The renal resistive index: is it a misnomer?

Changes in renal microcirculation in patients with nephrotic and nephritic syndrome: The role of resistive index

BACKGROUND

Renal Resistive Index (RRI) is an important and non-invasive parameter of renal damage and it is associated with abnormal microcirculation or to a parenchymal injury. The aim of our study was to compare the RRI in a cohort of patients with renal diseases categorized in three groups: nephrotic syndrome (NS), acute nephritic syndrome (ANS) and patients with urinary abnormalities (UA).

METHODS

Four hundred eighty-two patients with median age of 48 years (IQR 34-62) with indications for kidney disease were included in the study. Biochemical analyses, clinical assessment with detection of NS, ANS and UA and comorbidities were reported. Renal Doppler ultrasound with RRI was evaluated in all patients at the time of enrolment.

RESULTS

NS was present in 81 (16.8 %) patients while ANS in 81 (16.8 %) and UA in 228 (47.3 %) patients. Patients with ANS showed significant higher RRI compared to both patients with NS [0.71 (IQR 0.67-0.78) vs 0.68 (0.63-0.73), p < 0.001] and UA [0.71 (0.67-0.78) vs 0.65 (0.61-0.71), p < 0.001]; RRI was higher in NS patients than in patients with UA [0.68 (0.63-0.73) vs 0.65 (0.61-0.71), p < 0.001]. Patients with ANS had significantly lower median estimated glomerular filtration rate (eGFR) compared respectively to NS and UA patients [19.7 ml/min vs 54.8 ml/min and vs 72.3 ml/min, p < 0.001], while renal length was significantly higher in patients with NS compared to both patients with ANS and UA [111.88 mm vs 101.98 mm and vs 106.15, p < 0.001]. Patients with ANS had more frequently hematuria and RRI ≥ 0.70 (p < 0.001) compared to both patients with NS and patients with UA. The multiple regression analysis, weighted for age, showed that RRI inversely correlates with eGFR (β coefficient = -0.430, p < 0.001).

CONCLUSIONS

Higher and pathological RRI were found in ANS than NS and UA. Renal resistive index in ANS reflects changes in intrarenal perfusion and microvascular dysfunction related to disease characteristics.

Carotid and Renal Vascular Disease

This article review covers carotid artery disease, abdominal aortic aneurysm, and atherosclerotic renal artery disease. It overviews each condition's clinical presentation, diagnosis, medical management, and interventional approach. Carotid artery disease is characterized by hemispheric and neuropsychological manifestations, which can help detect this condition. Screening for carotid artery stenosis is recommended in high-risk individuals and can be performed using different methods, with carotid duplex ultrasonography being the preferred option. Carotid endarterectomy and carotid artery stenting are indicated based on specific criteria and patient characteristics. An abdominal aortic aneurysm is often asymptomatic, but abdominal, back, or flank pain may sometimes be present. Ultrasonography is an effective method for screening and monitoring abdominal aortic aneurysms, with high sensitivity and specificity. Smoking cessation is a crucial intervention for preventing further enlargement of small aortic aneurysms. Repair of abdominal aortic aneurysm is recommended based on the aneurysm size, growth rate, and the presence of symptoms. Endovascular repair is preferred when suitable anatomy is present. Atherosclerotic renal artery disease is associated with resistant hypertension, renal failure, and occasionally pulmonary edema. Doppler ultrasonography is a valuable diagnostic tool for detecting it, while the renal resistive index provides additional insights into disease severity and treatment response. Revascularization is not routinely recommended for atherosclerotic renal artery disease, but it may be considered in specific cases, such as renal arterial fibromuscular dysplasia or unexplained congestive heart failure.

Arterial Hypertension and the Hidden Disease of the Eye: Diagnostic Tools and Therapeutic Strategies

Hypertension is a major cardiovascular risk factor that is responsible for a heavy burden of morbidity and mortality worldwide. A critical aspect of cardiovascular risk estimation in hypertensive patients depends on the assessment of hypertension-mediated organ damage (HMOD), namely the generalized structural and functional changes in major organs induced by persistently elevated blood pressure values. The vasculature of the eye shares several common structural, functional, and embryological features with that of the heart, brain, and kidney. Since retinal microcirculation offers the unique advantage of being directly accessible to non-invasive and relatively simple investigation tools, there has been considerable interest in the development and modernization of techniques that allow the assessment of the retinal vessels’ structural and functional features in health and disease. With the advent of artificial intelligence and the application of sophisticated physics technologies to human sciences, consistent steps forward have been made in the study of the ocular fundus as a privileged site for diagnostic and prognostic assessment of diverse disease conditions. In this narrative review, we will recapitulate the main ocular imaging techniques that are currently relevant from a clinical and/or research standpoint, with reference to their pathophysiological basis and their possible diagnostic and prognostic relevance. A possible non pharmacological approach to prevent the onset and progression of retinopathy in the presence of hypertension and related cardiovascular risk factors and diseases will also be discussed.

