Úvod a ciele: Zistilo sa, že obehové časy pečene merané pomocou kontrastnej ultrasonografie a elasticita pečene dokázali predpovedať klinicky signifikantnú portálnu hypertenziu. Nie je však zatiaľ dostatočne preskúmané, či by obehové časy pečene dokázali predpovedať nepriaznivý priebeh aj u pacientov s klinicky diagnostikovanou cirhózou, ktorí vo väčšine prípadov majú klinicky signifikantnú portálnu hypertenziu. Cieľom našej štúdie bolo zhodnotiť význam obehových časov a elasticity pečene v predikcii nepriaznivého priebehu cirhózy a porovnať ich s MELD (model for end-stage liver disease). Metódy: Sledovaná skupina zahŕňala 48 po sebe idúcich ambulantných pacientov s cirhózou v 2.–4. štádiu podľa D´Amica. Pacienti v štádiu 4. mohli mať len ikterus, pacienti s ostatnými komplikáciami portálnej hypertenzie neboli zahrnutí. Meranie obehových časov bolo vykonané počas kontrolného ultrasonografie. Obehové časy boli merané od intravenóznej aplikácie kontrastnej látky (SonoVue) a jej príchodu do hepatálnej žily (venózny čas/hepatic vein arrival time – HVAT) alebo časového rozdielu medzi kontrastným signálom vo vetve a. hepatica a hepatálnej žily (obeh pečene/hepatic transit time – HTT) v sekundách. Elasticita pečene bola meraná pomocou tranzientnej elastografie (Fibroscan). Obehové časy a elasticita boli merané pri vstupe do sledovania. Pacienti boli následne sledovaní počas 1 roka. Nepriaznivý priebeh cirhózy bol definovaný ako objavenie sa klinicky zjavného ascitu alebo hospitalizácie pre chorobu pečene alebo úmrtia. Výsledky: Priemerný vek bol 61 rokov, pomer ženy/muži bol 23/25. Pri vstupe do štúdie bol medián Childova-Pughova skóre 5 (IQR 5,0–6,0), MELD 9,5 (IQR 7,6–12,1), medián HVAT bol 22 s (IQR 19–25) a HTT 6 (IQR 5–9). HTT aj HVAT negatívne korelovali s Childovom-Pughovom skóre (-0,351, resp. -0,441; p = 0,002) a MELD (-0,479, resp. -0,388; p = 0,006) skóre. Po dobu jedného roka bol nepriaznivý priebeh zaznamenaný v 11 prípadoch (22,9 %), vrátane 6 úmrtí a 5 hospitalizácií. Medián HVAT bol v prípadoch s nepriaznivým priebehom 20 s (IQR 19,3–23,5) porovnaní s 22 s (IQR 19 do 26, p = 0,32). Prípady s nepriaznivým priebehom mali signifikantne vyššie MELD (12,9 vs 8,5), Childovo-Pughovo skóre (7,0 vs 5,0) a elasticitu pečene (52,5 vs 21,05 kPa) (p <0,05). AUROC pre HVAT, elasticitu pečene a MELD v predikcii nepriaznivého priebehu bol 0,60 (95% CI 0,414–0,785), 0,767 (0,56–0,98) a 0,813 (0,66–0,97). Čas HVAT nebol schopný predpovedať nepriaznivý klinický výsledok, ale elasticita pečene > 35,3 kPa zvýšila toto riziko 10,3-násobne a MELD > 11 bodov 8,5-násobne. Záver: U pacientov s klinicky diagnostikovanou cirhózou s prítomnou klinicky signifikantnou portálnou hypertenziou obehové časy pečene nepreukázali schopnosť predpovedať nepriaznivý priebeh do jedného roka. Naopak, meranie elasticity pečene sa ukázalo ako klinicky prospešné s prognostickou hodnotou porovnateľnou s MELD. Kľúčové slová: elasticita pečene – klinicky diagnostikovaná cirhóza – MELD – obehové časy pečene – portálna hypertenzia
Introduction and objectives: Hepatic transit times measured by the contrast enhanced ultrasonography and liver elasticity were found to predict a clinically significant portal hypertension. However, these modalities we not yet sufficiently evaluated in predicting adverse clinical outcome in patients with clinically diagnosed cirrhosis (D´Amico stages > 1), having a clinically significant portal hypertension. The aim of our study was to assess the predictive power of the liver transit times and the liver elasticity on an adverse clinical outcome of clinically diagnosed cirrhosis compared with the MELD score. Methods: The study group included 48 consecutive outpatients with cirrhosis in the 2., 3. and 4. D’Amico stages. Patients with stage 4 could have jaundice, patients with other complications of portal hypertension were excluded. Transit times were measured from the time of intravenous administration of contrast agent (Sonovue) to a signal appearance in a hepatic vein (hepatic vein arrival time, HVAT) or time difference between the contrast signal in the hepatic artery and hepatic vein (hepatic transit time, HTT) in seconds. Elasticity was measured using the transient elastography (Fibroscan). The transit times and elasticity were measured at baseline and patients were followed for up for 1 year. Adverse outcome of cirrhosis was defined as the appearance of clinically