Novel theory and potential applications of central diastolic pressure decay time constant

Central aortic diastolic pressure decay time constant ( τ ) is according to the two-element Windkessel model equal to the product of total peripheral resistance ( R ) times total arterial compliance ( C ). As such, it is related to arterial stiffness, which has considerable pathophysiological relevance in the assessment of vascular health. This study aimed to investigate the relationship of the constant τ with the product T MBP cPP , given by heart period ( T ) times the ratio of mean blood pressure (MBP) to central pulse pressure ( cPP ). The relationship was derived by performing linear fitting on an in silico population of n1 = 3818 virtual subjects, and was subsequently evaluated on in vivo data (n2 = 2263) from the large Asklepios study. The resulted expression was found to be τ = k ' T MBP cPP , withk ' = 0.7 (R2 = 0.9). The evaluation of the equation on the in vivo human data reported high agreement between the estimated and reference τ values, with a correlation coefficient equal to 0.94 and a normalized RMSE equal to 5.5%. Moreover, the analysis provided evidence that the coefficient k ' is age- and gender-independent. The proposed formula provides novel theoretical insights in the relationship between τ and central blood pressure features. In addition, it may allow for the evaluation of τ without the need for acquiring the entire central blood pressure wave, especially when an approximation of the cPP is feasible. This study adds to the current literature by contributing to the accessibility of an additional biomarker, such as the central diastolic pressure decay time constant, for the improved assessment of vascular ageing.

Corrigendum: Determination of aortic characteristic impedance and total arterial compliance from regional pulse wave velocities using machine learning: an in silico study

[This corrects the article DOI: 10.3389/fbioe.2021.649866.].

Corrigendum: Estimation of left ventricular end-systolic elastance from brachial pressure waveform via deep learning

[This corrects the article DOI: 10.3389/fbioe.2021.754003.].

Modulation of Pulsatile Left Ventricular Afterload by Renal Denervation in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Arterial stiffening contributes to hemodynamic derangements in heart failure with preserved ejection fraction (HFpEF). We sought to investigate the impact of renal denervation on pulsatile left ventricular loading in patients with HFpEF and hypertensive patients without heart failure (control).

METHODS

Patients underwent renal denervation for treatment of hypertension and were followed up at 3 months at a single center. A validated computer model of the arterial tree, noninvasive aortic flow curves, left ventricular volumes, and E/e' as inputs were used to determine key parameters of left ventricular vascular load.

RESULTS

In comparison to controls (n=30), patients with HFpEF (n=30) demonstrated lower total arterial compliance (mean difference, -0.41 [95% CI, -0.72 to -0.10] mL/mm Hg), higher impedance of the proximal aorta (Zc: 0.02; 0.01 to 0.04 mHg·s/mL), premature wave reflections (shorter backward wave transit time normalized to ejection time: -3.5; -6.5% to -0.5%), and higher wave reflection magnitude (reflection coefficient: 7.3; 2.8% to 11.9%). Overall, daytime systolic (-9.2; -12.2 to -6.2 mm Hg) and diastolic blood pressures (-5.9; -7.6 to -4.1 mm Hg) as well as blood pressure variability (-2.0; -3.0 to -0.9 mm Hg) decreased after renal denervation. In patients with HFpEF, total arterial compliance (0.42; 0.17 to 0.67 mL/mm Hg) and backward transit time normalized to ejection time (1.7; 0.4% to 3.0%) increased; Zc (-0.01; -0.02 to -0.01 mm Hg·s/mL) and reflection coefficient (-2.6; -5.0% to -0.3%) decreased after renal denervation. This was accompanied by a symptomatic improvement in patients with HFpEF.

CONCLUSION

HFpEF is characterized by heightened aortic stiffness and unfavorable pulsatile left ventricular load. These abnormalities are partly normalized after renal denervation.

Wet adhesive hydrogels to correct malacic trachea (tracheomalacia) A proof of concept

Tracheomalacia (TM) is a condition characterized by a weak tracheal cartilage and/or muscle, resulting in excessive collapse of the airway in the newborns. Current treatments including tracheal reconstruction, tracheoplasty, endo- and extra-luminal stents have limitations. To address these limitations, this work proposes a new strategy by wrapping an adhesive hydrogel patch around a malacic trachea. Through a numerical model, first it was demonstrated that a hydrogel patch with sufficient mechanical and adhesion strength can preserve the trachea's physiological shape. Accordingly, a new hydrogel providing robust adhesion on wet tracheal surfaces was synthesized employing the hydroxyethyl acrylamide (HEAam) and polyethylene glycol methacrylate (PEGDMA) as main polymer network and crosslinker, respectively. Ex vivo experiments revealed that the adhesive hydrogel patches can restrain the collapsing of malacic trachea under negative pressure. This study may open the possibility of using an adhesive hydrogel as a new approach in the difficult clinical situation of tracheomalacia.

On the similarity between aortic and carotid pressure diastolic decay: a mathematical modelling study

Aortic diastolic pressure decay (DPD) has been shown to have considerable pathophysiological relevance in the assessment of vascular health, as it is significantly affected by arterial stiffening. Nonetheless, the aortic pressure waveform is rarely available and hence the utility of the aortic DPD is limited. On the other hand, carotid blood pressure is often used as a surrogate of central (aortic) blood pressure in cardiovascular monitoring. Although the two waveforms are inherently different, it is unknown whether the aortic DPD shares a common pattern with the carotid DPD. In this study, we compared the DPD time constant of the aorta (aortic RC) and the DPD time constant of the carotid artery (carotid RC) using an in-silico-generated healthy population from a previously validated one-dimensional numerical model of the arterial tree. Our results demonstrated that there is near-absolute agreement between the aortic RC and the carotid RC. In particular, a correlation of ~ 1 was reported for a distribution of aortic/carotid RC values equal to 1.76 ± 0.94 s/1.74 ± 0.87 s. To the best of our knowledge, this is the first study to compare the DPD of the aortic and the carotid pressure waveform. The findings indicate a strong correlation between carotid DPD and aortic DPD, supported by the examination of curve shape and the diastolic decay time constant across a wide range of simulated cardiovascular conditions. Additional investigation is required to validate these results in human subjects and assess their applicability in vivo.

Design and computational optimization of compliance-matching aortic grafts

Introduction: Synthetic vascular grafts have been widely used in clinical practice for aortic replacement surgery. Despite their high rates of surgical success, they remain significantly less compliant than the native aorta, resulting in a phenomenon called compliance mismatch. This incompatibility of elastic properties may cause serious post-operative complications, including hypertension and myocardial hypertrophy. Methods: To mitigate the risk for these complications, we designed a multi-layer compliance-matching stent-graft, that we optimized computationally using finite element analysis, and subsequently evaluated in vitro. Results: We found that our compliance-matching grafts attained the distensibility of healthy human aortas, including those of young adults, thereby significantly exceeding the distensibility of gold-standard grafts. The compliant grafts maintained their properties in a wide range of conditions that are expected after the implantation. Furthermore, the computational model predicted the graft radius with enough accuracy to allow computational optimization to be performed effectively. Conclusion: Compliance-matching grafts may offer a valuable improvement over existing prostheses and they could potentially mitigate the risk for post-operative complications attributed to excessive graft stiffness.

