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At least 451 records · Page 25Linked to original sources

PubMed2005

Assessment of the amplitude of oscillations associated with high-frequency components of physiological tremor: impact of loading and signal differentiation.

The goal of this study was accurate quantification of the amplitude of high-frequency components of physiological tremor (PT) in units of displacement, velocity, and acceleration. In addition, changes of amplitude with finger loading were compared within specific frequency bands. Index finger tremor was measured for 20 healthy subjects using a high-resolution laser, simultaneously with an accelerometer, under two conditions, unloaded and loaded (70 g). By use of an accurate filtering technique, oscillations within six predetermined frequency bands were isolated. Results showed that overall mean tremor amplitude under the unloaded condition was 0.0973 mm in displacement units, 4.525 mm s(-1) in velocity units, and 301.526 mm s(-2) in acceleration units. Although the mean amplitude of oscillations located within the 16.5-30 Hz band was 0.009 mm and represented only 10% of total tremor amplitude, amplitude of acceleration within the 16.5-30 Hz band was 191 mm s(-2) and represented 60% of total acceleration amplitude. Mean amplitude increased significantly with loading (displacement, t=-2.67, P=0.015; velocity, t=-4.33, P=0.000; acceleration, t=-3.48, P=0.002) but the magnitude of that change was different in each frequency band and its relative importance depended on the level of signal differentiation. Velocity was the only measure that retained sensitivity to changes in amplitude with loading in the low and high-frequency components of PT. In conclusion, this study provides, for the first time, accurate quantification of the amplitude of oscillation of high-frequency components of PT. In addition, it provides clear evidence that the velocity of tremor oscillation is more suitable for detection of the impact of finger loading because it enables detection of amplitude changes in both the low and high-frequency components of PT.

Adolescent↗

PubMed1993

A static dynamometer measuring multidirectional torques exerted simultaneously at the hip and knee.

The function of a static dynamometer measuring torques exerted simultaneously in the different anatomical planes of the hip (flexion-extension, abduction-adduction and internal-external rotation) and knee (flexion-extension) is described. Muscular torques were calculated in real time using a desktop computer from measurements of orthogonal forces applied at two locations and the lever arm values measured in each subject. The reliability of the force transducers was explored by examining their output, using calibrated weights, on three different days. The results were identical over this period of time, indicating that the transducers are highly reliable. A mechanical simulator of a lower limb was constructed to generate specific or combined torques of known values at the hip and knee. The torques measured by the dynamometer were found to be highly concordant with the known torques applied by the simulator, indicating that the torque measurements were valid. The usefulness of the dynamometer is demonstrated by evaluating the activity of the rectus femoris and biceps femoris muscles during static efforts exerted in various directions at the hip. In addition, the mechanical action of biarticular muscles at the hip was evaluated by quantification of hip torques during efforts exerted at the knee. From these results, it has been concluded that the present biarticular and multidirectional dynamometer is a valid, reliable and precise instrument that may prove to be useful in evaluating the muscular function of the lower limb.

Biophysics↗

PubMedDate not supplied

[Perthes' disease in scintigraphy - early diagnosis, course and therapeutic consequences].

A four year study on radionuclide imaging in Perthes's disease is reported. The results reveal that radionuclide imaging facilitates the earliest diagnosis possible as well as the differentiation against other affections of the hip. In eleven cases (diagnoses ascertained by X-ray follow up or biopsy) the duration of the course of Perthes' disease was shortened and the ultimate outcome was improved because of the early onset of therapy. Follow up examinations with radionuclide imaging and quantification of uptake reveal the extent of revascularisation of the necrosis of the femoral head and the epiphyseal plate at any point in time during the course of the disease. This leads to prognostic and therapeutic consequences, particularly in view of expected head at risk signs in the development of Perthes' disease.

Adolescent↗

PubMedDate not supplied

[Biomarkers for toxicity and metabolic abnormalities of the main severe poisonings. Clinical and toxicologic symptoms. Conservative determination].

