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At least 613 records · Page 34Linked to original sources
PubMed2003

Development of an electrochemical immunosensor for alanine aminotransferase.

Alanine aminotransferase (ALT) has been regarded as one of the most sensitive indicators of hepatocellular damage. While ALT is widely used in the practice of medicine, few attempts have been made to develop biosensors applicable to the on-site diagnosis of liver diseases. In the hope of developing an immunosensor for measurement of ALT activity, we have generated monoclonal antibodies to human recombinant ALT and fabricated them for use in a sensor. The ALT immunosensor was composed of the followings: (1) anti-ALT antibody-immobilized outer membrane; (2) pyruvate oxidase-absorbed inner membrane; (3) a self assembled monolayer mediator-coated gold working electrode and an Ag/AgCl reference electrode. The chronoamperometric measurement of the immunosensor was performed with 40 microl of PBS containing substrates and ALT without a washing step in less than 5 min. The dynamic range of ALT immunosensor was presented as five orders of magnitude, ranging between 10 pg/ml and 1 microg/ml. The detection limit and the sensitivity were 10 pg/ml and 26.3 nA/(ng/ml), respectively. In the meantime, the enzyme sensor fabricated without anti-ALT antibody showed much poorer analytical values. The dynamic range, the detection limit, and the sensitivity were 10 ng/ml-100 microg/ml, 10 ng/ml and 11.4 nA/(ng/ml), respectively. The presented results indicated that the immunosensor system provided much better technical performance in all of the aspects evaluated than did the enzyme sensor without the immobilized-antibody.

Adsorption↗
PubMed2000

Monaural and binaural loudness measures in cochlear implant users with contralateral residual hearing.

OBJECTIVE: The aim was to measure the loudness of monaural and binaural stimuli in a group of cochlear implant users who had residual hearing in the nonimplanted ear, and to consider the implications of these measures for a binaural fitting consisting of a hearing aid and an implant in opposite ears. Three independent hypotheses were addressed: that the shapes of the electric and acoustic loudness growth functions would be similar, although the dynamic ranges would differ; that standard implant and hearing aid fittings would result in substantial loudness mismatches between the acoustic and electric signals; and that loudness summation would occur for binaural combinations of electric and acoustic signals. DESIGN: A modified version of the "Loudness Growth in 1/2-Octave Bands" method (Allen, Hall, & Jeng, 1990) was used to measure loudness growth for each ear of nine subjects. At the time of the experiment, the subject group included all implant users in Melbourne and Denver who were available for research and who also had sufficient residual hearing to use a hearing aid in the nonimplanted ear. Five acoustic frequencies and five electrodes were measured for each subject. The same subjects also estimated the loudness of a set of stimuli including monaural and binaural signals chosen to cover the loudness range from very soft to loud. RESULTS: The shapes of the averaged loudness growth functions were similar in impaired and electrically stimulated ears, although the shapes of iso-loudness curves were quite different in the two ears, and dynamic ranges varied considerably. Calculations based on the psychophysical data demonstrated that standard fitting procedures for cochlear implants and hearing aids lead to a complex pattern of loudness differences between the ears. A substantial amount of loudness summation was observed for the binaural stimuli, with most summation occurring when the acoustic and electric components were of equal loudness. This is consistent with observations for subjects with normal hearing and subjects with bilaterally impaired hearing. CONCLUSIONS: These experiments provide data on which criteria and methods for the binaural fitting of cochlear implants and hearing aids may be based. It is unlikely that standard monaural fitting methods for cochlear implants and hearing aids will result in balanced loudness between the two ears across a reasonably broad range of frequencies and levels. It is also likely that output levels of both devices will need to be reduced relative to a monaural fitting to compensate for the binaural summation of loudness in some listeners.

Adult↗
PubMed2001

[Specific aspects of rhinomanometry in children with nasal septum deformity in the region of absorbing part of the nasal valve].

Available are original data on rhinomanometry in children with nasal septum distortion in the anterior part. Nasal patency before and after anemisation of the mucosa was measured in health and disease. Pressure in collapse of the nasal valve in children is higher than in adults, while dynamic range of the valve action in growing flow of the inspired air is more noticeable. In distortion of the nasal septum at the level of the absorbing part of the nasal valve anemisation reduces the air flow while the dynamic range is not detected. It is discussed whether early surgical intervention in children under sparing approach to nasal structures is valid.

