Retinal capillary and arteriolar changes in patients with chronic kidney disease

Effect of blood pressure variability on hypertensive retinopathy

PURPOSE

This study intends to investigate the correlation between blood pressure variability (BPV) levels and the use of optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) to measure retinal microvasculature in hypertensive patients.

METHODS

All individuals in the study had 24-hour ambulatory blood pressure monitoring and bilateral OCT and OCTA exams, and only data from the right eye were analyzed statistically.

RESULTS

The study included 170 individuals, with 60 in the control group. The experimental group was separated into two groups based on the average real variability (ARV) median, with 55 in the low ARV group and 55 in the high ARV group. The mean thicknesses of the Retinal Nerve Fiber Layer (RNFL), internal limiting membrane-retinal pigment epithelial cell layer (ILM-RPE), vessel density (VD), and perfusion density (PD) in the high-ARV group were substantially lower in the low-ARV and control groups (p＜0.05). Multiple linear regression analysis revealed that disease duration, age, and 24 h diastolic standard deviation all affected RNFL mean thickness (p＜0.05). VD and PD were influenced by disease duration, systolic-ARV, daytime systolic blood pressure, intraocular pressure(IOP), and best-corrected visual acuity (BCVA) (p＜0.05). And the change in VD was connected to best-corrected visual acuity.

CONCLUSION

Hypertensive retinopathy is related to BPV. In clinical practice, we can assess the degree of BPV and retinopathy in hypertensive patients to track the progression of hypertension-mediated organ damage (HMOD). Correction of BPV may help treat or postpone the progression of HOMD.

Deep learning-based fundus image analysis for cardiovascular disease: a review

It is well established that the retina provides insights beyond the eye. Through observation of retinal microvascular changes, studies have shown that the retina contains information related to cardiovascular disease. Despite the tremendous efforts toward reducing the effects of cardiovascular diseases, they remain a global challenge and a significant public health concern. Conventionally, predicting the risk of cardiovascular disease involves the assessment of preclinical features, risk factors, or biomarkers. However, they are associated with cost implications, and tests to acquire predictive parameters are invasive. Artificial intelligence systems, particularly deep learning (DL) methods applied to fundus images have been generating significant interest as an adjunct assessment tool with the potential of enhancing efforts to prevent cardiovascular disease mortality. Risk factors such as age, gender, smoking status, hypertension, and diabetes can be predicted from fundus images using DL applications with comparable performance to human beings. A clinical change to incorporate DL systems for the analysis of fundus images as an equally good test over more expensive and invasive procedures may require conducting prospective clinical trials to mitigate all the possible ethical challenges and medicolegal implications. This review presents current evidence regarding the use of DL applications on fundus images to predict cardiovascular disease.

Impact of type 1 diabetes and its duration on wall-to-lumen ratio and blood flow in retinal arterioles

BACKGROUND

Subclinical damage to both the small and large vessels may contribute to the development and progression of cardiovascular disease. Scanning laser Doppler flowmetry (SLDF), an established method used to measure retinal microcirculation, has been successfully applied in hypertensive and post-stroke patients.

METHODS

Retinal microcirculation was assessed in 158 patients with type 1 diabetes and 38 age-matched healthy controls. The diabetics were divided into 3 groups: group A with diabetes duration <12 months, group B with diabetes with 1-10 years, and group C >10 years of diabetes. Retinal capillary structure and perfusion were evaluated using a Heidelberg retina flowmeter and automatically analyzed with full-field perfusion imaging.

RESULTS

Age and BMI were comparable in all the diabetic patients and the controls (mean age 24.8 ± 4.7 years, mean BMI 22.9 ± 4.1). In the univariate analyses, RCF (retinal capillary flow) was significantly higher in group A (297 ± 121 arbitrary units [AU]) vs group B (236 ± 52 AU; p = 0.007) and group C (236 ± 70 AU; p = 0.008) and comparable to that of the controls (p = 0.46). Additionally, the WLR (Wall-to-Lumen Ratio) was highest in group C compared to the other diabetic subgroups and controls (p = 0.001). Multivariate regression analyses including age, BMI, sex, HbA1c, smoking, systolic blood pressure, and diabetes duration as covariates, showed, that only diabetes duration was significantly associated with WLR variations, whereas HbA1c was significantly linked to retinal capillary flow levels.