The members of the joint group "Toxicology and Clinical Biology" of the French Society of Clinical Biology (SFBC), the French Society of Analytical Toxicology (SFTA), and the Society of Clinical Toxicology (STC), suggest guidelines to meet the requirements of clinical biologists who are not specialized in toxicology. Based on good laboratory practice they propose a number of guidelines. Three synthetic tables have been established. They are not only toxicity biomarkers and metabolic disorders associated with the main severe intoxications, but also clinical signs that are observed during these intoxications, finally biological sampling as a precautionary measure. The table also takes into account approximately fifty xenobiotics: main clinical signs emergency, identification or quantification of the suspected product, useful biological markers, therapeutic, quantitations necessary to take into consideration patient care, and poison antidotes, are described. Recommendations regarding medical and forensic techniques are also proposed by the group. It is also necessary to collect and store biological samples when the individual patients are in charge. These samples will be analyzed or not depending on the individual case history.

Biomarkers↗

PubMed2005

Quantification of muscle fiber strain during in vivo repetitive stretch-shortening cycles.

Muscles subjected to lengthening contractions exhibit evidence of subcellular disruption, arguably a result of fiber strain magnitude. Due to the difficulty associated with measuring fiber strains during lengthening contractions, fiber length estimates have been used to formulate relationships between the magnitude of injury and mechanical measures such as fiber strain. In such protocols, the series compliance is typically minimized by removing the distal tendon and/or preactivating the muscle. These in vitro and in situ experiments do not represent physiological contractions well where fiber strain and muscle strain may be disassociated; thus the mechanisms of in vivo muscle injury remain elusive. The purpose of this paper was to quantify fiber strains during lengthening contractions in vivo and assess the potential role of fiber strain in muscle injury following repetitive stretch-shortening cycles. Using intact New Zealand White rabbit dorsiflexors, fiber strain and joint torque were measured during 50 stretch-shortening cycles. We were able to show that fiber length changes are disassociated from muscle tendon unit length changes and that complex fiber dynamics during these cycles prevent easy estimates of fiber strains. In addition, fiber strains vary, depending on how they are defined, and vary from repetition to repetition, thereby further complicating the potential relationship between muscle injury and fiber strain. We conclude from this study that, during in vivo stretch-shortening cycles, the relationship between fiber strain and muscle injury is complex. This is due, in part, to temporal effects of repeated loading on fiber strain magnitude that may be explained by an increasing compliance of the contractile element as exercise progresses.

Adaptation, Physiological↗

PubMed2006

Speed modulation in hylobatid bipedalism: a kinematic analysis.

Gibbons are highly arboreal apes, and it is expected that their bipedal locomotion will show some particularities related to the arboreal environment. Previous research has shown that, during hylobatid bipedalism, unsupported phases are rare and stride frequencies are relatively low. This study confirms previous findings, and we suggest that low stride frequencies and the absence of unsupported phases are ways to reduce disadvantageous branch oscillations during arboreal travel. Despite these restrictions, gibbons are able to locomote at a wide range of speeds, implying that they likely exploit other mechanisms to modulate their locomotor speed. To investigate this possibility, we collected video images of a large number of spontaneous bipedal bouts of four untrained white-handed gibbons by using an instrumented walkway with four synchronized cameras. These video images were digitized to obtain a quantification of the 3D kinematics of hylobatid bipedalism. We defined a large number of spatiotemporal and kinematic gait variables, and the relationship between these gait variables and (dimensionless) speed was statistically tested. It was found that gibbons mainly increase stride length to increase their locomotor speed; the main speed-modulating mechanisms are hip and ankle excursion and coupled knee and ankle extension at toe-off. Although aerial phases are rare, gibbons generally adopt a bipedal bouncing gait at most speeds and a clear-cut gait transition, as seen in human locomotion, is absent. Comparison with human and bonobo bipedalism showed that the variability of the 3D joint angles of the hind limb are comparable during human and gibbon bipedalism, and much lower than during bonobo bipedalism. The low variability found in gibbons might be related to constraints imposed by the arboreal environment. These arboreal constraints clearly affect the bipedal gait characteristics of gibbons, but do not constrain the ability to adopt a bipedal bouncing gait during terrestrial locomotion.

Animals↗

PubMed1996

Determination of angiogenesis adds information to estrogen receptor status in predicting the efficacy of adjuvant tamoxifen in node-positive breast cancer patients.

