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Design Innovation Paper

Design of a Pulsatile Flow Facility to Evaluate Thrombogenic Potential of Implantable Cardiac Devices

[+] Author and Article Information
Sivakkumar Arjunon, Neelakantan Saikrishnan

The Wallace H. Coulter
School of Biomedical Engineering,
Georgia Institute of Technology and Emory University,
Atlanta, GA 30318

Pablo Hidalgo Ardana

School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30318

Shalv Madhani

Department of Bioengineering,
University of Pittsburgh,
Pittsburgh, PA 15261

Brent Foster

Radiology and Imaging Science Department,
National Institutes of Health (NIH),
Bethesda, MD 20892

Ari Glezer

School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Ajit P. Yoganathan

The Wallace H. Coulter
School of Biomedical Engineering,
Georgia Institute of Technology and Emory University,
Atlanta, GA 30318
School of Chemical and Biomolecular Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Manuscript received May 9, 2014; final manuscript received January 9, 2015; published online February 11, 2015. Assoc. Editor: Ender A. Finol.

J Biomech Eng 137(4), 045001 (Apr 01, 2015) (11 pages) Paper No: BIO-14-1203; doi: 10.1115/1.4029579 History: Received May 09, 2014; Revised January 09, 2015; Online February 11, 2015

Due to expensive nature of clinical trials, implantable cardiac devices should first be extensively characterized in vitro. Prosthetic heart valves (PHVs), an important class of these devices, have been shown to be associated with thromboembolic complications. Although various in vitro systems have been designed to quantify blood-cell damage and platelet activation caused by nonphysiological hemodynamic shear stresses in these PHVs, very few systems attempt to characterize both blood damage and fluid dynamics aspects of PHVs in the same test system. Various numerical modeling methodologies are also evolving to simulate the structural mechanics, fluid mechanics, and blood damage aspects of these devices. This article presents a completely hemocompatible small-volume test-platform that can be used for thrombogenicity studies and experimental fluid mechanics characterization. Using a programmable piston pump to drive freshly drawn human blood inside a cylindrical column, the presented system can simulate various physiological and pathophysiological conditions in testing PHVs. The system includes a modular device-mounting chamber, and in this presented case, a 23 mm St. Jude Medical (SJM) Regents® mechanical heart valve (MHV) in aortic position was used as the test device. The system was validated for its capability to quantify blood damage by measuring blood damage induced by the tester itself (using freshly drawn whole human blood). Blood damage levels were ascertained through clinically relevant assays on human blood while fluid dynamics were characterized using time-resolved particle image velocimetry (PIV) using a blood-mimicking fluid. Blood damage induced by the tester itself, assessed through Thrombin-anti-Thrombin (TAT), Prothrombin factor 1.2 (PF1.2), and hemolysis (Drabkins assay), was within clinically accepted levels. The hydrodynamic performance of the tester showed consistent, repeatable physiological pressure and flow conditions. In addition, the system contains proximity sensors to accurately capture leaflet motion during the entire cardiac cycle. The PIV results showed skewing of the leakage jet, caused by the asymmetric closing of the two leaflets. All these results are critical to characterizing the blood damage and fluid dynamics characteristics of the SJM Regents® MHV, proving the utility of this tester as a precise system for assessing the hemodynamics and thrombogenicity for various PHVs.

FIGURES IN THIS ARTICLE
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References

Figures

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Fig. 1

Schematic of the system design showing the pump (linear actuator and motor), blood containing test section, and the pressure regulation system

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Fig. 2

Modular chambers that can be plugged into the tester to simultaneously study fluid dynamics and blood damage levels. (a) Chamber to study flow in MHV leaflet-hinges, (b) an inferior vena-cava filter design and chamber to mount the filter, and (c) a MHV with transparent ring and its chamber with an axisymmetric aortic sinus.

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Fig. 3

(a) Valve holder with SJM valve, (b) test system showing the actuator at the bottom, middle test section with bypass tube, flexible bag inside the compliance chamber at the top

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Fig. 4

Top figure illustrates the arrangement of the sensor, emitter, and leaflets during both opening and closing of MHV. Bottom flow-curve figure shows the part of the cardiac cycle that was studied using PIV.

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Fig. 5

Pressure variation on aortic and ventricular side of the MHV, averaged over 15 cycles, are shown after filtering high frequency oscillations. The negative section of flow curve indicates closing and leakage volumes of the MHV.

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Fig. 6

(a) Leaflet position traces of leaflet 1 and leaflet during a single cardiac cycle. In the vertical axis, an angle of 7 deg corresponds to fully open position and an angle of 60 deg corresponds to fully closed position. (b) Spread of single-leaflet position traces sampled over 100 cycles.

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Fig. 7

Top two rows: plot of PIV velocity magnitude in the ventricular side of the valve for two cardiac cycles. The change in direction of dotted lines (between cycle 1 and cycle 2) during the closing phase indicates the vectoring of the leakage jet due to asynchronous leaflet closing during cycle 2. Bottom two rows: PIV velocity vectors and vorticity contours for two cardiac cycles (top and bottom).

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Fig. 8

Blood coagulation indicators: (a) TAT, (b) hemolysis, and (c) PF1.2 showing that the coagulation potential of the tester was less than that induced when the MHV was mounted in the tester

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