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Results for “Repeatability and Reproducibility”

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PubMed1993

In vivo evaluation of visco-elasticity in a biological tube. Part 1. Stress relaxation in the female urethra studied by cross-sectional area and pressure measurements.

The urethral response to a sudden forced dilatation was studied by a mathematical analysis of the pressure response in ten healthy women. A total of 60 dilatations, using various sizes and velocities of deformation, were performed in the high-pressure zone. The decay in pressure during relaxation proved to follow an exponential equation of the following form: Y = Z + C alpha e-t/tau alpha + C beta e-t/tau beta, where Z is the equilibrium pressure, C alpha and C beta are pressure decay, and T alpha and T beta are time constants. The time constants were unaffected by the circumstances of dilatation, whereas all the other parameters were correlated to size or velocity of dilatation, or both. The time constants showed a fairly high reproducibility when repeated after one weak. The method is presumed to characterise the tissue composition of the periluminal tissue layers and may prove useful in the evaluation of the normal urethral sphincter function. Furthermore, it may prove of value in the elucidation of the pathophysiology of stress urinary incontinence.

Adult↗

PubMed1996

High-dose pamidronate in the management of resistant Paget's disease.

Current recommendations for the total dose of intravenous pamidronate to be used in the treatment of Paget's disease range up to 400 mg per course, although up to 980 mg has been suggested for resistant cases. However, in a proportion of Paget's disease patients remission is difficult to induce and maintain. In five patients with resistant symptomatic Paget's disease, in whom a variety of antipagetic therapies had failed to induce remission, we have examined the effects of high dose pamidronate (1.44-2.52 g intravenously over 12-42 weeks). All five subjects had a marked symptomatic improvement, and disease activity was suppressed to a greater extent than had been achieved previously, but in only one did alkaline phosphatase activity suppress into the normal range. A plateau in the biochemical response was evident, with successive pamidronate doses of 120 mg producing smaller decrements in alkaline phosphatase. The plateau was reproducible on repeated courses. Bone biopsies in two patients showed continued pagetic activity with an increased mineralization rate and no osteomalacia. Worthwhile clinical and biochemical improvements can be obtained in patients with resistant Paget's disease by the use of high-dose pamidronate. Though this approach does not seem to cause defective mineralization, it may be difficult to suppress disease activity completely.

Aged↗

PubMed1997

Image processing assessment of femoral osteopenia.

Visual assessment of femoral osteopenia (the radiographic presentation of osteoporosis) is unreliable. Many of the short-comings of observer grading can be overcome by digital image analysis. Our group has developed algorithms to make automatic assessment of osteopenia from clinical radiographs. Texture Analysis Models (TA) commonly used in image analysis were investigated as measures of osteopenia. Unlike densitometric methods, TA characterizes properties of the structure of the image (ie, trabecular patterns). A group of women were analyzed whose subjects ranged from those at risk of osteoporosis (n = 24) to normal (n = 40). Using an IBM PC, frame-grabber, camera, and light-box, we appraised five statistical TA algorithms for assessment of the femoral neck in standard pelvic radiographs: (1) Fractal Signature (FS) describes the image's fractal nature. (2) Auto-Correlation of unaltered and Sobel Edge Transformed images (ACSE) measures image spatial self-similarity. (3) Co-occurrence Matrices (CM) gives the joint probability of greylevels with distance/direction and describes statistical relationships of image variation. (4) Textural Spectrum (TS) neighborhood pixel relationships measure regional directional and pixel-inversion properties. (5) Eular Numbers (EN) describe texture by properties (such as connectivity) of binary images. Good reproducibility from repeated analysis of radiographs was shown using both paired t-tests and Altman-Bland's methods. We have shown a correlation between femoral neck bone mineral density (BMD-the "gold standard" of osteoporosis assessment) and textural measures for all five algorithms. Significant measures of osteopenia were: ACSE (r = 0.6, P < .001), CM (r = -0.69, P < .001), FS (r = 0.35, P < .01), TS (r = 0.52, P < .001) and EN (r = -0.39, P < .01). Relationships were also found between textural characteristics and age/weight. TA techniques characterize the radiographic changes of bone in osteoporosis. Technology based on these ideas may have a place alongside BMD measurements in the assessment of this condition.