Child↗
PubMedDate not supplied

Encoding strategies for three-direction phase-contrast MR imaging of flow.

Three encoding strategies for the measurement of flow velocities in arbitrary directions with phase-contrast magnetic resonance imaging are presented; their noise and dynamic range performance are compared by means of theoretical analysis and computer simulation. A six-point measurement strategy is shown to be quite inefficient in terms of velocity variance per unit time. A simple four-point method exhibits equal dynamic range; its noise depends on flow direction but on average is equal to that of the six-point method. An alternate, balanced four-point method has noise that is direction independent and has, depending on implementation, possibly lower noise levels. Either four-point method is more efficient and is preferred over the six-point approach.

Blood Flow Velocity↗
PubMed1984

The representation of contrast and other stimulus parameters by single neurons in area 17 of the cat.

The responses of neurons in area 17 were tested as a function of various stimulus parameters. The thresholds of individual cortical neurons were at contrasts between 0.01 and 0.1 (increment of 0.5 X 10(-1) cd/m-2 on a background of 3 cd/m-2), the dynamic ranges were 1.0-2.0 log units of increment, and all cells showed a response decrease at increments above a certain maximum (supersaturation response). The averaged contrast/response curve for all neurons was S-shaped in the logarithmic plot, had a dynamic range of 2.5 log units, reached its maximum at a contrast of 0.75 and supersaturated above this level. The contrast/sensitivity curves changed their slope under different stimulus conditions. They became flatter when the non-dominant eye was stimulated as compared to dominant eye stimulation or when the stimulation was done at a non-optimal orientation or direction, and they became steeper when both eyes were stimulated. But the maximum was reached at the same contrast and supersaturation was seen above maximum contrast no matter whether a cell was strongly (e.g. binocular stimulation at optimal orientation) or weakly excited (non-dominant or non-optimal orientation stimulation). After normalization, the averaged population contrast/response curves were virtually identical at all stimulus conditions. It was concluded, that range as well as maximum and supersaturation of cortical contrast/response curves are determined before the input reaches the cortex, and that the cortical cells summate, essentially, linearly. The findings furthermore demonstrate that the supersaturation of the cortical input must be due to subtractive inhibition, and that the same is true for the orientation sensitive inhibition in the cortex itself. Both, the peripheral contrast and the cortical orientation dependent inhibition cannot be explained by multiplicative inhibition. The fact, that the responses of neurons depend on many variables relativates their significance for feature representation.

Animals↗
PubMed1981

Primary afferent and sacral dorsal horn neuron responses to vaginal probing in the cat.

An analysis was made of primary afferent and dorsal horn neuron responses to stimulation of genitalia of female cats. Three types of primary afferents responded to vaginal probing. The most common type responded maximally to the on- and off-ramps of non-noxious pressure applied directly to the clitoris. A second type responded similar but to surrounding labia mucosa. The third type showed a tonic discharge during deep vaginal-cervical probing. None of the primary afferents that responded to vaginal probing exhibited after-responses to any stimulus. However, a majority (76%) of wide dynamic range dorsal horn neurons showed increased rates of firing that outlasted the duration of vaginal probing by at least 28 sec. No other type of dorsal horn neuron responded in this manner. It appears that after-responses of wide dynamic range neurons to vaginal stimulation cannot be attributed to after-responses of primary afferents or to supraspinal mechanisms but are produced by mechanisms within the spinal cord.

Animals↗
PubMed1983

Multichannel electrical stimulation of the auditory nerve in man. I. Basic psychophysics.

