Plenary Lecture

Vortex Dynamics in Cardiac Flows

PAVLOS P. VLACHOS
O. PIERRAKOS
Mechanical Engineering Department .
School of Biomedical engineering and Sciences
Virginia Tech

Abstract: Left-ventricular (LV) flows are by nature intricate involving unsteadiness, inhomogeneity, anisotropy, and transition to turbulence. In the presence of a diseased condition, such as unhealthy or prosthetic heart valves, the complexity of the flow is further increased and the pumping efficiency of the left heart is compromised. It is thus imperative that we understand the complex cardiac energetics and physics of blood flow in both healthy and diseased hearts.
Recent studies have speculated that the flow dynamics of the left ventricle during diastolic filling may play a critical role in dictating overall cardiac health. Yet to date, no other study has provided quantitative proof of this hypothesis. The present work provides the first results that quantify and punctuate the significance of vortex dynamics and turbulence in the cardiac hydrodynamic efficiency and departs from the conventional paradigm that assessed cardiac efficiency using only transvalvular pressure losses.
By employing a state-of-the-art, high frequency and high resolution, planar flow diagnostic method, Time Resolved Digital Particle Image Velocimetry (TRDPIV), we investigated the complex dynamics of LV flows and the spatio-temporal evolution of large-scale vortices and turbulent eddies during a complete period of the heart cycle. We documented in detail the complex hemodynamic characteristics and energetics of LV flows and assessed the intricate structures that are generated in the LV due to the roll-up of shear layers and vortex shedding past the valve leaflets, the vortex ring formation and turbulence dissipation.
We demonstrate that despite popular belief, cardiac energetics are not dominated by turbulence. In contrast it is the formation of large scale vortex rings that govern the hydrodynamic efficiency of the ventricle.
The research herein enabled the development of tools for application in all cardiac energetic studies (unhealthy valves, tissue engineered valves, cardiac remodeling stages, and even congestive heart failure) and aid in better diagnosis of the efficiency and performance of the heart.

Brief Biography of the Speaker:
Dr Vlachos is assistant professor in the Mechanical Engineering Dept at Virginia Tech. He received his BS in Mechanical Engineering from the National Technical University of Athens (1995) and his MS (1998) and PhD (2000) in Engineering Mechanics from Virginia Tech. On August 2003 he assumed his current position as assistant professor on tenure track with the Dept. of Mechanical Engineering at Virginia Tech. His research focuses on experimental fluid mechanics addressing a variety of flows, primarily, wall bounded flows, vortex dynamics, biofluid mechanics and multi-phase flows. During the past 4 years he has attracted government and industry funded research on the order of $5.5 million with and has served as principal investigator for 18 projects. Dr. Vlachos has authored over 90 peer reviewed technical papers that appeared in archival journals and conference proceedings. He also holds five patents.
Dr Vlachos has received the Dean’s Award for Outstanding Assistant Professor in spring of ‘05. He also received the 2005 MIT T. F. Ogilvie Young Investigator in Fluid Mechanics Award. He s a recipient of 2006 NSF CAREER Award for his work on the fluid dynamics of arterial flows. In 2006 he was one out of approximately 80 engineers across all disciplines nationwide to be selected to participate in the National Academies of Engineering Frontiers of Engineering symposium.