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At least 847 records · Page 47Linked to original sources
PubMed1997

Analytical performance and clinical utility of a sensitive immunoassay for determination of human cardiac troponin I.

OBJECTIVES: To determine the serum and plasma level of human cardiac troponin I (cTnI) resulting from myocardial damage, we have developed a sensitive and specific one-step enzyme immunoassay to measure cardiac troponin I. DESIGN AND METHODS: The COBAS cTnI assay is a semi-automated one-step solid phase immunoassay compatible with the COBAS Core. The assay is performed in a sandwich type format using a polyclonal goat antibody capture and two highly specific horseradish peroxidase conjugated monoclonal antibody detectors directed against different epitopes of the cTnI molecule. Calibrators were made with purified recombinant cTnI. RESULTS: The level of cTnI was determined in 84 healthy donors with no evidence of myocardial injury, resulting in a lower limit of detection (LLD) of 0.09 microgram/L. The upper reference limit (URL) of the normal reference range was calculated as 0.20 microgram/L. The dynamic range of the consequent EIA was between 0.09 and 6.0 micrograms/L with a total assay time of 45 min. Intra-assay and inter-assay variances (CVs) were < or = 4%. Cross-reactivity with fast and slow skeletal troponin I was absent in concentrations up to 2.0 mg/L. Common interferents yielded negative results in the cTnI assay. Clinical utility was confirmed by measuring the circulating serum or plasma levels of cardiac troponin I in serial samples from marathon runners, clinical samples from trauma patients, and patients presenting to the Emergency Department with complaints of chest pain. Results were further evaluated using clinical diagnosis at discharge and quantified concentrations of other cardiac markers by a Stratus analyzer and ELISA procedures. CONCLUSIONS: Results from normal and clinical samples assayed in house for cTnI concentrations indicate that the Spectral EIA is a highly sensitive means of quantifying cTnI levels in serum and plasma for acute cardiac syndrome. The cardiac specificity of cTnI over other well-known cardiac markers is reflected in experimental results and parallel clinical diagnosis.

Animals↗
PubMed2003

Coding of the contrasts in natural images by populations of neurons in primary visual cortex (V1).

It is possible to discriminate between grating contrasts over a 300-fold contrast range, whereas V1 neurons have very limited dynamic ranges. Using populations of model neurons with contrast-response parameters taken from electrophysiological studies (cat and macaque), we investigated ways of combining responses to code contrast over the full range. One model implemented a pooling rule that retained information about individual response patterns. The second summed responses indiscriminately. We measured accuracy of contrast identification over a wide range of contrasts and found the first model to be more accurate; the mutual information between actual and estimated contrast was also greatest for this model. The accuracy peak for the population of cat neurons coincided with the peak of the distribution of contrasts in natural images, suggesting an ecological match. Macaque neurons seem better able to code contrasts that are slightly higher on average than those found in the natural environment.

Animals↗
PubMed2001

Organic chloramine analysis and free chlorine quantification by electrospray and atmospheric pressure chemical ionization tandem mass spectrometry.

Atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), together with tandem mass spectrometry (MSn), are used to study the mechanism of chlorination of amines and to develop a method for qualitative and quantitative determination of organic chloramines. Cyclohexylamine and 1,4-butanediamine (putrescine) are used as model compounds to investigate the mechanisms of the reactions between primary aliphatic amines and hypochlorous acid (aqueous Cl2). The chlorination products are identified and characterized by collision-induced dissociation (CID) and H/D exchange. Chlorination occurs by electrophilic addition of Cl+ and may be followed by HCl elimination, hydrolysis, or, in the case of diamines, amine elimination by intramolecular nucleophilic substitution. The relative rates of chlorination at amine and chloramine nitrogens are a function of pH and depend on the basicity of the amine. A novel method for active chlorine quantification using ESI or APCI mass spectrometry is suggested on the basis of the extent of chlorination of a sacrifical amine standard. This measurement has a limit of detection for N-chlorocyclohexylamine in the range of 0.1-10 microM, a linear dynamic range of 10(2)-10(3), and an accuracy of +/-10%, as determined for wastewater samples.