apparent ascites and/or hospitalization for liver disease and/or death within 1 year. Results: The mean age was 61 years, with female/male ratio 23/25. At baseline, the median Child-Pugh score was 5 (IQR 5.0–6.0), MELD 9.5 (IQR 7.6 to 12.1), median HVAT was 22 s (IQR 19–25) and HTT 6 (IQR 5–9). HTT and HVAT negatively correlated with Child-Pugh (-0.351 and -0.441, p = 0.002) and MELD (-0.479 and -0.388, p = 0.006) scores. The adverse outcome at 1-year was observed in 11 cases (22.9 %), including 6 deaths and 5 hospitalizations. Median HVAT in those with/without the adverse outcome was 20 seconds (IQR 19.3–23.5) compared with 22 s (IQR 19–26, p = 0.32). Cases with adverse outcome had significantly higher MELD (12.9 vs 8.5), Child-Pugh score (7.0 vs 5.0) and the liver elasticity (52.5 vs 21.5 kPa) (p < 0.05). The AUROC of the HVAT, liver elasticity and MELD for the prediction of the adverse outcome was 0.60 (95% CI 0.414 to 0.785), 0.767 (0.56 to 0.98) and 0.813 (0.66 to 0.97). Unlike HVAT, the liver elasticity > 35.3 kPa increased the risk of the adverse outcome 10.3-times and MELD score > 11 points 8.5-times. Conclusion: In patients with clinically diagnosed cirrhosis having a clinically significant portal hypertension hepatic transit times do not predict the 1-year adverse clinical outcome. However, the liver elasticity > 35.3 kPa appears clinically useful with a prognostic value comparable with MELD. Key words: clinically diagnosed cirrhosis – hepatic transit times – liver elasticity – MELD – portal hypertension
- MeSH
- Elasticity Imaging Techniques * methods MeSH
- Risk Assessment MeSH
- Data Interpretation, Statistical MeSH
- Liver Cirrhosis * physiopathology MeSH
- Liver Circulation MeSH
- Contrast Media MeSH
- Middle Aged MeSH
- Humans MeSH
- Hypertension, Portal * physiopathology MeSH
- Predictive Value of Tests MeSH
- Prognosis MeSH
- Blood Flow Velocity MeSH
- Aged MeSH
- Severity of Illness Index MeSH
- Ultrasonography methods MeSH
- Hepatic Veins physiopathology ultrasonography MeSH
- Check Tag
- Middle Aged MeSH
- Humans MeSH
- Male MeSH
- Aged MeSH
- Female MeSH
- Publication type
- Research Support, Non-U.S. Gov't MeSH
PURPOSE OF THE STUDY Decision-making in treatment of an acute compartment syndrome is based on clinical assessment, supported by invasive monitoring. Thus, evolving compartment syndrome may require repeated pressure measurements. In suspected cases of potential compartment syndromes clinical assessment alone seems to be unreliable. The objective of this study was to investigate the feasibility of a non-invasive application estimating whole compartmental elasticity by ultrasound, which may improve accuracy of diagnostics. MATERIAL AND METHODS In an in-vitro model, using an artificial container simulating dimensions of the human anterior tibial compartment, intracompartmental pressures (p) were raised subsequently up to 80 mm Hg by infusion of saline solution. The compartmental depth (mm) in the cross-section view was measured before and after manual probe compression (100 mm Hg) upon the surface resulting in a linear compartmental displacement (Δd). This was repeated at rising compartmental pressures. The resulting displacements were related to the corresponding intra-compartmental pressures simulated in our model. A hypothesized relationship between pressures related compartmental displacement and the elasticity at elevated compartment pressures was investigated. RESULTS With rising compartmental pressures, a non-linear, reciprocal proportional relation between the displacement (mm) and the intra-compartmental pressure (mm Hg) occurred. The Pearson's coefficient showed a high correlation (r2 = -0.960). The intraobserver reliability value kappa resulted in a statistically high reliability (κ = 0.840). The inter-observer value indicated a fair reliability (κ = 0.640). CONCLUSIONS Our model reveals that a strong correlation between compartmental strain displacements assessed by ultrasound and the intra-compartmental pressure changes occurs. Further studies are required to prove whether this assessment is transferable to human muscle tissue. Determining the complete compartmental elasticity by ultrasound enhancement, this application may improve detection of early signs of potential compartment syndrome. Key words: compartment syndrome, intra-compartmental pressure, non-invasive diagnostic, elasticity measurement, elastography.
