Sublingual functional capillary rarefaction in chronic heart failure

Renal macro- and microcirculatory perturbations in acute kidney injury and chronic kidney disease associated with heart failure and cardiac surgery

Chronic kidney disease (CKD) affects 50% of patients with heart failure. The pathophysiology of CKD in heart failure is proposed to be driven by macrocirculatory hemodynamic changes, including reduced cardiac output and elevated central venous pressure. However, our understanding of renal microcirculation in heart failure and CKD remains limited. This is largely due to the lack of noninvasive techniques to assess renal microcirculation in patients. Moreover, there is a lack of clinically relevant animal models of heart failure and CKD to advance our understanding of the timing and magnitude of renal microcirculatory dysfunction. Patients with heart failure and CKD commonly require cardiac surgery with cardiopulmonary bypass (CPB) to improve their prognosis. However, acute kidney injury (AKI) is a frequent unresolved clinical complication in these patients. There is emerging evidence that renal microcirculatory dysfunction, characterized by renal medullary hypoperfusion and hypoxia, plays a critical role in the pathogenesis of cardiac surgery-associated AKI. In this review, we consolidate the preclinical and clinical evidence of renal macro- and microcirculatory perturbations in heart failure and cardiac surgery requiring CPB. We also examine emerging biomarkers and therapies that may improve health outcomes for this vulnerable patient population by targeting the renal microcirculation.

Effects of cardiac rehabilitation on in vivo nailfold microcirculation in patients with cardiovascular disease

This study aimed to explore the impact of cardiac rehabilitation (CR) on in vivo and ex vivo microcirculation, exercise capacity, and oxidative stress in patients with cardiovascular disease (CVD). The study included patients with acute coronary syndrome (ACS; n = 45; age, 69.0 ± 14.1 years) and heart failure (HF; n = 66; age, 77.3 ± 10.7 years) who underwent supervised CR during hospitalization. The control group comprised patients without CVD (NCVD; n = 20; age, 75.9 ± 11.2 years). In vivo microcirculatory observations using nailfold video capillary endoscopy at rest and during hyperemia, exercise capacity, and oxidative stress were assessed at baseline and 12 weeks after discharge. Baseline capillary densities were significantly lower in the ACS (5.0 ± 1.7 capillaries/mm2) and HF (4.9 ± 1.7 capillaries/mm2) groups than in the NCVD group (6.5 ± 1.1 capillaries/mm2, p < 0.01). Similarly, capillary density during reactive hyperemia was significantly lower in the ACS (5.8 ± 1.7 capillaries/mm2) and HF (5.4 ± 1.8 capillaries/mm2) groups than in the NCVD group (7.3 ± 1.4 capillaries/mm2, p < 0.01). Patients with ACS and HF had increased capillary densities at 12 weeks compared with at baseline (p < 0.05). This improvement was particularly pronounced among post-discharge outpatient CR participants (n = 20). Grip strength, exercise capacity, and oxidative stress improved at 12 weeks. Baseline capillary density changes were positively correlated with grip strength changes (r = 0.45, p < 0.001). CR significantly improved nailfold capillary density in patients with ACS and HF 12 weeks after discharge.

Endothelial Dysfunction and Cardiovascular Disease: Hyperbaric Oxygen Therapy as an Emerging Therapeutic Modality?

Maintaining the physiological function of the vascular endothelium and endothelial glycocalyx is crucial for the prevention of cardiovascular disease, which is one of the leading causes of morbidity and mortality worldwide. Damage to these structures can lead to atherosclerosis, hypertension, and other cardiovascular problems, especially in individuals with risk factors such as diabetes and obesity. Endothelial dysfunction is associated with ischemic disease and has a negative impact on overall cardiovascular health. The aim of this review was to comprehensively summarize the crucial role of the vascular endothelium and glycocalyx in cardiovascular health and associated thrombo-inflammatory conditions. It highlights how endothelial dysfunction, influenced by factors such as diabetes, chronic kidney disease, and obesity, leads to adverse cardiovascular outcomes, including heart failure. Recent evidence suggests that hyperbaric oxygen therapy (HBOT) may offer therapeutic benefits in the treatment of cardiovascular risk factors and disease. This review presents the current evidence on the mechanisms by which HBOT promotes angiogenesis, shows antimicrobial and immunomodulatory effects, enhances antioxidant defenses, and stimulates stem cell activity. The latest findings on important topics will be presented, including the effects of HBOT on endothelial dysfunction, cardiac function, atherosclerosis, plaque stability, and endothelial integrity. In addition, the role of HBOT in alleviating cardiovascular risk factors such as hypertension, aging, obesity, and glucose metabolism regulation is discussed, along with its impact on inflammation in cardiovascular disease and its potential benefit in ischemia-reperfusion injury. While HBOT demonstrates significant therapeutic potential, the review also addresses potential risks associated with excessive oxidative stress and oxygen toxicity. By combining information on the molecular mechanisms of HBOT and its effects on the maintenance of vascular homeostasis, this review provides valuable insights into the development of innovative therapeutic strategies aimed at protecting and restoring endothelial function to prevent and treat cardiovascular diseases.

From bench to bedside: A review of the application and potential of microcirculatory assessment by hand-held videomicroscopy

In clinical practice, there is vast knowledge regarding the evaluation of macrocirculatory parameters, such as systemic blood pressure and cardiac output, for the hemodynamic monitoring of patients. However, assessment of the microcirculation has not yet been incorporated into the bedside armamentarium. Hand-held intravital video microscopy enables the direct, noninvasive, evaluation of the sublingual microcirculation at the bedside, offering insights into the status of the systemic microcirculation. It is easily performed and may be employed in several clinical settings, providing immediate results that may help guide patient management. Therefore, the incorporation of hand-held intravital video microscopy into clinical practice may lead to tremendous improvements in the quality of care of critical, unstable patients or offer new data in the evaluation of patients with chronic diseases, especially those with microcirculatory involvement, such as occurs in diabetes.

Capillary rarefaction: a missing link in renal and cardiovascular disease?

