PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “interaction frequencies”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 847 records · Page 47Linked to original sources
PubMed1990

Frequency-dependent selection: the high potential for permanent genetic variation in the diallelic, pairwise interaction model.

A detailed analytic and numerical study is made of the potential for permanent genetic variation in frequency-dependent models based on pairwise interactions among genotypes at a single diallelic locus. The full equilibrium structure and qualitative gene-frequency dynamics are derived analytically for a symmetric model, in which pairwise fitnesses are chiefly determined by the genetic similarity of the individuals involved. This is supplemented by an extensive numerical investigation of the general model, the symmetric model, and nine other special cases. Together the results show that there is a high potential for permanent genetic diversity in the pairwise interaction model, and provide insight into the extent to which various forms of genotypic interactions enhance or reduce this potential. Technically, although two stable polymorphic equilibria are possible, the increased likelihood of maintaining both alleles, and the poor performance of protected polymorphism conditions as a measure of this likelihood, are primarily due to a greater variety and frequency of equilibrium patterns with one stable polymorphic equilibrium, in conjunction with a disproportionately large domain of attraction for stable internal equilibria.

Alleles↗
PubMed1997

Cultural aspects of meals and meal frequency.

The present paper presents a certain number of cultural elements which interact in the determination of the frequency of food intake. Approaches from various perspectives (historical, ethnological, anthropological, sociological) draw attention to two major aspects relating to the periodicity of food intake: the extreme cultural diversity and the continual modifications which have occurred over time and space. The various cultural models change and are subject to multiple influences, for example, cross-cultural, economic and historical. In addition, there are interactions between the models. The definitions of food intake and frequency play a major role in building up consumers' perceptions. These various perceptions are multiple (perception of self, of food and its virtues, the rules and moral values of consumption) and finally influence behaviours. Finally, and taking into account the systems of beliefs, the very nature of feeding behaviours may carry feelings of guilt for the subject. The study of real behaviours and their relationship with health is still incomplete for reasons of methodology and also of conceptual definition. In future, data collection has to take into account real behaviour as well as subjective perceptions and value judgements. A specific effort has to be made in the future to develop methodology. This should allow the collection of reliable data and particularly comparisons between studies, without oversimplifying and distorting cultural specificities.

Attitude↗
PubMed1995

Evaluation of vestibular and visual oculomotor function.

The visual system interacts synergistically with the vestibular system. A normally functioning vestibulo-ocular reflex is necessary but not sufficient for optimum visual acuity during head motion. Studies of dynamic visual acuity, the acuity achieved during relative motion of visual targets or of the observer, indicate that motion of images on the retina markedly compromises vision. The vestibulo-ocular reflex normally provides a substantial measure of stabilization of the retina during head movements, but purely vestibular compensatory eye movements are not sufficiently precise for optimal vision under all circumstances. Other mechanisms, including visual tracking, motor preprogramming, prediction, and mental set, interact synergistically to optimize the gain (eye velocity divided by head velocity) of compensatory head movements. All of these mechanisms are limited in their capacity to produce effective visual-vestibular interaction at higher rotational frequencies and velocities. It is under these conditions that vestibular deficits give rise to symptoms of oscillopsia. Patients having vestibular lesions exploit mechanisms of visual-vestibular interaction to compensate by substitution for deficient vestibular function. Thus, for accurate topographic clinical diagnosis of vestibular lesions, testing conditions should isolate purely vestibular responses. This may be done by testing reflex eye movements during passively generated rotations in darkness, or perhaps by testing during other types of motion under conditions of extreme frequency and velocity sufficient to attenuate the effects of visual-vestibular interaction. This article reviews clinical tests of vestibular function in relation to synergistic interactions with vision.

Aging↗
PubMed2005

Increased neuronal communication accompanying sentence comprehension.

The main purpose of this study was to examine large-scale oscillatory activity and frequency-related neuronal synchronization during the comprehension of English spoken sentences of different complexity. Therefore, EEG coherence during the processing of subject-subject (SS)- and more complex subject-object (SO)-relatives was computed using an adaptive fitting approach of bivariate auto-regressive moving average (ARMA) models which enabled the continuous calculation of coherence in the course of sentence processing with a high frequency resolution according to the dynamic changes of the EEG signals. Coherence differences between sentence types were observed in the theta (4-7 Hz), beta-1 (13-18 Hz) and gamma (30-34 Hz) frequency ranges, though emerging during the processing of different parts of these sentences: gamma differences were evident mainly during the relative clause while theta and beta-1 differed significantly following the end of the relative clause. These findings reveal no simple one to one map between EEG frequencies and cognitive operations necessary for sentence comprehension. Instead, they indicate a complex interplay and dynamic interaction between different EEG frequencies and verbal working memory, episodic memory, attention, morpho-syntactic and semantic-pragmatic analyses, which though distinct often co-occur.