CONCLUSIONS

New-onset diabetes is associated with an increase in RCF, which then gradually decreased with the duration of the disease. Structural changes of the retinal arterioles estimated via WLR are evident later in the course of diabetes, especially when the disease duration exceeded 10 years.

Association of urinary angiotensinogen with renal arteriolar remodeling in chronic kidney disease

OBJECTIVE

Renin-angiotensin system (RAS) might be associated with arteriolar remodeling. The present study aimed to explore the hitherto unknown relationship between renal RAS and renal arteriolar remodeling and to elucidate whether altered renal RAS subsequently affects renal function in patients with chronic kidney disease (CKD).

METHODS

In this retrospective study, patients with various CKDs not using RAS inhibitors who underwent renal biopsy were included in cross-sectional and longitudinal analyses. Urinary angiotensinogen (UAGT) levels and wall/lumen ratio (WLR) were determined to evaluate renal RAS and renal arteriolar remodeling, respectively. The association between ln(UAGT) and ln(WLR) was cross-sectionally examined using a liner regression model. Furthermore, the association of ln(UAGT) with subsequent changes in estimated glomerular filtration rate (eGFR) per year were longitudinally examined in the largest subgroup of patients who were diagnosed with IgA nephropathy.

RESULTS

In the overall cohort (n = 54), the median age, blood pressures, eGFR, and WLR were 37 years, 120/73 mmHg, 85 ml/min per 1.73 m2, and 0.93, respectively. Ln(UAGT) was significantly and positively associated with ln(WLR) even after adjusting for classical and nonclassical clinical renal risk factors. In patients with IgA nephropathy, higher ln(UAGT) was associated with higher ln(WLR). Ln(UAGT) also tended to be associated with a greater decline in eGFR per year over a median period of 8.7 years, even after adjusting for potential confounding factors.

CONCLUSION

In patients with CKD, renal RAS might be associated with renal arteriolar remodeling and future decline in eGFR, independent of potential risk factors.

Retinal capillary rarefaction is associated with arterial and kidney damage in hypertension

Microvascular disease and rarefaction are key pathological hallmarks of hypertension. The retina uniquely allows direct, non-invasive investigation of the microvasculature. Recently developed optical coherence tomography angiography now allows investigation of the fine retinal capillaries, which may provide a superior marker of overall vascular damage. This was a prospective cross-sectional study to collect retinal capillary density data on 300 normal eyes from 150 hypertensive adults, and to investigate possible associations with other organ damage markers. The average age of participants was 54 years and there was a greater proportion of males (85; 57%) than females. Multivariate, confounder adjusted linear regression showed that retinal capillary rarefaction in the parafovea was associated with increased pulse wave velocity (β = − 0.4, P = 0.04), log-albumin/creatinine ratio (β = − 0.71, P = 0.003), and with reduced estimated glomerular filtration rate (β = 0.04, P = 0.02). Comparable significant associations were also found for whole-image vascular-density, for foveal vascular-density significant associations were found with pulse wave velocity and estimated glomerular filtration rate only. Our results indicate that retinal capillary rarefaction is associated with arterial stiffness and impaired kidney function. Retinal capillary rarefaction may represent a useful and simple test to assess the integrated burden of hypertension on the microvasculature irrespective of current blood pressure levels.

