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PubMed1993

[Technological characteristics of endoscopic high frequency current and laser interventions].

High frequency current and laser radiation perform two possibilities to generate therapeutic and surgical heat. The integration of these two technologies into endoscopy resulted in important ancillary techniques in the hands of a surgeon. Starting from the principal methods for coagulation and dissection of tissue the respective technological aspects at the interaction of high frequency currents and intensive laser radiation with different wavelengths on biological tissue are illustrated. Mono- and bipolar HF-techniques as well as the light-guide assisted laser method in the contact and non-contact mode are explained. The special problems in endoscopy arising from the reduction in visibility by haemorrhages and the development of smoke at the thermally induced coagulation may be overcome successfully by the simultaneous instillation of a nearly isolating liquid during the HF-treatment. The so-called electrohydrothermosation (EHT) method is presented and several probes and instruments for endoscopic hemostasis and microsurgery are explained. For an increase in safety at the endoscopic application of HF-current the use of the bipolar technique is recommended and several technological developments used in this mode are pointed out. It is shown that the absorption of radiation through the water-content of the tissue is mainly responsible for the reactions which may be produced with laser-light. Furthermore it is mentioned that the range of lasers which might be used has a large spectrum of medical applications which had been even increased especially by the new erbium and holmium solid state lasers.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocoagulation↗

PubMed2002

Drug-drug interactions in the elderly.

OBJECTIVE: To detect the frequency of potential drug-drug interactions (DDIs) in an outpatient group of elderly people in 6 European countries, as well as to describe differences among countries. DATA SOURCES AND METHODS: Drug use data were collected from 1601 elderly persons living in 6 European countries. The study population participated in a controlled intervention study over 18 months investigating the impact of pharmaceutical care. Potential DDIs were studied using a computerized detection program. RESULTS: The elderly population used on average 7.0 drugs per person; 46% had at least 1 drug combination possibly leading to a DDI. On average, there were 0.83 potential DDIs per person. Almost 10% of the potential DDIs were classified to be avoided according to the Swedish interaction classification system, but nearly one-third of them were to be avoided only for predisposed patients. The risk of subtherapeutic effect as a result of a potential DDI was as common as the risk of adverse reactions. Furthermore, we found differences in the frequency and type of potential DDIs among the countries. CONCLUSIONS: Potential DDIs are common in elderly people using many drugs and are part of a normal drug regimen. Some combinations are likely to have negative effects; more attention must be focused on detecting and monitoring patients using such combinations. As differences in potential DDIs among countries were found, the reasons for this variability need to be explored in further studies.

Aged↗

PubMed2004

ARTSTREAM: a neural network model of auditory scene analysis and source segregation.

Multiple sound sources often contain harmonics that overlap and may be degraded by environmental noise. The auditory system is capable of teasing apart these sources into distinct mental objects, or streams. Such an 'auditory scene analysis' enables the brain to solve the cocktail party problem. A neural network model of auditory scene analysis, called the ARTSTREAM model, is presented to propose how the brain accomplishes this feat. The model clarifies how the frequency components that correspond to a given acoustic source may be coherently grouped together into a distinct stream based on pitch and spatial location cues. The model also clarifies how multiple streams may be distinguished and separated by the brain. Streams are formed as spectral-pitch resonances that emerge through feedback interactions between frequency-specific spectral representations of a sound source and its pitch. First, the model transforms a sound into a spatial pattern of frequency-specific activation across a spectral stream layer. The sound has multiple parallel representations at this layer. A sound's spectral representation activates a bottom-up filter that is sensitive to the harmonics of the sound's pitch. This filter activates a pitch category which, in turn, activates a top-down expectation that is also sensitive to the harmonics of the pitch. Resonance develops when the spectral and pitch representations mutually reinforce one another. Resonance provides the coherence that allows one voice or instrument to be tracked through a noisy multiple source environment. Spectral components are suppressed if they do not match harmonics of the top-down expectation that is read-out by the selected pitch, thereby allowing another stream to capture these components, as in the 'old-plus-new heuristic' of Bregman. Multiple simultaneously occurring spectral-pitch resonances can hereby emerge. These resonance and matching mechanisms are specialized versions of Adaptive Resonance Theory, or ART, which clarifies how pitch representations can self-organize during learning of harmonic bottom-up filters and top-down expectations. The model also clarifies how spatial location cues can help to disambiguate two sources with similar spectral cues. Data are simulated from psychophysical grouping experiments, such as how a tone sweeping upwards in frequency creates a bounce percept by grouping with a downward sweeping tone due to proximity in frequency, even if noise replaces the tones at their intersection point. Illusory auditory percepts are also simulated, such as the auditory continuity illusion of a tone continuing through a noise burst even if the tone is not present during the noise, and the scale illusion of Deutsch whereby downward and upward scales presented alternately to the two ears are regrouped based on frequency proximity, leading to a bounce percept. Since related sorts of resonances have been used to quantitatively simulate psychophysical data about speech perception, the model strengthens the hypothesis that ART-like mechanisms are used at multiple levels of the auditory system. Proposals for developing the model to explain more complex streaming data are also provided.

