Retinal vessel multifractals predict pial collateral status in patients with acute ischemic stroke

Genetic determinants of insufficiency of the collateral circulation

It has been estimated that approximately two million neurons, sixteen billion synapses and twelve kilometers of axons are lost each minute following anterior large-vessel stroke. The level of collateral blood flow has become recognized as a primary determinant of the pace of this loss and an important factor in clinical decision-making. Many of the topics in this review cover recent developments that have not been reviewed elsewhere. These include that: the number and diameter of collaterals and collateral blood flow vary greatly in the brain and other tissues of healthy individuals; a large percentage of individuals are deficient in collaterals; the underlying mechanism arises primarily from naturally occurring polymorphisms in genes/genetic loci within the pathway that drives collateral formation during development; evidence indicates collateral abundance does not exhibit sexual dimorphism; and that collaterals-besides their function as endogenous bypass vessels-may have a physiological role in optimizing oxygen delivery. Animal and human studies in brain and other tissues, where available, are reviewed. Details of many of the studies are provided so that the strength of the findings and conclusions can be assessed without consulting the original literature. Key questions that remain unanswered and strategies to address them are also discussed.

Association of Circulating Neprilysin with BMI, Cardiovascular Health, and Kidney Function in High-Risk Pregnancies: A Pilot Study

BACKGROUND/OBJECTIVES

Inadequate cardiovascular adaptation during pregnancy impairs endothelial function and vascular resistance, contributing to complications such as pre-eclampsia (PE) and gestational hypertension (GH). Neprilysin (NEP), a protease involved in vascular regulation, has been linked to PE, but its role in endothelial function and vascular adaptation remains unclear. This pilot study investigates the associations between soluble neprilysin (sNEP) and markers of vascular and renal function in high-risk pregnancies without PE.

METHODS

Observed parameters were analyzed in 29 high-risk pregnant women across early, mid-, and late pregnancy. sNEP levels were analyzed alongside body mass index (BMI), endothelial dysfunction (ADMA), arterial stiffness (pulse wave velocity, PWV), retinal microvasculature (central retinal arteriolar and venular equivalents, CRAE and CRVE), and kidney function markers. The impact of gestational hypertension (GH) and prior smoking on sNEP levels was also evaluated.

RESULTS

In early and mid-pregnancy, sNEP was inversely associated with BMI. During mid-pregnancy, sNEP showed a positive correlation with CRAE and an inverse correlation with PWV, suggesting reduced arterial stiffness. By late pregnancy, sNEP was positively associated with glomerular filtration rate and inversely correlated with creatinine and protein levels, reflecting improved kidney function. Women with GH exhibited elevated sNEP, while former smokers had lower sNEP levels in early pregnancy.

CONCLUSIONS

These findings suggest that sNEP plays a role in vascular and renal adaption during pregnancy, offering new perspectives on vascular tone regulation in high-risk pregnancies. Further research is needed to clarify these mechanisms and their clinical relevance.

Determinants of Leptomeningeal Collateral Status in Acute Ischemic Stroke: A Systematic Review and Meta-Analysis of Observational Studies

BACKGROUND

Leptomeningeal collateral status is a major determinant of outcomes in patients with acute ischemic stroke; however, the factors that determine collateral status are not well understood. We conducted a comprehensive systematic review and meta-analysis to identify determinants associated with collateral status in patients with anterior circulation infarction.

METHODS AND RESULTS

The PubMed, EMBASE, Web of Science, and Cochrane Central Register of Controlled Trials databases were searched for studies that reported the determinants of leptomeningeal collateral status in acute ischemic stroke between January 2000 and June 2023. A random-effects meta-analysis model was used to pool the determinants of leptomeningeal collateral status. Eighty-one studies with 17 366 patients met the inclusion criteria. We analyzed 31 potential risk factors, and the results indicated that worse leptomeningeal collateral status was significantly associated with older age (weighted mean difference, 1.22 [95% CI, 0.69 to 1.76]), male sex (odds ratio [OR], 1.12 [95% CI, 1.02 to 1.23]), hypertension (OR, 1.27 [95% CI, 1.15 to 1.40]), diabetes (OR, 1.21 [95% CI, 1.10 to 1.33]), atrial fibrillation (OR, 1.26 [95% CI, 1.09 to 1.46]), cardioembolic stroke (OR, 1.27 [95% CI, 1.04 to 1.55]), internal carotid artery occlusion (OR, 1.84 [95% CI, 1.50 to 2.25]), and higher admission blood glucose (weighted mean difference, 8.74 [95% CI, 2.52 to 18.51]).

