Medical device designers must develop catheters that avoid harming the vascular pathway during therapy delivery. To better characterize the necessary design features to minimize damage to central and peripheral vessels, the vascular pathway used for femoral delivery of a cardiac device is studied through high resolution, computed tomography images of fresh, human cadavers. Comparisons of the amount and location of vessel calcification are made between specified anatomical sections. Though the potential complications may be less fatal, the descending aorta and iliac regions were found to be most susceptible to embolism in our analysis.

Every year in the United States, 4,500 deaths occur from abdominal aortic aneurysm (AAA) rupture. Aneurysms develop when the arterial wall weakens. Many risk factors can contribute to aneurysm formation, including age, sex, ethnicity, smoking and hypertension [1]. AAAs are the most common form of aneurysm because the aorta experiences the highest wall shear stress (WSS) of any vessels in the human body. These aneurysms are 5–6% prevalent in men and 1–2% in women, both over 65 years of age [2]. In the aorta, high WSS causes plaque formation, but in peripheral arteries where the flow rate is lower, atherosclerosis can also trigger aneurysm formation.

While great strides continue to be made in the treatment of congestive heart failure using mechanical ventricular assist devices (VADs), several longstanding difficulties associated with pumping blood continue to limit their long-term use. Among the most troublesome has been the persistent risk of clot formation at the blood-device interface, which generally requires VAD recipients to undergo costly — and potentially dangerous — anticoagulation therapy for the duration of the implant. Another serious and persistent problem with long-term use of these pumps is the increased risk of infection associated with the use of percutaneous drivelines. To address these issues we are currently exploring a new approach to blood pump design that aims to solve both these problems by avoiding them altogether. Toward that end, we propose to harness the body’s own endogenous energy stores in order to eliminate the need to transmit energy across the skin. Further, we intend to transfer the energy from this internal power source to the circulation without contacting the blood to obviate the thrombogenic risks imposed by devices placed directly into the bloodstream. To power the implant we will employ a device developed previously by our group called a muscle energy converter (MEC), shown in Figure 1 . The MEC is, in essence, an implantable hydraulic actuator powered by the latissimus dorsi (LD) muscle with the capacity to transmit up to 1.37 joules of contractile work per stroke [ 1 ]. By training the muscle to express fatigue-resistant oxidative fibers and stimulating the LD to contract in coordination with the cardiac cycle, the MEC captures and transmits this contractile energy as a high-pressure low-volume (5 cc) hydraulic pulse that can be used, in principle, to actuate an implanted pulsatile blood pump. The goal of this research is to use the low-volume output of the MEC to drive a polymer-based aortic compression device for long-term circulatory support. In this context it is important to note that the idea of applying a counterpulsation device around the ascending aorta is not new. Indeed, this approach has been validated by clinical trials recently completed by Sunshine Heart Inc. showing that displacing 20 cc of blood at the aortic root has significant therapeutic benefits [ 2 ]. Unfortunately, while the pneumatic ‘C-Pulse’ device solves the blood-contacting problem, it suffers from the same limitations as traditional VADs — i.e., driveline infections. The device described here achieves the same volumetric displacement as the SSH device via geometric amplification of MEC outputs. Thus, through this mechanism we believe the low-volume power output of the MEC can be used to support heart failure patients while addressing the major limitations associated with long-term VAD use.

Left ventricular assist devices (LVADs) are mechanical pumps that provide full or partial support of the circulation in patients with varying degrees of heart failure (HF). This simulation study explores the hemodynamic effects of a continuous flow pump deployed in the Ascending Aorta (AAo) specifically focusing on: (a) perfusion of the coronary arterial circulation and (b) the effect of induced non-physiologic, swirling flow discharged by the pump on perfusion to head-neck vessels of the aortic arch.

Evaluating the risk of endograft migration is important for long-term durability of endovascular aneurysm repair (EVAR) technique. In this paper we apply a step-wise coupled finite element approach to evaluate the risk of endograft migration in representative aorta models subjected to in-vivo hemodynamic displacement forces. Device stability is observed to be a strong function of aortic geometry (tortuosity, proximal fixation) with increased tortuosity or lower proximal fixation leading to greater risk of device migration.

