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PubMed1988

[High-frequency artificial respiration. II. Intratracheal high-frequency pressure changes with a rotation-valve catheter].

From the history of ventilatory support, the early studies of Auer und Meltzer only now seem to find a functional explanation. A rotating valve mounted on the tip of an endotracheal tube delivers a widespread gas bolus. The turbulent flow acts as a stirring device on the intrapulmonary gas volume. The method reduces the directional selectivity that typically limits the efficiency of jet ventilation. Systematically changing the rotational frequency between 10 and 80 Hz allows sequential stimulation, compartment by compartment, of the entire lung, which also gives rise to frequency-dependent local air-trapping that sequentially inflates different compartments. Jet ventilation and high-frequency oscillation were compared in dogs with the rotating valve tube by taking blood gas samples from 4-6 intrapulmonary veins: jet ventilation is characterized by preponderant ventilation of lung compartments opposite the lower aperture of the endotracheal tube. High-frequency oscillation induces a frequency dependent repartition of alveolar ventilation. The rotating valve tube definitely contributes to the homogenisation of alveolar ventilation in a manner that is less dependant upon segmental compliance than conventional ventilation.

Animals↗

PubMed1996

[Retrospective estimation of the frequency of heterozygous beta-thalassemia in the Crimean Tartar population. Formulation of the problem. Estimation of the gametic contribution to a mixed population from frequencies of the ABO blood group genes].

Polymorphism of the beta-thalassemia gene frequency in non-indigenous populations of Central Asia, especially Crimean Tartars, is often explained by inter-ethnic marriages. The frequencies of these marriages, however, are not sufficient to produce the observed gene frequencies. Because of this, an estimation of the extent of Uzbek gametic contribution to the ethnic group of Crimean Tartar origin was conducted using data on the frequencies of ABO blood group genes. The maximum-likelihood estimate obtained (0.325) was used to determine the heterozygous beta-thalassemia frequency of the ancestral Crimean Tartar population.

ABO Blood-Group System↗

PubMed1989

Cholinergic modulation of frequency receptive fields in auditory cortex: II. Frequency-specific effects of anticholinesterases provide evidence for a modulatory action of endogenous ACh.

Exogenously applied muscarinic agonists--for example, acetylcholine (ACh) and acetyl-beta-methacholine (MCh)--modify frequency receptive fields in auditory cortex of unanesthetized animals in a frequency-specific rather than global manner. The present study sought to relate these findings to endogenous actions of ACh by using the anticholinesterase agents eserine sulphate and soman (0-1,2,2-trimethylpropylmethylphosphonofluoridate) to facilitate the effects of endogenous ACh. Frequency receptive fields (FRF) were determined by presenting sequences of different isointensity tones before, during, and after application of ACh, MCh, eserine, or soman; also the cholinesterase blockers were applied between applications of ACh or MCh. The major effects produced by the inhibitors were similar to those of the agonists. Predominant effects were frequency-specific changes in FRF. Further, eserine and soman, similar to ACh and MCh, produced shifts in the best frequency (BF) of FRF due mainly to coordinated depression of responses to the BF and increased responses to adjacent, non-BF. The results indicate that exogenous and endogenous ACh, acting via muscarinic receptors, can significantly influence the physiological functioning of cortical neurons and consequently their processing of sensory information.

Acetylcholine↗

PubMed1997

Time-frequency analysis of the first heart sound. Part 2: An appropriate time-frequency representation technique.

A simulated first heart sound (S1) signal is used to determine the best technique for analysing physiological S1 from the following five time-frequency representations (TFR): the spectrogram, time-varying autoregressive modelling, binomial reduced interference distribution, Bessel distribution and cone-kernel distribution (CKD). To provide information on the time and frequency resolutions of each TFR technique, the instantaneous frequency and the -3 dB bandwidth as functions of time were computed for each simulated component of the S1. The performance index for selecting the best technique was based on the relative error and the correlation coefficient of the instantaneous frequency function between the theoretical distribution and the computed TFR. This index served to select the best technique. The sensitivity of each technique to noise and to small variations of the signal parameters was also evaluated. The results of the comparative study show that, although important limitations were found for all five TFRs tested, the CKD appears to be the best technique for the time-frequency analysis of multicomponent signals such as the simulated S1.

Heart↗

PubMed2003

Latitudinal clines in Drosophila melanogaster: body size, allozyme frequencies, inversion frequencies, and the insulin-signalling pathway.

