Negative Compression Research Articles

Unusual deep vein thrombosis sites: magnetic resonance venography in patients with negative compression ultrasound and symptomatic pulmonary embolism

To evaluate the clinical characteristics of patients with pulmonary embolism (PE), negative compression ultrasound (CUS) of the lower limbs and detection of unusual deep vein thrombosis (DVT) sites by means of magnetic resonance (MR) venography. A retrospective data analysis of PE patients hospitalized at our institution from April 2009 to 2011. From April 2009 to 2011, a total of 762 PE patients were treated at our institution. In 169 of these patients CUS for DVT was negative. In these patients MR venography was performed for further evaluation. We found venous thrombosis at unusual sites in 12 of these patients. Due to free floating thrombus masses and fear of life-threatening PE progression we inserted an inferior vena cava filter in three of these 12 patients. The leading venous thromboembolism risk factor in our patients was immobilization (5 patients, 41.7%). We conclude that especially in patients with PE and negative CUS of the lower limbs a thrombosis of the pelvic veins should be considered in case of symptoms for venous thrombosis in this area. Further diagnostic work-up with MR venography should be scheduled in these patients especially in patients with risk factor immobilization as therapeutic consequences might occur.

The Wells rule and D‐dimer for the diagnosis of isolated distal deep vein thrombosis

Pretest clinical probability with the Wells rule and D-dimer have been widely investigated for the diagnosis of symptomatic proximal deep vein thrombosis (DVT) of the lower limbs, but they have not been formally tested for symptomatic isolated distal DVT diagnosis. To evaluate the diagnostic accuracy of the Wells rule and D-dimer for isolated distal DVT. This was a single-center, cross-sectional study including 873 consecutive outpatients with suspected DVT, in whom pretest clinical probability determination, D-dimer determination (STA Liatest; cut-off of < 500 ng mL(-1) ) and complete compression ultrasonography of both lower limbs were performed. The isolated distal DVT prevalence was 12.4% (90/725). The sensitivity of the Wells rule for isolated distal DVT was 47% (95% confidence interval [CI] 36-57%), the specificity was 74% (95% CI 70-77%), and the negative and positive predictive values were 91% (95% CI 88-93%) and 20% (95% CI 15-26%), respectively. Patients with isolated distal DVT had higher D-dimer levels than patients without DVT (1759 ± 1576 vs. 862 ± 1079 ng mL(-1) , P = 0.0001). D-dimer was negative in 13 patients with isolated distal DVT. D-dimer sensitivity and specificity for isolated distal DVT were 84% (95% CI 75-91%) and 50% (95% CI 46-54%), respectively, with a negative predictive value of 96% (95% CI 93-98%). In patients with low pretest clinical probability, the D-dimer negative predictive value was 99% (95% CI 95-100%). In clinically suspected DVT with negative proximal compression ultrasonography, pretest clinical probability with the Wells rule has a low diagnostic accuracy for isolated distal DVT. D-dimer has a better negative predictive value, but alone it does not exclude isolated distal DVT. In patients with low pretest clinical probability, D-dimer had a negative predictive value of > 95% for isolated distal DVT.

Real-time measurement of skin erythema variation by negative compression: pilot study

Skin erythema has been widely used as a diagnostic parameter in dermatology. This study describes a methodology for real-time measurement of skin erythema variation induced by negative compression. This study developed an optical measurement probe, which includes a RGB color sensor that translates in the vertical direction, with the magnitude of vertical translation dependening on the amount of skin deformation. Real-time measurement of erythema variation as a function of both negative compression and time was performed in vivo on 10 measurement sites located on the back of each of 12 volunteers who participated in this study. Negative compression was sequentially applied from -30 to -80 kPa and continuously at a constant magnitude (-80 kPa) condition. The results showed that skin erythema was uniformly induced at the measurement sites and linearly increased as a function of both negative compression and time. A wide range of individual variation was noted for skin erythema, which may be due to variations in anisotropic skin properties between volunteers. This study demonstrated the clinical feasibility of a novel optical device for skin erythema measurement. Future studies are needed to investigate the clinical applications of this device.

