Arteriolar Flow Research Articles

BIOMICROSCOPY OF THE CAPILLARY FLOW - INTERDISCIPLINARY APPROACH AND EFFECTIVENESS OF PATHOLOGICAL CONDITIONS DIAGNOSTICS

The goal – to evaluate the features and diagnostic value of the capillary bedbiomicroscopy results in various pathological conditions.Material and methods. The paper presents data on microcirculation study in patientsof various ages (adults and children) with different somatic pathologies (with diabetesmellitus, arterial hypertension, chronic gastroduodenitis, acute bronchitis) comparedwith healthy persons. The state of microcirculation was recorded using a digital USBmicroscope and evaluated by qualitative and semi quantitative assessment.Results. In patients with diabetes, the most changes in the form of capillariesand venules microaneurism, reduction of the functioning vessels number, slowingblood flow, decrease of arteriolo-venular coefficient were registered. In arterialhypertension, the signs of an increase in peripheral resistance were dominated, andin inflammatory diseases of the gastroduodenal zone and during bronchitis there wasa slowing of blood flow in arterioles and capillaries, an increase in the vascularity ofarterioles and the erythrocytes adhesion inside vessels.Conclusions. Biomicroscopy is simple and informative method for studyingmicrocirculation both chronic and acute diseases, the volume and nature of violationspredominantly depends on the type of pathology, its severity and duration.

An integrated lumped-parameter model of the cardiovascular system for the simulation of acute ischemic stroke: description of instantaneous changes in hemodynamics.

Acute Ischemic Stroke (AIS) is defined as the acute condition of occlusion of a cerebral artery and is often caused by a Hypertensive Condition (HC). Due to its sudden occurrence, AIS is not observable the right moment it occurs, thus information about instantaneous changes in hemodynamics is limited. This study aimed to propose an integrated Lumped Parameter (LP) model of the cardiovascular system to simulate an AIS and describe instantaneous changes in hemodynamics. In the integrated LP model of the cardiovascular system, heart chambers have been modelled with elastance systems with controlled pressure inputs; heart valves have been modelled with static open/closed pressure-controlled valves; eventually, the vasculature has been modelled with resistor-inductor-capacitor (RLC) direct circuits and have been linked to the rest of the system through a series connection. After simulating physiological conditions, HC has been simulated by changing pressure inputs and constant RLC parameters. Then, AIS occurring in arteries of different sizes have been simulated by considering time-dependent RLC parameters due to the elimination from the model of the occluding artery; instantaneous changes in hemodynamics have been evaluated by Systemic Arteriolar Flow (Qa) and Systemic Arteriolar Pressure (Pa) drop with respect to those measured in HC. Occlusion of arteries of different sizes leaded to an average Qa drop of 0.38 ml/s per cardiac cycle (with minimum and maximum values of 0.04 ml/s and 1.93 ml/s) and average Pa drop of 0.39 mmHg, (with minimum and maximum values of 0.04 mmHg and 1.98 mmHg). In conclusion, hemodynamic variations due to AIS are very small with respect to HC. A direct relation between the inverse of the length of the artery in which the occlusion occurs and the hemodynamic variations has been highlighted; this may allow to link the severity of AIS to the length of the interested artery.

Targeted septal branch microcirculatory embolization with tris-acryl gelatin microspheres in hypertrophic obstructive cardiomyopathy

