Magnetic suspension of the rotor of a ventricular assist device of mixed flow type

Abstract:  This work presents results of preliminary studies concerning application of magnetic bearing in a ventricular assist device (VAD) being developed by Dante Pazzanese Institute of Cardiology—IDPC (São Paulo, Brazil). The VAD-IDPC has a novel architecture that distinguishes from other known VADs. In this, the rotor has a conical geometry with spiral impellers, showing characteristics that are intermediate between a centrifugal VAD and an axial VAD. The effectiveness of this new type of blood pumping principle was showed by tests and by using it in heart surgery for external blood circulation. However, the developed VAD uses a combination of ball bearings and mechanical seals, limiting the life for some 10 h, making impossible its long-term use or its use as an implantable VAD. As a part of development of an implantable VAD, this work aims at the replacement of ball bearings by a magnetic bearing. The most important magnetic bearing principles are studied and the magnetic bearing developed by Escola Politécnica of São Paulo University (EPUSP-MB) is elected because of its very simple architecture. Besides presenting the principle of the EPUSP-MB, this work presents one possible alternative for applying the EPUSP-MB in the IDPC-VAD.     

连续浅缝法修补膜周型室间隔缺损

目的探讨连续浅缝法修补单纯膜周型室间隔缺损(pVSD)法的效果。方法选取2002年1月至2004年10月我院收治的体重10kg以内(≤10kg)50例单纯膜周型室间隔缺损患者,均采用自体心包连续浅缝法修补。结果主动脉阻断时间32±21min(14-52min),体外循环时间56±35min(29-69min)。无°房室传导阻滞发生,9例发生右束支传导阻滞,2例结性心律。2例膜周偏流出道型VSD患者因前上缘残余分流分别为0.4cm和0.3cm,再次手术修补;1例后下缘残留细束样分流,直径0.15cm,随访6个月后自愈;10例膜周偏流出道型VSD患者剪开三尖瓣,8例垂直瓣环,2例平行瓣环;1例三尖瓣中度反流,随访无加重;5例轻度反流,4例轻微反流,随访均无加重;1例心包积液;1例再次进入手术室止血。结论连续浅缝法是修补单纯膜周型室间隔缺损的有效外科纠治方法。     

Nikaidoh术治疗完全型大动脉错位伴室间隔缺损和肺动脉狭窄的早期结果

目的回顾性研究Nikaidoh术治疗完全型大动脉错位伴室间隔缺损和肺动脉狭窄(TGA/VSD/PS)的早期结果。方法在2004年1月至2005年12月期间,有8例TGA/VSD/PS患者在我院接受Nikaidoh术矫治,手术年龄4～29个月(11.4±7.6个月),体重5.2～11.0kg(8.0±1.9kg);所有患者房室连接一致,其中伴房室瓣骑跨1例,左肺动脉狭窄1例,本组患者术前均未行其他手术,手术均采用改良Nikaidoh术,即主动脉根部移位和重建左、右心室流出道,除1例冠状动脉同时移植和使用Homograft重建右心室流出道外,用自体心包补片扩大重建右心室流出道。结果手术死亡1例,无1例出现明显左室流出道梗阻(LVOTO)和右室流出道梗阻(RVOTO),轻度肺动脉反流3例,中度4例,除1例死亡患者外,其余左心功能均正常;随访时间平均8.8个月(3～18个月),7例存活;心功能状况佳,射血分数(EF)0.64±0.02;短轴缩短率(FS)0.33±0.02。未出现进展性主动脉瓣反流、LVOTO、RVOTO和肺动脉反流加重。结论Nikaidoh术适宜于治疗TGA/VSD/PS,尤其当解剖上存在不宜行Rastelli术的患者,早期结果良好。     

Fluid force predictions and experimental measurements for a magnetically levitated pediatric ventricular assist device