Behaviour and design of composite beams subjected to negative bending and compression

This paper investigates the behaviour of steel–concrete composite beams subjected to the combined effects of negative bending and axial compression. For this study, six full-scale tests were conducted on composite beams subjected to negative moment while compression was applied simultaneously. The level of the applied axial compression varied from low to high. Following the tests, a nonlinear finite element model was developed and calibrated against the experimental results. The model was found to be capable of predicting the nonlinear response and the ultimate failure modes of the tested beams. The developed finite element model was further used to carry out a series of parametric analyses on a range of composite sections commonly used in practice. It was found that, when a compressive load acts in the composite section, the negative moment capacity of a composite beam is significantly reduced and local buckling in the steel beam is more pronounced, compromising the ductility of the section. Rigid plastic analysis based on sectional equilibrium can reasonably predict the combined strength of a composite section and, thus, can be used conservatively in the design practice. Detailing with longitudinal stiffeners in the web of the steel beam in the regions of negative bending eliminate web buckling and increase the rotational capacity of the composite section. Based on the experimental outcomes and the finite element analyses a simplified design model is proposed for use in engineering practice.

Chirped-pulse amplification system based on chirp reversal and near-field spatial reversal with common tiled grating pair as stretcher and compressor

Chirped-pulse amplification system based on chirp reversal in optical parametric chirped-pulse amplification is proposed and experimentally demonstrated. The operation of this system can be described as negative stretching-temporal chirp reversal-energy amplification-negative compression, in which the pulse is stretched and compressed with the same gratings. Stand-alone stretcher adopting lenses or concave mirrors with large aperture can be omitted. Simulations showed that this work mode can also increase the cut-off band-pass of the whole system and increase the output energy by 15-17%. In addition, the stability of a tiled-grating compressor can be improved with this work mode.

Influence of heat loss, preferential diffusion, and stretch on a conical flame in an impinging jet flow

In this study, we aim at studying the structure of a negatively stretched conical methane/air flame in a positively stretched flow under the influence of preferential diffusion, curvature stretch, flow stretch, and external heat loss by using large activation energy asymptotics. Parameters for the open and closed flame tips in the analysis consist of the curvature stretch and aerodynamic straining coupled with Lewis number (Le). The curvature stretch, which is negative stretch or compression, strengthens and weakens the burning intensity of the and conical flame, respectively. The opposite holds for aerodynamic straining, which is positive stretch. Additionally, irrespective of or , the external heat loss weakens the burning intensity and has a significant influence on the structure of conical flame tips. For rich methane/air conical flames (), closed tip solutions are obtained. Furthermore, the burning intensity is enhanced with increasing curvature stretch or decreasing flow stretch. Conversely, the curvature stretch weakens the burning intensity of the lean methane/air conical flames () and eventually leads to tip opening, that is, local flame extinction. The burning intensity is further reduced with the increase of curvature stretch or external heat loss, or with the decrease of flow stretch. Note that the openings become wider for open-tip conical flames when the external heat loss increases or flow stretch decreases.

An Expansion Method of Reliable Data Transmission of the Short-Message Communication on Satellite Network

Short-message communication mechanism is one of the most frequently methods used on the field of satellite data transmission. Under the existing satellite network, we provide an expansion method of reliable data transmission of short message communication named EMRDT-SMC, which solves negative compression problem of transmission capacity expansion when the amount of short message is below normal, and also solves reliable data transmission problem while satellite microwave transmission causes short message loss. Based on the measurement over a small test-bed, it shows that the method EMRDT-SMC can obtain the better network performance.

Diagnostic value of single complete compression ultrasonography in pregnant and postpartum women with suspected deep vein thrombosis: prospective study

Objective To assess the safety of using single complete compression ultrasonography in pregnant and postpartum women to rule out deep vein thrombosis.Design Prospective outcome study.Setting Two tertiary care centres and...

Covalent Functionalization of Strained Graphene

An enhancement of the chemical activity of graphene is evidenced by first-principles modelling of the chemisorption of hydrogen, fluorine, oxygen and hydroxyl groups on strained graphene. For the case of negative strain or compression, chemisorption of the single hydrogen, fluorine or hydroxyl group is energetically more favourable than those of their pairs on different sublattices. This behaviour stabilizes the magnetism caused by the chemisorption being against its destruction by the pair formations. Initially flat, compressed graphene is shown to buckle spontaneously right after chemisorption of single adatoms. Unlike hydrogenation or fluorination, the oxidation process turns from the endothermic to exothermic for all types of the strain and depends on the direction of applied strains. Such properties will be useful in designing graphene devices utilizing functionalization as well as mechanical strains.

Antagonism between Extreme Negative Linear Compression and Spin Crossover in [Fe(dpp)2(NCS)2]⋅py

A scissor-like geometric mechanism is responsible for the strongest negative linear compression effect yet observed in a molecular material, [Fe(dpp)(2)(NCS)(2)]⋅py (see picture; dpp=dipyrido[3,2-a:2'3'-c]phenazine), C gray, N blue, S yellow, Fe red). The same mechanism is also responsible for suppressing the high-spin to low-spin transition under pressure.

