Mild renal dysfunction and renal vascular resistance in primary hypertension

Research on the correlation between the renal resistive index, renal microvessel density, and fibrosis

BACKGROUND

This study was designed to investigate the relationship between the renal resistive index (RRI), renal microvessel density (RMD), and fibrosis in patients with chronic kidney disease (CKD).

METHODS

A total of 73 CKD patients were included in the study. Prior to kidney biopsy, we recorded the RRI of the interlobar artery and the estimated glomerular filtration rate (eGFR). Immunohistochemical analysis was performed to assess CD34 expression, and Masson staining was used to evaluate histopathological specimens for RMD and the degree of fibrosis. The percentage of the positive area (PPA) was recorded. Subsequently, we investigated the correlation between RRI, RMD, and kidney fibrosis.

RESULTS

RMD (CD34 PPA-total and CD34 PPA-peritubular capillary) showed a slight increase in early CKD stages (1-2) and gradually declined from CKD stages 2 to 5. No correlation was observed between the RRI and RMD or between the RRI and fibrosis across CKD stages 1 to 5. However, across CKD stages 2 to 5, RRI negatively correlated with CD34 PPA-glomerulus (r = -0.353, p = 0.022), but no correlation was found with CD34 PPA-total, CD34 PPA-peritubular capillary, or kidney fibrosis. eGFR showed a positive correlation with RMD (CD34 PPA-total, CD34 PPA-peritubular capillary, and CD34 PPA-glomerulus) across CKD stages 2 to 5, while no correlation was found from CKD stages 1 to 5.

CONCLUSION

There was no correlation between RRI and RMD or between RRI and fibrosis across CKD stages 1 to 5 (RRI ≤ 0.7).

Lipocalin-2, Soluble Transferrin Receptor, and Erythropoietin in Anemia During Mild Renal Dysfunction

Background

Mild renal dysfunction (MRD) is a common condition often associated with diabetes or inflammation and regarded as a risk factor for cardiovascular disease in patients with hypertension. Few studies have examined the role of lipocalin-2 (LCN2) as a regulator of iron and a contributor to anemia in MRD. The aim of this study was to investigate the relationship between LCN2, soluble transferrin receptor (sTfR), erythropoietin (EPO), reticulocyte production, and the prevalence of anemia in MRD.

Methods

A total of 235 subjects with MRD were evaluated. LCN2, sTfR, EPO, and iron levels were measured. Reticulocyte maturity index (RMI) and corrected LCN2 (cLCN2) values were calculated using reticulocyte subpopulations and the inflammation index, respectively.

Results

Subjects with LCN2 elevation had significantly higher sTfR and significantly lower RMI levels than those without LCN2 elevation. Compared to subjects without LCN2 elevation, those with LCN2 elevation exhibited significantly lower hemoglobin (12.9 ± 1.6 g/dL vs 14.0 ± 1.7 g/dL, p < 0.001) and more prevalent anemia (27.7% vs 13.3%, p = 0.008). Patients with anemia had significantly higher LCN2 and cLCN2 than those without anemia. LCN2 was positively correlated with sTfR and negatively correlated with RMI but not EPO. Elevated LCN2 led to a 1.3-fold increase in the prevalence of anemia (odds ratio: 1.302; 95% CI: 1.012-2.527; p < 0.001).

Conclusion

LCN2 elevation may contribute to the development of anemia in MRD, particularly in conjunction with restricted iron availability and suppressed reticulocyte production.

The renal resistive index is associated with microvascular remodeling in patients with severe obesity

BACKGROUND

Renal hemodynamics is impaired since the early stage of cardiometabolic disease. However, in obesity, its noninvasive ultrasound assessment still fails to provide pathophysiologic and clinical meaningfulness. We aimed to explore the relationship between peripheral microcirculation and renal hemodynamics in severe obesity.

METHODS

We enrolled fifty severely obese patients with an indication for bariatric referring to our outpatient clinic. Patients underwent an extensive reno-metabolic examination, paired with Doppler ultrasound and measurement of the renal resistive index (RRI). On the day of the surgery, visceral fat biopsies were collected to perform an ex-vivo complete microcirculatory assessment. Media-to-lumen ratio (M/L) and vascular response to acetylcholine (ACh), alone or co-incubated with N G -nitro arginine methyl ester (L-NAME), were measured.

RESULTS

Patients were stratified according to their normotensive (NT) or hypertensive (HT) status. HT had lower estimated glomerular filtration rate and higher RRI compared to NT, while the presence and extent of albuminuria were similar between the two groups. Concerning microcirculatory assessment, there were no differences between groups as regards the microvascular structure, while the vasorelaxation to ACh was lower in HT ( P = 0.042). Multivariable analysis showed a relationship between M/L and RRI ( P  = 0.016, St. β 0.37) and between albuminuria and the inhibitory response of L-NAME to Ach vasodilation ( P   =  0.036, St. β = -0.34). Notably, all these correlations were consistent also after adjustment for confounding factors.

CONCLUSIONS

The RRI and albuminuria relationship with microvascular remodeling in patients affected by severe obesity supports the clinical implementation of RRI to improve risk stratification in obesity and suggests a tight pathophysiologic connection between renal haemodynamics and microcirculatory disruption.

