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PubMed1999

Is there a conflict between minimizing effort and energy expenditure with increasing velocities of muscle contraction in humans?

1. The present study examined the possibility that minimizing effort conflicts with minimizing energy expenditure at different velocities of muscle contraction during cycling. 2. Six normal subjects underwent incremental exercise on an electrically stabilized cycle ergometer. Power output increased by 45 W every 3 min to exhaustion at pedalling frequencies of 40, 60, 80 and 100 r.p.m. on separate days. Energy expenditure (oxygen uptake), leg effort and dyspnoea (Borg 0-10 scale) were measured in parallel at the end of each minute. 3. All six subjects completed 10 min of exercise achieving 180 W for all four pedalling frequencies. Two-way analysis of variance indicated that oxygen uptake (P < 0.0001), leg effort (P < 0.0001) and dyspnoea (P < 0.0001) increased with duration of exercise and power output; oxygen uptake (P < 0.0001) and leg effort (P < 0.05) were significantly different between pedalling frequencies; the interactions were not significant. Oxygen uptake was minimal at 60 r.p.m., and increased at both higher and lower pedalling frequencies. Both leg effort and dyspnoea were minimal at 80 r.p.m.; leg effort intensified at higher and lower pedalling frequencies; and dyspnoea was most intense at 100 r.p.m. 4. There was a conflict between minimization of energy expenditure and leg effort at power outputs less than 180 W. Minimizing effort occurred at the expense of an increase in energy expenditure.

Adult↗

PubMed1993

Real-time multiband dynamic compression and noise reduction for binaural hearing aids.

A multi-signal-processor set-up is introduced that is used for real-time implementation of digital hearing aid algorithms that operate on stereophonic (i.e., binaural) input signals and perform signal processing in the frequency domain. A multiband dynamic compression algorithm was implemented which operates in 24 critical band filter channels, allows for interaction between frequency bands and stereo channels, and is fitted to the hearing of the individual patient by a loudness scaling method. In addition, a binaural noise reduction algorithm was implemented that amplifies sound emanating from the front and suppresses lateral noise sources as well as reverberation. These algorithms were optimized with respect to their processing parameters and by minimizing the processing artifacts. Different versions of the algorithms were tested in six listeners with sensorineural hearing impairment using both subjective quality assessment methods and speech intelligibility measurements in different acoustical situations. For most subjects, linear frequency shaping was subjectively assessed to be negative, although it improved speech intelligibility in noise. Additional compression was assessed to be positive and did not deteriorate speech intelligibility as long as the processing parameters were fitted carefully. All noise reduction strategies employed here were subjectively assessed to be positive. Although the suppression of reverberation only slightly improved speech intelligibility, a combination of directional filtering and dereverberation provided a substantial improvement in speech intelligibility for most subjects and for a certain range of signal-to-noise ratios. The real-time implementation was very helpful in optimizing and testing the algorithms, and the overall results indicate that carefully designed and fitted binaural hearing aids might be very beneficial for a large number of patients.

Adult↗

PubMed1982

Frequency and distribution studies of asymmetrical versus symmetrical chromosome aberrations.

Two aspects of the relationship between Asymmetrical (A) and Symmetrical (S) radiation-induced chromosomal aberrations are considered in this paper. (1) Are A and S truly alternative modes of lesion interactions? Relative frequencies for chromatid-type and chromosome-type are examined, and new lymphocyte data using banding is used to look at this, and also for parallelism in chromosome participation of the two forms for various aberration categories. All the tests applied suggest that A and S are alternative interaction modes. (2) The long-term survival characteristics of A and S are discussed, and the differences in expected frequencies of derived S per surviving cell from chromosome-type and chromatid-types are stressed. Since many in vivo tissues have varying mixtures of potential chromatid and chromosome aberration-bearing target cells, ultimate cell survival and derived S frequencies may differ between tissues for the same absorbed dose. An Appendix gives Relative Corrected Lengths (RCL) for chromosomes of the human karyotype which should be used when testing the various exchange aberration categories for random chromosome participation.

Cell Cycle↗

PubMed2002

Dissociable processing of temporal structure in repetitive eye-hand movements in Parkinson's disease.

