Development of the PSU Child Pump.

The Pennsylvania State University (PSU) Child Pump, a centrifugal continuous-flow ventricular assist device (cf-VAD), is being developed as a suitable long-term implantable device for pediatric heart failure patients between 10 and 35 kg, body surface area (BSA) of 0.5-1.2 m 2 , 1-11 years of age, and requiring a mean cardiac output of 1.

Kinetic and Dynamic Effects on Degradation of von Willebrand Factor.

The loss of high molecular weight multimers (HMWM) of von Willebrand factor (vWF) in aortic stenosis (AS) and continuous-flow left ventricular assist devices (cf-LVADs) is believed to be associated with high turbulent blood shear. The objective of this study is to understand the degradation mechanism of HMWM in terms of exposure time (kinetic) and flow regime (dynamics) within clinically relevant pathophysiologic conditions. A custom high-shear rotary device capable of creating fully controlled exposure times and flows was used.

In Vivo Evaluation of a Physiologic Control System for Rotary Blood Pumps Based on the Left Ventricular Pressure-Volume Loop.

Current generation continuous flow assist devices to operate at a fixed speed, which limits preload response and exercise capacity in left ventricular assist device (LVAD) patients. A feedback control system was developed to automatically adjust pump speed based on direct measurements of ventricular loading using a custom cannula tip with an integrated pressure sensor and volume-sensing conductance electrodes. The input to the control system is the integral of the left ventricular (LV) pressure versus conductance loop (PGA) over each cardiac cycle.

Miniaturized Fontan Circulation Assist Device: Chronic In Vivo Evaluation.

We have miniaturized and optimized our implantable rotary blood pump developed to provide long-term mechanical right heart support for patients who have failing Fontan circulation. The objective of this study was to evaluate the miniaturized Fontan circulation assist device (mini-FCAD) during 30-day sheep studies (n = 5). A complete right heart bypass was performed and all return flow was supported by the pump.

Dynamics of Blood Flows in Aortic Stenosis: Mild, Moderate, and Severe.

Supraphysiologic high shear stresses created in calcific aortic stenosis (AS) are known to cause hemostatic abnormalities, however, the relationship between the complex blood flows over the severity of AS and hemostatic abnormalities still remains unclear. This study systematically characterized the blood flow in mild, moderate, and severe AS. A series of large eddy simulations (LES) validated by particle image velocimetry were performed on physiologically representative AS models with a peak physiologic flow condition of 18 liter per minute.

Stress and Exposure Time on von Willebrand Factor Degradation.

Despite the prevailing use of the continuous flow left ventricular assist devices (cf-LVAD), acquired von Willebrand syndrome (AvWS) associated with cf-LVAD still remains a major complication. As AvWS is known to be dependent on shear stress (τ) and exposure time (t ), this study examined the degradation of high molecular weight multimers (HMWM) of von Willebrand factor (vWF) in terms of τ and t . Two custom apparatus, i.

Acquired Von Willebrand Syndrome and Blood Pump Design.

The existence of acquired von Willebrand syndrome (AVWS) in patients with continuous flow left ventricular assist devices (LVADs) is well documented and has been verified by numerous investigators. AVWS has not been observed to occur in pulsatile devices such as the SynCardia total artificial heart (TAH), the HeartMate XVE, and the Thoratec pulsatile ventricular assist device (PVAD) used as a single pump. AVWS can also occur in patients with aortic stenosis, ventricular septal defect, mitral stenosis, and patent ductus arteriosus.

Chronic In Vivo Test of a Right Heart Replacement Blood Pump for Failed Fontan Circulation.

An implantable rotary blood pump was developed to provide long-term mechanical right heart support for patients who have failing Fontan circulation. The objective of this study was to evaluate the pump in vivo in a 30 day sheep study. Pump speed was set at 3,900 rpm for the duration of the study, and pump power was between 4.

Cannula Tip With Integrated Volume Sensor for Rotary Blood Pump Control: Early-Stage Development.

The lack of direct measurement of left ventricular unloading is a significant impediment to the development of an automatic speed control system for continuous-flow left ventricular assist devices (cf-LVADs). We have developed an inlet cannula tip for cf-LVADs with integrated electrodes for volume sensing based on conductance. Four platinum-iridium ring electrodes were installed into grooves on a cannula body constructed from polyetheretherketone (PEEK).

Determination of Reynolds Shear Stress Level for Hemolysis.

Reynolds shear stress (RSS) has served as a metric for the effect of turbulence on hemolysis. Forstrom (1969) and Sallam and Hwang (1984) determined the RSS threshold for hemolysis to be 50,000 and 4,000 dyne/cm, respectively, using a turbulent jet. Despite the order of magnitude discrepancy, the threshold by Sallam and Hwang has been frequently cited for hemolytic potential in blood pumps.

Continuous flow left ventricular pump support and its effect on regional left ventricular wall stress: finite element analysis study.

