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Results for “Repeatability and Reproducibility”

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At least 541 records · Page 30Linked to original sources

PubMed1990

The use of Doppler ultrasound in the study of fetal cardiovascular physiology.

Doppler velocimetry of the uteroplacental and umbilical arteries provides an opportunity for the safe, reproducible and repeatable study of these circulations and already has led to an increased knowledge of the pathophysiology of pregnancy induced hypertension and intra-uterine growth retardation. This technique, which has only recently been introduced widely into obstetrics, also permits the study of the cardiovascular effects on the fetus of maternally administered drugs. The use of Doppler for these purposes is illustrated with particular reference to intra-uterine growth retardation and the use of the antihypertensive drugs, atenolol and nifedipine.

Animals↗

PubMed1990

A non-invasive method for fractionated stereotactic irradiation of brain tumors with linear accelerator.

A new technique for fractionated stereotactic irradiation of intracranial lesions is described. The treatment is based on a versatile, non-invasive interface for stereotactic localization of the brain target imaged by computed tomography (CT), angiography or magnetic resonance tomography (MRT), and subsequent repetitive stereotactic irradiation of the target using a linear accelerator. The fractionation of the stereotactic irradiation was intended to meet the requirements of the basic principles of radiobiology. The radiophysical evaluation using phantoms, and the clinical results in a small number of patients, demonstrated a good reproducibility between repeated positionings of the target in the isocenter of the accelerator, and a high degree of accuracy in the treatment of brain lesions.

Adult↗

PubMed1992

Dynamics of responses of V1 neurons evoked by stimulation of different zones of receptive field.

The dynamics of receptive fields of 73 neurons in area 17 of cat visual cortex were studied using the temporal slice method. Three-dimensional maps of the receptive fields were plotted using the criterion of spike number in successive fragments (step 10 or 20 ms) of responses to 100 local flashes presented at different parts of the receptive field in random order. The size and configuration of such dynamically recorded receptive fields were then estimated. This allowed us to reveal the dynamic reorganization of all receptive fields 20-400 ms after stimulation. A small zone of responses appeared in the receptive field after initial latency, then it widened, received definitive configuration, and after that decreased and disappeared. The effect was reproducible under repeated estimations. The relationships between receptive field and the previously described orientation tuning dynamics, as well as between dynamics of receptive fields and their summation zones, mechanisms and possible functional meaning of the revealed effects for signal processing in the primary visual cortex are discussed.

Animals↗

PubMed1993

Sensitive liquid chromatographic method for the determination of a specific M1 agonist, LY246708, an investigational agent with potential for the treatment of Alzheimer's disease, in human plasma.

A reversed-phase HPLC method is reported for the determination of a new M1 agonist, LY246708, in human plasma. The compound and an internal standard were extracted from plasma with hexane at basic pH. The organic extract was evaporated to dryness and the residue was reconstituted with mobile phase [0.5% diethylamine (pH 3, adjusted with phosphoric acid)-acetonitrile (70:30, v/v)]. The analytes were separated from endogenous substances on a Zorbax CN column; the effluent was monitored by measuring its absorbance at 296 nm. The limit of quantification was determined at 1.5 ng/ml and the response was linear from 1.5 to 20 ng/ml. Validation studies showed the method to be both repeatable and reproducible. Its robustness was demonstrated by transfer between analytical laboratories and continued use in support of pharmacokinetic studies and therapeutic monitoring of the compound.

Alzheimer Disease↗

PubMed1993

Measurement of left ventricular mass in hypertrophic cardiomyopathy using MRI: comparison with echocardiography.