[Development, clinical manifestations and diagnosis of retinal changes in chronic kidney disease]

Chronic kidney disease (CKD) is a significant public health problem with a high risk of developing age-dependent eye diseases. Renal glomeruli and the choroid have similar structures and vascular networks; the internal hematoretinal barrier and the glomerular filtration barrier have similar developmental path; the renin-angiotensin-aldosterone hormonal system is found in both the eye and the kidneys. All this determines the similarity of physiological and pathogenetic features of the development of diseases associated with these organs. The article discusses general risk factors and pathophysiological mechanisms of development of retinal and renal lesions in CKD, the influence of various factors of pathogenesis on their development and progression. The anatomical similarity of vascularization, accompanied by microvascular changes in the retina and kidneys, leads to similar complications in both organs. Optical coherence tomography (OCT) and optical coherence tomography angiography (OCT-A) are accurate, well reproducible and non-invasive methods for diagnosing and assessing changes in the retinal microvascular bed, which make it possible to assess microvasculature changes in the kidneys. In CKD, the retina shows signs of impaired capillary perfusion, a decrease in their density, expansion of intercapillary spaces, a rarefaction of the density of the parafoveolar capillary network, which may indicate a decrease in peritubular capillary blood flow, blood circulation of the kidneys in general and their ischemia. Significant thinning of the retina and choroid, along with a decrease in macular volume, even in the initial stages of CKD, is accompanied by impaired renal function (changes in the estimated glomerular filtration rate and urinary albumin excretion), which is a sign of systemic microvascular lesion and pathological process in the kidneys. Therefore, monitoring of retinal vessels using OCT and OCT-A can become a reliable indicator of the progression of renal microvascular changes at any stage of the disease.

Microvascular disease in chronic kidney disease: the base of the iceberg in cardiovascular comorbidity

Chronic kidney disease (CKD) is a relentlessly progressive disease with a very high mortality mainly due to cardiovascular complications. Endothelial dysfunction is well documented in CKD and permanent loss of endothelial homeostasis leads to progressive organ damage. Most of the vast endothelial surface area is part of the microcirculation, but most research in CKD-related cardiovascular disease (CVD) has been devoted to macrovascular complications. We have reviewed all publications evaluating structure and function of the microcirculation in humans with CKD and animals with experimental CKD. Microvascular rarefaction, defined as a loss of perfused microvessels resulting in a significant decrease in microvascular density, is a quintessential finding in these studies. The median microvascular density was reduced by 29% in skeletal muscle and 24% in the heart in animal models of CKD and by 32% in human biopsy, autopsy and imaging studies. CKD induces rarefaction due to the loss of coherent vessel systems distal to the level of smaller arterioles, generating a typical heterogeneous pattern with avascular patches, resulting in a dysfunctional endothelium with diminished perfusion, shunting and tissue hypoxia. Endothelial cell apoptosis, hypertension, multiple metabolic, endocrine and immune disturbances of the uremic milieu and specifically, a dysregulated angiogenesis, all contribute to the multifactorial pathogenesis. By setting the stage for the development of tissue fibrosis and end organ failure, microvascular rarefaction is a principal pathogenic factor in the development of severe organ dysfunction in CKD patients, especially CVD, cerebrovascular dysfunction, muscular atrophy, cachexia, and progression of kidney disease. Treatment strategies for microvascular disease are urgently needed.

Impact of blood pressure control on retinal microvasculature in patients with chronic kidney disease

Chronic kidney disease (CKD) is an emerging disease worldwide. We investigated the relationship between blood pressure (BP) control and parafoveal retinal microvascular changes in patients with CKD. This case–control study enrolled 256 patients with CKD (stage 3–5) and 70 age‐matched healthy controls. Optical coherence tomography angiography showed lower superficial vascular plexus (SVP) vessel density, lower deep vascular plexus (DVP) vessel density, and larger SVP flow void area in the CKD group. The BP parameters at enrollment and during the year before enrollment were collected in patients with CKD. Partial correlation was used to determine the relationship between BP parameters and microvascular parameters after controlling for age, sex, diabetes mellitus, axial length, and intraocular pressure. The maximum systolic blood pressure (SBP) (p = 0.003) and within-patient standard deviation (SD) of SBP (p = 0.006) in 1 year were negatively correlated with SVP vessel density. The average SBP (p = 0.040), maximum SBP (p = 0.001), within-patient SD of SBP (p < 0.001) and proportion of high BP measurement (p = 0.011) in 1 year were positively correlated with the SVP flow void area. We concluded that long-term SBP was correlated with SVP microvascular injury in patients with CKD. Superficial retinal microvascular changes may be a potential biomarker for prior long-term BP control in these patients.