Cardiac output estimated from an uncalibrated radial blood pressure waveform: validation in an in-silico-generated population

Background: Cardiac output is essential for patient management in critically ill patients. The state-of-the-art for cardiac output monitoring bears limitations that pertain to the invasive nature of the method, high costs, and associated complications. Hence, the determination of cardiac output in a non-invasive, accurate, and reliable way remains an unmet need. The advent of wearable technologies has directed research towards the exploitation of wearable-sensed data to improve hemodynamical monitoring. Methods: We developed an artificial neural networks (ANN)-enabled modelling approach to estimate cardiac output from radial blood pressure waveform. In silico data including a variety of arterial pulse waves and cardiovascular parameters from 3,818 virtual subjects were used for the analysis. Of particular interest was to investigate whether the uncalibrated, namely, normalized between 0 and 1, radial blood pressure waveform contains sufficient information to derive cardiac output accurately in an in silico population. Specifically, a training/testing pipeline was adopted for the development of two artificial neural networks models using as input: the calibrated radial blood pressure waveform (ANN_calradBP), or the uncalibrated radial blood pressure waveform (ANN_uncalradBP). Results: Artificial neural networks models provided precise cardiac output estimations across the extensive range of cardiovascular profiles, with accuracy being higher for the ANN_calradBP. Pearson's correlation coefficient and limits of agreement were found to be equal to [0.98 and (-0.44, 0.53) L/min] and [0.95 and (-0.84, 0.73) L/min] for ANN_calradBP and ANN_uncalradBP, respectively. The method's sensitivity to major cardiovascular parameters, such as heart rate, aortic blood pressure, and total arterial compliance was evaluated. Discussion: The study findings indicate that the uncalibrated radial blood pressure waveform provides sample information for accurately deriving cardiac output in an in silico population of virtual subjects. Validation of our results using in vivo human data will verify the clinical utility of the proposed model, while it will enable research applications for the integration of the model in wearable sensing systems, such as smartwatches or other consumer devices.

Quantification of the Phenomena Affecting Reflective Arterial Photoplethysmography

Photoplethysmography (PPG) is a widely emerging method to assess vascular health in humans. The origins of the signal of reflective PPG on peripheral arteries have not been thoroughly investigated. We aimed to identify and quantify the optical and biomechanical processes that influence the reflective PPG signal. We developed a theoretical model to describe the dependence of reflected light on the pressure, flow rate, and the hemorheological properties of erythrocytes. To verify the theory, we designed a silicone model of a human radial artery, inserted it in a mock circulatory circuit filled with porcine blood, and imposed static and pulsatile flow conditions. We found a positive, linear relationship between the pressure and the PPG and a negative, non-linear relationship, of comparable magnitude, between the flow and the PPG. Additionally, we quantified the effects of the erythrocyte disorientation and aggregation. The theoretical model based on pressure and flow rate yielded more accurate predictions, compared to the model using pressure alone. Our results indicate that the PPG waveform is not a suitable surrogate for intraluminal pressure and that flow rate significantly affects PPG. Further validation of the proposed methodology in vivo could enable the non-invasive estimation of arterial pressure from PPG and increase the accuracy of health-monitoring devices.

The Impact of Left Ventricular Performance and Afterload on the Evaluation of Aortic Valve Stenosis: A 1D Mathematical Modeling Approach

The transaortic valvular pressure gradient (TPG) plays a central role in decision-making for patients suffering from severe aortic stenosis. However, the flow-dependence nature of the TPG makes the diagnosis of aortic stenosis challenging since the markers of cardiac performance and afterload present high physiological interdependence and thus, isolated effects cannot be measured directly in vivo. We used a validated 1D mathematical model of the cardiovascular system, coupled with a model of aortic stenosis, to assess and quantify the independent effect of the main left ventricular performance parameters (end-systolic (Ees) and end-diastolic (Eed) elastance) and principal afterload indices (total vascular resistance (TVR) and total arterial compliance (TAC)) on the TPG for different levels of aortic stenosis. In patients with critical aortic stenosis (aortic valve area (AVA) ≤ 0.6 cm2), a 10% increase of Eed from the baseline value was associated with the most important effect on the TPG (−5.6 ± 0.5 mmHg, p < 0.001), followed by a similar increase of Ees (3.4 ± 0.1 mmHg, p < 0.001), in TAC (1.3 ±0.2 mmHg, p < 0.001) and TVR (−0.7 ± 0.04 mmHg, p < 0.001). The interdependence of the TPG left ventricular performance and afterload indices become stronger with increased aortic stenosis severity. Disregarding their effects may lead to an underestimation of stenosis severity and a potential delay in therapeutic intervention. Therefore, a comprehensive evaluation of left ventricular function and afterload should be performed, especially in cases of diagnostic challenge, since it may offer the pathophysiological mechanism that explains the mismatch between aortic severity and the TPG.

Prognostic Implications of the Novel Pulmonary Hypertension Definition in Patients with Aortic Stenosis after Transcatheter Valve Replacement

Introduction: Pulmonary hypertension (PH), traditionally defined as a mean pulmonary artery pressure (PAP) ≥ 25 mmHg, is associated with poor outcomes in patients undergoing a transcatheter aortic valve replacement (TAVR) for severe aortic stenosis (AS). Recently, a novel definition for PH has been proposed, placing the cut-off value of mean PAP at 20 mmHg, and introducing pulmonary vascular resistance as an exclusive indicator for the pre-capillary involvement. In light of the novel criteria, whether PH still preserves its prognostic significance remains unknown. Methods: The study population consisted of 380 patients with AS, who underwent a right heart catheterization before TAVR. The cohort was divided according to the presence of PH (n = 174, 45.7%) or not. Patients with PH were further divided into the following groups: (1) Pre-capillary PH ((Pre-capPH), n = 46, 12.1%); (2) Isolated post-capillary PH ((IpcPH), n = 78, 20.5%); (3) Combined pre and post-capillary PH ((CpcPH), n = 82, 21.6%). The primary endpoint was all-cause mortality at 1 year. Results: A total of 246 patients (64.7%) exhibited mean PAP > 20 mmHg. Overall, the presence of PH was associated with higher 1-year mortality rates (hazard ratio (HR) 2.8, 95% CI: 1.4−5.8, p = 0.004). Compared to patients with no PH, Pre-capPH and CpcPH (but not IpcPH) were related to higher 1-year mortality (HR 2.7, 95% CI: 1.0−7.2, p = 0.041 and HR 3.9, 95% CI: 1.8−8.5, p = 0.001, respectively). This remained significant even after the adjustment for baseline comorbidities. Conclusions: Pre-interventional PH according to the novel hemodynamic criteria, is linked with poor outcomes in patients undergoing TAVR for severe AS. However, this is mainly driven by patients with mean PAP ≥ 25 mmHg. Patients with a pre-capillary PH component as defined by increased PVR present an even worse prognosis as compared to patients with isolated post-capillary or no PH who present comparable 1-year mortality rates.

Arterial Wave Reflection and Aortic Valve Stenosis: Diagnostic Challenges and Prognostic Significance

Introduction

Arterial wave reflection is an important component of the left ventricular afterload, affecting both pressure and flow to the aorta. The aim of the present study was to evaluate the impact of wave reflection on transvalvular pressure gradients (TPG), a key parameter for the evaluation of aortic valve stenosis (AS), as well as its prognostic significance in patients with AS undergoing a transcatheter aortic valve replacement (TAVR).

