Flow-assisting devices

Flow Aids. Flow aids are devices used to assist in discharging materials from a bin or other storage container. The best use of such a device is when gravity alone is insufficient or impractical to provide rehable discharge. However, in many instances, flow aid devices are ovemsed in appHcations in which they are either uimecessary or create new problems. 

Ca.rdia.c-AssistDevices. The principal cardiac-assist device, the intra-aortic balloon pump (lABP), is used primarily to support patients before or after open-heart surgery, or patients who go into cardiogenic shock. As of the mid-1990s, the lABP was being used more often to stabilize heart attack victims, especially in community hospitals which do not provide open-heart surgery. The procedure consists of a balloon catheter inserted into the aorta which expands and contracts to assist blood flow into the circulatory system and to reduce the heart s workload by about 20%. The disposable balloon is powered by an external pump console. 

Vatta M, Stetson SJ, Jimenez S, et al. Molecular normalization of dystrophin in the failing left and right ventricle of patients treated with either pulsatile or continuous flow-type ventricular assist devices. J Am Coll Cardiol. Mar3 2004 43(5) 811-817. 

Lao, A.I.K., Trau, D., Hsing, I., Miniaturized flow fractionation device assisted by a pulsed electric field for nanoparticle separation. Anal. Chem. 2002, 74, 5364-5369. 

X Biomaterials has reiterated the need for the development of blood-compatible materials since progress in this field is a condition for advances in the application of cardiocirculatory-assist devices and other procedures which require continuous or intermittent handling of blood (I). For example, the task force has specifically identified the development of small-diameter blood vessel prostheses and chronic blood access catheters as priority applications of blood-compatible materials. Both of these devices are used in low-flow situations where red thrombus formation (i.e., intrinsic clotting system activation) predominates (2). 

Type of end use — this may deal with transmission of information (biopotentials, temperature, pressure, blood flow rate), energy (electrical stimulation, power for heart-assist devices), transfer of matter (cannula for blood), and load (attachment of a prosthesis) ... 

Cardiovascular disease, namely, coronary artery disease, remains the leading cause of death in the developed nations. Over the last few years, MEMS sensors have advanced the understanding of blood flow, namely, fluid shear stress, in arterial circulation. Fluid shear stress is defined as the frictional force acting tangentially on the surface of a blood vessel wall. Furthermore, the measurement of wall shear stress is important to study the durability of prosthetic valves and to monitor thrombosis or blood clots in cardiopulmonary bypass machines, artificial hearts, and left ventricular assist devices. Luminal shear stress measurement predicts the development of atherosclerotic plaque in patients at risk for acute heart attacks. In this context, the application of microscale hot-wire anemometry bridges fluid mechanics of blood flow with vascular biology. 

FIGURE 20.16 The Heaitmate II (Thotatec Corporation, Pleasanton, California) is an axial-flow ventricular assist device currently under development. Unlike the pusher plate and pneumatic sac designs shown in Fig. 20.15, the Heaitmate II provides continuous flow support without pulsatile pressure changes. The Heartmate II is much smaller than the Novacor. Thoratec, and Heaitmate VE VADs. 

Frazier O, Gemmato C, Myers TJ, Gregoric ID, Radovancevic B, Loyalka P, et al. Initial clinical experience with the Heartmate II axial-flow left ventricular assist device. Tex Heart Inst J 2007 34(3) 275. 

Lanmen M, Kanfmann T, Timms D, Schlanstein P, Jansen S, Gregory S, et al. Flow analysis of ventiicnlar assist device inflow and outflow cannula positioning nsing a naturally shaped ventricle and aortic branch. Artif Organs 2010 34(10) 798-806. 

Left ventricular assist devices Support heart function and blood flow... 

Starling RC, Naka Y, Boyle AJ, et al. Results of the post-U.S. Food and Dmg Administration-approval study with a continuous flow left ventricular assist device as a bridge to heart transplantation a prospective study using the INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support). JAm Coll Cardiol May 2011 57(19) 1890-8. 

Ramakrishna, H., Pajaro, O., 2011. Heart transplantation in the era of continuous flow ventricular assist devices and the total artificial heart will new technologies surpass the gold standard Annals of Cardiac Anaesthesia 14, 174-175. 

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