Renal Flow Research Articles

Focus on renal blood flow in mechanically ventilated patients with SARS-CoV-2: a prospective pilot study.

Mechanically ventilated patients with ARDS due to the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) seem particularly susceptible to AKI. Our hypothesis was that the renal blood flow could be more compromised in SARS-CoV-2 patients than in patients with “classical” ARDS. We compared the renal resistivity index (RRI) and the renal venous flow (RVF) in ARDS patients with SARS-CoV-2 and in ARDS patients due to other etiologies. Prospective, observational pilot study performed on 30 mechanically ventilated patients (15 with SARS-COV-2 ARDS and 15 with ARDS). Mechanical ventilation settings included constant-flow controlled ventilation, a tidal volume of 6 ml/kg of ideal body weight and the PEEP level titrated to the lowest driving pressure. Ultrasound Doppler measurements of RRI and RVF pattern were performed in each patient. Patients with SARS-COV-2 ARDS had higher RRI than patients with ARDS (0.71[0.67–0.78] vs 0.64[0.60–0.74], p = 0.04). RVF was not-continuous in 9/15 patients (71%) in the SARS-COV-2 ARDS group and in and 5/15 (33%) in the ARDS group (p = 0.27). A linear correlation was found between PEEP and RRI in patients with SARS-COV-2 ARDS (r2 = 0.31; p = 0.03) but not in patients with ARDS. Occurrence of AKI was 53% in patients with SARS-COV-2 ARDS and 33% in patients with ARDS (p = 0.46). We found a more pronounced impairment in renal blood flow in mechanically ventilated patients with SARS-COV-2 ARDS, compared with patients with “classical” ARDS.Supplementary InformationThe online version of this article (10.1007/s10877-020-00633-5) contains supplementary material, which is available to authorized users.

Patient-specific computational flow modelling for assessing hemodynamic changes following fenestrated endovascular aneurysm repair

ObjectiveThis study aimed to develop an accessible patient-specific computational flow modelling pipeline for evaluating the hemodynamic performance of fenestrated endovascular aneurysm repair (fEVAR), with the hypothesis that computational flow modelling can detect aortic branch hemodynamic changes associated with fEVAR graft implantation. MethodsPatients who underwent fEVAR for juxtarenal aortic aneurysms with the Cook ZFEN were retrospectively selected. Using open-source SimVascular software, preoperative and postoperative visceral aortic anatomy was manually segmented from computed tomography angiograms. Three-dimensional geometric models were then discretized into tetrahedral finite element meshes. Patient-specific pulsatile in-flow conditions were derived from known supraceliac aortic flow waveforms and adjusted for patient body surface area, average resting heart rate, and blood pressure. Outlet boundary conditions consisted of three-element Windkessel models approximated from physiologic flow splits. Rigid wall flow simulations were then performed on preoperative and postoperative models with the same inflow and outflow conditions. We used SimVascular's incompressible Navier-Stokes solver to perform blood flow simulations on a cluster using 72 cores. ResultsPreoperative and postoperative flow simulations were performed for 10 patients undergoing fEVAR with a total of 30 target vessels (20 renal stents, 10 mesenteric scallops). Postoperative models required a higher mean number of mesh elements to reach mesh convergence (3.2 ± 1.8 × 106 vs 2.6 ± 1.1 × 106; P = .005) with a longer mean computational time (10.3 ± 6.3 hours vs 7.8 ± 3.5 hours; P = .04) compared with preoperative models. fEVAR was associated with small but statistically significant increases in mean peak proximal aortic arterial pressure (140.3 ± 11.0 mm Hg vs 136.9 ± 8.7 mm Hg; P = .02) and peak renal artery pressure (131.6 ± 14.8 mm Hg vs 128.9 ± 11.8 mm Hg; P = .04) compared with preoperative simulations. No differences were observed in peak pressure in the celiac, superior mesenteric, or distal aortic arteries (P = .17-.96). When measuring blood flow, the only observed difference was an increase in peak renal flow rate after fEVAR (17.5 ± 3.8 mL/s vs 16.9 ± 3.5 mL/s; P = .04). fEVAR was not associated with changes in the mean pressure or the mean flow rate in the celiac, superior mesenteric, or renal arteries (P = .06-.98). Stenting of the renal arteries did not induce significant changes time-averaged wall shear stress in the proximal renal artery (23.4 ± 8.1 dynes/cm2 vs 23.2 ± 8.4 dynes/cm2; P = .98) or distal renal artery (32.7 ± 13.9 dynes/cm2 vs 29.6 ± 11.8 dynes/cm2; P = .23). In addition, computational visualization of cross-sectional velocity profiles revealed low flow disturbances associated with protrusion of renal graft fabric into the aortic lumen. ConclusionsIn a pilot study involving a selective cohort of patients who underwent uncomplicated fEVAR, patient-specific flow modelling was a feasible method for assessing the hemodynamic performance of various two-vessel fenestrated device configurations and revealed subtle differences in computationally derived peak branch pressure and blood flow rates. Structural changes in aortic flow geometry after fEVAR do not seem to affect computationally estimated renovisceral branch perfusion or wall shear stress adversely. Additional studies with invasive angiography or phase contrast magnetic resonance imaging are required to clinically validate these findings. (JVS–Vascular Science 2021;2:53-69.) Clinical RelevanceUsing a computational flow modelling for assessing the hemodynamic performance of fenestrated endovascular aneurysm repair (fEVAR), this real-world, patient-specific study included 10 participants and found that structural changes in aortic flow geometry after fEVAR did not seem to adversely impact estimated renal or visceral branch perfusion metrics (eg, peak and mean arterial pressure and flow rates) or wall shear stress. These findings overall support the ongoing clinical use of commercially available fEVAR devices for repair of juxtarenal aortic aneurysms, and provides a computational framework for future evaluation of fEVAR configurations in a preoperative or postoperative settings.

