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PubMed2003

[The study of compressive strength of phosphate-bonded investment materials].

OBJECTIVE: The purpose of this study was to compare the compressive strength of phosphate-bonded investments. METHODS: The three sorts of investments were mixed according to manufacturer's recommendation before poured in the molds. After heated up to 900 degrees C, every sample was mounted on a universal experimental machine to test its compressive strength in ambient. RESULTS: Significant differences were found between the four groups(P < 0.01). CONCLUSION: From the data above it is concluded that the compressive strength of X-20 Chrome Investment mixed with the special liquid was the highest.

Compressive Strength↗
PubMed1992

Cholesterol in model membranes. A molecular dynamics simulation.

Molecular dynamics simulations of a model membrane with inserted cholesterol molecules have been performed to study the perturbing influence of cholesterol. In the fluid phase of a lipid bilayer at 13 mol% concentration of cholesterol, local ordering of the hydrocarbon chains is induced. This perturbation decays with the distance from the cholesterol, and the effect extends 1.25 nm. It can be monitored in several ways, e.g., by an order parameter corresponding to deuterium nuclear magnetic resonance quadrupolar splittings, by the fraction of gauche bonds, or by the local bilayer thickness. At constant surface density, the local ordering is accompanied by disordering of the bulk phase, and, consequently, the net ordering effect is small. After compressing the system laterally in accordance with experimentally known surface areas, the bulk order parameters agree with those of a pure system, and the average order parameters are in accordance with experimental data. The necessity for this lateral compression is supported by calculated lateral pressures. At lower cholesterol concentration (3%), no direct perturbing effect is observed. A smaller lateral pressure than in a pure system indicates that the system with cholesterol is expected to have a smaller surface area, which would result in an increase of the order parameters, thus accounting for the experimental observations. The lack of spatial variation is, however, puzzling and may indicate a cooperative ordering effect.

Cholesterol↗
PubMed1973

Lateral phase separations in membrane lipids and the mechanism of sugar transport in Escherichia coli.

Changes in slope of Arrhenius plots for transport can, in some instances, be detected at two different temperatures for cells that have a relatively simple fatty-acid composition in the membrane lipids. These characteristic temperatures correlate with the characteristic temperatures that define changes of state in membrane phospholipids as revealed by the paramagnetic resonance of the spin label TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl). The higher of these characteristic temperatures is that at which the formation of solid patches of membrane lipids is first detected. The lower is the end point of the course of lateral phase separations, at which all the membrane lipids are in a solid phase. For cells enriched for elaidic acid, the rate of transport increase by as much as 2-fold as the temperature is decreased by less than 1 degrees , at the higher characteristic temperature. At this characteristic temperature, lateral phase separations begin in the membrane phospholipids. This is also the temperature where one predicts a striking increase in the lateral compressibility of the membrane lipids. These data are thus interpreted to indicate that a component of the transport system vertically penetrates one or both monolayer faces of the membrane during transport, or that some other event involving the lateral compression of the phospholipids is important for transport.

Biological Transport, Active↗
PubMed2003

Tail profile: a more accurate system for analyzing DNA damage using the Comet assay.

The Comet assay (single cell gel electrophoresis assay) measures DNA strand breaks in individual cells. In the assay cells are embedded in agarose, lysed, and electrophoresed under low voltage, allowing migration of damaged DNA. The DNA is stained and subsequently viewed with an epifluorescent microscope. If DNA damage has occurred the electrophoresed DNA fragments appear as a diffuse tail behind the nucleus known as a "comet". Many computer-aided analysis systems are currently in use to quantify the amount of DNA damage that is represented by a comet image. Here, we present a novel method of analysis known as "tail profile". This method of analysis provides several advantages over currently employed methods, which rely primarily on the "tail moment" method of analysis. We compared the amount of DNA damage reported from both the tail profile and tail moment methods of analysis and observed a 26% (P<0.0001) increase in damage detected by tail profile across the 10-25 microm range of tail length, where the majority of the relevant comet data is concentrated. We further report that this increase in sensitivity is not only limited to assessing DNA damage, but also to gathering data from DNA repair assays. Furthermore, we demonstrate increased functionality and extended data analysis capabilities with the use of a compressed collection of images called a "comet chip" and through a visual representation of data called a "profile plot". Use of the custom macros enabled us to detect an unexpected characteristic of the electrophoretic profile, giving us novel insight into the nature of comet analysis. In addition to the increased analytical sensitivity proffered by this system, the tail profile macros are upgradeable and platform independent.