Many latitudinal clines exist in Drosophila melanogaster: in adult body size, in allele frequency at allozyme loci, and in frequencies of common cosmopolitan inversions. The question is raised whether these latitudinal clines are causally related. This review aims to connect data from two very different fields of study, evolutionary biology and cell biology, in explaining such natural genetic variation in D. melanogaster body size and development time. It is argued that adult body size clines, inversion frequency clines, and clines in allele frequency at loci involved in glycolysis and glycogen storage are part of the same adaptive strategy. Selection pressure is expected to differ at opposite ends of the clines. At high latitudes, selection on D. melanogaster would favour high larval growth rate at low temperatures, and resource storage in adults to survive winter. At low latitudes selection would favour lower larval critical size to survive crowding, and increased male activity leading to high male reproductive success. Studies of the insulin-signalling pathway in D. melanogaster point to the involvement of this pathway in metabolism and adult body size. The genes involved in the insulin-signalling pathway are associated with common cosmopolitan inversions that show latitudinal clines. Each chromosome region connected with a large common cosmopolitan inversion possesses a gene of the insulin transmembrane complex, a gene of the intermediate pathway and a gene of the TOR branch. The hypothesis is presented that temperate D. melanogaster populations have a higher frequency of a 'thrifty' genotype corresponding to high insulin level or high signal level, while tropical populations possess a more 'spendthrift' genotype corresponding to low insulin or low signal level.

Animals↗

PubMed1991

Frequency potentiation in granule cells in vivo at theta frequency perforant path stimulation.

The effect of frequency potentiation on the postsynaptic potential in granule cells was studied stimulating the perforant path in curarized and urethanized rats. At stimulation frequencies between 2.0-5.0 Hz, synaptic efficacy in eliciting an orthodromic action potential increased despite the hyperpolarization of the transmembrane potential. The excitatory postsynaptic potential (EPSP) slope and duration also increased while the inhibitory postsynaptic potential (IPSP) was reduced. Stimulation frequencies greater than 5.0 Hz produced similar changes in the transmembrane potential and EPSP-IPSP sequence, but they did not increase synaptic efficacy. The frequency potentiation at frequencies into the theta band suggest that this potentiation participates in theta rhythm genesis in this structure which, in turn, suggests that the fascia dentata could work as a band-pass filter. In 12.5% of cases postpotentiation was also observed.

Action Potentials↗

PubMed1986

Doppler frequency ratio and peak frequency in the assessment of carotid artery disease: a comparative study with angiography.

A retrospective analysis compared the sensitivity, specificity, and predictive value of two methods using noninvasive Doppler ultrasound for detecting the severity of carotid artery disease. Doppler spectral analyses were used in determining the peak systolic frequency (PF) found within the stenosis, as well as the ratio of the peak systolic frequency distal to the stenosis, to the peak systolic frequency within the stenosis (f2/f1). The results of the noninvasive tests were compared with carotid arteriography. The sensitivity of the two methods were similar, but the specificity of f2/f1 was much higher (98%) than PF (88%) with stenosis greater than 50%, and marginally better, 97 and 94%, respectively, with stenosis greater than 75%. The positive predictive value was also better for f2/f1 than PF; 91% and 71% for stenosis greater than 50%, and 77% and 67%, respectively for stenosis greater than 75%. The use of Doppler frequency ratio in conjunction with peak frequency measurements provide a quantitative and fairly accurate evaluation of the severity of carotid artery disease.

Carotid Arteries↗

PubMed1996

Processing of modulation frequency in the dorsal cochlear nucleus of the guinea pig: sinusoidal frequency-modulated tones.

