Investigation of pediatric neck response and muscle activation in low-speed frontal impacts

Pediatric necks present different responses and injury patterns compared with those of adults in motor vehicle crashes (MVCs). To evaluate the effect of different muscle modeling methodologies, three muscle models were developed and simulated under low-speed frontal impact conditions with an average peak acceleration of 3g's. The muscle activation curve for the curve-guided model, the muscle segment was curved using guiding nodes, was further optimized based on experimental data. The pediatric neck model was also simulated under more severe frontal impact conditions with an average peak acceleration of 8g's. Simulation results revealed that the curve-guided model needed more muscle force than the straight-guided model, in which the muscle segment was straight with guiding nodes, and the curve-constrained model, in which the muscle segment was curved without guiding nodes and which imposes more constraints on the head and neck than the curve-guided model. The predicted head responses for the child finite element neck model were within or close to the experimental corridors of 3- and 8-g's frontal impacts. The neck injuries for a 10-year-old child commonly occurred at the interspinous ligament in the C7–T1 segment. The model could be used to analyze the responses and injuries of pediatric neck and head in low-speed frontal impacts.     

Effects of obesity on occupant responses in frontal crashes: a simulation analysis using human body models

The objective of this study is to investigate the effects of obesity on occupant responses in frontal crashes using whole-body human finite element (FE) models representing occupants with different obesity levels. In this study, the geometry of THUMS 4 midsize male model was varied using mesh morphing techniques with target geometries defined by statistical models of external body contour and exterior ribcage geometry. Models with different body mass indices (BMIs) were calibrated against cadaver test data under high-speed abdomen loading and frontal crash conditions. A parametric analysis was performed to investigate the effects of BMI on occupant injuries in frontal crashes based on the Taguchi method while controlling for several vehicle design parameters. Simulations of obese occupants predicted significantly higher risks of injuries to the thorax and lower extremities in frontal crashes compared with non-obese occupants, which is consistent with previous field data analyses. These higher injury risks are mainly due to the increased body mass and relatively poor belt fit caused by soft tissues for obese occupants. This study demonstrated the feasibility of using a parametric human FE model to investigate the obesity effects on occupant responses in frontal crashes.     

Computer simulation of movement-generating cross-bridges.

A stochastic computational method was developed to study properties of cross-bridge models for muscle contraction, by following the time history of individual cross-bridge model of Andrew Huxley (1957) and a modified two-state model with more realistic behavior during steady stretching are used as examples. The method can readily compute steady-state force during shortening and stretching and force-transients following rapid changes in length. Computations of velocity with a steady load and of velocity transients are more sensitive to the randomness inherent in the stochastic method.     

Computer simulation of firefly flash sequences.

A new method is proposed for measuring nonsteady flow rates when this flow is pulsatile in nature. This method involves the use of indicators and does not require direct access to the vessel carrying the fluid. No knowledge of the associated mathematics is required for its application. The investigator infuses indator into the vessel leading into a capillary or similar labyrinth at a time-varying rate such that the indicator concentration at the outflow from the labyrinth remains constant in time. When this condition at the outflow has been achieved, the pulsatile flow rate at the inflow is given simply as the ratio of the varying infusion rate to the constant outflow indicator concentration.     

Computer simulation of brainstem respiratory activity.

A mathematical model of the medullary respiratory oscillator, composed of two mutually inhibiting populations (inspiratory and expiratory) of computer-simulated neurons, is presented. Each population consists of randomly interconnected subpopulations of excitatory and inhibitory neurons, is presented. Each population consists of randomly interconnected subpopulations of excitatory and inhibitory neurons. Neuronal coupling is such that either the inspiratory or expiratory population alone is capable of cyclic activity. Weak inhibitory connections between inspiratory and expiratory populations provide satisfactory reciprocating activity independent of the natural frequency of either population alone. Initiation and persistence of rhythmic activity is dependent on a diffused noncyclic excitatory input. Vagal discharge, simulated by phasic inhibition of inspiratory neurons, results in increased respiratory frequency with decreased inspiratory activity. In the absence of simulated vagal discharge, uniform facilitation of synaptic connections increases averaged activities of inspiratory and expiratory populations, with minor effect on frequency. In the presence of simulated vagal discharge, facilitation of synaptic connections increases both frequency and amplitude. The simulated effects of synaptic facilitation, with and without vagal discharge, mimic the physiological response to CO2 in the intact and vagotimized animal.     

Computer simulation of overshoot in saccadic eye movements.

The human horizontal eye movement system produces quick, precise, conjugate eye movements called saccades. These are important in normal vision. For example, reading tasks exclusively utilize saccadic eye movements. The majority of saccades have dynamic overshoot. The amplitude of this overshoot is independent of saccadic amplitude, and is such that it places the image of the stimulus within the retinal region of maximum acuity within a minimum of time. A computer based model of the saccadic mechanisms was used to study the origin of this overshoot. It was discussed that dynamic overshoot cannot be attributed to biomechanism properites of the eye movement mechanism, but must instead be explained by variations in the controlling nervous activity. The form of this neural controller signal is very similar to that required for a time optimal response of an inertial system.     