Materials and Methods

The study population consisted of 351 patients with AS (mean age 84 ± 6 years, 43% males) who underwent a complete hemodynamic evaluation before the TAVR. The baseline assessment included right and left heart catheterization, transthoracic echocardiography, and a thorough evaluation of the left ventricular afterload by means of wave separation analysis. The cohort was divided into quartiles according to the transit time of the backward pressure wave (BWTT). Primary endpoint was all-cause mortality at 1 year.

Results

Early arrival of the backward pressure wave was related to lower cardiac output (Q1: 3.7 ± 0.9 lt/min vs Q4: 4.4 ± 1.0 lt/min, p &lt; 0.001) and higher aortic systolic blood pressure (Q1: 132 ± 26 mmHg vs Q4: 117 ± 26 mmHg, p &lt; 0.001). TPG was significantly related to the BWTT, patients in the arrival group exhibiting the lowest TPG (mean TPG, Q1: 37.6 ± 12.7 mmHg vs Q4: 44.8 ± 14.7 mmHg, p = 0.005) for the same aortic valve area (AVA) (Q1: 0.58 ± 0.35 cm2 vs 0.61 ± 0.22 cm2, p = 0.303). In multivariate analysis, BWTT remained an independent determinant of mean TPG (beta 0.3, p = 0.002). Moreover, the prevalence of low-flow, low-gradient AS with preserved ejection fraction was higher in patients with early arterial reflection arrival (Q1: 33.3% vs Q4: 14.9%, p = 0.033). Finally, patients with early arrival of the reflected wave (Q1) exhibited higher all-cause mortality at 1 year after the TAVR (unadjusted HR: 2.33, 95% CI: 1.17–4.65, p = 0.016).

Conclusion

Early reflected wave arrival to the aortic root is associated with poor prognosis and significant aortic hemodynamic alterations in patients undergoing a TAVR for AS. This is related to a significant decrease in TPG for a given AVA, leading to a possible underestimation of the AS severity.

Low-Intensity Electrostimulation Enhances Neuroregeneration and Improves Erectile Function in a Rat Model of Cavernous Nerve Injury

BACKGROUND

Neurogenic erectile dysfunction (ED) following radical prostatectomy (RP) is a frequent complication often leading to erectile tissue remodeling and permanent ED. Low-intensity electrostimulation (LIES) has been shown to enhance peripheral nerve regeneration, however, its application on cavernous nerves (CN) has never been investigated.

AIMS

To investigate whether LIES enhances CN regeneration, improves erectile function (EF) recovery, and prevents corpora cavernosal remodeling after CN injury, which is a principal factor for ED following RP.

METHODS

Adult male Sprague-Dawley rats were divided into Sham, Bilateral Cavernous Nerve Injury (BCNI), and BCNI + LIES (1V, 0.1ms, 12Hz, 1h/day). After 7days, EF was assessed (ICP measurement). Penes and CN were collected for molecular analyses of TGF-β1, Il-6, CRP, eNOS, ERK and AKT protein levels in corpus cavernosum (CC), and immunohistological analysis of DHE, total collagen and α-SMA in CC and S-100, Tub-III, DAPI, TUNEL, and nNOS in CN.

OUTCOMES

Effects of LIES on EF, erectile tissue remodeling and CN structure.

RESULTS

EF was decreased (P < .05) 7 days after BCNI and increased (P < .05) by LIES. Intracavernosal reactive oxygen species (DHE) was increased (P < .05) after BCNI and normalized by LIES. Protein expressions of TGF-β1, IL-6, and CRP were increased in the penis (P < .05) after BCNI and normalized by LIES. The α-SMA and/or total collagen ratio was decreased (P < .05) after BCNI in the penis and normalized by LIES. Protein expression ratio of p-ERK/ERK and p-AKT/AKT did not change after BCNI but increased (P < .05) in LIES group. Myelination and number of nNOS positive cells in the CN were decreased (P < .05) after BCNI and normalized by LIES. The number of apoptotic nerve cells within the dorsal penile nerve was increased (P < .05) after BCNI and decreased (P < .05) by LIES compared to the BCNI group. There were no differences in eNOS expression in the penis between study groups.

CLINICAL TRANSLATION

LIES may offer a potential new tool for penile rehabilitation and ED management following RP, potentially enhancing EF recovery and minimizing the side effects of this surgery.

STRENGTHS & LIMITATIONS

This study provides evidence of the protective effect of LIES on EF and tissue remodeling following CN injury; nevertheless, this study has been conducted on animals and the translation to humans remains to be demonstrated. Further research to identify the underlying mechanisms of action is required.

CONCLUSION

This study demonstrates that LIES of the CN after CN injury protects CN structure, enhances EF recovery, and prevents corpora cavernosal remodeling. Sturny M, Karakus S, Fraga-Silva R, et al. Low-Intensity Electrostimulation Enhances Neuroregeneration and Improves Erectile Function in a Rat Model of Cavernous Nerve Injury. J Sex Med 2022;19:686-696.

Validation of a Non-invasive Inverse Problem-Solving Method for Stroke Volume

Stroke volume (SV) is a major biomarker of cardiac function, reflecting ventricular-vascular coupling. Despite this, hemodynamic monitoring and management seldomly includes assessments of SV and remains predominantly guided by brachial cuff blood pressure (BP). Recently, we proposed a mathematical inverse-problem solving method for acquiring non-invasive estimates of mean aortic flow and SV using age, weight, height and measurements of brachial BP and carotid-femoral pulse wave velocity (cfPWV). This approach relies on the adjustment of a validated one-dimensional model of the systemic circulation and applies an optimization process for deriving a quasi-personalized profile of an individual’s arterial hemodynamics. Following the promising results of our initial validation, our first aim was to validate our method against measurements of SV derived from magnetic resonance imaging (MRI) in healthy individuals covering a wide range of ages (n = 144; age range 18–85 years). Our second aim was to investigate whether the performance of the inverse problem-solving method for estimating SV is superior to traditional statistical approaches using multilinear regression models. We showed that the inverse method yielded higher agreement between estimated and reference data (r = 0.83, P &lt; 0.001) in comparison to the agreement achieved using a traditional regression model (r = 0.74, P &lt; 0.001) across a wide range of age decades. Our findings further verify the utility of the inverse method in the clinical setting and highlight the importance of physics-based mathematical modeling in improving predictive tools for hemodynamic monitoring.