Adult↗
PubMed1997

Interaction between sub- and supra-Nyquist spatial frequencies in peripheral vision.

In peripheral vision, high-frequency gratings beyond the Nyquist limit are visible as aliased patterns but, as shown previously, their visibility can be masked by superimposed sub-Nyquist gratings. Is the converse also true? Can supra-Nyquist gratings affect the detectability of sub-Nyquist gratings? In this study, we investigated the masking effect of high contrast, supra-Nyquist components of a compound grating on the contrast detection of sub-Nyquist components by employing a temporal three-alternative, forced-choice (3AFC) masking paradigm. We found that high-frequency, aliased gratings with contrast just 2 or 3 times above threshold can have a powerful masking effect on low-frequency, resolved gratings in peripheral vision. This result was surprising because prior results from sub-Nyquist masking studies in the fovea and the periphery have indicated that masking occurs only when the mask contrast is at least 5 times greater than threshold. Strong masking by supra-Nyquist gratings that are only just visible may be accounted for by an irregular sampling model in which the alias of the mask is distributed over a band of frequencies in the sub-Nyquist range. Furthermore, if undersampling is the explanation for the results of this study, then masking must occur after spatial sampling.

Contrast Sensitivity↗
PubMed1994

Marked interspecies variations concerning the interactions of camptothecin with serum albumins: a frequency-domain fluorescence spectroscopic study.

Camptothecin, an anticancer agent reknown for its novel mechanism of action and outstanding murine in vivo activity, has to date displayed only modest therapeutic utility against human cancers. The drug contains an delta-lactone ring moiety which, at pH7.4, hydrolyzes to yield a biologically inactive carboxylate form. Comparison of drug stability in both plasma and purified serum albumin samples revealed that ring opening occurred to a much greater extent in human samples versus those of other species. Multifrequency phase-modulation spectroscopic analyses of the intrinsic fluorescence emissions of the two drug forms revealed a physical explanation for the extensive ring opening observed in the presence of human serum albumin (HSA): the protein exhibited a marked 200-fold binding preference for the carboxylate (K = 1.2 x 10(6) M-1) relative to the lactone (K approximately 5.5 x 10(3) M-1). Serum albumins from other species were found to bind camptothecin carboxylate not nearly as tightly as HSA. Due to the unique capacity of human albumin to bind camptothecin carboxylate, resulting in extensive conversion of the drug to its biologically inactive form, it appears that the success of the agent in eradicating cancer in animal models may be inherently more difficult to duplicate in man.

Animals↗
PubMed2000

Coevolutionary clines across selection mosaics.

Much of the dynamics of coevolution may be driven by the interplay between geographic variation in reciprocal selection (selection mosaics) and the homogenizing action of gene flow. We develop a genetic model of geographically structured coevolution in which gene flow links coevolving communities that may differ in both the direction and magnitude of reciprocal selection. The results show that geographically structured coevolution may lead to allele-frequency clines within both interacting species when fitnesses are spatially uniform or spatially heterogeneous. Furthermore, the results show that the behavior and shape of clines differ dramatically among different types of coevolutionary interaction. Antagonistic interactions produce dynamic clines that change shape rapidly through time, producing shifting patterns of local adaptation and maladaptation. Unlike antagonistic interactions, mutualisms generate stable equilibrium patterns that lead to fixed spatial patterns of adaptation. Interactions that vary between mutualism and antagonism produce both equilibrium and dynamic clines. Furthermore, the results demonstrate that these interactions may allow mutualisms to persist throughout the geographic range of an interaction, despite pockets of locally antagonistic selection. In all cases, the coevolved spatial patterns of allele frequencies are sensitive to the relative contributions of gene flow, selection, and overall habitat size, indicating that the appropriate scale for studies of geographically structured coevolution depends on the relative contributions of each of these factors.

Alleles↗
PubMed2004

Frequency of concurrent use of warfarin with potentially interacting drugs.

