 kg of 19 ml per min per kg. His animals had relatively 

 low arterial blood pressures, the average being about 

 100 mm Hg, and a normal mean portal vein pressure 

 of 1 1 mm Hg. 



In several subsequent studies made with thermo- 

 stromuhrs, values between 16 and 20 ml per min per 

 kg were obtained. These include Grab et al. (59), 

 Soskin et al. (128), Grodins et al. (71), and Grindlay 

 et al. (70). Some of the dogs used were unanesthetized; 

 others were anesthetized with such agents as ether, 

 chloralose, or sodium pentobarbital. Arterial blood 

 pressure was given only in the report of Grab et al., 

 the mean being 100 mm Hg. 



These investigations were performed with in- 

 struments which have since been severely criticized, 

 the stromuhr because it introduces a flow resistance 

 into the vessel in which it is placed and the thermo- 

 stromuhr for a variety of reasons [see, for example, 

 Gregg (68)]. 



MacLeod & Pearce (97) cannulated the thoracic 

 vena cava of ether-anesthetized dogs, occluding it 

 above and below the entrance of the hepatic veins 

 with balloons, and collected the outflow before and 

 after portal vein ligation. The mean total liver outflow 

 in animals with an arterial blood pressure of about 

 140 mm Hg was 44 ml per min per kg. This was 

 reduced by 60 per cent upon portal vein occlusion, 

 indicating that the usual flow through the latter was 

 about 26 ml per min per kg. Blalock & Mason (17) 

 used a somewhat similar technique in unanesthetized 

 dogs to measure the hepatic venous outflow im- 

 mediately after hepatic arterial ligation and ob- 

 tained a mean value of 24 ml per min per kg. 



Electromagnetic flowmeters have been placed on 

 the portal vein by several groups of investigators. 

 Stewart et al. (129) and Drapanas et al. (41) found 

 the mean portal flow to be 25 ml per min per kg at 

 arterial pressures of about 140 mm Hg. Green et al. 

 (66) obtained a lower value, 1 7 ml per min per kg, 

 but the mean arterial pressure of their animals was 

 only slightly above 100 mm Hg. 



Direct measurements of portal venous flow by 

 cannulation and collection of the blood was made 

 by Heimburger et al. (75). They obtained a mean 

 value of 30 ml per min per kg; however, since they 

 collected the blood by gravity thus producing an 



unphysiological, negative pressure in the portal vein, 

 it seems likely that this value is too high. 



The highest value for portal venous flow has been 

 reported by Sapirstein (114). He injected radio- 

 potassium and radiorubidium into both rats and 

 dogs and observed that the concentration of these 

 isotopes in all organs except the brain remained 

 nearly constant for a period of approximately 10 to 

 60 sec after injection. He concluded that the ex- 

 traction ratios for these substances must necessarily 

 be the same for all the organs, and hence that the 

 fraction of injected isotope found in any organ was 

 equal to the fraction of the cardiac output passing 

 through the organ. By adding the isotope contents 

 of the organs drained by the portal vein, Sapirstein 

 found that 20 per cent of the cardiac output passed 

 through them, a value which agrees well with the 

 findings of the previous workers. However, when 

 Sapirstein converted this value to units of flow per 

 unit body weight, he obtained 34 ml per min per kg. 

 The discrepancy arises from the fact that his dogs 

 were small (6-8 kg) and had a mean cardiac output 

 by the K 42 -dilution technique of 170 ml per min per 

 kg. In the larger animals used by most investigators 

 (12-20 kg) the cardiac output is usually about 125 

 ml per min per kg, 20 per cent of which is 25 ml per 

 min per kg. 



The discrepancies among portal venous flows ob- 

 tained by various workers would seem in large part 

 to have been due to differences in arterial pressures 

 rather than to the measurement procedures. The 

 workers who found values of about 25 ml per min 

 per kg studied dogs having arterial pressures of 

 about 130 mm Hg, while those who observed 18 or 

 19 ml per min per kg used animals with pressures 

 of about 100 mm Hg. It would appear that the portal 

 venous blood flow in dogs of 10 to 20 kg body wt 

 having a "normar' arterial pressure of 130 mm Hg 

 is about 25 ml per min per kg. This is equivalent to 

 about 20 per cent of the cardiac output or approx- 

 imately 350 to 450 ml per min in a 15-kg animal. It 

 does not seem that this value is too much affected by 

 anesthesia with a variety of agents. 



A very few measurements of total portal flow in 

 other species can be found in the literature. Sapirstein 

 and co-workers (109, 113, 133) in three separate 

 studies found the portal flow in rats anesthetized with 

 sodium pentobarbital to be 14, 16, and 20 per cent 

 of the cardiac output. Fegler & Hill (44) using a 

 thermodilution technique in sheep obtained a very- 

 high portal flow of 31 per cent of the cardiac output; 

 however, as they pointed out, members of this 



