Valve Opening Area Research Articles

Computational Study on the Effects of Valve Orientation on the Hemodynamics and Leaflet Dynamics of Bioprosthetic Pulmonary Valves.

Pulmonary valves do not display a fibrous annulus as do other valves in the heart; thus, pulmonary valves can be implanted at multiple orientations and locations within the right ventricular outflow tract (RVOT). This gives surgeons more freedom when implanting the valve but it also results in uncertainties regarding placement, particularly with respect to valve orientation. We investigate the pulmonary artery hemodynamics and valve leaflet dynamics of pulmonary valve replacements (PVRs) with various orientations via fluid-structure interaction (FSI) models. A canonical model of the branching pulmonary artery is coupled with a dynamic model of a pulmonary valve, and from this we quantify the effect of valve implant orientation on the postvalvular hemodynamics and leaflet dynamics. Metrics such as turbulent kinetic energy (TKE), branch pulmonary artery flow distributions, projected valve opening area (PVOA), and pressure differentials across the valve leaflets are analyzed. Our results indicate that off-axis orientation results in higher pressure forces and flow and energy asymmetry, which potentially have implications for long-term durability of implanted bioprosthetic valves.

Enhancing pressure control of low-friction pneumatic actuator with eddy current damper via valve dead-zone compensation

This article addresses the high-performance pressure control of a pneumatic actuator that incorporates an air-bearing piston and an eddy current damper (ECD). After optimizing the pneumatic actuator, achieving precise pressure control relies on maintaining an accurate and stable airflow through the control valve. A terminal sliding mode adaptive control method (TSMAC) is proposed, proficiently integrating considerations for dead zone nonlinearities in the proportional valve and the effects of unmodeled disturbances in the pneumatic actuator. Using the opening area of the proportional valve as the input to the pneumatic system greatly simplifies the control process and reduces the workload required for valve parameter calibration. The Lyapunov-based stability analysis demonstrates that excellent asymptotic output tracking can be achieved with low steady-state error simply by knowing the boundaries of the valve opening area. The control effect of the proposed control strategy is compared with an adaptive backstepping sliding mode control method based on a linearly fitted proportional valve model on an established constant pressure control test bench. Experimental results under various loads and operating conditions illustrate the effectiveness of the proposed approach.

In-vivo validation of a nomogram with isostiffness-lines for the assessment of aortic stenosis severity

Abstract Background In patients with low-flow, low-gradient aortic stenosis, the aortic valve opening area (AVA) projected at a higher standardized transvalvular flow (Q) is used to assess the severity of aortic stenosis. It assumes a linear relation between Q and AVA. We investigated whether a sigmoid function better captured this relation and whether a nomogram could be constructed. Methods We measured instantaneous AVA and Q in 142 patients with the whole spectrum of AS including very low-flow situation on one ejection cycle. We defined a linear and a sigmoid function containing hyperparameters as well as the relative stiffness. Using a k-fold cross validation algorithm, we first trained the hyperparameters of each function on the subgroup of patients with normal aortic valve. Using the obtained hyperparameters, we then fitted the relative stiffness for each of the patients with AS on the lowest 70%, 50%, 30% and 10% Q of the {Q:AVA} data points of the ejection cycle. We then assessed the accuracy of the two models by computing the mean squared error (MSE) of the predicted AVA vs the measured AVA on the remaining 30%, 50%, 70% and 90% data points and the Akaike Information Criterion (AIC). A receiver operating characteristic (ROC) analysis with computation of its area under the curve (AUC) was performed on the entire range of possible threshold of the relative stiffness to discriminate between severe from non severe aortic stenosis. Results The sigmoid consistently better predicted the remaining 70%, 50%, 30% and 10% AVA than the linear model (MSE: 6.62e-6 vs 14.11e-6, 4.90e-6 vs 12.39e-6, 4.90e-6 vs 14.84e-6, 4.90e-6 vs 22.99e-6; AIC: -7933 vs -7428, -13341 vs -12328, -13341 vs -16990, -13341 vs -21031, respectively). The first figure depicts the assessment of the AVA predicted with the linear (left panel) and sigmoid (right panel) model with Q of the 30% highest Q values with linear regression. The black line on the linear regression graphs represent the identity function (f (x) = x). The closer to this line are the points, the more accurate is the prediction. In the ROC analysis, the calculated AUC was 0.88, performed on all patients with relative stiffness obtained on the first 70% Q of the {Q;AVA} data points. The most discriminative relative stiffness threshold was 1.51 with a corresponding accuracy of 0.85. The second figure depicts a nomogram with mean and confidence interval of iso-stiffness lines for each severity with the following color code: group of normal aortic valve in green, group of mild aortic stenosis in blue, group of moderate aortic stenosis in orange and group of severe aortic stenosis in red. The iso-stiffness line with most discriminant relative stiffness computed on the group of patients with moderate and severe aortic stenosis is depicted in black. Conclusion This study allows to construct a nomogram to compare the stiffness of the aortic valve of any patient at any Q, simplifying the severity grading system of AS.Accuracy of AVA predictionNomogram with iso-stiffness lines

