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PubMedDate not supplied

Improving the reliability of pattern electroretinogram recording.

The pattern electroretinogram (PERG) is a small electrical response of the retina to a reversing checkerboard pattern, usually less than 6 microV in amplitude. Unfortunately, the PERG can be obscured by artifacts such as blinks, eye movements, poor fixation, and amplifier saturation. Amplitude criterion artifact rejection systems found on commercial signal averagers eliminate large amplitude artifacts but are insensitive to small amplitude artifacts associated with amplifier saturation. Such saturation often occurs for several recording sweeps after large amplitude signals such as eye blinks are rejected. The presence of post-saturation artifacts complicates clinical PERG analysis. In this paper we describe procedures to remove these small amplitude artifacts from the PERG. These include computer selection of inputs for averaging and use of tracings with small input numbers to approximate PERG amplitudes. These procedures greatly reduce the variability of PERG amplitudes in the normal population, making PERG amplitude a more reliable clinical measure.

Adolescent↗
PubMed1996

Pesticide residue analyses in plant material by chromatographic methods: clean-up procedures and selective detectors.

This paper deals with the analysis of pesticide residues by chromatographic methods in samples of plant origin. Emphasis is put on the isolation and clean-up steps of the sample preparation for GC or LC determination. The problems of the extraction solvent selection and clean-up procedures using different types of adsorption column chromatography or gel permeation chromatography are discussed. Attention is also given to alternative techniques such as supercritical fluid extraction (SFE), matrix solid-phase dispersion (extraction) (MSPD) and sweep co-distillation that are used for sample processing prior to GC and LC analysis. Currently, pesticide residue analyses are typically multi-residue procedures with highly sensitive methods. Consumption of costly and toxic solvents is being minimized and fully automated analytical procedures can be expected in the future.

Chromatography↗
PubMed2001

Heterogeneity of Helicobacter pylori cag genotypes in experimentally infected mice.

Our aim was to assess whether the Helicobacter pylori population recovered from experimentally infected mice show heterogeneity in cag genotypes. Wild-type FVB/N mice were challenged with strain Hp1 and sacrificed 8 weeks later. Direct PCR on gastric tissue was performed using primers for glmM and cagA, and for these two genes and for cagE and virB11 using DNA from the infecting and the emerging strains. The gastric tissues of two of five mice were PCR+ for glmM but not cagA. For the infecting strain, the PCRs for all four genes studied were strongly positive, but the sweeps from the emerging strains from both mice gave weaker signals for cagA and cagE. Examination of single colonies showed reduced or absent signals for cagA and cagE in relation to glmM and virB11. Serial dilution PCR of sweep isolates from the mice showed a 10- to 100-fold decrease in cagA signal compared to the infecting strain. The decrease of cagA and cagE, but not virB11, amplification and lack of cagA hybridization in Southern blots indicates a selective loss of the right half of the cag island during murine infection. This phenomenon is consistent with host-induced adaptive changes of cag genotype in the population of colonizing H. pylori cells.

Animals↗
PubMed1977

[M- and real-time b-scan diagnostic criteria and pit-falls in right ventricular volume overload (author's transl)].

The observation of a characteristic "see-saw" motion of the interventricular septum (IVS) in real-time B-scan (RTBS) in right ventricular volume overload (RVVO) reveals features which have not been taken into account in diagnostic M-scan echocardiography. From an investigation of 20 patients it became apparent that the criteria (1) increase in right ventricular internal diameter and (2) "paradoxical" septal motion, so far used for the M-scan diagnosis of RVVO, should be complemented by further criteria: (3) hypertrophy of the IVS in longstanding RVVO, (4) increase in septal amplitude of motion towards the cardiac apex, (5) selective increasing apical septal hypertrophy and (6) an apparent random septal motion without any resultant main direction as an indication of a displaced fulcrum of the septal "see-saw". All features may be visualised by carrying out a continuous sweep in M-scanning. The criteria 2-5 may be understood as a result of increased apical work load compensating for the haemodynamic loss of the reversed upper septal motion ("RUSM"). The diagnosis of RVVO can be made more readily and reliably with RTBS echocardiography, underlining the utility of a combined use of one- and two-dimensional ultrasonography in diagnostic cardiology.

Blood Volume↗
PubMed2003

Picomolar analysis of flavins in biological samples by dynamic pH junction-sweeping capillary electrophoresis with laser-induced fluorescence detection.