Acoustic Stimulation↗

PubMed1977

[Ontogeny and function of rank order in a sibling group of greylag geese (Anser anser L.)].

Between the siblings of a family of greylag geese (Anser anser L.) a rank order is established by fighting during the first days after hatching, and also by other, more complex interactions. The position of each goose in the rank order can be defined by three groups of behaviour patterns (aggressive behaviour, "greetings", escape responses). A clear-cut ranking relation between two individuals is a prerequisite for their close cohesion. The survival function of rank order lies in diminishing the intensity and frequency of agonistic interactions, in diminishing social stress situations and in guaranteeing the close family cohesion.

Aggression↗

PubMed2006

Interaction induced shifts in O-H stretching frequency of water in halide-ion water clusters: a microscopic approach with a bond descriptor.

Based on conceptual density functional theory, two new descriptors, the normalized atom-condensed Fukui functions (NFFs) and bond deformation kernel (BDK), are proposed to describe the O-H stretching frequency shifts in water halide-ion clusters by including local polarizations in the system. NFF, along with BDK, can be successfully used to describe interactions between different atoms, especially in cases where polarizations are quite important.

Journal Article↗

PubMed1976

The impact of housing relocation on the elderly: an alternative methodological approach.

This article examines the impact of housing relocation on the patterns of interaction and life satisfaction of a sample of older, married adults living in an urban area of central Arkansas. Interviews were conducted with 115 individuals residing in congregate housing and with a matched sample of 105 persons living in independent residential units. Respondents in the two settings fail to demonstrate significant differences in frequencies of social interaction. Patterns of interaction in five specific areas also reveal no appreciable variation. In addition, the time-related effects of congregate dwelling are suggestive but not confirming of negative changes in both interaction and satisfaction. On the other hand, regardless of residential duration, health, sex or age, independent residents exhibit higher life satisfaction. The data suggest the congregate setting to possess insufficient resources to offset the objective and subjective decrements of old age.

Aged↗

PubMed2006

Regulation of bacterial priming and daughter strand synthesis through helicase-primase interactions.

The replisome is a multi-component molecular machine responsible for rapidly and accurately copying the genome of an organism. A central member of the bacterial replisome is DnaB, the replicative helicase, which separates the parental duplex to provide templates for newly synthesized daughter strands. A unique RNA polymerase, the DnaG primase, associates with DnaB to repeatedly initiate thousands of Okazaki fragments per replication cycle on the lagging strand. A number of studies have shown that the stability and frequency of the interaction between DnaG and DnaB determines Okazaki fragment length. More recent work indicates that each DnaB hexamer associates with multiple DnaG molecules and that these primases can coordinate with one another to regulate their activities at a replication fork. Together, disparate lines of evidence are beginning to suggest that Okazaki fragment initiation may be controlled in part by crosstalk between multiple primases bound to the helicase.

DNA↗

PubMed2000

Linear and nonlinear pathways of spectral information transmission in the cochlear nucleus.