Experimental evaluation of the effect of leakage in scroll compressor

This research gives an experimental investigation of the scroll compressor, with an emphasis on the effect of leakage on performance enhancement. The effect of gas leakage losses on com-pressor performance is studied both experimentally and conceptually. In the present study, we have modified the scroll compressor to bypass the refrigerant through an orifice called leakage and experimentally investigate the effect of valve opening area and angle to observe the effect of leak gas on compressor performance, compressor capacity loss, discharge line temperature rise, and discharge gas temperature. Experimental results indicated that the maximum per-centage rise in suction superheat is observed to be 7.13% at a maximum effective valve open-ing area of 0.33 m2, whereas the rise in discharge line temperature lies in the range of 0.8% to 2.75% over the entire range of effective leak area. In addition, based on experimentation the 8.9 % maximum compressor capacity loss is observed.

Potential Clinical Usefulness of Post-Valvular Contrast Densities to Determine the Severity of Aortic Valve Stenosis Using Computed Tomography.

Different methods are established for the changes in aortic valve stenosis with cardiac computed tomography angiography (CCTA), but the effect of the grade of stenosis on contrast densities around the valve has not been investigated. Using the information from flow dynamics in cases of increased velocity through narrowed lumen, the hypothesis was formed that flow changes can alter the contrast densities in stenotic post-valvular regions, and the density changes might correlate with the grade of stenosis. Forty patients with severe aortic stenosis and fifteen with a normal aortic valve were enrolled. With echocardiography, the peak/mean transvalvular gradients, peak transvalvular velocity, and aortic valve opening area were obtained. With CCTA, densities 4-5 mm above the aortic valve; at the junction of the left, right, and noncoronary cusp to the annulus; at the middle level of the left, right, and noncoronary sinuses of Valsalva in the center and the lateral points; at the sinotubular junction; and 4 cm from the sinotubular junction at the midline were measured. First, a comparison of the densities between the normal and stenotic valve was performed, and then possible correlations between echocardiography and CCTA values were investigated in the stenotic group. In all CCTA regions, significantly lower-density values were detected among stenotic valve patients compared to the normal aortic valve population. Additionally, in both groups, higher densities were measured in the peri-jet regions than in the lateral ones. Furthermore, a good correlation was found between the aortic valve opening area and the densities in almost all perivalvular areas. With regard to the densities at the junction of the non-coronary leaflet to the fibrotic annulus and at the most lateral point of the right sinus of Valsalva, a high level of correlation was found between all echocardiography and CCTA parameters. Lastly, with receiver operating characteristic curve measurements, area under the curve values were between 0.857 and 0.930. Certain CCTA density values, especially 4-5mm above the valve opening, can serve as auxiliary information to echocardiography when the severity of aortic valve stenosis is unclear.

Functional interaction of aortic valve and ascending aorta in patients after valve-sparing procedures

Pressure recovery (PR) is essential part of the post stenotic fluid mechanics and depends on the ratio of EOA/AA, the effective aortic valve orifice area (EOA) and aortic cross-sectional area (AA). In patients with advanced ascending aortic aneurysm and mildly diseased aortic valves, the effect of AA on pressure recovery and corresponding functional aortic valve opening area (ELCO) was evaluated before and after valve-sparing surgery (Dacron graft implantation). 66 Patients with ascending aortic aneurysm (mean aortic diameter 57 +/− 10 mm) and aortic valve-sparing surgery (32 reimplantation technique (David), 34 remodeling technique (Yacoub)) were routinely investigated by Doppler echocardiography. Dacron graft with a diameter between 26 and 34 mm were implanted. EOA was significantly declined after surgery (3.4 +/− 0.8 vs. 2.6 +/− 0.9cm2; p < 0.001). Insertion of Dacron prosthesis resulted in a significant reduction of AA (26.7 +/− 10.2 vs. 6.8 +/− 1.1cm2; p < 0.001) with increased ratio of EOA/AA (0.14 +/− 0.05 vs. 0.40 +/− 0.1; p < 0.001) and pressure recovery index (PRI; 0.24 +/− 0.08 vs. 0.44 +/− 0.06; p < 0.0001). Despite reduction of EOA, ELCO (= EOA corrected for PR) increased from 4.0 +/− 1.1 to 5.0 +/− 3.1cm2 (p < 0.01) with reduction in transvalvular LV stroke work (1005 +/− 814 to 351 +/− 407 mmHg × ml, p < 0.001) after surgery. These effects were significantly better in patients with Yacoub technique than with the David operation. The hemodynamic findings demonstrate a valve-vessel interaction almost entirely caused by a marked reduction in the ascending AA with significant PR gain. The greater hemodynamic benefit of the Yacoub technique due to higher EOA values compared to the David technique was evident and may be of clinical relevance.