There is experimental and clinical evidence that angiogenesis is involved in breast cancer progression and metastasis. To investigate whether the determination of angiogenesis adds prognostic information to the estrogen receptor (ER) status, we studied a series of 178 node-positive breast cancer patients, with a median follow-up time exceeding 5 years, treated with adjuvant tamoxifen (TAM). We assessed angiogenesis by the quantification of the intratumoral microvessel density and the determination of the Chalkley score using light microscopy. Microvessels were immunostained using the anti-CD31 antibody. The other features studied were ER status and the conventional clinicopathological prognostic indicators. Results were pooled from two collaborating Centers using Chalkley counts to convert intratumoral microvessel density to a common quantification system. We found that Chalkley score was not associated with any other feature studied. In univariate analysis, Chalkley score was significantly predictive of both relapse-free survival (RFS) and overall survival (OS; P < 0. 00001 and P = 0.00004, respectively). Likewise, ER status, the number of metastatic axillary nodes, histological grading, and tumor size were significantly predictive for RFS and OS. Cox multivariate analysis showed that Chalkley score was the strongest significant independent predictor of outcome. For RFS, ER status, the number of metastatic nodes, and histological grading also retained significance. For OS, the number of metastatic nodes, tumor size, and histological grading were independent prognostic factors. The joint assessment of the above variables had a satisfactory prognostic capability, as found using the Harrel statistics (c = 0. 77). These results suggest the validity of using Chalkley counts to assess and compare angiogenesis for prognostic purposes between different Centers. We found that angiogenesis adds significant prognostic information to ER status in predicting the outcome of breast cancer patients treated with adjuvant TAM. In fact, irrespective of the ER status, the patients with highly angiogenic tumors had a poor outcome, even if treated with TAM. For these patients, the inhibition of angiogenesis with specific angioinhibitory drugs may be a promising new therapeutic strategy.

Breast Neoplasms↗

PubMed2001

Optimization and validation of a rapid high-resolution T1-w 3D FLASH water excitation MRI sequence for the quantitative assessment of articular cartilage volume and thickness.

In view of follow up, survey and development of therapeutic strategies for osteoarthritis where cartilage deterioration plays an important role, a non invasive, reliable and quantitative assessment of the articular cartilage is desirable. The currently available high resolution T(1)-weighted (T1-w) 3D FLASH pulse sequences with frequency selective fat suppression are very time consuming. We have 1) optimized a high resolution T1-w 3D FLASH water excitation (WE) sequence for short acquisition time and cartilage visualization, and 2) validated this sequence for cartilage volume and thickness quantification. The spectral fat presaturation was replaced by selective water excitation. The flip angle of the WE sequence was optimized for the contrast to noise (C/N(cart)) ratio of cartilage. Sagittal datasets (voxel size: 0.31 x 0.31 x 2 mm(3)) of the knees of nine healthy volunteers were acquired both, with the 3D FLASH WE (17.2/6.6/30 degrees ) sequence (WE) and a previously validated 3D FLASH fat saturated (42/11/30 degrees ) sequence (FS). For validation of the WE sequence, cartilage volume, mean and maximal cartilage thickness of the two sequences were compared. Reproducibility was assessed by calculating the coefficient of variation (COV %) of 4 consecutive WE data sets in the volunteers. The acquisition time was reduced from 16'30" (FS) down to 7'14" for the WE sequence. Image contrast and visualization of the cartilage was very similar, but delineation of the basal layer of the cartilage was slightly improved with the WE sequence. A flip angle of 30 degrees provided the best C/N(cart) ratios (WE). Reproducibility (COV) was between 1.9 and 5.9%. Cartilage volume and thickness agreed within 4% between FS and WE sequence. The WE sequence allows for rapid, valid and reproducible quantification of articular cartilage volume and thickness, prerequisites for follow-up examinations. The reduced acquisition time (50% of FS) enables routine clinical application and thus may contribute to a broader assessment of osteoarthritis.

Adult↗

PubMed1985

The variable functional disability of the anterior cruciate ligament-deficient knee.