Abstract Background Alcohol septal ablation (ASA) has been shown to be an effective treatment in patients with hypertrophic obstructive cardiomyopathy (HOCM) who are refractory to medical treatment. ASA may cause some life-threatening complications including conduction disturbances, hemodynamic compromise, ventricular arrhythmias, distant and massive myocardial necrosis. Tris-acryl gelatin microspheres provide consistent and predictable results for effective targeted microcirculatory embolization. Purpose We aimed to report our initial experience in tris-acryl gelatin microspheres for septal ablation in HOCM. Methods Microspheres are biocompatible, hydrophilic, non-resorbable microspheres which are available in a range of calibrated sphere sizes. In our method, after the cannulation of the left anterior descending by a 6F-7F guiding catheter, a 0.014-inch guidewire is introduced through the catheter and advanced into the septal branch. This septal artery is selectively cannulated with a 4F catheter over the guidewire. Selective angiography of the septal artery is performed to show the anatomy and collateral branches to other coronary arteries. Contrast echocardiography is performed to make sure that the pertinent septal artery is the target vessel supplying the hypertrophied septum. A microcatheter is then advanced deep enough into the septal artery through the 4F catheter. Microspheres/contrast solution infused slowly under fluoroscopic guidance into the targeted septal branches initially using coronary arteriolar sized small particles (diameter 100–300 μm); then the particle size was stepped up to larger particles (diameter 300–500 μm) until a complete block of the arteriolar flow is achieved. Results Septal ablation with tris-acryl gelatin microspheres was performed in 6 patients (mean age = 47.8±11.5; 5 males). Immediately after the procedure peak left ventricular outflow (LVOT) gradient reduced significantly both for direct catheter (69.0±13.8 vs. 8.2±3.7 mmHg, P<0.001) and Doppler echocardiographic measurements (78.8±19.9 vs. 12.0±5.1 mmHg, P<0.001). Post-procedure peak serum CK- MB fraction concentration was 82±22 ng/ml (reference range is 0 - 4.9 ng/mL) and peak serum troponin T concentration was 1.2 ng/ml [(interquartile range, 0.4–1.4), (reference range is 0 - 0.017 ng/mL)]. LVOT tract gradient reduction persisted after 6 months follow-up. There was no significant complication during the procedure and within a 6 months follow-up period. Conclusions The novel strategy by targeted septal branch microcirculatory embolization with tris-acryl gelatin microspheres seems to be an efficient and safe approach to HOCM. Further experience is needed in order to assess the long-term efficacy and safety of this technique. Funding Acknowledgement Type of funding source: None

Full-field flicker evoked changes in parafoveal retinal blood flow

When retinal activity is increased by exposure to dynamic visual stimuli, blood vessels dilate and the flow of blood within vessels increases to meet the oxygen and glucose demands of the neurons. This relationship is termed ‘neurovascular coupling’ and it is critical for regulating control of the human retinal vasculature. In this study, we used a recently developed technique based on a dual-beam adaptive optics scanning laser ophthalmoscope to measure changes in red blood cell velocities, vessel diameter, and flow in interconnected small parafoveal retinal vessels (< 50 µm) of nine healthy participants. A full-field flicker stimulus was presented onto the retina to induce a vascular response to neural activity. Flicker stimulation increased blood velocity, vessel diameter, and therefore flow in arterioles, capillaries, and venules in all nine subjects. ANOVA and post hoc t-test showed significant increases in velocity and flow in arterioles and venules. These measurements indicate that the mechanism of neurovascular coupling systematically affects the vascular response in small retinal vessels in order to maintain hemodynamic regulation in the retina when exposed to visual stimulation, in our case flicker. Our findings may provide insight into future investigations on the impairments of neurovascular coupling from vascular diseases such as diabetic mellitus.

Electrical Propagation of Vasodilatory Signals in Capillary Networks.

We have developed a computational model to study electrical propagation of vasodilatory signals and arteriolar regulation of blood flow depending on the oxygen tension and agonist distribution in the capillary network. The involving key parameters of endothelial cell-to-cell electrical conductivity and plasma membrane area per unit volume were calibrated with the experimental data on an isolated endothelial tube of mouse skeletal feeding arteries. We have estimated the oxygen saturation parameters in terms of erythrocyte ATP release from the data of a left anterior descending coronary blood perfusion of dog. Regarding the acetylcholine-induced upstream conduction, our model shows that spatially uniform superfusion of acetylcholine attenuates the electrical signal propagation, and blocking calcium-activated potassium channels suppresses that attenuation. On the other hand, a local infusion of acetylcholine induces enhanced electrical propagation that corresponds to physiological relevance. Integrating the electrophysiology of endothelial tube and the electrophysiology/mechanics of a lumped arteriole, we show mechanistically that endothelial purinergic oxygen sensing of ATP released from erythrocytes and local infusion of acetylcholine are individually effective to induce vasodilatory signals to regulate blood flow in arterioles. We have recapitulated the upstream vasomotion in arterioles from the elevated oxygen tension in the downstream capillary domain. This study is a foundation for characterizing effective pharmaceutical strategies for ascending vasodilation and oxygenation.

Cerebral tissue pO2 response to treadmill exercise in awake mice

We exploited two-photon microscopy and Doppler optical coherence tomography to examine the cerebral blood flow and tissue pO2 response to forced treadmill exercise in awake mice. To our knowledge, this is the first study performing both direct measure of brain tissue pO2 during acute forced exercise and underlying microvascular response at capillary and non-capillary levels. We observed that cerebral perfusion and oxygenation are enhanced during running at 5 m/min compared to rest. At faster running speeds (10 and 15 m/min), decreasing trends in arteriolar and capillary flow speed were observed, which could be due to cerebral autoregulation and constriction of arterioles in response to blood pressure increase. However, tissue pO2 was maintained, likely due to an increase in RBC linear density. Higher cerebral oxygenation at exercise levels 5–15 m/min suggests beneficial effects of exercise in situations where oxygen delivery to the brain is compromised, such as in aging, atherosclerosis and Alzheimer Disease.