Elevated Intrarenal Resistive Index Predicted Faster Renal Function Decline and Long-Term Mortality in Non-Proteinuric Chronic Kidney Disease

Background. Intrarenal resistive index (RI) ≥ 0.80 predicts renal outcomes in proteinuric chronic kidney disease (CKD). However, this evidence in non-proteinuric patients with CKD of unknown etiology is lacking. In this study, we assessed the effect of intrarenal RI on renal function and all-cause mortality in non-proteinuric patients with CKD of unknown etiology despite an extensive diagnostic work-up. Methods. Non-proteinuric CKD patients were evaluated in a retrospective longitudinal study. Progression of renal disease was investigated by checking serum creatinine levels at 1, 3, and 5 years and defined by a creatinine level increase of at least 0.5 mg/dL. The discrimination performance of intrarenal RI in predicting the 5-year progression of renal disease was assessed by calculating the area under the receiver operating characteristic curve (AUROC). Results. One-hundred-thirty-one patients (76 ± 9 years, 56% males) were included. The median follow-up was 7.5 years (interquartile range 4.3−10.5) with a cumulative mortality of 53%, and 5-year renal disease progression occurred in 25%. Patients with intrarenal RI ≥ 0.80 had a faster increase of serum creatinine levels compared to those with RI < 0.80 (+0.06 mg/dL each year, 95% CI 0.02−0.10, p < 0.010). Each 0.1-unit increment of intrarenal RI was an independent determinant of 5-year renal disease progression (odds ratio 4.13, 95% CI 1.45−12.9, p = 0.010) and predictor of mortality (hazards ratio 1.80, 95% CI 1.05−3.09, p = 0.034). AUROCs of intrarenal RI for predicting 5-year renal disease progression and mortality were 0.66 (95% CI 0.57−0.76) and 0.67 (95% CI 0.58−0.74), respectively. Conclusions. In non-proteinuric patients with CKD of unknown etiology, increased intrarenal RI predicted both a faster decline in renal function and higher long-term mortality, but as a single marker, it showed poor discrimination performance.

Vasopressor Therapy and Blood Pressure Management in the Setting of Acute Kidney Injury

Acute kidney injury (AKI) is common in the setting of shock. Hemodynamic instability is a risk factor for the development of AKI, and pathophysiological mechanisms include loss of renal perfusion pressure and impaired microcirculation. Although restoration of mean arterial pressure (MAP) may mitigate the risk of AKI to some extent, evidence on this is conflicting. Also debatable is the optimal blood pressure needed to minimize the risk of kidney injury. A MAP of 65 mm Hg traditionally has been considered adequate to maintain renal perfusion pressure, and studies have failed to consistently show improved outcomes at higher levels of MAP. Therapeutic options to support renal perfusion consist of catecholamines, vasopressin, and angiotensin II. Although catecholamines are the most studied, they are associated with adverse events at higher doses, including AKI. Vasopressin and angiotensin II are noncatecholamine options to support blood pressure and may improve microcirculatory hemodynamics through unique mechanisms, including differential vasoconstriction of efferent and afferent arterioles within the nephron. Future areas of study include methods by which clinicians can measure renal blood flow in a macrocirculatory and microcirculatory way, a personalized approach to blood pressure management in septic shock using patient-specific measures of perfusion adequacy, and novel agents that may improve the microcirculation within the kidneys without causing adverse microcirculatory effects in other organs.

Comparison of renal arterial resistive index in type 2 diabetic nephropathy stage 0-4

Chronic kidney disease (CKD) is one of world health problems and its prevalence and incidence is increasing. Chronic Kidney Failure involves a range of pathophysiologic processes that are associated with impaired renal function, leading to cardiovascular morbidity and mortality. Renal artery resistive index (RI) is indicator of atherosclerotic change in small vessels. The current study was aimed to assess RI in diabetic nephropathy patients at stage 0-4 and to compare RRI with HbA1c, systolic blood pressure, diastolic blood pressure, albuminuria and glomerular filtration rate (GFR). In this cross sectional study,100 diabetic nephropathy patients who attend to nephrology clinic of Ali-ibn Abi Talib Hospital were entered to the study. Ultrasound Doppler renal resistive index was measured and other information was recorded from their last lab data that was recorded in their medical records. Variable included: systolic blood pressure, diastolic blood pressure, albuminuria, GFR, HbA1c. All data was analyzed by Pearson's Correlation Coefficient. The findings indicated a significant correlation of RI with systolic BP (p=0.04 R=0.75), microalbuminuria (P=0.001 R=0.67), and GFR (P=0.001 R=0.76), while diastolic BP (P=0/45 R=0/32), HbA1c (P=0/56 R=0/43) were not found to be associated with RI. The findings indicated that increased systolic blood pressure, albumin excretion (microalbuminuria) and severity of disease were capable of increasing RI values in diabetic nephropathy patients. In addition, decreased GFR.

Chronological renal resistive index increases related to atherosclerotic factors, and effect of renin-angiotensin system inhibitors

BACKGROUND

Renal resistive index (RI) calculated using renal Doppler ultrasonography (RDU) has recently been considered a clinically important indicator of renal outcome, survival, and systemic arteriosclerotic disorders. However, the cause of RI elevation remains unclear. The present study was an effort to first, identify the factors related to RI elevation, and second, understand the effect of renin-angiotensin system inhibitors (RAS-Is) on renal RI elevation.

METHODS

We carried out this single-center case-control study among 100 CKD patients, recruited from outpatients who underwent RDU more than twice, at least a year apart. The rate of renal RI change per year (dRIpy) was chosen as the dependent variable: [(last examined renal RI-initial examined renal RI)/(initial examined renal RI × period of observation) × 100 (%/year)]. We examined the association between dRIpy and other clinical and biological data.

