Search

In mitral valve replacement for mitral stenosis the persistence of a depressed cardiac performance immediately after operation has been outlined by several authors. The choice of a porcine central flow prosthesis, that has several theoretical advantages, should allow better acute hemodynamic results. Therefore ten patients have been studied by thermodilution methods and the variations in their hemodynamic parameters has been evaluated with a paired T-Test. Results confirm the persistence of a depressed cardiac function throughout the time span of the study (36 hours). This behaviour could be related to the use of Kirsch solution for myocardial protection. Therefore the authors compare a similar group of nine patients that underwent mitral valve replacement with differently designed prosthesis and the use of a St Thomas analogue cardioplegic solution. They conclude for the persistence, in the acute postoperative period, of an intrinsic myocardial dysfunction.

Previous studies have shown that the Carpentier-Edwards Magna (CEM) valve is an excellent bioprosthesis in terms of its systolic performance; indeed, it has been described as 'a stented valve with stentless performance'. However, valve performance is not only a matter of gradients; it is also necessary to evaluate the diastolic-phase performance. Previous in-vitro studies have shown that the CEM has an excessive total regurgitant volume. Hence, the study aim was to compare the hydrodynamics of the CEM, with the newly evolved version of this valve, the CEM Ease (CEME).The CEM and CEME valves (both 21 mm) were tested in the aortic chamber (23 mm diameter) of the Sheffield pulse duplicator. The tests were carried out at increasing pulse rates (PR; 70-100 beats/min), and at each pulse rate the valve was tested at different stroke volumes (SVs; 45-65 ml). The forward-flow pressure drop, closing leakage volumes and effective orifice area (EOA) were recorded.The CEM and CEME valves showed a comparable systolic-phase performance, there being no significant differences in terms of transvalvular gradient, EOA and stroke work loss, regardless of the PR and SV. In fact, the new CEME exhibited a significantly improved diastolic performance, with the total regurgitant volume being significantly lower, due especially to a reduced leakage volume and, to a lesser extent, a reduced closing volume.The study results indicated that the new CEME valve would maintain the excellent systolic performance of the previous CEM model, but with a significantly improved diastolic performance.

The study aim was to compare the hydrodynamics of the Carpentier-Edwards Magna 21 (CEM) and St. Jude Medical Biocor-Epic-Supra 21 (SJME) valves at increasing stroke volume and pulse rate in two different aortic conduits, namely straight and with sinuses of Valsalva present.Both valve types were tested in the aortic chamber of the Sheffield pulse duplicator, at rates of 70, 80 and 90 beats/min, and stroke volumes of 50 and 60 ml. The systolic and diastolic performances were each recorded. The leaflet coaptation time, ventricle isovolumetric time and maximum instantaneous flow rate were also recorded.Regardless of the aortic conduit, CEM valves showed a significantly lower gradient than SJME valves (p0.05), and a significantly larger effective orifice area (EOA) (p0.05); the latter parameter was unaffected for both valves, at an increasing pulse rate (p0.05). The maximum transvalvular flow velocity was significantly higher in the straight conduit for both valves (p0.05). With regards to diastole, the SJME valve showed the lowest regurgitant volume (p0.05). The leaflet coaptation time was significantly shorter for the SJME valve than for the CEM valve (p0.05), but when tested in a straight conduit it was shortened significantly for both valves (p0.05).An absence of the sinuses of Valsalva may modify the diastolic and systolic behaviors of the tissue valve leaflets by reducing the time required for leaflet coaptation, and increasing the valve closing volume and maximum transvalvular flow velocity. It is speculated that these hydrodynamic changes may increase the working stress on the valve tissue, leading to possible premature structural valve deterioration.

This paper illustrates an algorithm to balance the voltages across the DC-link capacitors of a three-level multiphase inverter feeding a star-connected load with an odd number of phases. The proposed strategy keeps the DC-link capacitors balanced in any operating condition and minimizes the low-frequency voltage oscillations, even during open-phase faults and with non-sinusoidal output currents. Finally, the paper identifies the operating region where the voltage oscillations of the DC-link capacitors can be canceled. The developed algorithm can maintain constant voltages even if the capacitors are unbalanced, and its performance is compared to that of other carrier-based algorithms. Experimental tests are carried out on a five-phase induction motor in healthy and faulty conditions.

