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Current Opinion in Nephrology and... Jul 2017Renal arteriovenous oxygen shunting has been proposed as a mechanism by which oxygen supplied to the kidney can bypass the renal parenchyma. Shunting could, therefore,... (Review)
Review
PURPOSE OF REVIEW
Renal arteriovenous oxygen shunting has been proposed as a mechanism by which oxygen supplied to the kidney can bypass the renal parenchyma. Shunting could, therefore, play a crucial role in renal hypoxia and hyperoxia. In the absence of suitable quantitative experimental methods, computational modeling has been employed in recent years to estimate the extent and potential impact of oxygen shunting.
RECENT FINDINGS
Overestimation of the separation distance between arteries and veins was suggested to be responsible for previous findings that only negligible amounts of oxygen are shunted in the preglomerular vasculature. However, models considering the correct separation distance and wrapping of artery-vein pairs still showed shunting at negligible levels of less than 1% of total renal oxygen delivery. The effect of reverse CO2 shunting on the oxygen-hemoglobin dissociation curve was found to impair, rather than promote, preglomerular oxygen shunting.
SUMMARY
Oxygen is unlikely to be shunted along the preglomerular vasculature in sufficient quantities to affect renal oxygenation. There may be substantial shunting at the level of the postglomerular vasculature, but more extensive efforts in structural imaging and computational modeling are needed to quantify it reliably.
Topics: Carbon Dioxide; Humans; Hypoxia; Kidney; Kidney Diseases; Kidney Glomerulus; Oxygen; Oxygen Consumption; Renal Artery; Renal Circulation; Renal Veins
PubMed: 28399018
DOI: 10.1097/MNH.0000000000000332 -
Physiological Reports Oct 2022The maternal cardiovascular system, led by renal volume regulatory responses, changes during pregnancy to ensure an adequate circulation for fetal development and...
The maternal cardiovascular system, led by renal volume regulatory responses, changes during pregnancy to ensure an adequate circulation for fetal development and growth. Circulatory maladjustment predisposes to hypertensive complications during pregnancy. Mathematical models can be used to gain insight in the gestational cardiovascular physiology. In this study, we developed an accurate, robust, and transparent model for renal autoregulation implemented in an existing circulatory gestational model. This renal autoregulation model aims to maintain steady glomerular pressure by the myogenic response, and glomerular filtration rate by tubuloglomerular feedback, both by inducing a change in the radius, and thus resistance, of the afferent arteriole. The modeled response of renal blood flow and the afferent arteriole following blood pressure increase were compared to published observations in rats. With solely the myogenic response, our model had a maximum deviation of 7% in change in renal blood flow and 7% in renal vascular resistance. When both the myogenic response and tubuloglomerular feedback were concurrently activated, the maximum deviation was 7% in change in renal blood flow and 5% in renal vascular resistance. These results show that our model is able to represent renal autoregulatory behavior comparable to empirical data. Further studies should focus on extending the model with other regulatory mechanisms to understand the hemodynamic changes in healthy and complicated pregnancy.
Topics: Animals; Blood Pressure; Glomerular Filtration Rate; Hemodynamics; Homeostasis; Kidney; Rats; Renal Circulation
PubMed: 36200318
DOI: 10.14814/phy2.15484 -
Nephrology (Carlton, Vic.) May 2021Diabetic kidney disease remains the leading cause of end-stage kidney disease and a major risk factor for cardiovascular disease. Large cardiovascular outcome trials and... (Review)
Review
Diabetic kidney disease remains the leading cause of end-stage kidney disease and a major risk factor for cardiovascular disease. Large cardiovascular outcome trials and dedicated kidney trials have shown that sodium-glucose cotransporter (SGLT)2 inhibitors reduce cardiovascular morbidity and mortality and attenuate hard renal outcomes in patients with type 2 diabetes (T2D). Underlying mechanisms explaining these renal benefits may be mediated by decreased glomerular hypertension, possibly by vasodilation of the post-glomerular arteriole. People with T2D often receive several different drugs, some of which could also impact the renal vasculature, and could therefore modify both renal efficacy and safety of SGLT2 inhibition. The most commonly prescribed drugs that could interact with SGLT2 inhibitors on renal haemodynamic function include renin-angiotensin system inhibitors, calcium channel blockers and diuretics. Herein, we review the effects of these drugs on renal haemodynamic function in people with T2D and focus on studies that measured glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) with gold-standard techniques. In addition, we posit, based on these observations, potential interactions with SGLT2 inhibitors with an emphasis on efficacy and safety.
