Initial hydrodynamic study on a new intraaortic axial flow pump: Dynamic aortic valve

Rotary blood pumps have been researched as implantable ventricular assist devices for years. To further reduce the complex of implanted axial pumps, the authors proposed a new concept of intraaortic axial pump, termed previously as “dynamic aortic valve (DAV)”. Instead of being driven by an intraaortic micro-electric motor, it was powered by a magnetic field from outside of body. To ensure the perfusion of coronary artery, the axial flow pump is to be implanted in the position of aortic valve. It could serve as either a blood pump or a mechanical valve depending on the power input. This research tested the feasibility of the new concept in model study. A column, made from permanent magnet, is jointed to an impeller in a concentric way to form a “rotor-impeller”. Supported by a hanging shaft cantilevered in the center of a rigid cage, the rotor-impeller can be turned by the magnetic field in the surrounding space. In the present prototype, the rotor is 8 mm in diameter and 15 mm in length, the impeller has 3 vanes with an outer diameter of 18 mm. The supporting cage is 22 mm in outer diameter and 20 mm in length. When tested, the DAV prototype is inserted into the tube of a mock circuit. The alternative magnetic field is produced by a rotating magnet placed side by side with the rotor-impeller at a distance of 30 mm. Once the alternative magnetic field is presented in the surrounding space, the DAV starts to turn, leading to a pressure difference and liquid flow in the tube. The flow rate or pressure difference is proportioned to rotary speed. At the maximal output of hydraulic power, the flow rate reached 5 L/min against an afterload of 100 mmHg. The maximal pressure difference generated by DAV at a rotation rate of 12600 r/min was 147 mmHg. The preliminary results demonstrated the feasibility of “DAV”, further research on this concept is justifiable.     

左心室脱血回注循环辅助法对急性心肌梗死血流动力学的改善作用

目的:实验观察左心室脱血回注循环辅助法对急性心肌梗死血流动力学的改善作用.方法:18只杂种犬分两组制作急性心肌梗死泵衰竭模型,治疗组给予左心室脱血回注循环辅助,对照组不进行治疗.观察比较两组间心律失常、死亡率、外周动脉压、肺动脉毛细血管楔嵌压(PCWP)、左心室舒张末期压(LVEDP)、左心室内径的变化.结果:治疗组室性期外收缩、心室纤颤发生率和死亡率显著低于对照组;对照组的外周动脉收缩压低于80 mmHg以下,治疗组维持在100mmHg以上(P＜0.01);治疗组PCWP和LVEDP值在45 min以后的各时段低于对照组(P＜0.01);治疗组的左室舒张末期内径小于对照组(P＜0.01).结论:左心室脱血回注循环辅助法能够减少急性心肌梗死泵衰竭的心室纤颤发生率和死亡率,有显著改善血流动力学、防止梗死后心肌扩张和有效的左心室辅助作用.     

可植入式心室辅助装置动物模型的建立

目的探讨建立可植入式心室辅助装置研究的实验动物模型。方法选取体质量120-180 kg小公牛7只,常规全麻后左侧第4肋间开胸,建立体外循环,体外循环辅助下诱颤后,植入自主研发的国产可植入式心室辅助装置（DIVAD,domestic-made implantable ventricular assist device）,DIVAD机械性能参数接近国际同类产品,泵尺寸29.5mm×72 mm,重量158 g,体外转速可达9000 r/min,流量可达8 L/min,整合流量计,并可通过体外控制器监测控制。DIVAD连接左室及降主动脉,转速3500-8000 r/min左右,行左室辅助。术后撤除体外循环,持续监测动物生命体征及DIVAD运转情况。肝素静滴维持ACT在正常值1.5-2倍之间。结果7只小牛术后全部复跳,均能成功撤离体外循环辅助,最长存活时间超过93 h,最短存活时间0.5 h,平均存活时间20.28 h。结论小牛可以作为DIVAD研究的合适动物模型,其围手术期处理有相应特点,小牛DIVAD实验模型的建立对于进一步研究改进DIVAD有重要作用。     

Left ventricular assist device: a functional comparison with heart transplantation

Background A growing number of patients with end-stage heart failure undergo implantation of ventricular assist devices as a bridge to heart transplantation. Objectives In this study we investigated whether functional and haemodynamic recovery after implantation is sufficient to warrant the use of them as long-term alternative to heart transplantation. Methods We compared peak VO₂ of a group of patients three months after implantation of a ventricular assist device and three months after heart transplantation. Furthermore, we analysed the degree of haemodynamic recovery, by comparing plasma levels of BNP and creatinine before and after implantation of the device. Results After implantation of a ventricular assist device, exercise capacity improved considerably; three months after implantation peak VO₂ was 20.0±4.9 ml/kg/min (52% of predicted for age and gender). After heart transplantation exercise capacity improved even further; 24.0±3.9 ml/ kg/min (62% of predicted for age and gender) (p<0.001). In the three months after implantation, BNP plasma levels decreased from 570±307 pmol/l to 31±25 pmol/l and creatinine levels decreased from 191±82 μmol/l to 82±25 μmol/l, indicating significant unloading of the ventricles and haemodynamic recovery. Conclusion With regard to functional and haemodynamic recovery, the effect of implantation of a ventricular assist device is sufficient to justify its use as an alternative to heart transplantation. (Neth Heart J 2008;16:41-6.)     