Objective We have analyzed, in a clinical multicenter study, the effect of cardiac surgery in adults with congenital heart disease in Italy. Methods We collected clinical data from 856 patients aged 19 years or older who underwent surgical intervention from January 1, 2000, to December 31, 2004. Patients were divided into 3 surgical groups: group 1, palliation (3.1%); group 2, repair (69.7%); and group 3, reoperation (27.4%). Results Preoperatively, 34.6% of patients were in New York Heart Association class I, 48.4% were in class II, 14.2% were in class III, and 2.8% were in class IV. Sinus rhythm was present in 83%. There were 1179 procedures performed in 856 patients (1.37 procedures per patient), with a hospital mortality of 3.1%. Overall mean intensive care unit stay was 2.3 days (range, 1–102 days). Major complications were reported in 247 (28.8%) patients, and postoperative arrhythmias were the most frequent. At a mean follow-up of 22 months (range, 1 month–5.5 years; completeness, 87%), late death occurred in 5 (0.5%) patients. New York Heart Association class was I in 79.3%, II in 17.6%, and III in 2.9%, and only 1 (0.11%) patient was in class IV. Overall survival estimates are 82.6%, 98.9%, and 91.8% at 5 years for groups 1, 2, and 3, respectively. Freedom from adverse events at 5 years is 91% for acyanotic patients versus 63.9% for preoperative cyanotic patients ( P Conclusions Surgical intervention for congenital heart disease in adults is a safe and low-risk treatment. However, patients presenting with preoperative cyanosis show a higher incidence of late adverse events and complications.

Rotary assembly stations are commonly used in automated manufacturing processes. These production platforms require the speed control of the plate and need power for the actuators and sensors located on the rotating frame. These requirements are usually met through a gearmotor and sliding electrical contacts. Among the solutions that avoid the slip-rings, this paper focuses on an integrated electric drive consisting of a gearless five-phase wound-rotor induction machine fed by two inverters, one placed on the stator reference frame and one placed on the rotating one. The main contribution is a novel control scheme that maximizes the power transferred to the rotating loads in compliance with the thermal constraint of the rotor and the voltage constraint of the rotor inverter. The theoretical analysis allows deriving an analytical solution to the control problem, and the experimental results confirm the effectiveness of the proposed algorithm.

Multiphase induction motors are receiving more and more interest in applications where safety and high reliability of operation are key items. Thus, condition monitoring of stator faults is crucial for guaranteeing high motor performance and efficiency. In this paper the behavior of an asymmetrical twelve-phase induction motor, with quadruple three-phase winding configuration, is investigated under high resistance connections affecting the stator windings. The analysis leads to a simple and effective methodology for detecting and localizing stator high resistance connections at incipient stage. The proposed approach is based on the computation of the voltage space vectors evaluated in the available four α-β planes. The performance of the proposed strategy is confirmed by means of numerical simulations.

This article presents a postfault control algorithm that minimizes the stator Joule losses in multiphase induction machines under an open-phase fault and for different star connection layouts. The key novelty is that the algorithm can be applied to any configuration of a multi- n -phase machine, independently of the connection of the neutral points. The latter is analytically derived and is based on the space vector representation of the machine model. In addition, it is shown that a low number of neutral points helps to reduce the winding losses in case of an open-phase fault but requires additional control regulators and computational efforts. The theory is applied to an asymmetrical quadruple-three-phase induction machine, which is configured to represent five different motor layouts. Finally, experimental results are presented to validate the control algorithm. The optimal solution that is given in this article can be employed for the control of symmetrical or asymmetrical multiphase machines with different star connection layouts and in any open-phase postfault operation.

In three-phase electric drives, overmodulation is commonly used to fully exploit the dc-bus voltage, increase the dynamic performance of the motor, and reduce the inverter switching frequency. The same advantages can be found in multiphase converters, where a higher number of degrees of freedom allows defining new operating modes. In this article, the extension of the overmodulation strategies of three-phase inverters to five-phase systems is investigated. Experimental tests on a five-phase induction motor drive are carried out to verify the feasibility of the developed techniques, the quality of the current waveforms, and the improvement in the dynamic performance of the drive.

The exploitation of the dc-link in multiphase inverters raises the problem of overmodulation, which has some peculiar traits compared to three-phase inverters. Typically, overmodulation allows exploiting the dc-bus voltage but suffers from the harmonic distortion of the output voltage. In multiphase inverters, overmodulation causes the pollution of the harmonic subspaces, which are usually independent of each other in the linear modulation range. The solution to the problem of the overmodulation is not unique and affects the performance of the drive. Several overmodulation techniques, which differ in the optimized quality index, have already been proposed for five- phase inverters in the literature. The contribution of this paper is to show with a rigorous analysis that the overmodulation problem can be transformed into a set of trigonometric inequalities, which can be easily solved. Experimental tests on a five-phase induction motor drive are carried out to verify the feasibility of the developed techniques and the quality of the current waveforms.