Comet Assay↗
PubMed2003

Encoding of compressive stress during indentation by group III and IV muscle mechano-nociceptors in rat gracilis muscle.

The mechanical state encoded by group III and IV muscle afferents, putative mechano-nociceptors, during indentation was examined using an isolated muscle-nerve preparation in a rat model. Gracilis muscle and its intact innervation were surgically removed from the medial thigh of the rat hindlimb and placed in a dish containing rodent synthetic interstitial fluid. The tendons of the muscle were coupled to an apparatus that could stretch and apply compression to the muscle. Using a standard teased-nerve preparation, the neural responses of single mechanically sensitive group III or IV afferents were identified. Afferents were classified as mechano-nociceptors on the basis of their graded response to noxious levels of compressive stress (or strain) as well as, in some cases, their polymodal response to noxious thermal stimuli. Mechano-nociceptors (n = 13) were stimulated using controlled compressive stress (10-30 kPa) or strain (40-80%) while simultaneously measuring displacement and force by compressing the muscle between a flat cylinder and a hard platform. Linear regression was used to evaluate the relationships between neural response and mechanical stress, force, strain, and displacement. The mean neural response (threshold: 1.1 +/- 0.4 kPa; sensitivity: 0.5 +/- 0.1 Hz/kPa; means +/- SE) was significantly and substantially more highly correlated with compressive stress than force, strain, or displacement. The data from this study support the hypothesis that muscle nociceptors stimulated by indentation encode compressive stress rather than force, strain, or displacement.

Animals↗
PubMed2001

[MR-venography using manual flow augmentation in an open low field MR system].

OBJECTIVE: To evaluate the feasibility of signal enhancement in the deep veins by means of manual compression of the calf (flow augmentation) as a new approach to MR venography in open configuration, low-field systems. METHODS: 10 healthy volunteers underwent MR venography of the calf unconstrained and during short localized manual compression. Gradient recalled echo sequences (FLASH, FISP) with repeated single slice acquisition and first-order gradient motion refocussing were tested in four protocols with and without arterial presaturation slabs (scan time 2.2 - 5.0 s per slice). The effect on flow enhancement was rated by means of a signal score. Interventional accessories, particularly an in-room LCD screen, were required for interactive application of compression manoeuvres. RESULTS: Sequences with arterial presaturation slabs were superior to those without regardless of the longer acquisition times. Careful targeting of compression to the mid-time of data acquisition was crucial to obtain marked flow acceleration. Enhancement was best in the case of proximally applied calf compression. Signal improvement was consistently achieved in the proximal parts of the posterior tibial and peroneal veins, but was only seen in 4/10 volunteers in the distal part of the anterior tibial vein. CONCLUSION: Flow augmentation by means of manual calf compression is a simple and effective complementary approach to MR venography in open configuration, low field MR systems.

Adult↗
PubMed2002

Is the root entry/exit zone important in microvascular compression syndromes?