CONCLUSIONS

Hypertension and diabetes could be modifiable risk factors associated with leptomeningeal collateral status. Older age and male sex could be nonmodified risk factors. Further high-quality therapeutic studies focusing on controlling risk factors are needed to support our findings.

Retinal blood vessel diameter changes with 60-day head-down bedrest are unaffected by antioxidant nutritional cocktail

Long-term human spaceflight can lead to cardiovascular deconditioning, but little is known about how weightlessness affects microcirculation. In this study, we examined how the retinal microvessels and cerebrovascular regulation of 19 healthy male participants responded to long-term head-down bedrest (HDBR), an earth-based analog for weightlessness. In addition, we examined whether an anti-inflammatory/antioxidant cocktail could prevent the vascular changes caused by HDBR. In all study participants, we found a decrease in retinal arteriolar diameter by HDBR day 8 and an increase in retinal venular diameter by HDBR day 16. Concurrently, blood pressure at the level of the middle cerebral artery and the cerebrovascular resistance index were higher during HDBR, while cerebral blood flow velocity was lower. None of these changes were reversed in participants receiving the anti-inflammatory/antioxidant cocktail, indicating that this cocktail was insufficient to restore the microvascular and cerebral blood flow changes induced by HDBR.

Greenspace exposure and the retinal microvasculature in healthy adults across three European cities

BACKGROUND

Emerging evidence points to the beneficial role of greenspace exposure in promoting cardiovascular health. Most studies have evaluated such associations with conventional cardiovascular endpoints such as mortality, morbidity, or macrovascular markers. In comparison, the microvasculature, a crucial compartment of the vascular system where early subclinical signs of cardiovascular problems appear, has not been studied in association with greenspace exposure. The current study assessed the association between surrounding greenness and microvascular status, as assessed by retinal vessel diameters.

METHODS

This study included a sample of healthy adults (n = 114 and 18-65 years old) residing in three European cities [Antwerp (Belgium), Barcelona (Spain), and London (UK)]. The exposures to greenspace at the home and work/school locations were characterized as average surrounding greenness [normalized difference vegetation index (NDVI)] within buffers of 100 m, 300 m, and 500 m. The central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE) were calculated from fundus pictures taken at three different time points. We developed linear mixed-effect models to estimate the association of greenspace exposure with indicators of retinal microvasculature, adjusted for relevant individual and area-level covariates.

RESULTS

We observed the most robust associations with CRVE. Higher levels of greenspace at work/school were associated with smaller retinal venules [(seasonal NDVI) 300m: 3.85, 95%CI -6.67,-1.03; 500m: 5.11, 95%CI -8.04, -2.18]. Findings for surrounding greenness and CRAE were not conclusive.

CONCLUSION

Our study suggests an association of greenspace exposure with better microvascular status, specifically for retinal venules. Future research is needed to confirm our findings across different contextual settings.

Acute effects of exercise on macro- and microvasculature in individuals with type 1 diabetes - a secondary outcome analysis

Background

Type 1 diabetes is a chronic autoimmune disease associated with insulin-producing beta cell destruction, declining insulin secretion, and elevated blood glucose. Physical activity improves glycaemic control and cardiovascular health. This study explores acute effects of maximal exhaustion induced by a cardiopulmonary exercise on macro- and microvascular parameters in type 1 diabetes.

Methodology

Twenty-five participants with type 1 diabetes (14 males, 11 females), aged 41.4 ± 11.87 years, BMI 23.7 ± 3.08, completed a repeated-measure study. Measurements pre-, post-, 30- and 60-minutes post-exhaustion involved a maximal incremental cardio-pulmonary exercise test. Macro- and microvascular parameters were assessed using VICORDER® and retinal blood vessel image analysis. Repeated measures ANOVA in SPSS (Version 27.0) analysed data.

Results

Post-exercise, heart rate increased (p<.001), and diastolic blood pressure decreased (p=.023). Diabetes duration correlated with pulse wave velocity (r=0.418, p=.047), diastolic blood pressure (r=0.470, p=.023), and central retinal arteriolar equivalent (r=0.492, p=.023).

Conclusion

In type 1 diabetes, cardiopulmonary exercise-induced exhaustion elevates heart rate and reduces diastolic blood pressure. Future research should explore extended, rigorous physical activity protocols for greater cardiovascular risk reduction.

