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Experimental Eye Research May 2024The retinal microcirculation system constitutes a unique terminal vessel bed of the systemic circulation, and its perfusion status is directly associated with the neural... (Review)
Review
The retinal microcirculation system constitutes a unique terminal vessel bed of the systemic circulation, and its perfusion status is directly associated with the neural function of the retina. This vascular network, essential for nourishing various layers of the retina, comprises two primary microcirculation systems: the retinal microcirculation and the choroidal microcirculation, with each system supplying blood to distinct retinal layers and maintaining the associated neural function. The blood flow of those capillaries is regulated via different mechanisms. However, a range of internal and external factors can disrupt the normal architecture and blood flow within the retinal microcirculation, leading to several retinal pathologies, including diabetic retinopathy, macular edema, and vascular occlusions. Metabolic disturbances such as hyperglycemia, hypertension, and dyslipidemia are known to modify retinal microcirculation through various pathways. These alterations are observable in chronic metabolic conditions like diabetes, coronary artery disease, and cerebral microvascular disease due to advances in non-invasive or minimally invasive retinal imaging techniques. Thus, examination of the retinal microcirculation can provide insights into the progression of numerous chronic metabolic disorders. This review discusses the anatomy, physiology and pathophysiology of the retinal microvascular system, with a particular emphasis on the connections between retinal microcirculation and systemic circulation in both healthy states and in the context of prevalent chronic metabolic diseases.
Topics: Humans; Microcirculation; Retinal Vessels; Metabolic Diseases; Retinal Diseases; Regional Blood Flow
PubMed: 38574944
DOI: 10.1016/j.exer.2024.109885 -
Interventional Cardiology Clinics Jan 2023Ischemic heart disease (IHD) affects more than 20 million adults in the United States. Although classically attributed to atherosclerosis of the epicardial coronary... (Review)
Review
Ischemic heart disease (IHD) affects more than 20 million adults in the United States. Although classically attributed to atherosclerosis of the epicardial coronary arteries, nearly half of patients with stable angina and IHD who undergo invasive coronary angiography do not have obstructive epicardial coronary artery disease. Ischemia with nonobstructive coronary arteries is frequently caused by microvascular angina with underlying coronary microvascular dysfunction (CMD). Greater understanding the pathophysiology, diagnosis, and treatment of CMD holds promise to improve clinical outcomes of patients with ischemic heart disease.
Topics: Adult; Humans; Microcirculation; Coronary Artery Disease; Microvascular Angina; Coronary Angiography
PubMed: 36372455
DOI: 10.1016/j.iccl.2022.09.010 -
Ceska a Slovenska Oftalmologie :... 2022Rheopheresis ranks among apheretic methods. It is a selective, extra-corporeal double cascade filtration treatment. First, the plasma is separated from blood elements in... (Review)
Review
Rheopheresis ranks among apheretic methods. It is a selective, extra-corporeal double cascade filtration treatment. First, the plasma is separated from blood elements in extra-corporeal circulation by passing through membrane filter. The plasma is then filtrated through the second filter in order to remove proteins with a high molecular mass, e.g. lipids, fibrinogen, α2-macroglobulin, von Willebrand factor, immunoglobulin IgM. The purified plasma is then returned together with the blood elements back to the patient. The aim of the procedure is to improve the microcirculation and rheological properties of the blood. Rheopheresis is well established method for the treatment of age-related macular degeneration, acute sensorineural hearing loss, calciphylaxis, systemic sclerosis or peripheral vascular disease.
Topics: Humans; Microcirculation; Hearing Loss, Sensorineural; Macular Degeneration; Plasmapheresis
PubMed: 36858956
DOI: 10.31348/2023/1 -
Scientific Reports Nov 2022Reliable assessment of the microcirculation is important to investigate microcirculatory properties in various disease states. The GlycoCheck system automatically...
