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Article

PIV Measurements of Flow in a Centrifugal Blood Pump: Time-Varying Flow

[+] Author and Article Information
Steven W. Day1

The University of Virginia, Charlottesville, VA 22903sday@alumni.virginia.edu

James C. McDaniel

The University of Virginia, Charlottesville, VA 22903

1

Corresponding author. Current address: Section of Evolution & Ecology, University of California, One Shields Avenue, Davis, CA 95616

J Biomech Eng 127(2), 254-263 (Sep 20, 2004) (10 pages) doi:10.1115/1.1865190 History: Received October 07, 2003; Revised September 20, 2004

Abstract

Measurements of the time-varying flow in a centrifugal blood pump operating as a left ventricular assist device (LVAD) are presented. This includes changes in both the pump flow rate as a function of the left ventricle contraction and the interaction of the rotating impeller and fixed exit volute. When operating with a pulsing ventricle, the flow rate through the LVAD varies from $0–11L∕min$ during each cycle of the heartbeat. Phase-averaged measurements of mean velocity and some turbulence statistics within several regions of the pump, including the inlet, blade passage, exit volute, and diffuser, are reported at 20 phases of the cardiac cycle. The transient flow fields are compared to the constant flow rate condition that was reported previously in order to investigate the transient effects within the pump. It is shown that the quasi-steady assumption is a fair treatment of the time varying flow field in all regions of this representative pump, which greatly simplifies the comprehension and modeling of this flow field. The measurements are further interpreted to identify the effects that the transient nature of the flow field will have on blood damage. Although regions of recirculation and stagnant flow exist at some phases of the cardiac cycle, there is no location where flow is stagnant during the entire heartbeat.

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Figures

Figure 1

Cut-away view of the pump showing the location of the three measurement planes within the pump: IE-inlet elbow, BP-Blade passage, CW-Cut-water.

Figure 2

Schematic of flow loop showing pulsed ventricle simulator (PVS), Left Ventricular Assist device under investigation (LVAD), arterial compliance (AC), venous compliance (VC), and valve for systemic resistance (R). Measurements of flow rate include flow through aortic valve (AoQ) and flow through LVAD (VADQ). Locations of pressure measurements are aortic pressure (AoP), ventricular (LVP), and atrial (LAP).

Figure 3

Measured physiological pressures and flow rates for a rotary LVAD over two heartbeats. Pump speed is constant at 2100rpm.

Figure 4

Phase averaged speed in the inlet elbow at 8 phases with phase, ϕ, and flow rate, Q, indicated for each.

Figure 5

Time evolution of mean speed and rms of fluctuating velocity near the inlet of inlet elbow during the rapid acceleration of flow and through systole and then through deceleration and diastole compared to steady flow at 11L∕min

Figure 6

Mean Speed in the blade passage

Figure 7

Phase-averaged flowfield at 13π∕10 in the blade passage compared to steady-state measurement at approximately the same flow rate, 4.5L∕min

Figure 8

Phase averaged mean velocity field in the cut-water at 8 phases of pulsatile flow

Figure 9

Profiles of mean velocity and MRSS at x=0.02m within the cut-water as a function of pulse phase (solid line) compared to contours for steady flow cases (dashed line)

Figure 10

Figure 11

Comparison of flow at 12π∕10 in the blade passage to steady flow at the same flow rate, 6L∕min

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