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Chiasma frequency data on 183 males were subjected to an analysis of covariance. There appeared to be little or no linear trend in chiasma frequency with age. This conclusion was supported by a detailed analysis of chiasma frequencies for each autosome from 21 males. There were, however, significant differences among investigators in reported mean chiasma frequencies.
Flash stimulation elicits oscillatory responses above 100 Hz in human visual cortex. It has been proposed that these are the result of retinal oscillations being directly relayed through the visual pathway to area V1. Experimental evidence, however, is scarce and contradictory. To address this issue, we performed a time-frequency analysis of simultaneously recorded retinal and cortical potentials. Matching frequencies would support the assumption of a direct relationship between retinal and cortical activities. In 4 of 7 subjects the frequency was significantly lower in the cortex than in the retina and in one subject it was significantly higher. The differences were in the range of 10-34 Hz and suggest that the cortical oscillations are not a simple echo of their retinal counterparts.
OBJECTIVE: To study nonsyndromic progressive sensorineural hearing impairment in patients with a COL11A2 mutation (DFNA13) in a Dutch kindred. STUDY DESIGN: Survey. SETTING: Department of otorhinolaryngology of a university hospital. PATIENTS: Twenty-one living members of a Dutch family (150 relatives in 5 generations; 49 were studied) with autosomal dominant nonsyndromic sensorineural hearing impairment showed linkage to the DFNA13 locus. Mutation analysis revealed a missense mutation in the COL11A2 gene. METHODS: History was taken, hearing threshold levels were measured in all affected persons, and penetrance was evaluated. Longitudinal analysis (using linear regression analysis of threshold-on-age data) was possible in only 1 case. Cross-sectional analysis comprised the comparison of threshold levels between different generations of the family. Also, hearing thresholds were corrected for median presbyacusis to find out whether the hearing impairment characteristic of this trait is stationary or progressive. Vestibular functions were evaluated with electronystagmography, by use of rotatory and caloric tests. RESULTS: Most of the affected persons dated their first hearing impairment symptoms to the second to third decade of life. A possibly reduced penetrance was found. Anamnestically, 4 affected persons had hearing impairment symptoms from early childhood onward. Longitudinal analysis in the proband (IV26) revealed the exceptional combination of congenital offset and substantial early progression. Most of the threshold levels differed significantly between the frequencies within each age group and, at the high frequencies (2-8 kHz), between the two age groups covered by generations IV and III (ages 30-38 years and 58-74 years, respectively); the latter could be attributed to presbyacusis. Various caloric abnormalities, including areflexia, were found in about half (8/17) of the tested subjects with sensorineural hearing impairment. CONCLUSIONS: Correction for age, hearing impairment-presumably present and stationary from an early age onward-showed the worst or second-worst threshold usually at 1, 2, and 6 kHz (3540 dB) or 8 kHz (50 dB), whereas the best or second-best threshold was found at 0.25 to 0.5 and 4 kHz (25 dB). Presbyacusis, presumably from the fourth decade of life onward, caused a change of the typically shaped audiogram described as midfrequency hearing impairment with additional high-frequency impairment.
This paper reports AcP frequencies in the Mbugu and Sango of Central Africa. Among 39 sub-Saharan populations, correlations between Pr allele frequencies and latitude, humidity and altitude indicate that AcP frequencies are significantly correlated with humidity, temperature and altitude. The first-order correlations (constant humidity) diminish by approximately 70% relative to the zero-order correlation.
High frequency jet ventilation (HFJV) experiments were performed in healthy anaesthetized mongrel dogs via a multilumen tracheal jet tube to examine the influence of gas flow, ventilatory frequency and inspiration time (as a percentage of the total ventilatory cycle) on gas exchange. We compared arterial PO2, PCO2 and cardiac output during periods of adequate intermittent positive pressure ventilation (IPPV) and periods of HFJV. Reducing gas flow by decreasing the number of activated valves and increasing the frequency to greater than 4 Hz resulted in less than optimal arterial PO2 and PCO2 compared with IPPV. This indicates that convection during HFJV is probably essential for efficient gas exchange. Inspiration time proved to be important in determining efficacy of ventilation for a fixed ventilator minute volume. Cardiac output during all HFJV settings was equal to or greater than cardiac output during IPPV, even as those HFJV settings that resulted in a positive end-expiratory pressure.