Throttling Loss Energy-Regeneration System Based on Pressure Difference Pump Control for Electric Forklifts

At present, the hydraulic systems of electric forklifts and traditional internal combustion forklifts are mostly valve-controlled speed-regulation systems, which have large throttling losses and potential energy waste. To further improve the energy-saving ability of electric forklifts, the forklift’s common working conditions are analyzed in this paper. A throttling loss energy-regeneration system based on pressure difference pump control is designed, and the system’s working principle is described. Aiming to deal with the problem that the pump−valve compound speed regulation with constant pressure difference could not realize high controllability and energy saving at the same time, a control strategy for variable pressure difference pump−valve compound speed regulation based on pressure balance control is proposed. The handle signal is positively related to the target speed of the oil cylinder. In the low-speed stage, the closed-loop control of the actual output torque of the motor/generator keeps the pressure difference across the proportional throttle valve unchanged, and the speed adjustment is realized by changing the opening of the proportional throttle valve. In the high-speed stage, the valve opening area is kept unchanged and the target pressure difference is changed to achieve the target speed. Finally, the feasibility of the control strategy is verified through an AMESim simulation, and the minimum pressure difference switching point is determined through experiments. The experiments show that the system’s energy-saving efficiency can reach 21.5% under a 1 t load. With the increase in the load, the system’s energy-saving efficiency can be further improved.

P357 DOES CARDIAC AMYLOIDOSIS EVER HIDE A SEVERE AORTIC STENOSIS A CASE REPORT

Abstract Case presentation: A 89-year-old man, with an history of paroxysmal atrial fibrillation and chronic renal disease, was admitted to our ER for acute decompensated heart failure. He reported dyspnea on minimal exertion and worsening peripheral edema. He had a history of heart failure and a severe aortic stenosis first diagnosed in 2020 with an echocardiogram demonstrating a left ventricular ejection fraction (LVEF) of 30% and a low-flow low-gradient aortic stenosis (AVA=0,6 cmq, mean pressure gradient=21 mmHg). Besides, in 2019, he underwent a 99m Tc MDP scintigraphy for a prostatic nodule which showed important myocardial uptake of the bone tracer highly suggestive of cardiac amyloidosis. Urinary light chain assessment and determination of immunoglobulin light chain levels were negative for AL amyloidosis. The electrocardiogram showed: sinus rhythm, low voltage in the frontal leads and complete left bundle branch block with secondary repolarization abnormalities. The patient underwent transthoracic echocardiography for staging the severity of the aortic valve stenosis, which revealed borderline results: the aortic valve area was 0.5 cmq with a transaortic mean pressure gradient of 20 mmHg (EF 25%, with GLS of −5%). Low-dose dobutamine stress echocardiography was performed. At rest conditions, there was global hypokinesia with an ejection fraction of 24%. Aortic valve mean pressure was 19 mmHg referring to a calculated aortic valve opening area of 0,78 cmq. Under peak dobutamine stress (30 mcg/kg/min), LVEF increased to 36%. On the basis of these diagnostic findings, aortic stenosis was classified as pseudo-severe due to systolic dysfunction of the left ventricle with preserved contractile reserve. Besides, aortic calcium score of 574 confirmed that the aortic stenosis was non severe. Conclusions This case results exemplary of the fact that amyloidosis does not always hide a severe stenosis. Actually the echo with dobutamine indicates a non-valvular reason for heart-failure and no indication for valve replacement.The discharge suggestions consists of clinical/ echo follow ups and TTR stabilizers. Anyway, Tafamidis is not recommended because of the age and the patient short life expectancy. The implantation of CCM which, during the action potential platea delivers non-excitatory electrical currents and enhances systolic function in patients with heart failure, is proposed to obtain an improvement of symptoms.