Movement takes place in multiple dimensions, including the temporal dimension, which itself may be made up of dissociable aspects. From this perspective, the present research tests three hypotheses: first, that the generation of regular, repetitive movement frequency is neurophysiologically dissociable from the generation of appropriate phase relations, or latencies, of such movements with respect to external stimuli; second, that the frontostriatal system is critically involved in the control of latency and not frequency and third that while the control of latency is closely linked to the effector motor system (e.g. eye, hand, etc.) the control of movement frequency is a more centralized function. These three hypotheses were investigated in nine Parkinson's disease (PD) patients with asymmetric akinetic-rigid syndrome and in nine age-matched control subjects in the context of repetitive eye-hand movements generated in response to regularly displaced visual stimuli and then the continuation of these movements in the immediate absence of the stimuli. PD patients demonstrated increased latencies for pointing movements, particularly with the affected hand, while their ability to follow and then reproduce the movement frequency remained largely intact. Interestingly, saccade latency was improved for controls and PD patients when pointing with the Less-affected hand and impaired with the More-affected hand. In contrast, saccade frequency was unaffected in these pointing conditions. These results support the hypothesis that movement frequency and latency controls are dissociable, with the frontostriatal system playing an important role in latency but not frequency control. The fact that pointing and saccade latency displayed a hand-effect, while movement frequency did not, also tends to support the hypothesis that latency control is linked to specific motor systems, including their interaction, whereas frequency control is more centralized.

Adult↗

PubMed2005

Low-frequency oscillations arising from competitive interactions between visual stimuli in macaque inferotemporal cortex.

Some neurons in the inferotemporal cortex (IT) of the macaque monkey respond to visual stimuli by firing action potentials in a series of sharply defined bursts at a frequency of about 5 Hz. The aim of the present study was to test the hypothesis that the oscillatory responses of these neurons depend on competitive interactions with other neurons selective for different stimuli. To test this hypothesis, we monitored responses to probe images displayed in the presence of other already visible backdrop images. Two stimuli were used in testing each neuron: a foveal image that, when displayed alone, elicited an excitatory response (the "object") and a peripheral image that, when displayed alone, elicited little or no activity (the "flanker"). We assessed the results of presenting these images separately and together in monkeys trained to maintain central fixation. Two novel phenomena emerged. First, displaying the object in the presence of the flanker enhanced the strength of the oscillatory component of the response to the object. This effect varied in strength across task contexts and may have depended on the monkey's allocating attention to the flanker. Second, displaying the flanker in the presence of the object gave rise to sometimes strong oscillations in which the initial phase was negative. This was all the more striking because the flanker by itself elicited little or no response. This effect was robust and invariant across task contexts. These results can be accounted for by competition between two neuronal populations, one selective for the object and the other for the flanker, if it is assumed that the visual responses of each population are subject to fatigue.

Action Potentials↗

PubMed1978

Survey of potential drug interaction incidence in an outpatient clinic population.

A study was conducted at a large VA outpatient facility to determine the total number of potential drug interactions resulting from outpatient clinic prescribing. Interactions classified as of moderate or major clinical significance were tabulated. No attempt was made to ascertain whether patients taking digoxin and a thiazide diuretic without a potassium supplement were having their serum potassium levels monitored or if patients had been instructed to space their antacid dosages away from potential reacting drugs. Of the 3028 patients studied, 710 received drugs which had the potential to interact. A dramatic increase of potential interactions was seen as the number of prescriptions received per patient increased. Drug combinations which had potential for interaction and frequency of prescription are listed.

Adult↗

PubMed2005

[Biological resonance as a possible mechanism of an ototoxic action of aminoglycoside antibiotics].

Literature data on mechanisms of an ototoxic action of aminoglycoside antibiotics (AGA) doubt pharmacological basis of this phenomenon. It is suggested that the above ototoxicity may result from wave interference between wave processes in the inner ear and electromagnetic AGA field. The interaction is primary, informative and initiate apoptosis of the hair cells of the internal ear. The model experiment showed feasibility of frequency-resonance interaction between AGA and biopreparations of the acoustic apparatus of the animals.