Patients with chronic kidney disease (CKD) have an increased risk for cardiovascular morbidity and mortality. Capillary rarefaction may be both one of the causes as well as a consequence of CKD and cardiovascular disease. We reviewed the published literature on human biopsy studies and conclude that renal capillary rarefaction occurs independently of the cause of renal function decline. Moreover, glomerular hypertrophy may be an early sign of generalized endothelial dysfunction, while peritubular capillary loss occurs in advanced renal disease. Recent studies with non-invasive measurements show that capillary rarefaction is detected systemically (e.g., in the skin) in individuals with albuminuria, as sign of early CKD and/or generalized endothelial dysfunction. Decreased capillary density is found in omental fat, muscle and heart biopsies of patients with advanced CKD as well as in skin, fat, muscle, brain and heart biopsies of individuals with cardiovascular risk factors. No biopsy studies have yet been performed on capillary rarefaction in individuals with early CKD. At present it is unknown whether individuals with CKD and cardiovascular disease merely share the same risk factors for capillary rarefaction, or whether there is a causal relationship between rarefaction in renal and systemic capillaries. Further studies on renal and systemic capillary rarefaction, including their temporal relationship and underlying mechanisms are needed. This review stresses the importance of preserving and maintaining capillary integrity and homeostasis in the prevention and management of renal and cardiovascular disease.

Myocardial Oedema as a Consequence of Viral Infection and Persistence-A Narrative Review with Focus on COVID-19 and Post COVID Sequelae

Microvascular integrity is a critical factor in myocardial fluid homeostasis. The subtle equilibrium between capillary filtration and lymphatic fluid removal is disturbed during pathological processes leading to inflammation, but also in hypoxia or due to alterations in vascular perfusion and coagulability. The degradation of the glycocalyx as the main component of the endothelial filtration barrier as well as pericyte disintegration results in the accumulation of interstitial and intracellular water. Moreover, lymphatic dysfunction evokes an increase in metabolic waste products, cytokines and inflammatory cells in the interstitial space contributing to myocardial oedema formation. This leads to myocardial stiffness and impaired contractility, eventually resulting in cardiomyocyte apoptosis, myocardial remodelling and fibrosis. The following article reviews pathophysiological inflammatory processes leading to myocardial oedema including myocarditis, ischaemia-reperfusion injury and viral infections with a special focus on the pathomechanisms evoked by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In addition, clinical implications including potential long-term effects due to viral persistence (long COVID), as well as treatment options, are discussed.

Micro- and Macrovascular Effects of Inflammation in Peripheral Artery Disease-Pathophysiology and Translational Therapeutic Approaches

Inflammation has a critical role in the development and progression of atherosclerosis. On the molecular level, inflammatory pathways negatively impact endothelial barrier properties and thus, tissue homeostasis. Conformational changes and destruction of the glycocalyx further promote pro-inflammatory pathways also contributing to pro-coagulability and a prothrombotic state. In addition, changes in the extracellular matrix composition lead to (peri-)vascular remodelling and alterations of the vessel wall, e.g., aneurysm formation. Moreover, progressive fibrosis leads to reduced tissue perfusion due to loss of functional capillaries. The present review aims at discussing the molecular and clinical effects of inflammatory processes on the micro- and macrovasculature with a focus on peripheral artery disease.

Toll-like Receptors as Pro-Thrombotic Drivers in Viral Infections: A Narrative Review

Toll-like receptors (TLRs) have a critical role in the pathogenesis and disease course of viral infections. The induced pro-inflammatory responses result in the disturbance of the endovascular surface layer and impair vascular homeostasis. The injury of the vessel wall further promotes pro-thrombotic and pro-coagulatory processes, eventually leading to micro-vessel plugging and tissue necrosis. Moreover, TLRs have a direct role in the sensing of viruses and platelet activation. TLR-mediated upregulation of von Willebrand factor release and neutrophil, as well as macrophage extra-cellular trap formation, further contribute to (micro-) thrombotic processes during inflammation. The following review focuses on TLR signaling pathways of TLRs expressed in humans provoking pro-thrombotic responses, which determine patient outcome during viral infections, especially in those with cardiovascular diseases.

The role of endothelial cell in cardiac hypertrophy: Focusing on angiogenesis and intercellular crosstalk

Cardiac hypertrophy is characterized by cardiac structural remodeling, fibrosis, microvascular rarefaction, and chronic inflammation. The heart is structurally organized by different cell types, including cardiomyocytes, fibroblasts, endothelial cells, and immune cells. These cells highly interact with each other by a number of paracrine or autocrine factors. Cell-cell communication is indispensable for cardiac development, but also plays a vital role in regulating cardiac response to damage. Although cardiomyocytes and fibroblasts are deemed as key regulators of hypertrophic stimulation, other cells, including endothelial cells, also exert important effects on cardiac hypertrophy. More particularly, endothelial cells are the most abundant cells in the heart, which make up the basic structure of blood vessels and are widespread around other cells in the heart, implicating the great and inbuilt advantage of intercellular crosstalk. Cardiac microvascular plexuses are essential for transport of liquids, nutrients, molecules and cells within the heart. Meanwhile, endothelial cell-mediated paracrine signals have multiple positive or negative influences on cardiac hypertrophy. However, a comprehensive discussion of these influences and consequences is required. This review aims to summarize the basic function of endothelial cells in angiogenesis, with an emphasis on angiogenic molecules under hypertrophic conditions. The secondary objective of the research is to fully discuss the key molecules involved in the intercellular crosstalk and the endothelial cell-mediated protective or detrimental effects on other cardiac cells. This review provides a more comprehensive understanding of the overall role of endothelial cells in cardiac hypertrophy and guides the therapeutic approaches and drug development of cardiac hypertrophy.