Evidence for a sigmoidal flow-to-valve opening relation in low-flow low-gradient aortic stenosis.

We analyzed the relationship between flow (Q) and aortic valve opening area (AVA) using a sequence of echocardiographic stress tests of increasing strength. Low-dose dobutamine stress echocardiography (DSE) has been used to differentiate pseudo-severe from true severe aortic stenoses. Because the Q-response to DSE is so variable between individuals, AVA has been projected to a standardized flow (AVAproj) using linear interpolation. A linear Q-to-AVA relation implies that AVA shows an unconstrained increase. We applied three stress maneuvers of increasing strength to investigate whether AVA shows signs of saturation. We performed an echocardiographic examination at rest, during the passive leg raise maneuver ("PLR"), maximal dobutamine infusion ("Dmax"), and their combination ("Dmax + PLR") in 45 patients with severe low-flow, low-gradient aortic stenosis. We analyzed the effect of the stress maneuver on Q, AVA, valve compliance (VC), and AVAproj. We also compared the proportion of patients with nonconclusive test (ΔQ < 20%) between stress maneuvers. We computed the Akaike information criterion (AIC) to compare a linear with a saturating function for the Q-AVA relation. Q gradually increased from "PLR" to "Dmax" to "Dmax + PLR" (P < 0.0001), whereas the number of nonconclusive tests concomitantly diminished from n = 35 to n = 3. The stress sequence increased AVA (P < 0.001) but decreased AVAproj (P = 0.006) and VC (P = 0.005). In the pooled Q-AVA data, the AIC value was lower for the saturating (sigmoidal) model compared with the linear model fitting (-1,593 vs. -1,504). "Dmax + PLR" is capable of reducing the number of nonconclusive DSE tests. With increasing stress strength, the Q-AVA relation progressively flattens, indicating saturation.NEW & NOTEWORTHY The relation between transaortic flow (Q) and aortic valve opening area (AVA) shows a saturation when three different stress maneuvers are used to increase Q as much as possible. This has implications for the assessment of aortic stenosis severity.

Sigmoid isostiffness-lines: An in-vitro model for the assessment of aortic stenosis severity.

IntroductionThe aortic valve opening area (AVA), used to quantify aortic stenosis severity, depends on the transvalvular flow rate (Q). The currently accepted clinical echocardiographic method assumes a linear relation between AVA and Q. We studied whether a sigmoid model better describes this relation and determined “isostiffness-lines” across a wide flow spectrum, thus allowing building a nomogram for the non-invasive estimation of valve stiffness.MethodsBoth AVA and instantaneous Q (Qinst) were measured at 10 different mean cardiac outputs of porcine aortic valves mounted in a pulsatile flow loop. The valves' cusps were chemically stiffened to obtain three stiffness grades and the procedure was repeated for each grade. The relative stiffness was defined as the ratio between LV work at grade with the added stiffness and at native stiffness grade. corresponding to the selected of the highest 3 and 5 cardiac output values was predicted in K-fold cross-validation using sequentially a linear and a sigmoid model. The accuracy of each model was assessed with the Akaike information criterion (AIC).ResultsThe sigmoid model predicted more accurately (AIC for prediction of AVA with of the 3 highest cardiac output values: –1,743 vs. –1,048; 5 highest cardiac output values: –1,471 vs. –878) than the linear model.ConclusionThis study suggests that the relation between AVA and Q can be better described by a sigmoid than a linear model. This construction of “isostiffness-lines” may be a useful method for the assessment of aortic stenosis in clinical echocardiography.

Serial measurements of myocardial efficiency in patients with aortic valve stenosis: pathophysiological insights and prognostic information