Absorptiometry, Photon↗

PubMed2002

Evaluation of flow limitation in elderly patients unable to perform a forced expiratory maneuver.

BACKGROUND AND AIMS: The assessment of pulmonary function in elderly persons is not often easy in the clinical practice because of poor patient collaboration. A new technique, negative expiratory pressure (NEP), should provide a simple, rapid and non-invasive method for detecting flow limitation without collaboration of the patients. Our aim was to investigate whether it is possible to detect an expiratory flow limitation during resting breathing with NEP in elderly patients unable to perform a forced expiratory maneuver. METHODS: In 15 elderly inpatients (4 males and 11 females, mean age 83+/-4.7 SD years) unable to realize the classical forced expiratory maneuver because of poor coordination or cognitive disturbance, we applied the NEP technique during spontaneous breathing. RESULTS: NEP application during resting breathing was easily and rapidly performed in all cases without side effects. During NEP (-5cmH2O and NEP -10cmH2O), 6 and 5/15 patients were flow limited; mean flow limitation was 60+/-9% and 70+/-15% respectively. These results were reproducible with repeated NEP tests. CONCLUSIONS: Application of negative pressure at the mouth during tidal expiration provides a simple method for detecting expiratory flow limitation during spontaneous breathing in elderly patients with poor collaboration.

Aged↗

PubMed2003

Interocclusal clearance during speech and in mandibular rest position. A comparison between different measuring methods.

BACKGROUND AND AIM: The interocclusal clearance during speech and in mandibular rest position shows an interindividual variation and influences the stability of prosthodontic reconstruction or orthodontic therapy, especially in patients with deep bite or cover-bite. Exact determination of the vertical dimension, not always a simple matter in practice, is controversially discussed with respect to the methodology. The aim of the present investigation was to compare three methods for determining interocclusal clearance during speech and in mandibular rest position. PATIENTS AND METHODS: Extraoral manual registration and electronic registration were used to evaluate 33 malocclusion-free patients. The measurements were repeated to determine the reproducibility. For disturbance-free objectification, the freeway space, i.e. the interocclusal clearance in mandibular rest position, was also recorded cephalometrically. RESULTS: None of these registration methods displayed clear-cut superiority to the others. Electronic registration is very time-consuming and should be confined to special cases. Sources of error in manual registration are increased movement of the measuring points marked on the skin during mandibular movement and the free handling of dividers. CONCLUSIONS: This method can be used only in connection with mm. consonants. Speaking the word "Ohio" yielded excessively high values in all methods, so that this word has to be rejected as a speech sample. Cephalometric registration produced values with slight interindividual variations. In practice, however, this method is unsuitable for use with orthodontic patients because of the additional radiation exposure involved in producing an additional lateral cephalogram. For good reproducibility, practicing or frequent repeating of the measuring method prior to definitive measuring is essential.

Adult↗

PubMed2001

Continuous on-line measurements of respiratory system, lung and chest wall mechanics during mechanic ventilation.