STUDY OBJECTIVE: To determine the rates of concomitant use of drugs known to interact with warfarin by increasing the prothrombin time expressed as the international normalized ratio (INR), decreasing the INR, or increasing bleeding risk without apparent changes in INR in a cohort of patients receiving long-term warfarin therapy. DESIGN: Retrospective, longitudinal cohort study. SETTING: Large pharmacy benefits manager database. PATIENTS: A total of 134,833 patients who were prescribed long-term warfarin from June 1, 1999-May 31, 2000. MEASUREMENTS AND MAIN RESULTS: Longitudinal pharmacy claims from the pharmacy benefits manager database were reviewed to identify coprescription of warfarin and drugs associated with significant interactions with warfarin. Of the 134,833 patients receiving long-term warfarin therapy, 109,998 (81.6%) were prescribed a concurrent prescription for at least one potentially interacting drug, including 87,346 (64.8%) who were prescribed one or more concomitant drugs associated with interactions known to increase the INR. Acetaminophen-containing products, prescribed for 22.7% of patients receiving concomitant prescriptions, and thyroid hormones, prescribed for 17.5%, were the most commonly prescribed concurrent drugs associated with an increased INR response. The most frequently prescribed interacting agents associated with a decreased INR response were trazodone (2.2%) and carbamazepine (1.1%). The most commonly prescribed agents independently associated with increased bleeding risk were cyclooxygenase-2 inhibitors. CONCLUSION: Many patients receiving warfarin therapy are treated with concomitant drugs that may interact with the warfarin. The high percentage of patients taking drugs that may increase INR or bleeding risk is a reminder that bleeding events are a likely adverse outcome of combining drugs that interact with warfarin. Careful warfarin management is necessary to avoid adverse events associated with drug interactions.

Adult↗
PubMed2002

Exploring a neural-network account of age-of-acquisition effects using repetition priming of faces.

The question of whether age-of-acquisition (AoA), frequency, and repetition priming effects occur at a common stage or at different stages of processing is addressed. Two single-stage accounts (i.e., cumulative frequency and a neural-network simulation) are considered in regard to their predictions concerning the interactions between AoA and frequency with aging and priming effects. A repetition-priming face-classification task was conducted on both older and younger participants to test these predictions. Consistent with the predictions of the neural-network simulation, AoA had an effect on reaction times that could not be explained by cumulative frequency alone. Also, as predicted by the simulation, the size of the priming effect was determined by the cumulative frequency of the item. It is discussed how this evidence is supportive of the notion that AoA , frequency, and priming all have effects at a common and single stage during face processing.

Adolescent↗
PubMed1968

The clinician's approach to drug interactions.

Drug interactions are important causes of both unexpected toxic and therapeutic effects. Adverse reactions due to drug interaction are proportional to the number of drugs given and the duration of administration. Although drug interactions may be beneficial, they are most often recognized when they increase mortality or morbidity. The frequency of adverse drug interactions in clinical practice makes it mandatory for physicians to know the drugs and mechanisms involved.A drug may potentiate or antagonize the effects of another drug by direct chemical or physical combination, by altering gastrointestinal absorption, by influencing metabolism, transport, or renal clearance, by changing the activity of a drug at its receptor site, or by modifying the patient's response to the drug by a variety of means. This article stresses the importance of avoiding multible drug therapy. When such treatment is unavoidable, patients must be carefully observed for evidence of intensified or diminished drug effect. Only this permits the detection and prevention of untoward drug interactions.

Acid-Base Equilibrium↗
PubMed1982

Parent-child interactions in normal and language-disordered children.

Interactions between young children and their parents or guardians are critical factors in child language acquisition. The purpose of this study is to describe verbal and nonverbal communication patterns that occur in parent-to-child and child-to-parent interactions with normally developing children and children with language disorders. Thirty verbal and nonverbal behaviors were analyzed from videotapes of mother-child interactions. As a group, the mothers of normally developing children did not differ from the mothers of children with language disorders in the frequency of use of verbal or nonverbal interactions or in the mean length of utterance. There were no significant differences between the groups of children in frequency of use of each interaction pattern. What was different was the number of significant relationships between measures of linguistic maturity of the normally developing children and their mothers' interaction patterns that were not apparent for the language-disordered children and their mothers. Mothers' frequency of interactions as expansions, exact, reduction imitation, use of questions, answers, acknowledgements, providing information, total nonverbal behaviors, and use of nonverbal deixis all were related to some measures of the normal child's linguistic maturity. These relationships were infrequent with the language disordered group.