Estimation of Left Ventricular End-Systolic Elastance From Brachial Pressure Waveform via Deep Learning

Determination of left ventricular (LV) end-systolic elastance (E es ) is of utmost importance for assessing the cardiac systolic function and hemodynamical state in humans. Yet, the clinical use of E es is not established due to the invasive nature and high costs of the existing measuring techniques. The objective of this study is to introduce a method to assess cardiac contractility, using as a sole measurement an arterial blood pressure (BP) waveform. Particularly, we aim to provide evidence on the potential in using the morphology of the brachial BP waveform and its time derivative for predicting LV E es via convolution neural networks (CNNs). The requirement of a broad training dataset is addressed by the use of an in silico dataset (n = 3,748) which is generated by a validated one-dimensional mathematical model of the cardiovasculature. We evaluated two CNN configurations: 1) a one-channel CNN (CNN1) with only the raw brachial BP signal as an input, and 2) a two-channel CNN (CNN2) using as inputs both the brachial BP wave and its time derivative. Accurate predictions were yielded using both CNN configurations. For CNN1, Pearson's correlation coefficient (r) and RMSE were equal to 0.86 and 0.27 mmHg/ml, respectively. The performance was found to be greatly improved for CNN2 (r = 0.97 and RMSE = 0.13 mmHg/ml). Moreover, all absolute errors from CNN2 were found to be less than 0.5 mmHg/ml. Importantly, the brachial BP wave appeared to be a promising source of information for estimating E es . Predictions were found to be in good agreement with the reference E es values over an extensive range of LV contractility values and loading conditions. Therefore, the proposed methodology could be easily transferred to the bedside and potentially facilitate the clinical use of E es for monitoring the contractile state of the heart in the real-life setting.

The effect of left ventricular contractility on arterial hemodynamics: A model-based investigation

Ventricular-arterial coupling is a major determinant of cardiovascular performance, however, there are still inherent difficulties in distinguishing ventricular from vascular effects on arterial pulse phenotypes. In the present study, we employed an extensive mathematical model of the cardiovascular system to investigate how sole changes in cardiac contractility might affect hemodynamics. We simulated two physiologically relevant cases of high and low contractility by altering the end-systolic elastance, E_es, (3 versus 1 mmHg/mL) under constant cardiac output and afterload, and subsequently performed pulse wave analysis and wave separation. The aortic forward pressure wave component was steeper for high E_es, which led to the change of the total pressure waveform from the characteristic Type A phenotype to Type C, and the decrease in augmentation index, AIx (-2.4% versus +18.1%). Additionally, the increase in E_es caused the pulse pressure amplification from the aorta to the radial artery to rise drastically (1.86 versus 1.39). Our results show that an increase in cardiac contractility alone, with no concomitant change in arterial properties, alters the shape of the forward pressure wave, which, consequently, changes central and peripheral pulse phenotypes. Indices based on the pressure waveform, like AIx, cannot be assumed to reflect only arterial properties.

Acute and Long-Term Effects of Aortic Compliance Decrease on Central Hemodynamics: A Modeling Analysis

Aortic compliance is an important determinant of cardiac afterload and a contributor to cardiovascular morbidity. In the present study, we sought to provide in silico insights into the acute as well as long-term effects of aortic compliance decrease on central hemodynamics. To that aim, we used a mathematical model of the cardiovascular system to simulate the hemodynamics (a) of a healthy young adult (baseline), (b) acutely after banding of the proximal aorta, (c) after the heart remodeled itself to match the increased afterload. The simulated pressure and flow waves were used for subsequent wave separation analysis. Aortic banding induced hypertension (SBP 106 mmHg at baseline versus 152 mmHg after banding), which was sustained after left ventricular (LV) remodeling. The main mechanism that drove hypertension was the enhancement of the forward wave, which became even more significant after LV remodeling (forward amplitude 30 mmHg at baseline versus 60 mmHg acutely after banding versus 64 mmHg after remodeling). Accordingly, the forward wave’s contribution to the total pulse pressure increased throughout this process, while the reflection coefficient acutely decreased and then remained roughly constant. Finally, LV remodeling was accompanied by a decrease in augmentation index (AIx 13% acutely after banding versus −3% after remodeling) and a change of the central pressure wave phenotype from the characteristic Type A (“old”) to Type C (“young”) phenotype. These findings provide valuable insights into the mechanisms of hypertension and provoke us to reconsider our understanding of AIx as a solely arterial parameter.

On the assessment of arterial compliance from carotid pressure waveform

In a progressively aging population, it is of utmost importance to develop reliable, noninvasive, and cost-effective tools to estimate biomarkers that can be indicative of cardiovascular risk. Various pathophysiological conditions are associated to changes in the total arterial compliance (C_T), and thus, its estimation via an accurate and simple method is valuable. Direct noninvasive measurement of C_T is not feasible in the clinical practice. Previous methods exist for indirect estimation of C_T, which, however, require noninvasive, yet complex and expensive, recordings of the central pressure and flow. Here, we introduce a novel, noninvasive method for estimating C_T from a single carotid waveform measurement using regression analysis. Features were extracted from the carotid wave and were combined with demographic data. A prediction pipeline was adopted for estimating C_T using, first, a feature-based regression analysis and, second, the raw carotid pulse wave. The proposed methodology was appraised using the large human cohort (N = 2,256) of the Asklepios study. Accurate estimates of C_T were yielded for both prediction schemes, namely, r = 0.83 and normalized root mean square error (nRMSE) = 9.58% for the feature-based model, and r = 0.83 and nRSME = 9.67% for the model that used the raw signal. The major advantage of this method pertains to the simplification of the technique offering easily applicable and convenient C_T monitoring. Such an approach could offer promising applications, ranging from fast and cost-efficient hemodynamical monitoring by the physician to integration in wearable technologies.NEW & NOTEWORTHY This article introduces a novel artificial intelligence method to estimate total arterial compliance (C_T) via exploiting the information provided by an uncalibrated carotid blood pressure waveform as well as typical clinical variables. The major finding of this study is that C_T, which is usually acquired using both pressure and flow waveforms, can be accurately derived by the use of the pressure wave alone. This method could potentially facilitate easily applicable and convenient monitoring of C_T.

Determination of Aortic Characteristic Impedance and Total Arterial Compliance From Regional Pulse Wave Velocities Using Machine Learning: An in-silico Study

In-vivo assessment of aortic characteristic impedance (Z ao ) and total arterial compliance (C T ) has been hampered by the need for either invasive or inconvenient and expensive methods to access simultaneous recordings of aortic pressure and flow, wall thickness, and cross-sectional area. In contrast, regional pulse wave velocity (PWV) measurements are non-invasive and clinically available. In this study, we present a non-invasive method for estimating Z ao and C T using cuff pressure, carotid-femoral PWV (cfPWV), and carotid-radial PWV (crPWV). Regression analysis is employed for both Z ao and C T . The regressors are trained and tested using a pool of virtual subjects (n = 3,818) generated from a previously validated in-silico model. Predictions achieved an accuracy of 7.40%, r = 0.90, and 6.26%, r = 0.95, for Z ao , and C T , respectively. The proposed approach constitutes a step forward to non-invasive screening of elastic vascular properties in humans by exploiting easily obtained measurements. This study could introduce a valuable tool for assessing arterial stiffness reducing the cost and the complexity of the required measuring techniques. Further clinical studies are required to validate the method in-vivo.

Apelin-13 Protects Corpus Cavernosum Against Fibrosis Induced by High-Fat Diet in an MMP-Dependent Mechanism

BACKGROUND

An increased fibrosis of the corpora cavernosa is a prevalent process that underlies most cases of erectile dysfunction. Apelin, an endogenous circulating peptide, has been documented as an important effector on cardiovascular homeostasis, controlling vascular function and reducing fibrosis in multiple pathological conditions. Recently, initial studies have shown that Apelin, acting through the APJ receptor, also modulates penile erection, however, the role of this system on penile structure and intracorporal collagen remodeling has not been investigated yet.

AIMS

Here we sought to investigate the effect of chronic Apelin treatment on the corpus cavernosum structure of hyperchOlesterolemic mice.