Basic psychophysical measurements were obtained from three patients implanted with multichannel cochlear implants. This paper presents measurements from stimulation of a single channel at a time (either monopolar or bipolar). The shape of the threshold vs. frequency curve can be partially related to the membrane biophysics of the remaining spiral ganglion and/or dendrites. Nerve survival in the region of the electrode may produce some increase in the dynamic range on that electrode. Loudness was related to the stimulus amplitude by a power law with exponents between 1.6 and 3.4, depending on frequency. Intensity discrimination was better than for normal auditory stimulation, but not enough to offset the small dynamic range for electrical stimulation. Measures of temporal integration were comparable to normals, indicating a central mechanism that is still intact in implant patients. No frequency analysis of the electrical signal was observed. Each electrode produced a unique pitch sensation, but they were not simply related to the tonotopic position of the stimulated electrode. Pitch increased over more than 4 octaves (for one patient) as the frequency was increased from 100 to 300 Hz, but above 300 Hz no pitch change was observed. Possibly the major limitation of single channel cochlear implants is the 1-2 ms integration time (probably due to the capacitative properties of the nerve membrane which acts as a low-pass filter at 100 Hz). Another limitation of electrical stimulation is that there is no spectral analysis of the electrical waveform so that temporal waveform alone determines the effective stimulus.

Auditory Threshold↗
PubMed2006

Effects of pulse rate on thresholds and loudness of biphasic and alternating monophasic pulse trains in electrical hearing.

Detection thresholds and most comfortable loudnesses (MCLs) were determined as a function of pulse rate for standard biphasic pulse trains (BP) and for anodic and cathodic monophasic phases alternating at fixed intervals (ALT-m). Three different phase durations were examined. With a 100-micros phase duration, thresholds for the ALT-m stimulus were substantially (up to 12 dB) lower than for the BP stimuli at relatively low rates (200 pps), but were similar to the BP thresholds at high rates (1000 pps). Thresholds for BP pulse trains decreased monotonically with increasing rate, whereas the function for ALT-m waveforms was non-monotonic with a maximum between 400 and 1000 pps. These trends occurred for three different cochlear implant devices, different electrode configurations, and, generally, for different phase durations (10.8, 25, and 100 micros/phase). However, at the shorter phase durations, thresholds remained lower for the ALT-m stimulus, even at 5000 pps, the highest rate studied. Dynamic ranges of the BP pulse trains increased with increasing rate, irrespective of the phase duration under test, but for the ALT-m stimuli this was only true at the shorter phase durations tested. At a 100-mus phase duration, dynamic ranges for the ALT-m waveforms did not differ significantly as a function of rate. The results confirm previous reports that delaying charge recovery, in this case by switching from a BP to an ALT-m wave shape, can substantially reduce thresholds [Van Wieringen, A., Carlyon, R.P., Laneau, J., Wouters, J., 2005. Effects of waveform shape on human sensitivity to electrical stimulation of the inner ear. Hear. Res. 200, 73-86; Carlyon, R.P., van Wieringen, A., Deeks, J.M., Long, C.J., Lyzenga, J, Wouters, J., 2005. Effect of inter-phase gap on the sensitivity of cochlear implant users to electrical stimulation. Hear. Res. 205, 210-224]. However, at high pulse rates, this advantage only occurs at short phase durations. In addition, we show that the complex interaction between the effects of pulse shape, rate, and phase duration on thresholds can be captured by the simple linear model described by Carlyon et al.

Adult↗
PubMed2005

Paradoxical strategy for treating chronic diseases where the therapeutic effect is derived from compensatory response rather than drug effect.

Reversing chronic conditions remains an elusive goal of medicine. The modern medical paradigm based on blocking overactive pathways or augmenting deficient pathways offers symptomatic benefit, but tolerance to therapy can develop and treatment cessation can produce rebound symptoms due to compensatory mechanisms. We propose a paradoxical strategy for treating chronic conditions based on harnessing compensatory mechanisms for therapeutic benefit. Many current drugs may be repurposed for a paradoxical indication where the therapeutic effect is derived from compensatory response, rather than drug effect. For example, although exercise is associated with acute adrenergia, paradoxical downregulation of baseline sympathovagal ratio occurs as a remodeling response. For conditions that manifest chronic sympathetic bias such as cardiovascular diseases, judicious administration of adrenergic agonists may induce compensatory downregulation of baseline sympathovagal ratio. The concept may generalize to many other diseases, especially those involving pathways which exhibit strong homeostatic tendencies such as the neurologic, immune, and endocrine systems. Careful consideration of chronobiologic features is necessary to optimize dosing strategies for modulating compensatory responses, and eccentric dosing schedules, shorter-acting formulations, or pulsatile delivery may be desirable in some cases. To what extent the effect of desensitization to current therapy is mistaken for disease progression in conditions such as diabetes, myopia, depression, and hypertension warrants investigation. The merits of combining behavioral and drug therapies such as diet-insulin therapy for diabetes and exercise-beta-blockade for cardiovascular disease should be revisited since there is a risk for exacerbating the underlying dysfunction. The reduced dynamic range of various environmental experiences and the tendency to revert to the mean through medical intervention, thermoregulation, and other modern lifestyle changes may play under-recognized roles in human diseases. Perhaps alternating agonists and antagonist may exercise the entire dynamic range of pathways and improve health.