Endothelial Ca2+ signaling-dependent vasodilation through transient receptor potential channels.

Ca2+ signaling of endothelial cells plays a critical role in controlling blood flow and pressure in small arteries and arterioles. As the impairment of endothelial function is closely associated with cardiovascular diseases (e.g., atherosclerosis, stroke, and hypertension), endothelial Ca2+ signaling mechanisms have received substantial attention. Increases in endothelial intracellular Ca2+ concentrations promote the synthesis and release of endothelial-derived hyperpolarizing factors (EDHFs, e.g., nitric oxide, prostacyclin, or K+ efflux) or directly result in endothelial-dependent hyperpolarization (EDH). These physiological alterations modulate vascular contractility and cause marked vasodilation in resistance arteries. Transient receptor potential (TRP) channels are nonselective cation channels that are present in the endothelium, vascular smooth muscle cells, or perivascular/sensory nerves. TRP channels are activated by diverse stimuli and are considered key biological apparatuses for the Ca2+ influx-dependent regulation of vasomotor reactivity in resistance arteries. Ca2+-permeable TRP channels, which are primarily found at spatially restricted microdomains in endothelial cells (e.g., myoendothelial projections), have a large unitary or binary conductance and contribute to EDHFs or EDH-induced vasodilation in concert with the activation of intermediate/small conductance Ca2+-sensitive K+ channels. It is likely that endothelial TRP channel dysfunction is related to the dysregulation of endothelial Ca2+ signaling and in turn gives rise to vascular-related diseases such as hypertension. Thus, investigations on the role of Ca2+ dynamics via TRP channels in endothelial cells are required to further comprehend how vascular tone or perfusion pressure are regulated in normal and pathophysiological conditions.

Aortic stiffness is associated with changes in retinal arteriole flow pulsatility mediated by local vasodilation in healthy young/middle-age adults

Aortic stiffness is associated with augmented pressure pulsatility in large conduit arteries and remodeling of the microcirculation. However, studies in humans examining the relation between aortic stiffness and end-organ microvascular flow pulsatility are limited. Therefore, we used the retinal microvasculature as an end-organ in vivo model to examine the hypothesis that aortic stiffness would be positively associated with microvascular flow pulsatility index (PI) (flow pulse amplitude/mean flow) in humans. In 40 young/middle-age healthy adults (25-60 yr old, 50% women), aortic stiffness (carotid-femoral pulse wave velocity, CFPWV) and retinal arteriole flow (laser speckle flowgraphy) were examined at rest and during metabolic vasodilation (light flicker). CFPWV and related increases in central pulse pressure (PP) were inversely correlated with arteriole lumen diameter independent of age (CFPWV: R = -0.52, P = 0.001; Central PP: R = -0.39, P = 0.014). Accordingly, microvascular resistance was positively related to CFPWV independent of age (R = 0.35, P = 0.031). Multiple linear regression showed that CFPWV was not a significant determinant of resting arteriole flow PI (β = -0.10, P = 0.64). However, during reduced retinal microvascular resistance using light flicker (P < 0.001), CFPWV was a significant determinant of the percent change in arteriole flow PI (β = 0.58, P = 0.046), but not mean flow (β = -0.17, P = 0.54), where reductions in arteriole flow PI were associated with lower CFPWV. In summary, our findings suggest that higher aortic stiffness and the related increase in central PP in healthy young/middle-age adults are associated with retinal arteriole narrowing and smaller reductions in arteriole flow pulsatility in response to dynamic conditions such as local metabolic vasodilation.NEW & NOTEWORTHY By using the human retinal microvasculature as an end-organ in vivo model, we confirm that aortic stiffness and related increases in central pulse pressure are inversely correlated with retinal arteriole lumen diameter and increased microvascular resistance among heathy young/middle-age adults. Additionally, higher aortic stiffness is not associated with excessive flow pulsatility in the retinal microvasculature under tonic conditions but may be related to limited reductions in retinal arteriole flow pulsatility in response to local vasodilation.