Feasibility and reproducibility of renal flow reserve with combined pressure and flow velocity measurements.

Feasibility and reproducibility of renal flow reserve with combined pressure and flow velocity measurements.

Abstract 13330: Intrarenal Doppler Ultrasonography Reflects Hemodynamics and Predicts Prognosis in Patients With Heart Failure

Introduction: We aimed to clarify clinical implications of intrarenal hemodynamics (congestion and hypoperfusion) assessed by intrarenal Doppler ultrasonography (IRD) and their prognostic impacts in patients with heart failure (HF). Methods and Results: We performed IRD and measured interlobar renal artery velocity time integral (VTI) and intrarenal venous flow (IRVF) patterns (monophasic or non-monophasic pattern) to assess intrarenal hypoperfusion and congestion in HF patients (n=341). These patients were categorized based on 1) VTI: high VTI (VTI ≥ 14.0 cm, n=231) or low VTI (VTI < 14.0 cm, n=103); and 2) IRVF: monophasic (n=36) or non-monophasic (n=305) pattern. We performed right-heart catheterization, and examined post-discharge cardiac event rate such as cardiac death and rehospitalization due to worsening HF. Regarding renal perfusion, cardiac index was positively correlated with VTI (R=0.270, P=0.040). Concerning renal congestion, levels of right atrial pressure were higher in monophasic pattern than in non-monophasic pattern (9.0 vs. 7.2 mmHg, P=0.029). Importantly, HF patients with low VTI and a monophasic IRVF pattern (subset 4) had the highest cardiac event rate ( Figure ). In the Cox proportional hazard analysis, the combination of low VTI and a monophasic IRVF pattern was found to be a strong predictor of cardiac events (HR 8.357, 95% CI 3.365-20.752). Conclusion: Intrarenal hypoperfusion and congestion assessed by IRD imaging reflected cardiac output and right atrial pressure, and was useful to risk-stratify HF patients.

Abstract 14468: Right Heart: Renal Venous Stasis Determinant in Acute Heart Failure

Introduction: The heart-kidney interaction in heart failure (HF) is a matter of special interest, especially due to its strong prognostic significance. The search for a reliable, non-invasive parameter with high pathophysiological and prognostic impact to evaluate HF-related renal congestion remains attractive. Doppler evaluation of intra-renal venous flow (IRVF) has been recently employed in HF patients, with a spectrum of findings ranging from a normal continuous flow to a monophasic discontinuous one, indicative of low and high degrees of renal congestion, respectively. Hypothesis: We postulated a role for right atrial dynamics in the renal congestion pathophysiology. The impairment in atrial deformation and pump function may play a primary role increasing the pulsatile backward load in the venous system, especially in acute heart failure (AHF) patients. Methods: 119 consecutive AHF patients were prospectively investigated within 48 hours from admission. Doppler-derived descriptors of renal hemodynamics included the renal arterial resistive index, IRVF pattern, venous impedance index and renal venous stasis index (RVSI). Results: Right atrial peak longitudinal strain (RAPLS) showed a strong correlation with IRVF pattern (Fig A) and various indices of RV function (TAPSE, S’, FAC) and RV coupling as represented by the TAPSE/PASP ratio (Fig B). At multivariate regression analysis, TAPSE/PASP ratio emerged as the main determinant of RVSI. On the other hand, considering only patients with a clearly impaired RV coupling (TAPSE/PASP <0.30), RAPLS emerged as the best determinant of RVSI (Fig C-D). Conclusions: Our data confirms the main role of the right heart in determining renal stasis in HF patients. When RV to pulmonary circulation uncoupling is severe, the right atrium becomes the key balancing factor in the venous renal flow response. Studies on the mechanistic contribution of the RA dysfunction and the recovery potential of interventions are warranted.