The goal of the authors has been to define the syndrome of the anterior cruciate ligament-deficient knee. These concepts have been applied to pertinent articles in order to explain the discrepancies and contrasting opinions in the literature. The authors have suggested guidelines for treatment based on the quantification of risk factors and a method for the prediction of the functional disability level of patients. Functional disability is activity level-related and is also related to the type of sport and the intensity level of play. Functional disability is symptomatically expressed by pain, swelling, and giving way, which must be correlated with a specific activity level.

Biomechanical Phenomena↗

PubMed1996

Quantification of aggrecan and link-protein mRNA in human articular cartilage of different ages by competitive reverse transcriptase-PCR.

A competitive reverse transcriptase-PCR (RT-PCR) assay has been developed for the quantification of particular mRNA species in human articular cartilage. Competitor RNA species were synthesized that differed from the amplified target sequence only by the central insertion of an EcoRI restriction site. By using known amounts of synthetic target and competitor RNA, it was shown that competitor RNA molecules designed in this way are reverse-transcribed and amplified with equal efficiency to the target of interest. Furthermore quantification could be performed during the plateau phase of the PCR, which was necessary when using ethidium bromide fluorescence as a detection system. The inhibition of aggrecan and link-protein mRNA expression by interleukin 1 or tumour necrosis factor in monolayers of human articular chondrocytes quantified by this competitive RT-PCR method compared favourably with Northern hybridization studies. The main advantage of this technique is that it can be used to quantify levels of mRNA with RNA extracted directly from 100 mg wet weight of human articular cartilage. Age-related changes in aggrecan and link-protein mRNA were therefore quantified in human articular cartilage directly after dissection from the joint. The concentration of link-protein mRNA was higher in immature cartilage than in mature cartilage when expressed relative to the amount of glyceraldehyde-3-phosphate dehydrogenase mRNA, but no age-related changes were observed in aggrecan mRNA expression. The ratio of aggrecan to link-protein mRNA was higher in mature cartilage than in immature tissue. These age-related differences in the molecular stoichiometry of aggrecan and link-protein mRNA might have implications with respect to the regulation of the formation and the stability of the proteoglycan aggregates in cartilage.

Aggrecans↗

PubMed2000

Adaptive, template moderated, spatially varying statistical classification.

A novel image segmentation algorithm was developed to allow the automatic segmentation of both normal and abnormal anatomy from medical images. The new algorithm is a form of spatially varying statistical classification, in which an explicit anatomical template is used to moderate the segmentation obtained by statistical classification. The algorithm consists of an iterated sequence of spatially varying classification and nonlinear registration, which forms an adaptive, template moderated (ATM), spatially varying statistical classification (SVC). Classification methods and nonlinear registration methods are often complementary, both in the tasks where they succeed and in the tasks where they fail. By integrating these approaches the new algorithm avoids many of the disadvantages of each approach alone while exploiting the combination. The ATM SVC algorithm was applied to several segmentation problems, involving different image contrast mechanisms and different locations in the body. Segmentation and validation experiments were carried out for problems involving the quantification of normal anatomy (MRI of brains of neonates) and pathology of various types (MRI of patients with multiple sclerosis, MRI of patients with brain tumors, MRI of patients with damaged knee cartilage). In each case, the ATM SVC algorithm provided a better segmentation than statistical classification or elastic matching alone.

Algorithms↗

PubMed2002

[Structural quantification in osteoarthritis of the knee using power spectral analysis].

An exact diagnosis of osteoarthritis is very important to prevent deterioration of ADL (activities of daily living) of the elderly. However, it is very difficult to diagnose the stage of osteoarthritis, and only a few indices for structural quantification of osteoarthritis have been reported. The purpose of this research is to investigate a new index for the bone structure in osteoarthritis. We examined right knees of 41 women aged from 34 to 85 years. Directivity index (DI) is a new index of bone structure calculated by directivity of the power spectrum from radiographs of tibial bone using fast Fourier transform (FFT). DI was obtained by subtracting the integral power value at 0 and 90 degree directions on the x-y plane of the two-dimensional power spectrum of tibial bone from the integral power value at a direction of 45 degrees. A significant relationship between the state of the knee joint by X-ray inspection and DI was indicated by evaluation of the correlation coefficient. However, no significant relationship was found between the state of the knee joint by X-ray inspection and the first moment of the Fourier power spectrum or the fractal dimension. There is a possibility that DI can estimate slight deformation of bone structure in osteoarthritis. In the future, we will apply DI to the prevention of osteoarthritis and a deterioration of ADL in the elderly.