Antagonism between Extreme Negative Linear Compression and Spin Crossover in [Fe(dpp)2(NCS)2]⋅py

Eine scherenähnliche Bewegung einzelner Moleküle von [Fe(dpp)2(NCS)2]⋅py (siehe Bild; dpp=Dipyrido[3,2-a:2′3′-c]phenazin), C grau, N blau, S gelb, Fe rot) führt zum stärksten bisher bekannten negativen linearen Kompressionseffekt in einem molekularen Material. Derselbe Mechanismus verursacht auch, dass der Übergang von High Spin zu Low Spin unter Druck unterdrückt wird.

Negative linear compression and expanding NH⋯N bonds in an imidazoline compound

The 3-dimensional network of NH⋯N hydrogen bonds and Cl⋯Cl hydrogen contacts in the crystal structure of 2-(3′-chlorophenyl)imidazoline exhibits an anomalous hydrostatic compression. The lengthening of hydrogen bonds NH⋯N and some CH⋯N contacts as well as their supramolecular architecture lead to anomalous expansion of the crystal along [x] and [y] on increasing pressure to 0.1 GPa. The mechanism of this phenomenon is due to the ‘stiffness’ of the NH⋯N and Cl⋯Cl interactions and ‘softness’ of other van der Waals contacts. Above 0.1 GPa all crystal directions become compressed. However, up to 1.20 GPa, the crystal remains in the same orthorhombic phase of polar space group Fdd2.

Numerical Modeling of Compression-Controlled Low-level Laser Probe for Increasing Photon Density in Soft Tissue

Various methods have been investigated to increase photon density in soft tissue, an important factor in low-level laser therapy. Previously we developed a compression-controlled low-level laser probe (CCLLP) utilizing mechanical negative compression, and experimentally verified its efficacy. In this study, we used Bezier curves to numerically simulate the skin deformation and photon density variation generated by the CCLLP. In addition, we numerically modeled changes in optical coefficients due to skin deformation using a linearization technique with appropriate parameterization. The simulated results were consistent with both human in vivo and porcine ex vivo experimental results, confirming the efficacy of the CCLLP.

Compression Ultrasonography of the Lower Extremity With Portable Vascular Ultrasonography Can Accurately Detect Deep Venous Thrombosis in the Emergency Department

Compression ultrasonography of the lower extremity is an established method of detecting proximal lower extremity deep venous thrombosis when performed by a certified operator in a vascular laboratory. Our objective is to determine the sensitivity and specificity of bedside 2-point compression ultrasonography performed in the emergency department (ED) with portable vascular ultrasonography for the detection of proximal lower extremity deep venous thrombosis. We did this by directly comparing emergency physician-performed ultrasonography to lower extremity duplex ultrasonography performed by the Department of Radiology. This was a prospective, cross-sectional study and diagnostic test assessment of a convenience sample of ED patients with a suspected lower extremity deep venous thrombosis, conducted at a single-center, urban, academic ED. All physicians had a 10-minute training session before enrolling patients. ED compression ultrasonography occurred before Department of Radiology ultrasonography and involved identification of 2 specific points: the common femoral and popliteal vessels, with subsequent compression of the common femoral and popliteal veins. The study result was considered positive for proximal lower extremity deep venous thrombosis if either vein was incompressible or a thrombus was visualized. Sensitivity and specificity were calculated with the final radiologist interpretation of the Department of Radiology ultrasonography as the criterion standard. A total of 47 physicians performed 199 2-point compression ultrasonographic examinations in the ED. Median number of examinations per physician was 2 (range 1 to 29 examinations; interquartile range 1 to 5 examinations). There were 45 proximal lower extremity deep venous thromboses observed on Department of Radiology evaluation, all correctly identified by ED 2-point compression ultrasonography. The 153 patients without proximal lower extremity deep venous thrombosis all had a negative ED compression ultrasonographic result. One patient with a negative Department of Radiology ultrasonographic result was found to have decreased compression of the popliteal vein on ED compression ultrasonography, giving a single false-positive result, yet repeated ultrasonography by the Department of Radiology 1 week later showed a popliteal deep venous thrombosis. The sensitivity and specificity of ED 2-point compression ultrasonography for deep venous thrombosis were 100% (95% confidence interval 92% to 100%) and 99% (95% confidence interval 96% to 100%), respectively. Emergency physician-performed 2-point compression ultrasonography of the lower extremity with a portable vascular ultrasonographic machine, conducted in the ED by this physician group and in this patient sample, accurately identified the presence and absence of proximal lower extremity deep venous thrombosis.