Abstract Background In patients with aortic valve stenosis (AS), the pathophysiological abnormalities involved in the transition to symptomatic heart failure are unclear. During progression of chronic heart failure, the coupling between myocardial stroke work and myocardial oxygen consumption, i.e. myocardial external efficiency (MEE), deteriorates. However, in AS patients it is unknown whether changes in MEE over time are involved in disease progression and whether MEE has prognostic information. Purpose In patients with AS, we 1) investigated changes in MEE over time and 2) studied if MEE was associated with long-term prognosis. Methods In a prospective design, we studied 10 healthy controls and 38 patients with moderate-severe, asymptomatic AS (aortic valve area 0.5±0.1 cm2/m2, mean gradient 31±12 mmHg) and left ventricular ejection fraction ≥50%. The patient group was evaluated by serial 11C-acetate positron emission tomography, cardiovascular magnetic resonance imaging and echocardiography with a median follow-up period of 2.8 years. Furthermore, we conducted an extended follow-up of patients for a median of 5.2 years to detect clinical events (defined as symptoms due to AS, aortic valve replacement, hospitalization due to heart failure or cardiovascular death) and related them to MEE changes. Results During follow-up AS patients mean aortic valve pressure gradients increased by 13 mmHg (9 to 17; p&amp;lt;0.001) (mean (95% confidence interval)) and aortic valve opening area declined by −0.15 cm2 (−0.20 to −0.09; p&amp;lt;0.001). Global longitudinal strain worsened by 2.6% (1.8 to 3.5; p&amp;lt;0.001) and N-terminal pro-B-type natriuretic peptide increased by 162 ng/L (28 to 296; p=0.02) whereas left ventricular ejection fraction and cardiac index did not change significantly. MEE increased during follow-up by 4.3% (1.9 to 6.8; p=0.001) from 25.2% (24.0 to 26.5) to 29.5% (27.3 to 31.8) and was higher compared to healthy volunteers 19.9% (18.1 to 21.8; p&amp;lt;0.001). The changes in MEE were positively correlated to changes in end-diastolic volume (r=0.58, p=0.005) and wall stress (r=0.54, p=0.01). There were no changes in MVO2 0.0 mL/min/100g (−0.8 to 0.8; p=0.98) during follow-up. As compared to event-free patients, patients who experienced a clinical event during long-term follow-up (n=24, 63%) had higher baseline MEE 26.5% (24.3 to 28.6) vs 23.8% (22.6 to 25.1) (p=0.04) and did not increase MEE during follow-up 1.9% (−1.8 to 5.6; p=0.28) vs 5.9% (2.6 to 9.2; p=0.002). Conclusion In asymptomatic AS patients, MEE increased over time in tandem with increasing transvalvular gradients and wall stress. Thus, the myocardium displayed an inherent capacity to improve the coupling between oxidative metabolism and contractile function in response to pressure overload. High baseline MEE and blunted MEE increase predicted a poor prognosis. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): Lundbeck FoundationArvid Nilssons Foundation

Computational Analysis of Flow Structures in Turbulent Ventricular Blood Flow Associated With Mitral Valve Intervention.

Cardiac disease and clinical intervention may both lead to an increased risk for thrombosis events due to a modified blood flow in the heart, and thereby a change in the mechanical stimuli of blood cells passing through the chambers of the heart. Specifically, the degree of platelet activation is influenced by the level and type of mechanical stresses in the blood flow. In this article we analyze the blood flow in the left ventricle of the heart through a computational model constructed from patient-specific data. The blood flow in the ventricle is modelled by the Navier-Stokes equations, and the flow through the mitral valve by a parameterized model which represents the projected opening of the valve. A finite element method is used to solve the equations, from which a simulation of the velocity and pressure of the blood flow is constructed. The intraventricular blood flow is complex, in particular in diastole when the inflow jet from the atrium breaks down into turbulent flow on a range of scales. A triple decomposition of the velocity gradient tensor is then used to distinguish between rigid body rotational flow, irrotational straining flow, and shear flow. The triple decomposition enables the separation of three fundamentally different flow structures, that each generates a distinct type of mechanical stimulus on the blood cells in the flow. We compare the results in a simulation where a mitral valve clip intervention is modelled, which leads to a significant modification of the intraventricular flow. Further, we perform a sensitivity study of the results with respect to the positioning of the clip. It was found that the shear in the simulation cases treated with clips increased more compared to the untreated case than the rotation and strain did. A decrease in valve opening area of 64% in one of the cases led to a 90% increase in rotation and strain, but a 150% increase in shear. The computational analysis opens up for improvements in models of shear-induced platelet activation, by offering an algorithm to distinguish shear from other modalities in intraventricular blood flow.

Investigation of Risk Factors for Postoperative Delirium after Transcatheter Aortic Valve Implantation: A Retrospective Study.

Transcatheter aortic valve implantation (TAVI) is an effective treatment for severe aortic stenosis (AS); however, postoperative delirium (POD) can worsen patient outcomes. This study aimed to examine the risk factors for POD after TAVI, including possible intervening factors. We included 87 patients (mean age: 83) who underwent TAVI between May 2014 and September 2018. POD was defined by the presence or absence of delirium on ICU admission, assessed using the Confusion Assessment Method for the ICU. Factors that showed significant differences in the univariate analysis were analyzed using a multiple logistic regression analysis. In total, 31 patients (36%) had POD after ICU admission, and 56 (64%) did not. The preoperative frailty score and aortic valve opening area (AVA) were significant risk factors for POD. The multivariate analysis also showed that both factors were independent risk factors for POD (area under the receiver operating characteristic curve: 0.805). There were no significant differences in the number of ICU days. However, postoperative hospitalization was significantly longer in the POD group (19 (17–31) days vs. 16 (13–22) days; p = 0.002). POD was associated with a narrow AVA and frailty; this suggests that frailty prevention interventions according to the AVA may be important.

