984 



HANDBOOK OF I'll YSIOl ( >< ,Y 



CIRCULATION II 



at the end of absorption and about to enter the 

 lymphatic system. Pappenheimer & Soto-Rivera 

 (282) have pointed out that the diffusion coefficients 

 of the plasma proteins are such that in the absence of 

 flow or mechanical movement relatively large con- 

 centration gradients are possible in the interstitial 

 fluid compartment. "'Even if all filtration and absorp- 

 tion processes were stopped, some 20 minutes would be 

 required to reach 90 per cent equalization of protein 

 concentration over a distance of 50 microns" (282). 

 In perfused limbs of cats the average protein osmotic 

 pressure of interstitial fluid was 1.4 ± 0.4 mm Hg, 

 corresponding to an average protein concentration of 

 0.7 ± 0.2 g per 100 ml. 



The average concentration of proteins in inter- 

 stitial fluid can also be estimated by a totally different 

 method. The dilution of labeled plasma albumins and 

 globulins after intravenous injection has shown that 

 the total mass of exchangeable plasma protein is 

 about twice the mass of plasma proteins in the blood 

 stream itself (103, 117). Sterling (352) found in man 

 that the average intravascular albumin averaged 

 117 g, the extracellular albumin, 147 g. Assuming 

 extravascular fluid volume to be the usual 15 per 

 cent of body weight, the average albumin concentra- 

 tion in extravascular fluid was calculated to be 1 .4 g 

 per 100 ml. By using Myant's figures (259) to estimate 

 globulin content in addition, the total average protein 

 concentration for extravascular fluid becomes ap- 

 proximately 2.1 g per 100 ml, which corresponds to 

 an average protein osmotic pressure, or LI,/, of 5 

 mm Hg. Similar calculations applied to the data of 

 Wasserman et al. (368, 372) yield slightly lower figures, 

 because in the dog the fraction of albumin and 

 globulin found normally in the interstitial fluid and 

 lymph appears to be rather less than that found by- 

 Sterling for albumin in man. Both estimates are 

 larger than those given by Pappenheimer and Soto- 

 Rivera (282) for the perfused leg of dogs as expected, 

 because the determinations made by the perfusion 

 method were restricted to the fluid in the immediate 

 vicinity of the capillaries and were limited to the 

 limb, both factors tending to give lower values. On 

 the other hand, calculations based upon exchangeable 

 protein mass include protein in the whole of the inter- 

 stitial fluid plus that in the lymphatics. In addition, 

 they include the extravascular fluids of the liver and 

 intestines where lymph is known to contain large 

 amounts of protein. Both factors tend to make the 

 figure for average LT,y greater for the whole body than 

 for the limb alone, but still not as high as that prob- 

 ably present in the liver and intestines. 



With this qualification it can be concluded that 

 LT,, lies between 0.1 and 5.0 mm Hg, with the lower 

 value applying to capillary filtrate in the limbs and 

 the higher including the total interstitial fluid of liver 

 and intestines, as well as lymph. This can be com- 

 pared to P,, which ranges from 1 to g mm Hg, with 

 the lower values in subcutaneous tissues and skin, the 

 higher values in muscle. The formulation given in 

 equation 1 . 1 can now, with certain license for pur- 

 poses of summary, be provided with very approxi- 

 mate values in mm Hg for man at heart level and 

 under resting conditions, viz. : 



FM. - 

 + - filtration 



k(P 

 c 



32 



pi 



p „ *v 



25 I to 9 0.1 to 5 



- - absorption 15 



With equal or greater license an average limb 

 capillary and lymphatic can be drawn, as in figure 5. 1 , 

 to summarize the filtration-absorption process as it 

 may operate to produce a small volume of lymph 

 with relatively high protein content. Table 5. 1 

 provides a schematic summary of the changes that 

 occur in the fluids of the limb during several of the 

 more thoroughly studied functional states. Ranges of 

 determined values are given whenever possible. 

 Figures in parentheses are values that can reasonably 

 be inferred on the basis of available evidence. They 

 are given merely to show the probable direction of 

 presumed change and its order of magnitude. In 

 some instances even inferences are impossible, as 

 indicated by a question mark. The columns are 

 given letters to correspond with the schematic 

 capillary in figure 5.1. 



Beginning at the top of the table with control con- 

 ditions and resting blood flow, the composition of 

 capillary filtrate has not been determined, but its 

 protein content may be inferred to be 0.2 to 0.4 g per 

 100 ml from the composition of capillary filtrate pro- 

 duced during mild venous congestion in man and 

 dog. The average protein content of interstitial fluid 

 ranges from 0.7 g per 100 ml in perfusion studies 

 (281) to 2.1 g per 100 ml by calculation from extra- 

 vascular protein mass. Lymph protein content range 

 from 1.3 to 3.3 g per 100 ml (386) and the volume 

 flow is small, requiring massage or passive movement 

 for collection of samples (76) as would be expected 

 with the absorption that occurs under resting condi- 

 tions. 



Conversely, in venous congestion the protein con- 

 centration in capillary filtrate is known but the 

 average and highest concentrations in interstitial 



