- Award ID(s):
- Publication Date:
- NSF-PAR ID:
- Journal Name:
- Journal of Brachial Plexus and Peripheral Nerve Injury
- Page Range or eLocation-ID:
- e8 to e14
- Sponsoring Org:
- National Science Foundation
More Like this
An in vitro Study to Investigate Biomechanical Responses of Peripheral Nerves in Hypoxic Neonatal PigletsAbstract 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.
Abstract Background Characterizing the biomechanical failure responses of neonatal peripheral nerves is critical in understanding stretch-related peripheral nerve injury mechanisms in neonates. Objective This in vitro study investigated the effects of prestretch magnitude and duration on the biomechanical failure behavior of neonatal piglet brachial plexus (BP) and tibial nerves. Methods BP and tibial nerves from 32 neonatal piglets were harvested and prestretched to 0, 10, or 20% strain for 90 or 300 seconds. These prestretched samples were then subjected to tensile loading until failure. Failure stress and strain were calculated from the obtained load-displacement data. Results Prestretch magnitude significantly affected failure stress but not the failure strain. BP nerves prestretched to 10 or 20% strain, exhibiting significantly lower failure stress than those prestretched to 0% strain for both prestretch durations (90 and 300 seconds). Likewise, tibial nerves prestretched to 10 or 20% strain for 300 seconds, exhibiting significantly lower failure stress than the 0% prestretch group. An effect of prestretch duration on failure stress was also observed in the BP nerves when subjected to 20% prestretch strain such that the failure stress was significantly lower for 300 seconds group than 90 seconds group. No significant differences in the failure strains were observed. When comparing BP and tibial nerve failuremore »
Phosphorus availability and leaching losses in annual and perennial cropping systems in an upper US Midwest landscape
AbstractExcessive phosphorus (P) applications to croplands can contribute to eutrophication of surface waters through surface runoff and subsurface (leaching) losses. We analyzed leaching losses of total dissolved P (TDP) from no-till corn, hybrid poplar (Populus nigra X P. maximowiczii), switchgrass (Panicum virgatum), miscanthus (Miscanthus giganteus), native grasses, and restored prairie, all planted in 2008 on former cropland in Michigan, USA. All crops except corn (13 kg P ha−1 year−1) were grown without P fertilization. Biomass was harvested at the end of each growing season except for poplar. Soil water at 1.2 m depth was sampled weekly to biweekly for TDP determination during March–November 2009–2016 using tension lysimeters. Soil test P (0–25 cm depth) was measured every autumn. Soil water TDP concentrations were usually below levels where eutrophication of surface waters is frequently observed (> 0.02 mg L−1) but often higher than in deep groundwater or nearby streams and lakes. Rates of P leaching, estimated from measured concentrations and modeled drainage, did not differ statistically among cropping systems across years; 7-year cropping system means ranged from 0.035 to 0.072 kg P ha−1 year−1 with large interannual variation. Leached P was positively related to STP, which decreased over the 7 years in all systems. These results indicate that both P-fertilized and unfertilized cropping systems may
Different paths, same destination: divergent action potential responses produce conserved cardiac fight‐or‐flight response in mouse and rabbit hearts
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 »
Dynamic rupture initiation and propagation in a fluid-injection laboratory setup with diagnostics across multiple temporal scalesFluids are known to trigger a broad range of slip events, from slow, creeping transients to dynamic earthquake ruptures. Yet, the detailed mechanics underlying these processes and the conditions leading to different rupture behaviors are not well understood. Here, we use a laboratory earthquake setup, capable of injecting pressurized fluids, to compare the rupture behavior for different rates of fluid injection, slow (megapascals per hour) versus fast (megapascals per second). We find that for the fast injection rates, dynamic ruptures are triggered at lower pressure levels and over spatial scales much smaller than the quasistatic theoretical estimates of nucleation sizes, suggesting that such fast injection rates constitute dynamic loading. In contrast, the relatively slow injection rates result in gradual nucleation processes, with the fluid spreading along the interface and causing stress changes consistent with gradually accelerating slow slip. The resulting dynamic ruptures propagating over wetted interfaces exhibit dynamic stress drops almost twice as large as those over the dry interfaces. These results suggest the need to take into account the rate of the pore-pressure increase when considering nucleation processes and motivate further investigation on how friction properties depend on the presence of fluids.