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PubMed1990

Time-domain analysis of auditory-nerve-fiber firing rates.

Time-domain analysis of firing-rate data from over 200 fibers from the auditory nerve of cat has been used to estimate the formants of the synthetic-syllable stimuli. Distinct groups of fibers are identified based on intervals between peaks in the fiber firing rates. The large extent of some of these groups--over an octave in terms of characteristic frequency--and the lack of short intervals in the longer-interval groups suggest that the behavior of the nonlinear cochlear filters for these signals is effectively wideband with steep high-frequency cutoffs. The measured intervals within each group are very similar, and correspond to the period of the formant that dominates the group's response. These intervals are used to estimate the dynamic speech formants. The overall formant estimates are better than those of the previous spectral analyses of the neural data, and the details of lower-formant dynamics are tracked more precisely. The direct temporal representation of the formant in contrasted with the diffuse spectral representation, the dependence of spectral peaks on nonformant parameters, and the distortion of the spectrum by rectification. It is concluded that a time-domain analysis of the responses to complex stimuli can be an important addition to frequency-domain analysis for neural data, cochlear models, and machine processing of speech.

Animals↗
PubMed2002

Fine temporal resolution of analytic phase reveals episodic synchronization by state transitions in gamma EEGs.

The analytic signal given by the Hilbert transform applied to an electroencephalographic (EEG) trace is a vector of instantaneous amplitude and phase at the temporal resolution of the digitizing interval (here 2 ms). The transform was applied after band-pass filtering for extracting the gamma band (20-80 Hz in rabbits) to time series from up to 64 EEG channels recorded simultaneously from high-density arrays giving spatial "windows" of 4 x 4 to 6 x 6 mm onto the visual, auditory, or somatosensory cortical surface. The time series of the analytic phase revealed phase locking for brief time segments in spatial patterns of nonzero phase values from multiple EEG that was punctuated by episodic phase decoherence. The derivative of the analytic phase revealed spikes occurring not quite simultaneously (within +/- 4 ms) across arrays aperiodically at mean rates in and below the theta range (3-7 Hz). Two measures of global synchronization over a group of channels were derived from analytic phase differences between pairs of channels on the same area of cortex. One was a synchronization index expressing phase locking. The other was a decoherence index estimating the variance in phase among multiple channels. Spectral analyses of the indices indicated that decoherence events recurred aperiodically at rates in and below the theta range of the EEGs. The results provide support for the hypothesis that neurons in mesoscopic neighborhoods in sensory cortices self-organize their activity by synaptic interactions into wave packets that have spatial patterns of amplitude (AM) and phase (PM) modulation of their spatially coherent carrier waves in the gamma range and that form and dissolve aperiodically at rates in and below the theta range. Each AM pattern is formed by a nonlinear state transition in the cortical dynamics, as shown by spikes in the derivative. Phase locking within each PM pattern is not at zero phase lag but over a fixed distribution of phase values that is consistent with the radially symmetric phase gradients already reported called "phase cones" detected by Fourier-based methods. The insight is suggested that sensory cortices are bistable comparably to cardiac dynamics, with a diastolic state that accepts sensory input and an abrupt transition to a systolic state that transmits perceptual output. Further support for this inference will require improvements in methods for temporal resolution of the times of onset of spatial patterns of phase modulation.

Animals↗
PubMed2004

Uniqueness in remote sensing of the inherent optical properties of ocean water.

We examine the problem of uniqueness in the relationship between the remote-sensing reflectance (Rrs) and the inherent optical properties (IOPs) of ocean water. The results point to the fact that diffuse reflectance of plane irradiance from ocean water is inherently ambiguous. Furthermore, in the 400 < lambda < 750 nm region of the spectrum, Rrs(lambda) also suffers from ambiguity caused by the similarity in wavelength dependence of the coefficients of absorption by particulate matter and of absorption by colored dissolved organic matter. The absorption coefficients have overlapping exponential responses, which lead to the fact that more than one combination of IOPs can produce nearly the same Rrs spectrum. This ambiguity in absorption parameters demands that we identify the regions of the Rrs spectrum where we can isolate the effects that are due only to scattering by particulates and to absorption by pure water. The results indicate that the spectral shape of the absorption coefficient of phytoplankton, a(ph)(lambda), cannot be derived from a multiparameter fit to Rrs(lambda). However, the magnitude and the spectral dependence of the absorption coefficient can be estimated from the difference between the measured Rrs(lambda) and the best fit to Rrs(lambda) in terms of IOPs that exclude a(ph)(lambda).

