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Use of XyCAM RI for Noninvasive Visualization and Analysis of Retinal Blood Flow Dynamics During Clinical Investigations.
DeBuc, DC, Rege, A, Smiddy, WE
Expert review of medical devices. 2021;(3):225-237
Abstract
INTRODUCTION Ocular blood flow plays a critical role in eye health by nourishing the retinal and ocular tissues with oxygen and nutrients and removal of ocular metabolic waste. Imaging of retinal and optic blood flow may provide insights for early and more specific diagnoses of ocular vascular disorder and facilitate eye-based biomarkers applicable to neurological health assessment and research. AREAS COVERED The ability of the XyCAM RI (Vasoptic Medical Inc., MD, USA) to visualize and to analyze ocular blood flow dynamics XyCAM RI using laser speckle contrast imaging is reviewed and compared with concurrent clinical ophthalmic imaging technologies like optical coherence tomography - angiography (OCT-A), fundus imaging, fluorescein angiography (FA), indocyanine green angiography (ICGA), laser Doppler flowmetry (LDF), and laser speckle flowgraphy (LSFG). EXPERT OPINION XyCAM RI, with its unprecedented imaging capabilities to assess blood flow dynamics provides a powerful tool to ophthalmic researchers and doctors to obtain greater clinical insights into the physiological status of the posterior segment and treatment approaches for various diseases in a very patient-friendly, noninvasive manner, unlike dye-based angiographic techniques such as FA or ICG. XyCAM RI is well suited as a modality that could close the gap between current screening and comprehensive eye exams.
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Baseline Factors Associated with Diabetic Retinopathy Improvement in RIDE/RISE.
Dhoot, DS, Hill, LF, Ghanekar, A, Tarnowski, KW, Ali, FS
Ophthalmology. Retina. 2021;(1):101-103
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Mechanisms Behind Blood Flow-Restricted Training and its Effect Toward Muscle Growth.
Hwang, PS, Willoughby, DS
Journal of strength and conditioning research. 2019;:S167-S179
Abstract
Hwang, P and Willoughby, DS. Mechanisms behind blood flow-restricted training and its effect toward muscle growth. J Strength Cond Res 33(7S): S167-S179, 2019-It is widely established throughout the literature that skeletal muscle can induce hypertrophic adaptations after progressive overload of moderate-to-high-intensity resistance training. However, there has recently been a growing body of research that shows that the combination of blood flow-restricted (BFR) training with low-intensity resistance exercise can induce similar gains in muscular strength and hypertrophic adaptations. The implementation of external pressure cuffs over the most proximal position of the limb extremities with the occlusion of venous outflow of blood distal to the occlusion site defines the BFR training protocol. There are various mechanisms through which BFR training may cause the stimulations for skeletal muscle hypertrophy and increases in strength. These may include increases in hormonal concentrations, increases within the components of the intracellular signaling pathways for muscle protein synthesis such as the mTOR pathway, increases within biomarkers denoting satellite cell activity and apparent patterns in fiber type recruitment. There have also been scientific findings demonstrating hypertrophic effects within both BFR limbs and non-BFR muscles during BFR training programs. The purpose behind this critical review will be to provide a comprehensive discussion on relevant literature that can help elucidate the potential underlying mechanisms leading to hypertrophic adaptations after BFR training programs. This review will also explicate the various findings within the literature that focalizes on both BFR limb and non-BFR muscle hypertrophy after bouts of BFR training. Furthermore, this critical review will also address the various needs for future research in the many components underlying the novel modality of BFR training.
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Retinal oximetry in patients with ischaemic retinal diseases.
Rilvén, S, Torp, TL, Grauslund, J
Acta ophthalmologica. 2017;(2):119-127
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The retinal oximeter is a new tool for non-invasive measurement of retinal oxygen saturation in humans. Several studies have investigated the associations between retinal oxygen saturation and retinal diseases. In the present systematic review, we examine whether there are associations between retinal oxygen saturation and retinal ischaemic diseases. We used PubMed and Embase to search for retinal oxygen saturation and retinal ischaemic diseases. Three separate searches identified a total of 79 publications. After two levels of manual screening, 10 studies were included: six about diabetic retinopathy (DR) and four about retinal vein occlusion. No studies about retinal artery occlusion were included. In diabetes, all studies found that increases in retinal venous oxygen saturation (rvSatO2 ) were associated with present as well as increasing levels of DR. Four of six studies also found increased retinal arterial oxygen saturation (raSatO2 ) in patients with DR. In patients with central retinal vein occlusion (CRVO), all studies found that rvSatO2 was reduced, but raSatO2 remained unchanged. Branch retinal vein occlusion was not associated with changes in retinal oxygen saturation, but this was based on a single study. In conclusion, DR is associated with increased rvSatO2 and might also be related to increased raSatO2 . Central retinal vein occlusion (CRVO) is correlated with increased rvSatO2 but unrelated to raSatO2 . Prospective studies are needed to expand these findings. These would tell whether retinal oximetry could be a potential tool for screening or a biomarker of treatment outcome in patients with ischaemic retinal diseases.