OBJECTIVE: We present a concept of on-line, manoeuvre-free monitoring of respiratory mechanics during dynamic conditions, displaying calculated alveolar pressure/volume curves continuously and separating lung and chest wall mechanics. DESIGN: Prospective observational study. SETTING: Intensive care unit of a university hospital. PATIENTS: Ten ventilator-treated patients with acute lung injury. INTERVENTIONS: Different positive end-expiratory pressure (PEEP) and tidal volumes, low flow inflation. MEASUREMENTS AND RESULTS: Previously validated methods were used to present a single-value dynostatic compliance for the whole breath and a dynostatic volume-dependent initial, middle and final compliance within the breath. A high individual variation of respiratory mechanics was observed. Reproducibility of repeated measurements was satisfactory (coefficients of variations for dynostatic volume-dependent compliance: < or =9.2% for total respiratory system, < or =18% for lung). Volume-dependent compliance showed a statistically significant pattern of successively decreasing compliance from the initial segment through the middle and final parts within each breath at all respiratory settings. This pattern became more prominent with increasing PEEP and tidal volume, indicating a greater distension of alveoli. No lower inflection point (LIP) was seen in patients with respiratory rate 20/min and PEEP at 4 cmH2O. A trial with low flow inflation in four of the patients showed formation of a LIP in three of them and an upper inflection in one. CONCLUSIONS: The monitoring concept revealed a constant pattern of successively decreasing compliance within each breath, which became more prominent with increasing PEEP and tidal volume. The monitoring concept offers a simple and reliable method of monitoring respiratory mechanics during ongoing ventilator treatment.

Adult↗

PubMed2006

Quality and performance measures in bone densitometry: part 1: errors and diagnosis.

INTRODUCTION: Bone densitometry is one of the main pillars in the assessment of osteoporosis. The most important modalities are dual x-ray absorptiometry (DXA), quantitative computed tomography (QCT), and quantitative ultrasound (QUS). MATERIALS AND METHODS: For each modality a variety of technical solutions and numerous commercial devices are available and widely used for patient measurements. While the field of bone densitometry may be considered mature, new modalities and devices are being introduced. Consequently, there is a constant need to assess and compare the quality of bone densitometry approaches and devices in a rigorous way. RESULTS: The International Commission on Radiation Units has commissioned a report on bone densitometry to address some of these issues, in particular to provide clear definitions of quantities and units used and to describe parameters and methods that can be used to compare and standardize densitometric equipment and measurements. One of the core chapters of the report summarizes quality and performance measures in bone densitometry. It is divided into four sections: physical performance measures, diagnosis, fracture risk, and monitoring. Here we publish part 1 of this chapter containing the first two sections: physical performance measures and issues in diagnosing osteoporosis. CONCLUSION: Following the international standard (ISO 5725-1), trueness, bias, repeatability, and reproducibility are defined along with terms common to osteoporosis research, such as accuracy and precision. Building on the conceptual definition of osteoporosis, diagnostic criteria are defined and discussed including criteria for reference data. Based on this, clinical performance measures commonly used for the diagnosis of osteoporosis are reviewed and discussed.

Absorptiometry, Photon↗

PubMed2002

Interlaboratory assessment of measurement precision and bias in the coulometric Karl Fischer determination of water.

The precision and bias of the coulometric Karl Fischer ASTM method D1533-00 have been assessed in a collaborative ASTM round robin program for a group of 34 laboratories. The test materials used in this study included water saturated 1-octanol (WSO), water saturated 1-butanol (WSB), and a series of new and used transformer oil samples. Fundamental systematic biases have been demonstrated in the accuracy of the measurement of water in the WSO, WSB, and transformer oil samples. The systematic bias in the measurement of the WSO and WSB standards indicates that for some laboratories either the instruments were not accurate or the quantity of the standard was not measured accurately. A second type of systematic bias consisted of measurement errors associated with the selection of the Karl Fischer solvent that was used with each instrument, and this was superimposed upon the error in the measurement of the water in the standards. Using the statistical calculation method ASTM D 6300 the repeatability and reproducibility for water in transformer oil were found to be 7 mg/kg and 14 mg/kg respectively. The method detection limit of water was 8 mg/kg oil. The method bias was estimated based on the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 2890, WSO, since no suitable reference material for water in transformer oil was available for this study.

Journal Article↗

PubMed2004

High-throughput analysis of phthalate esters in human serum by direct immersion SPME followed by isotope dilution-fast GC/MS.

