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Technical Briefs

An In Vitro Fluid Dynamic Study of Pediatric Cannulae: The Value of Animal Studies to Predict Human Flow

[+] Author and Article Information
Tobias C. Long, Joseph J. Pearson, Andrew C. Hankinson, Steven Deutsch

Department of Bioengineering,  The Pennsylvania State University, University Park, PA 16802

Keefe B. Manning1

Department of Bioengineering,  The Pennsylvania State University, University Park, PA 16802

1

Corresponding author.

J Biomech Eng 134(4), 044501 (Apr 20, 2012) (6 pages) doi:10.1115/1.4006428 History: Received December 01, 2011; Revised March 15, 2012; Posted March 23, 2012; Published April 18, 2012; Online April 20, 2012

A challenge to the development of pediatric ventricular assist devices (PVADs) is the use of the aortic cannulae attached to the devices. Cannulae used for pediatric application have small diameters and large pressure drops. Furthermore, during the development of the 12cc Penn State pediatric PVAD, particle image velocimetry (PIV) illustrated that hematocrit levels, through changes in blood viscoelasticity, affected the fluid dynamics. The objective of this study is to compare the fluid dynamics of a pediatric viscoelastic blood analog and a goat viscoelastic blood analog within the PVAD aortic cannula. Two acrylic models were manufactured to model the aortic cannula (6 mm and 8 mm diameters). PIV data was collected to examine the flow at the outlet of the VAD and in the aortic cannula at heart rates of 50 and 75 beats per minute (bpm). Three planes of data were taken, one at the centerline and two 1.5 mm above and below the centerline. Three more planes of data were taken orthogonal to the original planes. While a 75 bpm heart rate was used to represent normal operating conditions, a 50 bpm heart rate represented use of the PVAD during weaning. At 75 bpm, differences were evident between the two different fluids and the two models. Separation zones developed in the plane below the centerline for the higher hematocrit pediatric blood analog. This study raises question to the usefulness of animal testing results in regard to how well they predict the outcome of pediatric patients.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Viscosity comparison between the pediatric blood analog, whole pediatric blood, and goat blood

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Figure 2

Photograph of the acrylic cannula model (a). Section 1 (25.4 mm) represents the outlet port of the PVAD which has been made clear for this study. Section 2 (31.75 mm) represents the decreasing diameter within the cannula before it enters the aorta. Section 3 (101.6 mm, not fully shown) represents a continuation of the cannula into the aorta. Fluid flows from right to left in the model. The bottom line-diagram (b) and (c) demonstrates the difference in the two models.

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Figure 3

Bjork-Shiley valve showing four planes of interest (a). Side view of valve showing the planes as they are taken in the study (b).

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Figure 4

Highlighted upstream and downstream raw images showing the portions of the acrylic model that were imaged. The white line in the downstream view represents the overlap between the two field of views and correlates with the left-edge of the upstream image.

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Figure 5

Upstream peak velocities during the systolic cycle at the centerline plane of the 40 HCT blood analog (a) and the goat blood analog (b) at 75 bpm in 6 mm model

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Figure 6

Upstream peak velocities during the systolic cycle at the −1.5 mm plane of the 40 HCT blood analog (a) and the goat blood analog (b).

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Figure 7

Side view peak velocities during the systolic cycle at the centerline plane of the 40 HCT blood analog (a) and the goat blood analog (b) at 75 bpm in the 6 mm model

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Figure 8

Upstream peak velocities during the systolic cycle at the −1.5 mm plane of the 40 HCT blood analog (a) and the goat blood analog (b) in the 8 mm model

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Figure 9

Downstream peak velocities during the systolic cycle at the center plane of the 40 HCT blood analog (a) and the goat blood analog (b) in the 8 mm model at 75 bpm. The overlap point is consistent with Fig. 4.

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