Viscoelastic Characterization of Parasagittal Bridging Veins and Implications for Traumatic Brain Injury: A Pilot Study

Abstract

Many previous studies on the mechanical properties of Parasagittal Bridging Veins (PSBVs) found that strain rate had a significant effect on some mechanical properties, but did not extensively study the viscoelastic effects, which are difficult to detect with uniaxial simple tensile tests. In this study, relaxation tests and tests under cyclic loading were performed, and it was found that PSBVs do indeed exhibit clear viscoelastic effects. In addition, a complete viscoelastic model for the PSBVs is proposed and data from relaxation, cyclic load and load-unload tests for triangular loads are used to find reference values that characterize the viscoelastic behavior of the PSBVs. Although such models have been proposed for other types of blood vessels, this is the first study that clearly demonstrates the existence of viscoelastic effects from an experimental point of view and also proposes a specific model to explain the data obtained. Finally, this study provides reference values for the usual viscoelastic properties, which would allow more accurate numerical simulation of PSBVs by means of computational models.

Injury Metrics for Assessing the Risk of Acute Subdural Hematoma in Traumatic Events

“…The only widely used injury metric or risk index to assess the likelihood of ASDH is the RMDM [ 13 , 14 , 15 ]. However, the empirical data from Löwenhielm which were used to construct RMDM [ 13 , 17 ] are in question, as it appears that many authors have not found ultimate strain to decay noticeably with strain rate in the range [ 11 , 12 , 22 , 25 ]. Using recent data, it has been found that at low strain rate , , increases significantly [ 11 ] and from s no significant changes are detected [ 12 ].…”

“…A limitation of the empirical data used is that viscoelastic effects in CBVs have been insufficiently studied [ 25 ]. Moreover, failure data available correspond to loading curves in which the strain rate is approximately constant.…”

“…That could be producing somewhat larger instantaneous force peaks than the actually existent ones. It should also be investigated whether the deduced failure force for monotonic loading curves needs some correction because of the viscoelastic preconditioning also discussed in [ 25 , 51 ].…”

“…In fact, it is important to note that, after Löwenhielm’s work, a good number of published studies of the mechanical properties of CBVs have been done [ 11 , 12 , 23 , 24 , 25 ]. All the newer studies have much better precision data than the first studies, essentially due to improved measurement accuracy, so these data can be properly used to propose a more accurate and suitable injury metric.…”

“…Actually, the same idea can be applied to longitudinal stress and ultimate stress (or, equivalently, to current axial force and ultimate axial force). Recent data show that the ultimate stress depends on the strain rate [ 11 , 25 ], and a statistical analysis of the expected value of and its variation in terms of the strain rate allows to build new injury metrics on more accurate and precise recent data than the available data from Löwenhielm. Let be the expected value of ultimate strain , given a strain rate , then, a possible injury metric would be to divide the instantaneous stress by the expected value for ultimate stress at the current strain rate.…”