Reliable assessment of the microcirculation is important to investigate microcirculatory properties in various disease states. The GlycoCheck system automatically analyzes sublingual sidestream dark field images to determine the perfused boundary region (PBR; a measure of glycocalyx thickness), red blood cell filling percentage, and microvascular vessel density. Although GlycoCheck has been used to study the microcirculation in patients, little is known about the reproducibility of measurements in healthy volunteers. We assessed intra- and interobserver agreement by having two experienced observers perform three consecutive microcirculation measurements with the GlycoCheck system in 49 healthy volunteers. Intraobserver agreement of single measurements were poor (intraclass correlation coefficients (ICCs) < 0.4) for PBR, red blood cell filling percentage and microvascular vessel density. ICCs increased to values > 0.6 (indicating good reproducibility) for all parameters when performing and averaging three consecutive measurements. No systematic differences were observed between observers for any parameter. Interobserver variability was fair for PBR (ICC = 0.53) and red blood cell filling percentage (ICC = 0.58) and poor for perfused vessel density (ICC = 0.20). In conclusion, GlycoCheck software can be used with acceptable reliability and reproducibility for microcirculation measurements on a population level when averaging three consecutive measurements. Repeated measurements are preferably performed by the same observer.
Topics: Humans; Microcirculation; Reproducibility of Results; Healthy Volunteers; Glycocalyx; Erythrocytes
PubMed: 36400927
DOI: 10.1038/s41598-022-22947-x -
Journal of Applied Physiology... Mar 2022Extracorporeal membrane oxygenation (ECMO) is a procedure used to aid respiratory function in critical patients, involving extracorporeal circulation (ECC) of blood....
Extracorporeal membrane oxygenation (ECMO) is a procedure used to aid respiratory function in critical patients, involving extracorporeal circulation (ECC) of blood. There is a limited number of studies quantifying the hemodynamic effects of ECC procedures on the microcirculation. We sought to mimic veno-arterial-ECMO flow conditions by use of a scaled-down circuit primed with either lactate Ringer (LR) or 5% human serum albumin (HSA). The circuit was first tested using benchtop runs with blood, and subsequently used for in vivo experiments in Golden Syrian hamsters instrumented with a dorsal window chamber to allow for quantification of microvascular hemodynamics and functional capillary density (FCD). Results showed significant impairment in FCD, and a reduction of arteriolar and venular blood flow, with HSA providing significant higher blood flows and FCD compared with LR. Changes in hematocrit and RBC labeling after ECC reflected a shift in plasma volume, which may stem from a loss in intravascular oncotic pressure due to priming fluids. The distribution of hemoglobin oxygen saturation in the microvasculature showed a significant decrease in venules after ECC. In addition, major organs such as the kidney and heart showed increases in both inflammatory and damage markers. These results suggest that ECC impairs microvasculature function and promotes ischemia and hypoxia in the tissues, which can be vital to understanding comorbid clinical outcomes from ECC procedures such as acute kidney injury and multiorgan dysfunction. ECC reduces microvascular perfusion, with no full recovery 24 h after ECC. HSA performed better as compared with LR in terms of FCD and venule flow, as well as venule oxygen saturation. Increases in inflammatory and damage markers in key organs were observed within all organs analyzed.
Topics: Animals; Capillaries; Cricetinae; Extracorporeal Circulation; Humans; Microcirculation; Microvessels; Oxygen; Perfusion
PubMed: 35085033
DOI: 10.1152/japplphysiol.00726.2021 -
Heart (British Cardiac Society) Jul 2023We aimed to evaluate the microcirculatory resistance (MR) and myocardial metabolic adaptations at rest and in response to increased cardiac workload in patients with...
OBJECTIVE
We aimed to evaluate the microcirculatory resistance (MR) and myocardial metabolic adaptations at rest and in response to increased cardiac workload in patients with suspected coronary microvascular dysfunction (CMD).
METHODS
Patients with objective ischaemia and/or myocardial injury and non-obstructive coronary artery disease underwent thermodilution-derived microcirculatory assessment and transcardiac blood sampling during graded exercise with adenosine-mediated hyperaemia. We measured MR at rest and following supine cycle ergometry. Patients (n=24) were stratified by the resting index of MR (IMR) into normal-IMR (IMR<22U, n=12) and high-IMR groups (IMR≥22U, n=12).
