FLOW VISUALIZATION STUDY OF WORLDHEART LEVACORTM VADUNDER SYNCHRONOUS PULSATILE CONDITIONS

Fangjun Shu,♥ Stijn Vandenberghe,♥ Philip J Miller and James F Antaki ♥

♥ BioMedical Engineering, Carnegie Mellon University Bioengineering, University of Pittsburgh, WorldHeart, Inc.

INTRODUCTION• Rotary (Turbodynamic) blood pumps are

typically designed for a single “best efficiency” operating point; however in practice they must operate over a wide dynamic range of flow and pressure conditions: due to the varying demands of the body, and due to the pulsations caused by the native heart.

• Pulsatility causes very complicated time-dependent fluid dynamics within the pump.

• Time-varying CFD analyses over the full range of operating conditions are prohibitive.

• These studies were performed to characterize the time-varying hemodynamics experimentally through flow visualization.

FLOW VISUALIZATION:

The fluid dynamics within the outlet diffuser and part of the blade to blade region of the impeller was investigated using a 2D PIV system. Glycerol/water (35/65 V%) mixture seeded with 7 μm fluorescent particles was used as working fluid.

The camera was triggered using pump encoder and ventricle volume signals, giving image pairs of 16 cardiac phases with the impeller in a fixed position.

RESULTSSTEADY STATE:

12

34

51

2

3

4

5

PIV was conducted at 5 steady-state conditions including 3 pump speeds and 3 flow coefficients.

Camera

No flow separation was observed within the outlet diffuser at nominal flow coefficient. At fixed flow coefficient, flow similarity is apparent.

PIV measurement region

4 1 5

2 3 Smooth flow & separated flow in the outlet under low and high flow coefficient

The velocity field relative to the impeller was acquired by subtracting the circumferential velocity (ωr) from the absolute velocity field. Flow recirculation was observed within the blade-blade region at low flow coefficient.

2 31

PULSATILE CONDITIONS:

A

B

C

D

• At 1500 rpm, intermittent flow recirculation was observed in the blade to blade region.• For both speeds, intermittent flow separations were observed within the outlet diffuser.

LOW (1500 rpm)Absolute velocity Relative velocity

NOMINAL (2250 rpm) Absolute velocity Relative

velocity

CONCLUSIONS• PIV measurements were conducted for

the prototype WorldHeart LevacorTM pump in both steady state and pulsatile conditions.

Steady State

• Under steady state conditions, the flow field within the critical regions of interest exhibited similitude according to the non-dimensional flow coefficient.

• Steady state nominal flow conditions at all three speeds demonstrated well-behaved velocity fields, absent of separation and recirculation.

Pulsatile

• At low RPM, the (mock) ventricular contribution to the velocity field was relatively strong, inducing transient regurgitation, flow separation (outlet diffuser) and flow recirculation (blade-blade region).

• At nominal RPM, regurgitation and flow recirculation no longer exist.

SV(ml)

HR(BPM)

MAP(mmHg)

Pump RPMLow

(1500)Nominal(2250)

High(3000)

75 60 80 X X X50 90 80 X X X

37.5 120 80 X X X

Condition 1

A B C D A B C D

Condition 2

C

D

A

B

METHODSPUMP AND FLOW LOOP:

The experimental version of the pump was shaft-driven and was fitted with a transparent (acrylic) housing to permit visualization of the flow path.

Experimental setup

The pump was interposed into a modified Vivitro cardiovascular simulator, comprised of a reciprocating positive displacement pump, reservoir, ventricle, compliance chamber, and flow restrictor, connected by PVC tubing.

Levacore VAD

Results of two representative conditions (low and nominal pump speed) are presented.