1506 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



peared to be favored at the expense of the rest of the 

 circulation. The cycle could be repeated with addi- 

 tional hemorrhages. Ultimately, peripheral vasocon- 

 striction failed to maintain an adequate systemic 

 pressure, and renal plasma flow and glomerular filtra- 

 tion fell to low values. It was inferred that at this 

 stage afferent arteriolar vasoconstriction closed the 

 renal circulation in an effort to maintain circulation 

 to vital centers. In view of the possible unreliability 

 of the Fick method (C PAB /E PAB ) during hypotension 

 and shock according to Balint & Fekete (8), this in- 

 terpretation may not be warranted. The indirect 

 method gave them much lower values than did the 

 direct, giving the erroneous impression of marked in- 

 crease in renal vascular resistance and marked de- 

 crease in the renal fraction of the cardiac output. 



Corcoran & Page (62) induced hemorrhagic shock 

 in anesthetized dogs by controlled bleeding to main- 

 tain pressure at about 60 mm Hg for 70 min, followed 

 by transfusion. This cycle was repeated two or three 

 times. Clearances (C D or Ci n ) decreased to zero or 

 nearly so during hypotension. Repeated reduction 

 and restoration of blood pressure led ultimately to a 

 permanent reduction in renal blood flow. Since this 

 phenomenon occurred in dogs with denervated kid- 

 neys, it was suggested that the reduced function was 

 the result of appearance in the blood of vasoconstrictor 

 substances. Again, caution must be exercised in inter- 

 pretation because of the unreliability of indirect 

 methods. 



Selkurt (270) noted the persistence of a small flow 

 of blood through the kidneys of anesthetized dogs 

 (direct venous outflow) subjected to hemorrhage of 

 2 to 5 per cent of body weight to bring blood pressure 

 to consecutive 60 and 40 mm Hg pressure stages, 

 held 90 and 45 min, respectively. Clearances could 

 not be followed because of extreme oliguria and 

 anuria. Renal vascular resistance (calculated from 

 direct flow) was not excessively increased early in the 

 60 mm Hg pressure stage period [experimental/ 

 control = avg. 1.15 (0.73-2.07)], possibly because of 

 operation of renal autonomy. But at the end of the 

 period at 40 mm, the ratio averaged 3.04 (1.53-6. 15). 

 Enhanced vasoconstrictor activity as the result of 

 additional hemorrhage, plus increased release of cir- 

 culating pressor materials, such as catecholamines 

 (325) or serotonin (63), could have accounted for the 

 enhanced vasoconstriction. 



On transfusion, renal vascular resistance returned 

 almost to control value, but increased again second- 

 arily as normovolemic shock developed. Terminally, 

 this was as great as 4.7 times the control Because of 



variable degrees of tubular damage, the clearances of 

 PAH and creatinine could not be relied upon for 

 accurate measurement of plasma flow and GFR after 

 transfusion. 



tourniquet and traumatic shock. Allowing for the 

 time factor and sequences of events, the changes in- 

 duced in renal function by tourniquet shock in dogs 

 are much the same as observed after hemorrhage. 

 Corcoran el al. (63) applied leg tourniquets tight 

 enough to block venous return but not necessarily 

 arterial inflow. RPF and GFR progressively fell until 

 at 90 min they were 25 per cent of control. Blood 

 pressure decreased about 25 per cent, with increased 

 hematocrit ratio. On release of the tourniquet which 

 had been in place for 200 min, blood flow might re- 

 cover for a time, then decline again if shock ensued. 

 With development of shock E D , which had remained 

 normal, declined to 0.50. Because flow decreased 

 somewhat, even in the denervated kidney, the vaso- 

 constriction must have been partly of humoral origin. 

 Increased release of serotonin was considered as a 

 possibility. Catecholamine output could have been 

 enhanced. 



The effects of tourniquet application and limb 

 crushing in anesthetized dogs was studied by Eggleton 

 et al. (80), the tourniquets being left in place for 4 to 5 

 hours. On release, blood pressure fell and urine flow- 

 ceased. With gum acacia infusion to restore pressure, 

 the creatinine clearance still remained about one- 

 third of control. The basis for the reduced creatinine 

 clearance was not satisfactorily explained, but afferent 

 impulses to vasomotor centers, and release of humoral 

 substances which might be vasoconstrictor to the 

 kidney could be considered as possibilities. Back 

 diffusion through damaged tubules did not appear 

 likely under the circumstances of their experiment. 

 Fleming & Bigelow (88) made direct visual observa- 

 tions of cortical blood flow of kidneys with crushing 

 injury to the hind legs. They saw agglutination of the 

 cells in vessels of 20 to 30 ju size as large clumps In 

 capillaries, the clumps were seen intermittently ob- 

 structing the lumen, often causing stasis or even ap- 

 parent reversal of flow. 



traumatic injuries in man. Lauson el al. (175) re- 

 ported renal function studies in shock of varied etiolo- 

 gies in man but mostly resulting from hemorrhage 

 and skeletal trauma. Keeping in mind the limitations 

 of the clearance methods for measurement of blood 

 flow and filtration rate under the unfavorable condi- 

 tions that apply in shock, general conclusions emerge 