Journal Article↗
PubMed1998

Counting of single protein molecules at interfaces and application of this technique in early-stage diagnosis.

The fluorescence-based detection and counting of single protein molecules after specific binding to antibodies at interfaces is presented. A diode laser was used as the excitation source. The unspecific binding at the interface has been reduced to a level of only 0.1% of the maximum signal level. At present, the detection limit of this molecule-counting process is in the range of 10(-17) mol/L, and the dynamic range of the signal corresponds to 7 orders of magnitude of antigen concentration, but these values are not limiting. As a preliminary application in early-stage diagnosis, we have investigated the detection of a single cardiac actin molecule in human plasma, which is of interest in myocardial infarction diagnosis.

Actins↗
PubMed2001

Screening method for nitroaromatic compounds in water based on solid-phase microextraction and infrared spectroscopy.

A new method is described for determining nitroaromatic compounds in water that combines solid-phase microextraction (SPME) and infrared (IR) spectroscopy. In this method, the compounds are extracted from a 250-mL volume of water into a small square (3.2 cm x 3.2 cm x 61.2 microm thick) of silicone polycarbonate copolymer film (MEM-213). Five nitroaromatic compounds, including 2,4,6-trinitrotoluene (TNT), were chosen to evaluate the SPME/IR procedure. Quantitation limits for the five test compounds range from 50 microg/L for TNT to 400 microg/L for nitrobenzene. Precision values, determined at aqueous concentrations of four times the quantitation limit, range from 4 to 7%, and linear dynamic ranges extend to the maximum limit of the IR instrumentation. The potential of this SPME/IR method for determining nitroaromatics in natural water samples was also investigated by extracting "real world" soil samples contaminated with TNT. Results obtained from the SPME/ IR determination of the diluted extracts were in reasonable agreement with those obtained from dichloromethane extraction followed by gas chromatographic analysis.

Chromatography, Gas↗
PubMed1994

Rotary scanning equalization radiography: an efficient geometry for equalization mammography.

The detection of cancer in the radiographically dense breast is problematic, since the breast will produce a range of exposure that exceeds the useful dynamic range of high contrast film-screen combinations. It has been shown previously that mammographic scanning equalization radiography (MSER) can be used to overcome the latitude limitations of film-screen mammography. However, the tube loading of MSER is orders of magnitude greater than conventional mammography. A new rotary geometry for equalization radiography is proposed, in which the image receptor is exposed by repeated scans of a modulated slot beam, oriented at a variety of scanning angles with respect to the object. The superposition of the exposure from appropriately modulated, rotated slot beams produces an entrance exposure that will effectively equalize the film exposure. The principle advantages of this geometry is its simplicity and reduced tube loading. To determine the effectiveness and feasibility of RSER the effect of conventional, MSER, and RSER have been numerically simulated on the appearance of clinical mammograms, the relative heat loading, and the fraction of the breast imaged with high contrast are calculated. It is found that RSER produces images that are free of artefacts, and exhibit a similar degree of equalization, as found in MSER images. RSER accomplishes this with only four scanning angles, and a beam that is approximately 4 cm wide. The resulting tube loading is only three times greater than that found in conventional imaging. Numerical simulations indicate that RSER is a simple, feasible means of overcoming the latitude limitations of film-screen mammography.

Computer Simulation↗
PubMed1996

Practical application of a scan-rotate equalization geometry to mammography.