Absorptiometry, Photon↗

PubMed1998

Separation and quantification by ion-association capillary zone electrophoresis of unsaturated disaccharide units of chondroitin sulfates and oligosaccharides derived from hyaluronan.

An analytical method has been developed for assay of unsaturated disaccharides of chondroitin sulfates and of oligosaccharides (tetra- and hexasaccharides) of hyaluronan, using ion-association capillary zone electrophoresis. Samples were applied at the anode (the usual polarity), using a borate buffer modified by an ion-pairing reagent, tetrabutylammonium (TBA) phosphate, and the effect of the concentration of the ion-pairing reagent on various electrophoretic parameters (electroosmotic flow, electrophoretic mobility of products, capacity factors) was observed. Increasing concentrations of the reagent led to a decrease of zeta potential, probably due to specific adsorption of the quaternary ammonium ion onto the capillary wall. The authors propose a mechanism of separation, in which anionic borate complexes are formed and interact with TBA ion inside the capillary tube. The capillary electrophoretic system described is potentially a powerful method for specific measurement of the concentrations in joint tissues of chondroitin 4-sulfate, chondroitin 6-sulfate, and hyaluronan, whose relative abundances may vary in various diseases or after local treatments with, for example, antiinflammatory drugs, chondroprotective agents, or orthopedic implants.

Chondroitin Sulfates↗

PubMed2003

Comparative quantification of health risks conceptual framework and methodological issues.

Reliable and comparable analysis of risks to health is key for preventing disease and injury. Causal attribution of morbidity and mortality to risk factors has traditionally been conducted in the context of methodological traditions of individual risk factors, often in a limited number of settings, restricting comparability.In this paper, we discuss the conceptual and methodological issues for quantifying the population health effects of individual or groups of risk factors in various levels of causality using knowledge from different scientific disciplines. The issues include: comparing the burden of disease due to the observed exposure distribution in a population with the burden from a hypothetical distribution or series of distributions, rather than a single reference level such as non-exposed; considering the multiple stages in the causal network of interactions among risk factor(s) and disease outcome to allow making inferences about some combinations of risk factors for which epidemiological studies have not been conducted, including the joint effects of multiple risk factors; calculating the health loss due to risk factor(s) as a time-indexed "stream" of disease burden due to a time-indexed "stream" of exposure, including consideration of discounting; and the sources of uncertainty.

Journal Article↗

PubMed2006

Bilirubin kinetic modeling for quantification of extracorporeal liver support.

BACKGROUND/AIM: To provide a measure of treatment dose for extracorporeal liver support (ELS). METHODS: The kinetics of conjugated bilirubin were described by a two-compartment model (Vc, Vp) with central elimination (K) and constant generation rate (G). The transfer of solute between compartments was modeled by intercompartmental clearance (Kpc). The central compartment (Vc) was assumed as a constant fraction of total volume (Vc = 0.3*Vt). RESULTS: Eight patients were studied during 35 treatments lasting 6 h each. The average K, Vt, Kpc, G, and mass of conjugated bilirubin removed were 18.6 +/- 3.9 ml/min, 9.1 +/- 3.8 liters, 103 +/- 108 ml/min, 0.33 +/- 0.15 mg/min, and 641 +/- 275 mg, respectively. The reduction ratio (48 +/- 10%) measured as the change in post- to pre-treatment concentrations underestimated the modeled fraction of bilirubin mass removed (54 +/- 13%) essentially because of significant conjugated bilirubin appearance during treatments. CONCLUSIONS: Kinetic analysis provides an improved measure of treatment dose as generation, distribution, and elimination of conjugated bilirubin are jointly considered.

Aged↗

PubMed2002

Characterization of the integrity of three-dimensional trabecular bone microstructure by connectivity and shape analysis using high-resolution magnetic resonance imaging in vivo.