Frequency- and amplitude-modulated (FM and AM, respectively) tones are important information-bearing elements in voice sounds and can also be produced by the spatial movement of sound sources. Zhao and Liang (1995) recently reported the response features of dorsal cochlear nucleus (DCN) neurons to AM tones. In the present study, the responses of the guinea pig DCN neurons to sinusoidal FM (SFM) tones were examined. Discharges of the DCN units to the SFM tones phase-locked to the stimulus modulation frequencies (fm). The phase-locked discharge patterns existed over broad ranges of modulation parameters and at stimulus levels as high as 95 dB SPL or modulation depths (dm) as low as 2%. Robust phase-locking to the fm was observed in samples of all DCN unit types studied. The means of best fm (Bfm) and upper limit fm (ULfm) of all recorded units were 510 Hz and 940 Hz, respectively. Pauser/Buildup (P/B) units had mean maximum synchronization index (SImax) of 0.57. ON units had the highest Bfm with the mean of 646 Hz and subtype ON-S showed the highest mean of SImax at 0.63. Phase-locking to the fm was independent of discharge rates and existed even when the discharge rates were reduced to the background spontaneous rate (SR). A few units showed stronger synchronous responses to the square and triangular FM stimuli instead of the SFM tones. The relationship between the modulated responses and the unit's response area were further examined. The fm phase-locking occurred to modulation bands (or frequency ranges) within the response area, with the modulation bands as narrow as +/- 160 Hz in the central inhibitory areas of the type IV units. As the width of the modulation band changed within a unit's response area, the phases of the fm phase-locked responses of P/B units linearly changed while for Onset units, the change was lesser. The P/B and Onset units had a pi phase shift and a pi/2 phase change, respectively, as carrier frequencies (fc5) passed through characteristic frequencies (CF) and the excitatory/inhibitory response boundaries. The phase-locked responses to the fms were dependent on the SR but were independent of the CF. Low-SR (< or = 2 spikes/s) units had higher synchronization of responses to the fm than the high-SR (> 2 spikes/s) units (SImax = 0.64 and 0.42 respectively). These results suggest that the temporal characteristics of the fm is effectively represented in the responses of DCN units to the SFM tones. Such temporal encoding behavior can play an important role in the processing of the complex sounds in the auditory system. These results also have implications for a possible role for the DCN is in identifying the spatial movement of a sound source.

Acoustic Stimulation↗

PubMed1998

High-frequency oscillation and centroid frequency of diaphragm EMG during inspiratory loading.

Power spectra were derived from the diaphragm electromyogram (EMG) in anesthetized rabbits subjected to inspiratory resistive loading (IRL) with airway pressure swings of 40-60 cm H2O for 20 min to 2 h. Shifts in the centroid frequencies of the power spectra were found to be associated with the appearance of power spectral peaks in the range of 105-140 Hz, termed high-frequency oscillation, or HFO. Such peaks have been described before in phrenic nerve activity and in the diaphragm EMG. However, these peaks have not previously been connected with the shifts in centroid frequency seen during loaded breathing. Although such changes in frequency content have been taken to indicate fatigue in the diaphragm, we find that HFO can also cause a shift in centroid frequency during loaded breathing, an effect whose relation to fatigue has yet to be established.

Air Pressure↗

PubMed1999

Effects of 20-min audio-visual stimulation (AVS) at dominant alpha frequency and twice dominant alpha frequency on the cortical EEG.

The effects of audio-visual stimulation at the dominant alpha frequency and twice dominant alpha frequency on the EEG were investigated. An eyes-closed baseline EEG determined each subject's dominant alpha frequency. Subjects were stimulated at their dominant alpha frequency and at twice dominant alpha frequency for 20 min on two occasions. A 30-min post-session eyes-closed EEG was recorded after each session. Power data were analyzed for 19 locations in six bandpasses using repeated-measures ANOVAs and appropriate post-hoc tests. Alpha stimulation significantly increased power over baseline levels in the delta 1, delta 2, theta, beta 1 and beta 2, with significant effects remaining 30 min later in beta 1. Twice alpha stimulation significantly increased theta, beta 1 and beta 2 power over baseline levels, with significant effects remaining 30 min later in theta, alpha, beta 1 and beta 2.

Acoustic Stimulation↗

PubMed2003

The human primary somatosensory cortex response contains components related to stimulus frequency and perception in a frequency discrimination task.