The synergism of B and T lymphocyte attenuator (BTLA) and cytotoxic T lymphocyte associated antigen-4 (CTLA-4) attenuated acute T-cell mediated rejection and prolonged renal graft survival.

BackgroundAcute T-cell mediated rejection (TCMR) continues to be a major problem in the area of kidney transplantation. The B and T lymphocyte attenuator (BTLA) and cytotoxic T lymphocyte associated antigen-4 (CTLA-4) were recently found costimulatory molecules. The research aims to explore the inhibitory synergism of BTLA and CTLA-4 in TCMR.MethodsWe investigated the suppressive role of overexpressed BTLA and CTLA-4 in vitro. The rat kidney transplantation model was established to explore the effect of combined overexpressed BTLA and CTLA-4 in recipients of kidney transplantation. The grafts and peripheral blood were harvested for renal function, histology, immunohistochemical and flow cytometry analysis.ResultsCombination therapy decreased the secretion of interleukin-2 (IL-2) and proliferation of T cells compared to the single therapy and the control group. Decrease of interstitium monocyte infiltration and especially intimal arteritis in the graft was observed with the combination therapy, with remarkable reduction of numbers and proliferation response of T cells in peripheral blood and grafts. Combined overexpressed BTLA and CTLA-4 attenuated the acute TCMR after kidney transplantation and improved the graft function and prolonged the graft survival. The inhibiting role against TCMR in the combination therapy group was more effective than single therapy.ConclusionsThe synergism of BTLA and CTLA-4 attenuated acute TCMR after kidney transplantation by suppressing T cell activation and proliferation.

Doppler Interrogation of the Femoral Vein in the Critically Ill Patient: The Fastest Potential Acoustic Window to Diagnose Right Ventricular Dysfunction?

To report the use of common femoral vein Doppler interrogation as a simple technique to diagnose right ventricular dysfunction. Case report. Cardiac surgical ICU. Postoperative cardiac surgical patients. Common femoral pulsed-wave and color Doppler examination associated with hepatic, portal, and renal venous Doppler measurement were obtained in both patients and before and after treatment in patient number 1. In addition, right ventricular pressure waveform examination was obtained in patient number 2. The technique to obtain common femoral venous Doppler is described. Two cases of patients presenting with right ventricular dysfunction and fluid overload with portal and renal venous congestion in the perioperative period undergoing complex multivalvular cardiac surgery are presented. Hemodynamic waveform monitoring was performed alongside echocardiographic, hepatic, and renal venous flow Doppler assessment, and spectral Doppler profiles of the common femoral veins were examined. Those findings were useful in confirming our diagnosis and guiding our response to treatment. An algorithm was developed and tested on two additional hemodynamically unstable patients. Doppler examination of the common femoral vein is a simple, fast, and noninvasive technique that could be useful to rule in the presence of right ventricular dysfunction with venous congestion and help guide the management of such patients.

The Effect of Decongestion on Intrarenal Venous Flow Patterns in Patients With Acute Heart Failure

BackgroundDiscontinuous intrarenal venous flow patterns, as assessed by renal Doppler ultrasound examination, are associated with changes in hemodynamics such as volume expansion and poorer diuretic response in patients with heart failure (HF). We aimed to study intrarenal venous and arterial flow patterns after decongestive treatment in patients with acute HF. Methods and ResultsFifteen patients with acute HF were enrolled. Intrarenal venous and arterial flow patterns were assessed at baseline, 1 hour after administration of loop diuretics, at day 2 and day 3. Among patients hospitalized for acute HF, 13 (87%) had a discontinuous venous flow pattern at admission. After decongestive treatment, a significant improvement of the venous impedance index (P = .021) and venous discontinuity index (P = .004) was observed at day 3 compared with baseline. There was no effect on the intrarenal arterial flow patterns. ConclusionsIn patients who exhibit discontinuous renal venous flow patterns hospitalized for decongestive treatment owing to acute HF led to a normalization of intrarenal venous flow to a continuous pattern.

Critically Ill COVID-19 Patients With Acute Kidney Injury Have Reduced Renal Blood Flow and Perfusion Despite Preserved Cardiac Function: A Case-Control Study Using Contrast-Enhanced Ultrasound.