Sensitive capillary electrophoresis (CE) methods are required for emerging areas of biochemical research such as the metabolome. In this report, dynamic pH junction-sweeping CE with laser-induced fluorescence (LIF) detection is applied as a robust single method to analyze trace amounts of three flavin derivatives, riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD), from several types of samples including bacterial cell extracts, recombinant protein, and biological fluids. Submicromolar amounts of flavin coenzymes were measured directly from formic acid cell extracts of Bacillus subtilis. Significant differences in flavin concentration were measured in cell extracts derived from either glucose or malate as the carbon source in the culture media. Quantitative assessment of FAD and FMN content from selected flavoenzymes was demonstrated after heat denaturation to release noncovalently bound coenzymes and deproteinization. This method was also applied to the analysis of free flavins in pooled human plasma and urine without the need for laborious off-line sample preconcentration. Picomolar detectability of flavins by CE-LIF detection was realized with on-line preconcentration (up to 15% capillary length used for injection) by dynamic pH junction-sweeping, resulting in a limit of detection (S/N = 3) of about 4.0 pM for FAD and FMN. This represents over a 60-fold improvement in concentration sensitivity compared to those of previous techniques using conventional injections. The method was validated in terms of reproducibility, sensitivity, linearity, and specificity. Flavin analysis by dynamic pH junction-sweeping CE-LIF offers a simple, yet sensitive way to analyze trace levels of flavin metabolites from complex biological samples.

Bacillus subtilis↗
PubMed2006

Transient solidlike behavior near the cylinder/disorder transition in block copolymer solutions.

A nearly symmetric polystyrene-block-polyisoprene diblock copolymer dissolved at a concentration of 40% in styrene-selective solvents exhibited a cylinder-to-disorder transition upon heating. The solvents used were diethyl phthalate (DEP) and 75:25 and 50:50 mixtures of DEP with di-n-butyl phthalate (DBP). In DEP, the most styrene-selective of the three solvents, rheological measurements indicated a distinct plateau in the temperature-dependent elastic modulus across the 8 degrees C interval above the order-disorder transition temperature, T(ODT) = 116 degrees C. Previous small-angle neutron scattering measurements in this regime indicated the equilibrium phase to be a liquidlike solution of approximately spherical micelles. An isothermal frequency sweep in this regime indicated a very long relaxation time. Annealing eventually led to the recovery of liquidlike rheological response, over a time scale of hours. Qualitatively similar phenomena were also observed in 75:25 DEP/DBP and 50:50 DEP/DBP solutions, except the fact that the temperature window of the transient response is narrow and the time scale for the recovery diminishes significantly. Neither small-angle X-ray scattering nor static birefringence gave any clear signature of the transient structure. The structure that leads to the transient rheological response is attributed to micellar congestion due to the slow relaxation of anisotropic micelles into an equilibrium distribution of micelles. Possible origins of the remarkable solvent selectivity dependence are also discussed.

Butadienes↗
PubMed1998

Magnetic sensor data acquisition for three-dimensional ultrasound of the orbit.

PURPOSE: Three-dimensional (3D) B-mode ultrasound imaging is now possible using a magnetic sensor data acquisition system to localise data points, allowing free-hand scanning. We report the first use of this freehand scanning system for insonation of the orbit. METHODS: We insonated 10 orbits in 5 volunteers (all men; mean age 37 years) with an Acuson 128XP ultrasound system and a 7.5 MHz transducer. Power-Doppler was used to image vascular structures. Data were acquired using a new magnetic sensor system with detectors mounted on the transducer. Free-hand scanning was done using sweeping or fan-like and linear movements over 20-30 s to cover the orbit, with retrospective measurements of orbital structures. A 3D reconstruction was performed via an external workstation. RESULTS: All orbits were adequately imaged by one data acquisition. Selected intraorbital structures were identified and their course followed, including optic nerve and central vessels, as well as short and long ciliary vessels. The mean transverse area of the optic nerve was 5.6 +/- 1.1 mm2; the diameter of the optic nerve was 3.0 +/- 0.3 mm. The lateral rectus muscle was clearly seen, with a mean diameter of 4.9 +/- 0.3 mm, at the level of optic nerve head. CONCLUSION: Three-dimensional ultrasound of the orbit allows imaging of the location, course and relationships of intraorbital vessels, the optic nerve and the lateral rectus muscles with one data acquisition, as well as quantitative measurements not possible with 2D images alone. This method allows rapid, free-hand data acquisition, with a multitude of potential clinical applications.