Journal Article↗
PubMed2006

Timing noise measurement of 320 GHz optical pulses using an improved optoelectronic harmonic mixer.

An improved optoelectronic harmonic mixer (OEHM) has been employed for measuring the timing noise of 320 GHz optical pulses that are generated from a 160 GHz mode-locked laser diode by the temporal Talbot effect. The OEHM makes use of a low-drive voltage LiNbO3 modulator and a W-band unitraveling carrier photodiode for converting the 320 GHz pulse intensity into a low-frequency electrical signal. The time domain demodulation technique has been used for the precise evaluation of phase noise power spectral density. The rms timing jitter has been estimated to be 311 fs for the 10 Hz-18.6 MHz bandwidth.

Journal Article↗
PubMed2004

Rapid quantification of carotenoids and fat in Atlantic Salmon (Salmo salar L.) by Raman spectroscopy and chemometrics.

Raman spectroscopy (785 nm excitation) was used to determine the overall carotenoid (astaxanthin and cantaxanthin) and fat content in 49 samples of ground muscle tissue from farmed Atlantic salmon (Salmo salar L.). Chemically determined contents ranged from 1.0 to 6.8 mg/kg carotenoids and 36 to 205 g/kg fat. In addition to the raw Raman spectra, three types of spectral preprocessing were evaluated: the first derivative, subtraction of the fitted fourth-order polynomial (POLY), and the intensity normalized versions of POLY (POLY-SNV). Further, variable selection based on significance testing by use of jack-knifing was performed on each spectral data set. Partial least-squares regression resulted in a root mean square error of prediction of 0.33 mg/kg (R = 0.97) for carotenoids for the variable selected versions of all the preprocessed spectral data sets. The fat content was best estimated by the variable selected POLYSNV, resulting in a root mean square error of prediction of 15.5 g/kg (R = 0.95). Both preprocessing and variable selection improved the regression models significantly. The results demonstrate that Raman spectroscopy is a suitable method for simultaneous, rapid, and nondestructive quantification of both pigments and fat in ground salmon muscle tissue.

Animals↗
PubMed1994

Changes in gonadotrophin secretion during childhood and puberty.

The changes in gonadotrophin secretion in childhood and puberty involve changes in the pulsatile pattern as well as mean concentration. We have examined pulsatile secretion using 24-h LH profiles in 78 children aged 4.2-15.6 years and six adult men. The profiles were analysed by a method which gives an estimate of peak and baseline levels and by spectral analysis. Prepubertal children were divided into groups by age and pubertal children by pubertal stage. Baseline LH levels in children aged 4.2-6.9 years were higher than in those aged 7.1-9.8 years. Pulse frequency in both groups was slow (periodicities 140-200 min). In the oldest prepubertal group there was an increase in peak levels with increased spectral power at periodicities of 100-120 min. Pulse frequency did not change in puberty (periodicity 120-160 min). Girls demonstrated an increase in both peak and baseline LH concentrations in early puberty. Boys had an increase in only peak levels in early puberty; there was no increase in baseline concentrations until a testicular volume of 10 ml was attained. In conclusion, these data show that LH levels do not reach a nadir until 8 years of age. We have detected a sex difference in the pattern of LH secretion seen in early puberty, and this mirrors clinical findings. The mature pattern attained by the end of puberty in both sexes is probably important for fertility.

Adolescent↗
PubMed1999

Effects of mental task on heart rate variability during graded head-up tilt.

In this study, we used spectral analysis of heart rate variability (HRV) to estimate the changes in autonomic control in response to disparate stimuli produced by mental task and graded head-up tilting. The low frequency (LF) component of HRV provided a quantitative index of the sympathetic and parasympathetic (vagal) activities controlling the heart rate (HR), while the high frequency (HF) component of HRV provided an index of the vagal tone. We studied 17 healthy male subjects (21-25 yr of age) who were placed on a tilt-table and the graded tilt-protocol involved tilted sine angles 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0. These tilt-protocols were repeated with or without the mental task, which consisted of auditory distinctive reaction-time tasks. The basal autonomic mode against the graded head-up tilt was characterized by reciprocal changes in sympathetic and vagal tones. There were significant increases of HR corresponding to the mental task with lower tilt-angle, albeit the changes with higher tilt angles were not significant. Furthermore, there were increases and decreases of the LF component induced by the mental task at lower and higher tilt-angles, respectively. These results revealed that the different responses of HR and LF component against the same tasks could be derived from the alterations of autonomic mode during gradual changes in autonomic control.