RESULTS

Among 100 CKD patients, the average serum creatinine and eGFR were 1.76 ± 0.84 mg/dL and 37.0 ± 18.2 ml/min/1.73 m², respectively. The average dRIpy in all patients was 1.8 ± 1.4%/year. The linear multiple regression demonstrated that dRIpy was positively associated with the presence of diabetes mellitus (DM) and high low-density lipoprotein cholesterol (LDL) levels, and negatively with eGFR and RAS-I use.

CONCLUSIONS

This study demonstrated that the elevation of RI was related to DM, eGFR, high LDL, and the use of RAS-Is. In particular, RAS-Is could contribute towards suppressing the elevation of RI in CKD patients and towards preventing the development of renal failure in CKD patients.

Renal resistive index in hypertensive patients

Spectral Doppler ultrasonography provides the evaluation of renal resistive index (RRI), a noninvasive and reproducible measure to investigate arterial compliance and/or resistance. RRI seems to possess an important role in the evaluation of diverse cases of secondary hypertension. In essential hypertension, RRI is associated with subclinical markers of target organ damage and reflects renal disease progression beyond albuminuria and creatinine clearance. Also, RRI can estimate cardiovascular and renal risk. The evaluation of RRI may also help the therapeutic decisions. Given its simple assessment, RRI emerges as a simple method and a "multifunctional" tool that could help on the cardiovascular risk evaluation of the hypertensive patient.

Should renal color Doppler ultrasonography be a routine test in newly diagnosed hypertensive patient?

: European Society of Hypertension/European Society of Cardiology guidelines recommend calculation of estimated glomerular filtration rate and evaluation of urinary albumin excretion rate as routine tests in the initial evaluation and during the follow-up of all hypertensive patients. However, from a clinical point of view, renal ultrasound - a noninvasive, readily available and cheap imaging modality - could contribute to the better evaluation of a hypertensive patient by identifying common causes of secondary hypertension (HTN) originating from the kidney and more recently by detecting renal injury in severe or long-standing essential HTN by measuring renal resistive indexes. The purpose of this review is to summarize the actual evidence which could support a larger use of renal ultrasound in the work-up of patients with newly diagnosed HTN.

Increased renal resistive index in type 2 diabetes: Clinical relevance, mechanisms and future directions

Type 2 diabetes is a global health challenge. In type 2 diabetes both microvascular (nephropathy, retinopathy, neuropathy) and macrovascular complications arise. In kidney, renal pathological changes leading to diabetic nephropathy are mainly secondary to atherosclerosis of the intra and extra renal arteries together with microangiopathy of the glomerular capillaries, afferent arterioles and efferent arterioles. Renal resistive index (RRI) is defined as a ratio of the difference between maximum and minimum (end-diastolic) flow velocity to maximum flow velocity derived from the Doppler measurements of main renal and intrarenal (segmental/interlobar) arteries. Renal resistive index is tightly related to renal arteriolosclerosis, and represents an integrated index of arterial compliance, pulsatility and downstream microvascular impedance. In meantime, growing suggest that RRI has also been closely related with atherosclerosis. Most studies performed in type 2 diabetes showed RRI is increased in type 2 diabetes. In this review, we summarize the data regarding RRI with regard to performed studies, pathogenesis and prognosis, especially focusing on type 2 diabetes (T2D). We also review the data regarding the development of metabolic syndrome (MetS) and RRI.

Is carotid sonography a useful tool for predicting functional capabilities in ischemic stroke patients following carotid artery stenting?

Carotid stenosis is a major cause of stroke and timely intervention with stenting manipulation can significantly reduce the risk of secondary stroke. The impact of stenting procedures on patient functional capabilities has not yet been explored. The primary aim of this study was to examine associations between periprocedural carotid sonography parameters and post-treatment functional capabilities in stroke patients.Sixty-seven patients who received carotid stenting at 1 angiography laboratory were included. Prestenting and poststenting carotid duplex data were recorded and resistance index (RI) differences at various carotid system locations were compared. The modified Rankin Scale (mRS) was used to assess functional capability. All of the studied parameters were analyzed by SPSS (version 16.0, SPSS Inc, Chicago, IL).Following stenting, mRS scores improved (n = 44) or remained stationary (n = 23). Net contralateral internal carotid artery (ICA) RI for patients with improved mRS was lower compared to that for patients with stationary mRS (median = 0.040 vs 0.11; P = 0.003). The contralateral common carotid artery RI before and after stenting differed significantly (P < 0.050) in both. The ipsilateral ICA RI differed (P < 0.050) only in patients with improved mRS. The difference in mean transit time, Barthel index, net ipsilateral ICA RI, net contralateral external carotid artery RI, postipsilateral common carotid artery RI, and postipsilateral ICA RI differed significantly between different baseline stroke severity groups (P < 0.050).Carotid artery stenting improved physical function in a proportion of ischemic stroke patients with carotid stenosis. Carotid ultrasound is a useful assessment tool to predict likely functional outcomes following carotid artery stenting.

Role of Extracranial Carotid Duplex and Computed Tomography Perfusion Scanning in Evaluating Perfusion Status of Pericarotid Stenting

Carotid stenting is an effective treatment of choice in terms of treating ischemic stroke patients with concomitant carotid stenosis. Though computed tomography perfusion scan has been recognized as a standard tool to monitor/follow up this group of patients, not everyone could endure due to underlying medical illness. In contrast, carotid duplex is a noninvasive assessment tool and could track patient clinical condition in real time. In this study we found that “resistance index” of the carotid ultrasound could detect flow changes before and after the stenting procedure, thus having great capacity to replace the role of computed tomography perfusion exam.