The presence of dense fibroglandular tissue within the breast is the most significant cause of failure to detect breast cancer with mammography. The dense tissue often produces a range of exposure which exceeds the useful dynamic range of film-screen mammography. It has been shown that equalization radiography overcomes the latitude limitations of film-screen imaging. Equalization compensates for regional variations in x-ray transmission within the patient through spatial modulation of the entrance exposure. We have proposed rotary scanning equalization radiography (RSER), a scan-rotate geometry for efficient equalization radiography. In RSER the image receptor is exposed by repeated scans of a source-modulated fan beam. The fan beam is rotated with respect to the patient between scans. Numerical simulations and theoretical analysis have shown that the superposition of exposure from appropriately modulated fan beams at a variety of angles is an entrance exposure that effectively equalizes the film exposure. The design and characteristics of a prototype RSER imaging system are described. Anthropomorphic breast phantom images are used to determine the improvement in image contrast obtained with RSER, the expected tube loading, and the presence of artifacts. RSER increases the fraction of the breast imaged with high contrast (at least 90% of peak gradient) from 46% (conventional mammography) to 80%. Subjective examination of the phantom images show that RSER achieves image quality very similar to that of much less efficient equalization geometries with only 2.7 times greater tube loading than conventional mammography. As predicted by theoretical analysis of exposure artifacts in RSER, the prototype RSER system is relatively immune to artifacts. Exposure artifacts were demonstrated for extreme variations in x-ray transmission within the patient. These results show that RSER is an efficient, practical means of overcoming the latitude limitations of film-screen mammography, and improving the detection of breast cancer.

Biophysical Phenomena↗
PubMed2005

Congenital stationary night blindness type 2 mutations S229P, G369D, L1068P, and W1440X alter channel gating or functional expression of Ca(v)1.4 L-type Ca2+ channels.

Mutations in the CACNA1F gene (voltage-dependent L-type calcium channel alpha1F subunit) encoding retinal Ca(v)1.4 L-type Ca2+ channels cause X-linked recessive congenital stationary night blindness type 2 (CSNB2). Many of them are predicted to yield nonfunctional channels. Complete loss of Ca(v)1.4 function is therefore regarded as a pathogenetic mechanism for the impaired signaling from photoreceptors to second-order retinal neurons. We investigated the functional consequences of CSNB2 missense mutations S229P, G369D, and L1068P and the C-terminal truncation mutant W1440X. After expression in Xenopus laevis oocytes or human embryonic kidney tsA-201 cells, inward Ca2+ current (I(Ca)) and inward Ba2+ current (I(Ba)) could be recorded from mutations G369D and L1068P. G369D shifted the half-maximal voltage for channel activation (V(0.5,act)) significantly to more negative potentials (>11 mV), slowed inactivation, and removed Ca2+-dependent inactivation. The L1068P mutant yielded currents only in the presence of the channel activator BayK8644. Currents (I(Ba)) inactivated faster than wild type (WT) and recovered more slowly from inactivation (I(Ba) and I(Ca)). No channel activity could be measured for mutants S229P and W1440X after oocyte expression. No W1440X alpha1 protein was detected after expression in tsA-201 cells, whereas S229P (as well as G369D and L1068P) alpha1 subunits were expressed at levels indistinguishable from WT (n = 3). Our data provide unequivocal evidence that CSNB2 missense mutations can induce severe changes in Ca(v)1.4 function, which may decrease (L1068P and S229P) or even increase (G369D) channel activity. The lower activation range of G369D can explain the reduced dynamic range of photoreceptor signaling. Moreover, we demonstrate that loss of channel function of one (L1068P) CSNB2 mutation can be rescued by a Ca2+ channel activator.

Animals↗
PubMed2002

Chimerism analysis in sex-mismatched murine transplantation using quantitative real-time PCR.

Marine experimental stem cell transplantations require the accurate discrimination and quantification of donor cells from host cells. A Y-chromosome-specific, quantitative real-time PCR (kinetic PCR) protocol for blood-derived DNA was developed. The assay sensitivity was extremely high with accurate detection of only 10 pg (six copies of Y target DNA) in a variable background of female DNA background ranging from 2.5 to 50 ng. The dynamic range of the assay provided accurate results ranging from 2.2 x 10(-2)% to 100% of male DNA in female background. The kinetic PCR assay can be used in all mouse strains, and a sample size as low as 2.5 ng total DNA is sufficient for analysis. Therefore, kinetic PCR allows engraftment kinetic studies on repeated blood draws of individual animals with no need for sacrifice. Compared to conventional PCR, the assay is much simplified, as neither the accurate adjustment of sample DNA concentration nor a post-reaction analysis procedure is required. The procedure is simple, free of radioactivity, and permits a throughput of 500-600 reactions per day.