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Evaluating ocular blood flow.
Maram, J, Srinivas, S, Sadda, SR
Indian journal of ophthalmology. 2017;(5):337-346
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Studies have shown that vascular impairment plays an important role in the etiology and pathogenesis of various ocular diseases including glaucoma, age-related macular degeneration, diabetic retinopathy, and retinal venous occlusive disease. Thus, qualitative and quantitative assessment of ocular blood flow (BF) is a topic of interest for early disease detection, diagnosis, and management. Owing to the rapid improvement in technology, there are several invasive and noninvasive techniques available for evaluating ocular BF, with each of these techniques having their own limitations and advantages. This article reviews these important techniques, with a particular focus on Doppler Fourier domain optical coherence tomography (OCT) and OCT-angiography.
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Influence of L-citrulline and watermelon supplementation on vascular function and exercise performance.
Figueroa, A, Wong, A, Jaime, SJ, Gonzales, JU
Current opinion in clinical nutrition and metabolic care. 2017;(1):92-98
Abstract
PURPOSE OF REVIEW L-Citrulline, either synthetic or in watermelon, may improve vascular function through increased L-arginine bioavailability and nitric oxide synthesis. This article analyses potential vascular benefits of L-citrulline and watermelon supplementation at rest and during exercise. RECENT FINDINGS There is clear evidence that acute L-citrulline ingestion increases plasma L-arginine, the substrate for endothelial nitric oxide synthesis. However, the subsequent acute improvement in nitric oxide production and mediated vasodilation is inconsistent, which likely explains the inability of acute L-citrulline or watermelon to improve exercise tolerance. Recent studies have shown that chronic L-citrulline supplementation increases nitric oxide synthesis, decreases blood pressure, and may increase peripheral blood flow. These changes are paralleled by improvements in skeletal muscle oxygenation and performance during endurance exercise. The antihypertensive effect of L-citrulline/watermelon supplementation is evident in adults with prehypertension or hypertension, but not in normotensives. However, L-citrulline supplementation may attenuate the blood pressure response to exercise in normotensive men. SUMMARY The beneficial vascular effects of L-citrulline/watermelon supplementation may stem from improvements in the L-arginine/nitric oxide pathway. Reductions in resting blood pressure with L-citrulline/watermelon supplementation may have major implications for individuals with prehypertension and hypertension. L-Citrulline supplementation, but not acute ingestion, have shown to improve exercise performance in young healthy adults.
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Endothelial function in patients with chronic obstructive pulmonary disease: a systematic review of studies using flow mediated dilatation.
Vaes, AW, Spruit, MA, Theunis, J, Goswami, N, Vanfleteren, LE, Franssen, FME, Wouters, EFM, De Boever, P
Expert review of respiratory medicine. 2017;(12):1021-1031
Abstract
BACKGROUND Cardiovascular disease is an important cause of morbidity and mortality in chronic obstructive pulmonary disease (COPD). Endothelial function may be involved in the pathogenesis of cardiovascular disease. In contrast to the attention given to pulmonary endothelial dysfunction, little is known about peripheral vascular changes in COPD. Therefore, we reviewed the literature on peripheral endothelial function in COPD. METHODS Databases were screened for studies using ultrasound-based flow-mediated dilation (FMD), the reference method for assessing peripheral endothelial function, in stable COPD patients. Pooled effect sizes were calculated using random effects model. RESULTS 17 studies were identified, with a total of 1228 participants (724 COPD patients; 504 controls). Pooled analysis demonstrated an impaired endothelial-dependent FMD (-3.22%; 95% confidence interval (CI) -4.74 to -1.69; p < 0.001; I2 = 96%) and endothelial-independent FMD (-2.86%; 95%CI -5.63 to -0.09; p = 0.04; I2 = 83%) in COPD patients when compared with smoking and non-smoking controls. CONCLUSION This review provides evidence for impaired peripheral endothelial function in COPD. Since impaired endothelial function may contribute to cardiovascular morbidity, a more comprehensive cardiovascular phenotyping is considered important in COPD to address cardiovascular risk. A high frequency of cardiovascular comorbidity is observed in COPD patients, and therefore well-controlled, larger studies that investigate endothelial function in COPD patients are recommended.
