Blood-pool MRI assessment of myocardial microvascular reactivity

Purpose

The ability to non-invasively image myocardial microvascular dilation and constriction is essential to assessing intact function and dysfunction. Yet, conventional measurements based on blood oxygenation are not specific to changes in blood volume. The purpose of this study was to extend to the heart a blood-pool MRI approach for assessing vasomodulation in the presence of blood gas changes and investigate if sex-related differences exist.

Methods

Animals [five male and five female healthy Sprague Dawley rats (200-500 g)] were intubated, ventilated, and cycled through room air (normoxia) and hypercapnia (10% CO2) in 10-minute cycles after i.v. injection of blood-pool agent Ablavar (0.3 mmol/kg). Pre-contrast T1 maps and T1-weighted 3D CINE were acquired on a 3 Tesla preclinical MRI scanner, followed by repeated 3D CINE every 5 min until the end of the gas regime. Invasive laser Doppler flowmetry of myocardial perfusion was performed to corroborate MRI results.

Results

Myocardial microvascular dilation to hypercapnia and constriction to normoxia were readily visualized on T1 maps. Over 10 min of hypercapnia, female myocardial T1 reduced by 20% (vasodilation), while no significant change was observed in the male myocardium. After return to normoxia, myocardial T1 increased (vasoconstriction) in both sexes (18% in females and 16% in males). Laser Doppler perfusion measurements confirmed vasomodulatory responses observed on MRI.

Conclusion

Blood-pool MRI is sensitive and specific to vasomodulation in the myocardial microcirculation. Sex-related differences exist in the healthy myocardium in response to mild hypercapnic stimuli.

Panax ginseng against myocardial ischemia/reperfusion injury: A review of preclinical evidence and potential mechanisms

ETHNOPHARMACOLOGICAL RELEVANCE

Panax ginseng C. A. Meyer (P. ginseng) is effective in the prevention and treatment of myocardial ischemia-reperfusion (I/R) injury. The mechanism by which P. ginseng exerts cardioprotective effects is complex. P. ginseng contains many pharmacologically active ingredients, such as molecular glycosides, polyphenols, and polysaccharides. P. ginseng and each of its active components can potentially act against myocardial I/R injury. Myocardial I/R was originally a treatment for myocardial ischemia, but it also induced irreversible damage, including oxygen-containing free radicals, calcium overload, energy metabolism disorder, mitochondrial dysfunction, inflammation, microvascular injury, autophagy, and apoptosis.

AIM OF THE STUDY

This study aimed to clarify the protective effects of P. ginseng and its active ingredients against myocardial I/R injury, so as to provide experimental evidence and new insights for the research and application of P. ginseng in the field of myocardial I/R injury.

MATERIALS AND METHODS

This review was based on a search of PubMed, NCBI, Embase, and Web of Science databases from their inception to February 21, 2022, using terms such as "ginseng," "ginsenosides," and "myocardial reperfusion injury." In this review, we first summarized the active ingredients of P. ginseng, including ginsenosides, ginseng polysaccharides, and phytosterols, as well as the pathophysiological mechanisms of myocardial I/R injury. Importantly, preclinical models with myocardial I/R injury and potential mechanisms of these active ingredients of P. ginseng for the prevention and treatment of myocardial disorders were generally summarized.

RESULTS

P. ginseng and its active components can regulate oxidative stress related proteins, inflammatory cytokines, and apoptosis factors, while protecting the myocardium and preventing myocardial I/R injury. Therefore, P. ginseng can play a role in the prevention and treatment of myocardial I/R injury.

CONCLUSIONS

P. ginseng has a certain curative effect on myocardial I/R injury. It can prevent and treat myocardial I/R injury in several ways. When ginseng exerts its effects, should be based on the theory of traditional Chinese medicine and with the help of modern medicine; the clinical efficacy of P. ginseng in preventing and treating myocardial I/R injury can be improved.