Animals↗
PubMed2026

Blood Plasma Analysis in Ovarian Cancer Patients Using an AFM/MS Approach: Effect of Sample Dilution on Proteome Depth.

Early detection of ovarian cancer remains challenging because of the lack of sensitive and reproducible blood-based biomarkers. A major challenge in plasma proteomics is the extremely wide dynamic range of protein concentrations, which prevents simultaneous detection of both high- and low abundance proteins and limits the identification of disease-associated signals. In this study, we applied a combined atomic force microscopy and mass spectrometry (AFM/MS) approach to investigate how sample dilution affects plasma proteome coverage and the detection of differences between healthy donors and patients with stage I and stage III ovarian cancer. Plasma samples were analyzed at two dilution levels (1:100 and 1:10,000). At 1:100 dilution, a total of 235 proteins were identified across all samples, representing the union of all replicates and groups. The reproducible CORE proteome comprised 169 proteins in the Healthy group, 183 in the Stage I group, and 193 in the Stage III group. Differential analysis revealed distinct, non-overlapping protein sets at each dilution level. At 1:100 dilution, most altered proteins were decreased in patients and corresponded to major plasma components, including complement proteins and protease inhibitors. At 1:10,000 dilution, most altered proteins were increased and were predominantly immunoglobulin-related proteins, along with complement regulatory components. These findings show that sample dilution determines which fraction of the plasma proteome is observable. Here, proteome depth refers to the total number of non-redundant proteins accessible within the analytical workflow. When CORE sets from all groups were combined, 216 proteins were identified at 1:100 and 149 at 1:10,000, with 133 shared between the two dilution conditions. The higher dilution contributed 16 additional CORE proteins not detected in the 1:100 CORE union, increasing the combined CORE set to 232 proteins. Thus, higher dilution alone did not increase proteome depth, but provided complementary protein identifications that increased cumulative proteome depth when both dilution conditions were considered together. This effect reflects dilution-dependent selectivity in the composition of the detectable protein subset.

Humans↗
PubMed1999

Responses of neurons in the region of human thalamic principal somatic sensory nucleus to mechanical and thermal stimuli graded into the painful range.

The role of the region of the principal somatic sensory nucleus of the human thalamus (ventral caudal - Vc) in signaling painful sensations is unclear. We have now studied the response of cells (n = 57) in this region to both thermal and mechanical stimuli graded into the painful range during surgeries (n = 24) for treatment of movement disorders. Fifteen cells had a graded response to mechanical stimuli extending into the painful range and, thus, were classified in the wide dynamic range (WDR) category. The mean stimulus-response function of cells in the WDR class, normalized to baseline, showed a fourfold mean increase in firing rate above baseline across the mechanical series of stimuli. Seven of these cells responded to heat stimuli (WDR-H) and two responded to cold stimuli (WDR-C). Twenty-five cells were in a class (multiple receptive - MR) that showed a response to both brush and compressive stimuli, although the responses were not graded into the painful range. Three of these cells (MR-H) had a response to heat stimuli and five cells responded to cold stimuli (MR-C). Nine cells responded to brushing without a response to the compressive stimuli (low threshold - LT). Cells responsive to painful mechanical and thermal stimuli were located throughout the thalamic region where cells responded to nonpainful cutaneous stimulation. These results show that cells in the region of the human thalamic principal somatic sensory nucleus respond to mechanical and thermal stimuli extending into the painful range.

Cold Temperature↗
PubMed1993

Acoustic response properties of single units in the torus semicircularis of the goldfish, Carassius auratus.