Platelet extracellular vesicles drive inflammasome-IL1β-dependent lung injury in Sickle Cell Disease

Abstract Intraerythrocytic polymerization of hemoglobin S promotes hemolysis and vaso-occlusive events in the microvasculature of sickle cell disease (SCD) patients. Although platelet-neutrophil aggregates-dependent vaso-occlusion is known to occur in the lung and contribute to lung injury, the etiological mechanisms that trigger acute chest syndrome are largely unknown. Here, we use intravital imaging of the lung in transgenic humanized SCD mice and in vitro imaging of SCD patient blood flowing through a microfluidic system to identify the innate-immune mechanism that promotes platelet-neutrophil aggregate-dependent lung vaso-occlusion and injury in SCD. Platelet-inflammasome activation led to generation of IL-1β and caspase-1 carrying platelet extracellular vesicles (EVs) that bind to neutrophils and promote platelet-neutrophil aggregation in lung arterioles of SCD mice in vivo and SCD human blood in microfluidics in vitro. The inflammasome activation, platelet EV generation and platelet-neutrophil aggregation were enhanced by the presence of lipopolysaccharide at a nanogram dose in SCD but not control human blood. Inhibition of the inflammasome effector caspase-1 or IL-1β pathway attenuated platelet EV generation, prevented platelet-neutrophil aggregation, and restored microvascular blood flow in lung arterioles of SCD mice in vivo and SCD human blood in microfluidics in vitro. These results are the first to identify that platelet-inflammasome dependent shedding of IL-1β and caspase-1 carrying platelet EVs promote lung vaso-occlusion in SCD. The current findings also highlight the therapeutic potential of targeting the platelet-inflammasome dependent innate immune pathway to prevent acute chest syndrome in SCD.

The relation between aortic stiffness and retinal microvascular flow pulsatility is attenuated by higher vascular resistance in healthy adults

Aortic stiffness is associated with increased risk of cerebrovascular disease and cognitive impairments with aging, although the mechanism that contribute to this link are not well‐defined. Increases in carotid artery flow pulsatility coincide with elevated aortic stiffness and may contribute to microvascular brain damage, but studies confirming augmented flow pulsatility in the downstream microvasculature have been limited. Given the ability to assess the retinal microvasculature non‐invasively in humans and evidence that disease‐ and age‐related alterations in the retinal microvasculature mirror changes in the cerebral microvasculature, we examined the hypothesis that age‐related increases in aortic stiffness would be correlated with higher retinal arteriole flow pulsatility (systolic flow – diastolic flow / mean flow). Among 33 healthy adults (age range: 25–60 years, 47% women), aortic stiffness was assessed by carotid‐femoral pulse wave velocity (CFPWV). Retinal arteriole flow pulsatility was quantified using laser speckle flowgraphy before and during a reduction in retinal vascular resistance via 30 s of diffuse luminance flicker. Multiple regression analysis including CFPWV, mean arterial pressure (MAP), and heart rate (HR) as independent variables demonstrated that lower MAP and HR, but not higher CFPWV, were significant determinants of greater flow pulsatility at baseline (CFPWV: β=0.10, P=0.548; MAP: β= −0.40, P=0.021; HR: β= −0.50, P=0.002; model R2=0.43, P=0.001). However, after reducing retinal vascular resistance (P&lt;0.001) via 30s of diffuse luminance flicker, multiple regression analysis demonstrated that higher CFPWV was a significant determinant of greater retinal arteriole flow pulsatility (β=0.35, P=0.026) in addition to lower MAP (β= −0.54, P=0.001) and HR (β= −0.43, P=0.005) (model R2=0.51, P&lt;0.001). In summary, no relation was observed between higher CFPWV and retinal arteriole flow pulsatility at rest, but a positive relation was observed during arteriole vasodilation. These findings suggest that greater vascular resistance may be an important compensatory mechanism to reduce transmission of flow pulsatility.Support or Funding InformationAHA 17POST33440101, T32 HL07121 NHLBI (P01HL014388), U54 TR001356 and AHA (13DG143400012).

Platelet Extracellular Vesicles Drive Inflammasome-IL-1β-Dependent Lung Injury in Sickle Cell Disease.