METHODS

Apolipoprotein gene-deleted (ApoE^-/-) mice were fed with a Western diet for 11 weeks and received Apelin-13 (2 mg/kg/day) or vehicle during the last 3 weeks. Penile samples were obtained for histological and biochemical analyses to assess the intracorporal collagen content and key proteins expression. Furthermore, the effect of Apelin-13 was evaluated in cultured NIH3T3 mouse fibroblasts stimulated with TGF-β.

OUTCOME

Local expression of Apelin-13 in mouse corpus cavernosum and its protective effect against fibrosis.

RESULTS

Apelin and APJ receptor were expressed (gene and protein) within the corpus cavernosum of ApoE^-/- mice, indicating a local modulation of the Apelin system. Interestingly, 3 weeks of Apelin-13 treatment strongly reduced intracavernosal collagen content. In addition, Apelin-13 enhanced total matrix metalloproteinase (MMP) activity in the mice penis, which was associated with an increased protein expression of MMP-1, MMP-3, MMP-8, and MMP-9, while tissue inhibitor of metalloproteinase were unaltered. These beneficial actions were not associated with changes in nNOS or eNOS protein expression, intracavernosal reactive oxygen species content, or atherosclerotic plaque deposition. Additionally, in cultured fibroblast, Apelin-13 inhibited TGF-β-induced fibroblast to myofibroblast differentiation and collagen production, possibly through the activation of ERK1/2 kinase.

CLINICAL TRANSLATION

These results point out Apelin/APJ system as a potential target to treat intracavernosal fibrosis-related disorders.

STRENGTH & LIMITATIONS

These results provide the first evidence of the Apelin system's positive role on erectile tissue structure/remodeling. Nevertheless, additional functional study addressing erectile response would bring extended validation regarding the relevance of such effect.

CONCLUSION

These results suggest a local modulation of the Apelin system within the corpus cavernosum. Remarkably, Apelin-13 reduced intracavernosal fibrosis in hypercholesterolemic mice by: (i) enhancing MMPs expression and activity; and (ii) inhibiting fibroblast differentiation into myofibroblast. Altogether, these results suggest an essential protective role of Apelin, indicating Apelin/APJ system as a promising candidate for the development of fibrosis-associated erectile dysfunction treatments. Sturny M, Anguenot L Costa-Fraga FP, et al. Apelin-13 Protects Corpus Cavernosum Against Fibrosis Induced by High-Fat Diet in an MMP-Dependent Mechanism. J Sex Med 2021;18:875-888.

AI-Based Estimation of End-Systolic Elastance From Arm-Pressure and Systolic Time Intervals

Left ventricular end-systolic elastance (E_es) is a major determinant of cardiac systolic function and ventricular-arterial interaction. Previous methods for the E_es estimation require the use of the echocardiographic ejection fraction (EF). However, given that EF expresses the stroke volume as a fraction of end-diastolic volume (EDV), accurate interpretation of EF is attainable only with the additional measurement of EDV. Hence, there is still need for a simple, reliable, noninvasive method to estimate E_es. This study proposes a novel artificial intelligence—based approach to estimate E_es using the information embedded in clinically relevant systolic time intervals, namely the pre-ejection period (PEP) and ejection time (ET). We developed a training/testing scheme using virtual subjects (n = 4,645) from a previously validated in-silico model. Extreme Gradient Boosting regressor was employed to model E_es using as inputs arm cuff pressure, PEP, and ET. Results showed that E_es can be predicted with high accuracy achieving a normalized RMSE equal to 9.15% (r = 0.92) for a wide range of E_es values from 1.2 to 4.5 mmHg/ml. The proposed model was found to be less sensitive to measurement errors (±10–30% of the actual value) in blood pressure, presenting low test errors for the different levels of noise (RMSE did not exceed 0.32 mmHg/ml). In contrast, a high sensitivity was reported for measurements errors in the systolic timing features. It was demonstrated that E_es can be reliably estimated from the traditional arm-pressure and echocardiographic PEP and ET. This approach constitutes a step towards the development of an easy and clinically applicable method for assessing left ventricular systolic function.

Follicular regulatory helper T cells control the response of regulatory B cells to a high-cholesterol diet

AIMS

B cell functions in the process of atherogenesis have been investigated but several aspects remain to be clarified.

METHODS AND RESULTS

In this study, we show that follicular regulatory helper T cells (TFR) control regulatory B cell (BREG) populations in Apoe-/- mice models on a high-cholesterol diet (HCD). Feeding mice with HCD resulted in up-regulation of TFR and BREG cell populations, causing the suppression of proatherogenic follicular helper T cell (TFH) response. TFH cell modulation is correlated with the growth of atherosclerotic plaque size in thoracoabdominal aortas and aortic root plaques, suggesting that TFR cells are atheroprotective. During adoptive transfer experiments, TFR cells transferred into HCD mice decreased TFH cell populations, atherosclerotic plaque size, while BREG cell population and lymphangiogenesis are significantly increased.

CONCLUSION

Our results demonstrate that, through different strategies, both TFR and TFH cells modulate anti- and pro-atherosclerotic immune processes in an Apoe-/- mice model since TFR cells are able to regulate both TFH and BREG cell populations as well as lymphangiogenesis and lipoprotein metabolism.

In vivo application and validation of a novel noninvasive method to estimate the end-systolic elastance

Accurate assessment of the left ventricular (LV) systolic function is indispensable in the clinic. However, estimation of a precise index of cardiac contractility, i.e., the end-systolic elastance (E_es), is invasive and cannot be established as clinical routine. The aim of this work was to present and validate a methodology that allows for the estimation of E_es from simple and readily available noninvasive measurements. The method is based on a validated model of the cardiovascular system and noninvasive data from arm-cuff pressure and routine echocardiography to render the model patient-specific. Briefly, the algorithm first uses the measured aortic flow as model input and optimizes the properties of the arterial system model to achieve correct prediction of the patient's peripheral pressure. In a second step, the personalized arterial system is coupled with the cardiac model (time-varying elastance model) and the LV systolic properties, including E_es, are tuned to predict accurately the aortic flow waveform. The algorithm was validated against invasive measurements of E_es (multiple pressure-volume loop analysis) taken from n = 10 patients with heart failure with preserved ejection fraction and n = 9 patients without heart failure. Invasive measurements of E_es (median = 2.4 mmHg/mL, range = [1.0, 5.0] mmHg/mL) agreed well with method predictions (normalized root mean square error = 9%, ρ = 0.89, bias = -0.1 mmHg/mL, and limits of agreement = [-0.9, 0.6] mmHg/mL). This is a promising first step toward the development of a valuable tool that can be used by clinicians to assess systolic performance of the LV in the critically ill.NEW & NOTEWORTHY In this study, we present a novel model-based method to estimate the left ventricular (LV) end-systolic elastance (E_es) according to measurement of the patient's arm-cuff pressure and a routine echocardiography examination. The proposed method was validated in vivo against invasive multiple-loop measurements of E_es, achieving high correlation and low bias. This tool could be most valuable for clinicians to assess the cardiovascular health of critically ill patients.