Retina Fundus Photograph-Based Artificial Intelligence Algorithms in Medicine: A Systematic Review

We conducted a systematic review of research in artificial intelligence (AI) for retinal fundus photographic images. We highlighted the use of various AI algorithms, including deep learning (DL) models, for application in ophthalmic and non-ophthalmic (i.e., systemic) disorders. We found that the use of AI algorithms for the interpretation of retinal images, compared to clinical data and physician experts, represents an innovative solution with demonstrated superior accuracy in identifying many ophthalmic (e.g., diabetic retinopathy (DR), age-related macular degeneration (AMD), optic nerve disorders), and non-ophthalmic disorders (e.g., dementia, cardiovascular disease). There has been a significant amount of clinical and imaging data for this research, leading to the potential incorporation of AI and DL for automated analysis. AI has the potential to transform healthcare by improving accuracy, speed, and workflow, lowering cost, increasing access, reducing mistakes, and transforming healthcare worker education and training.

AI-integrated ocular imaging for predicting cardiovascular disease: advancements and future outlook

Cardiovascular disease (CVD) remains the leading cause of death worldwide. Assessing of CVD risk plays an essential role in identifying individuals at higher risk and enables the implementation of targeted intervention strategies, leading to improved CVD prevalence reduction and patient survival rates. The ocular vasculature, particularly the retinal vasculature, has emerged as a potential means for CVD risk stratification due to its anatomical similarities and physiological characteristics shared with other vital organs, such as the brain and heart. The integration of artificial intelligence (AI) into ocular imaging has the potential to overcome limitations associated with traditional semi-automated image analysis, including inefficiency and manual measurement errors. Furthermore, AI techniques may uncover novel and subtle features that contribute to the identification of ocular biomarkers associated with CVD. This review provides a comprehensive overview of advancements made in AI-based ocular image analysis for predicting CVD, including the prediction of CVD risk factors, the replacement of traditional CVD biomarkers (e.g., CT-scan measured coronary artery calcium score), and the prediction of symptomatic CVD events. The review covers a range of ocular imaging modalities, including colour fundus photography, optical coherence tomography, and optical coherence tomography angiography, and other types of images like external eye images. Additionally, the review addresses the current limitations of AI research in this field and discusses the challenges associated with translating AI algorithms into clinical practice.

Retinal venular vessel diameters are smaller during ten days of bed rest

Older individuals experience cardiovascular dysfunction during extended bedridden hospital or care home stays. Bed rest is also used as a model to simulate accelerated vascular deconditioning occurring during spaceflight. This study investigates changes in retinal microcirculation during a ten-day bed rest protocol. Ten healthy young males (22.9 ± 4.7 years; body mass index: 23.6 ± 2.5 kg·m-2) participated in a strictly controlled repeated-measures bed rest study lasting ten days. High-resolution images were obtained using a hand-held fundus camera at baseline, daily during the 10 days of bed rest, and 1 day after re-ambulation. Retinal vessel analysis was performed using a semi-automated software system to obtain metrics for retinal arteriolar and venular diameters, central retinal artery equivalent and central retinal vein equivalent, respectively. Data analysis employed a mixed linear model. At the end of the bed rest period, a significant decrease in retinal venular diameter was observed, indicated by a significantly lower central retinal vein equivalent (from 226.1 µm, CI 8.90, to 211.4 µm, CI 8.28, p = .026), while no significant changes in central retinal artery equivalent were noted. Prolonged bed rest confinement resulted in a significant (up to 6.5%) reduction in retinal venular diameter. These findings suggest that the changes in retinal venular diameter during bedrest may be attributed to plasma volume losses and reflect overall (cardio)-vascular deconditioning.

Sex Variations in Retinal Microcirculation Response to Lower Body Negative Pressure

INTRODUCTION

Lower body negative pressure (LBNP) is routinely used to induce central hypovolemia. LBNP leads to a shift in blood to the lower extremities. While the effects of LBNP on physiological responses and large arteries have been widely reported, there is almost no literature regarding how these cephalad fluid shifts affect the microvasculature. The present study evaluated the changes in retinal microcirculation parameters induced by LBNP in both males and females.

METHODOLOGY

Forty-four participants were recruited for the present study. The retinal measurements were performed at six time points during the LBNP protocol. To prevent the development of cardiovascular collapse (syncope) in the healthy participants, graded LBNP until a maximum of -40 mmHg was applied. A non-mydriatic, hand-held Optomed Aurora retinal camera was used to capture the retinal images. MONA Reva software (version 2.1.1) was used to analyze the central retinal arterial and venous diameter changes during the LBNP application. Repeated measures ANOVAs, including sex as the between-subjects factor and the grade of the LBNP as the within-subjects factor, were performed.

RESULTS

No significant changes in retinal microcirculation were observed between the evaluated time points or across the sexes.