OBJECTIVE: Microvascular compression syndromes such as trigeminal neuralgia, hemifacial spasm, and disabling positional vertigo involve an artery or vein compressing a cranial nerve. A cranial nerve is composed of a central nervous system (CNS) segment and a peripheral nervous system (PNS) segment separated by the root entry/exit zone (REZ). Although vascular compression can occur at any point along the cranial nerve, it has been generally assumed that only vascular contact at the REZ of the affected cranial nerve can cause symptoms. On the basis of personal surgical experience, we propose that vascular compression of the CNS segment alone causes symptoms. This has important repercussions for the future diagnosis and treatment of microvascular compression syndromes, especially the cochleovestibular compression syndrome. METHODS: For the anatomic study, four autopsy specimens and one surgical biopsy specimen of the vestibulocochlear nerve were microscopically and ultramicroscopically analyzed for structural differences between the CNS and PNS segments. For the clinical study, five patients with the clinical picture of cochleovestibular compression syndrome were treated by microsurgical decompression at the level of the CNS segment and not the REZ. One patient underwent reoperation for recurrent symptoms 4 years later, and a 4-mm vestibular neurectomy was performed at that stage. We performed an epidemiological analysis to demonstrate that the known incidences of trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia are related to the length of their respective CNS segments. RESULTS: Histological differences between the PNS and CNS segments suggest that the PNS segment is more resistant to compression. This was confirmed by neurophysiological data from intraoperative monitoring in posterior fossa surgery and experimental studies. We found a clear epidemiological correlation between the length of the CNS segment, which differed among cranial nerves, and the incidence of the microvascular compression syndrome. Successful decompression of the CNS segment in patients without compression at the REZ of the vestibulocochlear nerve for disabling positional vertigo provides clinical support for this hypothesis. CONCLUSION: The evidence we present supports the hypothesis that vascular compression syndromes arise from vascular contact along the CNS segment of the cranial nerves.

Blood Vessels↗
PubMed2002

Medical image compression by sampling DCT coefficients.

Advanced medical imaging requires storage of large quantities of digitized clinical data. Due to the constrained bandwidth and storage capacity, however, a medical image must be compressed before transmission and storage. Among the existing compression schemes, transform coding is one of the most effective strategies. Image data in spatial domain will be transformed into spectral domain after the transformation to attain more compression gains. Based on the quantization strategy, coefficients of low amplitude in the transformed domain are discarded and significant coefficients are preserved to increase the compression ratio without inducing salient distortion. In this paper, we use an adaptive sampling algorithm by calculating the difference area between correct points and predicted points to decide the significant coefficients. Recording or transmitting the significant coefficients instead of the whole coefficients achieves the goal of compression. On the decoder side, a linear equation is employed to reconstruct the coefficients between two sequent significant coefficients. Simulations are carried out to different medical images, which include sonogram, angiogram, computed tomography, and X-ray images. Consequent images demonstrate the performance at compression ratios of 20-45 without perceptible alterations. In addition, two doctors are invited to verify that the decoded quality is acceptable for practical diagnosis. Therefore, our proposed method is found to preserve information fidelity while reducing the amount of data.

Algorithms↗
PubMed2003

Early radiographic and clinical results of balloon kyphoplasty for the treatment of osteoporotic vertebral compression fractures.

STUDY DESIGN: A prospective consecutive cohort study of clinical and radiographic outcomes after kyphoplasty for treatment of osteoporotic vertebral compression fractures. OBJECTIVES: To measure changes in spinal deformity, activity level, and pain after kyphoplasty treatment. SUMMARY OF BACKGROUND DATA: Pain and kyphosis caused by osteoporotic vertebral compression fractures adversely affect quality of life and survival. Kyphoplasty involves the inflation of a balloon bone tamp, percutaneously placed in a fractured vertebral body, followed by deposition of bone cement into the resulting cavity. Previous reports indicate that kyphoplasty improves patient function and restores height of collapsed vertebral bodies, but limited data about the effects of kyphoplasty on spinal sagittal alignment are available. METHODS: Twenty-nine patients with osteoporotic vertebral compression fractures who did not respond to medical therapy were treated by kyphoplasty. These patients underwent 37 operations to treat 61 vertebral compression fractures between T6 and L5. Sagittal alignment was analyzed from standing radiographs (pre- and postkyphoplasty). Patient surveys were used to assess pain relief, improvement in activity, and satisfaction with the surgical procedure. RESULTS: In this cohort, a mean of 8.8 degrees (range 0-29 degrees ) of correction of local spinal kyphosis was achieved with kyphoplasty. Thirty of 52 fractures (17 patients) were considered reducible and had >5 degrees of correction, with a mean improvement in sagittal alignment of this population of 14.2 degrees. Patient surveys revealed significant pain reduction within the first week after surgery and improved activity levels for a majority of patients. CONCLUSIONS: Kyphoplasty improves physical function, reduces pain, and may correct kyphotic deformity associated with vertebral compression fractures.