Somatosensory stimulation of primary somatosensory cortex (SI) using frequency discrimination offers a direct, well-defined and accessible way of studying cortical decisions at the locus of early input processing. Animal studies have identified and classified the neuronal responses in SI but they have not yet resolved whether during prolonged stimulation the collective SI response just passively reflects the input or actively participates in the comparison and decision processes. This question was investigated using tomographic analysis of single trial magnetoencephalographic data. Four right-handed males participated in a frequency discrimination task to detect changes in the frequency of an electrical stimulus applied to the right-hand digits 2+3+4. The subjects received approximately 600 pairs of stimuli with Stim1 always at 21 Hz, while Stim2 was either 21 Hz (50%) or varied from 22 to 29 Hz in steps of 1 Hz. Both stimuli were 1 s duration, separated by a 1 s interval of no stimulation. The left-SI was the most consistently activated area and showed the first activation peak at 35-48 ms after Stim1 onset and sustained activity during both stimulus periods. During the Stim2 period, we found that the left-SI activation started to differ significantly between two groups of trials (21 versus 26-29 Hz) within the first 100 ms and this difference was sustained and enhanced thereafter (approximately 600 ms). When only correct responses from the above two groups were used, the difference was even higher at later latencies (approximately 650 ms). For one subject who had enough trials of same perception to different input frequencies, e.g. responded 21 Hz to Stim2 at 21 Hz (correct) and 26-29 Hz (error), we found the sustained difference only before 650 ms. Our results suggest that SI is involved with the analysis of an input frequency and related to perception and decision at different latencies.

Adult↗

PubMed2003

Learning in discrimination of frequency or modulation rate: generalization to fundamental frequency discrimination.

Fifteen initially inexperienced subjects were trained for 4 weeks (12 2-h sessions) in frequency discrimination with pure tones around 88, 250, or 1605 Hz, or amplitude modulation rate discrimination of noise bands, using modulation rates around 88 or 250 Hz. Before, in the middle of, and after this training period, pure-tone frequency discrimination thresholds (DLFs), harmonic complex tone fundamental frequency discrimination thresholds (DLF0s), and amplitude modulation rate discrimination thresholds (DLFMs) were measured in several conditions including the trained one. Training in pure-tone frequency discrimination resulted in significantly larger improvements in DLF0s when the test complexes contained resolved harmonics than when they were composed of unresolved harmonics. This result supports the hypothesis that the discrimination of the F0 of resolved harmonics shares common underlying mechanisms with the frequency discrimination of pure tones. Training in rate discrimination did not result in larger DLF0 improvements for unresolved than for resolved harmonics.

Acoustic Stimulation↗

PubMed1997

Low-frequency suppression of auditory nerve responses to characteristic frequency tones.

The effects of low-frequency (50, 100, 200 and 400 Hz) 'suppressor' tones on responses to moderate-level characteristic frequency (CF) tones were measured in chinchilla auditory nerve fibers. Two-tone interactions were evident at suppressor intensities of 70-100 dB SPL. In this range, the average response rate decreased as a function of increasing suppressor level and the instantaneous response rate was modulated periodically. At suppression threshold, the phase of suppression typically coincided with basilar membrane displacement toward scala tympani, regardless of CF. At higher suppressor levels, two suppression maxima coexisted, synchronous with peak basilar membrane displacement toward scala tympani and scala vestibuli. Modulation and rate-suppression thresholds did not vary as a function of spontaneous activity and were only minimally correlated with fiber sensitivity. Except for fibers with CF < 1 kHz, modulation and rate-suppression thresholds were lower than rate and phase-locking thresholds for the suppressor tones presented alone. In the case of high-CF fibers with low spontaneous activity, excitation thresholds could exceed suppression thresholds by more than 30 dB. The strength of modulation decreased systematically with increasing suppressor frequency. For a given suppressor frequency, modulation was strongest in high-CF fibers and weakest in low-CF fibers. The present findings strongly support the notion that low-frequency suppression in auditory nerve fibers largely reflects an underlying basilar membrane phenomenon closely related to compressive non-linearity.

Acoustic Stimulation↗

PubMed2003

Frequency-domain method based on the singular value decomposition for frequency-selective NMR spectroscopy.

In several applications of NMR spectroscopy the user is interested only in the components lying in a small frequency band of the spectrum. A frequency selective analysis deals precisely with this kind of NMR spectroscopy: parameter estimation of only those spectroscopic components that lie in a preselected frequency band of the NMR data spectrum, with as little interference as possible from the out-of-band components and in a computationally efficient way. In this paper we introduce a frequency-domain singular value decomposition (SVD)-based method for frequency selective spectroscopy that is computationally simple, statistically accurate, and which has a firm theoretical basis. To illustrate the good performance of the proposed method we present a number of numerical examples for both simulated and in vitro NMR data.

Algorithms↗

PubMed2002

A reexamination of stimulus-frequency effects in recognition: two mirrors for low- and high-frequency pseudowords.