Left ventricular dilatation and subclinical renal damage in primary hypertension

OBJECTIVE

A new classification of left ventricular geometry based on left ventricular dilatation and concentricity has recently been developed. This classification identifies subgroups differing with regard to systemic haemodynamics, left ventricular function and cardiovascular prognosis. We investigated the relationship between the new classification of left ventricular geometry and subclinical renal damage, namely urine albumin excretion and early intrarenal vascular changes in primary hypertensive patients.

METHODS

A total of 449 untreated hypertensive patients were studied. Four different patterns of left ventricular hypertrophy (eccentric nondilated, eccentric dilated, concentric nondilated and concentric dilated hypertrophy) were identified by echocardiography. Albuminuria was measured as the albumin-to-creatinine ratio. Early intrarenal vascular changes, expressed as the renal volume to resistive index ratio, were evaluated by ultrasound and Doppler scan.

RESULTS

Patients with concentric dilated left ventricular hypertrophy had higher albumin excretion rates (P = 0.0258) and prevalence of microalbuminuria (P < 0.0001) and lower renal volume to resistive index ratio than patients with concentric nondilated hypertrophy (P = 0.0093). Patients with eccentric dilated hypertrophy showed a higher prevalence of microalbuminuria than patients with eccentric nondilated hypertrophy (P < 0.0001). Moreover, patients with chamber dilatation showed a higher prevalence of microalbuminuria (P = 0.0002) and lower renal volume to resistive index ratio (P = 0.0107) than patients without chamber dilatation. After adjusting for potentially confounding variables, left ventricular chamber dilatation was an independent predictor of subclinical renal damage.

CONCLUSION

Left ventricular dilatation is associated with subclinical renal damage in hypertension. These findings extend previous reports and provide a pathophysiological rationale for the observed unfavourable prognosis in patients with left ventricular dilatation.

Predictive value of dynamic renal resistive index (DRIN) for renal outcome in type 2 diabetes and essential hypertension: a prospective study

BACKGROUND

Hypertension (EH) and type 2 diabetes (T2DM) are major causes of chronic kidney disease (CKD) and identification of predictors of CKD onset is advisable. We aimed to assess whether dynamic renal resistive index (DRIN), as well as other markers of systemic vascular damage, are able to predict albuminuria onset and estimated glomerular filtration rate (eGFR) decline in patients with T2DM or EH.

METHODS

In this prospective observational cohort study, 27 T2DM and 43 EH patients, free of CKD at baseline, were followed-up for 4.1 ± 0.6 years. Resistive Index (RI), endothelium-dependent (FMD) and independent vasodilation in the brachial artery (after glyceryl trinitrate - GTN - 25 μg s.l.), carotid-femoral Pulse Wave Velocity (PWV), Augmentation Index (AIx), DRIN (%RI change after GTN 25 μg s.l.) were evaluated.

RESULTS

Patients developing microalbuminuria were older, more frequently T2DM, with higher UACR at baseline, and showed higher DRIN (-2.8 ± 6.7 vs -10.6 ± 6.4 %, p = 0.01) and PWV (9.9 ± 1.3 vs 7.9 ± 1.5 m/s, p = 0.004) at baseline. The best predictors of microalbuminuria onset were DRIN > -5.16 % in T2DM (sensitivity 0.83, specificity 0.80) and PWV > 8.6 m/s in EH (sensitivity 0.96, specificity 1.00). Individuals whose eGFR declined (n = 27) had higher eGFR at baseline, but similar vascular characteristics; however in EH showing eGFR decline, baseline DRIN and PWV were higher. PWV showed a steeper progression during follow-up in patients developing albuminuria (Visit-outcome interaction: p = 0.01), while DRIN was early compromised but no further impaired (Visit-outcome interaction: p = 0.04).

CONCLUSIONS

PWV and DRIN are able to predict microalbuminuria onset in newly diagnosed EH and T2DM. DRIN is early compromised in T2DM patients developing microalbuminuria.

Renal resistive index as a marker of vascular damage in cardiovascular diseases

The article presents changeability of renal resistive index (RRI) in various cardiovascular diseases and considers the usefulness of the marker and interpretational difficulties of the index. The values of RRI are not specific to an individual disease, but in a selected group of patients, it seems to be a perfect marker of cardiovasculorenal changes and a predictor of rapid loss of a renal function. The RRI usually does not reflect the vascular resistance, but is dependent on total and local vascular bed compliance changing with age, in the course of consecutive diseases and the influence of drugs. Under specific conditions, RRI appears to be a good marker of vascular damage. This review summarizes current concepts in RRI interpretation against the cardiovascular pathologies, focusing on the vascular damage association with regard to the complex nature of RRI value variability.

Renal Stenting for Kidney Salvage in the Management of Renal Artery Atherosclerotic Stenosis

We studied the usefulness of preoperative resistance index to select patients who will benefit most from renal stenting. Sixty-two patients underwent renal stenting. All had chronic renal insufficiency with serum creatinine values ranging from 1.5 to 2.5 mg/dL and blood urea nitrogen between 80 and 107 mg/dL. All treated renal artery stenosis were >70%. Reduction in blood pressure in the early stages was observed in 39 (62.9%) patients; 31 (79.4%) patients returned to preoperative values within 12 months. A progressive reduction in creatinine values and blood urea nitrogen was reached in 43 (69.4%) patients, 12 (19.4%) patients remained unchanged, and the remaining 7 (11.2%) patients worsened. The best improvement in renal function was obtained in patients with a resistance index of ≤0.75 A preoperative resistance index up to 0.75 could be used as an indicator to predict which candidates will have improved renal function after stenting.

