Statistical analysis of the aerosol elemental composition in an industrial belt.
Explore the source record for details and available documents.
Aerosols↗
Biomedical subjects
S Kumaresan
Publications and source records attributed to S Kumaresan.
A countrywide post-marketing surveillance of nimesulide suspension.
Explore the source record for details and available documents.
Anti-Inflammatory Agents, Non-Steroidal↗
Biomechanics of the cervical spine Part 2. Cervical spine soft tissue responses and biomechanical modeling.
OBJECTIVE: The responses and contributions of the soft tissue structures of the human neck are described with a focus on mathematical modeling. Spinal ligaments, intervertebral discs, zygapophysial joints, and uncovertebral joints of the cervical spine are included. Finite element modeling approaches have been emphasized. Representative data relevant to the development and execution of the model are discussed. A brief description is given on the functional mechanical role of the soft tissue components. Geometrical characteristics such as length and cross-sectional areas, and material properties such as force-displacement and stress-strain responses, are described for all components. Modeling approaches are discussed for each soft tissue structure. The final discussion emphasizes the normal and abnormal (e.g., degenerative joint disease, iatrogenic alteration, trauma) behaviors of the cervical spine with a focus on all these soft tissue responses. A brief description is provided on the modeling of the developmental biomechanics of the pediatric spine with a focus on soft tissues. Relevance. Experimentally validated models based on accurate geometry, material property, boundary, and loading conditions are useful to delineate the clinical biomechanics of the spine. Both external and internal responses of the various spinal components, a data set not obtainable directly from experiments, can be determined using computational models. Since soft tissues control the complex structural response, an accurate simulation of their anatomic, functional, and biomechanical characteristics is necessary to understand the behavior of the cervical spine under normal and abnormal conditions such as facetectomy, discectomy, laminectomy, and fusion.
Adult↗
Contribution of disc degeneration to osteophyte formation in the cervical spine: a biomechanical investigation.
Cervical spine disorders such as spondylotic radiculopathy and myelopathy are often related to osteophyte formation. Bone remodeling experimental-analytical studies have correlated biomechanical responses such as stress and strain energy density to the formation of bony outgrowth. Using these responses of the spinal components, the present study was conducted to investigate the basis for the occurrence of disc-related pathological conditions. An anatomically accurate and validated intact finite element model of the C4-C5-C6 cervical spine was used to simulate progressive disc degeneration at the C5-C6 level. Slight degeneration included an alteration of material properties of the nucleus pulposus representing the dehydration process. Moderate degeneration included an alteration of fiber content and material properties of the anulus fibrosus representing the disintegrated nature of the anulus in addition to dehydrated nucleus. Severe degeneration included decrease in the intervertebral disc height with dehydrated nucleus and disintegrated anulus. The intact and three degenerated models were exercised under compression, and the overall force-displacement response, local segmental stiffness, anulus fiber strain, disc bulge, anulus stress, load shared by the disc and facet joints, pressure in the disc, facet and uncovertebral joints, and strain energy density and stress in the vertebral cortex were determined. The overall stiffness (C4-C6) increased with the severity of degeneration. The segmental stiffness at the degenerated level (C5-C6) increased with the severity of degeneration. Intervertebral disc bulge and anulus stress and strain decreased at the degenerated level. The strain energy density and stress in vertebral cortex increased adjacent to the degenerated disc. Specifically, the anterior region of the cortex responded with a higher increase in these responses. The increased strain energy density and stress in the vertebral cortex over time may induce the remodeling process according to Wolff's law, leading to the formation of osteophytes.
Biomechanical Phenomena↗
Comparison of biomechanical head-neck responses of hybrid III dummy and whole body cadaver during inverted drops.
The anthropometric hybrid III dummy test device is the most widely used physical model to assess the injury severity during automotive crashes. The dummy was designed to replicate the human neck in flexion and frontal impacts. Various investigators have compared the dummy neck with living human and cadaveric responses in frontal impacts. However, the comparison between the whole body human cadaver and dummy under an inverted drop is currently lacking. This study was designed to review the exiting data and obtain the comparative data between the human cadaver and the dummy. The vertical whole body cadaver drops from our laboratory and literature have been used. There exists a wide variation between the human and dummy neck responses. The dummy neck was approximately two to four times stiffer under axial compression in the quasi-static or in the dynamic mode. The present comparison will provide a basis to better design the anthropometric dummies in order to obtain an improved injury assessment during inverted drops.
