Assessment of renal perfusion impairment in a rat model of acute renal congestion using contrast-enhanced ultrasonography.

Renal congestion is caused by elevated central venous pressure (CVP), and decreases glomerular filtration in patients with congestive heart failure. Since real-time contrast-enhanced ultrasonography (CEUS) using microbubble-based contrast agents can visualize the perfused microvascular bed, we sought to evaluate the impairment of renal perfusion during acute renal congestion with CEUS. In Wister rats, CEUS of kidney was performed with the direct monitoring of CVP and intra-renal pressure (IRP). When CVP was elevated to 10 and 15 mmHg after the bolus injection of normal saline via the femoral vein, peak intensity (PI, dB) and time to PI (TTP) in the renal cortex and medulla were compared with control rats. There was a strong correlation between IRP and CVP (r = 0.95, p < 0.0001). In the congestion model, more time was required for enhancement of the parenchyma, especially in the medulla compared to control; TTP of the medulla and cortex at 15 mmHg CVP (CVP15) was significantly prolonged compared with controls (medulla, 4351 ± 98 vs. 1415 ± 267 ms, p = 0.003; cortex, 3219 ± 106 vs. 1335 ± 264 ms, p = 0.005). In addition, medullary PI at CVP15 decreased, but not significantly, compared to those of controls and at 10 mmHg CVP (20.1 ± 0.9, 22.8 ± 1.6, 21.6 ± 0.2 dB). In contrast, cortical PIs at CVP15 were significantly lower than that of control (24.6 ± 1.0 vs. 31.4 ± 1.0 dB, p = 0.007). CEUS revealed that impaired renal parenchymal flow in an acute congestion model is accompanied with increased renal interstitial pressure.