Computer simulation of the effects of shoe cushioning on internal and external loading during running impacts

Biomechanical aspects of running injuries are often inferred from external loading measurements. However, previous research has suggested that relationships between external loading and potential injury-inducing internal loads can be complex and nonintuitive. Further, the loading response to training interventions can vary widely between subjects. In this study, we use a subject-specific computer simulation approach to estimate internal and external loading of the distal tibia during the impact phase for two runners when running in shoes with different midsole cushioning parameters. The results suggest that: (1) changes in tibial loading induced by footwear are not reflected by changes in ground reaction force (GRF) magnitudes; (2) the GRF loading rate is a better surrogate measure of tibial loading and stress fracture risk than the GRF magnitude; and (3) averaging results across groups may potentially mask differential responses to training interventions between individuals.     

Computer simulation of surface-induced aggregation of ferritin.

Models are presented describing the transient mass-transport limited adsorption and cluster growth of ferritin at a solid surface. Computer simulations are carried out on a hexagonal lattice using a computer model that can be characterized as a two-dimensional stochastic cellular automaton allowing different rules regarding association, lateral interaction and dissociation to be incorporated in the model. The fractal dimensions of individual clusters were extracted from simulated aggregates and for similar rules found to be consistent with literature values on reversible diffusion-limited aggregation in two dimensions. The distribution of clusters versus free surface were shown to be affected by neighbor-dependent association probability. Low fractal dimension clusters were generated by a combination of strong lateral cohesion and neighbor-dependent dissociation to the bulk. By comparing computer simulated aggregation to experimental electron micrographs of adsorbed ferritin layers it is suggested that neighbor-dependent association, neighbor-dependent dissociation and lateral interactions are important factors in the complex dynamics of adsorbed protein layers.     

Computer simulation of the synchronization of the sinoatrial central cell in response to periodic stimulation of the vagus nerve

The effect of periodic stimulation of the vagus nerve on the activity of the central cell of the sinoatrial node has been simulated. The regions of synchronization and desynchronization have been revealed, and the phase shift at different stimulation frequencies has been estimated. The positive chronotropic effect has been shown to occur at some frequencies of stimulation.     

Electromyography responses of pediatric and young adult volunteers in low-speed frontal impacts

No electromyography (EMG) responses data exist of children exposed to dynamic impacts similar to automotive crashes, thereby, limiting active musculature representation in computational occupant biomechanics models. This study measured the surface EMG responses of three neck, one torso and one lower extremity muscles during low-speed frontal impact sled tests (average maximum acceleration: 3.8 g; rise time: 58.2 ms) performed on seated, restrained pediatric (n = 11, 8–14 years) and young adult (n = 9, 18–30 years) male subjects. The timing and magnitude of the EMG responses were compared between the two age groups. Two normalization techniques were separately implemented and evaluated: maximum voluntary EMG (MVE) and neck cross-sectional area (CSA). The MVE-normalized EMG data indicated a positive correlation with age in the rectus femoris for EMG latency; there was no correlation with age for peak EMG amplitudes for the evaluated muscles. The cervical paraspinous exhibited shorter latencies compared with the other muscles (2–143 ms). Overall, the erector spinae and rectus femoris peak amplitudes were relatively small. Neck CSA-normalized peak EMG amplitudes negatively correlated with age for the cervical paraspinous and sternocleidomastoid. These data can be useful to incorporate active musculature in computational models, though it may not need to be age-specific in low-speed loading environments.     

In-vitro head and neck response to impact

Two unembalmed and one embalmed human cadaveric head-neck systems were instrumented and subjected to central forehead impact of ballistically suspended 3.07-kg aluminum shell at velocities ranging from 50 to 345 cm/s. Occipital skull accelerations and disk pressures were measured by transducers, while the deformation of the system was determined by framing camera data. The results were found to be in accord with those from corresponding tests in artificial head-neck replica. Initial and terminal X-ray examination of the structure revealed no evidence of either skull or vertebral fractures.     

Computer simulation of mutagenesis

A FORTRAN program is described which simulates point-substitution mutations in the DNA strands of typical organisms. Its objective is to help students to understand the significance and structure of the genetic code, and the mechanisms and effects of mutagenesis. The program is intended to be used as part of an elementary course in genetics at degree level.     

Sex dependent behavioral response to frontal cortical suction lesions in the rat

Previous reports indicate that male rats given right (but not left) frontal cortical suction lesions develop hyperactivity accompanied by cortical norepinephrine depletions. In this study, female rats given such lesions to either hemisphere developed bilateral cortical norepinephrine depletions but no hyperactivity. Right lesion male rats developed both catecholamine depletions and hyperactivity. Thus, the lateralized hyperactivity response to these cortical lesions is sex-dependent and may involve sex differences in subcortical neural pathways.     

Computer simulation for hormones related to primary thyropathy

We propose a mathematical model of the human hypothalamus-anterior pituitary-thyroid system regulating basal metabolism, and practice computer simulation concerning primary thyropathy such as Graves' disease, hypothyroidism, T ₄-toxicosis and T ₃-toxicosis by use of this model. In order to throw light on properties of the system, indicial responses of the hormones, T ₄, T ₃, rT ₃, and TSH, and the function of the thyroid gland are computed. Medical treatments for Graves' disease and for hypothyroidism are simulated with a view to enhancing clinical significance. Performance of the simulation leads to an interesting result that when the convertion rate of blood T ₄ to blood T ₃ increases, explicit T ₃-toxicosis occurs, although the function of the thyroid gland is normal.