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TECHNICAL PAPERS: Fluids/Heat/Transport

Correspondence of Low Mean Shear and High Harmonic Content in the Porcine Iliac Arteries

[+] Author and Article Information
Heather A. Himburg, Morton H. Friedman

Department of Biomedical Engineering, Duke University, Durham, NC

J Biomech Eng 128(6), 852-856 (May 16, 2006) (5 pages) doi:10.1115/1.2354211 History: Received February 13, 2006; Revised May 16, 2006

Abstract

Background. Temporal variations in shear stress have been suggested to affect endothelial cell biology. To better quantify the range of dynamic shear forces that occur in vivo, the frequency content of shear variations that occur naturally over a cardiac cycle in the iliac arteries was determined. Method of Approach. Computational fluid dynamic calculations were performed in six iliac arteries from three juvenile swine. Fourier analysis of the time-varying shear stress computed at the arterial wall was performed to determine the prevalence of shear forces occurring at higher frequencies in these arteries. Results. While most of each artery experienced shear forces predominantly at the frequency of the heart rate, the frequency spectra at certain regions were dominated by shear forces at higher frequencies. Regions whose frequency spectra were dominated by higher harmonics generally experienced lower mean shear stress. The negative correlation between shear and dominant harmonic was significant $(p=0.002$). Conclusions. Since lesion development typically occurs in regions experiencing low time-average shear stress, this result suggests that the frequency content of the shear exposure may also be a contributing factor in lesion development. A better understanding of the vascular response to shear components of different frequencies might help rationalize the notion of "disturbed flow" as a hemodynamic entity.

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Figures

Figure 1

Cast of a porcine abdominal aorta and its major iliac branches

Figure 2

The inlet flow waveform applied uniformly at the aortic inlet

Figure 3

The calculated time-varying shear stress at five locations in a left iliac artery. (A) 2-D depiction of the left iliac artery indicating the selected locations. Arrow indicates flow direction and location of flow divider. (B) Time-varying shear stress at the five sites.

Figure 4

Frequency spectra of the time-varying shear stress at the sites in (A). Ordinate is normalized amplitude.

Figure 5

(a) Maps of the dominant harmonic in each iliac artery. (b) Corresponding time-average shear stress maps. The arrow in the top panel indicates the circumflex iliac ostium. In all images the direction of flow is from right to left. Black arrow indicates location of the flow divider.

Figure 6

The time-average shear stress in the six arteries as a function of the dominant harmonic. Solid black line is best fit based on linear regression.

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