Acute kidney injury (AKI) is a common complication of COVID-19 critical illness but the pathophysiology is uncertain. Some evidence has indicated that a vascular aetiology may be implicated. We used contrast-enhanced ultrasound (CEUS) and echocardiography to study renal perfusion and global blood flow and compared our findings with measurements taken in a group of septic shock patients and healthy volunteers. Prospective case-control study. Renal perfusion variables were assessed with CEUS; macrovascular blood flow was assessed using Doppler analysis of large renal vessels; echocardiography was used to assess right and left heart function and cardiac output. CEUS-derived parameters were reduced in COVID-19 associated AKI compared with healthy controls (perfusion index 3,415 vs. 548 a.u., P = 0·001; renal blood volume 7,794 vs. 3,338 a.u., P = 0·04). Renal arterial flow quantified using time averaged peak velocity was also reduced compared with healthy controls (36·6 cm/s vs. 20·9 cm/s, P = 0.004) despite cardiac index being similar between groups (2.8 L/min/m2 vs. 3.7 L/min/m2, P = 0.07). There were no differences in CEUS-derived or cardiac parameters between COVID-19 and septic shock patients but patients with septic shock had more heterogeneous perfusion variables. Both large and small vessel blood flow is reduced in patients with COVID-19 associated AKI compared with healthy controls, which does not appear to be a consequence of right or left heart dysfunction. A reno-vascular pathogenesis of COVID-19 AKI seems likely.

4D flow MRI for the assessment of renal transplant dysfunction: initial results.

(1) Determine inter-observer reproducibility and test-retest repeatability of 4D flow parameters in renal allograft vessels; (2) determine if 4D flow measurements in the renal artery (RA) and renal vein (RV) can distinguish between functional and dysfunctional allografts; (3) correlate haemodynamic parameters with estimated glomerular filtration rate (eGFR), perfusion measured with dynamic contrast-enhanced MRI (DCE-MRI) and histopathology. Twenty-five prospectively recruited renal transplant patients (stable function/chronic renal allograft dysfunction, 12/13) underwent 4D flow MRI at 1.5T. 4D flow coronal oblique acquisitions were performed in the transplant renal artery (RA) (velocity encoding parameter, VENC = 120cm/s) and renal vein (RV) (VENC = 45cm/s). Test-retest repeatability (n = 3) and inter-observer reproducibility (n = 10) were assessed by Cohen's kappa, coefficient of variation (CoV) and Bland-Altman statistics. Haemodynamic parameters were compared between patients and correlated to the estimated glomerular filtration rate, DCE-MRI parameters (n = 10) and histopathology from allograft biopsies (n = 15). For inter-observer reproducibility, kappa was > 0.99 and 0.62 and CoV of flow was 12.6% and 7.8% for RA and RV, respectively. For test-retest repeatability, kappa was > 0.99 and 0.5 and CoV of flow was 27.3% and 59.4%, for RA and RV, respectively. RA (p = 0.039) and RV (p = 0.019) flow were both significantly reduced in dysfunctional allografts. Both identified chronic allograft dysfunction with good diagnostic performance (RA: AUC = 0.76, p = 0.036; RV: AUC = 0.8, p = 0.018). RA flow correlated negatively with histopathologic interstitial fibrosis score ci (ρ = - 0.6, p = 0.03). 4D flow parameters had better repeatability in the RA than in the RV. RA and RV flow can identify chronic renal allograft dysfunction, with RA flow correlating with histopathologic interstitial fibrosis score. • Inter-observer reproducibility of 4D flow measurements was acceptable in both the transplant renal artery and vein, but test-retest repeatability was better in the renal artery than in the renal vein. • Blood flow measurements obtained with 4D flow MRI in the renal artery and renal vein are significantly reduced in dysfunctional renal transplants. • Renal transplant artery flow correlated negatively with histopathologic interstitial fibrosis score.

THE INFLUENCE OF IMMEDIATE GRAFT BLOOD FLOW ON EARLY GRAFT FUNCTION

Introduction: The aim of this study is to evaluate the impact of intraoperative allograft vascular flow on the early kidney graft function. Methods: A total of 47 patients underwent kidney transplantation from January 2017 to June 2019 at Linkou Chang Gung Memorial Hospital. The majority anastomosis of graft vessels were done with end-to-side manner to the external iliac vessels. Real-time graft blood flow was measured with transit time flowmeter(Transonic HT353) after ureteroneocystostomy. Graft arterial and venous blood glow was measured separately. The early outcomes including postoperative creatinine level and daily urine output were analized accordingly. Results: The median age was 45.7(13-68) years and 22(46.8%) patients were female. Among the 47 recipients, 35 received kidneys from living related donors and 12 from deceased donors. The mean renal artery blood flow was 450.74 ml/min (median=425) and the mean renal vein flow was 541.49 ml/min (median=470). With multivariate regression on creatinine declining ratio, graft arterial blood flow has significant impact on day 2 and 3 while graft venous blood flow was significant on day 1, 2, 3, 7 and 30 (p<0.05). As for urine output, graft arterial flow was significantly associated with more urine output on day 0-1 and day 0-2 but not any further after day 3. Graft venous flow had no impact on urine amount postoperatively. Conclusion: Graft arterial blood flow was significantly associated with creatinine declining ratio and urine output amount whilst graft venous blood flow showed more persistent association with creatinine declining ratio during early postoperative phase.