Sustained high-pressure in the spinal subarachnoid space while arterial expansion is low may be linked to syrinx development

Syringomyelia (a spinal cord cyst) usually develops as a result of conditions that cause cerebrospinal fluid (CSF) obstruction. The mechanism of syrinx formation and enlargement remains unclear, though previous studies suggest that the fluid enters via the perivascular spaces (PVS) of the penetrating arteries of the spinal cord, and that alterations in the CSF pulse timing and pressure could contribute to enhanced PVS inflow. This study uses an idealised computational model of the PVS to investigate the factors that influence peri-arterial fluid flow. First, we used three sample patient-specific models to explore whether changes in subarachnoid space (SAS) pressures in individuals with and without syringomyelia could influence PVS inflow. Second we conducted a parametric study to determine how features of the CSF pulse altered perivascular fluid, including alterations to timing and magnitude of the peak SAS pressure, the timing of reversal from high to low pressure (diastolic phase), and the area under the pressure–time curve. The model for the patient with syringomyelia had higher net CSF inflow to the PVS than the two subjects without syringomyelia. In the parametric study, only increasing the area under the high pressure region of the SAS pulse substantially increased PVS inflow, when coupled with a temporal shift in arterial and SAS pulses. This suggests that a period of sustained high SAS pressure while arterial diameter is low may increase net CSF pumping into the PVS.     

Left ventricular assist device for end-stage heart failure: results of the first LVAD destination program in the Netherlands

PurposeMechanical circulatory support with a continuous-flow left ventricular assist device (LVAD) may be a valuable treatment in end-stage heart failure patients for an extended period of time. The purpose of this study was to evaluate the safety and efficacy of implantation of a continuous-flow LVAD in end-stage heart failure patients within the first destination program in the Netherlands.MethodsA third-generation LVAD was implanted in 16 heart failure patients (age 61 ± 8; 81 % male; left ventricular ejection fraction 20 ± 6 %) as destination therapy. All patients were ineligible for heart transplant. At baseline, 3 and 6 months, New York Heart Association (NYHA) functional class, quality-of-life and exercise capacity were assessed. Clinical adverse events were registered.ResultsSurvival at 30 days and 6 months was 88 and 75 %, respectively. In the postoperative phase, 6 (38 %) patients required continuous veno-venous haemofiltration for renal failure and 2 (13 %) patients required extracorporeal membrane oxygenation because of severe right ventricular failure. During follow-up, NYHA functional class and quality-of-life improved from 3.7 ± 0.1 to 2.3 ± 0.1 and 57 ± 5 to 23 ± 3 at 6 months (P < 0.001), respectively. The 6 min walking distance improved from 168 ± 42 m to 291 ± 29 m at 6 months (P = 0.001).ConclusionContinuous-flow LVAD therapy is a promising treatment for patients with end-stage heart failure ineligible for heart transplant.     

The effect of turbulent motion on the diffusion of microorganisms

The effect of turbulent fluid motion on the diffusion of simple organisms is discussed. The net reproduction rate and the turbulent flow are assumed to be Gaussian-correlated random variables. For homogeneous istropic turbulence, simple equations for the average concentration of the organisms are derived in terms of the energy density of the fluid. It is shown that the effective diffusivity generated by the motion is positive-definite, and is independent of the helicity of the flow.     

Numerical simulation of blood flow in the left ventricle and aortic sinus using magnetic resonance imaging and computational fluid dynamics

Understanding cardiac blood flow patterns has many applications in analysing haemodynamics and for the clinical assessment of heart function. In this study, numerical simulations of blood flow in a patient-specific anatomical model of the left ventricle (LV) and the aortic sinus are presented. The realistic 3D geometry of both LV and aortic sinus is extracted from the processing of magnetic resonance imaging (MRI). Furthermore, motion of inner walls of LV and aortic sinus is obtained from cine-MR image analysis and is used as a constraint to a numerical computational fluid dynamics (CFD) model based on the moving boundary approach. Arbitrary Lagrangian–Eulerian finite element method formulation is used for the numerical solution of the transient dynamic equations of the fluid domain. Simulation results include detailed flow characteristics such as velocity, pressure and wall shear stress for the whole domain. The aortic outflow is compared with data obtained by phase-contrast MRI. Good agreement was found between simulation results and these measurements.     

Feasibility of fast ventricular tachycardia mapping using the Rhythmia ™ system in a patient with an Impella ™

Use of 3D navigation systems may be sometimes impossible in patients with left ventricular assist devices because of major electromagnetical interferences with some 3D systems based on magnetic localization. Mapping with the Rhythmia ™ system in patients implanted with an Impella ™ is described to be non feasible. We relate how to overcome this technical issues in this case.