Adult↗
PubMed2004

Transient blockade of the CD11d/CD18 integrin reduces secondary damage after spinal cord injury, improving sensory, autonomic, and motor function.

The early inflammatory response to spinal cord injury (SCI) causes significant secondary damage. Strategies that nonselectively suppress inflammation have not improved outcomes after SCI, perhaps because inflammation has both adverse and beneficial effects after SCI. We have shown that the selective, time-limited action of a monoclonal antibody (mAb) to the CD11d subunit of the CD11d/CD18 integrin, delivered intravenously during the first 48 hr after SCI in rats, markedly decreases the infiltration of neutrophils and delays the entry of hematogenous monocyte-macrophages into the injured cord. We hypothesized that this targeted strategy would lead to neuroprotection and improved neurological outcomes. In this study the development of chronic pain was detected in rats by assessing mechanical allodynia on the trunk and hindpaws 2 weeks to 3 months after a clinically relevant clip-compression SCI at the twelfth thoracic segment. The anti-CD11d mAb treatment reduced this pain by half. Motor performance also improved as rats were able to plantar-place their hindpaws and use them for weight support instead of sweeping movements only. Improved cardiovascular outcome was shown after SCI at the fourth thoracic segment by significant decreases in autonomic dysreflexia. Locomotor performance was also improved. These functional changes correlated with significantly greater amounts and increased organization of myelin and neurofilament near the lesion. The improved neurological recovery after the specific reduction of early inflammation after SCI demonstrates that this selective strategy increases tissue at the injury site and improves its functional capacity. This early neuroprotective treatment would be an ideal foundation for building later cell-based therapies.

Animals↗
PubMed1985

Response threshold determination of the brain stem auditory evoked response: a comparison of the phase versus magnitude derived from the fast Fourier transform.

An ensemble of 10 groups of brain stem evoked responses (BAERs), each consisting of 200 sweeps, was collected for different intensity levels and for a no-stimulus condition. A fast Fourier transform was calculated for the separate groups, which permitted a phase variance to be derived. The phase variance was compared to the magnitude value for selected frequency components making up the BAER. It was found that the phase variance was a better predictor of signal than magnitude. The superiority of prediction by phase results from intersubject variation being smaller for phase compared to magnitude.

Acoustic Stimulation↗
PubMed2006

Types of filtration.

There are a multitude of filter designs and mechanisms utilized within the biopharmaceutical industry. Prefilters are commonly pleated or wound filter fleeces manufactured from melt-blown random fiber matrices. These filters are used to remove a high contaminant content within the fluid. Prefilters have a large band of retention ratings and can be optimized to all necessary applications. The most common application for prefilters is to protect membrane filters, which are tighter and more selective than prefilters. Membrane filters are used to polish or sterilize fluids. These filters need to be integrity testable to assess whether or not they meet the performance criteria. Cross-flow filtration can be utilized with micro- or ultrafiltration membranes. The fluid sweeps over the membrane layer and therefore keeps it unblocked. This mode of filtration also allows diafiltration or concentration of fluid streams. Nanofilters are commonly used as viral removal filters. The most common retention rating of these filters is 20 or 50 nm.

Biopharmaceutics↗
PubMed1986

Encoding timing and intensity in the ventral cochlear nucleus of the cat.