Thermodynamic and Acoustic Properties of Mixtures of Dibromomethane + Heptane

Densities and speeds of ultrasound in binary mixtures of dibromomethane with heptane have been measured within the temperature range from 288.15 K to 318.15 K. From the experimental data, the thermodynamic excess volume, molar isobaric expansion, molar isentropic compression, and ultrasonic speed were calculated. The excess volume and excess isentropic compression have opposite signs, whereas the excess isobaric expansion is an S-shaped function of the mole fraction. An explanation was suggested to account for the excesses in terms of intermolecular interactions. It involved energetic and steric factors. Moreover, it was shown that the positive excess sound speed results almost entirely from the negative excess compression.

Development of compression-controlled low-level laser probe system: towards clinical application

Various physico-chemical tissue optical clearing (TOC) methods have been suggested to maximize photon density in tissue. In order to enhance photon density, a compression-controlled low-level laser probe (CCLLP) system was developed by utilizing the principle of mechanical tissue compression. Negative compression (NC) was applied to the laser probes built in various diameters and simultaneously the laser was irradiated into ex-vivo porcine skin samples. Laser photon density (LPD) was evaluated as a function of NC and probe diameter by analyzing 2D diffusion images of the laser exposures. The CCLLP system resulted in a concentrated laser beam profile, which means enhancement of the LPD. As indicators of LPD, the laser peak intensity increased and the full width at half maximum (FWHM) decreased as a function of NC. The peak intensity at –30 kPa increased 2.74, 3.22, and 3.64 fold at laser probe diameters of 20, 30, and 40 mm, respectively. In addition, sample temperature was measured with a thermal camera and increased 0.4 K at –30 kPa after 60 s of laser irradiation as a result of enhanced LPD. The CCLLP system effectively demonstrated enhancement of the LPD in tissue and potentially its clinical feasibility.

Pretest probability estimation in the evaluation of patients with possible deep vein thrombosis

Introduction An estimation of pretest probability is integral to the proper interpretation of a negative compression ultrasound in the diagnostic assessment of lower-extremity deep vein thrombosis. We sought to determine the rate, method, and predictors of pretest probability estimation in such patients. Methods This cross-sectional study of outpatients was conducted in a suburban community hospital in 2006. Estimation of pretest probability was done by enzyme-linked immunosorbent assay d-dimer, Wells criteria, and unstructured clinical impression. Using logistic regression analysis, we measured predictors of documented risk assessment. A cohort analysis was undertaken to compare 3-month thromboembolic outcomes between risk groups. Results Among 524 cases, 289 (55.2%) underwent pretest probability estimation using the following methods: enzyme-linked immunosorbent assay d-dimer (228; 43.5%), clinical impression (106; 20.2%), and Wells criteria (24; 4.6%), with 69 (13.2%) patients undergoing a combination of at least two methods. Patient factors were not predictive of pretest probability estimation, but the specialty of the clinician was predictive; emergency physicians ( P < .0001) and specialty clinicians ( P = .001) were less likely than primary care clinicians to perform risk assessment. Thromboembolic events within 3 months were experienced by 0 of 52 patients in the explicitly low-risk group, 4 (1.8%) of 219 in the explicitly moderate- to high-risk group, and 1 (0.4%) of 226 in the group that did not undergo explicit risk assessment. Conclusions Negative ultrasounds in the workup of deep vein thrombosis are commonly interpreted in isolation apart from pretest probability estimations. Risk assessments varied by physician specialties. Opportunities exist for improvement in the diagnostic evaluation of these patients.