Zinc complexation improves angiotensin II receptor type 1 blockade and in vivo antihypertensive activity of telmisartan

Background: Angiotensin II receptor blockers were designed as therapeutic agents to block the binding site of the angiotensin II receptor type 1 (AT1R). Methodology: The structure of telmisartan was modified by coordination to the biometal Zn(II), resulting in the compound ZnTelm. Its antihypertensive activity and cellular mechanisms in comparison to telmisartan were studied. Results: Compared with telmisartan, ZnTelm displayed stronger binding to AT1R (binding studies on AT1R-transfected human embryonic kidney cells) and a greater reduction of reactive oxygen species and cytosolic calcium concentration induced by angiotensin II. The antihypertensive activity of the complex (assessed in an N(G)-Nitro-L-arginine methyl ester-induced hypertension model) was significantly higher. ZnTelm also reduced hypertrophy in aortic artery rings and tubular collagen deposition. Conclusion: ZnTelm enhances the AT1R blockade and consequently its antihypertensive effect.

Acute effects of transcatheter aortic valve replacement on the ventricular-aortic interaction

Transcatheter aortic valve replacement (TAVR) is linked with an immediate increase in aortic systolic blood pressure and maximal flow, as well as steeper aortic pressure and flow wave upstrokes. After TAVR, the forward wave pumped by the heart is enhanced. Although the arterial properties remain unchanged, the central augmentation index (AIx) is markedly decreased after TAVR. This challenges the interpretation of AIx as a solely vascular measure in patients with aortic valve stenosis.

MRI after successful eyeWatchTM implantation

The eyeWatch^TM is a new glaucoma drainage device that includes an adjustable mechanism that can vary the resistance to aqueous humor outflow during the postoperative period to reduce the burden of postoperative intraocular pressure (IOP) management. The mechanism contains a magnetic rotor that can be adjusted using an external magnetic control unit. Adjustments of the position of the rotor are performed mostly in the initial postoperative follow-up period in order to reach the target IOP. However, for some patients, it might be necessary to perform MRI for the sake of medical investigations. As the MRI is creating a strong magnetic field, this magnetic field is likely to interact with the adjustable rotor of the eyeWatch^TM, resulting in modification of the IOP. We report the case of an 82-old female patient successfully operated with the implantation of an eyeWatch^TM. The patient underwent a cerebral MRI for persistent headache. Shortly after the MRI procedure, the patient was checked at the eye clinic to assess the position of the rotor and to measure the IOP. The eyeWatch^TM was readjusted to the former position set before undergoing the MRI. No complications were reported in the follow-up after MRI. This case demonstrates that MRI examinations can be safely performed after glaucoma surgery using an eyeWatch^TM without compromising on the quality of the imaging or the stability of the IOP. This is a complication-free procedure that only requires checking the new position of the rotor and re-adjusting the implant, if necessary, to achieve the target IOP.

Early Morphofunctional Changes in AngII-Infused Mice Contribute to Regional Onset of Aortic Aneurysm and Dissection

Aortic aneurysms and dissections are silent and lethal conditions, whose pathogenesis remains incompletely understood. Although angiotensin II (AngII)-infused ApoE-/- mice have been widely used to study aortic aneurysm and dissection, early morphofunctional alterations preceding the onset of these conditions remain unknown. The goal of this study was to unveil early morphofunctional changes underlying the onset of aneurysm and dissection. At 3 days post-AngII infusion, suprarenal abdominal aorta presented significant volumetric dilatation and microstructural damage. Ex vivo assessment of vascular reactivity of the suprarenal dissection-prone aorta and its side branches, showed an endothelial and contractile dysfunctions that were severe in the suprarenal aorta, moderate distally, and absent in the side branches, mirroring the susceptibility to dissection of these different vascular segments. Early and specific morphofunctional changes of the suprarenal aorta may contribute to the regional onset of aortic aneurysm and dissection by exacerbating the biomechanical burden arising from its side branches.

Characterization of the Renin-Angiotensin System in Aged Cavernosal Tissue and its Role in Penile Fibrosis

BACKGROUND

The renin-angiotensin system (RAS) plays an important role in erectile function. The RAS contains 2 major axes: one deleterious, composed of ACE-Ang II-AT1 receptor, and another protective, composed of ACE2-Ang-(1-7)-Mas receptor. While aging is a well-known cause for development of male sexual disorders, little is known about local regulation of the RAS in age-related erectile dysfunction (ED).

AIM

The present study aimed to assess regulation of the RAS in aging-associated ED rat model and evaluate possible options for disease management through pharmacological modulation of the RAS.

METHODS

Penile tissues were harvested from 3-, 12-, and 24-month-old Wistar rats. Local expression of major RAS components and ED markers was measured by RT-PCR. Protein expression of RAS components was assessed by western blot. Collagen deposition was measured by Sirius Red and immunohistochemical staining. Evaluation of collagen content was also performed in penile sections of Mas-knockout mice by Sirius Red and Masson's trichrome stainings. Finally, the effect of Ang-(1-7) pretreatment on TGF-β-induced myofibroblast activation was studied in primary cavernosal and immortalized fibroblasts.

OUTCOMES

Experimental results highlighted the essential role of the RAS in modulation of cavernosal fibrosis.

RESULTS

The present study demonstrates local expression of angiotensinogen mRNA alongside with major RAS components, which suggests local autonomous functioning of the RAS within penile tissue. Gene expression analysis revealed strong positive correlation between ACE-Ang II-AT1 axis with markers for inflammation and fibrosis. While corpus cavernosum from 24-month-old rats was characterized by increased collagen deposition, protein expression of ACE, AT1, and Mas was shown to be upregulated in the penile tissue of this group. At the same time, penile sections from Mas-knockout mice (FVB/N background) were also shown to have increased collagen deposition. Finally, it was demonstrated that Ang-(1-7) treatment of primary cavernosal and immortalized fibroblasts was able to alleviate TGF-β-induced fibroblast-to-myofibroblast transition.

CLINICAL TRANSLATION

The present study suggests Ang-(1-7) treatment as a possible strategy for pharmacological management of fibrosis-associated ED in aging.

STRENGTHS & LIMITATIONS

The link between the RAS and penile fibrosis, indicated by a holistic screening of different ED markers, was confirmed by in vivo and in vitro data. However, results, presented in the manuscript, need to be further reinforced by human data. Important to note, the main goal of the study was to characterize RAS regulation in aging condition rather than state any causal relationships.

CONCLUSION

Present study characterizes RAS regulation in aging-associated ED and indicates its important role in cavernosal fibrosis. Bragina ME, Costa-Fraga F, Sturny M, et al. Characterization of the Renin-Angiotensin System in Aged Cavernosal Tissue and its Role in Penile Fibrosis. J Sex Med 2020;17:2129-2140.

Standardization and Validation of Fluorescence-Based Quantitative Assay to Study Human Platelet Adhesion to Extracellular-Matrix in a 384-Well Plate

Platelets play a crucial role in the immunological response and are involved in the pathological settings of vascular diseases, and their adhesion to the extracellular matrix is important to bring leukocytes close to the endothelial cells and to form and stabilize the thrombus. Currently there are several methods to study platelet adhesion; however, the optimal parameters to perform the assay vary among studies, which hinders their comparison and reproducibility. Here, a standardization and validation of a fluorescence-based quantitative adhesion assay to study platelet-ECM interaction in a high-throughput screening format is proposed. Our study confirms that fluorescence-based quantitative assays can be effectively used to detect platelet adhesion, in which BCECF-AM presents the highest sensitivity in comparison to other dyes.