Visual measurement of valve opening area with improved subpixel edge location

The opening area error of the gas valve is mainly caused by machining, assembling errors and transmission clearances. Accurate measurement of the opening area is important for the production quality inspection of gas valves. This paper proposes a novel solution with a specific measurement system. Due to the reflective effect of the valve surface, the valve opening’s saliency is enhanced by the combination of top lighting and camera exposure. Then, a partial image is used to extract the single closed edge of the valve opening. To obtain the precise edge position, a subpixel location based on the rotating area effect is applied. Finally, the area computation based on the minimum circumscribed circle and the maximum inner circle of the edge is provided. The experiment results prove the system reliability, and the general significances of the proposed algorithms.

An in-vitro model of stiffened aortic valves to develop an iso-stiffness-lines graph for aortic stenosis classification

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Bern Center for Precision Medicine (BCPM) Introduction The echocardiographic diagnosis of aortic stenosis (AS) is established by assessing its maximal opening area (OA). The behavior of OA is dependent on transvalvular flow which can be low in case of low-flow, low-gradient AS. However, the complicated decision tree of the current guidelines for the assessment of AS does not consider flow but rather a stroke volume and does not take into account the size of the valve. This experiment was designed to create a graphical representation of the OA versus flow for various valve stiffness values to eventually build a model with iso-stiffness lines and simplify the assessment of aortic stenosis Methods We filmed a harvested porcine aortic valve mounted in a pulsatile flow loop during the ejection time with a high speed camera (2000Hz), measured for each time point OA and the instantaneous flow through the aortic valve at 10 different mean flow rates (ranging from 0.5 to 5.0 liters/min). We stiffened the valve by treating it with a protein cross-linking agent (formaldehyde) to yield a total of three stiffness grades (a, b, c) and repeated the procedure for each of those grades. We divided both OA and flow, by the area of left ventricular outflow tract (LVOT) in order to account for different valve sizes. We plotted each OA against its corresponding flow after correcting for the intersignal delay. In order to analyze the cycle portion corresponding to the most steady flow, we only included the 5% highest instantaneous flow rates (for each of the 10 mean flow rates). We then measured the relative stiffness by measuring the relative pump work between stiffness grades, 1 being defined as the native stiffness grade. We predicted relative stiffness grade of each valve in a k-fold validation algorithm (each valve being sequentially taken as the test set and all the other remaining valves in the training set), taking a sigmoid function model. Finally we performed a linear regression of each measured and predicted stiffness grade of each valve to assess the accuracy of the model. Results We could analyze 11 valves and performed an 11-fold cross validation. We could predict the relative stiffness of each of the valve with a good slope value (slope = 0.898) and a modest accuracy (r = 0.639). Conclusions We could predict with modest accuracy the inherent stiffness of the valve only with valve size, flow and opening area, all information available with echocardiography. This will allow to create iso-stiffness line to better classify valve stenosis and compare any patient on one single graph at any flow or valve" size, potentially simplifying the grading system of aortic stenosis, especially for patient with low-flow, low-gradient AS. Abstract Figure. Combination of Flow and OA Abstract Figure. 3 stiffness stages and Cross-validation

Design and Analysis of Prosthetic Heart Valves and Assessing the Effects of Leaflet Design on the Mechanical Attributes of the Valves

Prosthetic heart valves are commonly used as a treatment for aortic valve deficiencies. The performance of these prosthetic valves should be in accordance with the natural heart valve with respect to opening and closing, blood flow, and vortex formation. These performance parameters depend on the design of leaflets and overall geometrical parameters of the valve. To better understand the effects of leaflet design on the performance of the valve, we have carried out fully coupled fluid–structure interaction analyses of opening and closing of prosthetic heart valves with various leaflet designs. Maximum stress, valve opening, and flow stream pattern are obtained for different valve designs and used to assess the performance of the valves. The results show that the stress and the valve opening depend on the curvature and the inclination of the leaflets. A 3D model is designed based on the obtained results, and a full FSI analysis is performed to assess its performance. The results show that the presented design gives better values for valve opening area and leaflet stresses than that in the published data.