Solid-phase microextraction (SPME) coupled to gas chromatography/mass spectrometry (GC/MS) was applied to the determination of phthalate esters in human serum. The present method decreased the sample preparation time by a factor of 50 by using direct immersion SPME with an 85-microm polyacrylate fiber to extract phthalate esters from the matrix. The use of fast GC/MS further improves total analysis time when compared to other techniques. Isotope dilution was successfully applied to improve the precision, reproducibility, and repeatability of the SPME method. The linear dynamic range spans several orders of magnitude from low ppb to ppm levels, and the LOD for the method is 15 pg microL(-1) on average with RSDs less than 4% for the six phthalate esters included in this study.

Calibration↗

PubMed2005

Organotin analysis by gas chromatography-pulsed flame-photometric detection (GC-PFPD).

Monobutyltin (MBuT), dibutyltin (DBuT), and tributyltin (TBuT) mixtures have been separated and quantified by gas chromatography with pulsed flame-photometric detection (GC-PFPD). The compounds were first derivatized with NaBEt4, then extracted with hexane and injected into the GC in splitless mode. Optimum GC and detector conditions were established. For GC, various injector temperatures and oven temperature programs were tested. For the PFPD detector, gate settings (gate delay and gate width) and detector temperature were optimized. A very good linearity was obtained up to 100-150 ppb for all organotin compounds. The detection limits obtained were: MBuT (0.7 ppb), DBuT (0.8 ppb), and TBuT (0.6 ppb). RSD for repeatability and reproducibility were well below 20% when the instrument was in routine operation. A biological sample (CRM 477) was also analyzed for organotins. Extraction from the biological matrix was performed with TMAH. Besides the increased risk of contamination, the derivatization step seemed to be critical. pH and amount of derivatizing agent were tested. When using an internal standard (TPrT) between 90% and 110% of the certified amounts of organotin were recovered.

Animals↗

PubMed2005

Residual aqueous ozone determination by gas diffusion reverse flow injection analysis.

A novel system based on reverse flow injection analysis with a gaseous diffusion step (GD-r-FIA) has been developed for the analysis of ozone. It includes an automatic microburet injection system. The ozone diffuses through a microporous membrane of polyvinylidene difluoride (PVDF) from the donor stream to the acceptor stream containing nitrite ions. The nitrite concentration in the acceptor solution decreases due to the ozone reduction reaction. In this way, a simple indirect measurement of the ozone concentration can be performed using the Griess-Ilosvay reaction for the nitrite ion. This correlates with the decrease in absorbance of the azoic dye formed with the ozone concentration in the donor stream. The system has been optimised by investigating the effect of the nitrite concentration in the acceptor stream on the diffusion flow. The optimum nitrite concentration was set at 0.250 ppm with a flow rate of 1.5 ml/min. The efficiency of the ozone diffusion through the membrane was only 4.4%. This affects the average sensitivity, which is low (0.0092+/-0.0012 AU/ppm), although the detection limit is similar to that obtained with other reported methods (0.03 ppm). The main advantage of the system reported here is that it has a linear range that is an order of magnitude broader than those observed for other GD-FIA systems. This is especially useful for continuous monitoring systems, since the residual ozone concentration is normally between 0.05 and 5.0 ppm. Additionally, using the reverse flow injection analysis (FIA) technique minimises chemical consumption and residue generation. Finally, the stability of the ozone solution and the repeatability and reproducibility of the method have been studied.

Journal Article↗

PubMed2005

Electroanalytical method for determination of the pesticide dichlorvos using gold-disk microelectrodes.

