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PubMed1985

Manipulation of sensitivity in visual field investigation.

Sophistication of computer software and flexibility of stimulus and background luminance parameters in static perimeter design offer the opportunity for increased information in the assessment of the visual field. Relationships between dynamic ranges and resulting sensitivity gradients in a group of 10 normal 21 year old subjects using the Octopus automated perimeter, the Dicon Autoperimeter 2000 and the Friedmann VFA II are assessed. Inadequacies in the use of normative data to assess the visual field are noted. Implications for the use of dynamic range/sensitivity gradient relationships in visual field assessment without reliance on normative data are discussed.

Adult↗
PubMed1979

A new transducer for respiratory monitoring. A description of a hot-wire anemometer and a test procedure for general use.

A respiratory transducer based on the constant temperature anemometry principle has been developed for respiratory monitoring, and as a tool for bedside evaluation of pulmonary function. The transducer is characterized by a dynamic range from 0-2.5 1/s and an upper limiting frequency of 50 Hz. It is designed with a view to a low pressure drop of 2.5 mbar/1/s and a minimum dead space of 5 ml. The transducer has been tested using a generally applicable procedure which includes both static and dynamic test set-ups. The influence of variation in gas composition, temperature and pressure, together with variations in tidal volume and respiration rate, have been investigated. The results show that the transducer registers the immediate value of gas flow-rate with a mean error less than 5-10% in all situations which are predictable in clinical use. The mean error can be reduced to less than 5% when systematic errors are eliminated.

Anesthesia, General↗
PubMed2000

Enhanced analytical sensitivity of a quantitative PCR for CMV using a modified nucleic-acid extraction procedure.

Accurate and rapid diagnosis of CMV disease in immunocompromised individuals remains a challenge. Quantitative polymerase chain reaction (QPCR) methods for detection of CMV in peripheral blood mononuclear cells (PBMC) have improved the positive and negative predictive value of PCR for diagnosis of CMV disease. However, detection of CMV in plasma has demonstrated a lower negative predictive value for plasma as compared with PBMC. To enhance the sensitivity of the QPCR assay for plasma specimens, plasma samples were centrifuged before nucleic-acid extraction and the extracted DNA resolubilized in reduced volume. Optimization of the nucleic-acid extraction focused on decreasing or eliminating the presence of inhibitors in the pelleted plasma. Quantitation was achieved by co-amplifying an internal quantitative standard (IS) with the same primer sequences as CMV. PCR products were detected by hybridization in a 96-well microtiter plate coated with a CMV or IS specific probe. The precision of the QPCR assay for samples prepared from untreated and from pelleted plasma was then assessed. The coefficient of variation for both types of samples was almost identical and the magnitude of the coefficient of variations was reduced by a factor of ten if the data were log transformed. Linearity of the QPCR assay extended over a 3.3-log range for both types of samples but the range of linearity for pelleted plasma was 20 to 40,000 viral copies/ml (vc/ml) in contrast to 300 to 400,000 vc/ml for plasma. Thus, centrifugation of plasma before nucleic-acid extraction and resuspension of extracted CMV DNA in reduced volume enhanced the analytical sensitivity approximately tenfold over the dynamic range of the assay.

Centrifugation↗
PubMed1998

A computer-controlled variable light attenuator for protection and autoranging of a laser-induced fluorescence detector for capillary zone electrophoresis.

Photodetectors have a limited range over which they can measure light intensities for any particular setting. The intensity of light reaching the detector can be kept within this range by using a liquid crystal variable light attenuator controlled by a computer that continuously checks the amount of light reaching the detector and adjusts the attenuation to an appropriate level. Using such a system we have constructed an intensified charge-coupled device (ICCD) camera-based detector with a dynamic range of over six orders of magnitude which is never exposed to damaging or saturating light levels.

Animals↗
PubMed2003

Development of quantitative vitellogenin-ELISAs for fish test species used in endocrine disruptor screening.