Interplay of the adenosine system and NO in control of renal haemodynamics and excretion: Comparison of normoglycaemic and streptozotocin diabetic rats

The adenosine (Ado) system may participate in regulation of kidney function in diabetes mellitus (DM), therefore we explored its role and interrelation with NO in the control of renal circulation and excretion in normoglycemic (NG) and streptozotocin-diabetic (DM) rats. Effects of theophylline (Theo), a non-selective Ado receptor antagonist, were examined in anaesthetized NG or in streptozotocin induced diabetic (DM) rats, untreated or after blockade of NO synthesis with l-NAME. We measured arterial blood pressure (MABP), whole kidney blood flow and renal regional flows: cortical and outer- and inner-medullary (IMBF), determined as laser-Doppler fluxes. Renal excretion of water, total solutes and sodium and in situ renal tissue NO signal (selective electrodes) were also determined. Theo experiments disclosed minor baseline vasoconstrictor and vasodilator tone in the kidney of NG and DM rats, respectively. NO blockade increased baseline MABP and decreased renal haemodynamics, similarly in NG and DM rats, indicating comparable vasodilator influence of NO in the two groups. Unexpectedly, in all rats with intact NO synthesis, Ado receptor blockade increased kidney tissue NO. In NO-deficient NG and DM rats, Ado receptor blockade induced comparable renal vasodilatation, suggesting similar vasoconstrictor influence of the Ado system. However, DM rats showed an unexplained association of decreased MABP and IMBF and increased NO signal. Higher baseline renal excretion in DM rats indicated inhibition of renal tubular reabsorption due to the prevalence of natriuretic A2 over antinatriuretic A1 receptors. In conclusion, the experiments provided new insights in functional interrelation of adenosine and NO in normoglycaemia and streptozotocin-diabetes.

Low-energy shock wave pretreatment recruit circulating endothelial progenitor cells to attenuate renal ischaemia reperfusion injury.

Low‐energy shock wave (LESW) has been recognized as a promising non‐invasive intervention to prevent the organs or tissues against ischaemia reperfusion injury (IRI), whereas its effect on kidney injury is rarely explored. To investigate the protective role of pretreatment with LESW on renal IRI in rats, animals were randomly divided into Sham, LESW, IRI and LESW + IRI groups. At 4, 12, 24 hours and 3 and 7 days after reperfusion, serum samples and renal tissues were harvested for performing the analysis of renal function, histopathology, immunohistochemistry, flow cytometry and Western blot, as well as enzyme‐linked immunosorbent assay. Moreover, circulating endothelial progenitor cells (EPCs) were isolated, labelled with fluorescent dye and injected by tail vein. The fluorescent signals of EPCs were detected using fluorescence microscope and in vivo imaging system to track the distribution of injected circulating EPCs. Results showed that pretreatment with LESW could significantly reduce kidney injury biomarkers, tubular damage, and cell apoptosis, and promote cell proliferation and vascularization in IRI kidneys. The renoprotective role of LESW pretreatment would be attributed to the remarkably increased EPCs in the treated kidneys, part of which were recruited from circulation through SDF‐1/CXCR7 pathway. In conclusion, pretreatment with LESW could increase the recruitment of circulating EPCs to attenuate and repair renal IRI.

A lumped-parameter model for kidney pressure during stone removal

AbstractIn this paper, we consider a lumped-parameter model to predict renal pressures and flow rate during a minimally invasive surgery for kidney stone removal, ureterorenoscopy. A ureteroscope is an endoscope designed to work within the ureter and the kidney and consists of a long shaft containing a narrow, cylindrical pipe, called the working channel. Fluid flows through the working channel into the kidney. A second pipe, the ‘access sheath’, surrounds the shaft of the scope, allowing fluid to flow back out of the urinary system. We modify and extend a previously developed model ( Oratis et al., 2018) through the use of an exponential, instead of linear, constitutive law for kidney compliance and by exploring the effects of variable flow resistance, dependent on the presence of auxiliary ‘working tools’ in the working channel and the cross-sectional shapes of the tools, working channel, scope shaft and access sheath. We motivate the chosen function for kidney compliance and validate the model predictions, with ex vivo experimental data. Although the predicted and measured flow rates agree, we find some disagreement between theory and experiment for kidney pressure. We hypothesize that this is caused by spatial pressure variation in the renal pelvis, i.e. unaccounted for in the lumped-parameter model. We support this hypothesis through numerical simulations of the steady Navier–Stokes equations in a simplified geometry. We also determine the optimal cross-sectional shapes for the scope and access sheath (for fixed areas) to minimize kidney pressure and maximize flow rate.

Defense mechanisms to increasing back pressure for hepatic oxygen transport and venous return in porcine fecal peritonitis.

