Biomechanics of Brain and Spinal-Cord Injury: Analysis of Neuropathologic and Neurophysiology Experiments

This study analyzes 46 brain and 48 spinal-cord impact experiments. The velocity of brain impact was 2.0-10.0 m/s and displacement, 0.75-5.0 mm (5.3-33% compression) using a controlled pneumatic impact. The velocity of spinal-cord impact was 1.5-6.0 m/s and displacement, 1.25-3.25 mm (25-65% compression). Brain injury varied from cortical contusion, diffuse axonal injury (DAI), to fatalities, and spinal-cord injury from temporary to complete loss of somatosensory-evoked potentials. Logist functions were determined for each injury severity and various biomechanical parameters, VC, C, V, and combinations. Brain and spinal-cord injury is most strongly correlated to VC, the viscous response. The goodness-of-fit was x² = 22.1, R-0.84 and p< 0.0000 for fatal brain injury, x² = 27.5, R = 0.96 and p< 0.0000 for cortical contusion, and x² = 17.7, R = 0.49 and p < 0.0001 for partial recovery of spinal-cord conduction. Neural tissue is viscoelastic, with a rate-dependent tolerance related to energy absorption. VC is a measure of energy absorption by impact deformation and is predictive of neural contusion, DAI, long-duration coma, spinal-cord dysfunction, and death. Tolerances for various severities of neural injury are presented. At the tissue level, VC is the product of strain and strain-rate, ε dε/dt. The research shows that strain is not a sufficient parameter of neural injury risk, and that the product of strain and strain-rate is a key biomechanical parameter for brain and spinal-cord injury.     

Light effects on nutrient-limited,oceanic primary production

Phytoplankton growth dynamics were investigated throughout the photic zone at three stations in the North Central Pacific Gyre south of the Hawaiian Islands. Ambient nutrients, vertical light profiles, phytoplankton biomass, and primary production were measured. Photosynthetically active radiation, measured with a submarine quantaspectrophotometer, illustrates vertical variations in photic spectral quality and is presented as incident quanta flux of visible light. Primary production was determined throughout the photic zone under conditions where the samples were collected, injected with ¹⁴C, and incubated under entirely in situ conditions to eliminate preincubation perturbation and to ensure representative response to both light quality and quantity. Oceanic phytoplankton activity is described as a continuous function of incident light under the prevailing low nutrient conditions, and the important rate constants are calculated based upon field data from oligotrophic regions. The vertical profiles of phytoplankton activity and incident quanta flux are analyzed in terms of a substrate-limited system according to the equqtion A _(z) = A _max (q (_(z) – q _o) [K + (q (_(z)) – q (_o], where q(_z) is the quanta flux at a given depth, and A(_z) is the phytoplankton assimilation number at that depth. This is done on the rationale that systematically declining levels of quanta flux, vertically, represent corresponding declines in the availability of substrate for the photochemical processes of photosynthesis. Comparison of data from isolated oceanic regions with those from a station located 15 miles off Oahu show that although large differences in the phytoplankton parameters are evident throughout the entire photic zones of these regions, the hyperbolic A(_z)-q(_z) relationship describes the data fairly well in both cases. The comparison suggests that this relationship may apply to the general case of an oligotrophic water column. These experiments show trends which may be useful for diagnosing phytoplankton activity in the field where N and P levels are low.Oceanic Institute Contribution No. 77-131.     

A Comparison of Volunteer,BioRID P3 and Hybrid III Performance in Rear Impacts

The most important tool for testing seat-systems in rear impacts is a crash test dummy. However, investigators have noted limitations of the most commonly used dummy, the Hybrid III. The BioRID I is a step closer to a biofidelic crash test dummy, but it is not user-friendly and the straightening of the thoracic spine kyphosis is smaller than that 220of humans. To reduce these problems, a new BioRID prototype was developed, the P3. It has new neck muscle substitutes, a softer thoracic spine and a softer rubber torso than does the BioRID I.