Aged↗
PubMed2004

Integrin-mediated mechanotransduction processes in TGFbeta-stimulated monolayer-expanded chondrocytes.

Previous studies have demonstrated that passage in monolayer detrimentally affects the response of articular chondrocytes to the application of dynamic compression. Transforming growth factor beta (TGFbeta) is known to regulate metabolic processes in articular cartilage and can enhance the re-expression of a chondrocytic phenotype following monolayer expansion. The current study tests the hypothesis that TGFbeta also modulates the response of monolayer-expanded human chondrocytes to the application of dynamic compression, via an integrin-mediated mechanotransduction process. The data presented demonstrate that TGFbeta3 enhanced 35SO4 and [3H]thymidine incorporation and inhibited nitrite release after 48 h of culture when compared to unsupplemented constructs. Dynamic compression also enhanced 35SO4 and [3H]thymidine incorporation and inhibited nitrite release in the presence of TGFbeta3. By contrast, dynamic compression did not alter these parameters in the absence of the growth factor. The addition of the peptide, GRGDSP, which acts as a competitive ligand for the alpha5beta1 integrin, reversed the compression-induced stimulation of 35SO4 incorporation, [3H]thymidine incorporation, and suppression of nitrite release. No effect was observed when the control peptide, GRADSP, was used. The current data clearly demonstrate that the dynamic compression-induced changes observed in cell metabolism for human monolayer-expanded chondrocytes were dependent on the presence of TGFbeta3 and are integrin-mediated.

Adolescent↗
PubMed1998

Plating techniques and plate orientation in repair of mandibular angle fractures: an in vitro study.

A biomechanical model utilizing polystyrene mandibles was devised to evaluate the fixation efficacy of various plating techniques for repair of mandibular angle fractures. A simple angle fracture was created in the mandible models at a standardized location and was repaired using five different plating techniques. Each experimental group consisted of 15 mandibles, with fracture site, plate placement, load application, and fracture displacement measurement standardized to ensure consistency among experimental groups. Measurement of fracture distraction under load application generated a load deformation curve and corresponding slope for each technique. Comparison of load deformation slopes allowed assessment of fixation stability. When applied with a subapical, medially placed monocortical tension band, bicortical compression plating demonstrated the most stable fracture fixation. The data show that biplanar plate placement in both monocortical noncompression and bicortical compression techniques yields a stronger fixation than monoplanar placement.

Biomechanical Phenomena↗
PubMed2000

Anisotropic response of the human knee joint meniscus to unconfined compression.

The response of meniscal tissue to axial, radial and circumferential compressive forces was measured at physiologically relevant levels of load in eight pairs of human knee joint menisci. Compression was unconfined and uniaxial. Stress strain data were fitted to a two-parameter exponential model. The tissue was found to be significantly stiffer to axial compressive forces than to radial and circumferential forces. No significant difference was found between the responses to circumferential and radial forces.

Aged↗
PubMed2004

Mechanical properties and anthropometry of the human infant head.