Single units of the goldfish torus semicircularis (TS) were recorded in response to pure tones. Response areas (RA) were obtained by recording the number of spikes evoked by tones in a range of frequencies and levels within the units' dynamic range. RAs gave estimates of best sensitivity (BS), characteristic frequency (CF), most excitatory frequency at each level (BF), and Q10dB. Peri-stimulus-time histograms (PSTH), interspike interval histograms (ISIH), and period histograms were obtained at various frequencies and levels to describe the units' temporal response patterns. The distribution of CF is nonuniform with modes at 155, 455, and 855 Hz. The distribution of the coefficient of synchronization to standard tones is also nonuniform, revealing a dichotomy between units with little or no phase-locking and those that phase-lock strongly. PSTHs for units without significant phase-locking vary widely and include patterns resembling those of the mammalian auditory brainstem. Compared with saccular afferents, torus units tend to have lower spontaneous rates, greater sensitivity, and sharper tuning. Unlike saccular afferents, BF is independent of level for most torus units. Some torus units are similar to saccular afferents while others reveal significant transformations of information between the periphery and the midbrain.

Acoustic Stimulation↗
PubMed2005

Simultaneous analysis of thebaine, 6-MAM and six abused opiates in postmortem fluids and tissues using Zymark automated solid-phase extraction and gas chromatography-mass spectrometry.

Opiates are some of the most widely prescribed drugs in America and are often abused. Demonstrating the presence or absence of opiate compounds in postmortem fluids and/or tissues derived from fatal civil aviation accidents can have serious legal consequences and may help determine the cause of impairment and/or death. However, the consumption of poppy seed products can result in a positive opiate drug test. We have developed a simple method for the simultaneous determination of eight opiate compounds from one extraction. These compounds are hydrocodone, dihydrocodeine, codeine, oxycodone, hydromorphone, 6-monoacetylmorphine, morphine, and thebaine. The inclusion of thebaine is notable as it is an indicator of poppy seed consumption and may help explain morphine/codeine positives in cases where no opiate use was indicated. This method incorporates a Zymark RapidTracetrade mark automated solid-phase extraction system, gas chromatography/mass spectrometry, and trimethyl silane (TMS) and oxime-TMS derivatives. The limits of detection ranged from 0.78 to 12.5 ng/mL. The linear dynamic range for most analytes was 6.25-1600 ng/mL. The extraction efficiencies ranged from 70 to 103%. We applied this method to eight separate aviation fatalities where opiate compounds had previously been detected.

Autoanalysis↗
PubMed2004

Development of a portable immunoextraction-reversed-phase liquid chromatography system for field studies of herbicide residues.

A portable system based on immunoextraction and reversed-phase HPLC was developed for the field analysis of herbicides in groundwater and surface water. Atrazine, simazine, and cyanazine were used as model analytes for this work. These were measured in water by using three coupled columns: an anti-atrazine antibody column for the selective extraction of these analytes, a reversed-phase precolumn for their reconcentration, and a reversed-phase analytical column for their separation. Various factors were considered in the optimization of this system, including the binding properties of the immunoextraction column, the effect of flow rate on the performance of each column, the selection of sample volume, and the choice of mobile phases for the RPLC columns. A typical analysis with this system allowed the injection of one sample every 7.5 min and provided results for all three of the tested herbicides in less than 10 min. In the analysis of atrazine alone, samples could be injected every 4 min and results were obtained within 8 min. There was good correlation between this technique and a comparable benchtop system. The lower limits of detection for the given analytes were approximately 0.2-0.25 microg/L, with a linear range that extended to 20 microg/L and a dynamic range that went up to at least 100 microg/L. The use of this technique in the field was demonstrated through applications that involved the development of time and location profiles for triazine herbicides in environmental samples.

Acetonitriles↗
PubMed2006

Direct sampling of chemical weapons in water by photoionization mass spectrometry.