Impaired microcirculatory function, mitochondrial respiration, and oxygen utilization in skeletal muscle of claudicating patients with peripheral artery disease

Peripheral artery disease (PAD) is an atherosclerotic disease that impairs blood flow and muscle function in the lower limbs. A skeletal muscle myopathy characterized by mitochondrial dysfunction and oxidative damage is present in PAD; however, the underlying mechanisms are not well established. We investigated the impact of chronic ischemia on skeletal muscle microcirculatory function and its association with leg skeletal muscle mitochondrial function and oxygen delivery and utilization capacity in PAD. Gastrocnemius samples and arterioles were harvested from patients with PAD (n = 10) and age-matched controls (Con, n = 11). Endothelium-dependent and independent vasodilation was assessed in response to flow (30 μL·min-1), acetylcholine, and sodium nitroprusside (SNP). Skeletal muscle mitochondrial respiration was quantified by high-resolution respirometry, microvascular oxygen delivery, and utilization capacity (tissue oxygenation index, TOI) were assessed by near-infrared spectroscopy. Vasodilation was attenuated in PAD (P < 0.05) in response to acetylcholine (Con: 71.1 ± 11.1%, PAD: 45.7 ± 18.1%) and flow (Con: 46.6 ± 20.1%, PAD: 29.3 ± 10.5%) but not SNP (P = 0.30). Complex I + II state 3 respiration (P < 0.01) and TOI recovery rate were impaired in PAD (P < 0.05). Both flow and acetylcholine-mediated vasodilation were positively associated with complex I + II state 3 respiration (r = 0.5 and r = 0.5, respectively, P < 0.05). Flow-mediated vasodilation and complex I + II state 3 respiration were positively associated with TOI recovery rate (r = 0.8 and r = 0.7, respectively, P < 0.05). These findings suggest that chronic ischemia attenuates skeletal muscle arteriole endothelial function, which may be a key mediator for mitochondrial and microcirculatory dysfunction in the PAD leg skeletal muscle. Targeting microvascular dysfunction may be an effective strategy to prevent and/or reverse disease progression in PAD.NEW & NOTEWORTHY Ex vivo skeletal muscle arteriole endothelial function is impaired in claudicating patients with PAD, and this is associated with attenuated skeletal muscle mitochondrial respiration. In vivo skeletal muscle oxygen delivery and utilization capacity is compromised in PAD, and this may be due to microcirculatory and mitochondrial dysfunction. These results suggest that targeting skeletal muscle arteriole function may lead to improvements in skeletal muscle mitochondrial respiration and oxygen delivery and utilization capacity in claudicating patients with PAD.

Dynamic contrast enhanced - MRI efficiency in detecting embolization-induced perfusion defects in a rabbit model of critical-limb-ischemia

Critical limb ischemia (CLI) is a severe disease which affects about 2 million people in the US. Its prevalence is assessed at 800/100,000 population. However, no reliable tools are currently available to assess perfusion defects at the muscle tissue level. DCE-MRI is a technique that holds the potential to be effective in achieving this goal. However, preclinical studies performed with DCE-MRI have indicated low sensitivity assessing perfusion at resting state. To improve these previous results, in this work we propose new methodologies for data acquisition and analysis and we also revisit the biological model used for evaluation. Eleven rabbits underwent embolization of a lower limb. They were imaged at day 7 after embolization using DCE-MRI, performed on a 4.7 T small imaging device. Among them, n = 4 rabbits were used for MRI sequence optimization and n = 6 for data analysis after one exclusion. Normalized Areas under the curve (AUCn), and kinetic parameters such as K_trans and V_d resulting from the Tofts-Kety modeling (KTM) were calculated on the embolized and contralateral limbs. Average and heterogeneity features, consisting on standard-deviation and quantiles, were calculated on muscle groups and whole limbs. The Wilcoxon and Fisher-tests were performed to compare embolized and contralateral regions of interests. The Wilcoxon test was also used to compare features of parametric maps. Quantiles of 5 and 95% in the contralateral side were used to define low and high outliers. A P-value <0.05 was considered statistically significant. Average features were inefficient to identify injured muscles, in agreement with the low sensitivity of the technique previously reported by the literature. However, these findings were dramatically improved by the use of additional heterogeneity features (97% of total accuracy for group muscles, P < 0.01 and 100% of total accuracy for the total limbs). The mapping analysis and automatic outlier detection quantification improvement was explained by the presence of local hyperemia that impair the average calculations. The analysis with KTM did not provide any additional information compared to AUCn. The DCE technique can be effective in detecting embolization-induced disorders of limb muscles in a CLI model when heterogeneity is taken into account in the data processing, even without vascular stimulation. The simultaneous presence of areas of ischemia and hyperemia appeared as a signature of the injured limbs. These areas seem to reflect the simultaneous presence of infarcted areas and viable peripheral areas, characterized by a vascular response that is visible in DCE.