- MeSH
- Pulse Wave Analysis methods utilization MeSH
- Anesthesia methods utilization MeSH
- Carotid Arteries * anatomy & histology surgery innervation MeSH
- Animal Experimentation MeSH
- Heparin administration & dosage MeSH
- Hemorrhage etiology MeSH
- Blood Pressure Determination methods instrumentation utilization MeSH
- Elasticity physiology MeSH
- Dogs MeSH
- Carotid Sinus * surgery MeSH
- Statistics as Topic MeSH
- Stroke Volume physiology MeSH
- Animals MeSH
- Check Tag
- Male MeSH
- Dogs MeSH
- Female MeSH
- Animals MeSH
The outer parenchyma of carrot was tested using dynamic mechanical analysis (DMA), in air with 90% humidity between 30 and 90°C. Temperature plots of storage (SM i.e. elastic) and loss (LM i.e. inelastic) moduli were obtained. The SM and LM values were the basis for the calculation of the loss tangent (LT), the parameter expressing the ratio of inelastic to elastic parenchyma toughness. As expected, the tissue toughness decreased with increasing temperature. For both moduli, two characteristic temperature areas with temperature slope minima were observed--they were termed low (I) and high (II) temperature negative peaks on the temperature slope plots. It was shown that the negative peaks were related to an increase in the inelastic part of the tissue toughness. All plots were dependent on the temperature rate: increasing the temperature rate (from 0.5 to 2°C/min) resulted in a shift of both the negative peaks I and II to higher temperatures, thereby reducing I and increasing II. It was shown that the observed behaviour cannot be described by simple kinetic equations due to the time dependent and complicated character of the thermally induced changes. These changes were interpreted as a consequence of pore protein denaturation followed by changes of the stress inside the parenchyma cells.
This work deals with the mechanical characterization by depth-sensing indentation (DSI) of PLLA and PLDA composites reinforced with micro-particles of Mg (up to 15wt%), which is a challenging task since the indented volume must provide information of the bulk composite, i.e. contain enough reinforcement particles. The composites were fabricated by combining hot extrusion and compression moulding. Physico-chemical characterization by TGA and DSC indicates that Mg anticipates the thermal degradation of the polymers but does not compromise their stability during processing. Especial emphasis is devoted to determine the effect of strain rate and Mg content on mechanical behavior, thus important information about the visco-elastic behavior and time-dependent response of the composites is obtained. Relevant for the intended application is that Mg addition increases the elastic modulus and hardness of the polymeric matrices and induces a higher resistance to flow. The elastic modulus obtained by DSI experiments shows good agreement with that obtained by uniaxial compression tests. The results indicate that DSI experiments are a reliable method to calculate the modulus of polymeric composites reinforced with micro-particles. Taking into consideration the mechanical properties results, PLA/Mg composite could be used as substitute for biodegradable monolithic polymeric implants already in the market for orthopedics (freeform meshes, mini plates, screws, pins, …), craniomaxillofacial, or spine.
Digital models based on finite element (FE) analysis are widely used in orthopaedics to predict the stress or strain in the bone due to bone-implant interaction. The usability of the model depends strongly on the bone material description. The material model that is most commonly used is based on a constant Young's modulus or on the apparent density of bone obtained from computer tomography (CT) data. The Young's modulus of bone is described in many experimental works with large variations in the results. The concept of measuring and validating the material model of the pelvic bone based on modal analysis is introduced in this pilot study. The modal frequencies, damping, and shapes of the composite bone were measured precisely by an impact hammer at 239 points. An FE model was built using the data pertaining to the geometry and apparent density obtained from the CT of the composite bone. The isotropic homogeneous Young's modulus and Poisson's ratio of the cortical and trabecular bone were estimated from the optimisation procedure including Gaussian statistical properties. The performance of the updated model was investigated through the sensitivity analysis of the natural frequencies with respect to the material parameters. The maximal error between the numerical and experimental natural frequencies of the bone reached 1.74 % in the first modal shape. Finally, the optimised parameters were matched with the data sheets of the composite bone. The maximal difference between the calibrated material properties and that obtained from the data sheet was 34 %. The optimisation scheme of the FE model based on the modal analysis data provides extremely useful calibration of the FE models with the uncertainty bounds and without the influence of the boundary conditions.