Accidents, Traffic↗
Biomechanical modeling of penetrating traumatic head injuries: a finite element approach.
Due to advances in emergency medical care and modern techniques, treatment of gunshot wounds to the brain have improved and saved many lives. These advances were largely achieved using retrospective analysis of patients with recommendations for treatment. Biomechanical quantification of intracranial deformation/stress distribution associated with the type of weapon (e.g., projectile geometry) will advance clinical understanding of the mechanics of penetrating trauma. The present study was designed to delineate the biomechanical behavior of the human head under penetrating impact of two different projectile geometry using a nonlinear, three-dimensional finite element model. The human head model included the skull and brain. The qualitative comparison of the model output with each type of projectile during various time steps indicated that the deformation/stress progressed as the projectile penetrated the tissues. There is also a distinct difference in the patterns of displacement for each type of projectile. This observation matches our previous study using a physical gelatin model of delineate the penetrating wound profiles for different projectile types. The present study is a first step in the study of biomechanical modeling of penetrating traumatic brain injuries.
Biomechanical Phenomena↗
Pediatric neck injury scale factors and tolerance.
Although significant research efforts have been made to determine the tolerance for the adult neck, relatively little research has been conducted to derive the pediatric neck injury parameters. The existing approach to determine injury for the one, three and six year old pediatric populations is based on extrapolations from the adult male and calcaneal tendon tensile data. This study addresses the scale factors for pediatric age groups using data obtained from spinal components and neck geometry. The analysis included the determination of scale factors under extension, tension, compression and flexion loading modes as a function of age. The variations in biomechanical properties of each spinal component were determined from human cadaver studies. Active spinal components were identified under each loading mode and relationships were established for each component to obtain material-based scale factors. The scale factors and resulting injury tolerance values based on spine component material properties are more appropriate than values extrapolated from the calcaneal tendon.
Biomechanical Phenomena↗
Geometric and mechanical properties of human cervical spine ligaments.
This study characterized the geometry and mechanical properties of the cervical ligaments from C2-T1 levels. The lengths and cross-sectional areas of the anterior longitudinal ligament, posterior longitudinal ligament, joint capsules, ligamentum flavum, and interspinous ligament were determined from eight human cadavers using cryomicrotomy images. The geometry was defined based on spinal anatomy and its potential use in complex mathematical models. The biomechanical force-deflection, stiffness, energy, stress, and strain data were obtained from 25 cadavers using in situ axial tensile tests. Data were grouped into middle (C2-C5) and lower (C5-T1) cervical levels. Both the geometric length and area of cross section, and the biomechanical properties including the stiffness, stress, strain, energy, and Young's modulus, were presented for each of the five ligaments. In both groups, joint capsules and ligamentum flavum exhibited the highest cross-sectional area (p < 0.005), while the longitudinal ligaments had the highest length measurements. Although not reaching statistical significance, for all ligaments, cross-sectional areas were higher in the C5-T1 than in the C2-C5 group; and lengths were higher in the C2-C5 than in the C5-T1 group with the exception of the flavum (Table 1 in the main text). Force-deflection characteristics (plots) are provided for all ligaments in both groups. Failure strains were higher for the ligaments of the posterior (interspinous ligament, joint capsules, and ligamentum flavum) than the anterior complex (anterior and posterior longitudinal ligaments) in both groups. In contrast, the failure stress and Young's modulus were higher for the anterior and posterior longitudinal ligaments compared to the ligaments of the posterior complex in the two groups. However, similar tendencies in the structural responses (stiffness, energy) were not found in both groups. Researchers attempting to incorporate these data into stress-analysis models can choose the specific parameter(s) based on the complexity of the model used to study the biomechanical behavior of the human cervical spine.
Analysis of Variance↗
Biomechanical study of pediatric human cervical spine: a finite element approach.