Red blood cell sublethal damage: haemocompatibility is not the absence of haemolysis

Blood is a complex fluid owing to its two-phase suspension of formed cellular elements within a protein-rich plasma. Vital to its role in distributing nutrients throughout the circulatory system, the mechanical properties of blood - and particularly red blood cells (RBC)-primarily determine bulk flow characteristics and microcirculatory flux. Various factors impair the physical properties of RBC, including cellular senescence, many diseases, and exposure to mechanical forces. Indeed, the latter is increasingly relevant following the advent of modern life support, such as mechanical circulatory support (MCS), which induce unique interactions between blood and artificial environments that leave blood cells with the signature of aging, albeit accelerated, and crucially underlie various serious complications, including death. Accumulating evidence indicates that these complications appear to be associated with mechanical shear forces present within MCS that are not extreme enough to overtly rupture cells, yet may still induce "sublethal" injury and "fatigue" to vital blood constituents. Impaired RBC physical properties following elevated shear exposure-a hallmark of sublethal injury to blood-are notable and may explain, at least in part, systemic complications and premature mortality associated with MCS. Design of optimal next-generation MCS devices thus requires consideration of biocompatibility and blood-device interactions to minimize potential blood complications and promote clinical success. Presented herein is a contemporary understanding of "blood damage," with emphasis on shear exposures that alter microrheological function but do not overtly destroy cells (ie, sublethal damage). Identification of key cellular factors perturbed by supraphysiological shear exposure are examined, offering potential pathways to enhance design of MCS and blood-contacting medical devices.

Microvascular Thrombosis as a Critical Factor in Severe COVID-19

Platelet-endothelial interactions have a critical role in microcirculatory function, which maintains tissue homeostasis. The subtle equilibrium between platelets and the vessel wall is disturbed by the coronavirus disease 2019 (COVID-19), which affects all three components of Virchow's triad (endothelial injury, stasis and a hypercoagulable state). Endotheliitis, vasculitis, glycocalyx degradation, alterations in blood flow and viscosity, neutrophil extracellular trap formation and microparticle shedding are only few pathomechanisms contributing to endothelial damage and microthrombosis resulting in capillary plugging and tissue ischemia. In the following opinion paper, we discuss major pathological processes leading to microvascular endothelial activation and thrombosis formation as a possible major adverse factor driving the deterioration of patient disease course in severe COVID-19.

Cardiovascular Disease Management in the Context of Global Crisis

The outbreak of coronavirus disease 2019 (COVID-19) initiated a pandemic that has deteriorated health care access and thus disadvantaged vulnerable populations [...].

Microvascular perfusion, perfused boundary region and glycocalyx shedding in patients with autosomal dominant polycystic kidney disease: results from the GlycoScore III study

Background

Vascular abnormalities and endothelial dysfunction are part of the spectrum of autosomal dominant polycystic kidney disease (ADPKD). The mechanisms behind these manifestations, including potential effects on the endothelial surface layer (ESL) and glycocalyx integrity, remain unknown.

Methods

Forty-five ambulatory adult patients with ADPKD were enrolled in this prospective, observational, cross-sectional, single-centre study. Fifty-one healthy volunteers served as a control group. All participants underwent real-time microvascular perfusion measurements of the sublingual microcirculation using sidestream dark field imaging. After image acquisition, the perfused boundary region (PBR), an inverse parameter for red blood cell (RBC) penetration into the ESL, was automatically calculated. Microvascular perfusion was assessed by RBC filling and capillary density. Concentrations of circulating glycocalyx components were determined by enzyme-linked immunosorbent assay.

Results

ADPKD patients showed a significantly larger PBR compared with healthy controls (2.09 ± 0.23 µm versus 1.79 ± 0.25 µm; P < .001). This was accompanied by significantly lower RBC filling (70.4 ± 5.0% versus 77.9 ± 5.4%; P < .001) as well as a higher valid capillary density {318/mm² [interquartile range (IQR) 269-380] versus 273/mm² [230-327]; P = .007}. Significantly higher plasma concentrations of heparan sulphate (1625 ± 807 ng/ml versus 1329 ± 316 ng/ml; P = .034), hyaluronan (111 ng/ml [IQR 79-132] versus 92 ng/ml [82-98]; P = .042) and syndecan-1 were noted in ADPKD patients compared with healthy controls (35 ng/ml [IQR 27-57] versus 29 ng/ml [23-42]; P = .035).

Conclusions

Dimensions and integrity of the ESL are impaired in ADPKD patients. Increased capillary density may be a compensatory mechanism for vascular dysfunction to ensure sufficient tissue perfusion and oxygenation.

Usefulness of Serum Biomarkers of Endothelial Glycocalyx Damage in Prognosis of Decompensated Patients with Heart Failure with Reduced Ejection Fraction

The surface layer of endothelium contains the endothelial glycocalyx (eGC), consisting of proteoglycan polymers. Syndecan-1, heparan sulfate, and hyaluronic acid are major constituents of eGC, and their increasing detection in serum represents active degradation of eGC. Serum was obtained from patients with no heart failure (non-HF) and with HF with reduced ejection fraction (HFrEF) of <40%, either stable chronic HF (CHF) or acute decompensated HF (ADHF). Syndecan-1, heparan sulfate, and hyaluronic acid were measured for comparisons in the groups, adjusting for clinical and laboratory values. In our study cohort, 51 non-HF, 66 ADHF, and 72 patients with CHF were enrolled. Between ADHF and CHF, left ventricular (LV) mass index, LV ejection fraction, and pulmonary capillary wedge pressure did not differ. Patients with ADHF had significantly higher levels of eGC constituents compared with CHF and non-HF. During follow-up, 21 patients with HF died, and the mortality rate was higher in patients with higher serum syndecan-1 or heparan sulfate (log-rank p = 0.007 and 0.016, respectively). In multivariate analysis, a doubling of serum heparan sulfate concentration amounted to a 31.5% increase in all-cause mortality (hazard ratio = 1.315, confidence interval = 1.012-1.709, p = 0.040). In conclusion, serum biomarkers of eGC were elevated in ADHF (but not in CHF) in patients with HFrEF, suggesting the potential roles of eGC degradation and endothelial dysfunction in HF decompensation. Only elevated heparin sulfate was associated with higher all-cause mortality after adjusting for traditional risk variables in patients with HFrEF.