Human microvascular reactivity: a review of vasomodulating stimuli and non-invasive imaging assessment

The microvasculature serves an imperative function in regulating perfusion and nutrient exchange throughout the body, adaptively altering blood flow to preserve hemodynamic and metabolic homeostasis. Its normal functioning is vital to tissue health, whereas its dysfunction is present in many chronic conditions, including diabetes, heart disease, and cognitive decline. As microvascular dysfunction often appears early in disease progression, its detection can offer early diagnostic information. To detect microvascular dysfunction, one uses imaging to probe the microvasculature's ability to react to a stimulus, also known as microvascular reactivity (MVR). An assessment of MVR requires an integrated understanding of vascular physiology, techniques for stimulating reactivity, and available imaging methods to capture the dynamic response. Practical considerations, including compatibility between the selected stimulus and imaging approach, likewise require attention. In this review, we provide a comprehensive foundation necessary for informed imaging of MVR, with a particular focus on the challenging endeavor of assessing microvascular function in deep tissues.

Effects of upper limb ischemia-reperfusion on regional oxidative stress during aortic surgery with moderate hypothermia

INTRODUCTION

This study aims to evaluate the effect of acute, iatrogenic right arm ischemia and reperfusion (I/R) due to right axillary cannulation on regional oxidative stress using tissue perfusion markers such as central venous oxygen saturation, lactate, the difference between central venous and arterial CO₂ pressure, near-infrared spectroscopy (NIRS) measurements, and biomarkers like sialic acid, malondialdehyde, advanced oxidative protein products in aortic surgery with moderate hypothermia.

METHODS

Adult patients undergoing ascending aorta repair with antegrade cerebral perfusion via the axillary artery participated. Blood samples were collected from the internal jugular vein, right arm cubital vein, and left arm cubital vein, and analysis was performed at intraoperative time points.

RESULTS

Right-arm venous oxygen saturation levels are significantly lower than left arm and central venous, as expected in iatrogenic ischemia. Right arm lactate levels are significantly higher. Somatic right arm NIRS values are significantly lower than somatic left arm. There are no significant differences for biomarkers throughout the time points.

CONCLUSIONS

We have concluded that well-known markers reflect the results of ischemia-reperfusion more rapidly, and are more valuable than novel biomarkers. NIRS is a promising monitor in terms of providing information about tissue oxygenation. Oxidative stress biomarkers do not change quickly enough to give useful information in a short enough period of time; moreover, their costs are high and laboratory studies take time. Although axillary cannulation is controlled limb ischemia, the local effects of I/R did not completely normalize at the end of the surgery, and this regional I/R did not affect the global body organism.

Evaluation of microvascular permeability of skeletal muscle and texture analysis based on DCE-MRI in alloxan-induced diabetic rabbits

OBJECTIVES

To estimate the microvascular permeability and perfusion of skeletal muscle by using quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and explore the feasibility of using texture analysis (TA) to evaluate subtle structural changes of diabetic muscles.

METHODS

Twenty-four rabbits were randomly divided into diabetic (n = 14) and control (n = 10) groups, and underwent axial DCE-MRI of the multifidus muscle (0, 4, 8, 12, and 16 weeks after alloxan injection). The pharmacokinetic model was used to calculate the permeability parameters; texture parameters were extracted from volume transfer constant (K^trans) map. The two-sample t test/Mann-Whitney U test, repeated measures analysis of variance/Friedman test, and Pearson correlations were used for data analysis.

