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Technical Brief

A Novel In Vivo Approach to Assess Radial and Axial Distensibility of Large and Intermediate Pulmonary Artery Branches

[+] Author and Article Information
A. Bellofiore

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Madison, WI 53706-1609;
Department of Chemical,
Biomedical and Materials Engineering,
San José State University,
San José, CA 95192-0082

J. Henningsen, C. G. Lepak, L. Tian

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Madison, WI 53706-1609

A. Roldan-Alzate, D. W. Consigny, C. J. Francois

Department of Radiology,
University of Wisconsin-Madison,
Madison, WI 53792-3252

H. B. Kellihan

Department of Veterinary Medicine,
University of Wisconsin-Madison,
Madison, WI 53706-1102

N. C. Chesler

Department of Biomedical Engineering,
University of Wisconsin-Madison,
2146 ECB, 1550 Engineering Drive,
Madison, WI 53706-1609
e-mail: chesler@engr.wisc.edu

1Corresponding author.

Manuscript received April 28, 2014; final manuscript received January 10, 2015; published online February 5, 2015. Assoc. Editor: Jonathan Vande Geest.

J Biomech Eng 137(4), 044501 (Apr 01, 2015) (6 pages) Paper No: BIO-14-1182; doi: 10.1115/1.4029578 History: Received April 28, 2014; Revised January 10, 2015; Online February 05, 2015

Pulmonary arteries (PAs) distend to accommodate increases in cardiac output. PA distensibility protects the right ventricle (RV) from excessive increases in pressure. Loss of PA distensibility plays a critical role in the fatal progression of pulmonary arterial hypertension (PAH) toward RV failure. However, it is unclear how PA distensibility is distributed across the generations of PA branches, mainly because of the lack of appropriate in vivo methods to measure distensibility of vessels other than the large, conduit PAs. In this study, we propose a novel approach to assess the distensibility of individual PA branches. The metric of PA distensibility we used is the slope of the stretch ratio–pressure relationship. To measure distensibility, we combined invasive measurements of mean PA pressure with angiographic imaging of the PA network of six healthy female dogs. Stacks of 2D images of the PAs, obtained from either contrast enhanced magnetic resonance angiography (CE-MRA) or computed tomography digital subtraction angiography (CT-DSA), were used to reconstruct 3D surface models of the PA network, from the first bifurcation down to the sixth generation of branches. For each branch of the PA, we calculated radial and longitudinal stretch between baseline and a pressurized state obtained via acute embolization of the pulmonary vasculature. Our results indicated that large and intermediate PA branches have a radial distensibility consistently close to 2%/mmHg. Our axial distensibility data, albeit affected by larger variability, suggested that the PAs distal to the first generation may not significantly elongate in vivo, presumably due to spatial constraints. Results from both angiographic techniques were comparable to data from established phase-contrast (PC) magnetic resonance imaging (MRI) and ex vivo mechanical tests, which can only be used in the first branch generation. Our novel method can be used to characterize PA distensibility in PAH patients undergoing clinical right heart catheterization (RHC) in combination with MRI.

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Figures

Grahic Jump Location
Fig. 1

Flow chart of the process used to assess radial and axial distensibility from angiographic images. Stacks of 2D images, obtained with either CT-DSA or CE-MRA, were segmented to reconstruct 3D surface models of the PA network. Radial and axial distensibility were calculated for the first six branch generations. Note that in the text the branches R1 and L1 indicate the extralobar RPA and LPA, respectively.

Grahic Jump Location
Fig. 2

Change in average diameter of the six branch generations of RPA (solid line) and LPA (dashed line) from PRE to POST. Error bars show the SE. The straight dotted line represents the spatial resolution limit of CE-MRA (1.5 mm).

Grahic Jump Location
Fig. 3

Change in length of the six branch generations of RPA (solid line) and LPA (dashed line) from PRE to POST. Error bars show the SE. The straight dotted line represents the spatial resolution limit of CE-MRA (1.5 mm).

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