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Title: Biomechanical Responses of Neonatal Brachial Plexus to Mechanical Stretch
Abstract This study investigated the biomechanical responses of neonatal piglet brachial plexus (BP) segments—root/trunk, chord, and nerve at two different rates, 0.01 mm/second (quasistatic) and 10 mm/second (dynamic)—and compared their response to another peripheral nerve (tibial). Comparisons of mechanical responses at two different rates reported a significantly higher maximum load, maximum stress, and Young's modulus (E) values when subjected to dynamic rate. Among various BP segments, maximum stress was significantly higher in the nerve segments, followed by chord and then the root/trunk segments except no differences between chord and root/trunk segments at quasistatic rate. E values exhibited similar behavior except no differences between the chord and root/trunk segments at both rates and no differences between chord and nerve segments at quasistatic rate. No differences were observed in the strain values. When compared with the tibial nerve, only mechanical properties of BP nerves were similar to the tibial nerve. Mechanical stresses and E values reported in BP root/trunk and chord segments were significantly lower than tibial nerve at both rates. When comparing the failure pattern, at quasistatic rate, necking was observed at maximum load, before a complete rupture occurred. At dynamic rate, partial rupture at maximum load, followed by a full more » rupture, was observed. Occurrence of the rate-dependent failure phenomenon was highest in the root/trunk segments followed by chord and nerve segments. Differences in the maximum stress, E values, and failure pattern of BP segments confirm variability in their anatomical structure and warrant future histological studies to better understand their stretch responses. « less
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Award ID(s):
Publication Date:
Journal Name:
Journal of Brachial Plexus and Peripheral Nerve Injury
Page Range or eLocation-ID:
e8 to e14
Sponsoring Org:
National Science Foundation
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  1. Abstract Despite occurrence of neonatal hypoxia and peripheral nerve injuries in complicated birthing scenarios, the effect of hypoxia on the biomechanical responses of neonatal peripheral nerves is not studied. In this study, neonatal brachial plexus and tibial nerves, obtained from eight normal and eight hypoxic 3-5 days old piglets, were tested in uniaxial tension until failure at a rate of 0.01 mm/s or 10 mm/s. Failure load, stress, and modulus of elasticity were reported to be significantly lower in hypoxic neonatal brachial plexus (BP) and tibial nerves than respective normal tissue at both 0.01 and 10 mm/s rates. Failure strain was significantly lower in the hypoxic neonatal BP nerves only at 10 mm/s rate when compared to normal BP nerve. This is the first available data that indicates weaker mechanical behavior of hypoxic neonatal peripheral nerves as compared to normal tissue, and offers an understanding of the biomechanical responses of peripheral nerves of hypoxic neonatal piglets.
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  4. Key points

    Cardiac electrophysiology and Ca2+handling change rapidly during the fight‐or‐flight response to meet physiological demands.

    Despite dramatic differences in cardiac electrophysiology, the cardiac fight‐or‐flight response is highly conserved across species.

    In this study, we performed physiological sympathetic nerve stimulation (SNS) while optically mapping cardiac action potentials and intracellular Ca2+transients in innervated mouse and rabbit hearts.

    Despite similar heart rate and Ca2+handling responses between mouse and rabbit hearts, we found notable species differences in spatio‐temporal repolarization dynamics during SNS.

    Species‐specific computational models revealed that these electrophysiological differences allowed for enhanced Ca2+handling (i.e. enhanced inotropy) in each species, suggesting that electrophysiological responses are fine‐tuned across species to produce optimal cardiac fight‐or‐flight responses.


    Sympathetic activation of the heart results in positive chronotropy and inotropy, which together rapidly increase cardiac output. The precise mechanisms that produce the electrophysiological and Ca2+handling changes underlying chronotropic and inotropic responses have been studied in detail in isolated cardiac myocytes. However, few studies have examined the dynamic effects of physiological sympathetic nerve activation on cardiac action potentials (APs) and intracellular Ca2+transients (CaTs) in the intact heart. Here, we performed bilateral sympathetic nerve stimulation (SNS) in fully innervated, Langendorff‐perfused rabbit and mouse hearts. Dual optical mapping with voltage‐ and Ca2+‐sensitive dyes allowed formore »analysis of spatio‐temporal AP and CaT dynamics. The rabbit heart responded to SNS with a monotonic increase in heart rate (HR), monotonic decreases in AP and CaT duration (APD, CaTD), and a monotonic increase in CaT amplitude. The mouse heart had similar HR and CaT responses; however, a pronounced biphasic APD response occurred, with initial prolongation (50.9 ± 5.1 ms att = 0 svs. 60.6 ± 4.1 ms att = 15 s,P < 0.05) followed by shortening (46.5 ± 9.1 ms att = 60 s,P = NSvs. t = 0). We determined the biphasic APD response in mouse was partly due to dynamic changes in HR during SNS and was exacerbated by β‐adrenergic activation. Simulations with species‐specific cardiac models revealed that transient APD prolongation in mouse allowed for greater and more rapid CaT responses, suggesting more rapid increases in contractility; conversely, the rabbit heart requires APD shortening to produce optimal inotropic responses. Thus, while the cardiac fight‐or‐flight response is highly conserved between species, the underlying mechanisms orchestrating these effects differ significantly.

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