Artificial neural networks controller of active suspension for ambulance based on ISO standards

The level of vibration to which a patient is subjected in an ambulance is often too high. Ambulance personnel should take steps to reduce these vibrations. To avoid slowdowns and other barriers that create high vibration peaks, the speed is reduced or the ambulance deviates from the quicker or shorter path. This work implements Artificial Neural Network (ANN) control over five low-cost active shock absorbers proposed to decreasing the impact of vibration on a patient’s body during an ambulance ride. For this, the passive shock absorber is replaced by a new actuator consisting of a conventional hydraulic cylinder with a proportional butterfly valve placed outside the cylinder between its orifices. The ANN is used to adjust the damping coefficient. The ANN controller inputs are the accelerations of the sprung and unsprung masses, and the output is the valve opening area. Two forces may be exerted by this active suspension system: one is used to compensate for the mass of the stretcher, the patient and the medical equipment if present and a second is used to actively isolate the patient from the vibrations of the ambulance. The performance of the active suspension ambulance is contrasted to that of a traditional ambulance, in which the stretcher is rigidly linked to the ambulance body. When compared to alternative controllers, the findings showed that the proposed register controlled by ANN performed better. The simulations demonstrate that the active system may minimize the vibrations of the patient’s mass and the stretcher by more than 70% for random abnormalities in the road that meet the ISO2631-5 and ISO 8608 standards.

Three-year results of Ozaki surgery in patients aged ≥65 years: a multicentre study

Background. Currently, aortic valve stenosis is the most common disease of the native valve, which affects 5% of the elderly population. In symptomatic patients, aortic valve replacement is the ‘gold standard’. For patients aged ≥65 years, the use of biological prostheses is recommended. The Ozaki operation is an alternative to bioprostheses.Aim. The aim of this study was to evaluate the immediate and 3-year results of Ozaki surgery in patients aged ≥65 years.Methods. This was a prospective multicentre study conducted on 107 patients aged ≥65 years, who underwent the Ozaki procedure at three centres during 2016–2019. There were 46 (43%) men. The median age of the patients was 69 [67–74] years. Severe aortic stenosis was the major cause of aortic valve dysfunction (106 patients [99.1%]). Chronic heart failure III–IV functional class according to NYHA was diagnosed in 47 (43.9%) patients. The following complications were also registered: atrial fibrillation in 30 (28%) patients, a history of diabetes mellitus in 16 (15%) patients, chronic obstructive pulmonary disease in 14 (13.1%) patients and coronary artery disease in 42 (39.2%) patients. Bicuspid aortic valve was detected in 36 (34.6%) patients. There were 72 (67.2%) patients with a small annulus (≤21 mm) and 59 (55.14%) patients with a left ventricular ejection fraction of 64%. The median follow-up period was 23 [18–33] months. This study included all patients who underwent Ozaki surgery from 2016 to 2019.Results. No patient had any conversions. A total of 45 (42.1%) patients underwent combined interventions. The operation duration was 240 [214–300] min, cardiopulmonary bypass duration was 104 [93–120] min and aortic cross-clamp duration was 82 [72–95] min. The rate of hospital mortality was 1.9%, and the incidence rates of acute renal failure requiring haemodialysis, stroke, pacemaker implantation, sepsis and reoperation for bleeding were 1.9%, 0.9%, 1.9%, 0.9% and 0.9%, respectively. The hospitalisation duration was 14 [11–16] days. The gradients of peak and mean pressure on the aortic valve after surgery were 9 [7–13] and 4 [3–6] mmHg, respectively, and the effective valve opening area was 2.6 [2.3–2.9] cm2. None of the patients had moderate and severe aortic regurgitation. The 3-year overall survival and freedom from reoperation were 88.6% and 97%, respectively.Conclusion. The Ozaki operation in patients aged ≥65 years has good immediate results, with a hospital mortality rate of 1.9%, excellent haemodynamic parameters with an average pressure gradient across the aortic valve of 4 [3–6] mmHg and a valve opening area of 2.6 [2.3–2.9] cm2. The 3-year overall survival and freedom from reoperation were 88.6% and 97%, respectively. Further monitoring of these patients is required to evaluate long-term results, and there is also a need for randomised clinical trials comparing Ozaki operation with bioprostheses. Received 4 February 2021. Revised 21 June 2021. Accepted 23 June 2021. Funding: The study did not have sponsorship. Conflict of interest: Authors declare no conflict of interest. Contribution of the authorsConception and study design: I.I. Chernov, R.N. Komarov, D.G. Tarasov, Yu.S. Sinelnikov, A.V. Marchenko, V.B. Arutyunayan, K.Yu. ZhigalovData collection and analysis: B.K. Kadyraliev, A.M. Ismailbaev, B.M. Tlisov, D.A. Zorin, M.I. TcheglovStatistical analysis: S.T. EnginoevDrafting the article: I.I. Chernov, S.T. EnginoevCritical revision of the article: I.I. Chernov, R.N. Komarov, D.G. Tarasov, Yu.S. Sinelnikov, A.V. Marchenko, V.B. Arutyunayan, K.Yu. ZhigalovFinal approval of the version to be published: I.I. Chernov, S.T. Enginoev, R.N. Komarov, D.G. Tarasov, Yu.S. Sinelnikov, A.V. Marchenko, V.B. Arutyunayan, B.K. Kadyraliev, A.M. Ismailbaev, B.M. Tlisov, D.A. Zorin, M.I. Tcheglov, K.Yu. Zhigalov