Left ventricular mass (LVM) is an important consideration in the management of cardiac hypertrophy associated with hypertrophic cardiomyopathy (HCM), systemic hypertension, and other diseases. A brief MRI cardiac imaging procedure used to monitor regression of LVM during treatment would be beneficial in management of these patients, since echocardiograms cannot be obtained in all patients and since the volume of a hypertrophic heart can straightforwardly be assessed from a series of tomographic slices. The present study was designed to evaluate a brief cardiac MRI procedure for measurement of LVM in HCM and compare it to echocardiography. MRI images acquired in a simulated transverse body plane were used to evaluate the mass of the left ventricle in 6 ex vivo human hearts obtained at autopsy. The estimates of LVM by MRI in the ex-vivo hearts were within 8% of the actual LVM. MRI images were acquired to evaluate LVM in 5 normal subjects and 12 patients diagnosed with HCM. Echocardiography was accomplished on 4 of the normal subjects and 10 of the patients having HCM. There were no significant differences in LVM by MRI and echocardiographic techniques in normal subjects. Transverse MRI images acquired on normal subjects demonstrated that estimates of LVM are reproducible when repeated over 3-w to 3-mo intervals. Images selected for analysis represented the heart in an early diastolic phase. MRI and echocardiographic techniques demonstrated significant differences in LVM in HCM patients. Estimates of LVM in normal subjects and patients diagnosed with HCM were normalized for body weight. The LVM estimates for HCM patients were very significantly different than normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Weight↗

PubMed1989

A collaborative study of the analysis of doxycycline hyclate by high-performance liquid chromatography on polystyrene-divinylbenzene packing materials.

An improved method for the analysis of doxycycline hyclate by high-performance liquid chromatography using polystyrene-divinylbenzene column packings is described. The separation obtained with this method was compared with that of other, recently described methods. The improved method was examined in a collaborative study involving five separate laboratories, using 11 different columns and four discrete samples. The main component and impurities were determined. An analysis of variance showed absence of consistent laboratory bias and presence of significant laboratory-sample interaction. Estimates for the repeatability and reproducibility of the method, expressed as relative standard deviations (RSD) of the result of the determination of doxycycline, were found to be 0.9 and 1.2%, respectively.

Chromatography, High Pressure Liquid↗

PubMedDate not supplied

Collaborative study of the analysis of chlortetracycline hydrochloride by liquid chromatography on polystyrene-divinylbenzene packing materials.

A previously established method for the analysis of chlortetracycline by liquid chromatography using polystyrene-divinylbenzene stationary phases was examined in a multicentre study involving four laboratories and a total of 12 columns. Three chlortetracycline hydrochloride samples were analysed. The main component and the impurities were determined. An analysis of variance, treating each column as a different laboratory, showed absence of consistent laboratory bias and presence of significant laboratory-sample interaction. Estimates for the repeatability and reproducibility of the method, expressed as relative standard deviations of the result of the determination of chlortetracycline hydrochloride, were calculated to be 0.7 and 1.2%, respectively. When the analysis of variance was performed using only the results obtained on the wide pore (1000 A) stationary phases, the laboratory-sample interaction strongly decreased. It is therefore proposed to use such materials for the analysis of chlortetracycline.

Analysis of Variance↗

PubMed1996

Interlaboratory study of the analysis of ampicillin by liquid chromatography.

A liquid chromatographic method for the analysis of ampicillin was examined in a collaborative study involving seven laboratories. The method included an isocratic part, which is used in the assay. The isocratic part is similar to the assay method for ampicillin of the US Pharmacopeia XXIII Revision. When the isocratic part is combined with gradient elution, the method is suitable for purity control. Six samples of ampicillin (anhydrous, trihydrate and sodium salt) with varying purity were analysed. The main component and related substances were determined. An analysis of variance proved the absence of consistent laboratory bias. The laboratory-sample interaction was significant. Estimates of the repeatability and reproducibility of the method, expressed as standard deviations of the result of the determination of ampicillin, were calculated to be about 0.9 and 1.1 respectively.

Ampicillin↗

PubMed1989

Hemodynamic progression of aortic stenosis in adults assessed by Doppler echocardiography.