The yolk protein precursor vitellogenin (Vtg) in plasma has proved to be a simple and sensitive biomarker for assessing exposure of fish to environmental estrogens. Within international bodies such as the Organization for Economic Cooperation and Development (OECD) work is ongoing to develop screening and testing programmes for endocrine disrupting effects of new chemicals, and in the focus of this development are the fish test species common carp (Cyprinus carpio), fathead minnow (Pimephales promelas), zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). In this study we have developed quantitative enzyme linked immunosorbent assays (ELISAs) for Vtg in common carp/fathead minnow, zebrafish and Japanese medaka. The assays were developed using a combination of monoclonal and polyclonal fish Vtg antibodies in a sandwich format, using stabilized Vtg from the test species as a standard. The carp Vtg ELISA has a working range of 1-63 ng/mL, a minimal detection limit of 0.6 ng/mL, and may also be used for quantification of Vtg in fathead minnow. In fathead minnow whole-body homogenate samples, the practical detection limit is 400 ng/mL due to the matrix effect. The zebrafish Vtg ELISA has a working range of 0.5-63 ng/mL, a minimal detection limit of 0.4 ng/mL, and a practical detection limit of 200 ng/mL in whole-body homogenate samples. The medaka Vtg ELISA has a working range of 0.25-16 ng/mL, a minimal detection limit of 0.1 ng/mL, and a practical detection limit of 125 ng/mL in whole-body homogenate samples. The intra- and inter-assay variations were below 20% for all assays. The assays were evaluated with sets of representative samples spanning the wide dynamic range of Vtg-levels found in fish exposed to environmental estrogens, and all three assays are currently undergoing international inter-laboratory validation.

Animals↗
PubMed1993

Antimasking effects of the olivocochlear reflex. II. Enhancement of auditory-nerve response to masked tones.

1. The antimasking effects of olivocochlear (OC) efferent feedback were studied in anesthetized or decerebrate cats by comparing responses of single auditory-nerve fibers (ANFs) to tone bursts in continuous masking noise seen with and without addition of a moderate-level contralateral noise known to activate the OC reflex. Responses were measured as a function of tone-burst intensity, tone-burst frequency, and masker intensity and were analyzed so as to allow quantitative estimates of the detectability of the tone bursts against the noise background. 2. Addition of the contralateral OC elicitor both increased the maximum discharge rates to the masked tone bursts and decreased the rates to the ipsilateral masker. The rate increases to the tone bursts could be explained on the basis of a decrease in adaptation caused by decreasing the steady response to the masker. The result is a steepening of the rate-versus-level function for masked tone bursts and a concomitant increase in the estimated discriminability of small increments of tone-burst intensity. 3. For tone bursts at the fiber's characteristic frequency (CF), the OC effects on detection threshold for the masked tone bursts depended on masker level, with small increases in threshold for low masker levels and somewhat larger decreases in threshold for higher masker levels. For tone bursts below CF, OC effects, when present, always decreased the detection threshold. 4. The largest antimasking effects were seen for fibers with CFs between 6 and 12 kHz and for masker levels within 20 dB of the fiber's threshold to the masker. These trends appeared to hold for fibers of all spontaneous rates (SRs). 5. Enhancement of the response to unmasked tone bursts and concomitant decrease in the "spontaneous rate" was elicited by OC activation in fibers if threshold sensitivity approached -10 dB SPL. This "enhancement-in-quiet" appears to arise when an animal-generated noise produces a continuous response (in the absence of purposely applied sound) that is suppressed by OC activity. This finding raises questions as to the range of "true" spontaneous rates in the cat. 6. The results highlight two important distinctions between the effects of OC feedback in quiet versus those in noise. In quiet, the effects are predominately suppressive and are restricted to stimuli at frequencies near a fiber's CF and at intensities within its dynamic range. In continuous background noise, the OC reflex can enhance the responses to transient stimuli. Such effects are seen throughout the fiber's response area.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Ototoxic effects of salicylates on the responses of single cochlear nerve fibres and on cochlear potentials.

Anaesthetized cats were given 400 mg/kg sodium salicylate i.v. producing blood levels in excess of 300-400 mg/kg. Within 10 min of injection, thresholds of fibers had risen by values ranging from 13 to 21 dB. The elevation in thresholds progressed rapidly over the subsequent 5 or so hours, reaching a plateau in about 10 h. The Q10 dB values for tuning of the cochlear fibres decreased by a factor of 3-4 on average over the same period. Likewise, the dynamic range of response was significantly reduced. These effects on the cochlear fibres were reflected in the elevation of the gross cochlear action potential thresholds. In contrast to the findings with other types of cochlear pathology, the mean discharge rate of the subpopulation of cochlear fibres having discharge rates above 20 sp/s was significantly increased by an average of 10-20 sp/s. There was a tendency for this increase to be more marked for fibres with higher characteristic frequencies and to be inversely related to threshold. In addition, 63% of fibres had anomalous temporal patterns of spontaneous activity. In view of the relevance of these data on the ototoxic effects of salicylates for our understanding of tinnitus, the effects of direct electrical current stimulation via the round window have been studied. Positive currents up to at least 600 microA suppressed the spontaneous and evoked activity of all cochlear fibres studied in the normal cochlea. These findings are consistent with the effects of such current stimulation in patients with tinnitus of peripheral origin and support the hypothesis that the neural correlate of such tinnitus is hyperactivity at the cochlear nerve level.