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Eating and arterial endothelial function: a meta-analysis of the acute effects of meal consumption on flow-mediated dilation.
Thom, NJ, Early, AR, Hunt, BE, Harris, RA, Herring, MP
Obesity reviews : an official journal of the International Association for the Study of Obesity. 2016;(11):1080-1090
Abstract
Given that endothelial dysfunction precedes atherosclerotic cardiovascular disease, exploring the parameters that modify postprandial flow-mediated dilation (FMD) is important for public health. The objectives of the study are to estimate the population effect of meal ingestion on FMD and to determine how the effect varied based on patient characteristics and modifiable methodological features. Articles published before June 2015 were located using MEDLINE, PubMed and Web of Science. One hundred fifty-four effects were derived from 78 articles involving 2,548 subjects were selected. Included articles required measurement of FMD in adults before and after meal ingestion. Effects were analysed using an unstandardized mean gain random effects model, and significant moderators were analysed using meta-regression. Meal consumption significantly reduced FMD by a heterogeneous mean effect size delta (Δ) of -2.03 (95% CI: [-2.28, -1.77]), an ~2% reduction in FMD. FMD reductions were larger among normal weight individuals, males, those with a cardio-metabolic disorder, those with elevated baseline FMD, and individuals with impaired glucose tolerance at baseline. Macronutrient meal ingestion significantly reduced FMD, an effect that was moderated by body mass index, sex and two-way interactions between disease status and both baseline FMD and baseline blood glucose levels.
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Gender differences in ocular blood flow.
Schmidl, D, Schmetterer, L, Garhöfer, G, Popa-Cherecheanu, A
Current eye research. 2015;(2):201-12
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Gender medicine has been a major focus of research in recent years. The present review focuses on gender differences in the epidemiology of the most frequent ocular diseases that have been found to be associated with impaired ocular blood flow, such as age-related macular degeneration, glaucoma and diabetic retinopathy. Data have accumulated indicating that hormones have an important role in these diseases, since there are major differences in the prevalence and incidence between men and pre- and post-menopausal women. Whether this is related to vascular factors is, however, not entirely clear. Interestingly, the current knowledge about differences in ocular vascular parameters between men and women is sparse. Although little data is available, estrogen, progesterone and testosterone are most likely important regulators of blood flow in the retina and choroid, because they are key regulators of vascular tone in other organs. Estrogen seems to play a protective role since it decreases vascular resistance in large ocular vessels. Some studies indicate that hormone therapy is beneficial for ocular vascular disease in post-menopausal women. This evidence is, however, not sufficient to give any recommendation. Generally, remarkably few data are available on the role of sex hormones on ocular blood flow regulation, a topic that requires more attention in the future.
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Glial cell regulation of neuronal activity and blood flow in the retina by release of gliotransmitters.
Newman, EA
Philosophical transactions of the Royal Society of London. Series B, Biological sciences. 2015;(1672)
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Astrocytes in the brain release transmitters that actively modulate neuronal excitability and synaptic efficacy. Astrocytes also release vasoactive agents that contribute to neurovascular coupling. As reviewed in this article, Müller cells, the principal retinal glial cells, modulate neuronal activity and blood flow in the retina. Stimulated Müller cells release ATP which, following its conversion to adenosine by ectoenzymes, hyperpolarizes retinal ganglion cells by activation of A1 adenosine receptors. This results in the opening of G protein-coupled inwardly rectifying potassium (GIRK) channels and small conductance Ca(2+)-activated K(+) (SK) channels. Tonic release of ATP also contributes to the generation of tone in the retinal vasculature by activation of P2X receptors on vascular smooth muscle cells. Vascular tone is lost when glial cells are poisoned with the gliotoxin fluorocitrate. The glial release of vasoactive metabolites of arachidonic acid, including prostaglandin E2 (PGE2) and epoxyeicosatrienoic acids (EETs), contributes to neurovascular coupling in the retina. Neurovascular coupling is reduced when neuronal stimulation of glial cells is interrupted and when the synthesis of arachidonic acid metabolites is blocked. Neurovascular coupling is compromised in diabetic retinopathy owing to the loss of glial-mediated vasodilation. This loss can be reversed by inhibiting inducible nitric oxide synthase. It is likely that future research will reveal additional important functions of the release of transmitters from glial cells.