Doppler echocardiography was used to follow the hemodynamic severity of aortic stenosis. First, the reproducibility of repeat recordings (mean interval 28 +/- 36 days) of aortic jet velocity, made by two independent observers, was tested in 38 adults with aortic stenosis and unchanged clinical status. The two recordings of maximal velocity correlated well (r = 0.96, y = 0.88x + 0.46m/s, SEE = 0.21 m/s) with a mean coefficient of variation of 3.2%. Repeat recording of left ventricular outflow tract velocity by two independent observers in 10 other patients with aortic stenosis also correlated well (r = 0.94, y = 1.06x + 0.0 m/s, SEE = 0.06 m/s) with a mean coefficient of variation of 4.6%. Next, Doppler echocardiography was used to study 42 patients with aortic stenosis (mean age 66 years) over a follow-up interval of 6 to 43 months (mean 20). Maximal aortic jet velocity increased by 0.36 m/s per year (range -0.3 to +1.0 m/s per year). Mean transaortic pressure gradient changed by -7 to +23 (mean 8) mm Hg/year. Aortic valve area by the continuity equation (n = 25) decreased by 0 to 0.5 cm2/year (mean decrease 0.1 cm2/year). Some patients had a worsening of stenosis (decrease in valve area) even though they had no change or a decrease in pressure gradient, because of concurrent decreases in transaortic volume flow. Twenty-one patients (50%) developed new or progressive symptoms of aortic stenosis necessitating valve replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1996

Age-related and vasomotor stimuli-induced changes in renal vascular resistance detected by Doppler ultrasound.

Indirect measurement of renal vascular resistance by duplex Doppler waveform analysis was evaluated in relation to aging and some pathophysiological conditions. Baseline renal resistive index (RRI) (peak systolic frequency shift - lowest diastolic frequency shift/peak systolic frequency shift) was measured in healthy controls aged 20 to 85 years by analyzing the blood flow velocity waveform of interlobar arteries. RRI changes induced by sympathetic activation (cold pressor test and handgrip test) or by fluid load were evaluated. Both repeatability and reproducibility were very good, as the intra and interoperator variations were all less than their reproducibility coefficients. RRI showed a significant increase with aging (ANOVA P < .001), particularly evident in subjects older than 50 years. Both the cold pressor test and handgrip test induced in all the subjects (n = 16) a significant increase in RRI (P < .001), from 0.59 +/- 0.04 to 0.69 +/- 0.04 (12 +/- 6%) for the cold pressor test and from 0.57 +/- 0.03 to 0.66 +/- 0.03 (15 +/- 2%) for the handgrip test. In eight subjects intravenous fluid load (0.25 mL/kg/min of 0.9% NaCl for 120 min) caused a significant decrease in RRI (P < .001), from 0.62 +/- 0.02 to 0.53 +/- 0.01 (17 +/- 2%), which was inversely related to mean blood pressure rise (r = 0.71, P < .001). These data show that pulsed wave Doppler analysis is an accurate method for an indirect evaluation of changes in renal vascular resistance induced by common vasomotor stimuli.

Adult↗

PubMed1994

Radiosensitivity of new and established human melanoma cell lines: comparison of [3H]thymidine incorporation and soft agar clonogenic assays.

Seven new low-passage melanoma lines were developed in this laboratory from clinical melanoma specimens and characterised for chromosome complement, DNA ploidy and S-phase content. The radiosensitivity of these lines was compared with that of eight established melanoma cell lines, FME, MM-96, SK-MEL-5, SK-MEL-28, SK-MEL-2, MALME-3M, M19-MEL and LOX-IMVI, using a 96-well microculture assay technique. Dose-response curves were determined using a 5-day incubation period and 6-h terminal [3H]thymidine-labelling period. Radiation (60Co source) was carried out under a lead wedge to provide a radiation dose range of 0-10 Gy, or by irradiating part of the plate (radiation dose 0 or 2 Gy). Data for a range of cell densities in a single 96-well plate were combined into a single regression equation incorporating linear quadratic terms for radiation dose and cell density. SF2 values were defined as the amount of thymidine incorporated following a radiation dose of 2 Gy, expressed as a fraction of that of unirradiated cells, and varied from 0.36 to 0.93. The reproducibility in repeat assays, as defined by the standard error of determinations at different passage numbers, was +/- 0.04. The newly developed lines exhibited a similar range of radiosensitivity to that of the established lines, and melanin content did not correlate with resistance. For nine of the lines, radiation parameters were also determined using a modified Courtenay clonogenic soft agar assay technique, and the results compared with the thymidine incorporation results, and a significant linear correlation was found between SF2 and SF2' (r = 0.89). The linear (alpha) and quadratic (beta) terms of the best-fit linear quadratic dose-response curves, were significantly correlated between the two assays. It is concluded for this series of human melanoma lines that proliferation assays in 96-well plates provide radiosensitivity parameters comparable to those using clonogenic assays.