High central venous pressure (CVP) acutely decreases venous return. How this affects hepatic oxygen transport in sepsis remains unclear. The aim of this study was to evaluate the effects of repeated increases in CVP via standard nursing procedures (NPs) on hepato-splanchnic and renal oxygen transport in a prolonged porcine sepsis model. Twenty anesthetized and mechanically ventilated pigs with regional hemodynamics monitored were randomized to fecal peritonitis or controls (n = 10 pigs/group). Resuscitation was started after 8 h of observation and continued for 3 days. NPs were performed at baseline and 8 h, 32 h, 56 h, and 72 h after resuscitation started. NPs increased CVP by 4-7 mmHg in both groups. In controls, this was associated with less decrease in hepatic arterial (Qha; 62 ± 70 mL/min) than portal venous flow (Qpv; 364 ± 151 mL/min). Portal venous oxygen content and hepatic O2 delivery (Do2) and consumption (V̇o2) decreased by 11 ± 6 mL/dL and 0.9 ± 0.3 and 0.4 ± 0.3 mL·min-1·kg-1, respectively. In septic animals, hepatic Do2 decreased more in response to increasing CVP (1.5 ± 0.9 mL·min-1·kg-1), which was attributable to a larger fall in both Qha (88 ± 66 ml/min) and portal O2 content (14 ± 10 mL/dL, all P < 0.05). This resulted in numerically lower hepatic V̇o2 since O2 extraction did not increase significantly. In control conditions, a smaller decrease in Qha compared with Qpv helped to limit the reduction in hepatic V̇o2 in response to acute CVP increase. In sepsis, the contribution of Qha to maintain hepatic Do2 was reduced, which jeopardized hepatic V̇o2 further. Renal arterial flow was similarly affected by CVP increase as Qha.NEW & NOTEWORTHY Sepsis impairs intrinsic mechanisms to attenuate effects of increasing back pressure on hepatic oxygen transport.

Reduced Flow in Delayed Graft Function as Assessed by IVIM Is Associated With Time to Recovery Following Kidney Transplantation.

Delayed graft function (DGF), defined as the need for dialysis in the first week after kidney transplantation, frequently complicates posttransplantation care. The most common cause of DGF is ischemia-reperfusion injury (IRI). To date, no clinical tools can accurately estimate its severity, nor the time required for recovery of kidney function. To investigate if parameters related to directed flow and diffusion of water, as determined by intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI), could be used to differentiate DGF from normal graft function posttransplantation, predict time to recovery from DGF, and hence serve as a surrogate measure of IRI severity. Prospective, cross-sectional cohort study. Fifty consecutive kidney transplant recipients within 3-10 days posttransplantation at our hospital. 3.0T/IVIM-DWI. The following IVIM-DWI parameters were studied: flow-fraction (f), apparent diffusion coefficient (ADC), and total-ADC (ADCT ). Mean intrarenal resistive index (R.I.) from Doppler ultrasound was also included for a comparison of IVIM-DWI with the clinical standard of care. Welch's t-test, Spearman's correlation, and linear regression. f was significantly reduced in DGF compared to non-DGF patients in the cortex, medulla, and whole renal parenchyma (P < 0.05). Time to recovery with respect to MRI correlated negatively with f (P < 0.05; rho = -0.52 (cortex), and -0.65 [parenchyma]), ADC (P < 0.05; rho = -0.59 [cortex], 0.59 [medulla], and -0.59 [parenchyma]) and ADCT (P < 0.05; rho = -0.54 [cortex], and -0.52 [medulla]). Whole renal parenchymal f predicted time to recovery relative to MRI (P < 0.05, adjusted r-squared = 0.36). R.I. was significantly different between the groups but did not correlate with time to recovery with respect to MRI (rho = 0.43, P = 0.096). Quantification of renal flow using IVIM-DWI has the potential to serve as a surrogate measure of IRI severity to estimate the degree of and recovery from DGF. 2 TECHNICAL EFFICACY STAGE: 3.

Systemic haemodynamic, renal perfusion and renal oxygenation responses to changes in inspired oxygen fraction during total intravenous or volatile anaesthesia