Comparison of a new bioprosthetic mitral valve to other commercially available devices under controlled conditions in a porcine model.

Background/AimTo evaluate three mitral bioprostheses (of comparable measured internal diameters) under controlled, stable, hemodynamic and surgical conditions by bench, echocardiographic, computerized tomography and autopsy comparisons pre‐ and postvalve implantation.MethodsFifteen similar‐sized Yorkshire pigs underwent preprocedural computerized tomography anatomic screening. Of these, 12 had consistent anatomic features and underwent implantation of a mitral bioprosthesis via thoracotomy on cardiopulmonary bypass (CPB). Four valves from each of three manufacturers were implanted in randomized fashion: 27‐mm Epic, 27‐mm Mosaic, and 25‐mm Mitris bioprostheses. After CPB, epicardial echocardiographic studies were performed to assess hemodynamic function and define any paravalvular leaks, followed by postoperative gated contrast computerized tomography. After euthanasia, animals underwent necropsy for anatomic evaluation.ResultsAll 12 animals had successful valve implantation with no study deaths. Postoperative echocardiographic trans‐valve gradients varied among bioprosthesis manufacturers. The 25‐mm Mitris (5.1 ± 2.7)/(2.6 ± 1.3 torr) had the lowest peak/mean gradient and the 27‐mm Epic bioprosthesis had the highest (9.2 ± 3.7)/(4.6 ± 1.9 torr). Surgical valve opening area (SOA) varied with the 25‐mm Mitris having the largest SOA (2.4 ± 0.15 cm2) followed by the 27‐mm Mosaic (2.04 ± 0.23 cm2) and the 27‐mm Epic (1.8 ± 0.27 cm2) valve. Bench device orthogonal internal diameter measurements did not match manufacturer device size labeling: 25‐mm Mitris (23 × 23 mm), 27‐mm Mosaic (23 × 22 mm), 27‐mm Epic (21 × 21 mm).ConclusionsCurrent advertisement/packaging of commercial surgical mitral valves is not uniform. This study demonstrates marked variations in hemodynamics, valve opening area and anatomic dimensions between similar sized mitral bioprostheses. These data suggest a critical need for standardization and close scientific evaluation of surgical mitral bioprostheses to ensure optimal clinical outcomes.

Effect of non-linear leaflet material properties on aortic valve dynamics - A coupled fluid-structure approach

Due to complex structure of aortic valve (AV) leaflets and its strong interaction with the blood flow field, realistic and accurate modeling of the valve deformations comes with many challenges. In this study, we aimed to investigate the effect of AV material properties on the valve deformations, by implementing different non-linear properties of the AV leaflets in three different material models. In the computations, we captured the dynamics between the leaflet deformations and blood flow field variations by using an iterative implicit fluid-structure interaction (FSI) approach. By comparison of the FSI simulation results of these three models, the effects of hyperelasticity and anisotropy on the valve deformations have been studied in detail. The simulation results reveal the fact that the material characteristics strongly affect the deformation characteristics of the leaflets in the systolic phase. The material anisotropy stabilizes the leaflet movements during the systolic phase, which helps decreasing the flutters of the leaflets during the peak jet blood flow. Similarly, it has been observed that the hyperelastic behavior yields an increase in the valve opening area during systolic phase which prevents the risk of excessive work of the heart due to high pressure difference. Furthermore, simulation results indicate that the stress levels in hyperelastic model are much lower, compared to the stress levels in linear elastic one. This suggests that the non-linear material character of the leaflets decreases the risk of calcification.