Aminoglycosides↗

PubMed1995

Muscle fatigue and muscle length interaction: effect on the EMG frequency components.

Muscle fatigue can be identified by a decrease in the frequency components of the EMG signal, typically represented by a fall in the center frequency (fc). In addition, changes in muscle length have been demonstrated to independently alter the EMG fc. What remains unknown is the interaction between muscle fatigue and muscle length changes on the EMG fc. To address this question, a human biceps model of muscle fatigue, consisting of repetitive non-isometric contractions until task failure was studied. EMG signals from the biceps brachii were acquired via surface electrodes, and muscle length was determined by recording elbow angle. Five subjects developed biceps fatigue by repeating contractions of 50% maximal force until task failure. Fatigue produced a decrease in EMG fc at all muscle lengths. For the first three quarters of fatigue development there was a similar degree of reduction in EMG fc at all muscle lengths. But as task failure approached, there was a greater reduction in EMG fc at the shortest muscle length relative to the longest muscle length (41% reduction from baseline versus 30% reduction from baseline, respectively). The effect of muscle length independent of fatigue was such that a 20% increase in length would result in approximately an 18% fall in EMG fc. In conclusion, during fatigue development muscle length significantly influences the EMG fc, and it may be an important factor to consider when utilizing the EMG fc to detect muscle fatigue.

Adult↗

PubMed1996

The effects of weak extremely low frequency magnetic fields on calcium/calmodulin interactions.

Mechanisms by which weak electromagnetic fields may affect biological systems are of current interest because of their potential health effects. Lednev has proposed an ion parametric resonance hypothesis (Lednev, 1991, Bioelectromagnetics, 12:71-75), which predicts that when the ac, frequency of a combined dc-ac magnetic field equals the cyclotron frequency of calcium, the affinity of calcium for calcium-binding proteins such as calmodulin will be markedly affected. The present study evaluated Lednev's theory using two independent systems, each sensitive to changes in the affinity of calcium for calmodulin. One of the systems used was the calcium/calmodulin-dependent activation of myosin light chain kinase, a system similar to that previously used by Lednev. The other system monitored optical changes in the binding of a fluorescent peptide to the calcium/calmodulin complex. Each system was exposed to a 20.9 microT static field superimposed on a 20.9 microT sinusoidal field over a narrow frequency range centered at 16 Hz, the cyclotron frequency of the unhydrated calcium ion. In contrast to Lednev's predictions, no significant effect of combined dc-ac magnetic fields on calcium/calmodulin interactions was indicated in either experimental system.

Animals↗

PubMed2003

Large round bale feeder design affects hay utilization and beef cow behavior.

One hundred sixty beef cows (631 +/- 78 kg) were used to evaluate the quantity of hay loss and feeding behaviors from different round bale feeders. Twenty cows were allotted by weight and body condition score to one of eight pens with four feeder designs: cone, ring, trailer, or cradle. All feeder types provided approximately 37 cm of linear feeder space per animal. Alfalfa and orchardgrass round bales were weighed and sampled before feeding. Hay that fell onto the concrete surrounding the feeder was considered waste and was collected and sampled daily. At the end of a 7-d period, each feeder type was assigned to a different pen for a second 7-d period. On four consecutive days in each period, animal behavior was recorded using a time-lapse video system. Data were collected from 5-min observational intervals from the video tapes every 0.5 h each day. Feeder access, occupancy rate, and occurrence of agonistic interactions were recorded. Dry matter hay waste was 3.5, 6.1, 11.4, and 14.6% for the cone, ring, trailer, and cradle feeders, respectively. Calculated dry matter intake of hay ranged from 1.8 to 2.0% of body weight and was not different among feeder type (P < 0.05). Percentage of organic matter, neutral detergent fiber, acid detergent fiber, and crude protein were all lower and acid detergent lignin was higher in the recovered waste compared to the hay fed (P < 0.05). Cows feeding from the cradle feeder had nearly three times the agonistic interactions and four times the frequency of entrances compared to cows feeding from the other feeder types (P < 0.05). Feed losses were positively correlated with agonistic interactions, frequency of regular and irregular entrances, and feeder occupancy rate (P < 0.05). Agonistic interactions by cows and frequency of feeder entrances differed among feeders and were correlated to feeder design induced feed losses.