At the level of the cochlear nucleus (CN), the auditory pathway divides into several parallel circuits, each of which provides a different representation of the acoustic signal. Here, the representation of the power spectrum of an acoustic signal is analyzed for two CN principal cells-chopper neurons of the ventral CN and type IV neurons of the dorsal CN. The analysis is based on a weighting function model that relates the discharge rate of a neuron to first- and second-order transformations of the power spectrum. In chopper neurons, the transformation of spectral level into rate is a linear (i.e., first-order) or nearly linear function. This transformation is a predominantly excitatory process involving multiple frequency components, centered in a narrow frequency range about best frequency, that usually are processed independently of each other. In contrast, type IV neurons encode spectral information linearly only near threshold. At higher stimulus levels, these neurons are strongly inhibited by spectral notches, a behavior that cannot be explained by level transformations of first- or second-order. Type IV weighting functions reveal complex excitatory and inhibitory interactions that involve frequency components spanning a wider range than that seen in choppers. These findings suggest that chopper and type IV neurons form parallel pathways of spectral information transmission that are governed by two different mechanisms. Although choppers use a predominantly linear mechanism to transmit tonotopic representations of spectra, type IV neurons use highly nonlinear processes to signal the presence of wide-band spectral features.

Acoustic Stimulation↗

PubMed1987

Post-partum changes in hormones and sexual behaviour in captive groups of marmosets (Callithrix jacchus).

Video-tape recordings were made of behavioural interactions in eight family groups of marmosets for 24-30 days after parturition. Blood samples were collected from females for measurement of plasma luteinizing hormone (LH) and progesterone. A pre-ovulatory LH surge occurred in six females between days 10-18 (mean +/- sem, 13.8 +/- 1.3 days). In these groups, sexual interactions increased in frequency during the post-partum period and males began to initiate mounts on days 1, 2, 2, 6, 8 and 10 respectively. Mount and ejaculation frequencies increased significantly during the peri-ovulatory phase as compared to the pre-ovulatory phase and females were more proceptive and receptive than in the early post-partum period. Peri-ovulatory increases in sexual activity were more pronounced in 3 groups in which females had failed to conceive. In the remaining 3 groups, sexual interactions tended to continue at higher levels into the post-ovulatory phase when the females were pregnant. In captive marmoset groups, copulatory behaviour during the post-partum period is stimulated by changes in non-behavioural cues from the female (increased sexual attractiveness to the male) as well as by changes in her behaviour (proceptivity, receptivity) which vary in importance between individuals.

Aggression↗

PubMed1986

The effect of high frequency oscillatory ventilation on pulmonary stretch receptors in the dog.

High frequency oscillatory ventilation is a form of artificial ventilation where the tidal volume is less than the anatomical dead space. The efficacy of gas exchange depends upon the oscillatory frequency, volume, bias flow and the airway pressure. The present study was undertaken to determine the influence of oscillatory frequency, oscillatory volume and mean airway pressure upon the activity of pulmonary stretch receptors and rapidly adapting receptors during high frequency oscillatory ventilation. The experiments were conducted on dogs anaesthetized with either chloralose or nembutal. In Series I (16 slowly adapting stretch receptors) the effects of changing in turn, the oscillatory frequency, oscillatory volume and mean airway pressure were examined. The bias flow was held constant. Significant changes in the frequency of discharge of slowly adapting stretch receptors occurred only with alterations in oscillatory frequency (8,16,28 Hz) and mean airway pressure (3, 6 & 9 cm H2O). No significant changes in the activity of slowly adapting stretch receptors were observed when the oscillatory volume was altered (2.5, 5.0 & 7.5 ml/kg). With each manoeuvre there were significant small increments in intrathoracic gas volume. In Series II (16 slowly adapting stretch receptors) the interaction between oscillatory frequency and mean airway pressure was studied. The effect of each was greatest at the lowest value of the other variable. In Series III the effect of changing oscillatory frequency on the discharge from rapidly adapting receptors were examined. It was found that changes in frequency at a fixed airway pressure (3 cm H2O) and oscillatory volume failed to alter the activity significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed2001

Angiotensin-converting enzyme and angiotensinogen gene polymorphisms are non-randomly distributed in oral contraceptive-induced hypertension.