This paper reports the use of laboratory-prepared gold microelectrodes and square-wave voltammetry for analytical determination of low concentrations of the pesticide dichlorvos in pure and natural water samples. After optimization of the experimental and voltammetric conditions, the best voltammetric responses-current intensity and voltammetric profile-were obtained in 0.1 mol L(-1) NaClO4 with f=100 s(-1), a=50 mV, and DeltaE(s)=2 mV. The observed detection and quantification limits in pure water were 7.8 and 26.0 microg L(-1), respectively. The reproducibility and repeatability of the method were also determined; the results were 1.4% (n=5) and 1.2% (n=10), respectively. Possible interfering effects were evaluated in natural water samples collected at different points with different levels of contamination from agricultural, domestic, or industrial waste from an urban stream. Results showed that the detection and quantification limits increased as a function of the quantity of organic matter present in the samples. Nonetheless, the values observed for these method characteristics were below the maximum value allowed by the Brazilian code for organophosphorus pesticides in water samples. Recovery curves constructed using the standard addition method were shown to be satisfactory compared with those obtained from high-performance liquid chromatography, confirming the suitability of the method for analysis of natural water samples. Finally, when the method was used to determine dichlorvos in spiked cows' milk samples, satisfactory recovery and relative standard deviations were obtained.

Animals↗

PubMed2006

Validated multi-component CZE-UV procedure for the quantification of human hemorphin LVV-H7 in plasma stability studies.

The human hemorphin LVV-H7 is an endogenous cleavage product of the hemoglobin beta, gamma, epsilon or delta chain exhibiting potential pharmaceutical relevance for blood pressure regulation, the treatment of Alzheimer's disease or learning deficiencies. Here we present the development of a multi-component capillary zone electrophoretic method (CZE-UV), allowing the simultaneous quantification of LVV-H7 and four N-terminal degradation products generated in EDTA plasma. Hemorphins in the supernatant of precipitated plasma samples are quantified by external calibration. Validation of the procedure oriented towards international pharmaceutical guidelines and demonstrated excellent linearity (r2 > or = 0.999), good precision (repeatability and reproducibility below 11%), accuracy (-8.4%-4%), ruggedness and an appropriate lower limit of quantification (LLOQ 1.0 microg mL(-1)). This procedure was applied to stability studies of LVV-H7 in human EDTA plasma attended by profiling metabolites using qualitative MALDI-TOF MS analysis. We detected the activity of a soluble plasma form of aminopeptidase M causing successive N-terminal truncation. This is the first time that LVV-H7 degradation as well as its metabolite production have systematically been monitored by a quantitative CZE-UV procedure, underlining the growing importance of such techniques in peptide analysis. In addition, our results give useful hints for future drug development of LVV-H7.

Alzheimer Disease↗

PubMed2006

Precision of Raman depolarization and optical attenuation measurements of sound tooth enamel.

The demineralization of enamel that is associated with early caries formation affects the optical properties of the enamel. Polarized Raman spectroscopy and optical coherence tomography have been used to detect these changes and potentially offer a means to detect and monitor early caries development. The total optical attenuation coefficient as measured by optical coherence tomography and the polarization anisotropy of the Raman peak arising from the symmetric nu(1) vibration of PO4(3-) at approximately 959 cm(-1) have been demonstrated as being sensitive markers of early caries. This ex vivo study on extracted human teeth demonstrates that these measurements can be made with reasonable precision with concomitantly good repeatability and reproducibility in sound enamel. Such reliability is crucial for these techniques to have a practical clinical value.

Bicuspid↗

PubMed2001

Determination of Mn, Fe, and Cu in chemically-treated wood pulps by the XRF addition method.

A rapid X-ray fluorescence addition method has been developed for quantification of the technically most important metals in wood pulp matrix (Mn, Fe, and Cu). Pretreatment consisted of just two steps: first, acid was added to the sample to achieve homogeneous distribution of the metals; the pulp was then pressed lightly on to Mylar film. Total analysis time was less than 10 min. The concentration range investigated was up to 15 mg kg(-1) for Mn and up to 5 mg kg(-1) for Fe and Cu. Metal concentrations in Scandinavian pulps are not expected to exceed these amounts. The quantification limit was 2 mg kg(-1) for all three metals. The reproducibilities and repeatabilities were concentration-dependent and varied between 3 and 19% and between 1 and 17%, respectively. The squares of the linear correlation coefficients between measured intensity and added metal concentration were 0.994, 0.950, and 0.932 for Mn, Fe, and Cu, respectively.