Impaired Endothelial Glycocalyx Predicts Adverse Outcome in Subjects Without Overt Cardiovascular Disease: a 6-Year Follow-up Study

We investigated whether disturbance of glycocalyx integrity is related with increased cardiovascular risk. In 600 healthy subjects, we measured perfused boundary region (PBR), a marker of glycocalyx integrity, in sublingual microvessels with diameter ranging 5-25 µm using a dedicated camera (Sideview Darkfield Imaging). Increased PBR indicates reduced glycocalyx thickness. We prospectively monitored the occurrence of cardiovascular events (MACE-death, myocardial infarction, and stroke) during a 6-year follow-up. Fifty-seven MACE were documented. Increased values of PBR5-25 predicted higher risk for MACE in a model including sex, age, hyperlipidemia, diabetes, hypertension, smoking, family history of coronary disease, treatment with ACEi/ARBs, or lipid-lowering agents (hazard ratio (HR), 6.44, p = 0.011; net reclassification improvement (NRI), 28%; C-statistic: 0.761). PBR5-25 was an independent and additive predictor of outcome when added in a model including the European Heart SCORE, diabetes, family history of CAD, and medication (HR, 4.71; NRI: 39.7%, C-statistic from 0.653 to 0.693; p < 0.01).Glycocalyx integrity is an independent and additive predictor to risk factors for MACE at 6-year follow-up in individuals without cardiovascular disease. ClinicalTrials.govIdentifier:NCT04646252. PBR5-25 was an independent and additive predictor of adverse cardiovascular events in a model including the European Heart SCORE, diabetes, family history of coronary disease, and medication (HR: 4.71, NRI: 39.7%, C-statistic from 0.653 to 0.693; p < 0.01, NRI:37.9%).

Evaluation of endothelial cell-specific molecule-1 as a biomarker of glycocalyx damage in canine myxomatous mitral valve disease

Background

Endothelial cell-specific molecule-1 (ESM-1) has emerged as a potential biomarker for cardiovascular disease in humans. Myxomatous mitral valve disease (MMVD) is the most common heart disease in dogs, and we hypothesized that MMVD causes chronic inflammation that increases susceptibility to endothelial glycocalyx (eGCX) damage. In this study, we measured the concentration of ESM-1 in a group of dogs with MMVD and evaluated factors affecting eGCX damage.

Results

Sixty-four dogs (control, n = 6; MMVD, n = 58) were enrolled in this study. There was no significant difference in serum ESM-1 concentrations among the MMVD stages. The serum ESM-1 concentration was significantly higher in the death group than in the alive group in MMVD dogs. (p = 0.006). In five dogs with MMVD, serum ESM-1 concentrations tended to decrease when the cardiac drug (pimobendan, furosemide, and digoxin) dose was increased.

Conclusions

In cases where MMVD progressed to decompensated heart failure with clinical symptoms and resulted in death, the concentration of serum ESM-1 increased significantly. Therefore, ESM-1 could be utilized as a new potential negative prognostic factor in patients with MMVD.

New Noninvasive Methods to Evaluate Microvascular Structure and Function

The structural and functional alterations of microvessels are detected because of physiological aging and in several cardiometabolic diseases, including hypertension, diabetes, and obesity. The small resistance arteries of these patients show an increase in the media or total wall thickness to internal lumen diameter ratio (MLR or WLR), often accompanied by endothelial dysfunction. For decades, micromyography has been considered as a gold standard method for evaluating microvascular structural alterations through the measurement of MLR or WLR of subcutaneous small vessels dissected from tissue biopsies. Micromyography is the most common and reliable method for assessing microcirculatory endothelial function ex vivo, while strain-gauge venous plethysmography is considered the reference technique for in vivo studies. Recently, several noninvasive methods have been proposed to extend the microvasculature evaluation to a broader range of patients and clinical settings. Scanning laser Doppler flowmetry and adaptive optics are increasingly used to estimate the WLR of retinal arterioles. Microvascular endothelial function may be evaluated in the retina by flicker light stimulus, in the finger by tonometric approaches, or in the cutaneous or sublingual tissues by laser Doppler flowmetry or intravital microscopy. The main limitation of these techniques is the lack of robust evidence on their prognostic value, which currently reduces their widespread use in daily clinical practice. Ongoing and future studies will overcome this issue, hopefully moving the noninvasive assessment of the microvascular function and structure from bench to bedside.

Microvascular rarefaction in patients with cerebrovascular events

Capillary density rarefaction and endothelial dysfunction contribute to chronic hypoperfusion and cerebral small vessel disease. Previous animal experiments revealed spatiotemporal microvascular remodeling directing post-stroke brain reorganization. We hypothesized that microcirculatory changes during acute cerebrovascular events could be reflected systemically and visualized sublingually. In a prospective observational trial in vivo sublingual sidestream darkfield videomicroscopy was performed in twenty-one patients with either acute stroke (n = 13 ischemic, n = 1 ischemic with hemorrhagic transformation and n = 2 hemorrhagic stroke) or transitory ischemic attacks (n = 5) within 24 h after hospital admission and compared to an age- and sex-matched control group. Repetitive measurements were performed on the third day and after one week. Functional and perfused total capillary density was rarefied in the overall patient group (3060 vs 3717 μm/mm², p = 0.001 and 5263 vs 6550 μm/mm², p = 0.002, respectively) and in patients with ischemic strokes (2897 vs. 3717 μm/mm², p < 0.001 and 5263 vs. 6550 μm/mm², p = 0.006, respectively) when compared to healthy controls. The perfused boundary region (PBR), which was measured as an inverse indicator of glycocalyx thickness, was markedly related to red blood cell (RBC) filling percentage (regarded as an estimate of microvessel perfusion) in the overall patient group (r = -0.843, p < 0.001), in patients with ischemic strokes (r = -0.82, p = 0.001) as well as in healthy volunteers (r = -0.845, p < 0.001). In addition, there were significant associations between platelet count or platelet aggregation values (as measured by whole blood impedance aggregometry) and microvascular parameters in the overall patient collective, as well as in patients with ischemic strokes. In conclusion, cerebrovascular events are associated with altered systemic microvascular perfusion.