Although considerable effort has been made to understand the biomechanical behavior of the adult cervical spine, relatively little information is available on the response of the pediatric cervical spine to external forces. Since significant anatomical differences exist between the adult and pediatric cervical spines, distinct biomechanical responses are expected. The present study quantified the biomechanical responses of human pediatric spines by incorporating their unique developmental anatomical features. One-, three-, and six-year-old cervical spines were simulated using the finite element modeling technique, and their responses computed and compared with the adult spine response. The effects of pure overall structural scaling of the adult spine, local component developmental anatomy variations that occur to the actual pediatric spines, and structural scaling combined with local component anatomy variations on the responses of the pediatric spines were studied. Age- and component-related developmental anatomical features included variations in the ossification centers, cartilages, growth plates, vertebral centrum, facet joints, and annular fibers and nucleus pulposus of the intervertebral discs. The flexibility responses of the models were determined under pure compression, pure flexion, pure extension, and varying degrees of combined compression-flexion and compression-extension. The pediatric spine responses obtained with the pure overall (only geometric) scaling of the adult spine indicated that the flexibilities consistently increase in a uniform manner from six- to one-year-old spines under all loading cases. In contrast, incorporation of local anatomic changes specific to the pediatric spines of the three age groups (maintaining the same adult size) not only resulted in considerable increases in flexibilities, but the responses also varied as a function of the age of the pediatric spine and type of external loading. When the geometric scaling effects were added to these spines, the increases in flexibilities were slightly higher; however, the pattern of the responses remained the same as found in the previous approach. These results indicate that inclusion of developmental anatomical changes characteristic of the pediatric spines has more of a predominant effect on biomechanical responses than extrapolating responses of the adult spine based on pure overall geometric scaling.
Adult↗
Morphology of young and old cervical spine intervertebral disc tissues.
The intervertebral disc of the cervical spine undergoes degenerative changes during the aging process. Although many studies have reported the qualitative changes in the disc, methodology to quantify these changes is lacking. The present study was designed to quantify the geometrical variations of the nucleus pulposus, annulus fibrosus and uncovertebral joints. The age groups of specimens were classified as juvenile, adult and aged. Fresh intervertebral discs with adjacent vertebral bodies of the lower cervical spine of primates were isolated. The specimens were sectioned sequentially in a coronal plane. Sections were stained with Hematoxylin and Eosin, Verhoeff's, Safranin O, and Trichrome methods to distinguish the nucleus, annulus and uncovertebral joints. Histological images were examined using light microscopy and processed using a computer imaging program to trace the boundaries of the disc components. Dorsal-to-ventral depth and medial-to-lateral width of the nucleus pulposus, and its relative location to the annulus pulposus were also obtained. In the juvenile and adult discs, the nucleus appeared as a light opaque region with scattered notochordal cells with a clear distinction from the annulus region. In contrast, in the aged discs, the nucleus appeared as a dense region of amorphous, irregular collagen materials with less distinction from the annulus region. With the progression of aging, the dorsal-to-ventral depth of the nucleus decreased considerably compared to medial-to-lateral width. The uncovertebral joints were clear in the adult discs. The joints were less distinct in the aged discs and their size decreased. Quantification of three-dimensional geometrical variations will assist in better defining the disc tissue in the mathematical models.
Aging↗
Head-neck finite element model for motor vehicle inertial impact: material sensitivity analysis.
The aim of this study was to conduct a material sensitivity analysis using a head-neck finite element model (FEM). The model included the skull, C1-T1 vertebrae, intervertebral discs, facet joints, and biomechanically relevant ligaments. Poisson's ratio and elastic modulus of the head-neck components were varied. The loading condition included the impact load applied to the first thoracic vertebra. Commercially available software (LS-DYNA) was used for the analysis. Head angle versus time, head center of gravity trajectory, and head center of gravity angular acceleration responses were computed. In general, the variation of elastic modulus had a higher effect on the response compared to variation of Poisson's ratio. As the elastic modulus was increased, the head angle and angular acceleration increased. The present findings form a first step in the study of computational biomechanics of vehicular-related trauma.
Acceleration↗
Finite element model of human cervical spinal column.
The purpose of this study was to develop a detailed anatomically accurate finite element model (FEM) of the whole cervical column (C2-T1) using sagittal and coronal computed tomography (CT) scan images and cryomicrotome anatomical sections. The bony vertebrae were defined using CT scan images. The geometrical details of intervertebral discs, uncovertebral joints and ligaments were obtained from cryomicrotome sections. The following steps were used to develop the FEM: wire mesh, surface model and solid model. The wire mesh of each vertebra and disc was generated from the CT and cryomicrotome sections, respectively. The surface model was developed by connecting the wire mesh lines. The solid model was obtained by filling the volume enclosed by the surface model. Finally, the FEM was constructed by discretizing the solid model using the mapped-mesh option. Appropriate finite element types were assigned to each component. For example, the isoparametric eight-noded solid elements were used to define the cancellous bone of a vertebra. The material properties reported in literature were adopted in the model. Commercially available software (IDEAS and ABAQUS) was used to develop the FEM.