Adrenergic Agonists↗
PubMed2006

Electromotile hearing: acoustic tones mask psychophysical response to high-frequency electrical stimulation of intact guinea pig cochleae.

When sinusoidal electric stimulation is applied to the intact cochlea, a frequency-specific acoustic emission can be recorded in the ear canal. Acoustic emissions are produced by basilar membrane motion, and have been used to suggest a corresponding acoustic sensation termed "electromotile hearing." Electromotile hearing has been specifically attributed to electric stimulation of outer hair cells in the intact organ of Corti. To determine the nature of the auditory perception produced by electric stimulation of a cochlea with intact outer hair cells, guinea pigs were tested in a psychophysical task. First, subjects were trained to report detection of sinusoidal acoustic stimuli and dynamic range was assessed using response latency. Subjects were then implanted with a ball electrode placed into scala tympani. Following the surgical implant procedure, subjects were transferred to a task in which acoustic signals were replaced by sinusoidal electric stimulation, and dynamic range was assessed again. Finally, the ability of acoustic pure-tone stimuli to mask the detection of the electric signals was assessed. Based on the masking effects, it is concluded that sinusoidal electric stimulation of the intact cochlea results in perception of a tonal (rather than a broadband or noisy) sound at a frequency of 8 kHz or above.

Acoustics↗
PubMed2001

Time-resolved laser-induced plasma spectrometry for determination of minor elements in steelmaking process samples.

A pulsed Nd:YAG laser operating on the fourth (266 nm) and second (532 nm) harmonics has been used to generate plasmas on the target surface in air at atmospheric pressure. The influence of wavelength on quantitative analysis of 4 minor elements in stainless steel samples (Si, Ti, Nb and Mo) was investigated. Stainless steel samples with different elemental concentrations were prepared and analyzed by laser-induced plasma spectrometry (LIPS). The effect of laser wavelength on analytical figures of merit (calibration curves, correlation coefficients, linear dynamic ranges, analytical precision, and accuracy values) was found to be negligible when internal standardization (an Fe line) and time-resolved laser-induced plasma are employed. For both wavelengths, the calibration curves presented a good linearity and an acceptable linear dynamic range in the concentration interval investigated. For the four elements studied, limits of detection lower than 150 microg g(-1) were achieved. To evaluate the influence of wavelength on precision and accuracy, a set of fifteen high-alloyed steel samples from different stages of steelmaking process have been analyzed. Finally, the long-term stability of the analytical measurements for Mo with 532 nm wavelength has been discussed. RSD values were lower than 5.3% for the elements studied.

Journal Article↗
PubMedDate not supplied

Natural images and contrast encoding in bipolar cells in the retina of the land- and aquatic-phase tiger salamander.

