Mechanical properties of the dog renal capsule

Abstract

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.

Effect of Moderate Daily Exercise on Acute Glomerulonephritis

“…Urine albumin concentration was measured by radial immunodiffusion [19]. Kidney tissue was examined by standard light and electron microscopic tech niques previously described [14].…”

Strain-rate dependent material properties of the porcine and human kidney capsule

“…Employing an established method for capsule sample preparation (Herbert et al, 1976), symmetric samples were delicately excised using a surgical scalpel and a thin copper sheet template (Fig. 2).…”

“…Previous studies have elucidated the histology and quasi-static properties of the renal capsule (Yamada, 1970;Herbert et al, 1976;Farshad et al, 1999). However, due to the inherent viscoelastic properties of biological tissues, these data are not sufficient to accurately predict organ behavior under dynamic mechanical load.…”

“…Since the tissue is a membrane, and does not support bending or compressive loads, this loading modality provides an adequate characterization of the tissue for use in mathematical trauma models. Based upon assumed isotropy (Herbert et al, 1976) and the data obtained in this study, two possible constitutive equations are suggested for implementation of renal capsule material properties into a numerical trauma model.…”

Effect of Expansion of Renal Parenchymal Volume on Renal Function

“…By contrast, much greater increases in renal volume (AV) are present in acutely injured kidneys [1], yet at most, only modest increases in intrarenal pres sure have been found [3-8.14-17], Thus, the compliance (AV/AP) of such kidneys must be greatly increased. Based on our previous ex amination of the volume/pressure relationships of the renal capsule [13], it is clear that this in crease in whole kidney compliance must in volve a marked increase in compliance of the renal capsule. Furthermore, from our study of the decapsulaled kidney [I I], it appears that the compliance of the renal parenchyma must also be greatly increased to account for the marked swelling of acute renal injury.…”