RESULTS
The mean age was 57 years; 67% were males and 38% had hypertension. The normal-IMR group had increased IMR response to exercise (16±5 vs 23±12U, p=0.03) compared with the high-IMR group, who had persistently elevated IMR at rest and following exercise (38±19 vs 33±15U, p=0.39) despite similar exercise duration and rate-pressure product between the groups, both p>0.05. The normal-IMR group had augmented oxygen extraction ratio following exercise (53±18 vs 64±11%, p=0.03) compared with the high-IMR group (65±14 vs 59±11%, p=0.26). The postexercise lactate uptake was greater in the high-IMR (0.04±0.05 vs 0.11±0.07 mmol/L, p=0.004) compared with normal-IMR group (0.08±0.06 vs 0.09±0.09 mmol/L, p=0.67). The high-IMR group demonstrated greater troponin release following exercise compared with the normal-IMR group (0.13±0.12 vs 0.001±0.05 ng/L, p=0.03).
CONCLUSIONS
Patients with suspected CMD appear to have distinctive microcirculatory resistive and myocardial metabolic profiles at rest and in response to exercise. These differences in phenotypes may permit individualised therapies targeting microvascular responsiveness (normal-IMR group) and/or myocardial metabolic adaptations (normal-IMR and high-IMR groups).
Topics: Humans; Male; Female; Microcirculation; Coronary Artery Disease; Hemodynamics; Exercise; Coronary Angiography; Acute Coronary Syndrome; Angina Pectoris; Microvascular Angina
PubMed: 36931716
DOI: 10.1136/heartjnl-2022-322156 -
European Heart Journal Jan 2023It remains unknown whether the presence of coronary microcirculatory dysfunction (CMD) correlates with its equivalent condition in the brain, cerebral small vessel...
BACKGROUND
It remains unknown whether the presence of coronary microcirculatory dysfunction (CMD) correlates with its equivalent condition in the brain, cerebral small vessel disease (CSVD). The cerebral-coronary connection (C3), a prospective blinded study, investigated the prevalence of CMD in patients with coronary artery disease (CAD) and its association with CSVD and cognitive function.
METHODS AND RESULTS
Patients with documented CAD fulfilling inclusion criteria underwent physiological assessment of epicardial vessels and the microcirculation using intracoronary pressure and Doppler. Coronary microcirculation-related indices included coronary flow reserve (CFR) and hyperaemic microvascular resistance. Brain magnetic resonance imaging, transcranial Doppler (TCD), and neurocognitive examination were performed. Overall, 67 patients were included in the study (mean age 66 years, 73% female). Patients with abnormal CFR (<2.0) (55.2%) showed higher burden of white-matter hyperintensities: 43.2 vs. 20.0% (P = 0.044). After statistical adjustment, low CFR was associated with lower grey matter volume (P = 0.024) and with parameters of white-matter microstructural damage in diffusion-tensor imaging (lower fractional anisotropy and higher mean diffusivity, P = 0.029 and P = 0.032, respectively). Low CFR was associated with higher resistive (P = 0.027) and pulsatility (P = 0.043) values on TCD, and worse neurocognitive test scores (lower mini mental state examination, P = 0.025, and slower Trail Making Test A, P = 0.034).
CONCLUSIONS
Coronary microcirculatory dysfunction is frequent in patients with CAD and correlates with CSVD, abnormal cerebral flow haemodynamics, and significant cognitive impairment. These findings support the hypothesis that microvascular dysfunction in the heart and the brain are part of a single pathological process affecting microcirculation in patients with CAD.
CLINICAL TRIAL REGISTRATION
ClinicalTrials.gov NCT04131075.