OBJECTIVES AND METHODS: Oral contraceptives (OC) usage increases serum angiotensinogen levels to three to five times normal and about 5% of these women develop arterial hypertension. The genetic contribution to this susceptibility to OC-induced hypertension is poorly understood. We have analyzed the genotypes of 149 hypertensive and 101 normotensive women using oral contraceptives, for three genetic polymorphisms in genes of the renin-angiotensin system: an insertion/deletion (I/ D) in the angiotensin converting enzyme (ACE) gene, the T235M polymorphism of the angiotensinogen gene (AGT) and a point mutation in its promoter. RESULTS: After cessation of oral contraception the mean arterial pressures of the hypertensive women were separable into two non-overlapping groups; 88 of the women remained hypertensive and 61 returned to normal blood pressure. Both groups of hypertensive women had a similarly higher frequency of hypertensive relatives than the normotensive women, but were otherwise similar. The 235T allele of AGT was significantly increased in frequency in the 61 oral contraceptive-inducible hypertensive women compared with the controls and the 88 women that remained hypertensive. The ACE I/D genotypes were similarly distributed within the three groups of women, but were distinctly non-random in the oral contraceptive-induced hypertensive women when they were also classified by AGT genotype. CONCLUSION: This statistical interaction of genotype frequencies suggests that the genetic basis of susceptibility to OC-induced hypertension is complex.

Adult↗

PubMed1999

Detection of temporal structure depends on spatial structure.

Observers can more easily detect correlated patterns of temporal contrast modulation within hybrid visual images composed of two components when those components are drawn from the same original picture (Blake, R., & Yang, Y. (1997). Proceedings of the National Academy of Science, 94, 7115-7119). To learn whether spatial phase is a mediating variable, we measured thresholds for detection of contrast modulation over time among component gratings while manipulating spatial phase among those components. In Experiment 1, observers more easily detected correlated contrast modulation when two component gratings were aligned in peaks-subtract phase. Experiment 2 showed that this phase-dependent detectability of synchronized contrast modulation is mediated by the phase-dependent, non-linear interaction among spatial frequency channels. The rigorous evaluation of several a priori reasonable hypotheses indicates that the phase-dependent detectability is not based on local spatial features such as local luminance, contrast or luminance gradient. Taken together, our results indicate that the spatial phase relationship and the temporal correlation of contrast modulation of two component gratings are both important for triggering facilitatory interaction between neural analyzers tuned to those gratings.

Contrast Sensitivity↗

PubMed2002

Broken symmetries and pattern formation in two-frequency forced faraday waves.

We exploit the approximate (broken) symmetries of time translation, time reversal, and Hamiltonian structure to obtain general scaling laws governing the process of pattern formation in weakly damped Faraday waves. Using explicit parameter symmetries we determine, for the case of two-frequency forcing, how the strength of observed three-wave interactions depends on the frequency ratio and on the relative phase of the two driving terms. These symmetry-based predictions are verified for numerically calculated coefficients, and help explain the results of recent experiments.

Journal Article↗

PubMed1979

Plasma protein displacement interactions are rarely of clinical significance.

Drug interactions in general have been overemphasized with respect to both frequency and clinical importance. Interactions allegedly based on displacement of highly protein-bound drugs from plasma proteins are particularly misunderstood and the evidence supporting such interaction is typically incomplete. In those interactions where displacement has been most convincingly shown and a clinically important consequence ensues, an additional interaction mechanism has been present. On theoretical grounds such simple displacement interactions are not likely to be common, easy to detect or serious. If such interactions occur they will be transient.

Biotransformation↗

PubMed2004

Learning by ear: on the acquisition of case and gender marking by German-speaking children with normal hearing and with cochlear implants.