Rationale: Intraerythrocytic polymerization of Hb S promotes hemolysis and vasoocclusive events in the microvasculature of patients with sickle cell disease (SCD). Although platelet-neutrophil aggregate-dependent vasoocclusion is known to occur in the lung and contribute to acute chest syndrome, the etiological mechanisms that trigger acute chest syndrome are largely unknown.Objectives: To identify the innate immune mechanism that promotes platelet-neutrophil aggregate-dependent lung vasoocclusion and injury in SCD.Methods:In vivo imaging of the lung in transgenic humanized SCD mice and in vitro imaging of SCD patient blood flowing through a microfluidic system was performed. SCD mice were systemically challenged with nanogram quantities of LPS to trigger lung vasoocclusion.Measurements and Main Results: Platelet-inflammasome activation led to generation of IL-1β and caspase-1-carrying platelet extracellular vesicles (EVs) that bind to neutrophils and promote platelet-neutrophil aggregation in lung arterioles of SCD mice in vivo and SCD human blood in microfluidics in vitro. The inflammasome activation, platelet EV generation, and platelet-neutrophil aggregation were enhanced by the presence of LPS at a nanogram dose in SCD but not control human blood. Inhibition of the inflammasome effector caspase-1 or IL-1β pathway attenuated platelet EV generation, prevented platelet-neutrophil aggregation, and restored microvascular blood flow in lung arterioles of SCD mice in vivo and SCD human blood in microfluidics in vitro.Conclusions: These results are the first to identify that platelet-inflammasome-dependent shedding of IL-1β and caspase-1-carrying platelet EVs promote lung vasoocclusion in SCD. The current findings also highlight the therapeutic potential of targeting the platelet-inflammasome-dependent innate immune pathway to prevent acute chest syndrome.

Hyperinsulinemia does not cause de novo capillary recruitment in rat skeletal muscle.

ObjectiveThe effect of insulin on blood flow distribution within muscle microvasculature has been suggested to be important for glucose metabolism. However, the “capillary recruitment” hypothesis is still controversial and relies on studies using indirect contrast‐enhanced ultrasound (CEU) methods.MethodsWe studied how hyperinsulinemia effects capillary blood flow in rat extensor digitorum longus (EDL) muscle during euglycemic hyperinsulinemic clamp using intravital video microscopy (IVVM). Additionally, we modeled blood flow and microbubble distribution within the vascular tree under conditions observed during euglycemic hyperinsulinemic clamp experiments.ResultsEuglycemic hyperinsulinemia caused an increase in erythrocyte (80 ± 25%, P < .01) and plasma (53 ± 12%, P < .01) flow in rat EDL microvasculature. We found no evidence of de novo capillary recruitment within, or among, capillary networks supplied by different terminal arterioles; however, erythrocyte flow became slightly more homogenous. Our computational model predicts that a decrease in asymmetry at arteriolar bifurcations causes redistribution of microbubble flow among capillaries already perfused with erythrocytes and plasma, resulting in 25% more microbubbles flowing through capillaries.ConclusionsOur model suggests increase in CEU signal during hyperinsulinemia reflects a redistribution of arteriolar flow and not de novo capillary recruitment. IVVM experiments support this prediction showing increases in erythrocyte and plasma flow and not capillary recruitment.

Impaired Collateral Flow in Pial Arterioles of Aged Rats During Ischemic Stroke

Cerebral collateral circulation and age are critical factors in determining outcome from acute ischemic stroke. Aging may lead to rarefaction of cerebral collaterals, and thereby accelerate ischemic injury by reducing penumbral blood flow. Dynamic changes in pial collaterals after onset of cerebral ischemia may vary with age but have not been extensively studied. Here, laser speckle contrast imaging (LSCI) and two-photon laser scanning microscopy (TPLSM) were combined to monitor cerebral pial collaterals between the anterior cerebral artery (ACA) and the middle cerebral artery (MCA) in young adult and aged male Sprague Dawley rats during distal middle cerebral artery occlusion (dMCAo). Histological analysis showed that aged rats had significantly greater volumes of ischemic damage than young rats. LSCI showed that cerebral collateral perfusion declined over time after stroke in aged and young rats, and that this decline was significantly greater in aged rats. TPLSM demonstrated that pial arterioles narrowed faster after dMCAo in aged rats compared to young adult rats. Notably, while arteriole vessel narrowing was comparable 4.5 h after ischemic onset in aged and young adult rats, red blood cell velocity was stable in young adults but declined over time in aged rats. Overall, red blood cell flux through pial arterioles was significantly reduced at all time-points after 90 min post-dMCAo in aged rats relative to young adult rats. Thus, collateral failure is more severe in aged rats with significantly impaired pial collateral dynamics (reduced diameter, red blood cell velocity, and red blood cell flux) relative to young adult rats.