Adult↗
Comparative profiles of sodium valproate and ethosuximide on electro-behavioural correlates in gamma-hydroxybutyrate and pentylenetetrazol induced absence seizures in rats.
Sodium valproate (VPA) and ethosuximide (ESM) were compared on behavioural and EEG changes in gamma-hydroxybutyrate (GHB) and pentylenetetrazole (PTZ) rat models of Absence Seizures (AS). Both GHB, 100 mg/kg i.p. and PTZ, 20 mg/kg i.p., produced repetitive episodes of staring and immobility with concomitant 6 to 9 Hz spike and wave discharges (SWDs) in the EEG. The parameters used for drug evaluation were the number and duration of SWDs/hour. Though the number of SWDs/hour produced by GHB and PTZ were not significantly different, the duration of SWDs was significantly longer in GHB treated rats (P < 0.001) VPA and ESM, at 200 mg/kg i.p., reduced SWD number and duration in GHB pretreated rats, whereas ESM, 50 mg/kg i.p., was four times more effective than VPA, 200 mg/kg i.p., in the PTZ model. Phenytoin (PHY) 20 and Carbamazepine (CBZ) 10 mg/kg i.p., worsened AS, a feature which has also been reported clinically. Both rat models of experimental AS can be used to defect potential anti-absence activity in new chemical entities.
Animals↗
Finite element analysis of the cervical spine: a material property sensitivity study.
OBJECTIVE: The study determined the effect of variations in the material properties of the cervical spinal components on the output of the finite element analysis (external and internal responses of the cervical spine) under physiologic load vectors. DESIGN: A three-dimensional (3D) anatomically accurate finite element model comprising of the C4-C5-C6 cervical spine unit including the three vertebrae, two interconnecting intervertebral discs, and the anterior and posterior ligament complex is used. BACKGROUND: The effect of material property variations of spinal components on the human lumbar spine biomechanics is extensively studied. However, a similar investigation of the cervical spine is lacking. METHODS: Parametric studies on the variations in the material properties of all the cervical spine components including the cortical shell, cancellous core, endplates, intervertebral disc, posterior elements and ligaments were conducted by exercising the 3D finite element model under flexion, extension, lateral bending and axial torsion loading modes. Low, basic and high material property cases for each of the six components under all the four physiologic loading modes were considered in the finite element analysis. A total of 432 results were evaluated to analyze the external angular rotation, and the internal stresses in the middle vertebral body, the superior and inferior endplates and the two intervertebral discs. RESULTS: Variations in the material properties of the different cervical spinal components produced dissimilar changes in the external and internal responses. Variations in the material properties of the cancellous core, cortical shell, endplates and posterior element structures representing the hard tissues did not affect the external angular motion, and the internal stresses of the inferior and superior intervertebral discs under all four loading modes. In contrast, variations in the material properties of the intervertebral disc and ligament structures representing the soft tissues significantly altered the angular motion, and the stresses in the inferior and superior intervertebral discs of the cervical spine. CONCLUSION: The material properties of the soft tissue structures have a preponderant effect on the external and internal responses of the cervical spine compared with the changes in the material properties of the hard tissue structures. RELEVANCE: Bone remodeling (e.g., osteophyte) secondary to degeneration of the human cervical joints may be explained by a change in the material property of the soft tissues, coupled with an increase in stress (due to these material property variations) in the spinal components. Consequently, to accurately predict the biomedical effects of cervical spine degeneration, it is critical to accurately determine the material property of these components.
Adult↗
Finite element modeling of the cervical spine: role of intervertebral disc under axial and eccentric loads.
