99 6 



HANDBOOK OF PHYSIOLOGY 



CIRCl I .ATION II 



5 10 15 20 



CAPILLARY PRESSURE - cm woter 



fig. 6.6. Effects of severe chemical injury on fluid move- 

 ment through walls of frog's mesenteric capillaries. Slope of 

 lower regression line shows filtration coefficient, k c , for normal 

 capillaries. Slope of upper regression line indicates the 7-fold 

 increase of filtration coefficient found after injury. Filled circles 

 refer to injury by io^i alcohol in Ringer's fluid; plus signs, 

 to 1:10,000 mercuric chloride in Ringer's fluid. [From Landis 

 (200).] 



increased from the normal value of 0.0056 to ap- 

 proximately 0.0390 y? per sec per p* of capillary wall 

 per cm water of capillary pressure, indicating a 

 sevenfold increase of hydrodynamic conductivity. 

 Increased permeability of the injured wall to plasma 

 proteins is indicated by the absence of absorption even 

 at low capillary pressures and by the reduction of the 

 in vivo osmotic pressure of the plasma proteins from 

 the normal value of 1 1 cm water to between 3 and 4 

 cm water. Thus the effects of severe injury are a) in- 

 creased filtration, b) absence of absorption, c) reduced 

 effective osmotic pressure of the plasma proteins, 

 and d) eventual cessation of flow in any capillary 

 injured to the point of stasis. Diffusion rates have not 

 been measured in such capillaries. Presumably, since 

 capillary permeability to fluid and protein is greater, 

 net diffusion of small molecules should be increased 

 as long as blood flow continues. However, since net 

 diffusion is flow limited, its effectiveness in exchanges 

 of substances will decline as flow decreases and will 



soon cease in those capillaries that are filled with 

 stationary, closely packed erythrocytes. 



capillary pressure in injury. The appearance of 

 edema in injured regions is due primarily to increased 

 capillary permeability, but is enhanced by increased 

 capillary blood pressure. Local injury elevates capil- 

 lary blood pressure by at least two mechanisms: /) 

 the vasodilatation and increased blood flow which 

 are parts of the triple response to injury described by 

 Lewis (217), and 2) the temporary blockage of 

 capillary blood flow and passive congestion produced 

 by stasis (199). 



Application of a minute silver nitrate crystal to the 

 skin of the frog's web increases capillary pressure in 

 the neighborhood of the lesion to peak values which 

 are as much as double the earlier control values (205). 

 Within 10 to 20 min capillary pressure is again 

 within the normal range. In human skin the flare of 

 the triple response produced by histamine is accom- 

 panied by peak capillary pressures of 10 to 25 mm 

 Hg above preceding control values (203), but again 

 with relatively prompt return to control values. The 

 onset and duration of these elevations suggest that 

 they are a part of the flare due to the "axon reflex." 



Elevations of capillary blood pressure are also 

 found in capillaries injured to the point of stasis. 

 These elevations are more important in the formation 

 of edema fluid during injury because they occur in 

 vessels, the walls of which are permeable to protein 

 and hence already the site of rapid filtration without 

 any balancing absorption. Figure 6.7 shows the cycle 

 of pressure changes which occurred in one experi- 

 ment involving stasis and recovery. Control capillary 

 blood pressure, with normal blood flow, ranged from 

 12 to 15 cm water. At the time marked A 25 per cent 

 urethan was applied to the mesentery and the onset 

 of stasis, as indicated by visible loss of plasma, was 

 clearly present at B. The sharp rise of capillary pres- 

 sure between B and C occurred as the venous end of 

 the capillary was filled and blocked by packed 

 erythrocytes. As flow ceased capillary pressure rose 

 rapidly to approach the pressure in the feeding 

 arteriole. At C a pressure of 22.5 cm water merely 

 stopped the advance of erythrocytes toward the 

 pipette. Even 30 cm water did not move the cor- 

 puscles away so that capillary blood pressure was 

 well in excess of the 22.5 cm charted. The very rapid 

 filtration observed during this period is due, there- 

 fore, to increased permeability and also to high 

 capillary pressure. Between C and D this enhanced 

 filtration of whole plasma packed erythrocytes 



