Functional Assessment of the Circulation of the Single Kidney

Abstract

Abstract-Functional alterations in the renal circulation that can contribute to abnormal renal perfusion have been demonstrated in various models of renal injury. To detect impairments in renal vascular function, renal flow reserve can be determined by repeated measurements of renal blood flow (RBF) during pharmacological challenge with short-acting vasodilators that should increase RBF in kidneys that are not severely damaged structurally. Among the invasive techniques for such measurements, the most readily available is probably the intravascular Doppler, which can be employed during renal angiography for rapid evaluation of changes in RBF during intrarenal injections of vasoactive substances. High-resolution tomographic imaging techniques, like electron-beam x-ray computed tomography, further offer the potential for noninvasive measurements of renal parenchymal perfusion and function, in association with either intrarenal or systemic injections of vasoactive substances. Acetylcholine is a potent short-acting renal vasodilator that can be useful to assess the response of the renal microcirculation, define renal flow reserve, and examine the endothelium-dependent responses of RBF. Such assessments of the function of the renal circulation can assist in evaluation of patients with systemic or renal disease for early detection and monitoring of renovascular injury. Key Words: renal circulation Ⅲ renal blood flow Ⅲ computed tomography Ⅲ acetylcholine U nder normal conditions, basal renal vascular tone is well regulated by many vasoactive systems that keep renal blood flow (RBF) in equilibrium, 1 including the endothelium-derived relaxing factor NO, prostaglandins, and the reninangiotensin system. 2 Therefore, at an early stage of renal disease, RBF may be normal, and impaired renal vascular tone may become evident only as an attenuated response during stimulus with vasoactive substances or physiological challenges. The mechanisms of the attenuated response have been postulated to include decreased release of vasodilators (eg, NO, prostaglandins) and co-existing vasoconstrictors (eg, thromboxane, angiotensin II), which may be released or rendered unopposed during challenge. The altered functional response may precede structural renal damage and can serve as a marker for abnormal handling of daily challenges by the kidney. Such impairment has been demonstrated in various models of renal injury, like hypertension, hypercholesterolemia, renal artery stenosis, ischemia and reperfusion, acute renal failure, diabetes mellitus, and aging. Hence, utilization of vasodilators to examine renal flow reserve (RFR) can serve to disclose subtle functional vascular alterations 3 and may allow early detection and monitoring of renovascular injury. For example, residual responsiveness of the intrarenal circulation to challenge may also reflect renal viability and may conceivably predict success of subsequent therapy (eg, revascularization).Evaluation of the reactivity of the single-kidney circulation entails rapid and successive meas...

Correlation between noninvasive and endovascular Doppler in patients with atherosclerotic renal artery stenosis: A pilot study

“…Regulation of the renal circulation depends on resistance changes of arterioles, afferent and efferent vessels in response to neural, intrarenal, and humoral inputs such as nitric oxide, prostaglandins, and the renin‐angiotensin system [17, 18]. Renal disease, whether the result of hypertension, hyperlipidemia, diabetes mellitus, aging, or renal artery stenosis, may produce subtle alterations in control of vascular tone.…”

“…Renal disease, whether the result of hypertension, hyperlipidemia, diabetes mellitus, aging, or renal artery stenosis, may produce subtle alterations in control of vascular tone. These derangements may become apparent by assessing the response of the renal circulation to challenge with vasoactive substances [18]. Ordinarily, the renal circulation is robust and demonstrates a significant flow reserve [11, 19].…”

MECHANISMS MEDIATING PRESSURE NATRIURESIS: WHAT WE KNOW and WHAT WE NEED TO FIND OUT

“…Ideally, these methods should provide quantitative measurements of blood flow normalized for tissue mass or volume, on a whole‐kidney basis and also on the basis of anatomically defined kidney regions. The recent application of fast computed tomography to this issue has provided just such a method, 74 which can also, theoretically, be applied to human studies 75 . Magnetic resonance imaging techniques have also shown some promise for use in the determination of regional kidney perfusion in experimental animals and humans, although, at present, the resolution of these techniques is rather low 76,77 .…”

Acetylcholine-induced vasodilation in the perfused kidney of the streptozotocin-induced diabetic rat: role of prostacyclin

“…Thus, EDRFs distinct from NO may mediate part of the ACh-induced vasodilation. Although ACh is known to be a potent vasodilator of the renal vasculature (Ito et al, 1991;Hayashi et al, 1992;Lerman and Rodriguez-Porcel, 2001), the mechanisms mediating this response have not been clearly defined.…”