Markers of the Endothelial Glycocalyx Are Improved following Kidney Transplantation

INTRODUCTION

The endothelial glycocalyx on the vascular luminal surface contributes to endothelial health and function. Damage to this layer is indicative of vascular injury, reflected by increased levels of its shed constituents in serum and an increase in the perfused boundary region (PBR) when measured in sublingual capillaries using the GlycoCheck™ device. We aimed to examine the longitudinal effects of kidney transplantation on the glycocalyx by measuring biochemical markers of the glycocalyx and endothelial dysfunction and the PBR.

METHODS

We recruited healthy controls and stage 5 CKD patients scheduled to undergo a kidney transplant. Investigations were performed before transplant and then 1 and 3 months after transplantation. At each point, blood was collected for hyaluronan, syndecan-1, vascular cell adhesion molecule (VCAM-1), and von Willebrand factor (vWF), and a PBR measurement was performed.

RESULTS

Thirty healthy controls and 17 patients undergoing a kidney transplant were recruited (9 cadaveric and 8 live donation; 12 on dialysis and 5 pre-emptive). Before transplant, transplant recipients had greater evidence of glycocalyx damage than controls. After transplant, PBR improved from median 2.22 (range 1.29-2.73) to 1.98 (1.65-2.25) µm, p = 0.024, and syndecan-1 levels decreased from 98 (40-529) to 36 (20-328) ng/mL, p < 0.001. Similarly, VCAM-1 fell from 1,479 (751-2,428) at baseline to 823 (516-1,674) ng/mL, p < 0.001, and vWF reduced from 3,114 (1,549-5,197) to 2,007 (1,503-3,542) mIU/mL, p = 0.002. Serum levels of hyaluronan remained unchanged.

CONCLUSION

The combination of reduced PBR and syndecan-1 following transplant suggests that transplantation may improve glycocalyx stability at 3 months after transplant.

Impaired skeletal muscle fatigue resistance during cardiac hypertrophy is prevented by functional overload- or exercise-induced functional capillarity

KEY POINTS

Capillary rarefaction is hypothesized to contribute to impaired exercise tolerance in cardiovascular disease, but it remains a poorly exploited therapeutic target for improving skeletal muscle performance. Using an abdominal aortic coarctation rat model of compensatory cardiac hypertrophy, we determine the efficacy of aerobic exercise for the prevention of, and mechanical overload for, restoration of hindlimb muscle fatigue resistance and microvascular impairment in the early stages of heart disease. Impaired muscle fatigue resistance was found after development of cardiac hypertrophy, but this impairment was prevented by low-intensity aerobic exercise and recovered after mechanical stretch due to muscle overload. Changes in muscle fatigue resistance were closely related to functional (i.e. perfused) microvascular density, independent of arterial blood flow, emphasizing the critical importance of optimal capillary diffusion for skeletal muscle function. Pro-angiogenic therapies are an important tool for improving skeletal muscle function in the incipient stages of heart disease.

ABSTRACT

Microvascular rarefaction may contribute to declining skeletal muscle performance in cardiac and vascular diseases. It remains uncertain to what extent microvascular rarefaction occurs in the earliest stages of these conditions, if impaired blood flow is an aggravating factor and whether angiogenesis restores muscle performance. To investigate this, the effects of aerobic exercise (voluntary wheel running) and functional muscle overload on the performance, femoral blood flow (FBF) and microvascular perfusion of the extensor digitorum longus (EDL) were determined in a chronic rat model of compensatory cardiac hypertrophy (CCH, induced by surgically imposed abdominal aortic coarctation). CCH was associated with hypertension (P = 0.001 vs. Control) and increased relative heart mass (P < 0.001). Immediately upon placing the aortic band (i.e. before development of CCH), post-fatigue test FBF was reduced (P < 0.003), coinciding with attenuated fatigue resistance (P = 0.039) indicating an acute arterial perfusion constraint on muscle performance. While FBF was normalized during CCH in chronic groups (P > 0.05) fatigue resistance remained reduced (P = 0.039) and was associated with reduced (P = 0.009) functional capillarity after development of CCH without intervention, indicating a microvascular limitation to muscle performance. Normalization of functional capillarity after aerobic exercise (P = 0.065) and overload (P = 0.329) in CCH coincided with restoration to control levels of muscle fatigue resistance (P > 0.999), although overload-induced EDL hypertrophy (P = 0.027) and wheel-running velocity and duration (both P < 0.05) were attenuated after aortic banding. These data show that reductions in skeletal muscle performance during CCH can be countered by improving functional capillarity, providing a therapeutic target to improve skeletal muscle function in chronic diseases.

Human glycocalyx shedding: Systematic review and critical appraisal

BACKGROUND

The number of studies measuring breakdown products of the glycocalyx in plasma has increased rapidly during the past decade. The purpose of the present systematic review was to assess the current knowledge concerning the association between plasma concentrations of glycocalyx components and structural assessment of the endothelium.

METHODS

We performed a literature review of Pubmed to determine which glycocalyx components change in a wide variety of human diseases and conditions. We also searched for evidence of a relationship between plasma concentrations and the thickness of the endothelial glycocalyx layer as obtained by imaging methods.

RESULTS

Out of 3,454 publications, we identified 228 that met our inclusion criteria. The vast majority demonstrate an increase in plasma glycocalyx products. Sepsis and trauma are most frequently studied, and comprise approximately 40 publications. They usually report 3-4-foldt increased levels of glycocalyx degradation products, most commonly of syndecan-1. Surgery shows a variable picture. Cardiac surgery and transplantations are most likely to involve elevations of glycocalyx degradation products. Structural assessment using imaging methods show thinning of the endothelial glycocalyx layer in cardiovascular conditions and during major surgery, but thinning does not always correlate with the plasma concentrations of glycocalyx products. The few structural assessments performed do not currently support that capillary permeability is increased when the plasma levels of glycocalyx fragments in plasma are increased.

CONCLUSIONS

Shedding of glycocalyx components is a ubiquitous process that occurs during both acute and chronic inflammation with no sensitivity or specificity for a specific disease or condition.