BACKGROUND: The aim of this paper was to design a finite element model for a hinged PROSPON oncological knee endoprosthesis and to verify the model by comparison with ankle flexion angle using knee-bending experimental data obtained previously. METHOD: Visible Human Project CT scans were used to create a general lower extremity bones model and to compose a 3D CAD knee joint model to which muscles and ligaments were added. Into the assembly the designed finite element PROSPON prosthesis model was integrated and an analysis focused on the PEEK-OPTIMA hinge pin bushing stress state was carried out. To confirm the stress state analysis results, contact pressure was investigated. The analysis was performed in the knee-bending position within 15.4-69.4° hip joint flexion range. RESULTS: The results showed that the maximum stress achieved during the analysis (46.6 MPa) did not exceed the yield strength of the material (90 MPa); the condition of plastic stability was therefore met. The stress state analysis results were confirmed by the distribution of contact pressure during knee-bending. CONCLUSION: The applicability of our designed finite element model for the real implant behaviour prediction was proven on the basis of good correlation of the analytical and experimental ankle flexion angle data.
- MeSH
- Algorithms MeSH
- Finite Element Analysis MeSH
- Equipment Failure Analysis MeSH
- Models, Biological * MeSH
- Computer-Aided Design MeSH
- Knee Joint physiopathology MeSH
- Muscle, Skeletal physiopathology MeSH
- Humans MeSH
- Stress, Mechanical MeSH
- Elastic Modulus MeSH
- Bone Neoplasms physiopathology surgery MeSH
- Tensile Strength MeSH
- Compressive Strength MeSH
- Computer Simulation MeSH
- Prosthesis Fitting methods MeSH
- Prosthesis Design MeSH
- Knee Prosthesis * MeSH
- Tendons physiopathology MeSH
- Software MeSH
- Muscle Contraction MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Validation Study MeSH
In this paper, linearized approximations of both the forward and the inverse problems of resonant ultrasound spectroscopy for the determination of mechanical properties of thin surface layers are presented. The linear relations between the frequency shifts induced by the deposition of the layer and the in-plane elastic coefficients of the layer are derived and inverted, the applicability range of the obtained linear model is discussed by a comparison with nonlinear models and finite element method (FEM), and an algorithm for the estimation of experimental errors in the inversely determined elastic coefficients is described. In the final part of the paper, the linearized inverse procedure is applied to evaluate elastic coefficients of a 310 nm thick diamond-like carbon layer deposited on a silicon substrate.
A new method to estimate the selected viscoelastic parameters of foods using damped vibration analysis is presented for the evaluation of fruits and baked products. A flat disk is attached to the flat sample surface using a laser rangefinder that measures the sample thickness in advance, and it is locked by a trigger. Next, the trigger is released to allow the probe to press the sample through the force of gravity. The damped vibration of the probe caused by the deformation of the food is measured by monitoring the displacement of the probe via a linear encoder. The bulk modulus and viscosity are estimated using the fractional Zener model and mass. Young's modulus (E) is estimated independently by determining the maximum velocity of the probe using Hooke's law. Poisson's ratio (ν), and the shear modulus and viscosity are calculated by employing the estimated E and bulk modulus. The bulk modulus, bulk viscosity, shear modulus, shear viscosity, and E of apples were found to be higher than those of bananas. The bulk modulus, bulk viscosity, E, and shear modulus for white bread were lower than those for pound cake, but the ν values were higher, whereas those of sponge cake were intermediate. After drying the baked products for 1 day, most of the parameters of the samples increased, but the value of ν for white bread decreased. The proposed free-falling device estimated the four viscoelastic coefficients, Poisson's ratio, and Young's modulus of the food sample in less than 1 s.
- MeSH
- Elastic Modulus MeSH
- Elasticity * MeSH
- Viscosity MeSH
- Publication type
- Journal Article MeSH