Topics: Calcium Channel Blockers; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Diuretics; Drug Interactions; Hemodynamics; Humans; Renal Circulation; Renin-Angiotensin System; Sodium-Glucose Transporter 2 Inhibitors
PubMed: 33283420
DOI: 10.1111/nep.13839 -
American Journal of Hypertension Aug 2015Arterial stiffness is typical feature of vascular remodeling in chronic kidney disease (CKD). Increased arterial stiffness raises flow and pressure pulsatility and is... (Review)
Review
Arterial stiffness is typical feature of vascular remodeling in chronic kidney disease (CKD). Increased arterial stiffness raises flow and pressure pulsatility and is considered the principle pathogenic mechanism of isolated systolic hypertension, left ventricular hypertrophy, and congestive heart failure. Apart from the impact of arterial stiffness on left ventricular afterload, downstream transmission of pressure pulsatility to the level of microcirculation is suggested to promote injury of other susceptible organs. This may be of particular importance for kidney injury progression, since passive renal perfusion along with low resistance and input impedance in renal microvessels make kidneys particularly vulnerable to the damaging effect of systemic pulsatile pressure. Recent studies have provided evidence that arterial stiffness culminates in elevated pulsatility and resistance in renal microvasculature, promoting structural damage of small intra-renal arterioles. Further, prospective observational studies have shown that reduced aortic compliance is closely associated with the annual rate of renal function decline and represents independent predictor of kidney injury progression to end-stage renal disease among patients with CKD. This article provides insights into the cross-talk between macrocirculation and renal microcirculation and summarizes the currently available clinical evidence linking increased arterial stiffness with kidney disease progression.
Topics: Disease Progression; Heart Failure; Humans; Hypertension; Hypertrophy, Left Ventricular; Kidney Failure, Chronic; Pulsatile Flow; Renal Circulation; Renal Insufficiency, Chronic; Risk Factors; Vascular Remodeling; Vascular Resistance; Vascular Stiffness
PubMed: 25687879
DOI: 10.1093/ajh/hpv004 -
European Review For Medical and... 2016The purpose of the study is to further investigate the effects of increased intra-abdominal pressure (IAP) on renal hemodynamics and renal perfusion, and to evaluate the...
OBJECTIVE
The purpose of the study is to further investigate the effects of increased intra-abdominal pressure (IAP) on renal hemodynamics and renal perfusion, and to evaluate the renal cortical and sublingual microcirculation by sidestream dark field (SDF) imaging, both with a porcine model.
MATERIALS AND METHODS
IAP was increased stepwise to 10, 15, 20, 25 mmHg, during which hemodynamic parameters, urinary output, renal contrast-enhanced ultrasound (CEUS), sublingual and renal SDF videos were all recorded from 12 pigs.
RESULTS
Wash in time (WT) and time to peak (TTP) prolonged significantly (p<0.05), while peak intensity (PI) wash in slope (WS) and AUC (area under curve) in CEUS declined significantly (p<0.05) compared with baseline when IAP elevated to 25 mm Hg. With an increase of abdominal pressure, sublingual microvascular flow index (MFI) drop significantly, especially upon IAP was over 20 mmHg. But other parameters such as the total vascular density (TVD), De Backer Score, proportion of perfused vessels (PPV), perfused vessel density (PVD), and heterogeneity index (HI) of tongue were not significantly changed. With increasing IAP, renal vascular resistance increased and MFI decreased about 30%. RFG, instead of RFG showed a moderate correlation with AUC (R=0.47, p<0.05) and MFI (R=0.49, p<0.05).
CONCLUSIONS
CEUS is a safe, real-time dynamic, noninvasive and simple technique to evaluate renal microvascular perfusion in intra-abdominal hypertension. Descending slope, PI and AUC can be used for the diagnosis of the renal microvascular damage in a porcine model of IAP-induced renal impairment. Also, SDF on the surface of the kidney is a useful tool to evaluate the microcirculation of kidney but sublingual SDF imaging was barely useful.