Heparin prevents in vitro glycocalyx shedding induced by plasma from COVID-19 patients

The severe forms and worsened outcomes of COVID-19 (coronavirus disease 19) are closely associated with hypertension and cardiovascular disease. Endothelial cells express Angiotensin-Converting Enzyme 2 (ACE2), which is the entrance door for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The hallmarks of severe illness caused by SARS-CoV-2 infection are increased levels of IL-6, C-reactive protein, D-dimer, ferritin, neutrophilia and lymphopenia, pulmonary intravascular coagulopathy and microthrombi of alveolar capillaries. The endothelial glycocalyx, a proteoglycan- and glycoprotein-rich layer covering the luminal side of endothelial cells, contributes to vascular homeostasis. It regulates vascular tonus and permeability, prevents thrombosis, and modulates leukocyte adhesion and inflammatory response. We hypothesized that cytokine production and reactive oxygen species (ROS) generation associated with COVID-19 leads to glycocalyx degradation. A cohort of 20 hospitalized patients with a confirmed COVID-19 diagnosis and healthy subjects were enrolled in this study. Mechanisms associated with glycocalyx degradation in COVID-19 were investigated. Increased plasma concentrations of IL-6 and IL1-β, as well as increased lipid peroxidation and glycocalyx components were detected in plasma from COVID-19 patients compared to plasma from healthy subjects. Plasma from COVID-19 patients induced glycocalyx shedding in cultured human umbilical vein endothelial cells (HUVECs) and disrupted redox balance. Treatment of HUVECs with low molecular weight heparin inhibited the glycocalyx perturbation. In conclusion, plasma from COVID-19 patients promotes glycocalyx shedding and redox imbalance in endothelial cells, and heparin treatment potentially inhibits glycocalyx disruption.

Effects of a single aerobic exercise on perfused boundary region and microvascular perfusion: a field study

The endothelium and the glycocalyx play a pivotal role in regulating microvascular function and perfusion in health and critical illness. It is unknown today, whether aerobic exercise immediately affects dimensions of the endothelial surface layer (ESL) in relation to microvascular perfusion as a physiologic adaption to increased nutritional demands. This monocentric observational study was designed to determine real-time ESL and perfusion measurements of the sublingual microcirculation using sidestream dark field imaging performed in 14 healthy subjects before and after completing a 10 km trial running distance. A novel image acquisition and analysis software automatically analysed the perfused boundary region (PBR), an inverse parameter for red blood cell (RBC) penetration of the ESL, in vessels between 5 and 25 µm diameter. Microvascular perfusion was assessed by calculating RBC filling percentage. There was no significant immediate effect of exercise on PBR and RBC filling percentage. Linear regression analysis revealed a distinct association between change of PBR and change of RBC filling percentage (regression coefficient β: − 0.026; 95% confidence interval − 0.043 to − 0.009; p = 0.006). A single aerobic exercise did not induce a change of PBR or RBC filling percentage. The endothelium of the microvasculature facilitates efficient perfusion in vessels reacting with an increased endothelial surface layer.

Vascular Endothelial Glycocalyx Damage in COVID-19

The new coronavirus disease-2019 (COVID-19), which is spreading around the world and threatening people, is easily infecting a large number of people through airborne droplets; moreover, patients with hypertension, diabetes, obesity, and cardiovascular disease are more likely to experience severe conditions. Vascular endothelial dysfunction has been suggested as a common feature of high-risk patients prone to severe COVID-19, and measurement of vascular endothelial function may be recommended for predicting severe conditions in high-risk patients with COVID-19. However, fragmented vascular endothelial glycocalyx (VEGLX) is elevated in COVID-19 patients, suggesting that it may be useful as a prognostic indicator. Although the relationship between VEGLX and severe acute respiratory syndrome coronavirus 2 infections has not been well studied, some investigations into COVID-19 have clarified the relationship between VEGLX and the mechanism that leads to severe conditions. Clarifying the usefulness of VEGLX assessment as a predictive indicator of the development of severe complications is important as a strategy for confronting pandemics caused by new viruses with a high affinity for the vascular endothelium that may recur in the future.

High-intensity exercise impairs extradiaphragmatic respiratory muscle perfusion in patients with COPD

The study investigated whether high-intensity exercise impairs inspiratory and expiratory muscle perfusion in patients with chronic obstructive pulmonary disease (COPD). We compared respiratory local muscle perfusion between constant-load cycling[sustained at 80% peak work rate (WRpeak)] and voluntary normocapnic hyperpnea reproducing similar work of breathing (WoB) in 18 patients [forced expiratory volume in the first second (FEV₁): 58 ± 24% predicted]. Local muscle blood flow index (BFI), using indocyanine green dye, and fractional oxygen saturation (%StiO₂) were simultaneously assessed by near-infrared spectroscopy (NIRS) over the intercostal, scalene, rectus abdominis, and vastus lateralis muscles. Cardiac output (impedance cardiography), WoB (esophageal/gastric balloon catheter), and diaphragmatic and extradiaphragmatic respiratory muscle electromyographic activity (EMG) were also assessed throughout cycling and hyperpnea. Minute ventilation, breathing pattern, WoB, and respiratory muscle EMG were comparable between cycling and hyperpnea. During cycling, cardiac output and vastus lateralis BFI were significantly greater compared with hyperpnea [by +4.2 (2.6-5.9) L/min and +4.9 (2.2-7.8) nmol/s, respectively] (P < 0.01). Muscle BFI and %StiO₂ were, respectively, lower during cycling compared with hyperpnea in scalene [by -3.8 (-6.4 to -1.2) nmol/s and -6.6 (-8.2 to -5.1)%], intercostal [by -1.4 (-2.4 to -0.4) nmol/s and -6.0 (-8.6 to -3.3)%], and abdominal muscles [by -1.9 (-2.9 to -0.8) nmol/s and -6.3 (-9.1 to -3.4)%] (P < 0.001). The difference in respiratory (scalene and intercostal) muscle BFI between cycling and hyperpnea was associated with greater dyspnea (Borg CR10) scores (r = -0.54 and r = -0.49, respectively, P < 0.05). These results suggest that in patients with COPD, 1) locomotor muscle work during high-intensity exercise impairs extradiaphragmatic respiratory muscle perfusion and 2) insufficient adjustment in extradiaphragmatic respiratory muscle perfusion during high-intensity exercise may partly explain the increased sensations of dyspnea.NEW & NOTEWORTHY We simultaneously assessed the blood flow index (BFI) in three respiratory muscles during hyperpnea and high-intensity constant-load cycling sustained at comparable levels of work of breathing and respiratory neural drive in patients with COPD. We demonstrated that high-intensity exercise impairs respiratory muscle perfusion, as intercostal, scalene, and abdominal BFI increased during hyperpnea but not during cycling. Insufficient adjustment in respiratory muscle perfusion during exercise was associated with greater dyspnea sensations in patients with COPD.