The vulnerability of water supplies to toxic contamination calls for fast and effective means for screening water samples for multiple threats. We describe the use of photoionization (PI) mass spectrometry (MS) for high-speed, high-throughput screening and molecular identification of chemical weapons (CW) threats and other hazardous compounds. The screening technology can detect a wide range of compounds at subacute concentrations with no sample preparation and a sampling cycle time of approximately 45 s. The technology was tested with CW agents VX, GA, GB, GD, GF, HD, HN1, and HN3, in addition to riot agents and precursors. All are sensitively detected and give simple PI mass spectra dominated by the parent ion. The target application of the PI MS method is as a routine, real-time early warning system for CW agents and other hazardous compounds in air and in water. In this work, we also present comprehensive measurements for water analysis and report on the system detection limits, linearity, quantitation accuracy, and false positive (FP) and false negative rates for concentrations at subacute levels. The latter data are presented in the form of receiver operating characteristic curves of the form of detection probability P(D) versus FP probability P(FP). These measurements were made using the CW surrogate compounds, DMMP, DEMP, DEEP, and DIMP. Method detection limits (3sigma) obtained using a capillary injection method yielded 1, 6, 3, and 2 ng/mL, respectively. These results were obtained using 1-microL injections of water samples without any preparation, corresponding to mass detection limits of 1, 6, 3, and 2 pg, respectively. The linear range was about 3-4 decades and the dynamic range about 4-5 decades. The relative standard deviations were generally <10% at CW subacute concentrations levels.

Chemical Warfare Agents↗
PubMed1990

[The problems in the ultrasonography and its countermeasure].

The problems in the ultrasonographic examination are discussed in four categories as follows; 1) Problems arising from the characteristics of the ultrasonographic equipment such as limited field of view, poor resolution in the far field, dead space in examination of the liver, etc. 2) Problems related to the operation of the equipment such as optimizing the gain, STC, dynamic range, and selection of the focal depth and dynamic focus technique. 3) Problem concerning the interpretation of the ultrasonic images such as determining the orientation of the organ displayed on the image, intra-observer divergence in interpretation of the ultrasonogram. 4) Financial problems about ultrasonography.

Humans↗
PubMed2005

Scaling of dynamics with the range of interaction in short-range attractive colloids.

We numerically study the dependence of the dynamics on the range of interaction Delta for the short-range square well potential. We find that, for small Delta, dynamics scale exactly in the same way as thermodynamics, both for Newtonian and Brownian microscopic dynamics. For interaction ranges from a few percent down to the Baxter limit, the relative location of the attractive-glass line and the liquid-gas line does not depend on Delta. This proves that, in this class of potentials, disordered arrested states (gels) can be generated only as a result of a kinetically arrested phase separation.

Journal Article↗
PubMedDate not supplied

Retinal light adaptation--evidence for a feedback mechanism.

Light adaptation is the adjustment of retinal response properties to variations in ambient illumination. It enables the encoding of visual information over a millionfold intensity range, from moonlight to broad daylight, despite the relatively small dynamic range of response of visual neurones. We have studied the effects of light adaptation on the dynamics and sensitivity of visual responses of neurones in the turtle retina, by measuring the responses of horizontal cells in the retina to light which was modulated with a sinusoidal time course around various mean levels. As a quantitative measure of the transduction from light to neural signals, we calculated the gain of response at each frequency. Gain is defined as the amplitude of the modulated response component divided by the amplitude of light modulation. We report here that the gain (mV photon-1) at low temporal frequencies decreased as the mean light level increased. Over a 2 log-unit range of mean light levels, low-frequency gain was inversely proportional to the mean light level, as in Weber's law. However, at high temporal frequencies, the gain was almost independent of mean light level. Our results are reminiscent of Kelly's results on human temporal-frequency sensitivity in various states of light adaptation. We found that a family of horizontal-cell temporal frequency responses, measured at various mean light levels, could be accounted for by a negative feedback model in which the feedback strength is proportional to mean light level.

Adaptation, Physiological↗