Abstract WP338: Penetrating Arteriole Flow Dynamics and Capillary Transient Time Heterogeneity Following Experimental Stroke in Two Mouse Strains With Distinct Pial Collateral Circulation

Introduction: In the pathophysiology of ischemic stroke, Leptomeningeal collateral circulation plays a key role on the severity of infarction. Balb/C mice have impaired leptomeningeal collateral due to variants of Rabep2 on chromosome 7 ( Candq1 ), causing sever stroke compared to C57BL/6 mice with rich collateral anastomosis. However, it still remains unclear whether and how poor collateral circulation specifically affects hemodynamic adaptation of microvessels during cerebral ischemia. Method: Male C57BL/6 and Balb/C mice were subjected to distal middle cerebral artery occlusion (dMCAO) combined with 90 minutes-occlusion of the ipsilateral common carotid artery. A 4x4 mm 2 cranial window was created on the parietal cortex 2 mm lateral and 1 mm posterior from the bregma 3 weeks prior to imaging. Spatial and temporal changes of the total flow and axial velocity of the penetrating arterioles (PA), as well as mean transit time (MTT) and capillary transit time heterogeneity (CTTH) in the capillaries bordering the distal MCA and ACA branches were determined by optical coherent tomography-based microangiography and capillary velocimetry at baseline, during dMCAO, 1 hour, 1 day and 7 days after reperfusion in each strain. Results: Stroke-induced increase in CTTH in the region of middle cerebral artery was significantly greater in Balb/C compared to C57BL/6 mice, leading to significantly increased microvascular resistance and reduced oxygen extraction during MCAO and 1 hour after reperfusion in the former (P&lt;0.05). The total blood flow in PA reduced immediately after dMCAO in both strains of mice but it remained reduced in Balb/C mice after reperfusion in contrast to a sustainable recovery at 50% of prestroke level 7 days after stroke. Conclusion: Poor collateral anastomosis and impaired flow of penetrating arterioles is an additional risk factor for hemodynamic compromise during cerebral ischemia caused by reduced oxygen extraction, which may increase the severity of stroke.

Paracentral Acute Middle Maculopathy following Vitrectomy for Proliferative Diabetic Retinopathy: Incidence, Risk Factors, and Clinical Characteristics

To report the incidence of, risk factors for, and characteristics of paracentral acute middle maculopathy (PAMM) after 25-gauge pars plana vitrectomy for proliferative diabetic retinopathy (PDR). Retrospective, consecutive, interventional case series. Five hundred thirty eyes of 427 patients who underwent primary vitrectomy for PDR from 2013 through2016. The patients underwent measurement of best-corrected visual acuity (BCVA), fundus photography, and OCT before and within 2 weeks after vitrectomy. A generalized linear mixed-effects model was used to evaluate risk factors for development of PAMM. The incidence, associated risk factors, and clinical characteristics of PAMM following vitrectomy, including the change in BCVA in eyes with PAMM and the distribution of PAMM as determined by en face OCT. Four hundred ninety-six eyes of 395 patients who met the eligibility criteria were evaluated. The incidence of PAMM was 3.8% (15/395) for patients and 3.6% (18/496) for eyes. Multivariate analysis showed the significant risk factors for PAMM development to be younger age (mean age, 49 years in patients and 59 years in control participants; odds ratio [OR] 0.94; 95% confidence interval [CI], 0.89-0.99; P= 0.021) and female gender (66.7% of patients and 31.3% of control participants; OR, 4.48; 95% CI, 1.57-12.6; P= 0.005). The PAMM was distributed on either side of the causative arterioles. In 14 of the 18 eyes (78%), PAMM was located within a 3-mm diameter of the fovea. In 10 eyes (56%), PAMM measured 1 disc diameter or more, and in 5 eyes (28%), PAMM measured one third disc diameter or less. No emboli were found in any eyes; however, multiple segmental arterial constrictions were confirmed during vitrectomy in 1 eye. The BCVA decreased more than 2 lines in 2 eyes (5%). Paracentral acute middle maculopathy can develop after pars plana vitrectomy for PDR, especially in patients who are younger and female. Impaired blood flow in arterioles, which leads to tissue hypoxia, was associated with development of PAMM.

Vascular Cognitive Impairment Linked to Brain Endothelium Inflammation in Early Stages of Heart Failure in Mice.