Animals↗
PubMed1994

Synergism of interleukin 1 and interleukin 6 induces serum amyloid A production while depressing fibrinogen: a quantitative analysis.

OBJECTIVE: Production of the serum amyloid A (SAA) proteins in the liver of patients with arthritis can be increased from approximately 1 microgram/ml to > 1000 micrograms/ml, while fibrinogen (Fg) can be increased from 2 to 9 mg/ml. The increases appear to be regulated by mediators similar to those found in inflamed joints, e.g., interleukins 1 and 6 (IL-1 and IL-6, respectively). The sensitivity and dose response of SAA and Fg synthesis by hepatoma cells to IL-1 and IL-6 was investigated to understand the relationship between the inflammatory cytokines produced in inflamed joints and the acute phase protein response in the liver of arthritis patients. METHODS: SAA and Fg mRNA and protein production in human Hep3B cells stimulated by human monocyte conditioned medium (CM) containing known amounts of IL-1 and IL-6, or stimulated by corresponding concentrations of recombinant IL-1 and IL-6 was analyzed by ELISA and Northern blot hybridization techniques. RESULTS: Increases in SAA mRNA and protein were dose dependent in the presence of IL-1 and IL-6 at concentrations ranging from 0.1 and 1 ng/ml, respectively, to 10 and 100 ng/ml, respectively. In the presence of IL-1 receptor antagonist (IL-1ra), there was a 75% decrease in SAA production and > 100% increase in Fg production by cells stimulated with CM. CONCLUSION: Our results demonstrate that the thousand fold dynamic range associated with the acute phase SAA response requires IL-1 acting synergistically with cytokine(s) like IL-6. Optimum conditions for apoSAA production are suboptimal for Fg as indicated by the differential effects of IL-1ra.

Carcinoma, Hepatocellular↗
PubMed1989

Characterization of cat nasal afferents and brain stem neurones receiving ethmoidal input.

Stimulation of the nasal mucous membrane can initiate protective reflexes, particularly sneezing and apnea. Very little is known about the receptors in the nasal cavity responsible for initiating these reflexes, which are thought to be mediated by trigeminal rather than olfactory pathways. In the cat, the ethmoidal branch of the ophthalmic division of V carries this afferent information. The objectives of the present study were to determine a set of adequate nasal receptor stimuli capable of initiating these protective reflexes; to characterize the types of information carried in the ethmoidal nerve afferents, by recording from single fibers dissected from the nerve; to determine the conduction velocities of these afferents, by recording from the cell bodies of ethmoidal afferents in the trigeminal ganglion; and to study the second-order neurones in the brain stem on which these afferents make contact. Results of single fiber recording indicated that, in addition to being tactile, approximately half of the neurones studied also responded to noxious chemical stimuli. The conduction velocity of the majority of these afferents were found to be in the A-delta range. Second-order neurones in spinal trigeminal nucleus which had an input from the ethmoidal nerve could be divided into two classifications: (i) low threshold mechanoreceptive (LTM) neurones which received light tactile input and did not respond to noxious chemical or mechanical stimuli applied to the nasal cavity, and (ii) wide dynamic range (WDR) neurones which responded to both noxious and nonnoxious chemical or mechanical stimuli applied to the nasal cavity.

Afferent Pathways↗
PubMed2001

Development of a flow injection capillary chemiluminescent ELISA using an imprinted polymer instead of the antibody.