The adult head has been studied extensively and computationally modeled for impact, however there have been few studies that attempt to quantify the mechanical properties of the pediatric skull. Likewise, little documentation of pediatric anthropometry exists. We hypothesize that the properties of the human pediatric skull differ from the human adult skull and exhibit viscoelastic structural properties. Quasi-static and dynamic compression tests were performed using the whole head of three human neonate specimens (ages 1 to 11 days old). Whole head compression tests were performed in a MTS servo-hydraulic actuator. Testing was conducted using nondestructive quasi-static, and constant velocity protocols in the anterior-posterior and right-left directions. In addition, the pediatric head specimens were dropped from 15cm and 30cm and impact force-time histories were measured for five different locations: vertex, occiput, forehead, right and left parietal region. The compression stiffness values increased with an increase in velocity but were not significantly different between the anterior-posterior and right-left directions. Peak head acceleration during the head impact tests did not significantly vary between the five different impact locations. A three parameter model that included damping represented the pediatric head impact data more accurately than a simple mass-spring system. The compressive and impact stiffness of the pediatric heads were significantly more compliant than published adult values. Also, infant head dimensions, center of gravity and moment of inertia (Iyy) were determined. The CRABI 6-month dummy impact response was similar to the infant cadaver for impacts to the vertex, occiput, and forehead but dramatically stiffer in lateral impacts. These pediatric head anthropomorphic, compression, and impact data will provide a basis to validate whole head models and compare with ATD performance in similar exposures.

Journal Article↗
PubMed2002

Elastographic imaging using a handheld compressor.

Elastography is an emerging imaging modality that allows noninvasive imaging of tissue stiffness changes and stiffness values associated with pathology or as a result of therapy. However, many currently-used systems for elastography rely on a fixed geometry transducer and compressor system for imaging. This configuration is disadvantageous for imaging difficult-to-reach regions that are currently accessible with conventional ultrasound. In this paper, we describe a handheld, portable stepper motor controlled system for elastography. This system may reduce motion and jitter errors that are prevalent in completely 'freehand elastography' that employs hand-induced compressions using the transducer. The latter also requires collection of large amounts of data and use of strain estimation algorithms that may not be sensitive to phase changes or use additional preprocessing to minimize decorrelation effects. The stepper motor controlled handheld system provides controlled compressions and synchronized data acquisition. Our technique yields elastograms of a low-contrast phantom that have contrast levels and contrast-to-noise ratios that are comparable to those obtained with a fixed geometry system.

Animals↗
PubMed2006

A novel high-capacity data-embedding system.

In this paper, we present a novel data-embedding system with high embedding capacity. The embedding algorithm is based on the quantized projection embedding method with some enhancement to achieve high embedding rates. In particular, our system uses a random permutation of the columns of a Hadamard matrix as projection vectors and a fixed perceptual mask based on the JPEG default quantization table for the quantization step design. As a result, the data-embedding system achieves 1/167 (1 bit out of 167 raw image bits) to 1/84 hiding ratios with a BER of around 0.1% in the presence of JPEG compression attacks, while maintaining visual distortion at a minimum.

Algorithms↗
PubMed2006

Dissociation of mineral and collagen orientations may differentially adapt compact bone for regional loading environments: results from acoustic velocity measurements in deer calcanei.

In limb bone diaphyses, it is hypothesized that collagen and extra-fibrillar mineral are aligned differently in relatively simple loading conditions (e.g., habitual longitudinal compression) when compared to complex or potentially deleterious strain environments (e.g., habitual shear or tension). These putative differences in collagen/mineral organization might be adaptations that enhance toughness and fatigue resistance by controlling the direction of microdamage propagation. This study examined relationships between the non-uniform strain distribution of wild deer calcanei and elastic anisotropy of cortical bone specimens in three preparations: (1) demineralized (collagen only), (2) deproteinized (mineral only), and (3) untreated. Using simulated functional loading, the following strain data were obtained from the dorsal "compression", plantar "tension", and medial and lateral ("neutral axis") cortices of one calcaneus of each of seven pairs: (1) peak strain magnitude, (2) prevalent/predominant strain mode (compression, tension, shear), and (3) principal strain orientation with respect to the bone's long axis. In the contralateral calcanei, elastic anisotropy ratios (ARs) were calculated using acoustic velocity (longitudinal and transverse) measurements from a pair of orthogonally sliced specimens (representing each of three preparation types) from each cortex. In a separate set of seven adult calcanei, predominant collagen fiber orientation (CFO) was measured using circularly polarized light (CPL) in the four cortical locations. Results showed that, in general, elastic anisotropy was significant in each region, with ARs being significantly different from isotropy (where AR=1.0). Compared to CFO, mineral orientation more strongly influenced this anisotropy, which was most notable in the plantar "tension" cortex. High correlations (r values from -0.675 to -0.734, P<0.05) were found between collagen anisotropy obtained from acoustic data when compared to the CPL data. Significant correlations of mineral and collagen anisotropy were also found between strain mode, magnitude, and orientation (all r values approximately -0.750). The habitual compression, tension, and shear (neutral axis) regions also had different collagen/mineral organizations, which may be important in accommodating the well-known disparity in the mechanical properties of bone in these loading modes.