Sublingual microcirculation detects impaired perfusion in dehydrated older patients

BACKGROUND: Dehydration occurs frequently in older patients and constitutes a significant clinical problem. OBJECTIVE: This proof-of-concept study examines whether 1) sublingual measurement in dehydrated old patients is feasible, 2) frailty and incompliance in old, awake patients affects video-quality, 3) dehydration impacts microcirculation METHODS: This prospective observational study included clinically dehydrated patients aged ≥65 years immediately after admission. Dehydration was assessed clinically. A sidestream dark field camera (SDF) was used for measurement. Video-quality was evaluated with MIQS (microcirculation image quality score). Both AVA 4.3C- and AVA POEM-software analyzed the videos. Seventeen patients ≥65 years not showing dehydration served as control. RESULTS: Thirteen patients (8 female) were included. The average age was 83±8 years. The mini-mental test was 17±15 points, the Clinical Frailty Scale 4±3, the Barthel-Index 59±39. None of these parameters correlated with MIQS (3.4±4.2 SD (“acceptable”)). Dehydrated patients had a slightly impaired microcirculation, with a significantly lower percentage of perfused small vessels compared to control (83.1±7.7% versus 88.0±6.0%, P < 0.05). After rehydration, there was acute improvement in the microcirculation. CONCLUSIONS: Sublingual microcirculatory SDF-measurement is both, safe and valid for dehydrated old patients - regardless of frailty, age or cognitive performance. Dehydration leads to an impaired microcirculation.

Endothelial glycocalyx damage as a systemic inflammatory microvascular endotheliopathy in COVID-19

In atherosclerosis patients, vascular endothelial dysfunction is commonly observed alongside damage of the vascular endothelial glycocalyx, an extracellular matrix bound to and encapsulating the endothelial cells lining the blood vessel wall. Although atherosclerotic risk factors have been reported in severe patients with coronavirus disease 2019 (COVID-19), the exact mechanisms are unclear. The mortality associated with the COVID-19 outbreak is increased by comorbidities, including hypertension, diabetes, obesity, chronic obstructive pulmonary disease (COPD), and cardiovascular disease. Besides, older individuals and smokers have significantly worse outcomes. Interestingly, these comorbidities and risk factors are consistent with the pathophysiology that causes vascular endothelial glycocalyx damage. Moreover, vascular glycocalyx dysfunction causes microvascular leakage, which results in interstitial pulmonary abnormal shadows (multiple patchy shadows with a ground glass inter-pneumonic appearance). This is frequently followed by severe acute respiratory distress syndrome (ARDS), closely related to coagulo-fibrinolytic changes contributing to disseminated intravascular coagulation (DIC) and Kawasaki disease shock syndrome, as well as inducing activation of the coagulation cascade, leading to thromboembolism and multiple organ failure. Notably, SARS-CoV-2, the causative virus of COVID-19, binds to ACE2, which is abundantly present not only in human epithelia of the lung and the small intestine, but also in vascular endothelial cells and arterial smooth muscle cells. Moreover, COVID-19 can induce severe septic shock, and sepsis can easily lead to systemic degradation of the vascular endothelial glycocalyx. In the current review, we propose new concepts and therapeutic goals for COVID-19-related vascular endothelial glycocalyx damage, based on previous vascular endothelial medicine research.

Sublingual microcirculation in prehospital critical care medicine: A proof-of-concept study

OBJECTIVE

Diagnostic and risk stratification are limited in emergencies. The measurement of microcirculation might identify patients with poor perfusion but compensated macrocirculation such as in beginning shock. This proof-of-concept study examines whether sublingual prehospital sidestream dark-field microscopy is feasible.

METHODS

This prospective observational study included patients receiving medical aid by an emergency ambulance who had a spontaneous circulation and offered access to the sublingual mucosa. Sublingual measurement of microcirculation was performed using a sidestream dark field camera. Video quality was evaluated with microcirculation image quality score (microcirculation image quality score). AVA 4.3C software calculated microcirculatory parameters.

RESULTS

Thirty patients (47% male) were included. The average age was 63 years (±20 years SD), the severity of the disease (quantified by National Advisory Committee on Aeronautics) was 3.4 (±0.7 SD). Macrocirculation presented within the normal range. The most frequent cause preventing the measurement was a time-critical disease (64%). In 17 patients (57%), the videos could be analyzed immediately. The average quality of the video was 2.2 ± 0.45 points ('acceptable'). There were minor restrictions of microcirculation. Microcirculation correlated with National Advisory Committee on Aeronautics, but not with the macrocirculation. No complications occurred.

CONCLUSION

The prehospital sublingual measurement is safe and valid. Despite normal macrocirculation, microcirculation was impaired and correlated with National Advisory Committee on Aeronautics.

Impaired skeletal muscle performance as a consequence of random functional capillary rarefaction can be restored with overload-dependent angiogenesis

KEY POINTS

Loss of skeletal muscle capillaries is thought to contribute to a reduction in exercise tolerance, but the relative contribution of a compromised microcirculation with disease, in isolation of co-morbidities, to impaired muscle function is unknown. We therefore developed a novel method to randomly occlude capillaries in the rat hindlimb to mimic the capillary rarefaction observed in many conditions. We demonstrate that muscle fatigue resistance is closely coupled with functional microvascular density, independent of arterial blood flow, while disturbance of the microcirculation leads to long-term impairment of muscle function if left untreated. Mechanical stretch due to muscle overload causes a restoration of fatigue resistance via angiogenic remodelling. These observations highlight the importance of a healthy microcirculation and suggest that restoring impaired microvascular supply, regardless of disease co-morbidities, will assist recovery of exercise tolerance in a variety of conditions that limit quality of life.