Left ventricular assist device (LVAD) support unloads left ventricular (LV) pressure and volume and decreases wall stress. This study investigated the effect of systematic LVAD unloading on the 3-dimensional myocardial wall stress by employing finite element models containing layered fiber structure, active contractility, and passive stiffness. The HeartMate II(®) (Thoratec, Inc.

Ventricular contractility and compliance measured during axial flow blood pump support: in vitro study.

End-systolic elastance and end-diastolic compliance have been used to quantify systolic and diastolic function of the left ventricle (LV). In this study, the effective end-systolic elastance, (EES )eff , end-systolic volume intercept, (V0 )eff , and end-diastolic compliance of the LV were assessed at various levels of left ventricular assist device (LVAD) support. We tested the hypothesis that (EES )eff and (V0 )eff vary as a function of LVAD speed, while compliance does not change.

Rotary blood pump control using integrated inlet pressure sensor.

Due to improved reliability and reduced risk of thromboembolic events, continuous flow left ventricular assist devices are being used more commonly as a long term treatment for end-stage heart failure. As more and more patients with these devices are leaving the hospital, a reliable control system is needed that can adjust pump support in response to changes in physiologic demand. An inlet pressure sensor has been developed that can be integrated with existing assist devices.

Effective ventricular unloading by left ventricular assist device varies with stage of heart failure: cardiac simulator study.

Although the use of left ventricular assist devices (LVADs) as a bridge-to-recovery (BTR) has shown promise, clinical success has been limited due to the lack of understanding the timing of implantation, acute/chronic device setting, and explantation. This study investigated the effective ventricular unloading at different heart conditions by using a mock circulatory system (MCS) to provide a tool for pump parameter adjustments. We tested the hypothesis that effective unloading by LVAD at a given speed varies with the stage of heart failure.

Finite element modeling of the pulmonary autograft at systemic pressure before remodeling.

Background And Aim Of The Study: Pulmonary autograft dilatation requiring reoperation is an Achilles' heel of the Ross procedure, as exposure to systemic pressure increases autograft wall stress, which may in turn lead to tissue remodeling and aneurysmal pathology. However, the magnitude of autograft wall stress with the Ross procedure is unknown. The study aim was to develop a realistic finite element (FE) model of the autograft, and to perform simulations at systemic pressure to determine wall stress distribution immediately after the Ross operation.

Comparison of porcine pulmonary and aortic root material properties.

Background: The pulmonary autograft remodels when subjected to systemic pressure and subsequent dilation can lead to reoperation. Inherent material property differences between pulmonary and aortic roots may influence remodeling but are currently unknown. The objective of this study was to determine stiffness across a wide range of strain and compare nonlinear material properties of corresponding regions of native aortic and pulmonary roots.

Effect of adjustable passive constraint on the failing left ventricle: a finite-element model study.

Background: Passive constraint is used to prevent left ventricular dilation and subsequent remodeling. However, there has been concern about the effect of passive constraint on diastolic left ventricular chamber stiffness and pump function. This study determined the relationship between constraint, diastolic wall stress, chamber stiffness, and pump function.

A computationally efficient formal optimization of regional myocardial contractility in a sheep with left ventricular aneurysm.

A non-invasive method for estimating regional myocardial contractility in vivo would be of great value in the design and evaluation of new surgical and medical strategies to treat and/or prevent infarction-induced heart failure. As a first step towards developing such a method, an explicit finite element (FE) model-based formal optimization of regional myocardial contractility in a sheep with left ventricular (LV) aneurysm was performed using tagged magnetic resonance (MR) images and cardiac catheterization pressures. From the tagged MR images, 3-dimensional (3D) myocardial strains, LV volumes and geometry for the animal-specific 3D FE model of the LV were calculated, while the LV pressures provided physiological loading conditions.

Planar biaxial mechanical behavior of bioartificial tissues possessing prescribed fiber alignment.

Though it is widely accepted that fiber alignment has a great influence on the mechanical anisotropy of tissues, a systematic study of the influence of fiber alignment on the macroscopic mechanical behavior by native tissues is precluded due to their predefined microstructure and heterogeneity. Such a study is possible using collagen-based bioartificial tissues that allow for alignment to be prescribed during their fabrication. To generate a systemic variation of strength of fiber alignment, we made cruciform tissue constructs in Teflon molds that had arms of different aspect ratios.

Mechanical properties of surgical glues used in aortic root replacement.

Background: Surgical glues are used in mechanical, stentless bioprosthetic, and homograft aortic root replacements to seal and reinforce anastomotic suture lines. The aortic root normally undergoes substantial physiologic dilation and may be affected by the stiffness of applied sealants. We determined the material properties of four common commercial glues, comparing them with known properties of aortic root replacements.

Characterization of mechanical behavior of a porcine pulmonary artery strip using a randomized uniaxial stretch and stretch-rate protocol.

Background: Much of the experimental work in soft tissue mechanics has been focused on fitting approximate relations for specific tissue types from aggregate data on multiple samples of the tissue. Such relations are needed for modeling applications and have reasonable predictability - especially given the natural variance in specimens. There is, however, much theoretical and experimental work to be done in determining constitutive behaviors for particular specimens and tissues.