Biomechanics of diastolic dysfunction: a one-dimensional computational modeling approach

Diastolic dysfunction (DD) is a major component of heart failure with preserved ejection fraction (HFpEF). Accordingly, a profound understanding of the underlying biomechanical mechanisms involved in DD is needed to elucidate all aspects of HFpEF. In this study, we have developed a computational model of DD by leveraging the power of an advanced one-dimensional arterial network coupled to a four-chambered zero-dimensional cardiac model. The two main pathologies investigated were linked to the active relaxation of the myocardium and the passive stiffness of the left ventricular wall. These pathologies were quantified through two parameters for the biphasic delay of active relaxation, which simulate the early and late-phase relaxation delay, and one parameter for passive stiffness, which simulates the increased nonlinear stiffness of the ventricular wall. A parameter sensitivity analysis was conducted on each of the three parameters to investigate their effect in isolation. The three parameters were then concurrently adjusted to produce the three main phenotypes of DD. It was found that the impaired relaxation phenotype can be replicated by mainly manipulating the active relaxation, the pseudo-normal phenotype was replicated by manipulating both the active relaxation and passive stiffness, and, finally, the restricted phenotype was replicated by mainly changing the passive stiffness. This article presents a simple model producing a holistic and comprehensive replication of the main DD phenotypes and presents novel biomechanical insights on how key parameters defining the relaxation and stiffness properties of the myocardium affect the development and manifestation of DD.NEW & NOTEWORTHY This study uses a complete and validated computational model of the cardiovascular system to simulate the two main pathologies involved in diastolic dysfunction (DD), i.e., abnormal active relaxation and increased ventricular diastolic stiffness. The three phenotypes of DD were successfully replicated according to literature data. We elucidate the biomechanical effect of the relaxation pathologies involved and how these pathologies interact to create the various phenotypes of DD.

Noninvasive Cardiac Output and Central Systolic Pressure From Cuff-Pressure and Pulse Wave Velocity

GOAL

We introduce a novel approach to estimate cardiac output (CO) and central systolic blood pressure (cSBP) from noninvasive measurements of peripheral cuff-pressure and carotid-to-femoral pulse wave velocity (cf-PWV).

METHODS

The adjustment of a previously validated one-dimensional arterial tree model is achieved via an optimization process. In the optimization loop, compliance and resistance of the generic arterial tree model as well as aortic flow are adjusted so that simulated brachial systolic and diastolic pressures and cf-PWV converge towards the measured brachial systolic and diastolic pressures and cf-PWV. The process is repeated until full convergence in terms of both brachial pressures and cf-PWV is reached. To assess the accuracy of the proposed framework, we implemented the algorithm on in vivo anonymized data from 20 subjects and compared the method-derived estimates of CO and cSBP to patient-specific measurements obtained with Mobil-O-Graph apparatus (central pressure) and two-dimensional transthoracic echocardiography (aortic blood flow).

RESULTS

Both CO and cSBP estimates were found to be in good agreement with the reference values achieving an RMSE of 0.36 L/min and 2.46 mmHg, respectively. Low biases were reported, namely -0.04 ± 0.36 L/min for CO predictions and -0.27 ± 2.51 mmHg for cSBP predictions.

SIGNIFICANCE

Our one-dimensional model can be successfully "tuned" to partially patient-specific standards by using noninvasive, easily obtained peripheral measurement data. The in vivo evaluation demonstrated that this method can potentially be used to obtain central aortic hemodynamic parameters in a noninvasive and accurate way.

On the importance of the nonuniform aortic stiffening in the hemodynamics of physiological aging

Mathematical models of the arterial tree constitute a valuable tool to investigate the hemodynamics of aging and pathology. Rendering such models as patient specific could allow for the assessment of central hemodynamic variables of clinical interest. However, this task is challenging, particularly with respect to the tuning of the local area compliance that varies significantly along the arterial tree. Accordingly, in this study, we demonstrate the importance of taking into account the differential effects of aging on the stiffness of central and peripheral arteries when simulating a person’s hemodynamic profile. More specifically, we propose a simple method for effectively adapting the properties of a generic one-dimensional model of the arterial tree based on the subject’s age and noninvasive measurements of aortic flow and brachial pressure. A key element for the success of the method is the implementation of different mechanisms of arterial stiffening for young and old individuals. The designed methodology was tested and validated against in vivo data from a population of n = 20 adults. Carotid-to-femoral pulse wave velocity was accurately predicted by the model (mean error = 0.14 m/s, SD = 0.77 m/s), with the greatest deviations being observed for older subjects. In regard to aortic pressure, model-derived systolic blood pressure and augmentation index were both in good agreement (mean difference of 2.3 mmHg and 4.25%, respectively) with the predictions of a widely used commercial device (Mobil-O-Graph). These preliminary results encourage us to further validate the method in larger samples and consider its potential as a noninvasive tool for hemodynamic monitoring.

NEW & NOTEWORTHY We propose a technique for adapting the parameters of a validated one-dimensional model of the arterial tree using noninvasive measurements of aortic flow and brachial pressure. Emphasis is given on the adjustment of the arterial tree distensibility, which incorporates the nonuniform effects of aging on central and peripheral vessel elasticity. Our method could find application in the derivation of important hemodynamic indices, paving the way for novel diagnostic tools.

From Patients to Platelets and Back Again: Pharmacological Approaches to Glycoprotein VI, a Thrilling Antithrombotic Target with Minor Bleeding Risks

Despite significant advances in the treatment of thrombogenic diseases, antiplatelet therapies are still associated with a high bleeding risk. Consequently, potential benefits of preventing thromboembolic events by pharmacological agents need to be balanced with the potential harm of inducing hemorrhage. Glycoprotein VI (GPVI) is a platelet-specific receptor, which plays a crucial role in thrombus formation. GPVI deficiency has been identified in patients who suffer from significant reduction of collagen-induced thrombus formation, with a slight tendency for mild bleeding. However, an isolated GPVI deficiency can reduce thrombus formation while not resulting in severe bleeding. Together, these observations strongly suggest that physiological hemostasis does not require GPVI, but pharmacological GPVI modulation may provide novel “bleeding-free” antithrombotic therapies. In this review, we discuss recent findings regarding the biological role of GPVI in platelet-related disorders and highlight the efforts to develop potential therapeutic strategies based on its structure, signaling pathways, and biological effects.

Synchrotron-based visualization and segmentation of elastic lamellae in the mouse carotid artery during quasi-static pressure inflation

In computational aortic biomechanics, aortic and arterial tissue are typically modelled as a homogeneous layer, making abstraction not only of the layered structure of intima, media and adventitia but also of the microstructure that exists within these layers. Here, we present a novel method to visualize the microstructure of the tunica media along the entire circumference of the vessel. To that end, we developed a pressure-inflation device that is compatible with synchrotron-based phase-contrast imaging. Using freshly excised left common carotid arteries from n = 12 mice, we visualized how the lamellae and interlamellar layers inflate as the luminal pressure is increased from 0 to 120 mm Hg in quasi-static steps. A graph-based segmentation algorithm subsequently allowed us to automatically segment each of the three lamellae, resulting in a three-dimensional geometry that represents lamellae, interlamellar layers and adventitia at nine different pressure levels. Our results demonstrate that the three elastic lamellae unfold and stretch simultaneously as luminal pressure is increased. In the long term, we believe that the results presented in this work can be a first step towards a better understanding of the mechanics of the arterial microstructure.