Journal Article↗

PubMed2001

Ruthenium and ruthenium dioxide-modified graphite-ethylene/ propylene/diene and graphite-teflon composite electrodes as amperometric flow detectors. Application to the determination of methionine.

The flow injection amperometric performance of solid composite graphite electrodes with ethylene/propylene/diene (EPD) or Teflon as binding agents, and with Ru or RuO2 particles as electrocatalytic modifiers has been compared. Both, Ru and RuO2 modified electrodes exhibited electrocatalytic properties on the methionine oxidation process in alkaline media. The electrodes composition and the hydrodynamic and chemical variables were optimized. Graphite-EPD (GEPD) electrodes showed a better analytical performance than graphite-Teflon (GPTFE) electrodes. Furthermore, a better sensitivity, repeatability and reproducibility was observed for RuO2-GEPD electrodes when compared with Ru-GEPD electrodes. At an applied potential of +0.50 V, a detection limit for methionine of 4.8x10(-5) mol L(-1), similar to those reported in the literature for other RuO2-modified electrodes, was obtained. The analytical applicability of RuO2-GEPD electrodes was demonstrated by determining methionine in a complex pharmaceutical formulation.

Electrochemistry↗

PubMed1998

Pheromone-evoked potentials and oscillations in the antennal lobes of the sphinx moth Manduca sexta.

Using intra- and extracellular recording methods, we studied the activity of pheromone-responsive projection neurons in the antennal lobe of the moth Manduca sexta. Intracellularly recorded responses of neurons to antennal stimulation with the pheromone blend characteristically included both inhibitory and excitatory stages of various strengths. To observe the activity of larger groups of neurons, we recorded responses extracellularly in the macroglomerular complex of the antennal lobe. The macroglomerular complex is part of a specialized olfactory subsystem and the site of first-order central processing of sex-pheromonal information. Odors such as the pheromone blend and host-plant (tobacco) volatiles gave rise to evoked potentials that were reproducible upon repeated antennal stimulation. Evoked potentials showed overriding high-frequency oscillations when the antenna was stimulated with the pheromone blend or with either one of the two key pheromone components. The frequency of the oscillations was in the range of 30-50 Hz. Amplitude and frequency of the oscillations varied during the response to pheromonal stimulation. Recording intracellular and extracellular activity simultaneously revealed phase-locking of action potentials to potential oscillations. The results suggest that the activity of neurons of the macroglomerular complex was temporally synchronized, potentially to strengthen the pheromone signal and to improve olfactory perception.

Animals↗

PubMed2006

Mechanically induced intracellular calcium waves in osteoblasts demonstrate calcium fingerprints in bone cell mechanotransduction.

An early response to mechanical stimulation of bone cells in vitro is an increase in intracellular calcium concentration ([Ca (2+)](i)). This study analyzed the [Ca (2+)](i) wave area, magnitude, duration, rise time, fall time, and time to onset in individual osteoblasts for two identical bouts of mechanical stimulation separated by a 30-min rest period. The area under the [Ca (2+)](i) wave increased in the second loading bout compared to the first. This suggests that rest periods may potentiate mechanically induced intracellular calcium signals. Furthermore, many of the [Ca (2+)](i) wave parameters were strongly, positively correlated between the two bouts of mechanical stimulation. For example, in individual primary osteoblasts, if a cell had a large [Ca (2+)](i) wave area in the first bout it was likely to have a large [Ca (2+)](i) wave area in the second bout (r (2) = 0.933). These findings support the idea that individual bone cells have "calcium fingerprints" (i.e., a unique [Ca (2+)](i) wave profile that is reproducible for repeated exposure to a given stimulus).

Animals↗