CONCLUSIONS

Graded LBNP application did not lead to changes in the retinal microvasculature across the sexes. The present study is the first in the given area that attempted to capture the changes in retinal microcirculation caused by central hypovolemia during LBNP. However, further research is needed with higher LBNP levels, including those that can induce pre-fainting (presyncope), to fully understand how retinal microcirculation adapts during complete cardiovascular collapse (e.g., during hypovolemic shock) and/or during severe hemorrhage.

A narrative review of retinal vascular parameters and the applications (Part II): Diagnosis in stroke

The retina, as an external extension of the diencephalon, can be directly, noninvasively observed by ocular fundus photography. Therefore, it offers a convenient and feasible mode to study nervous system diseases. Caliber, tortuosity, and fractal dimension, as three commonly used retinal vascular parameters, are not only the reflection of structural changes in the retinal microcirculation but also capture the branching pattern or density changes of the retinal microvascular network. Therefore, it contributes to better reflecting the subclinical pathological changes (e.g., lacunar stroke and small cerebral vascular disease) and predicting the risk of incident stroke and recurrent stroke.

Vascular Responses following Light Therapy: A Pilot Study with Healthy Volunteers

(1) Background: Studies have reported the effectiveness of light therapy in various medical conditions. Our pilot study aimed to assess the effect of Maharishi light therapy (MLT) on physiological parameters, such as the heart rate (HR), HR variability (HRV), blood pressure (BP), BP variability (BPV), and the retinal microvasculature of healthy participants; (2) Methodology: Thirty (14 males and 16 females) healthy, non-smoking participants between 23 and 71 years old (46 ± 18 years) were included in this randomized crossover study. Each participant was tested with a placebo (using LED light) and gem lights, 24 h apart. Hemodynamic parameters were recorded during the session, and 24 h heart rate and BP levels were assessed via mobile devices. Retinal vascular responses were captured with fundus images and the subsequent analysis of retinal vessel widths. A linear model, using repeated measures ANOVA, was used to compare the responses across the sexes and to assess the effect of the MLT; (3) Results: Changes in the central retinal artery equivalent (CRAE) (p < 0.001) and central retinal vein equivalent (CRVE) (p = 0.002) parameters were observed. CRAE and CRVE decreased under MLT and increased under the placebo condition from before to after. However, the baseline values of the participants already differed significantly before the application of any therapy, and the variation in the retinal vessel diameters was already large in the baseline measurements. This suggests that the observed effect results may only reflect naturally occurring fluctuations in the microcirculation and not the effect of MLT. Furthermore, no significant effects were observed in any other investigated parameters; (4) Conclusion: Our study with healthy participants finds significant changes in retinal parameters, but the biological variation in the baseline measurements was large to begin with. This suggests that the observed effect results only reflect naturally occurring fluctuations in the microcirculation and not the effect of MLT. However, in the future, larger studies in which MLT is applied for longer periods and/or in patients with different diseases could discover the physiological impacts of this type of therapy.

Ischemic and haemorrhagic stroke risk estimation using a machine-learning-based retinal image analysis

Background

Stroke is the second leading cause of death worldwide, causing a considerable disease burden. Ischemic stroke is more frequent, but haemorrhagic stroke is responsible for more deaths. The clinical management and treatment are different, and it is advantageous to classify their risk as early as possible for disease prevention. Furthermore, retinal characteristics have been associated with stroke and can be used for stroke risk estimation. This study investigated machine learning approaches to retinal images for risk estimation and classification of ischemic and haemorrhagic stroke.

Study design

A case-control study was conducted in the Shenzhen Traditional Chinese Medicine Hospital. According to the computerized tomography scan (CT) or magnetic resonance imaging (MRI) results, stroke patients were classified as either ischemic or hemorrhage stroke. In addition, a control group was formed using non-stroke patients from the hospital and healthy individuals from the community. Baseline demographic and medical information was collected from participants' hospital medical records. Retinal images of both eyes of each participant were taken within 2 weeks of admission. Classification models using a machine-learning approach were developed. A 10-fold cross-validation method was used to validate the results.

Results

711 patients were included, with 145 ischemic stroke patients, 86 haemorrhagic stroke patients, and 480 controls. Based on 10-fold cross-validation, the ischemic stroke risk estimation has a sensitivity and a specificity of 91.0% and 94.8%, respectively. The area under the ROC curve for ischemic stroke is 0.929 (95% CI 0.900 to 0.958). The haemorrhagic stroke risk estimation has a sensitivity and a specificity of 93.0% and 97.1%, respectively. The area under the ROC curve is 0.951 (95% CI 0.918 to 0.983).

Conclusion

A fast and fully automatic method can be used for stroke subtype risk assessment and classification based on fundus photographs alone.