The purpose of this study is to specify the contribution of certain frequency regions to consonant place perception for normal-hearing listeners and listeners with high-frequency hearing loss, and to characterize the differences in stop-consonant place perception among these listeners. Stop-consonant recognition and error patterns were examined at various speech-presentation levels and under conditions of low- and high-pass filtering. Subjects included 18 normal-hearing listeners and a homogeneous group of 10 young, hearing-impaired individuals with high-frequency sensorineural hearing loss. Differential filtering effects on consonant place perception were consistent with the spectral composition of acoustic cues. Differences in consonant recognition and error patterns between normal-hearing and hearing-impaired listeners were observed when the stimulus bandwidth included regions of threshold elevation for the hearing-impaired listeners. Thus place-perception differences among listeners are, for the most part, associated with stimulus bandwidths corresponding to regions of hearing loss.
A procedure for estimating HLA phenotype frequencies from two- and three-locus haplotype frequencies is described. Formulae for this procedure are derived, and examples are presented to illustrate the application. The procedure is useful when multiple-locus phenotype frequencies from a laboratory control series are not available, or when a sufficiently large number of laboratory controls have not yet been typed for recently defined antigens or loci to yield stable multiple-locus rates for comparative purposes.
OBJECTIVE: To investigate the allelic polymorphism of CCR5triangle32, CCR5m303, CCR2b-64I and SDF1-3'A in Tibetan population in Lasa area of China. METHODS: The genomic DNA samples from 330 Tibetan subjects' whole blood samples were purified by use of QIAgen Blood Kit and identified by PCR or PCR-RFLP analyses. RESULTS: The mutation frequencies of CCR5triangle32 and CCR5m303 alleles were lower than 0.15%, and those of CCR2 b-64I and SDF1-3'A alleles were 29.42% and 19.24% respectively in the study samples. The allelic polymorphisms of the four alleles of Tibetan population were similar to those of Chinese Han population. Genotype distribution of the four alleles was in accordance with Hardy-Weinberg equilibrium. The above results suggest that Tibetan population may be relatively susceptive to HIV-1. CONCLUSION: The Chinese Tibetan may have a lower frequency of CCR5triangle32 and a higher frequency of CCR2b-64I allele, compared with Caucasian.
Electromagnetic radiations are named according to frequency or to wavelength (which is inversely proportional to frequency) and create electromagnetic fields (EMFs). Frequencies widely vary according to sources: high-voltage power lines, electrically heated beds, MRI, VDTs, microwave ovens, satellite, and radio/TV transmissions or cellular phone transmitters/receivers. Public concern has increased about the potential health effects of EMFs. There are arguments in favour of EMFs being biologically active, but no mechanism has been identified that explains the link between EMFs and bioeffects. Human data reviewed concern the potential reproductive effects (mainly spontaneous abortions, low birthweight and congenital malformations) of exposure to sources of EMFs: maternal residence, electrically heated beds, occupational exposure (mainly video display terminals), and medical exposures. The available epidemiologic studies all have limitations that prevent to draw clearcut conclusions on the effects of EMFs on human reproduction. EMFs are ubiquitous and unavoidable exposures. The matter of possible effects cannot be considered closed, but until our understanding of the biologic important parameters of EMFs exposures is stronger,design of new studies will be difficult and small epidemiologic studies are unlikely to provide definitive answers and should not be given high priority. No conclusion can be drawn for radiofrequencies and microwaves because of lack of data. There is no convincing evidence today that EMFs of the sort pregnant women or potential fathers meet in occupational or daily life exposures does any harm to the human reproductive process.
Low-frequency magnetic fields (MF) can increase the cytosolic calcium concentration ([Ca2+]i) in lymphocytes in the same manner as a physiological stimulus such as antibodies directed towards the CD3 complex. In this study, MF with various frequencies and flux densities were used, while [Ca2+]i changes were recorded using microfluorometry with fura-2 as a probe. The applied sinusoidal MF induced oscillatory changes of [Ca2+]i in the leukemic cell line Jurkat in a manner similar to that seen with stimulation by antibodies. The response at 0.15 mT was over a frequency range from 5 to 100 Hz, with a fairly broad peak having its maximum at 50 Hz. The result of testing increasing flux densities at 50 Hz was a threshold response with no effect below 0.04 mT and a plateau at 0.15 mT. On the basis of the characteristic calcium pattern resulting from an applied MF, we suggest that MF influence molecular events in regular signal transduction pathways of T cells.