In the last decade, the interest for higher reliability in several industrial applications has boosted the research activities in multiphase permanent magnet synchronous motors realized by multiple three-phase winding sets. In this study, a mathematical model of an asymmetric surface-mounted six-phase permanent magnet synchronous motor under high resistance connections was developed. By exploiting the intrinsic properties of multiphase machines in terms of degrees of freedom, an improved field-oriented control scheme is presented that allows online fault detection and a quite undisturbed operating condition of the machine under high resistance connections. More specifically, the proposed strategies for online fault-detection and fault-tolerance are based on the use of multi-reference frame current regulators. The feasibility of the proposed approach was theoretically analyzed, then confirmed by numerical simulations. In order to validate experimentally the proposed strategies, the entire control system was implemented using TMS-320F2812 based platform.

Background This single-center retrospective study assessed the variation of left ventricular ejection fraction (LVEF) after transapical transcatheter aortic valve implantation and its effect on survival. We also evaluated the effect of sheath diameter on LVEF. Methods We analyzed data of all consecutive patients who underwent transapical transcatheter aortic valve implantation with the Sapien (Edwards Lifesciences, Irvine, CA) device (and its evolutions) between 2009 and 2015. We analyzed the difference between preoperative LVEF and LVEF at discharge (ΔEF = LVEFpost-op – LVEFpre-op) and considered its interquartile range (±5%) as the cutoff. Patients were divided in three groups: (1) improved LVEF (ΔEF ≥ +5%); (2) unchanged LVEF (ΔEF –5% to +5%), and (3) worsened LVEF (ΔEF ≤ –5%). Survival was evaluated with Kaplan-Meier analysis, and logistic regression multivariable analysis was used to determine independent predictors of LVEF improvement. Results Data of 122 patients were analyzed. Patients in the three groups were distributed as follows: (group 1) 27 patients (22.1%), (group 2) 69 (56.6%), and (group 3) 26 (21.3%). The mean ΔEF was 12.7% ± 4.7% in group 1 and –10.8% ± 3.9% in group 3. The ΔEF was more likely to improve in patients with preoperative LVEF of less than 0.35 ( p = 0.014). There were no significant differences in survival ( p = 0.41), rehospitalization ( p = 0.472), and New York Heart Association Functional Classification ( p = 0.307) among the groups. The use of the smallest available sheath (18F) was not associated with a significant change of ΔEF. Conclusions LVEF worsened in a small number of patients after transapical transcatheter aortic valve implantation, but this change was not associated with worse postoperative outcomes. Patients with a low LVEF showed better improvement. The progressive reduction of sheath diameter does not have a significant effect on LVEF changes.

An array of proportional-resonant regulators is often used in shunt active power filters to control the grid currents and reduce the harmonic distortion caused by a distorting load. The voltage that is necessary to compensate for the current harmonics must be consistent with the available dc-link voltage. In this article, three adaptive algorithms for the exploitation of the dc-link voltage are developed and compared. These algorithms adaptively change the voltage saturation of each regulator to preserve the control capability of the fundamental component of the current when the available voltage is not enough to control the filter current. Simultaneously, they try to improve the quality of the grid current because the dc-link voltage of the active power filter is allocated to the regulators to compensate only the most significant harmonics. Some experimental results are shown to demonstrate the feasibility of the three algorithms.

Multiphase permanent-magnet synchronous machines (PMSMs) are receiving more and more interest in safety-critical modern industries owing to their higher reliability when compared with conventional three-phase PMSMs. Rotor magnets are critical components, which, in case of fault, directly affect the performance of the PMSMs. Thus, monitoring the rotor magnets status is essential to ensure both high level of efficiency and service continuity. The present study focuses on the investigation of a new approach for the detection of rotor magnet demagnetisation in a vector-controlled asymmetrical six-phase surface-mounted AC PMSM. The main contribution of the proposed technique is the assessment of a rotor demagnetisation fault index derived from the fifth and seventh harmonics of the stator voltage space vector evaluated in the α 5–β 5-plane, and already available in the control system platform. The performance of the proposed approach is evaluated using finite element analysis and numerical simulations, both validated by experimental tests.

This paper illustrates the control system of a five-phase wound-rotor induction machine that can be used in applications where, besides the torque generation, a certain amount of active power must be transferred to loads collocated on the rotor frame. This requirement is common in rotary assembly platforms, bottle filling and capping systems, that embed electric actuators, sensors and process controllers on a rotating disk. The use of a five-phase machine avoids the slipring contacts to feed the rotor load. However, the choice of the set-point values for the motor currents involves magnetic, electric and thermal constraints. The paper illustrates a methodology of analysis, and develops a technique to deliver power to the rotor loads through the third-order spatial component of the magnetic field, while keeping the motor torque under control and reducing the rotor current as much as possible to minimize the rotor Joule losses. The experimental tests on a scaled prototype demonstrate the practical potential of the machine.