The BioRID P3 was compared with volunteer test data in a rigid and a standard seal without head restraints. The dummy kinematic performance, pressure distribution between subject and seatback, neck loads and accelerations were compared with those of ten volunteers and a Hybrid III. The BioRID P3 provided repeatable test results and its response was very similar to that of the average volunteer in rear impacts at Δv = 9 km/h.     

Public perceptions of planning objectives for regional level management of wild reindeer in Norway

We examined community perceptions of preferred objectives for wild reindeer management in Southern Norway as the former population-based model is being replaced with an area-based, multi-level regional management model spanning large mountain regions. Communally oriented objectives are favoured over economic benefits to landowners. Environmental attitudes discriminate on many of the issues and can be useful factors in sorting out levels of support for proposed management actions and compromises in land use decisions. The regional reindeer plans create a new political context for land use management across large mountain areas which will require better cooperation among municipalities.     

Territory ownership and familiarity status affect how much male root voles (Microtus oeconomus) invest in territory defence

Neighbour–stranger discrimination occurs when individuals respond with more aggression to strangers than to territorial neighbours—a phenomenon termed the “dear enemy phenomenon” (DEP). We investigated the DEP with male and female root voles (Microtus oeconomus Pallas 1776) using field dyadic arena tests conducted in enclosures where we could test for the effects of familiarity (familiar versus stranger), ownership (resident versus intruder status) and resource-holding potential (body mass) on territorial behaviours. The results showed that males put more effort into territorial defence than females, and males could discriminate between neighbours and strangers. In males, aggressiveness was influenced by a significant two-way interaction between treatment and ownership. Male residents were more aggressive towards stranger intruders than towards neighbour intruders, while male intruders were less aggressive towards stranger residents than towards neighbour residents. In females, neither treatment nor ownership status had a significant effect on aggressiveness. Familiar males performed more social behaviours but less non-social behaviours than stranger males. Furthermore, there was a clear dominance hierarchy between residents and intruders in stranger dyads, with the male territory holders dominating the intruder in pairwise interactions. To our knowledge, these results demonstrate for the first time DEP in a small mammal with a known pedigree and present the first evidence for “prior resident advantage” in voles. We argue that both ownership status and familiarity status affect how much an individual invests in territory defence. The benefits of neighbour–stranger discrimination for male root voles and the absence of neighbour–stranger discrimination in female root voles are discussed.     

A Multi-body Integrated Vehicle-Occupant Model for Compatibility Studies in Frontal Crashes

Vehicle acceleration and passenger compartment intrusion primarily determine car occupant injury risk. A new integrated vehicle-occupant model was developed and validated to predict these vehicle responses in offset, concentrated or full-width impact with various objects. The multi-body mathematical model consisted of a compartment, dash-panel and toepan-area and a front structure. The front structure was subdivided in 12 segments and a power-train, which were connected to the firewall by kinematic joints. The joints used local stiffness obtained from load-cell barrier crash-tests, and enabled local deformation of the vehicle front Similarly, the dash-panel and toepan were connected to the compartment, which enabled local intrusion into the compartment. A vehicle interior was modeled to enable contact-interactions with occupants, and the firewall geometry was included for interactions with the power-train.

The vehicle-model was validated with full frontal and 50% offset data and predicted vehicle acceleration, crush profile and local intrusion well. The validity of the model indicates its applicability in a wide range of frontal (non-distributed) collisions. Due to the use of local stiffness data, the model can greatly improve accident reconstruction research especially in frontal offset and pole impacts at both high and low speeds. The vehicle-model can be easily adjusted by changing vehicle-mass, size, or local stiffnesses of the front structure, and is a useful tool in compatibility research to estimate trends in car crash compatibility.     

