Effect of increased renal pelvis pressure on the kidney of young pigs

Objective To study what impact the elevated intrarenal pelvic pressure (IPP) may have on the childhood kidney. Methods The childhood Guizhou miniature pigs were taken as the subjects and the elevated IPP animal models were established. The IPP pressure was set at levels of 0, 30, 60, 90 mmHg (1 mmHg=0.133 kPa). After the contrast agent was administered intravenously, the left renal cortical microvasculature blood perfusion was measured using contrast-enhanced ultrasonography (CEUS) at each pressure level respectively for 5 minutes. The retrograde pyelography by CEUS was performed at each pressure level for 5 minutes on the same side after the renal cortical microvasculature blood perfusion measurement. Finally the left kidney specimens were sent for pathology. Statistical study was performed on the cortical microvasculature perfusion difference between the various IPP level of 0, 30, 60, 90 mmHg. Results In the 10 repetitions, analysis of variance suggested the Peak intensity (PI) under 4 IPP levels was not all the same statistically (F=58.947, P 0.05); AS for PI, there was statistical difference between the 60 mmHg level and 0 mmHg level (t=5.332, P<0.01). The PI between 0 mmHg level and 90 mmHg level was different statistically (t=10.507, P<0.01). Rank sum test showed that the area under curve (AUC) under four IPP levels was statistically different (χ2=28.876, P<0.01). Compared with AUC under 0 mmHg level, the AUC under 30, 60, 90 mmHg level was statistically different respectively. AS for AUC, there was statistical difference between 0 mmHg and 30 mmHg (Z=-2.497, P<0.05). there was statistical difference between the 60 mmHg level and 0 mmHg level (Z=-2.701, P<0.05). The AUC between 0 mmHg level and 90 mmHg level was different statistically (Z=-2.803, P<0.05). Both the PI and the AUC indicated that the renal blood flow decreased rapidly with the increase of IPP. The retrograde pyelography by CEUS suggested the contrast agent penetrated into the cortex in 60% of subjects, which turned out to be the cortex lacerations in cortex by pathology. The pathology showed fibrin exudation in the Bowman capsule in 70% of specimens. However, all the gross examination for the kidneys suggested no overt rupture. Conclusion Before obvious gross damage emerge the elevated IPP has impacted the kidney microscopically, physiological and pathologically. The hidden injury should be noticed by the clinical staff especially for the young children. Key words: Nephrolith; Intrarenal pelvic pressure; Kidney injury