1) The study investigated fluid dynamics of a ventricular assist device (VAD) called the Spiral Vortex (SV) VAD using laser Doppler anemometry while pumping a blood analogue fluid under physiological conditions. 2) The flow was dominated by an irrotational vortex that accelerated and precessed in phase with the pumping diaphragm, and two unexpected structures enhanced wall washing. 3) Under a weaning mode, the main vortex coherence degraded and recirculation was observed, indicating a need for anticoagulation in this mode. Turbulence increased with asymmetric diaphragm buckling in both modes.

1. Surname: NUGENT Date of first submission: 14 March 2005
Given names: ALLEN HAROLD Date of final submission: 29 July 2005
School: GRADUATE SCHOOL OF Degree: PhD
BIOMEDICAL ENGINEERING Faculty: ENGINEERING
Institution: UNIVERSITY OF NEW SOUTH WALES
Title: FLUID DYNAMICAL INVESTIGATION OF A VENTRICULAR ASSIST DEVICE
Abstract:
The Spiral Vortex (SV) ventricular assist device (VAD) was investigated by 2-component laser
Doppler anemometry (LDA) while pumping a refractive index-matched blood analogue fluid. The VAD
was operated under physiological conditions corresponding to 75% assist (4 litres/minute) or weaning
from assist (2 litres /minute). Data were sampled on a 5-mm grid throughout most of the interior of the
blood chamber, using two orthogonal LDA configurations from which 3D velocity data were synthesised.
Data were subjected to statistical analysis of quasistatic time intervals and approximation by Fourier
series. The velocity vector fields were explored statically (via 2D plots) and dynamically (using 3D
animations of the reduced data). Reynolds stresses were computed and visualised in 2D. Fluid pathlines
were simulated and plotted in 3D.
The flow was found to be dominated by an irrotational vortex that accelerated and precessed in phase
with the pumping diaphragm. Two unexpected flow structures, a rising, swirling near-wall layer in
diastole and reflection of the outflow vortex upon valve closure, enhanced washing of the walls. The
thickness of the boundary layer was estimated to be 2 mm. Fluid velocities were generally lower than
those reported in steady-flow studies on the SV VAD, although turbulence was comparable.
Under the weaning mode, the coherence of the main vortex was degraded and flow recirculation was
observed distal to the inflow port; this operating mode must be regarded as an indication for
anticoagulation. In both pumping modes, turbulence was elevated in association with asymmetric
buckling of the pneumatically driven diaphragm.
Suboptimal orientation of the tilting-disc inlet valve gave rise to augmented turbulence production
and skewing of the main vortex; similar results were obtained for an axisymmetric polymer (Jellyfish)
valve, despite its advantageous haemodynamics. Flow stagnation was apparent where the inflow stream
impinged on the wall, opposite the inflow port.
The overall design of the SV VAD appears to almost ideal, in the context of current technology.
However, elimination of recirculation/stagnation zones, especially in the weaning mode, remains a
priority for the ultimate optimisation of haemocompatibility. Pulsatile VADs will probably never be
entirely free of flow recirculation and stagnation, and published claims to the contrary probably reflect
study limitations.