A flow injection competitive assay analogous to enzyme immunoassays has been developed using a molecularly imprinted polymer instead of the antibody. A glass capillary was modified by covalently attaching an imprinted polymer to the inner capillary wall. The herbicide 2,4-dichlorophenoxyacetic acid was used as a model analyte. The analyte was labeled with tobacco peroxidase, and chemiluminescence was used for detection in combination with a photomultiplier tube or a CCD camera. In a competitive mode, the analyte-peroxidase conjugate was passed together with the free analyte through the polymer-coated capillary mounted in a flow system. After a washing step, the chemiluminescent substrate was injected and the bound fraction of the conjugate was quantified by measuring the intensity of the emitted light. Calibration curves corresponding to analyte concentrations ranging from 0.5 ng mL(-1) to 50 microg mL(-1) (2.25 nM-225 microM) were obtained. A lowered detection limit by 2 orders of magnitude was obtained when detection was done in discontinuous mode and the chemiluminescence light was conducted inside the photomultiplier tube by an optical fiber bundle, thus yielding a dynamic range of 5 pg mL(-1)-100 ng mL(-1) (22.5 pM-450 nM).

2,4-Dichlorophenoxyacetic Acid↗
PubMed1984

[Systems theory of ultrasound pulse echo technic (2)].

Part two explains the terms, spatial resolution, range ambiguity and maximum frame rate of diagnostic pulse echo systems. Then the idealised system described in part one is completed by incorporating various band pass filters, which represent the effects of resonant piezoelectric transducers and electric filters of the TGC amplifiers. The influence of such band limiting components on spatial resolution and dynamic range are shown by numerical examples. Mathematical derivations are restricted to the necessary minimum and all formulae are illustrated by means of a substantial number of graphs.

Humans↗
PubMed2005

Sub-Tg dynamics in polycarbonate by neutron scattering and its relation with secondary gamma relaxation.

We have investigated the dynamics of phenylene rings in glassy bisphenol-A (BPA) polycarbonate (PC) by means of quasielastic neutron scattering. Taking advantage of selective deuteration of the samples, we have studied the incoherent scattering of hydrogens in phenylene rings on the one hand, and on the other hand the coherent quasielastic scattering of all the atoms in the sample. Two different types of neutron spectrometers, time of flight and backscattering, were used in order to cover a wide dynamic range, which extends from microscopic (approximately 10(-13) s) to mesoscopic (approximately 10(-9) s) times. Moreover, neutron-diffraction experiments with polarization analysis were carried out in order to characterize the structural features, and the relative coherent and incoherent contributions of the samples investigated. In contrast with previous studies of phenylene ring dynamics in BPA polysulfone performed by us also by neutron scattering, phenylene rings in BPA PC exhibit an "extra" motion in addition to those found for BPA polysulfone's phenylene rings. This extra motion of the rings in PC perfectly correlates with the main carbonate group motion followed by dielectric spectroscopy and allows us to (i) consistently interpret the PC's gamma relaxation in terms of two different motions; and (ii) experimentally confirm the relation between the motion of phenylene rings and carbonate groups within BPA PC formerly predicted by computational methods.

Journal Article↗
PubMed2002

High-cut characteristics of the baroreflex neural arc preserve baroreflex gain against pulsatile pressure.

A transfer function from baroreceptor pressure input to sympathetic nerve activity (SNA) shows derivative characteristics in the frequency range below 0.8 Hz in rabbits. These derivative characteristics contribute to a quick and stable arterial pressure (AP) regulation. However, if the derivative characteristics hold up to heart rate frequency, the pulsatile pressure input will yield a markedly augmented SNA signal. Such a signal would saturate the baroreflex signal transduction, thereby disabling the baroreflex regulation of AP. We hypothesized that the transfer gain at heart rate frequency would be much smaller than that predicted from extrapolating the derivative characteristics. In anesthetized rabbits (n = 6), we estimated the neural arc transfer function in the frequency range up to 10 Hz. The transfer gain was lost at a rate of -20 dB/decade when the input frequency exceeded 0.8 Hz. A numerical simulation indicated that the high-cut characteristics above 0.8 Hz were effective to attenuate the pulsatile signal and preserve the open-loop gain when the baroreflex dynamic range was finite.

Animals↗
PubMed2004

Dynamic properties of antennal responses to pheromone in two moth species.