The latest generation of artificial blood pumps incorporates the use of magnetic bearings to levitate the rotating component of the pump, the impeller. A magnetic suspension prevents the rotating impeller from contacting the internal surfaces of the pump and reduces regions of stagnant and high shear flow that surround fluid or mechanical bearings. Applying this third-generation technology, the Virginia Artificial Heart Institute has developed a ventricular assist device (VAD) to support infants and children. In consideration of the suspension design, the axial and radial fluid forces exerted on the rotor of the pediatric VAD were estimated using computational fluid dynamics (CFD) such that fluid perturbations would be counterbalanced. In addition, a prototype was built for experimental measurements of the axial fluid forces and estimations of the radial fluid forces during operation using a blood analog mixture. The axial fluid forces for a centered impeller position were found to range from 0.5 +/- 0.01 to 1 +/- 0.02 N in magnitude for 0.5 +/- 0.095 to 3.5 +/- 0.164 Lpm over rotational speeds of 6110 +/- 0.39 to 8030 +/- 0.57% rpm. The CFD predictions for the axial forces deviated from the experimental data by approximately 8.5% with a maximum difference of 18% at higher flow rates. Similarly for the off-centered impeller conditions, the maximum radial fluid force along the y-axis was found to be -0.57 +/- 0.17 N. The maximum cross-coupling force in the x direction was found to be larger with a maximum value of 0.74 +/- 0.22 N. This resulted in a 25-35% overestimate of the radial fluid force as compared to the CFD predictions; this overestimation will lead to a far more robust magnetic suspension design. The axial and radial forces estimated from the computational results are well within a range over which a compact magnetic suspension can compensate for flow perturbations. This study also serves as an effective and novel design methodology for blood pump developers employing magnetic suspensions. Following a final design evaluation, a magnetically suspended pediatric VAD will be constructed for extensive hydraulic and animal testing as well as additional validation of this design methodology.     

婴幼儿室间隔缺损合并重度肺动脉高压围手术期预后影响因素分析

目的探讨婴幼儿室间隔缺损合并重度肺动脉高压患者围手术期预后的影响因素,为此类患者的预后判断提供参考。方法选取2004～2012年北京安贞医院40例室间隔缺损合并重度肺动脉高压（PAPm〉50mmHg）的手术治疗患儿,男21例、女19例,年龄（7．2±3.3）岁,体重（19．6±7．1）kg。入选患儿随机分成两组：组Ⅰ（Group=0,n=20,男／女：12／8）经中心静脉持续泵入硝酸甘油;组Ⅱ（Group=1,n=20,男／女：9／11）,经中心静脉持续泵人前列腺素E1（PGE1）脂质微球。以气管内插管时间（Tintubation）为因变量（Y）,以患者年龄（Age）、体外循环时间（TCPB）、术后平均肺动脉压（PAPm）、术后肺血管阻力指数（PVRI）、术后体循环压力／肺循环压力（Ps/p）、用药分组（Group）、术后左心室每搏功指数（LVSWI）和术后右心室每搏功指数（RVSWI）为自变量（X）,采用多因素线性回归分析模型评价各影响因素的作用。结果40例患儿围手术期无死亡,无严重并发症发生。婴幼儿室间隔缺损合并重度肺动脉高压患者围手术期预后影响因素包括药物分组[Group,x1,P=0．004,95％CI（-71,-16）]、TCPB[x2,P=0．011,95％CI（0．9,5．8）]、术后PAPm[x3,P=0．004,95％CI（3．2,13．3）]、术后RVSWI[x4,P=0．003,95％CI（-16．9,-4．3）]和术后PVRI[x5,P=0．03,95％CI（-0．29,-0．02）]。标准化回归系数的回归方程为：Y=-0．60x1＋0．54x2＋2．22x3-1．70x4-0．15x5。结论在婴幼儿室间隔缺损合并重度肺动脉高压围手术期临床监测指标中,是否应用PGE1脂质微球、TCPB、术后PAPm、术后RVSWI和术后PVRI与患儿的预后转归密切相关。     

覆膜支架主动脉腔内修复术在Stanford B型主动脉夹层中的应用

目的观察覆膜支架主动脉腔内修复术（TEVAR）对Stanford B型主动脉夹层和降主动脉瘤的治疗效果。方法回顾性分析华西医院2013年3～6月采用TEVAR治疗Stanford B型主动脉夹层和降主动脉瘤患者20例的临床资料,其中男19例,女1例;年龄41～76（58．3±10．2）岁,分析其疗效。结果20例患者中,治愈18例,自动出院1例,术后死亡1例。随访满3个月者16例,随访率88．9％。全部随访患者支架范同内真腔管径有所恢复,假腔或瘤腔内血栓形成。结论TEVAR为Stanford B型主动脉瘤提供了一个新的选择,特别是为高龄和合并严重疾病的患者提供了新的治疗手段,优势明显,值得临床应用。     