Α systematic review and meta-analysis of the efficacy of aortic anastomotic devices

OBJECTIVE

One of the factors contributing to complications related to open repair of the aorta is the construction of a hand-sewn anastomosis. Aortic anastomotic devices (AADs), such as the intraluminal ringed graft (IRG), and the anastomotic stenting technique have been developed to perform a sutureless and less complicated anastomosis. This study performed a systematic review and meta-analysis of the literature reporting clinical use of AADs and aimed to assess, primarily, the effect of each device on 30-day overall and operation-related mortality and aortic cross-clamping time and, secondarily, the rate of successful two-sided application of the IRG device and the operation-related morbidity for each device.

METHODS

An electronic search was performed using MEDLINE, Scopus, ScienceDirect, and Cochrane Library by two independent authors. Our exclusion criteria included studies incorporating fewer than three patients and studies reporting results solely from animals or in vitro testing, results solely from end-to-side anastomosis, and results solely from endarterectomy procedures. The last search date was February 1, 2018.

RESULTS

A total of 41 studies were identified that reported outcomes for the use of three different device types: IRG, anastomotic stenting technique, and surgical staplers. The last two types were classified together as the non-IRG group. The meta-analysis included 27 studies with 50 cohorts incorporating 1260 patients. The median age of the incorporated patients was 61.4 years (range, 51-73 years), and 68.9% were male. The operations were performed for the treatment of acute aortic dissection in 82.3%. The pooled overall 30-day mortality rate varied by device type; IRG devices had a mean rate of all-cause mortality of 9.71%, whereas non-IRG devices were associated with a significantly (I² = 15.78%; P for Cochrane Q test < .19) lower rate of death (1.47%). The pooled mean aortic cross-clamping time was 35.83 minutes. Metaregression showed that the performance of two-sided anastomosis with the IRG device significantly decreased the aortic cross-clamping time. However, a successful two-sided ringed anastomosis was performed in approximately half of the cases.

CONCLUSIONS

Taking into account that the majority of operations were performed for the treatment of acute aortic dissection, AADs had a relatively low rate of 30-day mortality. Despite the observed heterogeneity in study protocols and the small sample size in the non-IRG group, the non-IRG group presented with the lowest 30-day mortality rate. Specific device-related complications between the different device types need further investigation.

Age-related changes in vascular responses to angiotensin-(1-7) in female mice

The vasodilatory effect of angiotensin-(1-7) seems to vary between sexes, and estradiol (E2) can modulate the magnitude of the Ang-(1-7) vasodilatory response in female rats. However, there are few studies addressing the influence of sex on the age-related vasodilatory effect of Ang-(1-7). Here, we evaluated the vasodilatory response to Ang-(1-7) on vascular ageing. Ang-(1-7) dose-response curves were determined in mice aortic rings from males (old and young) and females (E2 treated/non-treated old and young) mounted in an isolated organ chamber. Abdominal aortic rings were used for protein expression analysis and determination of reactive oxygen species (ROS) and nitric oxide (NO) production. Our results showed that the Ang-(1-7) vasodilatory effect was absent in aorta from old females, contrasting with a full response in vessels from young females. The Ang-(1-7) vasodilatory effect was restored by E2 replacement in old females. A robust increase in Mas receptor, SOD2, NRF-2 and NOX2 expression was observed in aorta from old females, which was normalized by E2. This effect of E2 was also associated with lower production of ROS and normal levels of NO. In conclusion, our data demonstrated that pathways involved in the Ang-(1-7) vasodilatory response in female mice is affected by hormonal changes in ageing and rescued by E2.

An optimized and validated 384-well plate assay to test platelet function in a high-throughput screening format

Despite significant advances in the treatment of cardiovascular diseases, antiplatelet therapies are still associated with a high risk of hemorrhage. In order to develop new drugs, methods to measure platelet function must be adapted for the high-throughput screening (HTS) format. Currently, all assays capable of assessing platelet function are either expensive, complex, or not validated, which makes them unsuitable for drug discovery. Here, we propose a simple, low-cost, and high-throughput-compatible platelet function assay, validated for the 384-well plate. In the proposed assay, agonist-induced platelet activity was assessed by three different methods: (i) measurement of light absorbance, which decreases with platelet aggregation; (ii) luminescence measurement, based on ATP release from activated platelets and luciferin-luciferase reaction; and (iii) automated bright-field microscopy of the wells and further quantification of platelet image area, described here for the first time. Brightfield imaging results were validated by demonstrating the similarity of dose-response curves obtained with absorbance and luminescence measurements after stimulating platelets, pre-incubated with prostaglandin E1 or tirofiban, and demonstrating the similarity of dose-response curves obtained with agonists. Assay quality was confirmed using the Z'-factor, a statistical parameter used to validate the robustness and suitability of an HTS assay. The results showed that, under high rotations per minute (1200 RPM), an acceptable Z'-factor score is reached for absorbance measurements (Z'-factor - 0.58) and automated brightfield imaging (Z'-factor - 0.52), without the need of replicates, while triplicates must be used to achieve an acceptable Z'-factor score (0.54) for luminescence measurements. Using low platelet concentration (4 × 10⁴/μl - 10 μl), the brightfield imaging test was further validated using washed platelets. Furthermore, drug screening was performed with compounds selected by structure-based virtual screening. Taken together, this study presents an optimized and validated assay for HTS to be used as a tool for antiplatelet drug discovery.

Apelin-13 treatment enhances the stability of atherosclerotic plaques

BACKGROUND

Apelin is an endogenous peptidergic system which modulates cardiovascular function. Recent studies pointed out a fundamental contribution of apelin on atherosclerosis development; however, such reports revealed contradictory data, and to date, it is difficult to accurately define a beneficial or deleterious role. To better understand apelin function on atherosclerosis, we aimed to investigate apelin-13 treatment effects on atherosclerotic plaques composition.

DESIGN

Apolipoprotein E gene-deleted mice were fed on Western-type diet for 11 weeks. Atherosclerotic plaque formation was induced in the carotid artery by a shear stress modifier device, which exposes the same vessel to distinct patterns of shear stress enabling the formation of plaques with different composition. Mice were treated with apelin-13 (2 mg kg^-1 day^-1 ) or vehicle for the last 3 weeks.

RESULTS

Apelin-13 treatment did not alter the lipid content of low shear stress- and oscillatory shear stress-induced plaques in the carotid. However, apelin-13 greatly ameliorated plaque stability by increasing intraplaque collagen content and reducing MMP-9 expression. Furthermore, apelin-13 decreased the infiltration of inflammatory cells (neutrophil and macrophage) and intraplaque reactive oxygen species content. Interestingly, apelin-13 treatment reduced total cholesterol, LDL levels and free fatty acid serum levels, while HDL, triglycerides serum levels were not significantly changed.

CONCLUSIONS

Apelin-13 treatment for 3 weeks did not alter the lesion size, but it significantly enhanced the stable phenotype of atherosclerotic plaques and improved serum lipid profile. These results indicate that activation of apelin system decreases plaque vulnerability.