BackgroundAlthough advanced heart failure (HF) is a clinically documented risk factor for vascular cognitive impairment, the occurrence and pathomechanisms of vascular cognitive impairment in early stages of HF are equivocal. Here, we characterize vascular cognitive impairment in the early stages of HF development and assess whether cerebral hypoperfusion or prothrombotic conditions are involved.Methods and ResultsTgαq*44 mice with slowly developing isolated HF triggered by cardiomyocyte‐specific overexpression of G‐αq*44 protein were studied before the end‐stage HF, at the ages of 3, 6, and 10 months: before left ventricle dysfunction; at the stage of early left ventricle diastolic dysfunction (with preserved ejection fraction); and left ventricle diastolic/systolic dysfunction, respectively. In 6‐ to 10‐month‐old but not in 3‐month‐old Tgαq*44 mice, behavioral and cognitive impairment was identified with compromised blood‐brain barrier permeability, most significantly in brain cortex, that was associated with myelin sheet loss and changes in astrocytes and microglia. Brain endothelial cells displayed increased E‐selectin immunoreactivity, which was accompanied by increased amyloid‐β1‐42 accumulation in piriform cortex and increased cortical oxidative stress (8‐OHdG immunoreactivity). Resting cerebral blood flow measured by magnetic resonance imaging in vivo was preserved, but ex vivo NO‐dependent cortical arteriole flow regulation was impaired. Platelet hyperreactivity was present in 3‐ to 10‐month‐old Tgαq*44 mice, but it was not associated with increased platelet‐dependent thrombogenicity.ConclusionsWe report for the first time that vascular cognitive impairment is already present in the early stage of HF development, even before left ventricle systolic dysfunction. The underlying pathomechanism, independent of brain hypoperfusion, involves preceding platelet hyperreactivity and brain endothelium inflammatory activation.

Impaired cerebral microcirculation induced by ammonium chloride in rats is due to cortical adenosine release

Liver failure results in hyperammonaemia, impaired regulation of cerebral microcirculation, encephalopathy, and death. However, the key mediator that alters cerebral microcirculation remains unidentified. In this study we show that topically applied ammonium significantly increases periarteriolar adenosine tone on the brain surface of healthy rats and is associated with a disturbed microcirculation. Cranial windows were prepared in anaesthetized Wistar rats. The flow velocities were measured by speckle contrast imaging and compared before and after 30 min of exposure to 10 mM ammonium chloride applied on the brain surface. These flow velocities were compared with those for control groups exposed to artificial cerebrospinal fluid or ammonium plus an adenosine receptor antagonist. A flow preservation curve was obtained by analysis of flow responses to a haemorrhagic hypotensive challenge and during stepwise exsanguination. The periarteriolar adenosine concentration was measured with enzymatic biosensors inserted in the cortex. After ammonium exposure the arteriolar flow velocity increased by a median (interquartile range) of 21.7% (23.4%) vs. 7.2% (10.2%) in controls (n = 10 and n = 6, respectively, p <0.05), and the arteriolar surface area increased. There was a profound rise in the periarteriolar adenosine concentration. During the hypotensive challenge the flow decreased by 27.8% (14.9%) vs. 9.2% (14.9%) in controls (p <0.05). The lower limit of flow preservation remained unaffected, 27.7 (3.9) mmHg vs. 27.6 (6.4) mmHg, whereas the autoregulatory index increased, 0.29 (0.33) flow units per millimetre of mercury vs. 0.03 (0.21) flow units per millimetre of mercury (p <0.05). When ammonium exposure was combined with topical application of an adenosine receptor antagonist, the autoregulatory index was normalized. Vasodilation of the cerebral microcirculation during exposure to ammonium chloride is associated with an increase in the adenosine tone. Application of a specific adenosine receptor antagonist restores the regulation of the microcirculation. This indicates that adenosine could be a key mediator of the brain dysfunction seen during hyperammonaemia and is a potential therapeutic target. In patients with liver failure, disturbances in brain function are caused in part by ammonium toxicity. In our project we studied how ammonia, through adenosine release, affects the blood flow in the brain of rats. In our experimental model we demonstrated that the detrimental effect of ammonia on blood flow regulation was counteracted by blocking the adenosine receptors in the brain. With this observation we identified a novel potential treatment target. If we can confirm our findings in a future clinical study, this might help patients with liver failure and the severe condition called hepatic encephalopathy.

Abstract WP410: Reduced Recovery of Penetrating Arteriole Flow and Increased Capillary Transit Time Heterogeneity After Stroke in Type 2 Diabetic Mice