Aggression↗

PubMed1985

Social interaction and interpersonal distance in normal and behaviorally disturbed boys.

Frequency of social interaction and interpersonal distance of 24 normal and 24 behaviorally disturbed white, preadolescent boys were examined. Each child's behavior was analyzed from videotapes that were recorded during four 60-min sessions, during which time the child played with the same unfamiliar peer, matched for age and emotional functioning. The results indicated that the frequency of global social interactions was a powerful discriminator between normal and disturbed boys at the older but not at the younger age levels. Proximity to peers and adults also was a powerful discriminator at both age levels. These results were discussed in relationship to the development of social skills in preadolescent children, the need to establish criteria for social competence, and the evaluation of social skills training programs from a development perspective.

Age Factors↗

PubMed1976

Change in a schizophrenic adolescent as a result of a series of rage-reduction treatments.

A 15-year-old schizophrenic girl with many autistic features was observed to have minimal gains from verbal (individual and family) psychotherapy. A course of six rage-reduction sessions was carried out. Effects of the treatment was assessed by daily ratings made by attendants in the ward setting and by a recreation therapist. Both short term and long term effects were assessed. Short term improvement was noted in the ward ratings on dimensions assessed: eye contact when requested; eye contact, spontaneous; speech quality; expression of feelings; interaction with peers; frequency of autistic behaviors; and interaction with adults. In recreation therapy (using fewer observations), short term improvements were noted in all except two of the dimensions: eye contact, spontaneous; and interaction with peers. Long term (pretreatment vs. post-treatment) gains were evident in the ward ratings on all areas except expression of feelings. In the recreation therapy setting, only frequency of autistic behavior showed a stable improvement. The therapist working with the patient also noticed more global changes, and suggested that rating such dimensions as depth of self-disclosure and willingness to confront important issues in verbal psychotherapy would also show interesting results. Methodological weaknesses of the study are mentioned, and guidelines for future work on this problem are suggested.

Adolescent↗

PubMed2000

Testing the counter model for perceptual identification: effects of repetition priming and word frequency.

The counter model for perceptual identification (Ratcliff & McKoon, 1997) differs from alternative views of word recognition in two important ways. First, it assumes that prior study of a word does not result in increased sensitivity but, rather, in bias. Second, the effects of word frequency and prior study are explained by different mechanisms. In the present experiment, study status and word frequency of target and foil were varied independently. Using a forced-choice task, we replicated the bias effect. However, we also found several interactions between frequency and prior study that are in direct conflict with the counter model. Most important, prior study of both alternatives resulted in an attenuation of the frequency effect and an increase in performance for low-frequency targets, but not for high-frequency targets. These findings suggest that the effects of frequency and prior study are not mediated by completely independent mechanisms.

Adult↗

PubMed1984

Dynamic interactions of evoked potentials in a polysensory cortex of the cat.

Interactions of acoustic and somatosensory evoked potentials were studied in the anterior suprasylvian gyrus of the cat. Two kinds of interaction could be observed: occlusion or facilitation. In most cases occlusion was observed. The interactions showed dynamic changes and were susceptible to different kinds of influences. After having determined the control values of interaction over a period of several minutes, reversible enhancement of occlusion was observed after synchronous activation of the acoustic and somatosensory inputs with 2 Hz frequency. The same effect could be observed during stimulation of the mesencephalic reticular formation with 200 Hz frequency. The interactions could also be influenced by amphetamine and gamma-glutamyltaurine, known as drugs capable of influencing the arousal level of the brain. During treatment with amphetamine the interaction was shifted in the facilitatory direction. The antagonists of amphetamine (haloperidol and reserpine) prevented this effect. The authors suggest that the interactions of acoustic and somatosensory responses are mediated by interneurons (inhibitory and/or excitatory) and particular stimulus situations and drugs are able to modify the equilibrium between excitatory and inhibitory subsystems.

Amphetamine↗

PubMed1977

Histocompatibility antigen-activated cytotoxic T lymphocytes. II. Estimates of the frequency and specificity of precursors.