Adult↗

PubMed2004

The ApoCorrect assay: a novel, rapid method to determine the biological functionality of radiolabeled and fluorescent Annexin A5.

We have demonstrated that imaging of programmed cell death (PCD) in patients is possible using 99mTc-Annexin A5. Because of the short half-life of the technetium label it is important to limit the time span between the preparation of 99mTc-Annexin A5 and its administration into the patient. Therefore methods of quality control that determine the biological active fraction in the 99mTc-Annexin A5 should be not only accurate and precise but also rapid. We report the development and validation of a rapid, simple assay measuring the biological active fraction of 99mTc-Annexin A5. The assay is based on a solid phase of paramagnetic beads which are coated with phospholipids. Annexin A5 binds to these beads with high affinity if phosphatidyl serine is present within the phospholipid coat. Furthermore the binding depends on Ca2+ ions and functional Ca2+/phospholipid binding sites of Annexin A5. The bead assay is specific, stability-indicating, repeatable, and reproducible. It allows one to determine within 25 min the biological active fraction of a 99mTc-Annexin A5 preparation. We dubbed this assay the ApoCorrect assay.

Annexin A5↗

PubMed2005

Electroimmobilization of proinsulin C-peptide to a quartz crystal microbalance sensor chip for protein affinity purification.

Proinsulin C-peptide was electroimmobilized to a quartz crystal microbalance sensor chip, localizing this low-pI peptide for covalent attachment to activated surface carboxyl groups. The resulting chip was used in a continuous flow biosensor to capture anti-C-peptide antibodies, which could subsequently be eluted in 5% formic acid between air bubbles for efficient recovery and mass spectrometric identification. The method is reproducible through repeated cycles, providing affinity purification of proteins under real-time monitoring of the binding and elution processes.

Amino Acid Sequence↗

PubMed2005

In vitro degradation of the antimicrobial human peptide HEM-gamma 130-146 in plasma analyzed by a validated quantitative LC-MS/MS procedure.

In stability studies during preclinical drug development, the human antimicrobial peptide hHEM-gamma 130-146 shows progressive N-terminal degradation in plasma. To determine this effect, we developed and validated a selective and quantitative muHPLC-MS/MS procedure for this compound. Following deproteinization by precipitation, reversed-phase separation is performed with a time-saving two-column design online coupled to an ion trap mass spectrometer for electrospray ionization MS detection. Using a linear calibration curve obtained with synthetic external standards ranging nearly two orders of magnitude, we achieved good precision (repeatability and reproducibility: 5-15%), accuracy (-3 to 15%), and ruggedness with a lower limit of quantification at 0.29 microg/ml plasma (0.15 microM). Because of good linearity (r2>0.999), the recovery (84+/-3%) and ion suppression (86+/-4% remaining intensity) were calculated from specifically prepared calibration curves. The developed procedure was applied to human and animal plasma samples. Incubations in the presence and absence of proteinase inhibitors revealed at least an aminopeptidase M activity for the initial N-terminal truncation of tryptophan (W130) and a putative glutaminyl-peptide cyclotransferase activity for the resulting intermediate starting with the bared glutamine residue (Q131). The calculated periods of half-change demonstrated exceeding interspecies variations, whereas the intraspecies variations were only between 20 and 30%. The current procedure is valuable as a generic method for pharmaceutical purposes, and data give important information for further development toward a potential natural drug candidate.

Amino Acid Sequence↗

PubMed2005

The electrochemical behaviour of ferrocene in a photocurable poly(methyl methacrylate-co-2-hydroxylethyl methacrylate) film for a glucose biosensor.

