9 8o 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



table 4 i . Interstitial Fluid Pressure, P t f, Ranges at Rest 



gastrocnemius and biceps (375)- Very high pressures, 

 up to 85 mm Hg, were found briefly in some muscles 

 during powerful contractions (375), and values lower 

 than average were common during anesthesia, hemor- 

 rhage, surgical operations, and shock (127-129). 



The effects of venous congestion, and consequent 

 filtration, on directly measured P , ; have been highly 

 variable, depending, as might be expected, upon the 



distensibility of the tissue studied. McMaster (239) 

 found pressures up to 32 cm water or 23 mm Hg in the 

 skin of the mouse (fig. 4.3), and up to 23 cm water or 

 1 7 mm Hg in human skin, in good agreement with 

 the calculated interstitial fluid pressures found by 

 Landis & Gibbon (209) in the congested forearm 

 (fig. 4.1). Mayerson & Burch (231) found much 

 lower maximum pressures in subcutaneous tissue of 

 man during venous congestion or during quiet stand- 

 ing, e.g., 5.6 to 8.8 cm water, while intramuscular 

 pressure rose to maxima of 22 cm water in nonfainting 

 subjects and only 1 1 cm water in fainting subjects. 



In isolated, perfused extremities Hyman (162) 

 and Pappenheimer & Soto-Rivera (282) found little 

 interference with prolonged filtration, and hence no 

 evidence of increased interstitial fluid pressure, until 

 manifest edema appeared. Hinshaw & Day (155), 

 however, made direct measurements of P, f in per- 

 fused extremities and found increases from control 

 values of 0.5 and 1.2 mm Hg to 8 and 15 mm Hg 

 when 1+ edema was present and to 10.5 and 24 mm 

 Hg when 2+ edema had appeared. This pressure 

 was enough to produce measurable collapse of blood 

 vessels. If this collapse involves the small veins it may 

 well distort fluid movement through changes in resist- 

 ance to flow, as well as through direct opposition to 

 capillary blood pressure itself. 



Interstitial fluid pressures up to 25 mm Hg help 

 explain the slowness with which edema forms in 

 normal human beings, despite the high capillary pres- 



fig. 4.3. Changes of interstitial fluid 

 pressure in the skin and lower leg of 

 mouse during and after venous con- 

 gestion of 40 mm Hg. Black dots 

 indicate pressure readings which yielded 

 neither inflow into the skin nor back- 

 flow into the apparatus; i.e., the pressure 

 of the extravascular fluid was accurately 

 balanced. Plus signs indicate pressure 

 readings at which fluid moved into the 

 tissues; i.e., pressure in the apparatus 

 was above interstitial pressure. Minus 

 signs show that backflow occurred into 

 the apparatus and that the plotted 

 pressure was lower than that of the 

 extravascular fluid. The interstitial 

 resistance during the control period is 

 shown by asterisks. [From McMaster 

 (239)-] 



320 



30.0 



b 



d 260 



o 



c 22 



O 2 



- 18.5 



4) 



§ 16.0 



<n 150 



g 130 



^ 11.0 



80 

 70 



42 



10 



20 



30 



40 



50 



60 



70 



80 



