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HANDBOOK OF PHYSIOLOGY ^ CIRCULATION II 



for the kidney circulation by Selkurt (271) connoted 

 an element of the viscous properties of the blood 

 looked upon as a fluid manifesting plastic flow. 



Intrarenal Pressure 



Such pressures have been obtained, with minor 

 variations in technique among various investigators, 

 by insertion of small-gauge needles (no. 24-27) into 

 the renal substance to varying depths, introduction 

 of small volumes of saline (0.1-1.0 mm 3 ) through 

 the needle tip, and reading the stabilized pressure 

 with low volume-displacement manometers. What 

 this pressure represents is debatable and probably 

 cannot be interpreted as interstitial pressure in the 

 classical sense. De Langen (71) has reviewed the 

 vagaries of renal interstitial pressure measurement. 

 The small pool of fluid immediately surrounding the 

 tip of the needle probably represents pressure from 

 damaged blood vessels, tubules, glomeruli, and lym- 

 phatics. Since it best reflects changes in venous pres- 

 sure, it would appear that these vessels are the usual 

 sites of entry. Swann et al. (302) have shown that 

 intrarenal pressure and arcuate vein pressure are 

 equal (coefficient of correlation 0.85) in a range of 

 intrarenal pressures of 6 to 73 mm Hg. 



Although in the strictest sense this should perhaps 

 only be called "needle" pressure, a designation pre- 

 ferred by Winton (343), Gottschalk (in, 112) has 

 chosen to call it interstitial pressure. Others have 

 designated it as "intrarenal pressure" (IRP), a term 

 preferred here in the belief that it reflects directly or 

 indirectly renal interstitial pressure as a part of the 

 integrated pressure which is recorded by the needle- 

 puncture technique. Renal interstitial pressure has 

 been considered to be the resultant of a number of 

 component factors: a) intravascular pressure and 

 volume, b) glomerular filtrate and urine volume, c) 

 external renal capsule elasticity, d) Bowman's capsule 

 volume and elasticity, and e) stroma rigidity. 



Winton (340-342) has employed an indirect method 

 to measure intrarenal pressure, which he has defined 

 as a pressure exerted in all directions throughout the 

 substance of the organ, tending to obliterate collapsi- 



table 4. Intrarenal Pressure (mm Hg) in Dog Kidney 



ble structures such as peripheral parts of tubules and 

 venules. In isolated dog kidneys, intrarenal pressure 

 was taken to approximate ureteral pressure when the 

 latter was elevated to a degree which caused a de- 

 crease in urine flow. 



Needle pressures for the dog kidney are summarized 

 in table 4. 



Gottschalk found the IRP somewhat lower in 

 smaller animals (rats, guinea pigs, rabbits, and cats), 

 averaging 10 mm Hg (4-19) in 65 animals, a value 

 equal to that found in dogs by Winton when he 

 employed his indirect method (340). 



FACTORS WHICH MODIFY INTRARENAL PRESSURE. Relation 



between venous pressure and IRP. When venous pressure 

 was raised by graded compression of the renal vein in 

 12 rats, rabbits, and dogs, the IRP was not affected 

 until venous pressure approached the pre-existing 

 intrarenal pressure, which then began to rise (111). 

 At renal venous pressures above 20 mm Hg, IRP 

 followed venous pressure very closely and was at most 

 1 or 2 mm Hg more than venous pressure through a 

 range exceeding 100 mm Hg. The results of Swann 

 et al. (300) in the dog were very comparable, except 

 that IRP started at a higher control value (25 mm 

 Hg). 



Relation of ureteral pressure and intrarenal pressure. 

 Increased ureteral pressure probably increases IRP 

 by compressing the intrarenal veins (111). In 12 

 rabbits and dogs elevating the ureteral pressure to 15 

 and 30 mm Hg raised the IRP from a control average 

 of 10 mm Hg to averages of 14 and 19 mm Hg, 

 respectively. Elevating ureteral pressure to 50 mm 

 Hg increased IRP from a control value of 8 to 2 1 mm 

 Hg in 11 rabbits and from 12 to 27 mm Hg in 4 

 dogs. Ureteral pressure is about half as effective as 

 venous pressure in elevating IRP. 



Arterial pressure influence on intrarenal pressure. Results 

 of different investigators are quite discordant. Winton 

 (341) in a range of 80 to 100 mm Hg found no con- 

 sistent change in IRP by the indirect method. The 

 other workers used needle punctures. Gottschalk 

 (111) observed no effect until mean arterial pressure 

 was reduced below 40 mm Hg, when IRP fell 

 abruptly. Miles & DeWardener (206) found that as 

 mean arterial pressure was decreased from 1 20 to 20 

 mm Hg in dogs by clamping the aorta, IRP fell from 

 27 to 10 mm Hg. Hinshaw et al. (143-145) also found 

 IRP varied with arterial pressure in the zone of 

 autoregulation. Swann et al. (301) found the best 

 correlation; a plot of IRP against arterial pressure 

 exhibited a coefficient of correlation of 0.85, and 