Ultrasound Doppler renal resistive index: a useful tool for the management of the hypertensive patient

The Doppler-derived renal resistive index has been used for years in a variety of clinical settings such as the assessment of chronic renal allograft rejection, detection and management of renal artery stenosis, evaluation of progression risk in chronic kidney disease, differential diagnosis in acute and chronic obstructive renal disease, and more recently as a predictor of renal and global outcome in the critically ill patient. More recently, evidence has been accumulating showing that an increased renal resistive index not only reflects changes in intrarenal perfusion but is also related to systemic hemodynamics and the presence of subclinical atherosclerosis, and may thus provide useful prognostic information in patients with primary hypertension. On the basis of these results, the evaluation of renal resistive index has been proposed in the assessment and management of patients with primary hypertension to complement other signs of renal abnormalities.

Predictive role of renal resistive index for clinical outcome after revascularization in hypertensive patients with atherosclerotic renal artery stenosis: a monocentric observational study

Background

The present study evaluated the predictive value of renal resistive index (RI) for renal function and blood pressure (BP) outcome in hypertensive patients with unilateral atherosclerotic renal artery stenosis submitted to successful revascularization.

Methods

In 158 hypertensive patients with atherosclerotic renal artery stenosis RI was acquired. Twelve months after revascularization, they were classified on the basis of renal function and BP outcome as benefit (BP < 140/90 mmHg or diastolic BP reduction > 15 mmHg with the same of reduced drugs; decrease in glomerular filtration rate > 20%), or failure.

Results

Regarding renal function outcome, RI in the stenotic and in the contralateral kidney were significantly higher in patients with failure (n = 20) than in those with benefit (0.72 ± 0.11 vs 0.61 ± 0.11 and 0.76 ± 0.08 vs 0.66 ± 0.09, p < 0.05). Among different cutpoints generated, RI in the contralateral kidney >0.73 provided the largest area under the curve (0.77), and the highest sensitivity (80%) and specificity (72%). In the multivariate logistic regression analysis, RI in the contralateral kidney >0.73 was an independent predictor of a failure in renal function outcome.

Regarding BP outcome, patients with no benefit from revascularization (n = 60) had similar RI in the stenotic and contralateral kidney (p = ns), but presented higher pulse pressure, albuminuria and hypertension duration in comparison to patients with improved BP control.

Conclusions

RI in the contralateral kidney is an independent predictor of renal function outcome after successful revascularization in hypertensive patients with unilateral atherosclerotic renal artery stenosis, whereas it is not able to predict blood pressure outcome.

Impact of cardiovascular organ damage on cortical renal perfusion in patients with chronic renal failure

Introduction. Properly preserved renal perfusion is the basic determinant of oxygenation, vitality, nutrition, and organ function and its structure. Perfusion disorders are functional changes and are ahead of the appearance of biochemical markers of organ damage. The aim of this study was to evaluate a relationship between the renal cortex perfusion and markers of cardiovascular organ damage in patients with stable chronic renal failure (CKD). Methods. Seventeen patients (2 F; 15 M; age 47 ± 16) with stable CKD at 2–4 stages and hypertension or signs of heart failure were enrolled in this study. Blood tests with an estimation of renal and cardiac functions, echocardiographic parameters, intima-media thickness (IMT), renal resistance index (RRI), and total (TPI), proximal (PPI), and distal (DPI) renal cortical perfusion intensity measurements were collected. Results. DPI was significantly lower than PPI. TPI significantly correlated with age, Cys, CKD-EPI (cystatin), and IMT, whereas DPI significantly depended on Cystain, CKD-EPI (cystatin; cystatin-creatinine), IMT, NT-proBNP, and troponin I. In multiple stepwise regression analysis model only CKD-EPI (cystatin) independently influenced DPI. Conclusions. Cardiovascular and kidney damage significantly influences renal cortical perfusion. Ultrasound measurement of renal perfusion could be a sensitive method for early investigation of cardiovascular and renal injuries.

Physiological biomarkers of acute kidney injury: a conceptual approach to improving outcomes

The past 5-10 years have brought significant advances in the identification and validation of novel biochemical biomarkers in the prevention and treatment of acute kidney injury (AKI). These biochemical biomarkers remain research tools but we anticipate that soon they will be employed in clinical practice. A Consensus Conference held by the Acute Dialysis Quality Initiative (ADQI) recently reviewed the evidence, and identified gaps and a research agenda. Furthermore, at this meeting was the birth of an initiative to comprehensively identify new opportunities to characterize the physiological changes during the course of AKI based upon a conceptual framework for the detection and monitoring of renal ischemia-reperfusion injury. This framework includes a transition from monitoring physiological biomarkers of adequate renal perfusion, to pathophysiologic biomarkers of renal hypoperfusion, and finally biomarkers of kidney cell structural injury/damage. Techniques to measure physiological changes in AKI include several physiological variables that might be used in an interactive way to supplement clinical information and biochemical damage biomarkers in the diagnosis and management of AKI. This review summarizes the spectrum of physiological parameters and potential new physiological methods that enable identification of high-risk patients for AKI, facilitate early diagnosis, and differential diagnosis to guide therapeutic management and prognostication. Finally, we propose a research agenda for the next 5 years to facilitate the development and validation of physiological biomarkers in AKI.

