Microcirculation最新文献

Objective

Microvascular blood flow simulations enhance understanding of microcirculatory phenomena at the micrometer scale by capturing heterogeneity in blood flow. However, imaged areas often only partially represent tissue regions, leading to numerous vessels crossing boundaries and strongly influencing simulated blood flows through imposed boundary conditions.

Methods

Two key methodological aspects of blood flow simulations are addressed: selecting appropriate boundary conditions and quantifying the inevitable impact of boundary condition uncertainties on model simulations. An adaptive method for pressure boundary conditions is proposed and rigorously evaluated in extensive brain cortical microvascular networks. The adaptive method is integrated into a Bayesian calibration framework, inferring distributions over thousands of unknown pressure boundary conditions and providing uncertainty estimates for model simulations.

Results

The adaptive method produces simulations consistent with reference data, yielding depth-dependent pressure drop profiles and layer-wise capillary blood flow profiles consistent with previous analysis. These hemodynamic phenomena generalize to biphasic blood flow simulation models incorporating in vivo viscosity formulations. Uncertainty quantification reveals a novel spatially heterogeneous and depth-dependent pattern in blood flow uncertainty.

Conclusions

The adaptive method for pressure boundary conditions will be useful in future applications of both forward and inverse blood flow simulations. Uncertainty quantification complements hemodynamic predictions with associated uncertainties.

Objectives

In healthy people, adipose tissue blood flow (ATBF) rises postprandially; however, in one third of them, this response is altered. These people are characterized by prolonged postprandial lipemia and higher cardiometabolic risk. Vasoactive intestinal peptide (VIP) is a gut neurotransmitter with a vasodilatory effect. The aim of the study was to assess the role of VIP in ATBF regulation and its postprandial blunting.

Methods

Plasma VIP and ATBF (¹³³Xenon washout technique) were measured during a 75 g oral glucose load in 16 healthy participants. ATBF was monitored in 12 individuals during in situ microinfusion of incremental doses of VIP (10⁻⁷, 10⁻⁶, 10⁻⁵ mol L⁻¹).

Results

Oral glucose induced no change in plasma VIP. Post-glucose ATBF measures identified 7 non-responders (peak blood flow < 50% of fasting values) and 9 responders. Compared to baseline (2.50 [1.96–3.59] mL·100 g⁻¹ min⁻¹), local microinfusion of VIP increased ATBF dose-dependently: 2.67 [2.18–3.89]; 4.35 [3.33–4.65]; and 7.91 [6.59–9.88] mL·100 g⁻¹ min⁻¹ (p < 0.0001) with a non-significant lower response to VIP in non-responders.

Conclusions

Our findings show a potent vasodilatory effect of VIP in adipose tissue and suggest that individuals with a blunted ATBF response to glucose load have a lower response. Whether the local unresponsiveness to VIP participates in this non-responder status has to be confirmed in larger studies.

Objective

Myotoxin injury of skeletal muscle disrupts myofibers and fragments capillaries. Following injury, myofibers and capillaries regenerate in concert; however, it remains unresolved whether myogenesis and angiogenesis are interdependent processes. We tested the hypothesis that myofiber regeneration is required for revascularization.

Methods

To limit myofiber regeneration, satellite cells were depleted by tamoxifen injections (+TMX) in adult Pax7-Cre^ERT2/+; Rosa^DTA/+ (Pax7-DTA) mice; vehicle injections (−TMX) served as controls. Two weeks later, the gluteus maximus muscle was injured by local injection of BaCl₂. Regeneration of myofibers and microvessels was assessed histologically. Microvascular perfusion was evaluated with fluorescent tracers injected into the bloodstream.

Results

Myofiber regeneration was minimal in +TMX. Through 21 days post injury (dpi), microvascular area (CD31 immunostaining) was similar between +TMX and −TMX, with disoriented microvessels prevailing in +TMX. At 7 dpi, fewer capillaries were perfused in +TMX compared to −TMX. At 21 dpi, EC area and capillary perfusion were not different between groups. For +TMX at 28 dpi, distinct regions with fewer perfused microvessels near “ghost” fibers were accompanied by adjacent areas of robust vascularity and clusters of adipocytes.

Conclusions

Following myotoxin injury after satellite cell ablation, angiogenesis ensues without myogenesis, and the microcirculation remodels according to changes in tissue composition.

Objective

This study investigates the effects of hyperglycemia on vascular morphology and hemodynamics during embryogenesis using the chick chorioallantoic membrane (CAM) model.

Methods

We employed a dual-modality, label-free imaging approach, Optical Coherence Tomography Angiography (OCTA) and biospeckle imaging, to evaluate microvascular architecture and real-time flow dynamics in chick embryos subjected to hyperglycemic conditions. Quantitative metrics such as vessel area, branching junctions, lacunarity, and biospeckle contrast were analyzed to assess angiogenic and metabolic responses.