Intracellular recordings were obtained from 57 cone-driven bipolar cells in the light-adapted retina of the land-phase (adult) tiger salamander (Ambystoma tigrinum). Responses to flashes of negative and positive contrast for centered spots of optimum spatial dimensions were analyzed as a function of contrast magnitude. On average, the contrast/response curves of depolarizing and hyperpolarizing bipolar cells in the land-phase animals were remarkably similar to those of aquatic-phase animals. Thus, the primary retinal mechanisms mediating contrast coding in the outer retina are conserved as the salamander evolves from the aquatic to the land phase. To evaluate contrast encoding in the context of natural environments, the distribution of contrasts in natural images was measured for 65 scenes. The results, in general agreement with other reports, show that the vast majority of contrasts in nature are very small. The efficient coding hypothesis of Laughlin was examined by comparing the average contrast/response curves of bipolar cells with the cumulative probability distribution of contrasts in natural images. Efficient coding was found at 20 cd/m2 but at lower levels of light adaptation, the contrast/response curves were much too shallow. Further experiments show that two fundamental physiological factors-light adaptation and the nonlinear transfer across the cone-bipolar synapse are essential for the emergence of efficient contrast coding. For both land- and aquatic-based animals, the extent and symmetry of the dynamic range of the contrast/response curves of both classes of bipolar cells varied greatly from cell to cell. This apparent substrate for distributed encoding is established at the bipolar cell level, since it is not found in cones. As a result, the dynamic range of the bipolar cell population brackets the distribution of contrasts found in natural images.

Adaptation, Ocular↗
PubMed1997

[The effects of isoflurane on the formalin-induced activity in the spinal dorsal horn of transected cat].

Although the formalin test is widely used in rodents, the electrical response to this stimulus and the effect of isoflurane on this response, has not been well understood in cats. We have therefore examined the effect of isoflurane on spinal wide-dynamic-range neuronal activity evoked by a subcutaneous (s.c.) formalin injection in cats. In decerebrate, spinal cord-transected cats (L 1-2), a s.c. injection of formaldehyde solution (0.05 ml; 5%) was performed in the receptive fields of spinal wide-dynamic-range neurons at the hind paw. Isoflurane (1.5%) inhalation was given 20 mins prior to formalin injection or 5 mins after the formalin injection. The formalin injection elicited an immediate and continuous discharge or burst activity in the neurons that lasted at least 90 min. Inhaled isoflurane was found to markedly inhibit this neuronal discharge. At 30 mins after discontinuing of isoflurane, the neuronal activity in both groups recovered to approximately 55% of the control value. These results suggest that formalin injection will reliably produce a continuous burst of neuronal activity in the spinal dorsal horn of cats, and that this activity can be markedly reduced by isoflurane. The ability of isoflurane to inhibit this neuronal response was not temporally related to the formalin injection.

Administration, Inhalation↗
PubMed2005

Platform influence on DNA microarray data in postmortem brain research.

In addition to the substantial biological diversity among humans, our limited ability to reliably measure expression changes of small magnitude significantly reduces our capacity to obtain convergent sets of transcriptome data in postmortem brain. In particular, differences in the structure and sensitivity/reproducibility of microarray platforms, and in the variety of tools used to analyze microarray data, strongly influence experimental outcome. In order to better understand the sensitivity, dynamic range, and reproducibility of three common DNA microarray platforms, we compared two human postmortem samples on cDNA microarrays with dual-fluorescence, oligonucleotide GeneChips (Affymetrix), and single-color gel matrix deposited CodeLink oligonucleotide arrays. All three microarray platforms reported a good dynamic range and high correlation in replicate experiments, but they failed to consistently identify the same genes as differentially expressed between the same samples. Given their reproducibility and proven accuracy, different microarray platforms appear to be measuring different things by nature of their design and function. This needs to be taken into account when comparing data across studies.

Brain↗
PubMed2000

Study of near infrared technology for intracranial hematoma detection.

Although intracranial hematoma detection only requires the continuous wave technique of near infrared spectroscopy (NIRS), previous studies have shown that there are still some problems in obtaining very accurate, reliable hematoma detection. Several of the most important limitations of NIR technology for hematoma detection such as the dynamic range of detection, hair absorption, optical contact, layered structure of the head, and depth of detection are reported in this article. A pulsed light source of variable intensity was designed and studied in order to overcome hair absorption and to increase the dynamic range and depth of detection. An adaptive elastic optical probe was made to improve the optical contact and decrease contact noise. A new microcontroller operated portable hematoma detector was developed. Due to the layered structure of the human head, simulation on a layered medium was analyzed experimentally. Model inhomogeneity tests and animal hematoma tests showed the effectiveness of the improved hematoma detector for intracranial hematoma detection.