Topics: Aged; Female; Humans; Male; Cognition; Coronary Angiography; Coronary Artery Disease; Coronary Vessels; Fractional Flow Reserve, Myocardial; Heart Diseases; Microcirculation; Myocardial Ischemia; Prospective Studies; Vascular Resistance
PubMed: 36337036
DOI: 10.1093/eurheartj/ehac521 -
Journal of Cerebral Blood Flow and... Oct 2021The blood-brain barrier (BBB) is dysfunctional in temporal lobe epilepsy (TLE). In this regard, microvascular changes are likely present. The aim of this review is to... (Review)
Review
The blood-brain barrier (BBB) is dysfunctional in temporal lobe epilepsy (TLE). In this regard, microvascular changes are likely present. The aim of this review is to provide an overview of the current knowledge on microvascular changes in epilepsy, and includes clinical and preclinical evidence of seizure induced angiogenesis, barriergenesis and microcirculatory alterations. Anatomical studies show increased microvascular density in the hippocampus, amygdala, and neocortex accompanied by BBB leakage in various rodent epilepsy models. In human TLE, a decrease in afferent vessels, morphologically abnormal vessels, and an increase in endothelial basement membranes have been observed. Both clinical and experimental evidence suggests that basement membrane changes, such as string vessels and protrusions, indicate and visualize a misbalance between endothelial cell proliferation and barriergenesis. Vascular endothelial growth factor (VEGF) appears to play a crucial role. Following an altered vascular anatomy, its physiological functioning is affected as expressed by neurovascular decoupling that subsequently leads to hypoperfusion, disrupted parenchymal homeostasis and potentially to seizures". Thus, epilepsy might be a condition characterized by disturbed cerebral microvasculature in which VEGF plays a pivotal role. Additional physiological data from patients is however required to validate findings from models and histological studies on patient biopsies.
Topics: Blood-Brain Barrier; Epilepsy; Female; Humans; Male; Microcirculation
PubMed: 33866850
DOI: 10.1177/0271678X211010388 -
Clinical Hemorheology and... 2023Currently, there are limited data on the effect of macrocirculatory hemodynamic changes on human microcirculation, especially during the induction of general anesthesia... (Observational Study)
Observational Study
OBJECTIVE
Currently, there are limited data on the effect of macrocirculatory hemodynamic changes on human microcirculation, especially during the induction of general anesthesia (GA).
METHODS
We performed a non-randomized observational trial on patients receiving GA for elective surgery. In the control group (CG), for GA induction sufentanil, propofol, and rocuronium was administered. Patients assigned to the esketamine group (EG) received additional esketamine for GA induction. Invasive blood pressure (IBP) and pulse contour cardiac output (CO) measurement were performed continuously. Microcirculation was assessed using cutaneous Laser Doppler Flowmetry (forehead and sternum LDF), peripheral and central Capillary Refill Time (pCRT, cCRT), as well as brachial temperature gradient (Tskin-diff) at baseline, 5, 10 and 15 minutes after induction of GA.
RESULTS
42 patients were included in the analysis (CG n = 22, EG n = 20). pCRT, cCRT, Tskin-diff, forehead and sternum LDF decreased following GA induction in both groups. IBP and CO were significantly more stable in esketamine group. However, the changes in the microcirculatory parameters were not significantly different between the groups.
CONCLUSIONS
The addition of esketamine for GA induction warranted better hemodynamic stability for the first five minutes, but had no significant effect on any of the cutaneous microcirculatory parameters measured.
Topics: Humans; Anesthesia, General; Hemodynamics; Microcirculation; Skin
PubMed: 37334583
DOI: 10.3233/CH-231711 -
Journal of Theoretical Biology Jul 2022We consider the flow of blood, treated as an incompressible Newtonian fluid, through vessels undergoing periodic oscillations. As remarked by many authors, in the...
We consider the flow of blood, treated as an incompressible Newtonian fluid, through vessels undergoing periodic oscillations. As remarked by many authors, in the absence of valves oscillations hinder the flow because of the lumen reduction. The underlying biological mechanism is the so-called vasomotion, observed long ago in small blood vessels. Here, we study the vasomotion in arterioles and provide its theoretical justification by analyzing the effect when the network of vessels downstream of the arterioles is considered. We thus explain both quantitatively and qualitatively, why the oscillations of the arteriole walls, a phenomenon that undoubtedly reduces blood flow at the level of the single arteriole, play a fundamental role in microcirculation. In "large" arterioles we analyze also the coupling between the vasomotion and the Fåhræus-Lindqvist effect (the tendency of the erythrocytes to accumulate towards the center). In particular, we prove that the presence of a cell depleted layer close to the vessel walls mitigates the disadvantage caused by the lumen reduction.
Topics: Arterioles; Erythrocytes; Microcirculation
PubMed: 35429550
DOI: 10.1016/j.jtbi.2022.111124