Using limiting dilutions of responding cells in mouse mixed leukocyte cultures, we obtained direct estimates of the minimum frequency of precursors of cytotoxic T lymphocytes (CTL.P) for a variety of antigens. Depending on the strain combination, there were as many as 4-15 CTL.P reactive to DBA/2 among 10(4) lymph node cells. Taking into account that only 5-10% of peripheral T lymphocytes have the potential to develop into cytotoxic T lymphocytes (CTLs) (6), this implies that at least 1-2% of all CTL.P are responsive to any given H-2 haplotype difference. Precursors of cytotoxic cells thus have the same high frequency of cells reactive to alloantigens of the major histocompatibility complex as found among proliferating cells in graft-vs.-host reactions and mixed lymphocyte interactions. The frequencies of CTL.P reactive to xenoantigens (rat) or trinitrophenyl-modified self were less than half the frequency of alloreactive CTL.P. A minority of the CTL.P specific for one H-2 haplotype were also reactive to a third party H-2 haplotype, presumably on the basis of recognition of shared determinants. By dilution of sensitized cells from single microcultures, it was shown that a single CTL.P undergoes a minimum of three to four cell divisions and generates at least 8-16 CTLs after antigenic activation.

Animals↗

PubMed1991

Alcohol drinking patterns and blood pressure.

BACKGROUND: Although blood pressure tends to increase with average alcohol consumption, little is known about the effects of drinking patterns on blood pressure. Therefore, the effects of average drinks per day and drinking pattern (defined as the independent and interactive effects of quantity and frequency) on blood pressure were compared. METHODS: Data were obtained from a random sample survey of 1,635 household residents in Erie County, New York. Alcohol-blood pressure relationships were examined using multiple regression analyses that controlled for the potentially confounding influence of 13 additional risk factors for elevated blood pressure. RESULTS: Consistent with prior research, a positive relationship was found between average drinks per day and diastolic and systolic blood pressure. Analyses examining the effect of drinking pattern indicated that drinking frequency had a positive effect on both diastolic and systolic blood pressure, whereas drinking quantity did not affect either. Furthermore, there was little evidence that the frequency-by-quantity interaction affected blood pressure. CONCLUSIONS: Low average alcohol intake and low blood pressure were associated with infrequent drinking, rather than with frequent drinking of small amounts of alcohol. Results suggest that the standard practice of averaging alcohol consumption may obscure important effects of drinking frequency on health.

Adult↗

PubMed2002

What exactly interacts with spelling-sound consistency in word naming?

Word frequency, age of acquisition (AoA), and imageability were combined with spelling-sound consistency, and their effects on word naming were examined. Frequency and AoA interacted with consistency (Experiments 1 and 2). Imageability did not (Experiment 3). Experiment 4 replicated Experiment 2 of E. Strain, K. E. Patterson, and M. S. Seidenberg's (1995) study and obtained the same apparent effect of imageability on naming. That effect disappeared when AoA was entered as a covariate. An explanation of the interactions of consistency with frequency and AoA is offered in terms of the properties of adaptive connectionist networks given gradual and cumulative training.

Humans↗

PubMedDate not supplied

Granulated metrial gland cells in the mouse placenta.

A study has been made of granulated metrial gland (GMG) cells and adjacent layer 1 cytotrophoblast in the labyrinthine placenta of the mouse. In those cellular associations in which both cell types appeared healthy with the light microscope, examination with the electron microscope identified features which may form part of the early stages in the interaction which can occur between GMG cells and some layer 1 trophoblast. These included microvillous processes from each cell forming an interdigitating network, a polarization of mitochondria in a GMG cell with interdigitating microvilli, platelets, and some GMG cells which appeared to form a specialized cell junction with a small lymphocyte. The latter observation indicates that a tripartite functional relationship may exist between lymphocytes, GMG cells and layer 1 labyrinthine trophoblast. In a quantitative analysis of GMG cells in the maternal blood spaces of placentae no significant differences in the numbers of GMG cells present in these spaces or involved in an interaction with layer 1 labyrinthine trophoblast were detected between inbred and outbred pregnancies. These results suggest that histocompatibility antigens are not significant factors in determining the frequency of interactions between GMG cells and trophoblast.

Animals↗