Physiological response properties of neurons in the ventral cochlear nucleus have a variety of features that are substantially different from the stereotypical auditory nerve responses that serve as the principal source of activation for these neurons. These emergent features are the result of the varying distribution of auditory nerve inputs on the soma and dendrites of the various cell types within the nucleus; the intrinsic membrane characteristics of the various cell types causing different responses to the same input in different cell types; and secondary excitatory and inhibitory inputs to different cell types. Well-isolated units were recorded with high-impedance glass microelectrodes, both intracellularly and extracellularly. Units were characterized by their temporal response to short tones, rate vs. intensity relation, and response areas. The principal response patterns were onset, chopper, and primary-like. Onset units are characterized by a well-timed first spike in response to tones at the characteristic frequency. For frequencies less than 1 kHz, onset units can entrain to the stimulus frequency with greater precision than their auditory nerve inputs. This implies that onset units receive converging inputs from a number of auditory nerve fibers. Onset units are divided into three subcategories, OC, OL, and OI. OC units have extraordinarily wide dynamic ranges and low-frequency selectivity. Some are capable of sustaining firing rates of 800 spikes/s at high intensities. They have the smallest standard deviation and coefficient of variation of the first spike latency of any cells in the cochlear nuclei. OC units are candidates for encoding intensity. OI and OL units differ from OC units in that they have dynamic ranges and frequency selectivity ranges much like those of auditory nerve fibers. They differ from one another in their steady-state firing rates; OI units fire mainly at the onset of a tone. OI units also differ from OL units in that they prefer frequency sweeps in the low to high direction. Primary-like-with-notch (PLN) units also respond to tones with a well-timed first spike. They differ from onset cells in that the onset peak is not always as precise as the spontaneous rate is higher. A comparison of spontaneous firing rate and saturation firing rate of PLN units with auditory nerve fibers suggest that PLN units receive one to four auditory nerve fiber inputs. Chopper units fire in a sustained regular manner when they are excited by sound.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed2005

Development of a fast method for determining psychophysical tuning curves.

Psychophysical tuning curves (PTCs) can be used to assess the frequency selectivity of the auditory system and to detect and delimit "dead regions" in the cochlea. However, the traditional method for determining PTCs takes too long for use in clinical practice. We evaluated a fast method for determining PTCs, using a band of noise that sweeps in centre frequency and a Békésy method to adjust the masker level required for threshold. The shapes of the PTCs were similar for the fast and traditional methods, for both normally hearing and hearing-impaired subjects. Rates of change of masker level of 2 dB/s or less gave the most reliable results. A relatively wide bandwidth (20 percent of the signal frequency or 320 Hz, whichever is the smaller) was needed to minimise the influence of beat detection. When the signal frequency fell within a dead region, the fast method gave PTCs with shifted tips.

Acoustic Stimulation↗
PubMed2004

Highly directional transurethral ultrasound applicators with rotational control for MRI-guided prostatic thermal therapy.

Transurethral ultrasound applicators with highly directional energy deposition and rotational control were investigated for precise treatment of benign prostatic hyperplasia (BPH) and adenocarcinoma of the prostate (CaP). Two types of catheter-based applicators were fabricated, using either 90 degrees sectored tubular (3.5 mm OD x 10 mm) or planar transducers (3.5 mm x 10 mm). They were constructed to be MRI compatible, minimally invasive and allow for manual rotation of the transducer array within a 10 mm cooling balloon. In vivo evaluations of the applicators were performed in canine prostates (n = 3) using MRI guidance (0.5 T interventional magnet). MR temperature imaging (MRTI) utilizing the proton resonance frequency shift method was used to acquire multiple-slice temperature overlays in real time for monitoring and guiding the thermal treatments. Post-treatment T1-weighted contrast-enhanced imaging and triphenyl tetrazolium chloride stained tissue sections were used to define regions of tissue coagulation. Single sonications with the 90 degrees tubular applicator (9-15 W, 12 min, 8 MHz) produced coagulated zones covering an 80 degrees wedge of the prostate extending from 1-2 mm outside the urethra to the outer boundary of the gland (16 mm radial coagulation). Single sonications with the planar applicator (15-20 W, 10 min, approximately 8 MHz) generated thermal lesions of approximately 30 degrees extending to the prostate boundary. Multiple sequential sonications (sweeping) of a planar applicator (12 W with eight rotations of 30 degrees each) demonstrated controllable coagulation of a 270 degrees contiguous section of the prostate extending to the capsule boundary. The feasibility of using highly directional transurethral ultrasound applicators with rotational capabilities to selectively coagulate regions of the prostate while monitoring and controlling the treatments with MRTI was demonstrated in this study.

Acoustics↗
PubMed1977

Host feeding patterns of Connecticut mosquitoes (Diptera: Culicidae).

Blood-engorged Coquillettidia perturbans, Psorophora ferox, Culex, Culiseta, and Aedes mosquitoes were collected principally by sweep net from salt marsh and woodland habitats in Connecticut. Of the 570 mosquitoes tested, precipitin tests identified the origins of 517 blood meals and revealed distinct host feeding patterns. Aedes mosquitoes fed chiefly on mammals; A. abserratus, A. cantator, and A. vexans showed selectivity for cattle and (or) horses. A. cantator also obtained blood from avian hosts and, in some instances, showed mixed passerine-mammal blood meals. These findings increase the vector potential of this salt marsh mosquito for eastern equine encephalomyelitis virus. Feedings on deer by A. abserratus suggest potential involvement of this mosquito in the transmission of certain subtypes of California encephalitis. Culex-pipiens, C. restuans, Culiseta melanura, and Cs. morsitans dyari acquired blood almost exclusively from passeriform birds.

