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Research Papers

Differences in the Microstructure and Biomechanical Properties of the Recurrent Laryngeal Nerve as a Function of Age and Location

[+] Author and Article Information
Megan J. Williams

Graduate Interdisciplinary Program of
Biomedical Engineering,
University of Arizona,
1130 North Mountain Avenue,
Tucson, AZ 85721
e-mail: mjoy@email.arizona.edu

Urs Utzinger

Department of Biomedical Engineering;
Graduate Interdisciplinary Program of
Biomedical Engineering,
University of Arizona,
Tucson, AZ 85721
BIO5 Institute,
University of Arizona,
Thomas W. Keating Bioresearch Building,
#131D, P.O. 210240,
Tucson, AZ 85721
e-mail: utzinger@email.arizona.edu

Julie M. Barkmeier-Kraemer

Voice and Swallowing Center,
The University of California—Davis,
2521 Stockton Blvd Suite 6200,
Sacramento, CA 95817
e-mail: jbark@ucdavis.edu

Jonathan P. Vande Geest

Associate Professor
Mem. ASME
Department of Aerospace and
Mechanical Engineering;
Department of Biomedical Engineering;
Graduate Interdisciplinary Program of
Biomedical Engineering,
University of Arizona,
Tucson, AZ 85721
BIO5 Institute,
University of Arizona,
Tucson, AZ 85721
e-mail: jpv1@email.arizona.edu

1Corresponding author.

Manuscript received January 22, 2014; final manuscript received April 30, 2014; accepted manuscript posted May 15, 2014; published online June 5, 2014. Assoc. Editor: Barclay Morrison.

J Biomech Eng 136(8), 081008 (Jun 05, 2014) (9 pages) Paper No: BIO-14-1044; doi: 10.1115/1.4027682 History: Received January 22, 2014; Revised April 30, 2014; Accepted May 15, 2014

Idiopathic onset of unilateral vocal fold paralysis (UVP) is caused by damage to the recurrent laryngeal nerve (RLN) and results in difficulty speaking, breathing, and swallowing. This damage may occur in this nerve as it loops around the aortic arch, which is in a dynamic biomechanical environment. The goal of this study is to determine if the location-dependent biomechanical and microstructural properties of the RLN are different in piglets versus adolescent pigs. The neck/distal and thoracic/proximal (near the aortic arch) regions of the RLN from eight adolescent pigs and six piglets were isolated and mechanically assessed in uni-axial tension. Two-photon imaging (second harmonic) data were collected at 5%, 10%, and 15% strain during the mechanical test. The tangential modulus (TM) and the strain energy density (W) were determined at each level of strain. The mean mode of the preferred fiber angle and the full width at half maximum (FWHM, a measure of fiber splay) were calculated from the imaging data. We found significantly larger values of TM, W, and FWHM in the proximal segments of the left RLN when compared to the distal segments (18.51 MPa ± 1.22 versus 10.78 MPa ± 1.22, p < 0.001 for TM, 0.046 MPa ± 0.01 versus 0.026 MPa ± 0.01, p < 0.003 for W, 15.52 deg ± 1.00 versus 12.98 deg ± 1.00, p < 0.001 for FWHM). TM and W were larger in the left segments than the right (15.32 MPa ± 1.20 versus 11.80 MPa ± 1.20, p < 0.002 for TM, 0.038 MPa ± 0.01 versus 0.028 MPa ± 0.01, p < 0.0001 for W). W was larger in piglets when compared to adolescent pigs (0.042 MPa ± 0.01 versus 0.025 MPa ± 0.01, p < 0.04). The proximal region of the left porcine RLN is more stiff than the distal region and has a higher degree of fiber splay. The left RLN of the adolescent pigs also displayed a higher degree of strain stiffening than the right. These differences may develop as a result of the more dynamic environment the left RLN is in as it loops around the aortic arch.

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References

Figures

Grahic Jump Location
Fig. 1

Anatomy of the right and left recurrent laryngeal nerve and surrounding environment. This figure has been reprinted and adapted from Deslauriers, J., 2007, “Anatomy of the Neck and Cervicothoracic Junction,” Thoracic Surg. Clin. 17, pp. 529–544. Copyright 2007 by Elsevier, Inc. [50].

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Fig. 2

Cauchy stress–stretch ratio data from a representative piglet specimen (a) and a representative adolescent pig specimen and (b) with corresponding fits with α and β values

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Fig. 3

Representative SHG multiphoton images of a proximal segment of piglet RLN (left) and a proximal segment of adolescent pig RLN (right) at 0% strain (top) and 15% strain (middle). SHG channel depicts the collagen content of the tissue. These images are taken approximately 100 μm into the adolescent pig segment and 60 μm into the piglet segment. The red arrows indicate the angle at which 90 deg is measured. Histograms (bottom) show the overall collagen fiber orientations throughout the tissue at 0% and 15% strains.

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Fig. 4

(a) Average TM is reported for adolescent and piglet nerves at each value of stretch; (b) average TM is reported for all adolescent and piglet RLN segments and all left and right RLN segments (*p < 0.002); and (c) average TM is reported for proximal and distal segments of the left and right RLN (*,†p < 0.001)

Grahic Jump Location
Fig. 5

(a) Average W is reported for adolescent and piglet nerves at each value of stretch; (b) average W is reported for all adolescent and piglet RLN segments (*p < 0.038) and all left and right RLN segments (†p < 0.001); (c) Average W is reported for all proximal and distal segments of adolescent pigs and piglets (‡,†p < 0.008; *,§p < 0.007); and (d) Average W is reported for all proximal and distal segments of the left and right RLN (*,†p < 0.002)

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Fig. 6

(a) Average values of α and β are reported for all adolescent pig and piglet RLN segments (*p < 0.006, †p < 0.014); (b) average α is reported for all proximal and distal segments of the left and right RLN (*p < 0.011)

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Fig. 7

(a) Average FWHM is reported for all proximal and distal segments of all left and right RLNs (†,*p < 0.004; ‡,§p < 0.001); (b) average mean mode is reported for all proximal and distal segments (*p < 0.004)

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