1476 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



0.1 







Abstand von N/erenoberfldche 



_l_ 



8 



10 



1Z 



It 



16 mm 



fig. 21. Zonary temperature gradients in the dog kidney (ordinate: AT compared to arterial blood; 

 abscissa: depth from kidney surface in mm). Rindenzone: cortical zone; Rinde-Markzone: juxta- 

 medullary zone; obere Markzone: upper medullary zone; untere Markzone: deep medullary zone. 

 [After Janssen & Grupp (151).] 



5,0 



f,0 



3,0- 



2,0 



1,0 



20 



to 



60 



80 



100 



fig. 22. Heat turnover in sec (abscissa) related to renal blood 

 flow in ml/g/min (ordinate). [After Grupp & Janssen (117).] 



Swann (342) has postulated, based in part on 

 estimates and in part on direct measurement of 

 intrarenal, arcuate vein, and renal vein pressure, 

 the hydrostatic pressures which probably exist in the 

 dog kidney. The estimates appear in figure 23. The 

 relatively high capillary pressures, compared to that 

 of the rat, may be due to the higher intrarenal pres- 

 sure recorded in the dog, 16 to 26 mm Hg, compared 

 to an average of 10 mm Hg in the rat. 



Critical Closure; Yield Pressure 



The term "critical closing pressure" (CCP) was 

 introduced by Burton (46) in his analysis of the physi- 

 cal factors controlling the equilibrium of small blood 

 vessels. Critical closing pressure is defined as the 

 arterial pressure in a local vascular bed at which 

 flow through the area becomes zero. When flow is 

 plotted against pressure, there is a positive intercept 

 on the pressure axis when flow is zero. It has been 

 suggested that CCP is dependent on vasomotor tone, 

 and hence can be used as an index of this tone. Its 

 relation to intrarenal tissue pressures becomes of 

 interest in connection with the latter's role in the 

 phenomenon of autoregulation of renal blood flow. 



Measurements of the so-called CCP for the kidney 



o 



have been made in cats by Yamada & Astrcim (4, 

 352), and in dogs by Hinshaw et al. (141). The tech- 

 nique involves perfusion of the in situ or isolated 

 organ by pump or from a reservoir at stready pres- 

 sures. Arterial and venous pressure are measured 

 with optical manometers or electromanometers. 

 Venous outflow is recorded. The decay gradients of 

 pressure and flow are recorded during brief occlusion 

 for an arbitrary period lasting 2 to 2.5 min as employed 



O 



by Yamada and Astrom or until pressures have 

 plateaued (Hinshaw et al.) and flow has stopped. 

 At the end of this time, arterial (Pa,) and venous 