Risk of Deep Vein Thrombosis Following a Single Negative Whole-Leg Compression Ultrasound

In patients with suspected lower extremity deep vein thrombosis (DVT), compression ultrasound (CUS) is typically the initial test to confirm or exclude DVT. Patients with an initial negative CUS result often require repeat CUS after 5 to 7 days. Whole-leg CUS may exclude proximal and distal DVT in a single evaluation. To determine the risk of venous thromboembolism after withholding anticoagulation in patients with suspected lower extremity DVT following a single negative whole-leg CUS result. MEDLINE, EMBASE, CINAHL, LILACS, Cochrane, and Health Technology Assessments databases were searched for articles published from January 1970 through November 2009. Supplemental searches were performed of Internet resources, reference lists, and by contacting content experts. Included studies were randomized controlled trials and prospective cohort studies of patients with suspected DVT and a negative whole-leg CUS result who did not receive anticoagulant therapy, and were followed up at least 90 days for venous thromboembolism events. Two authors independently reviewed and extracted data regarding a single positive or negative whole-leg CUS result, occurrence of venous thromboembolism during follow-up, and study quality. Seven studies were included totaling 4731 patients with negative whole-leg CUS examinations who did not receive anticoagulation. Of these, up to 647 patients (13.7%) had active cancer and up to 725 patients (15.3%) recently underwent a major surgery. Most participants were identified from an ambulatory setting. Venous thromboembolism or suspected venous thromboembolism-related death occurred in 34 patients (0.7%), including 11 patients with distal DVT (32.4%); 7 patients with proximal DVT (20.6%); 7 patients with nonfatal pulmonary emboli (20.6%); and 9 patients (26.5%) who died, possibly related to venous thromboembolism. Using a random-effects model with inverse variance weighting, the combined venous thromboembolism event rate at 3 months was 0.57% (95% confidence interval, 0.25%-0.89%). Withholding anticoagulation following a single negative whole-leg CUS result was associated with a low risk of venous thromboembolism during 3-month follow-up.

Predicting Deep Venous Thrombosis in Pregnancy: Out in “LEFt” Field?

In the nonpregnant general population, deep venous thrombosis (DVT) can be excluded at the initial presentation not only by clinical assessment and review of risk factors, but also by the clinician's assessment of probability using subjective criteria or prediction rules. Because of the absence of a validated prediction rule for diagnosing DVT during pregnancy, diagnosis in pregnant patients depends largely on the use of compression ultrasonography, the diagnostic reference standard that establishes the presence or absence of DVT. The aim of this cross-sectional study was to investigate the predictive accuracy of clinicians' subjective assessment of the probability of DVT in women with suspected DVT and to identify useful objective prediction variables. The participants were 194 unselected pregnant women with suspected first DVT. Potential study patients were identified by clinicians during the initial examination when the clinical assessment was consistent with DVT, and led to consultation with thrombosis experts who obtained informed consent for participation in the study. Before compression ultrasonography testing, the experts examined each study patient and categorized their pretest probability of DVT based on subjective criteria as low, moderate, or high. The sensitivity, specificity, negative predictive value, and likelihood ratios of the clinicians' subjective pretest probability were calculated. Patients defined as DVT positive had abnormal diagnostic compression ultrasonography results at the initial presentation or during serial testing, or had symptomatic DVT or pulmonary embolism on follow-up. Patients with negative compression ultrasonography at presentation and no venous thromboembolism on follow-up were defined as DVT negative. DVT was diagnosed in 17 women (8.8%). The prevalence of DVT in patients with low pretest probability (two-third of patients) was 1.5% (2/131), with a 95% confidence interval of 0.4% to 5.4% (P < 0.001). The prevalence among those with moderate or high pretest probability was considerably higher, 24.6% (15/61), with a 95% confidence interval of 15.5% to 36.7% (P < 0.001). Multivariate analysis identified 3 independent variables that were highly predictive of DVT in pregnant women: left leg symptoms, difference in calf circumference of 2 cm or more, and presentation during the first trimester of pregnancy. DVT was unlikely in the absence of all 3 variables, and its probability increased substantially if 1 or more was present. These findings demonstrate that probability of DVT in pregnant women with suspected DVT may be assessed with use of 3 easily determined objective variables. The data show that DVT is very unlikely with a very low pretest probability.

The anti-deformation performance of composite foundation of transmission tower in mining subsidence area

To improve the design method of foundation of transmission tower in mining subsidence area, and considering the interactions of transmission tower, ground and foundation, this paper presents a contrast research on the anti-deformation performance of two types of foundation (i.e. independent foundation and composite foundation with protecting apron) by finite element simulation. For valid simulation, we put forward the methods and principles of simplifying foundation and sand cushion. The research results indicate that, if the ground deforms in patterns of negative curvature, tension or compression, the structure stress and the horizontal support displacement of transmission tower can be reduced by 25% and 40% respectively by using composite foundation compared with independent foundation. If the ground deforms in pattern of positive curvature, the tower can be also protected by using the composite foundation instead of the independent ones, but the effect is less than that in the former three deformation patterns. The research findings provide the basis for improving the design method of transmission tower foundation in mining subsidence area.