Results

Hyperglycemia caused significant vascular attrition, including a 31% reduction in vessel area, 55% fewer vascular junctions, and a 58% increase in lacunarity, indicating fragmented and simplified networks. Biospeckle imaging revealed reduced blood flow velocities and elevated non-vascular speckle contrast, suggestive of metabolic stress and endothelial apoptosis. These vascular impairments extended to the retina, where hyperglycemic embryos exhibited thinner retinas, smaller lenses, and sparser retinal vasculature.

Conclusion

Our findings demonstrate that embryonic hyperglycemia leads to widespread vascular simplification and hemodynamic dysfunction, driven by oxidative stress and disrupted VEGF signaling. Unlike adult diabetic vasculopathy, the embryonic response involves global, not focal, vascular defects. This work establishes a novel multimodal imaging framework for studying developmental angiogenesis and lays the groundwork for future investigations into therapeutic strategies targeting diabetic embryopathy.

Objectives

The development of hemoglobin-based oxygen carriers (HBOCs) offers a promising alternative to traditional blood transfusions, addressing critical limitations such as the need for cold storage, blood type matching, and a short ex vivo shelf life. HBOCs mimic the oxygen-carrying function of red blood cells without the risk of transfusion-related complications. However, hemoglobin is prone to oxidation when freely circulating in the vasculature, resulting in methemoglobin formation. In this oxidized state, Hb does not transport oxygen, scavenges less nitric oxide, but it is more toxic. As continued research tries to develop effective HBOCs for use in emergency medicine, there needs to be an understanding of the microvascular and toxicological effects of the reduced and oxidized forms of Hb.

Materials and Methods

The study involved Golden Syrian Hamsters instrumented with a dorsal skin window chamber model to observe the acute effects resulting from a hypervolemic infusion (10% of the animal's blood volume) of human Hb [HbFe²⁺ (hHb)] or methemoglobin [HbFe³⁺ (met-hHb)] and lactated Ringer's solution as a volume control. Microhemodynamics, mean arterial pressure, heart rate, blood gases, and blood properties were measured.

Results

Mean arterial pressure (MAP) and heart rate (HR) were both altered; animals infused with hHb saw a significant increase in MAP and a decrease in HR, while animals infused with met-hHb saw a significant decrease in MAP and a decrease in HR. Infusion of hHb induced vasoconstriction and hypertension. However, infusion of met-hHb resulted in increased microvascular diameters compared to baseline, but a reduction in functional capillary density compared to baseline, alongside significant increases in inflammation, specifically in systemic and cardiac markers.

Conclusion

This study illuminates the complex impact of Hb oxidation on microvascular function and inflammation, pivotal to understanding the safety and efficacy of HBOC formulations. Future research should focus on strategies to regulate Hb oxidation to enhance therapeutic benefit and minimize detrimental effects in emergency medicine settings.

Background

Variations in resting pulsatile coronary flow velocity acceleration/deceleration characteristics (dU/dt) with respect to epicardial lesions and coronary microvascular dysfunction (CMD) remain incompletely understood.

Method

The coronary dU/dt pattern was extracted from the first derivative of the intracoronary Doppler velocity signal. Univariable and multivariable models evaluated the relationships between the dU/dt amplitudes, epicardial disease as well as CMD, defined by a blunted coronary flow reserve (CFR) adjusted for the concomitant epicardial disease severity (fractional flow reserve, FFR) yielding the microvascular resistance reserve (MRR). Functional CMD was defined by a blunted MRR (≤ 3.0) but normal hyperemic microvascular resistance (hMR < 2.5) whereas structural CMD was defined by a blunted MRR (≤ 3.0) combined with increased hMR (≥ 2.5). Six major acceleration or deceleration peaks were identified in each cardiac cycle; these were a (amplitude of peak diastolic acceleration), b (amplitude of early diastolic deceleration nadir), c (amplitude of peak diastolic re-acceleration), j (amplitude of end-diastolic deceleration nadir), x (amplitude of peak systolic acceleration), and z (amplitude of end-systolic deceleration nadir) waves.

Results

Functional CMD was associated with amplification of a (β = 55.944, 95% CI [21.112, 90.777], p = 0.002) and × (β = 44.069, 95% CI [20.182, 67.955], p < 0.001), b (β = −34.019, 95% CI [−50.865, −17.173], p < 0.001), j (β = −48.723, 95% CI [−71.272, −26.174], p < 0.001), and z (β = −31.047, 95% CI [−53.596, −8.498], p = 0.007) waves. Structural CMD was associated with blunted a (β = −76.938, 95% CI [−113.125, −40.751], p < 0.001) and j (β = 24.787, 95% CI [1.361, 48.213], p = 0.039).