An anatomically accurate, three-dimensional, nonlinear finite element model of the human cervical spine was developed using computed tomography images and cryomicrotome sections. The detailed model included the cortical bone, cancellous core, endplate, lamina, pedicle, transverse processes and spinous processes of the vertebrae; the annulus fibrosus and nucleus pulposus of the intervertebral discs; the uncovertebral joints; the articular cartilage, the synovial fluid and synovial membrane of the facet joints; and the anterior and posterior longitudinal ligaments, interspinous ligaments, capsular ligaments and ligamentum flavum. The finite element model was validated with experimental results: force-displacement and localized strain responses of the vertebral body and lateral masses under pure compression, and varying eccentric anterior-compression and posterior-compression loading modes. This experimentally validated finite element model was used to study the biomechanics of the cervical spine intervertebral disc by quantifying the internal axial and shear forces resisted by the ventral, middle, and dorsal regions of the disc under the above axial and eccentric loading modes. Results indicated that higher axial forces (compared to shear forces) were transmitted through different regions of the disc under all loading modes. While the ventral region of the disc resisted higher variations in axial force, the dorsal region transmitted higher shear forces under all loading modes. These findings may offer an insight to better understand the biomechanical role of the human cervical spine intervertebral disc.
Adult↗
Biomechanical effect of anterior cervical spine fusion on adjacent segments.
The biomechanical effects of superior (C4-C5) and inferior (C5-C6) level fusions with different graft materials on the adjacent unaltered components were quantified using an anatomically accurate and experimentally validated C4-C5-C6 finite element model. Smith-Robinson and Bailey-Badgley fusion procedures were analyzed with five different types of inter-body fusion materials with varying stiffnesses. Intact and surgically altered finite element models were subjected to physiologic compression, flexion, extension and lateral bending. The external axial and angular stiffness, and the internal unaltered intervertebral disc (C5-C6 for the superior and C4-C5 for inferior fusion) and C5 vertebral body stresses were determined. The superior level fusion resulted in the highest increase in external response in lateral bending for all implant materials in both surgical procedures. In contrast, the inferior level fusion produced a higher increase in the C4-C5 disc and C5 vertebral body stresses in compression than the superior level fusion in both surgical procedures. The increased internal stress responses reflecting the changes in the load-sharing following inferior level fusion may explain clinical observations such as enhanced degeneration subsequent to surgery. Because of the inclusion of three levels in the present multi-segment finite element model, it was possible to determine these responses in the unaltered adjacent components of the cervical spine.
Biocompatible Materials↗
Finite element modeling approaches of human cervical spine facet joint capsule.
The human cervical spine facet joint capsule was modeled using four nonlinear finite element approaches: slideline, contact surface, hyperelastic, and fluid models. Slideline elements and contact surface definitions were used in the first two models to simulate the synovial fluid between the articulating cartilages. Incompressible solid elements approximated the synovial fluid in the hyperelastic model. Hydrostatic fluid elements idealized the synovial fluid in the fluid model. The finite element analysis incorporated geometric, material and contact nonlinearities. All models were subjected to compression, flexion, extension, and lateral bending. The fluid model idealization better approximates the actual facet joint anatomy and its behavior than the gap assumption in the slideline and contact surface models, and the solid element simulation in the hyperelastic model.
Biomechanical Phenomena↗
Hematology and chemistry reference values for free-ranging harbor seals (Phoca vitulina) and the effects of hemolysis on chemistry values of captive harbor seals.
Most reported laboratory reference values for harbor seals (Phoca vitulina) are derived from captive seals, or stranded seals that have recovered from disease in marine mammal centers. This study established hematology and serum chemistry reference values for free-ranging harbor seals, using methods and that are current and readily available, and determined the effects of hemolysis on serum chemistry values of captive harbor seals. Blood samples were collected for hematologic and serum chemistry measurements from 14 clinically normal, adult male and female harbor seals and two juvenile harbor seals (approximate age 6 mo) captured in saltwater sloughs and estuaries near Moss Landing, California, USA. Values for amylase, globulin, and differential leukocyte count, not previously reported, were determined. In general, hematology and chemistry values in adults were similar to those reported for free-ranging and captive harbor seals, except for glucose, urea nitrogen, and lactate dehydrogenase (LDH) values, which were higher than those reported previously. Red blood cell counts in the two juveniles were higher than in adults and in young harbor seals studied previously. To determine the effects of hemolysis on serum chemistry values, two intensities of hemolysis were generated experimentally in blood collected from 11 harbor seals recovering from injuries or stranding at the Marine Mammal Center (Sausalito, California 94965, USA). Moderate hemolysis (++, 1 g/L hemoglobin, red-tinged) significantly increased LDH activity, whereas severe hemolysis ( , 2 g/L hemoglobin, cherry red) significantly increased total protein, albumin, calculated globulin, LDH, and total bilirubin and significantly decreased creatinine. The effects of hemolysis must be considered when chemistry results of harbor seals are interpreted.
Animals↗