The autoradiographic 6-thioguanine-resistant mutant lymphocyte assay and a chromosome aberration assay were used to determine the time-course of appearance and persistence of elevated frequencies of hprt variants and dicentric chromosomes in patients receiving x-irradiation therapy. Twelve cancer patients, treated with 180-200 cGy/day, 5 days/wk, for 3-7 wk, were studied before treatment, at various weekly intervals during treatment, and after treatment. The hprt mutation assays were done with frozen/thawed lymphocytes isolated from aliquots of the same blood samples used for the chromosome aberration assays. The hprt variant frequencies (Vfs) of only 4 of the 7 patients assayed at 2 wk of treatment were elevated over pre-treatment Vfs, but during the 3rd and 4th weeks of treatment there were significant (P less than 0.01) 5- to 15-fold increases in all Vfs. By 6-32 wk after treatment Vfs had fallen to levels only slightly higher than the mean pre-treatment Vf. The frequencies of cells with dicentric chromosomes were significantly increased (P less than 0.01) after 1 wk of radiotherapy, continued to increase during therapy, and remained elevated after treatment. Five multiple sclerosis patients were also studied before and at 2 and 4 wk intervals after treatment with monthly i.v. doses of 750 mg/m2 of cyclophosphamide (CP). There were no significant elevations in chromosome aberrations at these post-treatment sample times. Previous assays for hprt mutants, done with aloquots of the same blood samples (Ammenheuser et al.: Mutat Res 204:509-520, 1988), had shown 8- to 20-fold increases in Vfs 2 wk after the 1st CP treatment. Our results demonstrate the complementary nature of these two human monitoring assays and emphasize the importance of careful selection of optimal sampling times.
A method is presented for the rapid acquisition of frequency maps based on multiecho balanced steady-state free precession (balanced SSFP, fast imaging with steady precession (True FISP), fast imaging employing steady-state excitation (FIESTA), or balanced fast field echo (FFE)). This technique was applied to measure temperature changes within a gel phantom based on the temperature-sensitive water proton-resonance frequency. The frequency was determined as the slope of a linear fit of the phases measured at different TEs along the echo train. The signal-to-noise ratio (SNR) of multiecho SSFP was analyzed for different parameters, such as relaxation times and flip angle, as well as for different local field inhomogeneities. The theoretical and experimental results were compared with results from the established multiecho fast low-angle shot (FLASH) method. Depending on the given tissue parameters, a significant increase in the accuracy of the frequency/temperature shift estimation compared to FLASH was observed. Furthermore, balanced SSFP can be used with very short TRs without generating a saturation-related signal loss, which is essential for real-time temperature mapping.
Changes in membrane potential of single frog motor nerve fibres due to alternating current (ac) between 4 kHz and 20 kHz were recorded in the air gap equipment under constant current conditions at 20 degrees C. The experimental findings were compared with the results of computations on the basis of potential clamp data. Ac shifted mean membrane potential (averaged for every ac period) in the direction of depolarization. The mean depolarization Vm depended on current strength I; it disappeared when the sodium permeability was blocked, in the experiments by tetrodotoxin. In a current range between about 1 and 3 fold threshold strength the ac initiated repetitive activity with response frequencies v between averaged 120 Hz and 820 Hz or in the computations even higher; v depended logarithimically on current strength, but was independent of ac frequency. Elimination of current amplitude I from the nonlinear realtions v(I) and Vm(I) led to a linear function between v and Vm. Both v and Vm depended markedly on prepolarization of the node. The results were attributed to the preferred activation of the sodium permeability under maintained high frequency ac stimulation. Differences between computations and constant current experiments occurred for very long stimulus duration when rhythmical discharges died out in the experiment.
