Journal of biomechanics
-
Journal of biomechanics · May 2012
Flow resistance analysis of extracranial-to-intracranial (EC-IC) vein bypass.
Although brain bypass surgery has often been selected to treat internal carotid arteries (ICA) which are restricted by aneurysm or artery stenosis, its effectiveness has not been quantitatively evaluated. The purpose of this study is to propose an innovative approach for the evaluation of brain extracranial-to-intracranial (EC-IC) vein bypass surgery, based on the analysis of flow resistance in vein bypasses and within their contralateral carotid arteries through the use of computational fluid dynamics (CFD). Seven patients who underwent vein bypass surgery were examined with the use of high-resolution; computed tomography angiogram (CTA). ⋯ For the vein bypass, an average value of A was 0.0143 Pa/(ml/min)² and B 3.402 Pa/(ml/min), which was approximately that of a healthy ICA. However, in the case of a bypass utilising a venous conduit possessing a large-sized valve or existing size alteration, the flow resistance in that bypass would be higher than those found in the healthy ICA. An imbalance of flow resistances may impose conditions that could predispose hemodynamic failure or distal aneurysm development.
-
Journal of biomechanics · Apr 2012
Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football.
Concussion is a growing public health issue in the United States, and chronic traumatic encephalopathy (CTE) is the chief long-term concern linked to repeated concussions. Recently, attention has shifted toward subconcussive blows and the role they may play in the development of CTE. We recruited a cohort of high school football players for two seasons of observation. ⋯ In addition to those subjects who had sustained a concussion, a substantial portion of our cohort who did not sustain concussions showed significant neurophysiological changes. Stepwise regression indicated significant relationships between the number of blows sustained by a subject and the ensuing neurophysiological change. Our findings reinforce the hypothesis that the effects of repetitive blows to the head are cumulative and that repeated exposure to subconcussive blows is connected to pathologically altered neurophysiology.
-
Journal of biomechanics · Apr 2012
The presence of arachnoiditis affects the characteristics of CSF flow in the spinal subarachnoid space: a modelling study.
Syringomyelia is a neurological disorder characterised by high pressure fluid-filled cysts within the spinal cord. As syringomyelia is associated with abnormalities of the central nervous system that obstruct cerebrospinal fluid (CSF) flow, it is thought that changes in CSF dynamics play an important role in its pathogenesis. Using three-dimensional computational models of the spinal subarachnoid space (SAS), this study aims to determine SAS obstructions, such as arachnoiditis, change in CSF dynamics in the SAS. ⋯ The permeability of this porous obstruction was varied for the model with dorsal arachnoiditis. The results show that arachnoiditis increases flow resistance in the SAS and this is accompanied by a modest increase in magnitude and/or shift in timing (with respect to the cardiac cycle) of the CSF pressure drop across the region of arachnoiditis. This study suggests that syrinx formation may be related to a change in temporal CSF pulse pressure dynamics.
-
Journal of biomechanics · Apr 2012
Characterization of a hyper-viscoelastic phantom mimicking biological soft tissue using an abdominal pneumatic driver with magnetic resonance elastography (MRE).
The purpose of this study was to create a polymer phantom mimicking the mechanical properties of soft tissues using experimental tests and rheological models. Multifrequency Magnetic Resonance Elastography (MMRE) tests were performed on the present phantom with a pneumatic driver to characterize the viscoelastic (μ, η) properties using Voigt, Maxwell, Zener and Springpot models. To optimize the MMRE protocol, the driver behavior was analyzed with a vibrometer. ⋯ Rheological results demonstrated that Springpot model better revealed the viscoelastic properties (μ=3.45 kPa, η=6.17 Pas) of the phantom and the Mooney-Rivlin coefficients were C(10)=1.09.10(-2) MPa and C(01)=-8.96.10(-3) MPa corresponding to μ=3.95 kPa. These studies suggest that the phantom, mimicking soft tissue, could be used for preliminary MRE tests to identify the optimal parameters necessary for in vivo investigations. Further developments of the phantom may allow clinicians to more accurately mimic healthy and pathological soft tissues using MRE.
-
Prediction and control of bone drilling forces are critical to the success of many orthopaedic operations. Uncontrolled and large forces can cause drill-bit breakage, drill breakthrough, excessive heat generation, and mechanical damage to the bone. This paper presents a mechanistic model for prediction of thrust forces and torques experienced during bone drilling. ⋯ The thrust forces and torques were observed to vary considerably between bones from different animals. The forces from the model were seen to match well with those from the experimentation within the inherent variations from the bone characteristics. The model can be used to select favorable drilling conditions, to assist in robotic surgeries, and to design optimal orthopaedic drill bits.