Aedes↗
PubMed1991

In vivo voltammetric detection of neuropeptides with micro carbon fiber biosensors: possible selective detection of somatostatin.

The electrochemical activity of catechol- and indoleamines, measured by differential pulse voltammetry (DPV) with specifically electrically pretreated carbon fiber microelectrodes, has been utilized to develop sensitive assays for amine neurotransmitters and metabolites. So far, four oxidation peaks have been recorded in vivo between -200 and +500 mV and are well identified. We now report that by increasing the potential sweep range to +950 mV, a further peak, called Peak 5, was detected at +800 mV in vivo in the striatum of anesthetized rats. Neuropeptides containing tyrosine, tryptophan and/or cysteine appear to be electrochemically active between +600 and +900 mV in vitro in a buffered solution at pH 7.4. The present study investigates the chemical nature of Peak 5 and the possible contribution of electroactive neuropeptides to this in vivo voltammetric signal. Experiments performed in vitro and in vivo with amino acids, neuropeptides, or bacitracin (a potent peptidase inhibitor) support the view that Peak 5 is peptidergic. Furthermore, peripheral administration of cysteamine and intrastriatal injection of specific somatostatin antisera both cause the eventual disappearance of Peak 5, suggesting that somatostatin (which oxidases in vitro at approx +800 mV), or a structurally related peptide, could be the principal component of striatal Peak 5.

Animals↗
PubMed1994

Contrast modulated steady-state visual evoked potentials (CMSS VEPs): recording evoked potentials and related single cell responses in area 17 of the cat.

(1) The functional characteristics of the neuronal substrate, responding to the CMSS VEP stimulus, were studied by recording CMSS VEPs and related single unit activity in area 17 of the anaesthetised and paralysed cat. CMSS VEPs use an 8 Hz phase reversing (i.e., 16 reversals/sec) grating stimulus with rapid contrast sweeping and allow the contrast thresholds and lag values to be measured as a function of the spatial frequency. (2) The CMSS VEPs of the anaesthetised cat have a wave form similar to those of humans but are shifted to lower spatial frequencies, higher contrast thresholds and longer lag values. (3) The cellular response to a sinusoidal grating, phase reversing at 8 Hz, was studied in order to identify the neuronal substrate generating the CMSS VEPs. Sixty percent of the area 17 cells respond to this stimulus. Cells responding at 8 Hz reversal comprise a distinct subpopulation of visual cortical cells selective for higher velocities and lower spatial frequencies. (4) Although the CMSS VEPs contain almost exclusively energy at 16 Hz, the temporal response pattern of striate cells is quite disparate, including first and second harmonic response patterns as well as an intermediate type. (5) There is a near-perfect correlation between the contrast thresholds of single cells, obtained with the contrast swept stimulus and those obtained with a static contrast test, validating the technique of rapid linear contrast sweeping. (6) The influence of the temporal parameters of the contrast sweeping on the calculated contrast threshold was investigated at the neuronal level. These parameters only marginally influence the responses. (7) CMSS VEP contrast thresholds and neuronal thresholds were compared. The sensitivity of VEPs corresponds to that of the most sensitive neuronal generators. CMSS VEP lag values are longer than the values for individual neurones.

Animals↗
PubMed1986

Use of frequency-modulated radiofrequency pulses in MR imaging experiments.

With increasing field strength for whole-body MR scanners there is a need for rf pulses of higher bandwidth to perform selective excitation or inversion. AM pulses will have to become shorter thus leading to an enormous requirement for the peak power of the power amplifier. To reduce these requirements the use of frequency modulation is investigated. The effect of pulses based on a linear frequency sweep on the spin system is analyzed by calculation and computer simulation. It turns out that the nonlinear phases induced by those pulses may compensate each other, that therefore spin-echo experiments as usual in MR imaging may be performed, and that the required peak power may be reduced by up to a factor of 50.

Magnetic Resonance Spectroscopy↗