Child Language↗
PubMed2006

A pharmacoepidemiologic study of drug interactions in a Brazilian teaching hospital.

PURPOSE: Although drug-drug interactions constitute only a small proportion of adverse drug reactions, they are often predictable and therefore avoidable or manageable. There are few studies on drug-drug interactions from Brazil. This study aimed to assess the frequency of drug-drug interactions in prescriptions and their potential clinical significance in patients of a Brazilian teaching hospital. METHODS: From January to April 2004, a sample of 1785 drug prescriptions was drawn from a total of 11,250. Drug-drug interactions were identified by using Micromedex DrugReax System. Patients'records with major drug-drug interactions were reviewed by a pharmacist and a medical doctor looking for signs, symptoms, and lab tests that could indicate adverse drug reactions due to such interactions. RESULTS: From the 1785 prescriptions examined, 1089 (61%) were from the male adult ward. Patients' average age was 52.7 years (SD = 18.9; range, 12-98). The median number of drugs in each prescription was 7 (range, 2-26). At least 1 drug-drug interactions was present in 887 (49.7%) prescriptions. Regarding the severity of the clinical result, the interactions were classified as minor (20; 2.3%), moderate (184; 20.7%), major (30; 3.4%), and undetermined because of an incidence of more than 1 interaction in a single patient (653; 73.6%). From the 30 patients with major interactions, 17 (56.7%) presented adverse drug reactions induced by exposure to a major drug-drug interaction. CONCLUSIONS: Patients did suffer adverse drug reactions from major drug-drug interactions. Many physicians may be unaware of drug-drug interactions. Education, computerized prescribing systems and drug information, collaborative drug selection, and pharmaceutical care are strongly encouraged for physicians and pharmacists.

Adolescent↗
PubMed1992

Interaction of instructions with the recall strategy actually used in a paired-associates learning task.

Previous research suggests that interactive imagery produces memory performance superior to separation imagery, although the effects of instructions are less clear. Paired-associate learning was used to examine the effects of instructions (general memory, separation imagery, and interactive imagery) on recall, the frequency of using memory strategies (nonimaginal, separate image, and interactive image), and strategies' effectiveness. The numbers of correctly recalled items were fewer for subjects given general memory instructions than for subjects given separation or interactive imagery instructions which were not different from each other. Subjects reported using a variety of strategies. However, subjects given separation imagery instructions were more likely to report an interactive image than a separate image, and equally as likely to use interactive imagery as subjects given interactive imagery instructions. The present data suggest that subjects can effectively use a variety of memory strategies.

Adult↗
PubMed1997

Interactive edgewise mechanisms: form and function comparison with conventional edgewise brackets.

As the frequency of use of the interactive twin (I-twin) edgewise mechanisms and techniques become increasingly prevalent, it is important to consider how they compare with conventional twin (c-twin) edgewise bracket systems. Optimum intrabracket and interbracket forces in I-twins balance with capillary blood pressures. An unbiased, experimental in vitro, scanning electromicroscopy and in vivo clinical investigation of 83 patients was conducted to compare the frictional resistance of three different I-twin bracket systems, type A (Sigma, American Orthodontics), type B (Interactwin, Ormco Corp.), and type C (Damon, A-company) with three c-twins counterparts respectively types D, E, and F. The three interactive twin brackets were each self-seating by an integrated arm component and made significant incremental improvements to the conventional twins in three different ways. First, the I-twin types reduced frictional resistance by using arm engagement with a lower coefficient of friction and a reduced seating force against the arch wire. The reduced seating force friction produced initially small interbracket arch wire deflections for biocompatible tooth movement and, combined with a wide twin bracket, produced accurate rotation corrections. Reduced friction within the I-twin bracket consequently permitted the effective use of light forces for flowing biomechanics that maximized anchorage. In evaluating friction, two distinctly different interaction forces acting to seat the arch wire were also identified. Type A demonstrated active interaction with round arch wires that resulted in a low functional seating force responsible for early and complete tooth control in comparison to the high seating force of c-twins. Types B and C both showed passive interaction with seating force friction approximately equal to zero that required large rectangular dimension arch wires for full bracket expression. Second, a significant reduction in the time taken to change arch wires was found, improving clinical time management. Third, I-twins assisted bracket placement with both center-slot identification markers and coordinated bracket and bonding pad reference planes in three dimensions. In addition, they improved bracket hygiene compared with c-twins by minimizing the use of plaque-retentive conventional ligatures. Despite the reduced elastomer use, experimental and clinical results showed I-twins effectively conserved the traditional four tie-wing design for ease of colored elastomer placement where an increase in friction for anchorage was selectively required and to enhance patient acceptance and motivation. Finally, interactive twins could be used by the practitioner as conventional twins without the interactive arms making them fail-safe.