Acoustics↗
PubMed1997

Prevalence of retinal hemorrhages in pediatric patients after in-hospital cardiopulmonary resuscitation: a prospective study.

OBJECTIVE: Child abuse occurs in 1% of children in the United States every year; 10% of the traumatic injuries suffered by children under 5 years old are nonaccidental, and 5% to 20% of these nonaccidental injuries are lethal. Rapid characterization of the injury as nonaccidental is of considerable benefit to child protection workers and police investigators seeking to safeguard the child care environment and apprehend and prosecute those who have committed the crime of child abuse. Physically abused children present with a variety of well-described injuries that are usually easily identifiable. In some cases, however, particularly those involving children with the shaken baby syndrome, obvious signs of physical injury may not exist. Although external signs of such an injury are infrequent, the rapid acceleration-deceleration forces involved often cause subdural hematomas and retinal hemorrhages, hallmarks of the syndrome. Frequently, retinal hemorrhages may be the only presenting sign that child abuse has occurred. Complicating the interpretation of the finding of retinal hemorrhages is the belief by some physicians that retinal hemorrhages may be the result of chest compressions given during resuscitative efforts. The objective of this study is to determine the prevalence of retinal hemorrhages after inpatient cardiopulmonary resuscitation (CPR) in pediatric patients hospitalized for nontraumatic illnesses in an intensive care unit. DESIGN: Prospective clinical study. SETTING: Pediatric intensive care unit. PATIENTS: Forty-three pediatric patients receiving at least 1 minute of chest compressions as inpatients and surviving long enough for a retinal examination. Patients were excluded if they were admitted with evidence of trauma, documented retinal hemorrhages before the arrest, suspicion of child abuse, or diagnosis of near-drowning or seizures. All of the precipitating events leading to cardiopulmonary arrest occurred in our intensive care unit, eliminating the possibility of physical abuse as an etiology. INTERVENTIONS: None. MEASUREMENTS: Examination of the retina was performed by one of two pediatric ophthalmologists within 96 hours of CPR. The chart was reviewed for pertinent demographic information; the platelet count, prothrombin time, and partial thromboplastin time proximate to the CPR were recorded if they had been determined. RESULTS: A total of 43 pediatric patients hospitalized with nontraumatic illnesses survived 45 episodes of inpatient CPR. The mean age was 23 months (range, 1 month to 15.8 years), and 84% of the patients were under 2 years old. The majority of the patients (44%) were admitted to the intensive care unit after surgery for congenital heart disease, and another 21% were admitted for respiratory failure. The mean duration of chest compressions was 16.4 minutes +/- 17 minutes with 58% lasting between 1 and 10 minutes. Five patients had chest compressions lasting >40 minutes, and two patients had open chest cardiac massage. All patients survived their resuscitative efforts. Ninety-three percent of patients had an elevated prothrombin time and/or partial thromboplastin time while 49% were thrombocytopenic. Sixty-two percent of the patients had low platelet counts and an elevated prothrombin time and/or partial thromboplastin time. Small punctate retinal hemorrhages were found in only one patient. CONCLUSIONS: Retinal hemorrhages are rarely found after chest compressions in pediatric patients with nontraumatic illnesses, and those retinal hemorrhages that are found appear to be different from the hemorrhages found in the shaken baby syndrome. Despite the small number of patients in this prospective study, we believe that these data support the idea that chest compressions do not result in retinal hemorrhages in children with a normal coagulation profile and platelet count. A larger number of patients should be evaluated in a prospective multi-institutional study to achieve statistical significance

Adolescent↗