Angiotensin II type 2 receptor mediates sex differences in mice renal interlobar arteries response to angiotensin II

OBJECTIVE

Functional sex differences are described in several vascular beds. In the case of renal vessels, sex differences could influence processes like regulation of blood pressure and ion balance. Angiotensin II and nitric oxide are important regulators of renal vascular tone. Females have higher nitric oxide synthase expression, nitric oxide bioavailability and ratio of angiotensin II type 2/type 1 receptors. Thus, our objective was to examine whether renal interlobar arteries present sex differences in their response to angiotensin II, and whether angiotensin II type 2 receptors play a role in such differences.

METHODS

We investigated the isometric contraction and relaxation of interlobar arteries from female and male mice under blockade of nitric oxide synthases and angiotensin II type 2 receptors. We also investigated the expression of angiotensin II receptors (type 1 and 2) and endothelial nitric oxide synthase.

RESULTS

Significantly less intense contraction to angiotensin II were seen in arteries from females in comparison to male mice. Inhibition of nitric oxide synthases and endothelial removal abolished this difference. Angiotensin II type 2 receptors blockade enhanced contraction to angiotensin II in females, but not in males. Endothelial-dependent vasodilation was more dependent on nitric oxide in females than in males. Expression of angiotensin II type 1 and type 2 receptors was similar between sexes. Expression of endothelial nitric oxide synthase was higher in females.

CONCLUSION

A sex-specific, nitric oxide-mediated effect via angiotensin II type 2 receptors underlies the sex differences in the response of interlobar arteries to angiotensin II. Our findings may help understanding sex differences in renal hemodynamics and blood pressure control.

Renal Doppler ultrasound: a new tool to assess renal perfusion in critical illness

Despite our increasing ability to support vital organs and resuscitate patients, the morbidity and mortality of acute kidney injury (AKI) remain high in the intensive care unit (ICU). The ability to predict the occurrence of AKI is crucial for the development of preventive strategies. Early diagnosis of AKI requires markers that are sensitive and easily applicable in clinical practice. The use of Doppler ultrasonography to assess renal perfusion is increasing in many kidney diseases and in the ICU. The Doppler-based renal resistive index, which is a simple, rapid, noninvasive, and repeatable marker, could be a promising tool to prematurely detect the patients most at risk of developing AKI in the ICU and to distinguish transient from persistent AKI. Moreover, the resistive index could also be useful to adjust preventive or therapeutic modalities for the kidney perfusion at the bedside. The recent progress in ultrasound with contrast-enhanced ultrasound gives the opportunity to assess not only the kidney macrocirculation but also the kidney microcirculation in the ICU.

Renal resistive index and parathyroid hormone relationship with renal function in nondiabetic patients

INTRODUCTION

The renal resistive index (RRI) reflects intrarenal vascular resistance and stiffness, which are associated with chronic kidney disease. The links connecting renal function, intrarenal arterial resistance, and parathyroid hormone (PTH) with hypertension and metabolic factors remain elusive. The aim of this study is to investigate the possible relationship of RRI with glomerular filtration rate, PTH, hypertension, obesity (body mass index and waist-to-hip ratio), bioelectrical impedance analysis in body composition assessment, serum lipids, and insulin resistance assessed by homoeostasis model insulin resistance index.

PATIENTS AND METHODS

This study was carried out on 387 (246 women, 141 men) nondiabetic patients, between >25 and <75 years, referred to an Internal Medicine Clinic and Day Hospital for essential hypertension, overweightness-obesity, and/or dyslipidemia. Lower salt/lower calorie Mediterranean diet, physical activity increase, smoking withdrawal, and lifestyle counseling, provided by a health psychologist support, were prescribed.

RESULTS

Higher hypertension risk, present in 42.5% of the overall group of eligible patients (164/387), is associated with high PTH and high RRI, along with greater renal insufficiency, insulin resistance, and obesity. There is a straight linear relationship of RRI to PTH (0.202; p=0.009) in arterial hypertension, which is not observed in normal blood pressure patients. By gender-adjusted multiple linear regression analysis, it was found that fat mass, waist-to-hip ratio, and PTH account significantly for 62.3% of the variance to RRI in hypertensive patients.

CONCLUSION

Increased arterial stiffness and intrarenal arterial resistance are associated with higher PTH in arterial hypertension; obesity (defined by greater fat mass and waist-to-hip ratio) and PTH are the independent conditions that account significantly for higher RRI.

Dynamic evaluation of renal resistive index in normoalbuminuric patients with newly diagnosed hypertension or type 2 diabetes

AIM/HYPOTHESIS

Renal resistive index is a useful measure for quantifying alterations in renal blood flow. In the present study we evaluated resistive index at baseline and after vasodilation induced by nitroglycerine in normoalbuminuric patients with type 2 diabetes or essential hypertension, relating the values to indices of systemic vascular dysfunction.

METHODS

Newly diagnosed treatment-naïve type 2 diabetic (n = 32) and hypertensive patients (n = 49) were compared with 27 age- and sex-matched healthy controls. Renal resistive index was obtained by duplex ultrasound at baseline and after 25 μg sublingual nitroglycerine. Endothelium-dependent (flow-mediated dilation) and -independent (response to nitroglycerine) vasodilation in the brachial artery was assessed by computerised edge detection system. Carotid-femoral pulse-wave velocity and augmentation index were assessed by applanation tonometry. Nitrotyrosine levels, an index of oxidative stress, were also measured.

RESULTS

Resistive index was higher in diabetic than in hypertensive patients and controls (p < 0.001), while changes in resistive index induced by nitroglycerine were lower in hypertensive patients compared with controls (p < 0.01), and were further reduced in type 2 diabetic patients. Hypertensive and diabetic patients showed significantly increased arterial stiffness, nitrotyrosine levels and reduced endothelial function than controls (p < 0.05). Changes in resistive index induced by nitroglycerine were independently related to serum glucose, reactive hyperaemia and aortic pulse-wave velocity in the overall population.