The acquisition of case and gender marking on the definite and indefinite article was studied in a sample of 6 normally-hearing children and 9 children xith cochlear implants. Longitudinal spontaneous speech data are used. Children were matched by MLU, with 4 MLU levels: 1.8, 2.8, 3.6, 4.8. Age ranges for normally-hearing children were 1-4 to 3-8 and for children with cochlear implants 1;8 to 7;0. Frequencies of correctly marked article forms increased over MLU but less so in the hearing-impaired group. In both groups error rates were high. However, error patterns were different. In normally-hearing children errors of case predominated, in hearing-impaired children errors of gender and omission. Error patterns suggest that in normally-hearing children syntactic categorization interacts with input frequency and low discriminability of article forms. In the hearing-impaired group the article system is less advanced, despite higher frequencies of definite articles in adult speech. The predominance of article omission is discussed in terms of persisting perceptual problems or a working memory deficit.

Case-Control Studies↗

PubMed2005

An inverse methodology for high-frequency RF coil design for MRI with de-emphasized B1 fields.

An inverse methodology for the design of biologically loaded radio-frequency (RF) coils for magnetic resonance imaging applications is described. Free space time-harmonic electromagnetic Green's functions and de-emphasized B1 target fields are used to calculate the current density on the coil cylinder. In theory, with the B1 field de-emphasized in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the central overemphasis effect caused by field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T (170 MHz) is calculated using an inverse methodology with de-emphasized B1 target fields. An in-house finite-difference time-domain routine is employed to evaluate B1 field and signal intensity inside a homogenous cylindrical phantom and then a complete human head model. A comparison with a conventional RF birdcage coil is carried out and demonstrates that this method can help in decreasing the normal bright region caused by field/tissue interactions in head images at 170 MHz and higher field strengths.

Brain↗

PubMed1986

Measurement of small mechanical vibrations of brain tissue exposed to extremely-low-frequency electric fields.

Electromagnetic fields can interact with biological tissue both electrically and mechanically. This study investigated the mechanical interaction between brain tissue and an extremely-low-frequency (ELF) electric field by measuring the resultant vibrational amplitude. The exposure cell is a section of X-band waveguide that was modified by the addition of a center conductor to form a small TEM cell within the waveguide structure. The ELF signal is applied to the center conductor of the TEM cell. The applied ELF electric field generates an electrostrictive force on the surface of the brain tissue. This force causes the tissue to vibrate at a frequency equal to twice the frequency of the applied sinusoidal signal. An X-band signal is fed through the waveguide, scattered by the vibrating sample, and detected by a phase-sensitive receiver. Using a time-averaging spectrum analyzer, a vibration sensitivity of approximately 0.2 nmp-p can be achieved. The amplitude of the brain tissue vibrational response is constant for vibrational frequencies below 50 Hz; between 50 and 200 Hz resonant phenomena were observed; and above 200 Hz the amplitude fall-off is rapid.

Animals↗

PubMed2002

An experimental test of the relationship between temporal variability of feeding opportunities and baseline levels of corticosterone in a shorebird.

In this study, we tested the hypothesis that baseline corticosterone levels increase with a change from constant to variable feeding schedules. Captive red knots, Calidris canutus, were presented with food that was either available during the same time each day (constant) or starting at variable times during the day. Food intake rates, frequency of aggressive interactions, and baseline levels of corticosterone were measured. In the majority of cases, red knots showed higher plasma corticosterone concentrations during feeding schedules that were irregular than when food was available at consistent times. These findings are supported by a previous study that showed that red knots take a long time to adjust to the newly offered, predictable conditions of their aviary environment. The frequency of conflicts in the different groups and (size-corrected) body mass were not correlated with average corticosterone level. The results are examined in the light of literature showing that increases in corticosterone in response to acute, unpredictable events mediate behavioral responses such as increased explorative behavior and memory. For red knots that have to find their food on the temperate-zone mudflats in Western Europe, an increased circulating corticosterone level may be adaptive during periods when the patchily distribution of buried bivalves and the burying behavior of such prey presents them with a variable and unpredictable food supply.

Aggression↗