Journal of Applied Physiology, Vol 40, Issue 2 164-170, Copyright © 1976 by American Physiological Society
Mechanical properties of the dog renal capsule
L. A. Herbert, W. C. Chen, A. Hartmann and J. C. Garancis
The renal capsule is an important determinant of whole kidney
volume/pressure relationships. To gain further insights into its possible
role we examined the mechanical properties of the dog renal capsule using
standard materials testing procedures. From each of four locations on the
kidney surface, the following mechanical properties of the renal capsule
were determined: elastic modulus (force/unit of cross-sectional area
theoretically required to double the length of the specimen), tensile
stiffness (force/unit width theoretically required to double the length of
the specimen), ultimate strength (stress at time of fracture of the
specimen), and maximum strain (percent strain at time of the fracture of
the specimen). We found that the elastic modulus of the renal capsule from
all capsular sites was substantially greater than values previously
reported for dog aorta. The stiffness of the capsule covering the
anterior-posterior surface of the kidney was found to be about 50% greater
than the stiffness of the capsule covering the lateral and polar surfaces
of the kidney. The ultimate strength of the anterior-posterior capsule was
significantly greater than that of the lateral or polar capsule. This
finding may explain the clinical observation that the spontaneous rupture
of the renal capsule and parenchyma associated with the acute swelling of
transplant rejection is confined almost exclusively to the lateral and
polar portions of the renal capsule and cortex. The mean maximum strain at
each capsular site was about 35%. This degree of circumferential expansion
corresponds to about a doubling of kidney volume. Thus, this observation
suggests that the renal capsule is at risk to undergo spontaneous rupture
when renal volume increases of this magnitude are observed.
