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Technical Briefs

In Vitro Pulsatility Analysis of Axial-Flow and Centrifugal-Flow Left Ventricular Assist Devices

[+] Author and Article Information
J. Ryan Stanfield

Department of Mechanical Engineering,
University of Utah,
50 S Central Campus Dr.,
Rm. 2110, Salt Lake City, UT 84112
e-mail: ryan.stanfield@utah.edu

Craig H. Selzman

Department of Surgery,
Division of Cardiothoracic Surgery,
University of Utah,
30 N 1900 E, SOM 3C127,
Salt Lake City, UT 84132

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received October 6, 2012; final manuscript received January 21, 2013; accepted manuscript posted January 29, 2013; published online February 11, 2013. Assoc. Editor: Ender A. Finol.

J Biomech Eng 135(3), 034505 (Feb 11, 2013) (6 pages) Paper No: BIO-12-1466; doi: 10.1115/1.4023525 History: Received October 06, 2012; Revised January 21, 2013; Accepted January 29, 2013

Recently, continuous-flow ventricular assist devices (CF-VADs) have supplanted older, pulsatile-flow pumps, for treating patients with advanced heart failure. Despite the excellent results of the newer generation devices, the effects of long-term loss of pulsatility remain unknown. The aim of this study is to compare the ability of both axial and centrifugal continuous-flow pumps to intrinsically modify pulsatility when placed under physiologically diverse conditions. Four VADs, two axial- and two centrifugal-flow, were evaluated on a mock circulatory flow system. Each VAD was operated at a constant impeller speed over three hypothetical cardiac conditions: normo-tensive, hypertensive, and hypotensive. Pulsatility index (PI) was compared for each device under each condition. Centrifugal-flow devices had a higher PI than that of axial-flow pumps. Under normo-tension, flow PI was 0.98 ± 0.03 and 1.50 ± 0.02 for the axial and centrifugal groups, respectively (p < 0.01). Under hypertension, flow PI was 1.90 ± 0.16 and 4.21 ± 0.29 for the axial and centrifugal pumps, respectively (p = 0.01). Under hypotension, PI was 0.73 ± 0.02 and 0.78 ± 0.02 for the axial and centrifugal groups, respectively (p = 0.13). All tested CF-VADs were capable of maintaining some pulsatile-flow when connected in parallel with our mock ventricle. We conclude that centrifugal-flow devices outperform the axial pumps from the basis of PI under tested conditions.

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Figures

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Fig. 1

Schematic of mock circulation loop with pulsatile capability. PCC/SCC, pulmonary/systemic compliance chamber(s); LA, left atrium; LV, left ventricle. Not shown: unidirectional pericardial valves at “top” of LV to represent mitral and aortic valves.

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Fig. 2

Baseline oscillating pressure waveforms associated with each simulated cardiac condition: normo-tensive, hypertensive, and hypotensive. AoP, aortic pressure; LVP, left ventricular pressure (mm Hg).

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Fig. 3

Oscillating head and flow coefficient waveforms under all tested conditions for axial (A1, A2) and centrifugal (C1, C2) continuous-flow pumps. φ, flow coefficient; ψ, head coefficient. Left column are waveforms for all pumps under normo-tensive condition, middle column under hypertensive condition, right column under hypotensive condition.

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Fig. 4

Pressure-flow (first column: ΔP-Q; second column: ψ-φ) performance curves for all four devices under the three tested conditions. Q, flow rate (L/min); ΔP, pressure differential (mm Hg); φ, flow coefficient; ψ, head coefficient.

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Fig. 5

Hydraulic power (mW), supplied by each VAD in a typical cycle under the pulsatile cardiac conditions: (1) normo-tensive, (2) hypertensive, and (3) hypotensive

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