Renal Resistive Index of the Main Renal Arteries and Transmitral Flow in Hypertensive Patients

In hypertensive patients, diastolic dysfunction is related to increased resistive index (RI) of parenchymal renal arteries. To determine the existence of a link between RI of the main renal arteries (RRI) and diastolic dysfunction, a group of 127 hypertensive patients, with glomerular filtration rates >50 mL/min (mean estimated glomerular filtration rate: 88.6 ± 15.2 mL/min) and no comorbidities, was studied. RRI and transmitral flow were evaluated using the deceleration time (DT) and E/A ratio. A statistically significant correlation between RRI and DT (>240 ms) was noted (p < 0.001). The RRI cutoff that best discriminated patients with DT >240 ms was 0.675. For each unitary increment of 10 mm in DT, the log-transformed RRI significantly increased by a mean of 0.006 point (p < 0.001). This study revealed the importance of the link between RRI and transmitral DT in addition to the renowned significance of the increase in RI as a cardiovascular risk factor in hypertensive patients without comorbidities.

Association of renal resistance index and arterial stiffness on clinical outcomes in patients with mild-to-moderate renal dysfunction and presence or absence of heart failure with preserved ejection fraction

The renal arterial resistance index (RI) and the brachial-ankle pulse wave velocity (baPWV) are known as indicators of renal vascular resistance/systemic vascular damage and systemic arterial stiffness. The clinical significance of those parameters on clinical outcomes is poorly known in patients with and without heart failure with preserved ejection fraction (HFpEF). Baseline clinical data and the RI assessed by renal Doppler data, baPWV were obtained in patients with (HFpEF group, n = 60) and without HFpEF (non-HFpEF group, n = 51) who had a reduced estimated glomerular filtration rate (eGFR) of > 30 and < 60 mL/min/1.73 m²). We investigated the association between the RI and baPWV and major clinical outcomes including hospitalization for heart failure, cardiovascular death, myocardial infarction or unstable angina or other cardiovascular events and death from another cause. The RI and baPWV were greater in the HFpEF group than in the non-HF group (0.75 ± 0.07 vs. 0.69 ± 0.08, p < 0.001; 2002 ± 430 vs. 1762 ± 300 cm/s, p = 0.001). The RI correlated significantly with baPWV in the HFpEF (r = 0.382, p = 0.003) and non-HFpEF groups (r = 0.414, p = 0.002). During the median follow-up period of 54 months, major clinical outcomes occurred in 41 (36.9%) patients. The RI value, statin use and the presence of HFpEF were major factors for predicting clinical outcomes by multivariate analysis. Among the patients who had mild-to-moderate renal dysfunction, an increased RI and baPWV were observed in HFpEF patients as compared to non-HFpEF patients, but the baPWV similarly correlated with the RI value regardless of HFpFE patients or not. The strong association between the high RI value and presence of HFpEF and major clinical outcomes, suggests that not only the presence of HFpEF but also the high RI value may help to identify the high-risk patients leading to poor clinical outcomes.

Late Gadolinium Enhancement in Cardiac Magnetic Resonance Imaging Is Associated with High Renal Resistive Index in Patients with Systemic Sclerosis

INTRODUCTION

Systemic sclerosis (SSc) is a chronic autoimmune disease characterized by microvascular damage and fibrosis of the skin and internal organs. The major complications are lung fibrosis, pulmonary artery hypertension, scleroderma renal crisis, and cardiac involvement.

OBJECTIVE

The aim of this study was to assess renal and cardiac involvement in asymptomatic SSc patients using renal Doppler ultrasound (RDU) and cardiac magnetic resonance (CMR).

MATERIALS AND METHODS

We enrolled 26 consecutive SSc patients (21 female) according to 2013 ACR/EULAR criteria. Biochemical analysis, clinical evaluation, RDU with intrarenal hemodynamic parameters (renal resistive index [RRI], pulsatility index [PI], systolic/diastolic [S/D] ratio), and CMR with late gadolinium enhancement (LGE) were investigated at the time of enrollment.