Introduction: Capillary transit time heterogeneity (CTTH) is altered during functional activation and in pathological conditions, affecting the extraction efficiency of oxygen from blood. Diabetes deteriorates ischemic brain damage, although the impact of diabetes in microvascular environment remains insufficiently characterized. Cerebral microvascular blood flow is considered to be regulated by pericytes, which are reportedly less in the retina of diabetic patients. However, it still remains unclear whether type 2 diabetes (T2DM) specifically affects hemodynamic adaptation of microvessels during cerebral ischemia. Hypothesis: MTT and CTTH are increased after ischemic stroke and exacerbated by T2DM, which is associated with a greater hemodynamic compromise. Methods: A 4x4 mm 2 cranial window was created on the parietal cortex 2 mm lateral and 1 mm posterior from the bregma three weeks prior to imaging. Experimental stroke was induced by permanent distal middle cerebral artery occlusion (dMCAO) combined with 90 minutes-occlusion of the ipsilateral common carotid artery. Spatial and temporal changes of the total flow and axial velocity of the penetrating arterioles (PA), as well as mean transit time (MTT) and CTTH in the capillaries bordering the distal MCA and ACA branches were determined by optical coherent tomography-based microangiography and capillary velocimetry at baseline, during dMCAO, 1hr and 24 hrs after reperfusion in db/+ and db/db mice, a mouse model of obesity and T2DM. Results: Stroke-induced increase in MTT and CTTH was greater in the db/db compared to db/+ mice, leading to increased microvascular resistance and reduced oxygen extraction after stroke in the former. The total blood flow in PA reduced immediately after dMCAO in both strains of mice by nearly 80%, but it remained reduced in the db/db mice after reperfusion in contrast to a sustainable recovery at 50% of prestroke level. Conclusions: T2DM is an additional risk factor for hemodynamic compromise during cerebral ischemia, which may increase the severity of stroke. The mechanisms underlying T2DM exacerbated CTTH and reduced recovery of PA flow are under investigation.

Assessment of Human Adipose Tissue Microvascular Function Using Videomicroscopy.

While obesity is closely linked to the development of metabolic and cardiovascular disease, little is known about mechanisms that govern these processes. It is hypothesized that pro-atherogenic mediators released from fat tissues particularly in association with central/visceral adiposity may promote pathogenic vascular changes locally and systemically, and the notion that cardiovascular disease may be the consequence of adipose tissue dysfunction continues to evolve. Here, we describe a unique method of videomicroscopy that involves analysis of vasodilator and vasoconstrictor responses of intact small human arterioles removed from the adipose depot of living human subjects. Videomicroscopy is used to examine functional properties of isolated microvessels in response to pharmacological or physiological stimuli using a pressured system that mimics in vivo conditions. The technique is a useful approach to gain understanding of the pathophysiology and molecular mechanisms that contribute to vascular dysfunction locally within the adipose tissue milieu. Moreover, abnormalities in the adipose tissue microvasculature have also been linked with systemic diseases. We applied this technique to examine depot-specific vascular responses in obese subjects. We assessed endothelium-dependent vasodilation to both increased flow and acetylcholine in adipose arterioles (50 - 350 µm internal diameter, 2 - 3 mm in length) isolated from two different adipose depots during bariatric surgery from the same individual. We demonstrated that arterioles from visceral fat exhibit impaired endothelium-dependent vasodilation compared to vessels isolated from the subcutaneous depot. The findings suggest that the visceral microenvironment is associated with vascular endothelial dysfunction which may be relevant to clinical observation linking increased visceral adiposity to systemic disease mechanisms. The videomicroscopy technique can be used to examine vascular phenotypes from different fat depots as well as compare findings across individuals with different degrees of obesity and metabolic dysfunction. The method can also be used to examine vascular responses longitudinally in response to clinical interventions.

Síndrome hepatopulmonar en la era del trasplante hepático

The most common pulmonary complication of liver disease is the disruption of gas exchange, resulting in severe hypoxemia, a factor that alters the clinical course of patients with liver cirrhosis. One of these alterations is the hepatopulmonary syndrome, which is associated with a significant increase in morbidity and mortality, and is defined as a triad that includes liver disease, abnormal arterial oxygenation caused by demonstrable intrapulmonary vascular dilations, with consequent pulmonary shunt, and imbalance in diffusion and perfusion. An abnormal increase in pulmonary vascular resistance may also be found as a consequence of pulmonary arteriolar flow obstruction, resulting in clinical pulmonary hypertension called “portopulmonary hypertension”. This resembles primary pulmonary hypertension, with dyspnoea and fatigue, but without clinical or histopathological responses to therapies such as prostacyclin. These two pulmonary vascular conditions (hepatopulmonary syndrome and portopulmonary hypertension) in cirrhotic patients, or with portal hypertension, may coexist in the same patient, and hepatopulmonary syndrome usually develops before portopulmonary hypertension.Hepatopulmonary syndrome is thought to be mainly caused by two central processes: vasodilation and pulmonary angiogenesis, which are responsible for alterations in gas exchange, imbalance in ventilation-perfusion, and limitation of oxygen diffusion.This syndrome has currently become of special interest in the success of liver transplantation. Although it is rare, it is important to rapidly recognise its clinical expression in order to understand the pathogenesis involved in the patient with clinical, functional, and histological liver cirrhosis, given its progressive course and poor prognosis.