The tolerance of the frontal bone to blunt impact

The current understanding of the tolerance of the frontal bone to blunt impact is limited. Previous studies have utilized vastly different methods, which limits the use of statistical analyses to determine the tolerance of the frontal bone. The purpose of this study is to determine the tolerance of the frontal bone to blunt impact. Acoustic emission sensors were used to provide a noncensored measure of the frontal bone tolerance and were essential due to the increase in impactor force after fracture onset. In this study, risk functions for fracture were developed using parametric and nonparametric techniques. The results of the statistical analyses suggest that a 50% risk of frontal bone fracture occurs at a force between 1885 N and 2405 N. Subjects that were found to have a frontal sinus present within the impacted region had a significantly higher risk of sustaining a fracture. There was no association between subject age and fracture force. The results of the current study suggest that utilizing peak force as an estimate of fracture tolerance will overestimate the force necessary to create a frontal bone fracture.     

The impact of insulin administration during the mixed meal tolerance test

Diabet. Med. 29, 1279-1284 (2012) ABSTRACT: Aims The mixed meal tolerance test is the gold standard measure of endogenous insulin secretion. Practical issues limit the routine clinical use of this test, including omitting insulin prior to the ingestion of a high-carbohydrate liquid mixed meal, which can result in marked hyperglycaemia. We aimed to assess whether insulin omission is necessary during the mixed meal tolerance test and whether fasting C-peptide was a practical alternative to the test. Methods Ninety-one adults with insulin-treated diabetes (Type?1 n?=?56, Type?2 n?=?35) underwent two mixed meal tolerance tests; one standard without insulin and one with the patient's usual morning insulin. Results The 90-min serum C-peptide was highly correlated in the standard mixed meal tolerance test and the test with insulin (r?=?0.98, P?相似文献   

Impact orientation can significantly affect the outcome of a blunt impact to the rabbit patellofemoral joint

This laboratory has developed a subfracture, joint trauma model in rabbits. Using a dropped impact mass directed onto a slightly abducted joint, chronic softening of retropatellar cartilage and thickening of underlying subchondral bone are documented in studies to 1 year post-insult. It has been hypothesized that these tissue changes are initiated by stresses developed during impact loading. A previous analytical study by this laboratory suggests that tensile strains in retropatellar cartilage can be significantly lowered, without significantly changing the intensity of stresses in the underlying subchondral bone, by reorientation of patellar impact more centrally on the joint. In the current study comparative experiments were performed on groups of animals after either an impact directed on the slightly abducted limb or a more central impact. One-year post-trauma in animals subjected to the central-oriented impact no degradation of the shear modulus for the retropatellar cartilage was documented, but the thickness of the underlying subchondral bone was significantly increased. In contrast, alterations in cartilage and underlying bone following impact on the slightly abducted limb were consistent with previous studies. The current experimental investigation showed the sensitivity of post-trauma alterations in joint tissues to slight changes in the orientation of impact load on the joint. Interestingly, for this trauma model thickening of the underlying subchondral plate occurred without mechanical degradation of the overlying articular cartilage. This supports the current laboratory hypothesis that alterations in the subchondral bone and overlying cartilage occur independently in this animal model.     

A high-frequency lung injury mechanism in blunt thoracic impact

When a mechanical load is applied very rapidly to the thoracic wall, part of the internal damage is suspected to be due to a "high-frequency" injury mechanism, that is, a phenomenon in which waves are involved. This paper addresses a specific high-frequency mechanism for lung injury in which a stress wave is generated through rapid acceleration of the body wall. Displacement-related injuries, which are rather "low-frequency" phenomena, are not considered. The present work was done in the context of assessing behind armor blunt trauma (injury to thoracic organs occurring when a bullet is stopped by a body armor) through mathematical modeling. One aspect of the thorax response to high-speed blunt impact and an associated injury mechanism are investigated based on an idealized model of thorax and a set of computations presented in previous papers. The injury mechanism considered elucidates a possible mathematical relationship between the acceleration at the surface of the thoracic wall and the occurrence of lung injury.     

Biomechanical characterization of cartilages by a novel approach of blunt impact testing

The present article introduces a novel method of characterizing the macromechanical cartilage properties based on dynamic testing. The proposed approach of instrumented impact testing shows the possibility of more detailed investigation of the acting dynamic forces and corresponding deformations within the wide range of strain rates and loads, including the unloading part of stress-strain curves and hysteresis loops. The presented results of the unconfined compression testing of both the native joint cartilage tissues and potential substitute materials outlined the opportunity to measure the dissipation energy and thus to identify the initial mechanical deterioration symptoms and to introduce a better definition of material damage. Based on the analysis of measured specimen deformation, the intact and pathologically changed cartilage tissue can be distinguished and the differences revealed.     

Biological arches and changes to the curvilinear form of the aging maxilla

The facial skeleton can be conceptualized as a series of arches aligned along a vertical axis, with regional differences in shape. Previous work suggested that the maxilla undergoes differential growth with time. Because these arch forms resemble geometric forms, it may be possible to measure changes to their shape with the aging process. A contour analysis of the aging maxilla was undertaken. Computed tomographic data were assembled retrospectively. Only men were studied, and they were divided into two groups: young (aged 18 to 24 years; n = 6) and old (aged 40 to 66 years; n = 6). The computed tomography data were reconstructed into three-dimensional images and underwent standardization for comparison purposes. An axial view of the maxilla along the Frankfort horizontal was used for analysis. To quantify changes between curves, measurements were made of the vertical distance from eight equidistant points along each curve perimeter to a standardized baseline. Average arch forms for young and old men were then generated for comparison purposes. Each of the eight points along the older maxillary arch form existed further from the baseline than the younger arch form. This difference reached statistical significance at three of the eight points measured along the two curves. The greatest difference occurred at point 8 (p = .0006), which was at the medial maxilla near the nasomaxillary junction. The results of the study suggest that the actual contour of the maxilla undergoes changes as a result of the aging process. Mathematically defined idealized skeletal contours could help guide reconstructive surgery and aesthetic augmentation of the facial skeleton in the future. In addition, certain soft tissues of the face and torso seem to share a common shape (an alpha contour). This shape may also exhibit idealized forms open to quantitative analysis. The skeletal arch form and alpha contour most likely exhibit sexual dimorphism and will require further investigation. The ubiquity of the arch form in nature and possible implications for growth and development of the human facial skeleton are also discussed.     

Uncoupling proteins and their role in the regulation of brain and heart tolerance to impact of ischemia and reperfusion

Experimental data indicate that moderate uncoupling oxidative phosphorylation induces reduction in production of reactive oxygen species (ROS) and promotes an increase in survival of neurons and cardiomyocytes under hypoxia and re-oxygenation conditions. Uncoupling proteins (UCP) are expressed by cardiomyocytes and neurons. These proteins are involved in the thermogenesis, inhibit ROS generation by mitochondria, reduce deltaphi, elevate respiration rate of these organelles. It was established that UCP contributed to the elevation of cardiomyocyte and neuron tolerance of an impact of hypoxia and re-oxygenation. They also promote cell resistance to oxidative stress. Experimental data indicate the important role of the UCP in the neuroprotective and cardioprotective effects of ischemic preconditioning. At the same time, real contribution of the UCP in preconditioning is still to be verified.