Topics: Animals; Contrast Media; Disease Models, Animal; Hemodynamics; Intra-Abdominal Hypertension; Kidney; Kidney Cortex; Microcirculation; Renal Circulation; Swine; Vascular Resistance
PubMed: 26914119
DOI: No ID Found -
Journal of Magnetic Resonance Imaging :... Feb 2022Phase-contrast (PC) MRI is a feasible and valid noninvasive technique to measure renal artery blood flow, showing potential to support diagnosis and monitoring of renal... (Review)
Review
BACKGROUND
Phase-contrast (PC) MRI is a feasible and valid noninvasive technique to measure renal artery blood flow, showing potential to support diagnosis and monitoring of renal diseases. However, the variability in measured renal blood flow values across studies is large, most likely due to differences in PC-MRI acquisition and processing. Standardized acquisition and processing protocols are therefore needed to minimize this variability and maximize the potential of renal PC-MRI as a clinically useful tool.
PURPOSE
To build technical recommendations for the acquisition, processing, and analysis of renal 2D PC-MRI data in human subjects to promote standardization of renal blood flow measurements and facilitate the comparability of results across scanners and in multicenter clinical studies.
STUDY TYPE
Systematic consensus process using a modified Delphi method.
POPULATION
Not applicable.
SEQUENCE FIELD/STRENGTH
Renal fast gradient echo-based 2D PC-MRI.
ASSESSMENT
An international panel of 27 experts from Europe, the USA, Australia, and Japan with 6 (interquartile range 4-10) years of experience in 2D PC-MRI formulated consensus statements on renal 2D PC-MRI in two rounds of surveys. Starting from a recently published systematic review article, literature-based and data-driven statements regarding patient preparation, hardware, acquisition protocol, analysis steps, and data reporting were formulated.
STATISTICAL TESTS
Consensus was defined as ≥75% unanimity in response, and a clear preference was defined as 60-74% agreement among the experts.
RESULTS
Among 60 statements, 57 (95%) achieved consensus after the second-round survey, while the remaining three showed a clear preference. Consensus statements resulted in specific recommendations for subject preparation, 2D renal PC-MRI data acquisition, processing, and reporting.
DATA CONCLUSION
These recommendations might promote a widespread adoption of renal PC-MRI, and may help foster the set-up of multicenter studies aimed at defining reference values and building larger and more definitive evidence, and will facilitate clinical translation of PC-MRI.
LEVEL OF EVIDENCE
1 TECHNICAL EFFICACY STAGE: 1.
Topics: Consensus; Delphi Technique; Humans; Kidney; Magnetic Resonance Imaging; Multicenter Studies as Topic; Renal Circulation
PubMed: 33140551
DOI: 10.1002/jmri.27419 -
Current Opinion in Nephrology and... Nov 2016MRI can noninvasively assess the structure and function of the kidney in a single MRI scan session. This review summarizes recent advancements in functional renal MRI... (Review)
Review
PURPOSE OF REVIEW
MRI can noninvasively assess the structure and function of the kidney in a single MRI scan session. This review summarizes recent advancements in functional renal MRI techniques, with a particular focus on clinical applications.
RECENT FINDINGS
A number of MRI techniques now provide measures of relevance to the pathophysiology of kidney disease. Diffusion-weighted imaging, used in chronic kidney disease and renal transplantation, shows promise as a measure of renal fibrosis. Longitudinal relaxation time (T1) mapping has been utilized in cardiac MRI to measure fibrosis and oedema; recent work shows its potential in the kidney. Blood oxygen-level-dependent MRI to measure renal oxygenation has been extensively studied, but a number of other factors affect results making it hard to draw definite conclusions as to its utility as an independent measure. Phase contrast and arterial spin labelling can measure renal artery blood flow and renal perfusion without exogenous contrast, as opposed to dynamic contrast-enhanced studies. In general, current data on clinical use of functional renal MRI are restricted to cross-sectional studies.
SUMMARY
Renal MRI has seen significant recent advances. Current evidence demonstrates its potential, and next steps include wider evaluation of its clinical application.
Topics: Contrast Media; Fibrosis; Humans; Kidney; Kidney Diseases; Magnetic Resonance Imaging; Oxygen; Renal Circulation
PubMed: 27636770
DOI: 10.1097/MNH.0000000000000266 -
Seminars in Nephrology Jan 2015Traditionally, renal ischemia has been regarded as central to the pathogenesis of sepsis-associated acute kidney injury (SA-AKI). Accordingly, hemodynamic management of... (Review)
Review
Traditionally, renal ischemia has been regarded as central to the pathogenesis of sepsis-associated acute kidney injury (SA-AKI). Accordingly, hemodynamic management of SA-AKI has emphasized restoration of renal perfusion, whereas, experimentally, ischemia reperfusion models have been emphasized. However, in human beings, SA-AKI usually is accompanied by hyperdynamic circulation. Moreover, clinical and experimental evidence now suggests the importance of inflammatory mechanisms in the development of AKI and microcirculatory dysfunction more than systemic alteration in renal perfusion. In this review, we examine systemic, regional, and microcirculatory hemodynamics in SA-AKI, and attempt to rationalize the hemodynamic management of this condition.