Absorption↗
PubMed1987

Quantitative phase-flow MR imaging in dogs by using standard sequences: comparison with in vivo flow-meter measurements.

For evaluation of the feasibility and clinical potential of using the phase data from standard MR imaging sequences to measure blood flow, 11 vessels with diameters of 4 to 7 mm were imaged in seven dogs. The flow in either the superior mesenteric vein or the inferior vena cava was measured first at laparotomy (in ml/min) with electromagnetic flow meters. Immediately thereafter, these vessels were imaged by MR in 25-mm thick sections by using a standard spin echo (SE) 750/30 sequence with a Philips 0.5-T imager. Previous phase-flow calibration of the imager and sequence allowed calculation of the blood flow rates from the phase images that were used to measure the vessels' cross-sectional areas and blood phase values. Comparison of the measurements obtained with each technique showed a significant correlation (r = .977, p less than .05) between MR-imaging values and flow-meter measurements when the blood velocity was less than approximately 40 cm/sec, the known upper limit of the flow dynamic range for the MR hardware and sequence used. There was no correlation for blood velocities greater than 40 cm/sec. However, the range of blood flow velocities in dogs and man extends to more than 100 cm/sec. Thus, these results suggest that this technique might yield valuable adjunctive flow data in routine clinical imaging provided that improvements in hardware and software permit a larger dynamic range.

Animals↗
PubMed1996

Marginal shell of the anteroventral cochlear nucleus: intensity coding in single units of the unanesthetized, decerebrate cat.

Single units were recorded in the marginal shell (38 units in 10 cats) and central core (62 units in 15 cats) of the anteroventral cochlear nucleus (AVCN) in unanesthetized decerebrate cats. The recording sites of the shell units were verified in reconstructed electrode tracks, and those of the core units were verified for 18 units and based on the recording depth for 44 units. There was a substantial presence of strongly driven units in the AVCN shell exhibiting non-saturating rate-level functions to pure tone, noise or both with dynamic ranges as wide as 89 dB. This finding supports a hypothesis that the AVCN shell may play a role in encoding acoustic stimulus intensity. The AVCN shell and core populations were different as follows. The shell population had more units which had wide dynamic ranges, low spontaneous rates (SRs) or were acoustically weakly or not driven than the core population. These differences were statistically significant (P < 0.001, Fisher's exact test).

Animals↗
PubMed2006

Correlation of the turbo-MP RIA with ImmunoCAP FEIA for determination of food allergen-specific immunoglobulin E.

It has been reported that in vitro measurement of food-specific IgE can be used to accurately predict food allergy and reduce the risk associated with double-blinded placebo-controlled food challenges (DBPCFC). Our objective was to assess the performance characteristics of the Hycor Turbo-MP quantitative radioimmunoassay for food-specific IgE and to determine this method's comparability to another assay, the Pharmacia ImmunoCAP fluorescence enzyme immunoassay (FEIA). The dynamic range of the Turbo-MP assay is 0.05 to 100 IU/ml, compared to 0.35 to 100 IU/ml for the FEIA. Performance characteristics of the Turbo-MP assay (ie, reproducibility of the calibration curve, within-run precision, total precision, parallelism, and linearity) were determined using samples from the Hycor serum bank. The precision (CV) of IgE calibrator replicates was <10%. The total precision (CV) of the Turbo-MP assay ranged from 8.8% to 18.4% for specific IgE concentrations between 0.28 to 31.4 IU/ml. Testing of serial dilutions of sera with IgE specificities for egg white, cow's milk, codfish, wheat, peanut, and soybean showed that the assay is linear over the entire dynamic range. Serial dilution data (slopes of 1.01 to 1.10) showed parallelism to serial dilutions of the IgE calibrator (slope of 0.96). The Turbo-MP and FEIA methods were both used for quantitative assays of food-specific IgE in 457 serum samples obtained from a clinical reference laboratory. Comparison of specific IgE results by the Turbo-MP and FEIA methods for 6 major food allergens exhibited a slope of 0.99 (0.92 to 1.03) with a correlation coefficient of 0.81.

Allergens↗