Adult↗
PubMed2005

Exploratory analysis of simultaneous degradation of anthocyanins in the calyces of flowers of the Hibiscus sabdariffa species by PARAFAC model.

A three-way resolution method based on PARAFAC model was applied for the UV-Vis spectra to study the simultaneous degradation of anthocyanins extracted from fresh calyces of flowers of the Hibiscus sabdariffa. This methodology was used to resolve a chemical system, for which there was no a priori information about the composition or the pure spectra, a so-called black system. In the pH range from 1 to 13, seven species were identified: flavylium cation, carbinol, quinoidal base, E- and Z-chalcones and E- and Z-ionized chalcones. The concentration changes were determined as functions of pH at different wavelengths. The pK values for the acidity constants as well as tautomeric constant were estimated as 2.70, 3.54 and 0.14, respectively. The spectral profiles recovered by the chemometric methods are in excellent agreement with bands of experimental spectra reported in the literature for the species measured at specific pH values.

Anthocyanins↗
PubMed1985

Assessment of prosthetic mitral valve pressure gradients by means of ultrasound Doppler technique and on-line spectral analysis.

The blood speed through prosthetic mitral valves was determined using ultrasound Doppler techniques combined with on-line spectral analysis. Spectral analysis was particularly suitable for maximum velocity estimation due to its superior ability in discriminating between Doppler signals and white background noise. From a simplified Bernoulli equation the corresponding transprosthetic pressure drop was calculated and estimates were compared against pressure gradients obtained by conventional intracardiac catheterization. A close relationship between the ultrasonic- and the manometric transprosthetic pressure gradients was found, but the ultrasonic method tended to systematically underestimate the pressure gradients slightly.

Blood Flow Velocity↗
PubMed1986

Chronic maternal cigarette smoking and fetal abdominal aortic blood flow in humans.

The abdominal aortic blood flow was measured in 19 fetuses of nonsmoking mothers (NS) and five fetuses of smoking mothers (S) who consumed over 10 cigarettes per day throughout gestation. Serial blood flow measurements beginning in the mid-second trimester to term were made noninvasively with an ultrasonic duplex scanner. Biparietal and transverse abdominal diameters were used to estimate gestational age and fetal weight. Blood velocity spectral waveforms and lumen diameters were used to calculate blood flow (Q, ml/min) and weight normalized blood flow (Q/kg, ml/kg/min). Both Q and Q/kg for the two groups were significantly different by analysis of variance throughout the periods of observation. Third trimester Q and Q/kg (+/- SD) in the S group (738 +/- 20 ml/min and 278 +/- 36 ml/kg/min) were significantly higher (P less than 0.01) than values in the NS group (522 +/- 60 ml/min and 180 +/- 24 ml/kg/min). A redistribution of blood flow to the placenta resulting from an increase in fetal systemic vascular resistance is postulated.

Aorta, Abdominal↗
PubMed2003

Ambulatory monitoring of cardiovascular responses during behavioral modification of an aggressive dog.

Previous work from our lab has used the Dutch Ambulatory Monitoring System (AMS) to assess the cardiovascular responses and motility of large free-ranging species (e.g. horses). To further examine the utility of using the AMS with non-humans, a study investigating the heart rate (HR) and heart period variability (HRV) of a large canine undergoing behavioral modification therapy was undertaken. This treatment emulated a restraint and tactile pressure technique that has previously been used in horses. Cardiovascular responses and motility were continuously measured pre-treatment (exposure to a stimulus dog), during treatment (in-box), and post-treatment. The treatment consisted of placing the dog in a 110 cm (long) by 45 cm (wide) by 102 cm (height) wooden box that only covered the animals' torso and legs and allowed the head to be free. Once the dog was in the box, the body was covered with a lightweight material (grain product) to effect restraint and tactile pressure, which was followed by a repeat exposure to the stimulus animal. Results indicated decreased heart rate and an increased HRV during the intervention as compared to baseline with indices of motility changing in the expected directions. Estimates of respiratory frequency derived from the autoregressive spectral analysis indicated changes in respiration did not account for the cardiovascular effects. In conclusion, tactile pressure and restraint may be an important tool for behavioral modification in both humans and animals, and the AMS is a useful tool for collecting cardiovascular data on a variety of species in a great many contexts.