Biomechanical Phenomena↗
PubMed1991

Absence of a synergistic effect between moderate-power radio-frequency electromagnetic radiation and adriamycin on cell-cycle progression and sister-chromatid exchange.

In our laboratories we are conducting investigations of potential interactions between radio-frequency electromagnetic radiation (RFR) and chemicals that are toxic by different mechanisms to mammalian cells. The RFR is being tested at frequencies in the microwave range and at different power levels. We report here on the 1) ability of simultaneous RFR exposures to alter the distribution of cells in first and second mitoses from that after treatment by adriamycin alone, and 2) on the ability of simultaneous RFR exposure to alter the extent of sister chromatid exchanges (SCEs) induced by adriamycin alone. This chemical was selected because of its reported mechanism of action and because it is of interest in the treatment of cancer. In our studies, Chinese hamster ovary (CHO) cells were exposed for 2 h simultaneously to adriamycin and pulsed RFR at a frequency of 2,450 MHz and a specific absorption rate of 33.8 W/Kg. The maximal temperature (in the tissue-culture medium) was 39.7 +/- 0.2 degrees C. The experiments were controlled for chemical and RFR exposures, as well as for temperature. Verified statistically, the data indicate that the RFR did not affect changes in cell progression caused by adriamycin, and the RFR did not change the number of SCEs that were induced by the adriamycin, which adriamycin is known to affect cells by damaging their membranes and DNA.

Animals↗
PubMed2004

Geographic and within-population structure in variable resistance to parasite species and strains in a vertebrate host.

Host resistance to parasites and parasite infectivity may be subject to significant genetically determined variation within species. However, relatively little is known of how this variability is structured in natural vertebrate populations and their macroparasites. A laboratory experiment on host susceptibility-parasite infectivity variation in a wildlife host-parasite system (subspecies of the anuran X. laevis and their polystome flatworms), including 33 pairwise allopatric and sympatric host-parasite combinations (three parasite geographical isolates x 11 host full-sibling families, n=600), revealed a complex pattern of infection success. Results amongst host sibships from different localities suggested that infection success was subject to a highly significant locality x parasite isolate interaction. Within localities, a highly significant sibship x isolate interaction also occurred in one of two groups of sibships examined. The existence of such interactions suggests a potential for frequency-dependent, Red Queen-like selection. Interaction between locality and isolate was partly due to higher infection levels in sympatric combinations, consistent with a general pattern of host-specific adaptation. However, some allopatric combinations produced unpredictably high infection levels, resulting in very asymmetrical cross-infectivity patterns (where the reciprocal cross-infections produced negligible infection). This phylogeographically structured host-parasite system may, therefore, sometimes generate local parasite strains with high infectivity to allopatric hosts. Secondary contact between populations could thus result in significant, and unequal, transfer of parasites.

Animals↗
PubMed1987

Validity and reliability of the Experience-Sampling Method.

To understand the dynamics of mental health, it is essential to develop measures for the frequency and the patterning of mental processes in every-day-life situations. The Experience-Sampling Method (ESM) is an attempt to provide a valid instrument to describe variations in self-reports of mental processes. It can be used to obtain empirical data on the following types of variables: a) frequency and patterning of daily activity, social interaction, and changes in location; b) frequency, intensity, and patterning of psychological states, i.e., emotional, cognitive, and conative dimensions of experience; c) frequency and patterning of thoughts, including quality and intensity of thought disturbance. The article reviews practical and methodological issues of the ESM and presents evidence for its short- and long-term reliability when used as an instrument for assessing the variables outlined above. It also presents evidence for validity by showing correlation between ESM measures on the one hand and physiological measures, one-time psychological tests, and behavioral indices on the other. A number of studies with normal and clinical populations that have used the ESM are reviewed to demonstrate the range of issues to which the technique can be usefully applied.

Activities of Daily Living↗