CONCLUSIONS/INTERPRETATION

These results support the dynamic evaluation of renal resistive index as an early detector of renal vascular alterations in the presence of type 2 diabetes and hypertension, even before the onset of microalbuminuria.

Renal vascular response to angiotensin II inhibition in intensive antihypertensive treatment of essential hypertension

INTRODUCTION

High blood pressure (BP) leads to target organ damage. It is suggested that regression of early organ lesions is possible on condition of BP normalization. The study objective was to assess whether permanent reduction of BP to the recommended values modifies renal vascular response to acute angiotensin II inhibition in the Doppler captopril test (DCT) in patients with essential hypertension (EH).

MATERIAL AND METHODS

Twenty-nine persons (58 kidneys) were found eligible for the study: 18 patients with EH and 11 healthy volunteers constituting the control group. Glomerular filtration rate estimation (eGFR), 24-h ambulatory BP monitoring (ABPM) and DCT with evaluation of renal resistive index change (ΔRI) were performed before and after a 6-month period of intensive antihypertensive therapy (IAT). Additional ABPM was performed at the end of IAT.

RESULTS

The mean IAT period was 8.5 ±2.4 months. The mean 24-h values of systolic and diastolic BP in the EH group were significantly lower in the IAT period than at the beginning and at the end of the study. Significantly lower systolic and diastolic BP (p < 0.05) and improvement of renal function (eGFR 121 ±38 vs. 139 ±40 ml/min, p < 0.001) were found after IAT as compared to initial values. Before IAT, ΔRI was significantly lower in the EH group as compared to the controls, but no such differences were found after IAT.

CONCLUSIONS

In EH patients, intensive BP lowering to the recommended values was associated with improvement of renal function and normalisation of renal vascular response to acute angiotensin II inhibition.

Renal resistive index--a valid tool to assess renal endothelial function in humans?

BACKGROUND

In humans, renal endothelial function is assessed by the vasoconstrictive response to L-NG-monomethyl arginine (L-NMMA). We hypothesized that Doppler sonographic measurements of the renal resistive index in response to inhibition of nitric oxide synthase offer a new methodological approach for testing renal endothelial function.

METHODS

Forty-one patients without nephropathy were included. Para-aminohippurate and inulin clearance were performed under basal conditions and during L-NMMA infusion. In parallel, renal resistive index was assessed by Doppler sonography, and central blood pressure was determined.

RESULTS

Following nitric oxide synthase inhibition, renal resistive index increased significantly, and 29% of our patients developed Doppler sonographic diastolic zero flow. Renal plasma flow decreased in response to L-NMMA, and conversely, renal vascular resistance increased. There was no correlation of renal vascular resistance and renal resistive index at baseline and during nitric oxide synthase inhibition. Changes in renal resistive index were not related to changes in renal perfusion or renal vascular resistance. Renal resistive index correlated with central pulse pressure at baseline and during L-NMMA infusion, whereas renal vascular resistance did not correlate with central pulse pressure.

CONCLUSION

Our data do not support the hypothesis that renal resistive index is a tool to test renal endothelial function in humans and should not be used interchangeably with renal vascular resistance.

Intra-renal hemodynamics and carotid intima-media thickness in the metabolic syndrome

AIMS

Metabolic syndrome (MetS) is associated with increased cardiovascular risk. We hypothesize that early vascular changes are already present at the time of diagnosis of MetS. The relationship of different measures of early vascular impairment with body fat distribution and the natural progression of MetS was examined in newly diagnosed subjects non-pharmacologically treated.

METHODS

246 consecutively enrolled subjects were categorized according to the presence of MetS and type 2 diabetes (T2D). Intra-renal Doppler flow was used to ascertain resistive (RI) and pulsatility (PI) indices as markers of vascular resistance. Carotid intima-media thickness (IMT), cutis-rectis (CR) and rectis-aorta (RA) thicknesses were measured by ultrasonography; RA/CR ratio was used as measure of body fat distribution. Pro-inflammatory cytokines, C-reactive protein, oxidative markers insulin and adiponectin blood concentrations were also measured.

RESULTS

Baseline characteristics demonstrated increasing trends in biochemical, inflammatory, and oxidative parameters from MetS-, MetS+, to MetS+/T2D (p<0.001). After adjusting for age, the same increasing trends across the groups were observed in both sexes in IMT (p<0.001), RI (p<0.001) and PI (p<0.001). IMT correlated with RI (r=0.25; p<0.001), PI (r=0.26; p<0.001), and RA/CR ratio (r=0.43; p<0.001).

CONCLUSIONS

Carotid IMT and intra-renal resistances are elevated at an early stage in MetS and are associated with a dysregulated production of fat-derived hormones and cytokines.