BackgroundAnaesthesia-induced changes in renal perfusion are dependent on the choice of anaesthetic agent. However, the effects of varying inspired oxygen fraction (FiO2) on renal perfusion and oxygenation during TIVA (propofol + fentanyl) or volatile anaesthesia (VA; isoflurane) are unknown. MethodsIn 16 Merino ewes, we surgically implanted a renal artery flow probe and laser-Doppler and oxygen-sensing probes in the renal medulla and cortex. We compared the systemic and renal effects of graded alterations in FiO2 (0.21, 0.40, 0.60, and 1.0) during TIVA or VA and compared the changes with those in the non-anaesthetised state. ResultsCompared with the non-anaesthetised state, TIVA and VA decreased renal blood flow (−50% vs −75%), renal oxygen delivery (−50% vs −80%), and renal cortical (−40% vs −60%) and medullary perfusion (−50% vs −75%). At an FiO2 of 0.21, both anaesthetic regimens induced similar reductions in cortical (−58 vs −65%) and medullary (−37% vs −38%) oxygenation. At higher concentrations of FiO2, renal blood flow and renal tissue perfusion were not changed, but intrarenal oxygenation improved similarly under TIVA and VA. In particular, at an FiO2 of ≥0.40 and ≤0.60, cortical and medullary oxygen tension were similar to the non-anaesthetised state. ConclusionsIrrespective of FiO2, TIVA decreased renal and intrarenal perfusion less than VA, but at low FiO2 concentrations both led to equivalent reductions in renal cortical and medullary oxygenation. However, with FiO2 between 0.40 and 0.60 during TIVA or VA, both cortical and medullary oxygenation was maintained at normal physiological levels.

Estimation of Intraglomerular Pressure Using Invasive Renal Arterial Pressure and Flow Velocity Measurements in Humans.

Glomerular hyperfiltration resulting from an elevated intraglomerular pressure (Pglom) is an important cause of CKD, but there is no feasible method to directly assess Pglom in humans. We developed a model to estimate Pglom in patients from combined renal arterial pressure and flow measurements. We performed hemodynamic measurements in 34 patients undergoing renal or cardiac angiography under baseline conditions and during hyperemia induced by intrarenal dopamine infusion (30 μg/kg). For each participant during baseline and hyperemia, we fitted an adapted three-element Windkessel model that consisted of characteristic impedance, compliance, afferent resistance, and Pglom. We successfully analyzed data from 28 (82%) patients. Median age was 58 years (IQR, 52-65), median eGFR was 95 ml/min per 1.73 m2 (IQR, 74-100) using the CKD-EPI formula, 30% had microalbuminuria, and 32% had diabetes. The model showed a mean Pglom of 48.0 mm Hg (SD=10.1) at baseline. Under hyperemia, flow increased by 88% (95% CI, 68% to 111%). This resulted in a 165% (95% CI, 79% to 294%) increase in afferent compliance and a 13.1-mm Hg (95% CI, 10.0 to 16.3) decrease in Pglom. In multiple linear regression analysis, diabetes (coefficient, 10.1; 95% CI, 5.1 to 15.1), BMI (0.99 per kg/m2; 95% CI, 0.38 to 1.59), and renal perfusion pressure (0.42 per mm Hg; 95% CI, 0.25 to 0.59) were significantly positively associated with baseline Pglom. We constructed a model on the basis of proximal renal arterial pressure and flow velocity measurements that provides an overall estimate of glomerular pressure and afferent and efferent resistance in humans. The model provides a novel research technique to evaluate the hemodynamics of CKD on the basis of direct pressure and flow measurements. Functional HEmodynamics in patients with and without Renal Artery stenosis (HERA), NL40795.018.12 at the Dutch national trial registry (toetsingonline.nl).

Patient-Specific Computational Flow Modelling for Assessing Hemodynamic Changes Following Fenestrated Endovascular Aneurysm Repair