Non-Proliferative Diabetic Retinopathy Is Characterized by Nonuniform Alterations of Peripapillary Capillary Networks

Purpose

The purpose of this study was to use three-dimensional confocal microscopy to quantify the spatial patterns of capillary network alterations in nonproliferative diabetic retinopathy (NPDR).

Methods

The retinal microvasculature was perfusion-labelled in seven normal human donor eyes and six age-matched donor eyes with NPDR. The peripapillary microcirculation was studied using confocal scanning laser microscopy. Capillary density and diameters of the radial peripapillary capillary plexus (RPCP), superficial capillary plexus (SCP), intermediate capillary plexus (ICP), and deep capillary plexus (DCP) were quantified and compared. Three-dimensional visualization strategies were also used to compare the communications between capillary beds and precapillary arterioles and postcapillary venules.

Results

Mean capillary diameter was significantly increased in the NPDR group (P < 0.001). Intercapillary distance was significantly increased in the DCP (P = 0.004) and RPCP (P = 0.022) of the NPDR group (P = 0.010) but not the SCP (P = 0.155) or ICP (P = 0.103). The NPDR group was associated with an increased frequency of inflow communication between the SCP and ICP/DCP and a decreased frequency of communication between the SCP and RPCP (P = 0.023). There was no difference in the patterns of outflow communications between the two groups (P = 0.771).

Conclusions

This study demonstrates that capillary plexuses are nonuniformly perturbed in NPDR. These structural changes may be indicative of perturbations to blood flow patterns between different retinal layers. Our findings may aid the interpretation of previous clinical observations made using optical coherence tomography angiography as well as improve our understanding of the pathogenesis of NPDR.

Impact of hypertension on retinal capillary microvasculature using optical coherence tomographic angiography

Objective:

Reduction in capillary density or rarefaction is a hallmark of essential hypertension. We measured the retinal capillary density using noninvasive optical coherence tomographic angiography (OCT-A) in adults with treated systemic hypertension and determined possible correlations with ambulatory blood pressure (BP) and renal parameters.

Methods:

This observational cross-sectional study consisted of 153 normal eyes from 77 nondiabetic hypertensive adults [mean (SD) age, 58 (9) years; 49% women; 23% poorly controlled BP]. Data on 24-h ambulatory BP monitoring, serum creatinine, and urine microalbumin/creatinine ratio (MCR) were collected. Estimated glomerular filtration rate (eGFR) was calculated based on CKD-EPI Creatinine Equation. Retinal capillary density measured with the OCT-A (AngioVue) at superficial (SVP) and deep vascular plexuses (DVP). Linear regression was used to investigate the association of risk factors with capillary density.

Results:

Retinal capillary density (percentage) at DVP was reduced in patients with poorly controlled BP (SBP = 148 ± 8 mmHg; 27.2 ± 13.0) compared with those with well controlled BP (SBP = 125 ± 9 mmHg; 34.7 ± 11.3). In the multivariable analysis, poorly controlled BP [β = −6.49, 95% confidence interval (CI), −12.39 to −0.59], higher SBP (β = −0.23, 95% CI −0.44 to −0.02) and lower eGFR (β = 6.42, 95% CI 1.25–11.60) were associated with sparser retinal capillary density. Systemic factors were not associated with capillary density at SVP (all P > 0.05).

Conclusion:

In adults with treated systemic hypertension, retinal capillary density reduced with higher BP and poorer eGFR. These findings highlight the potential role of OCT-A to study early microvascular changes because of systemic hypertension.

