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Technical Briefs

Validation of a Pressure Diameter Method for Determining Modulus and Strain of Collagen Engagement for Long Branches of Bovine Pulmonary Arteries

[+] Author and Article Information
Mark Reusser1

Department of Bioengineering,  University of Colorado, Denver, CO 80045mark.reusser@ucdenver.edu

Kendall S. Hunter

Department of Bioengineering,  University of Colorado, Denver, CO 80045

Steven R. Lammers, Kurt R. Stenmark

Department of Pediatrics,Division of Critical Care,  University of Colorado, Denver, Colorado 80045

1

Corresponding author.

J Biomech Eng 134(5), 054501 (May 25, 2012) (7 pages) doi:10.1115/1.4006686 History: Received December 12, 2011; Revised March 28, 2012; Posted May 01, 2012; Published May 25, 2012; Online May 25, 2012

Recent studies have shown that capacitance measurements of large arteries provide better prognosis and diagnosis than tests of resistance alone in pulmonary hypertension (Mahapatra , 2006, “Relationship of Pulmonary Arterial Capacitance and Mortality in Idiopathic Pulmonary Arterial Hypertension,” J. Am. Coll. Cardiol., 47 (4), pp. 799–803; Reuben, 1971, “Compliance of the Human Pulmonary Arterial System in Disease,” Circ. Res., 29 , pp. 40–50]. Decreased arterial capacitance causes increased load to the heart and is the direct result of increased stiffness and elastic modulus of the arterial wall. Here, we validate a pressure-diameter (PD) method for comparing the elastic modulus and collagen engagement for post-hilar pulmonary arteries with a large range of arterial diameter. The tissue mechanics of the post-hilar arteries are not well-characterized in pulmonary hypertension. It is believed that future studies with this method will provide useful insight into the role of passive tissue mechanics of these arteries in the pathophysiology of pulmonary hypertension, eventually improving clinical diagnosis, prognosis, and treatment. Post-hilar pulmonary arteries, excised from healthy and hypertensive calves and healthy cows, were inflated over a range of 0 [mm Hg] to 110 [mm Hg] in an isolated tissue bath. Internal pressure was recorded with an electric pressure catheter. Artery diameter and longitudinal stretch were recorded photographically. Stress-strain data curves were extracted using Lame’s law of thick-walled tubes. Radial strips were removed from each section and tested in a uniaxial (MTS) tester for validation. Both the elastic modulus and collagen engagement strain were similar to results obtained by more traditional means. The average difference between measured values of the two methods for collagen engagement strain was 3.3% of the average value of the engagement strain. The average difference between the measured values of the two methods for modulus of elasticity was 7.4% of the average value of the modulus. The maximum, theoretical, relative error for the stress determined with the PD method was calculated at 20.3%. The PD method proved to be a suitable replacement for uniaxial strain tests in comparing collagen engagement strains. The method allowed faster testing of tissues of multiple diameters, while removing the effect of end conditions. The PD method will be of further utility in continued study of tissue mechanics in pulmonary hypertension studies.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Image of excised pulmonary artery branch showing placement of Loctite dots

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Figure 2

Basic schematic of testing setup

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Figure 3

Typical pressure diameter curve

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Figure 4

Flow diagram of tissue sectioning

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Figure 5

Smoothing function applied to typical stress-strain curve using PD method

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Figure 6

Bland-Altman plot for modulus of elasticity

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Figure 7

Bland-Altman plot for collagen engagement strain

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Figure 8

Typical PD and MTS stress-strain curves with PD error bars

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