Topics: Acute Kidney Injury; Hemodynamics; Humans; Kidney; Microcirculation; Renal Circulation; Sepsis
PubMed: 25795500
DOI: 10.1016/j.semnephrol.2015.01.007 -
American Journal of Physiology. Renal... Oct 2015When introduced clinically 6 years ago, renal denervation was thought to be the solution for all patients whose blood pressure could not be controlled by medication. The... (Review)
Review
When introduced clinically 6 years ago, renal denervation was thought to be the solution for all patients whose blood pressure could not be controlled by medication. The initial two studies, SYMPLICITY HTN-1 and HTN-2, demonstrated great magnitudes of blood pressure reduction within 6 mo of the procedure and were based on a number of assumptions that may not have been true, including strict adherence to medication and absence of white-coat hypertension. The SYMPLICITY HTN-3 trial controlled for all possible factors believed to influence the outcome, including the addition of a sham arm, and ultimately proved the demise of the initial overly optimistic expectations. This trial yielded a much lower blood pressure reduction compared with the previous SYMPLICITY trials. Since its publication in 2014, there have been many analyses to try and understand what accounted for the differences. Of all the variables examined that could influence blood pressure outcomes, the extent of the denervation procedure was determined to be inadequate. Beyond this, the physiological mechanisms that account for the heterogeneous fall in arterial pressure following renal denervation remain unclear, and experimental studies indicate dependence on more than simply reduced renal sympathetic activity. These and other related issues are discussed in this paper. Our perspective is that renal denervation works if done properly and used in the appropriate patient population. New studies with new approaches and catheters and appropriate controls will be starting later this year to reassess the efficacy and safety of renal denervation in humans.
Topics: Denervation; Drug Resistance; Humans; Hypertension, Renal; Kidney; Renal Circulation; Sympathectomy
PubMed: 26224718
DOI: 10.1152/ajprenal.00246.2015 -
Renal Failure Oct 2016The renal functional reserve (RFR) is the ability of the kidneys to increase renal plasma flow and glomerular filtration rate (GFR) in response to protein intake. It is...
The renal functional reserve (RFR) is the ability of the kidneys to increase renal plasma flow and glomerular filtration rate (GFR) in response to protein intake. It is a measure of functional and anatomic integrity of nephrons. It is not known what relation between RFR and kidney Doppler parameters. We aimed to study the relation between the RFR and renal hemodynamic parameters in hypertensive patients with and without nephropathy who had normal kidney function. Twenty-four hypertensive subjects with nephropathy (HTN-n, n = 10) and hypertension without nephropathy (HTN, n = 14) were included in the study. Control group included 11 healthy subjects. Baseline GFR (GFR1) and GFR after intake of egg protein 1 mg/kg of body weight were determined (GFR2). RFR was calculated by the following formula: (GFR2-GFR1)/GFR1 × 100%. Doppler ultrasonography was performed. Arterial blood pressure (BP), body mass index (BMI), and estimated GFR were also recorded. HTN and HTN-n groups had impaired levels of RFR compared with controls (p < 0.05), significantly decreased value of flow velocity parameters (Vmax, Vmin), and increased RRI compared with controls. There was significant negative correlation of RFR with blood pressure levels (sBP, r = -0.435, p = 0.009; dBP, r = -0.504, p = 0.002), RRI (r = -0.456, p = 0.008), micro albuminuria (MAU, r = -0.366, p = 0.031) and positive correlation with Vmax and Vmin (r = 0.556, p = 0.001 and r = 0.643, respectively, p < 0.001). Linear regression showed that RRI and MAU were independent predictors of decreased RFR. RFR is lower in hypertensive patients despite near-normal level of kidney function and is related to particular level of BP. RRI and MAU were independent predictors of decreased RFR.
Topics: Adult; Blood Pressure; Cross-Sectional Studies; Female; Follow-Up Studies; Glomerular Filtration Rate; Humans; Hypertension; Kidney; Male; Regional Blood Flow; Renal Artery; Renal Circulation; Ultrasonography, Doppler, Color
PubMed: 27470640
DOI: 10.1080/0886022X.2016.1214052