Conclusion

Epicardial disease severity is minimally associated with alterations in the resting dU/dt pattern, whereas CMD endotypes are associated with distinctively altered intrabeat pulsatility characteristics. Stronger acceleration magnitudes at rest do not indicate a healthier microcirculation or absence of CMD.

Trial Registration

ClinicalTrials.gov (NCT02328820)

Objectives

The amino acid homocysteine (HCY) has been implicated in the pathobiology of several conditions, including spaceflight-associated neuro-ocular syndrome (SANS)—a collection of symptoms affecting near vision in astronauts. Blood-retinal barrier (BRB) and blood–brain barrier (BBB) dysfunctions are implicated in the pathobiology of SANS. Our objective was to assess how HCY affects BRB/BBB permeability and the role of the NLRP3 inflammasome in the modulation of such effects.

Methods

Human brain and retinal microvascular endothelial cells (HBMECs and HRMECs) were treated with 100 μM HCY alone or in conjunction with NLRP3 inflammasome inhibitor MCC950 at 1 μM. The assays performed included fluorometric assays to measure cell viability, an enzyme assay for caspase-1, expression of BRB/BBB tight junction protein zonula occludens-1 (ZO-1) by RT-PCR, and barrier permeability using FITC-dextran.

Results

In HRMECs and HBMECs, HCY-induced endothelial monolayer hyperpermeability significantly (p < 0.05). In HBMECs, the effect was attenuated by MCC950 (p < 0.05). Increased Caspase-1 activity was observed in both cell types following the addition of HCY. Following HCY addition, gene expression results denoting barrier damage were observed, particularly that of ZO-1 (p < 0.05).

Conclusions

HCY induces hyperpermeability in retinal and brain endothelial cells. NLRP3-mediation in HCY-induced microvascular permeability is prominent in brain endothelial cells compared to retinal endothelial cells.

Objective

Synthetic hydrogels that support 3D cell culture are widely used as platforms for modeling disease, such as tissue fibrosis, which leads to mechanical stiffening of the extracellular matrix (ECM). To interrogate how mechanical stiffness of the ECM affects microvascular remodeling, we developed a bioactive poly(ethylene glycol) diacrylate (PEGDA) hydrogel model with tunable stiffness that permits microvascular sprouting.

Methods

Lung explants harvested from healthy and fibrotic mice were cultured ex vivo on PEGDA hydrogels for 7 days. Capillary sprouting from lung segments was evaluated via imaging and secreted angiogenic markers.

Results

Healthy lung explants had decreased sprout formation and length on stiffer hydrogels. The sprouts from fibrotic lung explants, however, were not impacted by hydrogel stiffness. This difference was associated with higher expression of angiogenic markers and matrix remodeling enzymes in the fibrotic lung explants.

Conclusions

Our results suggest a compensation in vasculature derived from fibrotic tissue to matrix mechanics in promoting angiogenic sprouting.

Background

Availability of oxygen (O₂) is essential for life and function of all cells of the human body (n ≈ 10¹³–10¹⁴ cells). COVID-19 patients often have impaired lung function with compromised oxygen uptake, but little is known about microvascular oxygen delivery and tissue oxygenation.

Objectives

Use the Oxygen Delivery Index (ODIN) concept to assess peripheral microvascular regulation and oxygen extraction in COVID-19 patients.

Methods

The ODIN concept includes two technologies (diffuse reflectance spectroscopy—DRS and computer assisted microscopy—CAM) for data acquisition from subepidermal nutritive capillaries. Output parameters are microvascular oxygen saturation (SmvO₂) and functional capillary density (FCD).

Results

Forty patients hospitalized for COVID-19 grouped into early discharge (< 7 days, n = 11), severe (beyond 7 days, n = 24) and non-survivors (n = 5), and healthy controls (n = 23) were examined.

Microvascular oxygen saturation (SmvO₂) and the corresponding O₂ extraction (SaO₂—SmvO₂) was 56% ± 4%/42% ± 9% (mean ± SD) in healthy controls (n = 11), 61 ± 10/37 ± 10 for historic controls (n = 12), significantly different (p < 0.01) as compared with all COVID-19 groups (early discharge: 40% ± 13%/54% ± 13%, severe: 34% ± 15%/60% ± 15%, non-survivors 22% ± 15%/73% ± 16%). FCD expressed as the relative number of red pixels (belonging to a capillary erythrocyte) in a CAM frame were reduced in alle patient groups as compared to historic controls (p < 0⋅05).

Conclusion

Results show skin microvascular dysregulation and tissue hypoxia in patients, indicative of hypoxia also in other tissues. We hypothesize that tissue hypoxia is a cause of reversible and non-reversible long COVID-19 symptoms and of mortality.