Human Volunteer Kinematics in Rear-End Sled Collisions

Validation of new crash test dummies for rear-end collision testing requires human response data from pertinent test situations. Eleven human volunteers were exposed to 23 low-speed rear impacts to determine human response in well-defined test seats, and to quantify repeatability, variability and the effect of seat design on human response.

The results showed vertical motion of the volunteers’ H-point caused by ramping up along the seat, and an upward motion of the volunteers’ torso and head. The latter was caused by a combination of ramping up along the seatback and straightening of the thoracic kyphosis. During the first 100 ms, the volunteers flexed their necks. Thereafter, the volunteers extended their necks. These new data have proven to be useful in validation of rear-impact dummies.     

Environmental Services Provided from Riparian Forests in the Nordic Countries

Riparian forests (RF) growing along streams, rivers and lakes comprise more than 2% of the forest area in the Nordic countries (considering a 10 m wide zone from the water body). They have special ecological functions in the landscape. They receive water and nutrients from the upslope areas, are important habitats for biodiversity, have large soil carbon stores, but may emit more greenhouse gases (GHG) than the uplands. In this article, we present a review of the environmental services related to water protection, terrestrial biodiversity, carbon storage and greenhouse gas dynamics provided by RF in the Nordic countries. We discuss the benefits and trade-offs when leaving the RF as a buffer against the impacts from upland forest management, in particular the impacts of clear cutting. Forest buffers are effective in protecting water quality and aquatic life, and have positive effects on terrestrial biodiversity, particularly when broader than 40 m, whereas the effect on the greenhouse gas exchange is unclear.     

Influence of the Anterior and Middle Cranial Fossae on Brain Kinematics During Sagittal Plane Head Rotation

A 2D physical model of the human head was used to investigate how the irregular skull base structure affects brain kinematics during sagittal plane head dynamics. The model consisted of a rigid skull vessel with interchangeable skull base structures. One version of the model used a skull base mimicking the irregular geometry of the human. A second version used a skull base structure approximating the anterior and middle fossae as a flat surface. Silicone gel simulated the brain and was separated from the vessel by a paraffin layer which provided a slip condition at the interface between the gel and vessel. The model was exposed to 7600 rad/s² peak rotational acceleration with 6 ms pulse duration and 5° forced rotation. After 90° free rotation, the model was decelerated during 30 ms. Five repeated tests were conducted with each version. Rigid body displacement, shear strain and principal strains were determined from high-speed video recorded trajectories of grid markers located at different positions in the surrogate brain. The humanlike skull base reduced peak displacements of the inferior surfaces of the temporal and frontal lobes up to 87% and 48%, respectively. Up to 48% and 36% higher peak strains were obtained in the frontal and superior regions of the surrogate brain in the version containing the humanlike skull base. In contrast, the humanlike skull base decreased peak strain up to 28% in the central region of the surrogate brain. The results indicate that the irregular skull base offers natural protection of nerves and vessels passing through fissures and foramina in the cranial floor but also that it affects kinematics in different regions throughout the cerebrum. Implications of these results are discussed with respect to brain injury and modeling of head impact.     

Male turnover reduces population growth: an enclosure experiment on voles

Turnover of individuals is assumed to cause disruptions of social organization, followed by reduced reproduction and survival. We tested how male turnover (removal of resident males and their replacement by unfamiliar males) affected population performance in experimental root vole (Microtus oeconomus) populations. The treatment simulated predation of adult males, with the subsequent replacement by immigrants, and provided insight into the interaction between extrinsic (i.e., predation) and intrinsic (i.e., social organization) factors. We showed that recruitment and female survival dramatically declined and that reproduction commenced slightly later in treatment populations compared with control populations. The treatment nearly halved the population growth rate. We suspect that recruitment failed due to infanticidal immigrating males. Reduced female survival was particularly apparent in treatment populations in which females exhibited a high degree of spatial overlap. Our experimental results show how males may significantly shape population dynamics and suggest how predation and social factors interact mechanistically.