Abstract Objective This study aimed to develop an accessible patient-specific computational flow modelling pipeline for evaluating the hemodynamic performance of fenestrated endovascular aneurysm repair (fEVAR), with the hypothesis that computational flow modelling can detect aortic branch hemodynamic changes associated with fEVAR graft implantation. Methods Patients who underwent fEVAR for juxtarenal aortic aneurysms with the Cook ZFEN were retrospectively selected. Using open-source SimVascular software, preoperative and postoperative visceral aortic anatomy was manually segmented from computed tomography angiograms. Three-dimensional geometric models were then discretized into tetrahedral finite element meshes. Patient-specific pulsatile in-flow conditions were derived from known supraceliac aortic flow waveforms and adjusted for patient body surface area, average resting heart rate, and blood pressure. Outlet boundary conditions consisted of three-element Windkessel models approximated from physiologic flow splits. Rigid wall flow simulations were then performed on preoperative and postoperative models with the same inflow and outflow conditions. We used SimVascular's incompressible Navier-Stokes solver to perform blood flow simulations on a cluster using 72 cores. Results Preoperative and postoperative flow simulations were performed for 10 patients undergoing fEVAR with a total of 30 target vessels (20 renal stents, 10 mesenteric scallops). Postoperative models required a higher mean number of mesh elements to reach mesh convergence (3.2 ± 1.8 × 106 vs 2.6 ± 1.1 × 106; P = .005) with a longer mean computational time (10.3 ± 6.3 hours vs 7.8 ± 3.5 hours; P = .04) compared with preoperative models. fEVAR was associated with small but statistically significant increases in mean peak proximal aortic arterial pressure (140.3 ± 11.0 mm Hg vs 136.9 ± 8.7 mm Hg; P = .02) and peak renal artery pressure (131.6 ± 14.8 mm Hg vs 128.9 ± 11.8 mm Hg; P = .04) compared with preoperative simulations. No differences were observed in peak pressure in the celiac, superior mesenteric, or distal aortic arteries (P = .17-.96). When measuring blood flow, the only observed difference was an increase in peak renal flow rate after fEVAR (17.5 ± 3.8 mL/s vs 16.9 ± 3.5 mL/s; P = .04). fEVAR was not associated with changes in the mean pressure or the mean flow rate in the celiac, superior mesenteric, or renal arteries (P = .06-.98). Stenting of the renal arteries did not induce significant changes time-averaged wall shear stress in the proximal renal artery (23.4 ± 8.1 dynes/cm2 vs 23.2 ± 8.4 dynes/cm2; P = .98) or distal renal artery (32.7 ± 13.9 dynes/cm2 vs 29.6 ± 11.8 dynes/cm2; P = .23). In addition, computational visualization of cross-sectional velocity profiles revealed low flow disturbances associated with protrusion of renal graft fabric into the aortic lumen. Conclusions In a pilot study involving a selective cohort of patients who underwent uncomplicated fEVAR, patient-specific flow modelling was a feasible method for assessing the hemodynamic performance of various two-vessel fenestrated device configurations and revealed subtle differences in computationally derived peak branch pressure and blood flow rates. Structural changes in aortic flow geometry after fEVAR do not seem to affect computationally estimated renovisceral branch perfusion or wall shear stress adversely. Additional studies with invasive angiography or phase contrast magnetic resonance imaging are required to clinically validate these findings. (JVS–Vascular Science 2021;▪:1-17.) Clinical Relevance Using a computational flow modelling for assessing the hemodynamic performance of fenestrated endovascular aneurysm repair (fEVAR), this real-world, patient-specific study included 10 participants and found that structural changes in aortic flow geometry after fEVAR did not seem to adversely impact estimated renal or visceral branch perfusion metrics (eg, peak and mean arterial pressure and flow rates) or wall shear stress. These findings overall support the ongoing clinical use of commercially available fEVAR devices for repair of juxtarenal aortic aneurysms, and provides a computational framework for future evaluation of fEVAR configurations in a preoperative or postoperative settings.

P0677CONTRAST-ENHANCED ULTRASOUND TO ASSESS RENAL MICROCIRCULATION IN PATIENTS WITH CHRONIC KIDNEY DISEASE

Abstract Background and Aims Vascular factors such as capillary rarefaction, increased vascular stiffness and reduced vasodilatation due to endothelial dysfunction probably play an important role in the pathophysiology of chronic kidney disease (CKD). However, our understanding of the underlying mechanisms is hampered by the lack of non-invasive techniques to quantify renal microvasculature in humans. The aim of this study was to assess whether contrast-enhanced ultrasonography (CEUS) can identify (1) differences in renal microcirculation and (2) the degree of nitroglycerin-induced vasodilatation (NIV) as a measure of renal flow reserve between CKD-patients and age-matched healthy volunteers. Method All participants underwent CEUS under standardized conditions. Sonovue© (0.015 ml/kg/min) was perfused as contrast agent until a steady state was obtained, followed by four destruction-refilling sequences. Outcome measure of CEUS was the mean (change in) perfusion index (PI) of the outer renal cortex (see figure for an example). In a subgroup of participants, CEUS was repeated before and five minutes after the sublingual administration of nitroglycerin (0.2mg). Renal resistive index (RRI) as a measure of vascular stiffness was also measured at each time point with Doppler ultrasound. Results A total of 38 healthy volunteers (aged 50±8 years, eGFR 95±13 ml/min/1.73 m, 69% women) and 18 CKD stage 2-3 patients (aged 55±15 years, eGFR 64±32 ml/min/1.73m, 56% women) were included. Renal PI was significantly lower in CKD patients (1304±762 vs 2989 ±2503 arbitrary units, p=0.034), whereas RRI did not differ (0.66± 0.07 vs 0.63± 0.04), p=0.10). PI was lower in CKD due to vascular nephropathy (n=3) or interstitial nephritis (n=4) than CKD due to diabetes (n=4) or other causes (7). In continuous analysis, PI correlated with eGFR (spearman’s r=0.54, p=0.005) but not with blood pressure. Renal PI did not change after nitroglycerin in both groups; RRI decreased in healthy (from 0.64±0.03 to 0.61±0.02, p=0.01) but not in CKD patients. Conclusion In this study, contrast-enhanced ultrasound identified important alterations in renal microperfusion in patients with moderate CKD. Whether a low perfusion index predicts renal function decline needs further study. Sublingual nitroglycerin seems to have limited potential as a new test of renal flow reserve.