Bone mineral density and bone structure are the main determinants of bone strength in osteoporosis. In this study we used high-resolution magnetic resonance imaging to visualize the bone microstructure in the finger phalanges in vivo and to assess the topological three-dimensional connectivity of the trabecular network and the shape of the trabeculae as measures of bone quality. We visualized the phalanges of young and elderly healthy volunteers in vivo with a spatial resolution of 152 microm x 152 microm x 280 microm. Image processing software to quantify three measures of connectedness was developed and tested: connectivity, global connectivity density, and local connectivity density. Global three-dimensional connectivity ranged from 904 to 1,607 connections. Global connectivity density ranged from 2.9 to 4.7 connections per mm with large intersubject differences. We found a decrease of local connectivity density with growing distance from the joint ranging from 5.1 to 0.2 connections per mm. These preliminary results represent a quantitative description of the well-known rarefication of the trabecular network when moving from epiphysis to the diaphysis. Three-dimensional visualization showed a dense network consisting mostly of rod-like trabeculae at the epiphysis changing to a less dense network of a few plate-like structures near the medullary canal. An algorithm for the quantitative classification of trabecular architecture with regard to plate or rod-like shape was tested for feasibility. We conclude that in vivo assessment of three-dimensional properties of the trabecular network is possible in human phalanges. Determination of connectivity and shape will allow quantification of structural aspects of osteoporotic changes and may improve assessment of fracture risk.

Adult↗

PubMed1999

Feature extraction and quantification of the variability of dynamic performance profiles due to the different sagittal lift characteristics.

Investigation of manual material handling (MMH) tasks, such as lifting, requires the quantification of the various kinematic and kinetic parameters of performance for assessment of the functional capacity and/or task demand profiles. Traditional statistical descriptive analyses usually involve computing the summary statistics (maximum, minimum, mean, and/or range) of the resulting performance parameters over the cycle duration (i.e., lifting/lowering cycle). Consequently, the significant information content of the time-varying signals is diminished, limiting the sensitivity of subsequent hypothesis testing procedures. The present study developed a methodology for representing and quantifying performance data variability of the kinematic and kinetic motion profiles due to the different lift characteristics (load, mode, and speed) during MMH tasks while capturing the temporal characteristics. Using a database of motion profiles from a manual lifting experiment, the Karhunen-Loeve Expansion (KLE) feature extraction technique was shown to be quite effective for representing the various motion profiles. The number of basis vectors (eigenvectors) and corresponding coefficients needed for accurate representation were substantially smaller than the original data set, resulting in data compression. Moreover, the effects of lift characteristics were investigated using analysis of variance techniques that recognize the vectorial constitution of the waveforms. The application of these techniques will enable the quantification of highly phasic profiles and enhance the ability to document the effect of intervening measures such as educational or physical training/exercise on the kinematic and kinetic patterns of performance. Additionally, the differential influence of lift characteristics on the variability of performance during different phases of lifting and lowering provides added resolution in the analysis of MMH tasks.

Adult↗

PubMedDate not supplied

Reflex torque response to movement of the spastic elbow: theoretical analyses and implications for quantification of spasticity.

A parametric model of the human reflex torque response to a large-amplitude, constant angular velocity elbow extension was developed in order to help quantify spasticity in hemiparetic stroke patients, and to better understand its pathophysiology. The model accounted for the routinely observed leveling of torque (i.e., a plateau) at a mean angular increment of 51 degrees +/- 10 degrees s.d. (n = 98) after the initial rise. This torque "plateau" was observed in all eight subjects, and in 98 of 125 trials across 25 experimental sessions. The occurrence of this plateau cannot be explained by decreases in elbow flexor moment arms during elbow extension. Rather, the plateau is attributable to a consistent leveling in muscle activation as confirmed both qualitatively from recordings of rectified, smoothed electromyograph (EMG) activity, and quantitatively using an EMG coefficient model. A parametric model was developed in which the pattern of muscle activation in the stretch reflex response of elbow flexors was described as a cumulative normal distribution with respect to joint angle. Two activation functions, one related to biceps and the other to brachioradialis/brachialis, were incorporated into the model in order to account for observations of a bimodal angular stiffness profile. The resulting model yielded biologically plausible parameters of the stretch reflex response which may prove useful for quantifying spasticity. In addition, the model parameters had clear pathophysiological analogs, which may help us understand the nature of the stretch reflex response in spastic muscles.

Adult↗