Acceleration↗
PubMedDate not supplied

[Electroencephalogram structure].

The representation of an electroencephalogram as a convolution of harmonic functions having negative decrements with discrete (evenly discontinuous) white Gaussian noise was considered. A substantiation of this representation is given. It was numerically shown that the convolution of the decrement damping alpha-rhythm of one frequency with discrete white noise is a narrow-band chaos, an irregular spindle-shaped activity, which results in the appearance of close spectral components in the spectrum of power. The estimation of the autocorrelation function represented a damping cosinusoid shifted in phase depending of the factor of fading. The absolute value of convolution described an envelope of the output signal. The average duration of spindles decreased as the module of the decrement increased.

Cerebral Cortex↗
PubMedDate not supplied

The relationship between respiratory sinus arrhythmia and heart rate during anesthesia in rat.

During inspiration the heart rate (HR) increases and during expiration it decreases. Contribution of respiratory sinus arrhythmia (RSA) to spontaneous heart rate variability (HRV) can be measured as the high frequency (HF) component of variation in consecutive R-R intervals on ECG. In conscious rats, slowing of HR is associated with an increase in HF. The aim of this study was to investigate whether this relationship between HF and HR is preserved during anesthesia in rat. A 15 minutes long ECG signal was recorded from rats (N=15) under moderate chloral hydrate (CHL) anesthesia. Recordings were extended with 45 minutes to investigate the effect of atropine (N=3), against controls (N=3). Short term HRV was investigated in 30 seconds long epochs. HF was considered the frequency band between 0.8 and 1.6 Hz. RSA was quantified as the relative spectral power of the HF. Respiratory frequency (RF) was quantified as the mean spectral frequency within the HF band. One minute estimates of HR, RSA and HF were calculated by averaging 3 epochs of 30 seconds overlapped 50%. The average HR was 427 +/- 3 bpm. The magnitude of RSA was 45 +/- 1% at a RF of 71 +/- 1 rpm. We found that: (1) the decrease in HR that occurs during CHL anesthesia in rat correlates with an increase in RSA; (2) atropine reduces RSA and the time-dependent decrease in HR; (3) the time-dependent increase in RSA is preserved after atropine. We conclude that the correlation between RSA and HR reflects the cardio-pulmonary coupling under parasympathetic control.

Anesthesia↗
PubMed2007

Reference and target region modeling of [11C]-(R)-PK11195 brain studies.

UNLABELLED: PET with [(11)C]-(R)-PK11195 is currently the modality of choice for the in vivo imaging of microglial activation in the human brain. In this work we devised a supervised clustering procedure and a new quantification methodology capable of producing binding potential (BP) estimates quantitatively comparable with those derived from plasma input with robust quantitative implementation at the pixel level. METHODS: The new methodology uses predefined kinetic classes to extract a gray matter reference tissue without specific tracer binding and devoid of spurious signals (in particular, blood pool and muscle). Kinetic classes were derived from an historical database of 12 healthy control subjects and from 3 patients with Huntington's disease. BP estimates were obtained using rank-shaping exponential spectral analysis (RS-ESA) (both plasma and reference input) and the simplified reference tissue model (SRTM). Comparison between plasma- derived BPs and those produced with the new reference methodology was performed using 6 additional healthy control subjects. Reliability of the new methodology was performed on 4 test-retest studies of patients with Alzheimer's disease. RESULTS: The new algorithm selected reference voxels in gray matter tissue avoiding regions with specific binding located, in particular, in the venous and arterial circulation. Using the new reference, BP values obtained using a plasma input and a reference input were in excellent agreement and highly correlated (r = 0.811, P < 10(-5)) when calculated with RS-ESA and less so (r = 0.507, P < 0.005) when SRTM was used. In the production of parametric maps, SRTM was used with the new reference extraction, resulting in test-retest variability (10.6%; mean ICC = 0.878) that was superior to that obtained using the previous unsupervised clustering approach (mean ICC = 0.596). CONCLUSION: Reference region modeling combined with supervised reference tissue extraction produces a robust and reproducible quantitative assessment of [(11)C]-(R)-PK11195 studies in the human brain.