Respiratory sinus arrhythmia (RSA) has been traditionally defined as the high-frequency component of heart-rate fluctuations (HRF) synchronous with the respiratory movements (RM), i.e., the frequency of RSA corresponds to the respiration rate. It can be shown that at defined relations of mean heart and respiration rate some essential effects must be taken into consideration in studies using RSA parameters. The relevance of these effects is shown and a new strategy of RSA quantification demanded, at least in neonates. The diagnostic importance, physiological background and future application of the low-frequency components of the neonatal HRF are reviewed on the basis of our own results. Nonrespiratory cardiovascular HRF cannot always be detected in the neonate by power spectral analysis. Movement-related HRF have a potential diagnostic importance per se, but may also artefactually disturb the quantification of other HRF components. Long-term trends can be used to describe sleep-state related trends and their disturbances.
The efficiency of gas mixing during sinusoidal oscillatory flow in a model of human lung cast was assessed by using a multibreath carbon dioxide washout manoeuvre. The experiments were performed at high frequencies (5, 10, 15 and 20 Hz) and low tidal volumes (50, 90 and 120 cm3). A particular effort was made to analyse the influence of flow oscillation conditions (f and VT) as well as the effect of resident alveolar gas density (molecular diffusion) on the effective diffusion coefficient (Deff). This longitudinal mixing parameter was found to be strongly dependent on the tidal volume (approximately proportional to VT1.4) and weakly dependent on the frequency (approximately proportional to f0.5). However, molecular diffusion was not, in general, a limiting factor in the gas transport process during high-frequency oscillation (HFO).
The basic parameters of the spectrogram, the Choi-Williams, and the Bessel distributions are adjusted to provide the best time-frequency representations (TFRs) of the simulated murmur signals of mitral stenosis, mitral regurgitation, aortic stenosis, aortic regurgitation, and of two musical murmurs. The initial adjustment of the parameters of each TFR technique is performed by computing and minimising the relative averaged absolute error between the frequency contours at -3 dB and -10 dB of each TFR of the simulated murmurs and those of the theoretical distribution of the same signals. The results show that the spectrogram generally provides very good to excellent performance in representing the TFRs of stenotic and regurgitant murmurs. Improvements provided by the Choi-Williams and the Bessel distributions are minor but not systematic for the two signal-to-noise ratios tested (0 and 30 dB) and for the two frequency contours estimated. The Bessel and the Choi-Williams distributions provide the best performance for the musical murmurs. The study shows that although a single technique cannot be optimal for all six murmurs, the spectrogram using a Hamming window of 30 ms is an acceptable compromise to detect the six simulated heart murmurs.
Frequencies of HPRT mutants (MFs), chromosomal aberrations with or without gaps (CA+; CA-), aberrant cells (AC), micronuclei (MN), sister-chromatid exchanges (SCEs) and cells with high frequencies of SCEs (HFCs) were measured in lymphocytes collected from 46 workers occupationally exposed to styrene and dichloromethane (DCM = methylene chloride). These parameters were also determined in 23 controls. Time-weighted average (TWA) values for styrene and DCM exposure during an 8-h working day were respectively 70 mg/m3 (range: 0-598) and 108 mg/m3 (range: 0-742). These values correspond to TWA values of 17 ppm styrene and 31 ppm DCM. In exposed workers, all cytogenetic parameters were significantly enhanced (P < 0.0001; one-sided), but, due to the lack of appropriate control data, no definite conclusions could be drawn concerning the mutagenicity of styrene/DCM exposure. Duration of exposure was not correlated with genetic effects analyzed. The TWA value for styrene was not correlated with the extent of genetic damage detected, but the TWA value for DCM was positively correlated with the frequencies of chromosome aberrations (with gaps) and aberrant cells. These observations make it difficult to decide whether styrene or DCM, or both chemicals, induced the cytogenetic effects observed in exposed workers. Using the present styrene/DCM data, earlier ethylene oxide data and unpublished epichlorohydrin data, the relative sensitivity of the genetic endpoints to detect genotoxic exposure was: HFC > CA- > CA+ > SCE > MN > HPRT.
High-frequency inflating and deflating triangular pulses of pressure were applied to air in the trachea of urethane-chloralose-anesthetized rabbits. Expiratory time was increased by high-frequency inflation (HFI) and decreased by high-frequency deflation (HFD). Both had little effect on inspiratory time or tidal phrenic nerve activity. HFD provoked more tonic type phrenic activity, with discharges being evident during the expiratory phase. It was demonstrated that HFI, which probably stimulates pulmonary stretch receptors, inhibits the initiation of inspiration and HFD, which probably stimulates irritant receptors, facilitates inspiration.