A single-step fabrication of a glucose biosensor with simultaneous immobilization of both ferrocene mediator and glucose oxidase in a photocurable methacrylic film consisting of poly(methyl methacrylate-co-2-hydroxylethyl methacrylate) was reported. The entrapped ferrocene showed reversible redox behaviour in the photocured film and no significant leaching of both entrapped ferrocene and enzyme glucose oxidase was observed because of the low water absorption properties of the co-polymer films. From electrochemical studies, ferrocene entrapped in the co-polymer film demonstrated slow diffusion properties. A linear glucose response range of 2-11 mM was obtained at low applied potential of +0.25 V. The glucose biosensor fabricated by this photocuring method yielded sensor reproducibility and repeatability with relative standard deviation of <10% and long-term stability of up to 14 days. The main advantage of the use of photocurable procedure is that biosensor membrane fabrication can be performed in a single step without any lengthy chemical immobilization of enzyme.

Biosensing Techniques↗

PubMed2004

Validation of the anthrax lethal toxin neutralization assay.

A validation of the performance characteristics of a toxin neutralization assay is presented. This in vitro assay measures the functional ability of antisera, containing antibodies to anthrax lethal toxin, to specifically protect J774A.1 cells against Bacillus anthracis lethal toxin cytotoxicity. This colormetric assay is based upon the reduction of MTT by living cells. Human and rabbit antisera produced against anthrax vaccine absorbed (AVA) were used to validate the assay. Results showed a high level of repeatability and reproducibility, particularly for a bio-assay. Inter-assay variability in absorbance values was the most prominent negative finding however, an acceptable level was demonstrated with a ratio [neutralization ratio (NR)] of the test serum 50% effective dose (ED(50)) to the reference standard ED(50). Accuracy was maintained, even in samples with minimal neutralizing capacity, and linearity was noted when sample dilutions resulted in accurate prediction of the Y(max)and Y(min). Specificity tests demonstrated that normal sera did not have an observable effect on the ability of the reference standard to neutralize toxin. The assay remained stable against time, temperature, and freeze/thaw effects on the reference standards, but not on the toxin. The assay also remained stable against media and solution storage effects. Cell passage number and cell plating density were two critical parameters identified during the robustness studies that may be responsible for inter-assay variability in absorbance values. The work was performed in accordance with the FDA's Bioanalytical Method Validation Guidance for Industry and the FDA's Good Laboratory Practice for Nonclinical Laboratory Studies (21 CFR Part 58).

Animals↗

PubMed2004

Comparative study of electron mediators used in the electrochemical oxidation of NADH.

A comparison of the behavior of six different redox mediators for the electrocatalysis of the oxidation of NADH, which are widely used in the construction of dehydrogenase-based biosensors, is reported. The redox mediators were, potassium hexacyanoferrate (II), Meldola's Blue (MB), dichlorophenolindophenol (DCPIP), p-benzoquinone (p-BQ), o-phenylenediamine (o-PDA) and 3,4-dihydroxybenzaldehyde (3,4-DHB). After incorporating each of them in the sensor system following four different strategies (in solution, entrapped in epoxy-composites, adsorbed or electropolymerized on the electrode surface), several aspects regarding repeatability and reproducibility were considered and compared.

Biosensing Techniques↗

PubMed2006

Screen-printed biosensors for glucose determination in grape juice.

An approach to the glucose determination by amperometric biosensing in wine industry applications is presented. Integrated screen-printed biosensors based on horseradish peroxidase (HRP) and glucose oxidase (GOx) have been developed. The experimental design methodology has been used to find the optimum conditions of the experimental variables, in such a way that a chronoamperometric response specific for glucose was recorded. Under these conditions, repeatability and reproducibility of the modified electrodes have been analyzed. The detection limit for glucose has been calculated taking into account the probability of false positive (alpha) and negative (beta), reaching a medium value of 4.37+/-0.21 micromol dm-3 (alpha=beta=0.05, and a replicate n=4). The biosensor was applied to the determination of glucose in white wine samples.

Beverages↗