Peripapillary microvascular changes in patients with systemic hypertension: An optical coherence tomography angiography study

The purpose of this study was to investigate changes in peripapillary microvasculature using optical coherence tomography angiography (OCTA) in systemic hypertension (HTN) patients. This was a cross-sectional study. Based on the duration of HTN, seventy-eight HTN patients were divided into two groups. (HTN group 1: <10 years, 38 eyes; HTN group 2: ≥10 years, 40 eyes) and 90 control subjects. All subjects underwent 6 × 6 mm OCTA scan centered on the optic nerve head. We analyzed peripapillary vessel density (VD) and perfusion density (PD) in superficial capillary plexus among three groups. The average ganglion cell-inner plexiform layer (GC-IPL) and retinal nerve fiber layer (RNFL) thicknesses of HTN group 2 were thinner than those of the control group (p = 0.016, and 0.035, respectively). HTN group 2 showed lower peripapillary VD and PD than the control group. However, there were no differences between HTN group 1 and the control group in OCT and peripapillary OCTA parameters. In HTN patients, the peripapillary VD, PD and GC-IPL, RNFL thicknesses correlated significantly. OCTA showed that the peripapillary VD and PD were lower in HTN patients with a duration ≥10 years compared with those of normal controls. Peripapillary microvasculature was correlated with the RNFL and GC-IPL thicknesses. HTN duration should therefore be considered when evaluating peripapillary microvasculature using OCTA.

Mechanisms of cognitive dysfunction in CKD

Cognitive impairment is an increasingly recognized major cause of chronic disability and is commonly found in patients with chronic kidney disease (CKD). Knowledge of the relationship between kidney dysfunction and impaired cognition may improve our understanding of other forms of cognitive dysfunction. Patients with CKD are at an increased risk (compared with the general population) of both dementia and its prodrome, mild cognitive impairment (MCI), which are characterized by deficits in executive functions, memory and attention. Brain imaging in patients with CKD has revealed damage to white matter in the prefrontal cortex and, in animal models, in the subcortical monoaminergic and cholinergic systems, accompanied by widespread macrovascular and microvascular damage. Unfortunately, current interventions that target cardiovascular risk factors (such as anti-hypertensive drugs, anti-platelet agents and statins) seem to have little or no effect on CKD-associated MCI, suggesting that the accumulation of uraemic neurotoxins may be more important than disturbed haemodynamic factors or lipid metabolism in MCI pathogenesis. Experimental models show that the brain monoaminergic system is susceptible to uraemic neurotoxins and that this system is responsible for the altered sleep pattern commonly observed in patients with CKD. Neural progenitor cells and the glymphatic system, which are important in Alzheimer disease pathogenesis, may also be involved in CKD-associated MCI. More detailed study of CKD-associated MCI is needed to fully understand its clinical relevance, underlying pathophysiology, possible means of early diagnosis and prevention, and whether there may be novel approaches and potential therapies with wider application to this and other forms of cognitive decline.

Association of renal function with retinal vessel density in patients with type 2 diabetes by using swept-source optical coherence tomographic angiography

AIMS

To investigate the relationship between retinal vessel density and renal function in patients with diabetes mellitus (DM) using non-invasive optical coherence tomographic angiography (OCTA).

METHODS

This prospective cross-sectional study recruited ocular-treatment-naïve patients with DM registered in the community of Guangzhou, China. The retinal vessel density of the superficial capillary plexus in the macula was obtained by using swept-source OCTA imaging. The Xiangya equation was used to calculate the estimated glomerular filtrate rate (eGFR). Participants were divided into the following groups by eGFR: no chronic kidney disease (non-CKD), mild CKD and moderate-to-severe CKD (MS-CKD).

RESULTS

A total of 874 patients with DM (874 eyes), with a mean age of 64.8±7.1 years, were included in the final analysis. The vessel density was significantly lower in patients with CKD than in non-CKD patients in a dose-response pattern, with a parafoveal vessel density of 49.1%±2.1% in non-CKD, 48.4%±1.9% in mild CKD and 47.2%±1.7% in MS-CKD (p<0.001). The sparser retinal capillaries were related to lower eGFR (β=0.037; 95% CI 0.025 to 0.049; p<0.001) and higher microalbuminuria (β = -0.023; 95% CI -0.039 to -0.008; p=0.002). The eGRF was independently associated with parafoveal vessel density (β=0.029; 95% CI 0.016 to 0.042; p<0.001), even after adjusting for other factors.

CONCLUSION

Retinal vessel density decreased with renal function impairment, underlining the potential value of OCTA to detect early microvascular damage in the kidney in patients with diabetes.