Relationship between renal resistive index and early target organ damage in patients with never-treated essential hypertension

The aim of our study was to evaluate renal resistive index (RI) value in never treated hypertensive patients in relation to ambulatory blood pressure measurement (ABPM) values and early target organ damage. The study included 318 subjects: 223 patients with never treated essential hypertension (mean age 37.1 years) and 95 normotensive healthy subjects (mean age 37.9 years). ABPM, echocardiography and carotid and renal arteries duplex color Doppler examinations were performed. RI values in patients with never treated essential hypertension were no different from the normotensive control group (0.59 +/- 0.05 vs 0.59 +/- 0.05; NS). In the untreated patients RI correlated significantly with 24-h pulse pressure (r=0.234; p<0.01) and ambulatory arterial stiffness index (AASI) values (r=0.274; p<0.001), intima-media thickness (IMT) (r=0.249; p<0.001), E'/A' (rho= -0.279; p<0.001) and relative wall thickness (RWT; r=0.185; p<0.01). In the multivariate stepwise analysis, RI values correlated independently with carotid IMT (beta=0.272; p=0.020) and 24-h AASI values (beta=0.305; p=0.009). In normotensive healthy controls, significant independent correlation between RI and carotid IMT and 24-h AASI values were also found. Our study may indicate limited value of RI in differentiating patients with uncomplicated hypertension with healthy controls. Renal resistive values were independently correlated with carotid IMT and AASI. These may suggest that renal vascular resistance is related to two markers for cardiovascular events both in the hypertensive and normotensive subjects.

Renal resistive index and long-term outcome in chronic nephropathies

PURPOSE

To assess the clinical validity of renal resistive index (RI) to determine prognosis and guide therapy over a long-term follow-up in patients with chronic nephropathies and to verify the commonly used threshold value of 0.70.

MATERIALS AND METHODS

Of patients referred to the nephrology center since 1995, 177 were initially enrolled and 86 were followed up for RI and renal function annually for 2-11 years (mean, 5.93 years +/- 2.92 [standard deviation]). All patients gave informed consent for the institutional review board-approved study. Correlations were determined between initial RI and age, estimated glomerular filtration rate (eGFR), proteinuria, hematuria, blood pressure, and biopsy scores. The sample was categorized in four groups on the basis of whether initial values of RI and eGFR were normal, and progression to renal failure was compared. With grouping of the sample by using initial RI (< or =0.61, 0.62-0.69, and > or =0.70), Kaplan-Meier analysis was used to obtain survival curves.

RESULTS

Initial RI correlated with final eGFR (R = -0.4, P < .001), systolic blood pressure (R = 0.39, P < .001), proteinuria (R = 0.28, P = .009), and age (R = 0.28, P = .007). In stepwise multiple regression analysis, RI emerged as the only independent risk factor for the progression to renal failure (P < .001). Among the four groups of patients with different initial RIs and eGFRs, the group with an initial RI of 0.70 or higher showed a worse outcome, independent of initial eGFR. In the Kaplan-Meier analysis by using initial RI, only the group with a value of 0.70 or higher showed a rapid decline of renal function (>50% decrease in eGFR in 6 years).

CONCLUSION

An RI of 0.70 or higher is predictive of an unfavorable outcome in patients with chronic nephropathies.

Renal arterial resistance in septic shock: effects of increasing mean arterial pressure with norepinephrine on the renal resistive index assessed with Doppler ultrasonography

OBJECTIVE

To determine the effects of increasing mean arterial pressure (MAP) on renal resistances assessed by Doppler ultrasonography in septic shock.

DESIGN AND SETTING

Prospective, single-center, nonrandomized, open-label trial in the surgical intensive care unit in a university teaching hospital.

PATIENTS AND PARTICIPANTS

11 patients with septic shock who required fluid resuscitation and norepinephrine to increase and maintain MAP at or above 65 mmHg.

INTERVENTIONS

Norepinephrine was titrated in 11 patients in septic shock during three consecutive not randomized periods of 2 h to achieve a MAP at successively 65, 75, and 85 mmHg.

MEASUREMENTS AND RESULTS

At the end of each period hemodynamic parameters and renal function variables (urinary output, creatinine, clearance) were measured, and Doppler ultrasonography was performed on interlobar arteries to assess the renal resistive index. When increasing MAP from 65 to 75 mmHg, urinary output increased significantly from 76 +/- 64 to 93 +/- 68 ml/h and the resistive index significantly decreased from 0.75 +/- 0.07 to 0.71 +/- 0.06. No difference was found between 75 and 85 mmHg.

CONCLUSIONS

Doppler ultrasonography and resistive index measurements may help determine in each patient the optimal MAP for renal blood flow and may be a relevant end-point to titrate the hemodynamic treatment in septic shock.

Ambulatory arterial stiffness index and renal abnormalities in primary hypertension

OBJECTIVE

Arterial stiffness is a predictor of cardiovascular mortality in the general population as well as in hypertension and end-stage renal disease. We investigated the relationship between a recently proposed ambulatory blood pressure monitoring-derived index of arterial stiffness and early signs of renal damage in patients with primary hypertension.

DESIGN AND SETTING

A total of 168 untreated patients with sustained primary hypertension were studied. Ambulatory arterial stiffness index (AASI) was calculated based on 24-h ambulatory blood pressure readings. Albuminuria was measured as the albumin to creatinine ratio. Creatinine clearance was estimated using the Cockcroft-Gault formula, and the interlobar resistive index was evaluated by renal ultrasound and Doppler examination.

RESULTS

AASI was positively related to urinary albumin excretion and resistive index, and was negatively related to estimated creatinine clearance and renal volume to the resistive index ratio. Patients with AASI above the median (i.e. > 0.51) showed a higher prevalence of microalbuminuria and a mild reduction in creatinine clearance. Moreover, patients with microalbuminuria or a mild reduction in creatinine clearance had significantly higher AASI values compared with those without, and the greater the renal involvement, the greater the AASI. After adjusting for several potentially confounding variables, we found that each standard deviation increase in AASI (i.e. 0.16) entails an almost twofold greater risk of renal involvement.

CONCLUSION

Increased AASI is independently associated with early signs of renal damage in patients with sustained primary hypertension. These results strengthen the usefulness of AASI and ambulatory blood pressure monitoring in cardiovascular risk assessment.