Algorithms↗
PubMed1976

[Contribution to stability test of daunoblastin solutions (author's transl)].

It is known that drugs are not unlimitedly stable. Dilutions of the antineoplastic agent daunoblastin used in the clinic and experimental work, were examined, whether they could be stored for several days. By means of impulscytophotometry, spectral-photometric measurements, counting of surviving cells and estimation of DNA-synthesis after culturing pieces of tissue in the presence of daunoblastin it could be established that this drug, diluted even four days ago, still possesses sufficient activity.

Animals↗
PubMed1984

Variability of carotid bruit spectral analysis.

The reproducibility of determination of stenosis of the carotid artery by bruit spectral analysis was studied in 20 patients with 29 cervical bruits. The tests were performed with the Spectraview, a dedicated microcomputer which performs the analysis by the method of Lees. The estimated residual lumen was calculated from the break frequency of the power spectrum at peak systole. Each patient was studied on five separate occasions during a week. The lowest day-to-day variation was found with those lesions with the smallest residual lumen diameter. Six patients with wide ranges had major swings of blood pressure or pulse. When the bruit analysis results from days with similar blood pressure and pulse were compared, there was a low variability. The lesser stenoses had a wider spread of break frequency, but in this range, the variation represented only small differences in lumen diameter. The results of this study indicate that bruit spectral analysis can estimate the residual lumen diameter with an acceptable day-to-day variation.

Aged↗
PubMed2002

Time-variant spectral analysis of heart rate variability during parabolic flight with and without LBNP.

Modifications of autonomic activity during parabolic flight were studied by a time-variant model able to estimate low (LF, 0.04-0.14 Hz) and high (HF, 0.14-0.35 Hz) frequency spectral components on a beat-to-beat basis. Ten subjects were studied with and without lower body negative pressure (LBNP). ECG and Gz load were digitized (500 Hz) and RR interval variability series extracted. Beat-to-beat mean RR, variance, LF and HF power were obtained. One-way ANOVA (p<0.01) was used to compare values obtained during starting 1Gz (I), first 1.8Gz (II), 0Gz (III), second 1.8Gz (IV), ending 1Gz (V). Without LBNP, total and LF power increased during 0Gz to 1.69 +/- 1.41 and 2.87 +/- 4.66 respectively (mean +/- SD, normalized by phase I value). With LBNP, their change during 0Gz (1.38 +/- 1.37 and 1.54 +/- l.04 respectively) reached significance only with phase II and phase V. Phase I HF power was higher than in the other phases, both without and with LBNP.

Journal Article↗
PubMed2000

Spectral compression of the electromyographic signal due to decreasing muscle fiber conduction velocity.

Spectral compression of the electromyographic (EMG) signal, due largely to decreasing muscle fiber conduction velocity, is commonly used as an indication of muscle fatigue. Current methods of estimating conduction velocity using characteristic frequencies such as the median frequency of the power spectrum, are based on an assumption of uniform spectral compression. To examine changes in the EMG frequency spectrum during fatigue, muscle fiber conduction velocity was measured during sustained, isometric contractions of the biceps brachii. Compression of the EMG power and amplitude spectra was simultaneously examined using the median frequency and an alternative method-the spectral distribution technique. The spectral distribution technique consistently gave a better estimate of the relative change in muscle fiber conduction velocity than either of the median frequencies. This was further examined using a physiologically based EMG simulation model, which confirmed these findings. The model indicated that firing statistics can significantly influence spectral compression, particularly the behavior of characteristic frequencies in the vicinity of the firing rates. The relative change in the median frequency, whether of the amplitude or frequency spectrum, was consistently greater than the relative change in conduction velocity. The most accurate indication of the relative change in conduction velocity was obtained by calculating the mean shift in the midfrequency region of the EMG amplitude spectrum using the spectral distribution technique.

Action Potentials↗