Aortic stiffness is not only associated with structural but also functional parameters of retinal microcirculation

OBJECTIVE

The aim of the study was to test the hypothesis that alterations in large arteries are associated with microvascular remodelling and decreased retinal capillary blood flow.

METHODS

The study group comprised of 88 patients with essential hypertension and 32 healthy controls. Retinal microcirculation was evaluated by scanning laser Doppler flowmetry. Macrovascular changes were assessed on the basis of arterial stiffness measurement (carotid-femoral pulse wave velocity), its hemodynamic consequences (central pulse pressure, augmentation pressure, augmentation index) and intima media thickness of common carotid artery.

RESULTS

Pulse wave velocity was inversely correlated to mean retinal capillary blood flow in hypertensive patients (R = -0.32, p < 0.01). This relationship remained significant in multivariate regression analysis after adjustment for age, sex, central systolic blood pressure (BP) and body mass index (β = -31.27, p < 0.001). Lumen diameter (LD) of retinal arterioles was significantly smaller in hypertensive then normotensive subjects (79.4 vs. 83.8, p = 0.03). Central and brachial systolic, diastolic and mean BPs were significantly correlated with LD and outer diameter of retinal arterioles. The relationship between LD and central BPs remained significant in multivariate analysis (β = -0.15, p = 0.03 for cSBP; β = -0.22, p = 0.04 for cDBP; β = -0.21, p = 0.03 for cMBP). Moreover, in a subgroup with cardiac damage central and brachial pulse pressure were positively associated with retinal wall thickness, wall cross sectional area, and wall to lumen ratio.

CONCLUSION

In conclusion, the study provides a strong evidence that microcirculation is coupled with macrocirculation not only in terms of structural but also functional parameters.

Evaluation of Cerebral Blood Flow Using Arterial Spin Labeling in Patients with Chronic Kidney Disease

목적

대상과 방법

결과

결론

The role of pericytes in brain disorders: from the periphery to the brain

It is becoming increasingly apparent that disorders of the brain microvasculature contribute to many neurological disorders. In recent years it has become clear that a major player in these events is the capillary pericyte which, in the brain, is now known to control the blood-brain barrier, regulate blood flow, influence immune cell entry and be crucial for angiogenesis. In this review we consider the under-explored possibility that peripheral diseases which affect the microvasculature, such as hypertension, kidney disease and diabetes, produce central nervous system (CNS) dysfunction by mechanisms affecting capillary pericytes within the CNS. We highlight how cellular messengers produced peripherally can act via signalling pathways within CNS pericytes to reshape blood vessels, restrict blood flow or compromise blood-brain barrier function, thus causing neuronal dysfunction. Increased understanding of how renin-angiotensin, Rho-kinase and PDGFRβ signalling affect CNS pericytes may suggest novel therapeutic approaches to reducing the CNS effects of peripheral disorders.

Early retinal microvascular abnormalities in patients with chronic kidney disease

Objective

To evaluate early retinal microvascular abnormalities in patients with chronic kidney disease (CKD) via optical coherence tomography angiography.

Methods

A cross‐sectional study. Two hundred patients with CKD stage ≧3 were enrolled in the CKD group, and 50 age‐matched healthy subjects were enrolled in the control group. Main outcome measures were the differences in parafoveal vessel densities in the superficial vascular plexus (SVP) and deep vascular plexus (DVP) between the CKD and control groups.

Results

The mean ages were 62.7 ± 10.1 in the CKD group and 61.9 ± 9.7 (P = 0.622) in the control group. The CKD group had reduced parafoveal vessel densities in SVP (46.7 ± 4.3 vs 49.7 ± 2.9, P < 0.001) and DVP (50.1 ± 4.1 vs 52. 6 ± 2.9, P < 0.001) when compared to those of the control group. In multiple linear regression models, age, diabetes, estimated glomerular filtration rate, and use of anti‐hypertensive drugs were factors associated with vessel density in SVP, whereas age, diabetes, and smoking were factors associated with vessel density in DVP.

Conclusion

Patients with CKD had reduced vessel densities in parafoveal SVP and DVP, as compared to that of control subjects. Microvasculature in the different retinal layers may be affected by different systemic factors.