Dynamic properties of pheromone plumes are behaviorally important in some moths for inducing upwind flight, but little is known about the time-dependent properties of odor transduction or the mechanisms that limit receptor dynamic sensitivity. We stimulated male antennae of two moth species, Cadra cautella and Spodoptera exigua, with pheromone plumes in a wind tunnel while recording electroantennograms (EAG) and concentration of a surrogate plume (propylene, which mimics a pheromone plume) using a photoionization detector (PID). Turbulent plumes were produced by mechanical baffles, creating broad frequency range dynamic concentration changes at the antennae. Frequency response functions and coherence functions between PID and EAG signals were used to measure the dynamic responses of the two species to pheromone blends and individual components. A single time constant filter fitted the responses of both species, but S. exigua was about three times faster than C. cautella. Responses to individual pheromone components were significantly different in S. exigua but not in C. cautella. We also fitted the data with a simple block-structured nonlinear cascade. This supported the simple filter model but also suggested that the response saturates at an early stage of chemotransduction.

Action Potentials↗
PubMed1996

Intracavity laser polarization spectrometer for biomolecule traces.

A polarization variant of an intracavity laser spectrometer based on the competition of beams in an argon ion laser, radiating a number of narrow lines in the 275 to 529 nm spectral range, is proposed and described for the spectral analysis of liquid samples, having broad absorption bands, mainly biomolecules in solutions. By careful optimization of the operating conditions, a procedure has been established that results in a minimal measurable absorbance decreased up to 10(-5) units of optical density. The examined spectrometer provides a wide dynamic range of analysis. A determination of trace contents of amino acids in methanol were carried out.

Journal Article↗
PubMed2006

Detection and monitoring of virus infections by real-time PCR.

The employment of polymerase chain reaction (PCR) techniques for virus detection and quantification offers the advantages of high sensitivity and reproducibility, combined with an extremely broad dynamic range. A number of qualitative and quantitative PCR virus assays have been described, but commercial PCR kits are available for quantitative analysis of a limited number of clinically important viruses only. In addition to permitting the assessment of viral load at a given time point, quantitative PCR tests offer the possibility of determining the dynamics of virus proliferation, monitoring of the response to treatment and, in viruses displaying persistence in defined cell types, distinction between latent and active infection. Moreover, from a technical point of view, the employment of sequential quantitative PCR assays in virus monitoring helps identifying false positive results caused by inadvertent contamination of samples with traces of viral nucleic acids or PCR products. In this review, we provide a survey of the current state-of-the-art in the application of the real-time PCR technology to virus analysis. Advantages and limitations of the RQ-PCR methodology, and quality control issues related to standardization and validation of diagnostic assays are discussed.

Computer Systems↗
PubMed2006

Temporal processing and adaptation in the songbird auditory forebrain.

Songbird auditory neurons must encode the dynamics of natural sounds at many volumes. We investigated how neural coding depends on the distribution of stimulus intensities. Using reverse-correlation, we modeled responses to amplitude-modulated sounds as the output of a linear filter and a nonlinear gain function, then asked how filters and nonlinearities depend on the stimulus mean and variance. Filter shape depended strongly on mean amplitude (volume): at low mean, most neurons integrated sound over many milliseconds, while at high mean, neurons responded more to local changes in amplitude. Increasing the variance (contrast) of amplitude modulations had less effect on filter shape but decreased the gain of firing in most cells. Both filter and gain changes occurred rapidly after a change in statistics, suggesting that they represent nonlinearities in processing. These changes may permit neurons to signal effectively over a wider dynamic range and are reminiscent of findings in other sensory systems.

Acclimatization↗
PubMed1998

ASIC-based event-driven 2D digital electron counter for TEM imaging.

A two-dimensional application specific integrated circuit (ASIC) based detector, designed for X-ray protein crystallography, has been tested to determine its suitability as a direct electron detector for TEM imaging in the voltage range of 20-400 keV. Several markedly different properties of this device distinguish it from the charge coupled device (CCD) detectors: (1) the ASIC detector can be used directly under electron bombardment in the voltage range stated above, therefore requiring no scintillator screen; (2) each active pixel of the device is an electron counter and generates digital output independently; (3) the readout of the device is frameless and event driven; (4) the device can be operated at the room temperature and is nearly noise free; and (5) the counting dynamic range of the device is virtually unlimited. It appears that an imaging system based on this type of device would be ideal for low-dose TEM imaging and online diffraction observation and recording, as well as more conventional imaging, providing the many advantages of direct digital readout for almost all applications.

Crystallography, X-Ray↗