To assess shear stress in the tortuous and dynamic arterial circulation, we developed polymer- and catheter-based sensors that are both flexible and deployable. The flexible MEMS device provides an entry point to address spatial and temporal components of shear stress in the complicated arterial configuration. Theoretical and Computational Fluid Dynamics (CFD) analyses were performed. Fluoroscope and angiogram provided the geometry of aorta, and the Doppler ultrasound provided the pulsatile velocity for the boundary conditions. The development of micro electro mechanical systems (MEMS) and nano-scale sensors in our group have provided a means to undertake study of atherogenic hemodynamics and vascular oxidative stress in localizing early atherosclerosis.

This paper describes a polymer-based shear stress sensor built on catheter for in vivo measurements and potential application in atherosclerosis diagnosis. MEMS shear stress sensor with backside wire bonding has been used to address in vitro applications for micro-scale hemodynamics with high temporal and spatial resolution. However, to assess shear stress in the tortuous and dynamic arterial circulation, we had to develop a new generation of polymer- and catheter-based sensors that are both flexible and deployable. The individual sensor was packaged near the tip of a catheter for intravascular shear stress analysis. The wire bonding and electrode leads were insulated by a film of Parylene C and were connected to the external circuit along the guide-wire. The sensor was deployed through the catheter into the aorta of New Zealand White (NZW) rabbits by the femoral cut-down procedure. Based on the heat transfer principle, the device was able to detect small temperature perturbation in response to the pulsatile flow at ∼200 beats/minutes in the rabbits. The sensor was calibrated in the presence of rabbit blood flow at 37.8°C. We demonstrated the feasibility of translating a polymerbased device for dynamic intravascular measurement with a potential for clinical applications in detecting coronary artery disease and stroke.

The characterization of blood flow is important to establish links between the hemodynamics and the occurrence of cardiovascular diseases. This study describes the development of a 3-D computational model able to predict the blood flow along the abdominal aorta, including the renal and iliac branches. Upstream branches in the abdominal aorta lead to more complex flow patterns downstream, intensifying reverse and asymmetric flow patterns. The focus is on the occurrence of reverse flow and the perturbations in blood flow patterns originated by the branches. Results show regions of recirculation in the walls of the abdominal aorta, renal and iliac branches. It is concluded that, the renal branches induces perturbations in blood flow and result in asymmetric velocity profiles.

This paper describes a polymer-based cardiovascular shear stress sensor built on catheter for atherosis diagnosis. This flexible sensor detects small temperature perturbation as fluid past the sensing elements leading to changes in the resistance, from which shear stress is inferred. MicroElectroMechanical System (MEMS) surface manufacture technology is utilized for fabrication of the devices with biocompatible materials, such as parylene C, Titanium (Ti) and Platinum (Pt). The temperature coefficient of resistance (TCR) of the sensor is 0.11%/°C. When a catheter-based sensor is positioned near the wall of the rabbit aorta, our 3-D computational fluid dynamic model demonstrates that flow disturbance is negligible under steady state in a straight segment. The sensor has been packaged with a catheter and will be deployed into the aorta of NZW rabbits for realtime shear stress measurement.

In this work we focus on the fluid-structure interaction (FSI) problem of a St. Jude Regent 23mm bi-leaflet mechanical heart valve (BMHV) implanted in modeled straight aorta geometry with a simplified sinus. A FSI solver based on a recently developed curvilinear grid/immersed boundary method fluid flow solver is developed. The current numerical simulation focuses on the acceleration phase within the cardiac cycle when the leaflets are opening following the incoming flow. The simulated results are compared with experimental data with regard to the leaflet kinematics as well as valve induced wake vortical structures and excellent agreement between the simulation and measurements is reported.

Atherosclerotic renal artery stenosis is a common manifestation of generalized atherosclerosis and is the most common disorder of the renal arterial circulation. Despite the proven efficacy of surgical revascularization, endovascular therapy has emerged as the preferred strategy for treatment. Balloon-expandable stents for aorta-ostial renal artery stenosis is demonstrated to be a safe and effective therapy [1].