The word-frequency mirror effect (more hits and fewer false alarms for low-frequency than for high-frequency words) has intrigued memory researchers, and multiple accounts have been offered to explain the result. In this study, participants were differentially familiarized to various pseudowords in a familiarization phase that spanned multiple weeks. Recognition tests given during the first week of familiarization replicated a result of W. T. Maddox and W. K. Estes (1997) that failed to show the classic word-frequency mirror effect for pseudowords; however, recognition tests given toward the end of training showed the classic mirror pattern. In addition, a stimulus-frequency mirror effect for "remember" vs. "know" judgments was obtained. These data are consistent with an account of the mirror effect that posits the involvement of dual processes for episodic recognition.

Attention↗

PubMed2000

Low-frequency acoustic modulations generated by the high-frequency portion of the cochlea, noninvasively recorded from the scalp of mice (Mus musculus).

Vocalizations often contain low-frequency modulations of the envelope of a high-frequency sound. The high-frequency portion of the cochlear nerve of mice (Mus musculus) generates a robust phase-locked response to these low-frequency modulations, and it can be easily recorded from the surface of the scalp. The cochlea is most sensitive to envelope modulation frequencies of approximately 500 to 2000 Hz. These responses have detection thresholds that are approximately 10 dB more sensitive than auditory brainstem responses, and they are very sharply tuned. These measurements may provide a nontraumatic means of repeatedly assessing cochlear functions involved in sound localization and perception of vocalizations.

Animals↗

PubMed2004

Regular meal frequency creates more appropriate insulin sensitivity and lipid profiles compared with irregular meal frequency in healthy lean women.

OBJECTIVE: To investigate the impact of irregular meal frequency on circulating lipids, insulin, glucose and uric acid concentrations which are known cardiovascular risk factors. DESIGN: A randomised crossover dietary intervention study. SETTING: Nottingham, UK--Healthy free-living women. SUBJECTS: A total of nine lean healthy women aged 18-42 y recruited via advertisement. INTERVENTION: A randomised crossover trial with two phases of 14 days each. In Phase 1, subjects consumed their normal diet on either 6 occasions per day (regular) or by following a variable meal frequency (3-9 meals/day, irregular). In Phase 2, subjects followed the alternative meal pattern to that followed in Phase 1, after a 2-week (wash-out) period. Subjects were asked to come to the laboratory after an overnight fast at the start and end of each phase. Blood samples were taken for measurement of circulating glucose, lipids, insulin and uric acid concentrations before and for 3 h after consumption of a high-carbohydrate test meal. RESULTS: Fasting glucose and insulin values were not affected by meal frequency, but peak insulin and AUC of insulin responses to the test meal were higher after the irregular compared to the regular eating patterns (P < 0.01). The irregular meal frequency was associated with higher fasting total (P < 0.01) and LDL (P < 0.05) cholesterol. CONCLUSION: The irregular meal frequency appears to produce a degree of insulin resistance and higher fasting lipid profiles, which may indicate a deleterious effect on these cardiovascular risk factors. SPONSORSHIP: : The Ministry of Health and Medical Education, IR Iran.

Adolescent↗

PubMed1991

Frequency discrimination as a function of signal frequency and level in normal-hearing and hearing-impaired listeners.

Frequency difference limens (DLFs) for pure tones were obtained over a wide range of frequencies and levels from 7 normal-hearing subjects and 16 ears of 12 listeners with sensorineural hearing losses. The normal data were fitted with a general prediction equation. Variability of the data around the DLFs estimated by the equation was quantified and used to evaluate the DLFs from the hearing-impaired listeners. The majority of DLFs from impaired listeners were poorer than one standard deviation above the estimates of the normal equation at all frequencies and sensation levels (SLs). The portion of the equation concerned with sensation level was fitted to each listener's data at each frequency. The slopes of these functions indicated that, on average, the rate of improvement of the DLF with sensation level was similar in the two groups of subjects. These results suggest that it would be reasonable to compare DLFs from normal-hearing and hearing-impaired listeners at equivalent sensation levels. The intercepts of the DLF-intensity functions represent asymptotic values obtained at high SLs. These asymptotic DLFs were abnormal in the majority of hearing-impaired subjects, with more than half the data in excess of two standard deviations above normal. However, among those subjects, the correlation between the DLF deficit and the amount of hearing loss at the test frequency was not strong (r = +.27).

Acoustics↗