RESULTS

The median PI value was significantly (p = 0.007) higher in SSc patients with LGE than in SSc patients without LGE (1.37 [1.28-1.58] vs. 1.12 [1.06-1.26]). The median RRI value was significantly (p = 0.002) higher in SSc patients with LGE than in SSc patients without LGE (0.68 [0.65-0.73] vs. 0.64 [0.63-0.65]). The median S/D ratio was significantly (p = 0.02) higher in SSc patients with LGE than in SSc patients without LGE (3.12 [2.83-3.76] vs. 2.78 [2.64-2.84]).

CONCLUSIONS

Our study, although performed on a small SSc population, showed RRI and LGE as markers of vascular and fibrotic damage. Early detection of cardiorenal involvement in SSc patients without symptoms is important to avoid further complications.

Renal Parenchymal Thickness in Patients with Systemic Sclerosis Is Related to Intrarenal Hemodynamic Variables and Raynaud Renal Phenomenon

Objective.

Renal involvement in systemic sclerosis (SSc) ranges from urinary abnormalities, reduction of glomerular filtration rate, and high renal resistive index, to scleroderma renal crisis. Intrarenal resistance indices are considered markers of renal SSc-associated vasculopathy. The aim of this study is to evaluate renal morphological variables, such as renal length, parenchymal thickness, atrophy index, and renal sinus in patients with SSc and to correlate it with renal function and hemodynamic variables.

Methods.

There were 92 patients with SSc and 40 healthy controls (HC) enrolled in this study. Doppler and renal ultrasound (US) including renal length, parenchymal thickness, atrophy index, renal sinus, and intrarenal resistive index were measured in patients with SSc and HC.

Results.

Renal US showed significant differences between HC and patients with SSc. The renal length (mm; 106.7 ± 5.1 vs 102.3 ± 8.4) and renal sinus (70.7 ± 7.9 vs 65.3 ± 7.7 mm) were significantly (p = 0.001) higher in HC than patients with SSc. The parenchymal thickness was significantly (p = 0.004) higher in HC than patients with SSc (18 ± 3.1 vs 16.3 ± 2.5 mm). Pulsatility index, resistive index, and systolic/diastolic ratio were significantly (p < 0.0001) lower in HC than patients with SSc. The renal length was significantly (p = 0.004) higher in diffuse cutaneous SSc (105 ± 8.4) than in limited cutaneous SSc (99.5 ± 7.5).

Conclusion.

In SSc, kidney involvement is subclinical and is related to vascular injury, Raynaud phenomenon, and chronic hypoxia that can modify renal morphology. Serum creatinine is a poor marker of renal damage, and renal US could be a useful tool — together with Doppler — to evaluate renal involvement in a systemic and chronic disease such as SSc.

Renal haemodynamics and coronary atherosclerotic burden are associated in patients with hypertension and mild coronary artery disease

Intrarenal hemodynamic alterations are independent predictors of cardiovascular events in different populations. It has been hypothesized that there is an association between renal hemodynamics and coronary atherosclerotic burden in patients with hypertension. Therefore, the present study examined the associations between renal hemodynamics, coronary atherosclerotic burden and carotid atherosclerotic disease. A total of 130 patients with hypertension aged between 30-80 years who had been referred for an elective coronary angiography were enrolled in the present study. A duplex ultrasound of the intrarenal vasculature was performed to evaluate the resistive index (RI), pulsatility index (PI) and acceleration time (AT). The carotid intima-media thickness was additionally assessed. A coronary angiography was performed to detect the atherosclerotic burden using the Gensini Score (GS). Based on the GS values, subjects were divided into quintiles (I: ≤9; II: 9-17; III: 17-30; IV: 30-44; and V: GS >44) as well as in subjects with mild (GS ≤30) or severe coronary disease (GS >30). A weak significant difference in PI was identified among quintiles (P=0.041), whereas, RI and AT did not differ significantly. PI was associated with GS in the group with low coronary atherosclerotic burden (GS ≤30; P=0.047), whereas, no association was detected in subjects with GS >30. This association remained following adjustment for age and left ventricular ejection fraction (P=0.025). In conclusion, renal vascular alterations were associated with coronary atherosclerotic burden in patients with hypertension with mild coronary disease.