RESULTS

In the diabetic group, K^trans and rate constant (K_ep) increased significantly at week 8 and then showed a decreasing trend. Extravascular extracellular space volume fraction (V_e) increased and plasma volume fraction (V_p) decreased significantly from the 8th week. Skewness began to decrease at the 4th week. Median K^trans and entropy increased significantly, while inverse difference moment decreased from the 8th week. Energy decreased while contrast increased only at week 8. Muscle fibre cross-sectional area was negatively correlated with V_e. The capillary-to-fibre ratio was positively correlated with V_p (p < 0.05, all).

CONCLUSIONS

Quantitative DCE-MRI can be used to evaluate microvascular permeability and perfusion in diabetic skeletal muscle at an early stage; TA based on K^trans map can identify microarchitectural modifications in diabetic muscles.

KEY POINTS

• Four quantitative parameters of DCE-MRI can be used to evaluate microvascular permeability and perfusion of skeletal muscle in diabetic models at early stages. • Texture analysis based on K^trans map can identify subtle structural changes in diabetic muscles.

Effects of cyclosporin A pre-treatment combined with etomidate post-treatment on lung injury induced by limb ischemia-reperfusion in rats

OBJECTIVES

To investigate the influence of cyclosporin A (CsA) pre-treatment and etomidate (ETO) post-treatment on lung injury induced by limb ischemia-reperfusion (I/R) in rats.

METHODS

Rats were randomly divided into five groups: sham, I/R, I/R+CsA, I/R+ETO, and I/R+CsA+ETO. Limb I/R lung injury was established by bilateral clamping of the femoral arteries for 2 hours. Following reperfusion for 3 hours, blood gas analysis was performed. Pathological changes were assessed using immunohistochemistry. The apoptosis index (AI) and wet/dry weight ratio (W/D) were calculated. Levels of Fas protein and FasL mRNA were assessed by western blotting and RT-PCR, respectively. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β were detected by ELISA.

RESULTS

I/R resulted in decreased PaO2 but increased AI, W/D, Fas, FasL mRNA, TNF-α and IL-1β. Scattered punctate apoptosis and necrosis were observed by immunohistochemistry. Compared with the I/R group, the I/R+ETO and I/R+CsA groups showed increased SpO2, decreased AI, W/D, Fas, FasL mRNA, TNF-α and IL-1β, and decreased numbers of apoptotic and necrotic cells. Combined treatment with CsA+ETO resulted in more dramatic changes in these parameters.

CONCLUSIONS

ETO post-treatment and CsA pretreatment reduced lung injury induced by limb I/R in rats. The mechanism may be related to synergistic inhibition of Fas/FasL signaling.

A novel MRI analysis for assessment of microvascular vasomodulation in low-perfusion skeletal muscle

Compromised microvascular reactivity underlies many conditions and injuries, but its assessment remains difficult, particularly in low perfusion tissues. In this paper, we develop a new mathematical model for the assessment of vasomodulation in low perfusion settings. A first-order model was developed to approximate changes in T₁ relaxation times as a result of vasomodulation. Healthy adult rats (N = 6) were imaged on a 3-Tesla clinical MRI scanner, and vasoactive response was probed on gadofosveset using hypercapnic gases at 20% and 5% CO₂ to induce vasoconstriction and vasodilation, respectively. MRI included dynamic 3D T₁ mapping and T₁-weighted images during gas challenge; heart rate was continuously monitored. Laser Doppler perfusion measurements were performed to corroborate MRI findings. The model was able to identify hypercapnia-mediated vasoconstriction and vasodilation through the partial derivative \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{\partial {T}_{1}}{\partial t}$$\end{document}∂T1∂t. MRI on animals revealed gradual vasoconstriction in the skeletal muscle bed in response to 20% CO₂ followed by gradual vasodilation on transitioning to 5% CO₂. These trends were confirmed on laser Doppler perfusion measurements. Our new mathematical model has the potential for detecting microvascular dysfunction that manifests in the early stages across multiple metabolic and ischemic pathologies.