ABSTRACT

To what extent microvascular rarefaction contributes to impaired skeletal muscle function remains unknown. Our understanding of whether pathological changes in the microcirculation can be reversed remains limited by a lack of basic physiological data in otherwise healthy tissue. The principal objectives here were to: (1) quantify the effect of random microvascular rarefaction on limb perfusion and muscle performance, and (2) determine if these changes could be reversed. We developed a novel protocol in rats whereby microspheres injected into the femoral artery allowed a unilateral reduction in functional capillary density in the extensor digitorum longus (EDL), and assessed acute and chronic effects on muscle function. Simultaneous bilateral EDL force and hindlimb blood flow measurements were made during electrical stimulation. Following functional capillary rarefaction there was an acute microsphere dose-dependent reduction in muscle fatigue resistance (P < 0.001), despite preserved femoral artery perfusion. Histological analysis of EDL samples taken from injected animals confirmed a positive correlation between the proportion of functional capillaries and fatigue resistance (P = 0.002). Such impaired performance persisted for at least 2 weeks (P = 0.016). Concomitant mechanical overload improved both perfused capillary density and fatigue resistance (P<0.05), confirming that the capacity for muscle remodelling was retained following chronic distributed ischaemia, and that the impact of capillary rarefaction could be alleviated. These results demonstrate that loss of functional capillaries is detrimental to muscle function, even in otherwise healthy tissue, independent of arterial perfusion. Restoration of muscle performance following a mechanical overload stimulus indicates that angiogenic treatments to alleviate microvascular rarefaction may be key to restoring exercise tolerance.

Functional capillary impairment in patients with ventricular assist devices

The implantation of continuous – flow ventricular assist devices (VAD) is suggested to evoke angiodysplasia contributing to adverse events such as gastrointestinal bleeding. We evaluated in vivo capillary density and glycocalyx dimensions to investigate possible systemic microvascular changes in patients with chronic heart failure and VAD support vs. standard medical treatment. Forty-two patients with VAD support were compared to forty-one patients with ischemic and non-ischemic chronic heart failure (CHF) on standard pharmacotherapy and to a group of forty-two healthy subjects in a prospective cross-sectional study. Sublingual microcirculation was visualized using Sidestream Darkfield videomicroscopy and functional and perfused total capillary densities were quantified. Patients with VAD implantation were followed for one year and bleeding events were recorded. Median time after VAD implantation was 18 months. Patients were treated with centrifugal-flow devices (n = 31) or axial-flow devices (n = 11). Median functional capillary density was significantly lower in patients with VAD therapy as compared to CHF patients (196 vs. 255/mm², p = 0.042, adjusted p-value). Functional and total capillary densities were 44% and 53% lower (both p < 0.001) in patients with VAD therapy when compared to healthy subjects. Cox regression analysis revealed loss of capillary density as a significant predictor of bleeding events during one -year follow-up of VAD patients (HR: 0.987, CI (95%): 0.977–0.998, p = 0.021 for functional and 0.992, CI (95%): 0.985–0.999, p = 0.03 for total capillary density). In conclusion, patients with VAD support exhibit capillary density rarefaction, which was associated with bleeding events. If confirmed independently, capillary impairment may be evaluated as novel marker of bleeding risk.

High intensity training improves cardiac function in healthy rats

Exercise training is a low cost and safe approach for reducing the risk of cardiovascular disease development. Currently, moderate-intensity training (MIT) is the most preferred exercise type. However, high-intensity interval training (HIIT) is gaining interest especially among athletes and healthy individuals. In this study, we examined cardiac remodeling resulting from MIT and HIIT in healthy rats. Healthy male Sprague-Dawley rats were randomly assigned to MIT or HIIT for 13 weeks. Animals kept sedentary (SED) were used as control. Cardiac function was evaluated with echocardiography and hemodynamic measurements. Heart tissue was stained for capillary density and fibrosis. After 13 weeks of training, only HIIT induced beneficial cardiac hypertrophy. Overall global cardiac parameters (such as ejection fraction, cardiac output and volumes) were improved similarly between both training modalities. At tissue level, collagen content was significantly and similarly reduced in both exercise groups. Finally, only HIIT increased significantly capillary density. Our data indicate that even if very different in design, HIIT and MIT appear to be equally effective in improving cardiac function in healthy rats. Furthermore, HIIT provides additional benefits through improved capillary density and should therefore be considered as a preferred training modality for athletes and for patients.

Increase in perfused boundary region of endothelial glycocalyx is associated with higher prevalence of ischemic heart disease and lesions of microcirculation and vascular wall

OBJECTIVE

PBR characterizes penetration of red blood cells inside glycocalyx and its thickness can have profound impact on microcirculation and other vascular parameters. The goal of our study was to reliably quantify PBR and assess its potential use as a new marker of cardiovascular pathology.

METHODS

The study included 208 patients (123 men and 85 women from 40 to 65 years of age) with various grades of cardiovascular SCORE risk index and IHD. PBR was quantified by sidestream dark field capillaroscopy with green light excitation. Cutaneous microcirculation was evaluated with laser Doppler fluorometry.

RESULTS

Elevated PBR values over 2 mm were associated with morphological and functional lesions of arterial wall and microcirculation and lowered levels of ApoA1 lipoprotein. Moreover, elevated PBR values were associated with 2.07-fold increase in prevalence of cerebral atherosclerosis (P = .015) and 2.42-fold increase in prevalence of IHD (P = .024). Increase in PBR was associated with elevated systolic blood pressure.

CONCLUSIONS

Thus, PBR can be considered a new highly reproducible and promising marker candidate for non-invasive diagnostics of IHD and cerebral atherosclerosis suggesting important role of microcirculation in development and progression of cardiovascular diseases.