急诊腔内修复术治疗合并灌注不良综合征的急性Stanford B型主动脉夹层

目的：探讨急诊行腔内修复术治疗合并灌注不良综合征的急性Stanford B型主动脉夹层的疗效及安全性。 方法：2006年1月—2013年12月,共收治23例合并灌注不良综合征的急性Stanford B型主动脉夹层患者,患者治疗前均经全主动脉CT血管造影确诊。其中男16例,女7例,年龄42~68岁;合并肾动脉灌注不良8例（单侧6例）,肠系膜上动脉灌注不良9例,单侧下肢动脉灌注不良5例,脊髓灌注不良1例;17例患者急诊行腔内修复术及相关辅助治疗,6例患者拒绝手术,予保守治疗。 结果：6例保守治疗患者均在2周内死亡。17例接受急诊手术患者均予覆膜支架封堵主动脉第一破口,其中13例封堵第一破口后,分支动脉灌注不良改善;1例第一破口位于降主动脉中段,先植入裸支架,扩张主动脉真腔后,再植入覆膜支架封堵第一破口;3例封堵第一破口后,尚需再植入单侧肾动脉或肠系膜上动脉裸支架。术后30 d无死亡病例。17例均随访3~36个月,1例术后半年死于心肌梗死,余均存活且未出现支架相关并发症。 结论：对于合并器官灌注不良的急性Stanford B型主动脉夹层患者,急诊行腔内修复术,恢复脏器供血,是挽救生命的重要方法。     

Horizontal right axillary minithoracotomy: aesthetic and effective option for atrial and ventricular septal defect repair in infants and toddlers

Introduction

Congenital heart defects treatment shows progressive reduction in morbidity and mortality, however, the scar, resulting from ventricular (VSD) and atrial septal defect (ASD) repair, may cause discomfort. Right axillary minithoracotomy approach, by avoiding the breast growth region, is an option for correction of these defects that may provide better aesthetic results at low cost. Since October 2011, we have been using this technique for repairing VSD and ASD defects as well as associated defects.

Objectives

To evaluate the efficacy of this method in children undergoing correction of VSD and ASD, to compare perioperative clinical outcomes with those repaired by median sternotomy, and to evaluate the aesthetic result.

Methods

Perioperative clinical data of 25 patients submitted to axillary thoracotomy were compared with data from a paired group of 25 patients with similar heart defects repaired by median sternotomy, from October 2011 to August 2012.

Results

Axillary approach was possible even in infants. There was no mortality and the main perioperative variables were similar in both groups, except for lower use of blood products in the axillary group (6/25) vs. control (13/25), with statistical difference (P =0.04). The VSD size varied from 7 to 15 mm in axillary group. Cannulation of the aorta and vena cavae was performed through the main incision, whose size ranged from 3 to 5 cm in the axillary group, with excellent aesthetic results.

Conclusion

The axillary thoracotomy was effective, allowing for a heart defect repair similar to the median sternotomy, with more satisfactory aesthetic results and reduced blood transfusion, and it can be safely used in infants.     

Design Method of a Foldable Ventricular Assist Device for Minimally Invasive Implantation

To date, ventricular assist devices (VADs) have become accepted as a therapeutic solution for end‐stage heart failure patients when a donor heart is not available. Newer generation VADs allow for a significant reduction in size and an improvement in reliability. However, the invasive implantation still limits this technology to critically ill patients. Recently, expandable/deployable devices have been investigated as a potential solution for minimally invasive insertion. Such a device can be inserted percutaneously via peripheral vessels in a collapsed form and operated in an expanded form at the desired location. A common structure of such foldable pumps comprises a memory alloy skeleton covered by flexible polyurethane material. The material properties allow elastic deformation to achieve the folded position and withstand the hydrodynamic forces during operation; however, determining the optimal geometry for such a structure is a complex challenge. The numerical finite element method (FEM) is widely used and provides accurate structural analysis, but computation time is considerably high during the initial design stage where various geometries need to be examined. This article details a simplified two‐dimensional analytical method to estimate the mechanical stress and deformation of memory alloy skeletons. The method was applied in design examples including two popular types of blade skeletons of a foldable VAD. Furthermore, three force distributions were simulated to evaluate the strength of the structures under different loading conditions experienced during pump operation. The results were verified with FEM simulations. The proposed two‐dimensional method gives a close stress and deformation estimation compared with three‐dimensional FEM simulations. The results confirm the feasibility of such a simplified analytical approach to reveal priorities for structural optimization before time‐consuming FEM simulations, providing an effective tool in the initial structural design stage of foldable minimally invasive VADs.